Abstract
Novel 2-substituted 1,3-bis[bis(3′,5′-di-tert-butylphenyl)phosphino]propanes (SciPROP-R; 1-R), as well as their iron complexes FeCl2(SciPROP-R) 2-R, are synthesized. Single-crystal X-ray analysis and solution-phase Fe K- and L-edge XAS of 2-R reveals that these complexes maintain tetrahedral geometry and hence paramagnetic high-spin properties both in the solid state and in the solution phase. 31P NMR results demonstrate that the superior coordination ability of SciPROP-TB (1-TB) is due to the bulky tert-butyl group at position 2 of the propane-1,3-diyl linker of the ligand. These novel iron-complexes catalyze Suzuki–Miyaura-type cross coupling under mild conditions. Notably, iron(II) chloride–1-TB complex (2-TB) exhibits excellent catalytic activity owing to the high coordination ability and electron-donating nature of 1-TB, being effective for chemoselective cross coupling between various alkyl chlorides and arylboron compounds.
1. Introduction
The transition-metal-catalyzed cross-coupling reaction is an indispensable chemical transformation in the synthesis of various functional organic molecules, such as pharmaceutical and agrochemical intermediates and electronic materials.1,2 Palladium and nickel catalysts have been prevailing in the cross-coupling reactions for several decades.3 However, the fact that these transition metals are rare, expensive and environmentally and ecologically harmful brings about unignorable concerns for the sustainability of chemical technology.4 New iron-based catalysts have emerged as the most promising alternatives for their cost-effectiveness, non-toxicity, and earth-abundance5 so as to replace these precious metal catalysts.
Researchers have developed several effective iron catalysts for cross-coupling reactions between various alkyl halides and aryl metal reagents, which are not straightforward with conventional palladium catalysts because of undesired β–hydride elimination of alkyl–palladium intermediates.6 Despite the significant progress in iron-catalyzed cross-coupling reactions during this decade, challenges remain in improving the efficiency, robustness and broadening the limited substrate scope. The weak coordination of ligands in iron complexes in the presence of excess aryl metal reagents restricts the catalyst lifetime. Hence, extensive catalyst loading of 1–10 mol% is often required to attain high product yields.7 For instance, when using the weakly coordinating tetramethylethylenediamine (TMEDA) as a ligand, a large excess of the ligand is required to achieve high selectivity and yields in iron-catalyzed cross-coupling reactions:6a,6e,8 the delicate balance of coordination and dissociation equilibrium of TMEDA determines the results.9 To overcome such disadvantages of the iron–TMEDA catalyst, we developed a bulky bisphosphine ligand (Spin-control-intended Ortho-Phenylene bisPhosphine; SciOPP) and the iron–SciOPP catalyzed cross-coupling reactions (Figure 1).6t,10–14
Iron–SciOPP complex in FeX2(SciOPP)-catalyzed cross-coupling reactions.
The iron–SciOPP catalyst drastically improved the catalytic activity, as well as the catalyst lifetime and substrate scope, in the cross-coupling reactions of alkyl halides, especially alkyl chlorides, considered to be among the most synthetically viable but also the most challenging substrate.15–17 Even with the improved activity of the iron-SciOPP catalyst, the cross-coupling of non-activated primary alkyl chlorides is demanding due to the instability of the corresponding primary alkyl radical intermediates. Only a few studies have reported cross-coupling reactions of primary, secondary, and tertiary alkyl chlorides, including FeCl2(dppp) and Fe(acac)3 for those of primary and secondary alkyl chlorides with aryl boronic esters;6u an iron–NHC catalyst for those of primary, secondary, or tertiary alkyl chlorides with aryl Grignard reagents;10e,10f and FeCl2(SciOPP) 3 catalyst for those of primary and secondary alkyl chlorides with aryl aluminate reagents.6s
These considerations motivated us to develop a new, more effective ligand for the iron-catalyzed cross-coupling of non-activated alkyl chlorides. Figure 2 shows the design of the novel bisphosphine ligand SciPROP-R, 2-R-substituted 1,3-bis[bis(3′,5′-di-tert-butylphenyl)phosphino]propane 1-R, where -R in SciPROP-R represents the substituent at position 2 of the propane-1,3-diyl linker. For SciPROP-TB (1-TB), R = tBu; for SciPROP-M (1-M), R = Me; and for SciPROP-H (1-H), R = H.18 It should be noted that Bedford and co-workers have reported the bulky 3,5-bis(trimethylsilyl)phenyl-substituted 1,3-bis(phosphino)propane, which is effective for the iron-catalyzed Suzuki–Miyaura-type coupling of benzyl bromide with tetraarylborate salts.6v
Design of FeCl2(SciPROP-R) 2-R.
Our design concept is as follows. (1) The sterically demanding 3,5-di-tert-butylphenyl groups on the phosphorous atoms are expected to induce kinetic stabilization to prevent extra coordination of the ligand and the nucleophile to the iron center,19 to ensure a coordinatively unsaturated tetrahedral geometry as observed for SciOPP.6t Furthermore, the 14-electron tetrahedral structure possesses S = 1 or 2 spin states. These states facilitate the homolytic cleavage of the carbon–halogen bond to generate alkyl radical intermediates, crucial in the iron-catalyzed cross-coupling reactions of alkyl halides.6a,6p,20 (2) The electron-donating ability of monoalkyl diaryl phosphine centers of 1-R is higher than that of the triarylphosphine centers of SciOPP.21 The resulting electron-rich iron center is expected to promote the halogen abstraction as mentioned above. (3) The substituents at position 2 of the propane-1,3-diyl linker are expected to induce conformational rigidity for stabilizing the chelate structure,22 thereby suppressing the dissociation of the ligand to prolong the catalyst lifetime.
Herein, we report the synthesis of 1,3-bis(phosphino)propane ligands SciPROP-R 1-R, as well as the corresponding iron complexes FeCl2(SciPROP-R) 2-R and their application in Suzuki–Miyaura-type cross-coupling reaction between non-activated alkyl chlorides and lithium aryl(tert-butyl) borates, demonstrating that 2-TB shows superior activity to that of existing analogous iron-complex catalysts. The solid- and solution-phase molecular structure of the new iron complexes FeCl2(SciPROP-R) 2-R are also determined unequivocally.
2. Results and Discussion
2.1 Synthesis of SciPROP-R
Scheme 1 shows the synthesis of SciPROP-R ligands 1-R via the phosphine borane intermediate. First, diethyl phosphite 4 reacts with (3,5-di-tert-butylphenyl)magnesium bromide, affording diarylphosphine oxide 5. The reduction of 5 and simultaneous complexation with borane were carried out to obtain diarylphosphine borane 6 by the slow addition of BH3·THF to a THF solution of 5. It should be noted that 6 easily decomposed when passed through silica-gel, even though secondary phosphine boranes are typically stable during purification by silica-gel column chromatography. The steric repulsion caused by the bulky 3,5-di-tert-butylphenyl substituents promotes the detachment of BH3 from 6, affording free phosphines and phosphine oxide upon reaction with atmospheric oxygen.23 Hence, 6 was used for the next step immediately after the post-synthesis treatment of evaporating the remaining BH3 and solvent, washing and extraction with water and EtOAc, and concentration in vacuo.
Synthesis of 1-R. Reaction conditions: a) 3,5-tBu2-C6H3MgBr, THF, rt, overnight. b) Slow addition of BH3·THF, THF, 60 °C, 8 h. c) BuLi, THF/hexane, −78 °C, 1 h. d) Alkyl diiodide, rt, 6–17 h. e) DABCO, toluene, 40 °C, 3–10 h.
The reaction of lithiated 6 with alkyl diiodides24 afforded the corresponding borane complexes SciPROP-R·2BH37-R. All 7-R complexes were stable to air and moisture. Hence, they were purified by standard silica-gel column chromatography or gel-permeation chromatography (GPC) under ambient conditions (see Experimental Section). Single crystals of 7-R were obtained from a CH2Cl2–ethanol solution, and their molecular structures were determined by X-ray crystallographic analysis.25
Finally, the treatment of 7-R with 1,4-diazabicyclo[2.2.2]octane (DABCO)26 gave analytically pure free SciPROP-TB (1-TB; 69%), SciPROP-M (1-M; 81%), and SciPROP-H (1-H; 72%) starting from 4. Gram-scale synthesis of these ligands demonstrated the feasibility of this synthetic route, and 37.6 g of 1-TB was obtained from 15.0 g of 4 (62% overall yield).27
2.2 Synthesis and Structure of Fe–SciPROP-R Complexes
Having the free ligands 1-R in hand, we prepared their iron(II) chloride complexes 2-R. Complex formation of iron salts and 1-R proceeded smoothly by simple mixing of iron(II) chloride tetrahydrate and 1-R in EtOH, affording the desired complexes 2-R (Scheme 2).
Synthesis of FeCl2(SciPROP-R) complexes 2-R.
The structures of 2-R in the crystal and solution states were determined by single-crystal X-ray diffraction and solution-phase X-ray absorption spectroscopy (XAS) analysis, respectively. We then compared these structures with the structure of FeCl2(SciOPP) 3.6t,12 Because the 2-R complexes are highly soluble in most organic solvents (even in hexane), only tiny single crystals were obtained by the vapor diffusion of ethanol into the hexane solution of 2-R. These crystals are not suitable for X-ray diffraction structural analysis using laboratory instruments. Therefore, synchrotron radiation-based X-ray diffraction analysis at SPring-8 (BL02B1, BL38B1, and BL40XU28) was used to elucidate the molecular structures of 2-R (Figures 3a–c and Tables S17–30).29
Molecular structures of a) 2-TB, b) 2-M, c) 2-H, and d) 3, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen atoms are omitted for clarity except the hydrogens at position 2 of the propane-1,3-diyl linker of the ligand.
A metal-ligand complexation with 1:1 molar ratio was confirmed from the X-ray structures of 2-R, in which coordinatively unsaturated tetrahedral geometry, similar to that of their SciOPP congeners 3,6t was observed (Figure 3d). For instance, the Fe–P and Fe–Cl bond lengths of 2-R (in the ranges of 2.43–2.48 and 2.22–2.25 Å) were similar to those of 3 (2.44–2.46 and 2.21–2.22 Å, respectively), as shown in Table 1. Similar Fe–P and Fe–Cl bond lengths were reported for tetrahedral cis-[FeCl2P2]-type complexes such as FeCl2(Ph3P)2,30 FeCl2(tBu2MeP)2,31 FeCl2(dippe),32 FeCl2(dcype),33 FeCl2(anphos),34 and FeCl2 [PhSi(CH2P-iPr2)3].35
Selected bond lengths and angles of 2-R and 3.
 |
|
Selected bond lengths and angles of 2-R and 3.
|
|
The structural differences between 2-R and 3 are quantitatively given in Table 2. The lengths of Fe–P and Fe–Cl bonds and the Cl1–Fe–Cl2 bond angle are only slightly different between 2-R and 3. However, the P1–Fe–P2 bond angles (2-TB: 88.50°, 2-M: 92.43°, and 2-H: 90.88°) of these complexes were significantly different, being 10% larger in 2-R than in 3 (80.63°), because of the six-membered chelate ring formation in the former.
Observed fractional changes in the bond lengths and angles around the iron center of 2-R, compared to 3.
 |
|
Observed fractional changes in the bond lengths and angles around the iron center of 2-R, compared to 3.
|
|
Interestingly, the chelate ring of 2-TB exhibited an unexpected boat-like conformation in the crystal state as in Figure 4, although the tert-butyl group is supposed to be at an equatorial position in the chair conformation according to the conformational analysis of cyclohexane systems (Figure 4). The density functional theory (DFT) calculation at B3LYP-GD3BJ/6-31G(d) level revealed that the boat-like conformation is more stable than the chair conformation.36
Chelate ring conformations in the X-ray molecular structures of FeCl2(SciPROP-R) 2-R a) 2-TB, b) 2-M, c) 2-H.
The solution-phase XAS using synchrotron radiation at BL14B2 and BL27SU37 beamlines of SPring-8 revealed that the boat-like confomation of 2-TB is retained in THF.38 We have used the method with which the solution-phase structures of paramagnetic organoiron species were elucidated in the mechanistic investigation of the iron-catalyzed Kumada–Tamao–Corriu-type cross-coupling reaction.10a,10f Accordingly, extended X-ray absorption fine structure (EXAFS) spectra at Fe K-edge were measured for a THF solution of 2-TB. The solution-phase structure of 2-TB was elucidated based on FEFF fitting simulation using the solid-phase atomic coordinates obtained from the single-crystal X-ray structural analysis (Figure 5).39
Fe K-edge EXAFS spectra of 2-TB in a THF solution (black line) and FEFF fitting results based on the atomic coordinate of single crystal X-ray analysis (red dotted line).
The corresponding solution-phase Fe L-edge XAS was measured for a THF solution of 2-TB using a specially designed flow cell.40 The observed L3 and L2 peaks at 708.4 and 721.8 eV are typical for high-spin state iron(II) complexes (Figure 6).41 This result is consistent with Evans’ analysis result of 2-TB: the tetrahedral geometry and the high-spin state of 2-TB are maintained in the THF solution.
Solution-phase Fe L-edge XAS spectrum of 2-TB in THF.
2.3 FeCl2(SciPROP-R) Complex-Catalyzed Suzuki–Miyaura-Type Cross-Coupling Reaction of Non-Activated Alkyl Chlorides
Table 3 summarizes the results obtained from the cross-coupling reaction of non-activated primary alkyl chlorides (in this case, 1-chlorodecane (8a)) with lithium phenyl(tert-butyl)borate 9a in the presence of the iron catalyst 2-R. Good performance was observed with the combination of iron(II) chloride and 1-TB, affording the cross-coupling product 1-decylbenzene (10a) with 59% yield by gas chromatography (GC) analysis, with negligible amounts of the by-products 1-decene and decane (Entry 1). The catalytic efficiency of 2-R was hence demonstrated, and the reactions selectively afforded the desired cross-coupling product of 10a (Entries 2–4). Although 3 and FeCl2(dppp) exhibited excellent catalytic activities for various coupling reactions,6o,6t,6u,6v,10–14,42 only 1–2% of the coupling product was obtained in these reactions, with non-negligible amounts of 1-decene and decane formed (Entries 5 and 6). Notably, 2-TB exhibited the highest catalytic activity with almost no by-products. The reaction proceeded more efficiently with the addition of 5 mol% excess ligand. Largely enhanced cross-coupling activity was observed for 2-TB and 2-M, affording 10a with yields greater than 99% and 56% (Entries 7 and 8). However, there was almost no enhancement of catalytic performance in the 2-H-, 3-, and FeCl2(dppp)-catalyzed reactions (Entries 9–11). The higher catalytic activity with 1-TB than those with 1-M and 1-H can be attributed to the coordination ability of 1-R. 31P NMR measurements showed clearly that their coordination abilities are in the order of 1-H < 1-M < 1-TB (see the data in SI), which resulted most likely in the higher stability of catalytic iron species coordinated by 1-TB.
Iron-catalyzed Suzuki–Miyaura-type cross-coupling reaction of 1-chlorodecane (8a) and lithium phenyl(tert-butyl)borate 9a.
 |
|
Iron-catalyzed Suzuki–Miyaura-type cross-coupling reaction of 1-chlorodecane (8a) and lithium phenyl(tert-butyl)borate 9a.
|
|
Having confirmed the high efficiency of 2-TB, its substrate scope for the coupling reactions between various primary alkyl chlorides and arylboron compounds was investigated. Table 4 shows the results. For the cross-coupling reaction of 8a with lithium 4-chlorophenyl(tert-butyl)borate 9b and lithium 4-methoxyphenyl(tert-butyl)borate 9c, 1-TB exhibited higher efficiency compared to SciOPP and dppp (Entries 1–5). Ethyl 4-chlorobutanoate (8c) and lithium 4-chlorophenyl(tert-butyl)borate 9b easily reacted in the presence of either 2-TB or 3 (Entries 6 and 7), while 1-TB showed higher efficiency than SciOPP during the cross-coupling reaction between 8c and 4-methoxyphenyl(tert-butyl)borate 9c (Entries 8 and 9). The reactions in Entries 8 and 10 confirmed that the addition of a Lewis acidic salt, MgBr2, was mandatory as reported in our previous studies.6p,6t,12a,12c,12d
Suzuki–Miyaura-type cross-coupling reaction of non-activated primary alkyl chlorides with arylborates catalyzed by 2-TB.
 |
|
Suzuki–Miyaura-type cross-coupling reaction of non-activated primary alkyl chlorides with arylborates catalyzed by 2-TB.
|
|
The reactions of 8c with lithium 4-chlorophenyl- (9b), 4-methoxyphenyl- (9c), 4-N-methylindol-5-yl- (9d), and 2-naphthyl (tert-butyl)borates (9e) afforded the desired cross-coupling products in 61%, 83%, 61%, and 82% isolated yields, respectively (Entries 6, 8, 11, and 12). Sterically demanding lithium 1-naphthyl(tert-butyl)borate afforded the corresponding product in 29% yield (Entry 13). The reactions of alkyl chlorides bearing an acetoxy or a cyano group, 8d and 8e, also proceeded smoothly to afford the coupling products, 10i–10k in 88%, 89%, and 62% isolated yields, respectively (Entries 15, 17 and 18). The reaction of 1-chloro-4-(2-chloroethyl)benzene (8f) procceded exclusively at the C(sp3)–Cl over the C(sp2)–Cl to give 10l in 73% isolated yield (Entry 20). These results exemplify the high functional group compatibility and chemoseletivity of the present coupling reaction. In addition, 1-TB comprehensively showed better reactivity and efficiency than SciOPP in the coupling reactions, especially with electron-rich 4-methoxyphenyl(tert-butyl)borate 9c (Entries 5, 9, 16, 19, and 21).
Notable SN2 selectivity was observed in the reaction of cinnamyl chloride 8g with 9c, where the coupling occurred at the terminal position to give the corresponding regioisomer 10m without the formation of 10n (Entry 22). Similarly, in the reaction of primary propargyl chloride 8h, the alkyne product 10o was generated in 91% isolated yield, while none of the allene product 10p was observed (Entry 23).
The reactions of radical clock substrates clarified the alkyl radical intermediates generated from the alkyl chlorides. In the reaction of 6-chloro-1-hexene (8i), ca. 2:1 mixture of non-cyclized product 10q and ring-closing product 10r were obtained in 62% and 35% NMR yield, respectively. The formation of 10r is indicative of the 5-exo cyclization of the corresponding alkyl radical (Entry 24). The reaction of (chloromethyl)cyclopropane (8j) afforded the ring-opening product 1-but-3-enyl-4-methoxybenzene (10s) with negligible amounts of 10t, also confirming the intermediacy of the corresponding alkyl radical (Entry 25).
Figure 7 shows a plausible mechanism based on the results above and previous studies on iron-catalyzed cross-couplings of alkyl halides.43 The reduction of iron pre-catalyst FeCl2(SciPROP-R) by lithium (tert-butyl)borate 9 gives an iron(I)(SciPROP-R) A.43a,43b The reactive species A abstracts a halogen atom from the alkyl chloride 8, forming an alkyl radical intermediate and the iron(II) intermediate B. The rearrangement of some types of alkyl radicals such as allyl, cyclopropylmethyl, or 5-hexen-1-yl radical occur at this moment. Then, the transmetalation of the intermediate B with 9 and MgBr2 gives the organoiron(II)(SciPROP-R) C. The radical recombination of organoiron(II)(SciPROP-R) C with alkyl radical affords the organoiron(III) intermediate D. Subsequently, the reductive elimination gives the product 10 and regenerates iron(I)(SciPROP-R) A.
Plausible catalytic cycle of the present coupling reaction.
3. Conclusion
Novel bisphosphine chelate ligands SciPROP-R 1-R and their iron complexes FeCl2(SciPROP-R) 2-R have been designed and synthesized. The structures of 2-R were elucidated by single-crystal X-ray analysis and solution-phase XAS. The relative coordination abilities of 1-R to iron(II) dichloride were determined by 31P NMR to be 1-H < 1-M < 1-TB. This order is in good accord with that of the cross-coupling activity observed in the reaction of 8a with 9a. The deactivation of catalysts is hence attributed likely to the easy dissociation of the ligands. In particular, 2-TB has exhibited excellent catalytic activity and chemoselectivity in the cross-couplings of non-activated primary alkyl chlorides with lithium aryl(tert-butyl)borates, which are difficult using conventional iron–bisphosphine and iron–diamine complex catalysts.
The bulky substituent at position 2 of the propane-1,3-diyl linker of the ligand enhances the coordination ability to prevent the undesired ligand dissociation, being key to achieve the observed high catalytic activity and selective formation of desired cross-coupling products. We hope that the rational ligand design described here spurs further development of iron-catalyzed cross-coupling reactions of unreactive substrates with low catalyst loading to overcome the limitations of conventional cross-coupling catalysts.
4. Experimental
Synthesis of Bis(3,5-di-tert-butylphenyl)phosphine Oxide 5
A solution of 3,5-di-tert-butylphenyl bromide (47.5 g, 0.18 mol) in THF (90 mL) was added dropwise over 4 h to a mixture of magnesium turnings (4.70 g, 0.19 mol) in THF (80 mL). After stirring at room temperature for an additional 2 h, to the reaction mixture was added diethyl phosphite 4 (6.5 mL, 51 mmol) at 0 °C and stirred at room temperature for 14 h. The resulting reaction mixture was treated with HCl (6 N, 150 mL) and the water layer was extracted with AcOEt (100 mL, three times). The combined organic layers were filtered with a pad of Florisil and evaporated in vacuo to afford the crude product as a yellow oil. The crude product was diluted with hexane and the resulting solution was filtered with a filter paper (ADVANTEC No. 2: 5 µm pore, 0.26 mm thickness) and concentrated in vacuo to give the title product as a white powder (14.6 g, 68% yield). Rf = 0.42 (hexane/AcOEt = 3/7); IR (neat) 3394, 2956, 2904, 2868, 2317 (P-H st), 1595, 1477, 1429, 1394, 1362, 1326, 1250, 1184 (P=O, st), 1149, 1022, 998, 955, 936, 885, 791, 712, 603, 557, 544, 519, 478 cm−1; m.p. = 160.6–161.1 °C; 1H NMR (CDCl3, 392 MHz) δ 1.31 (s, 36H), 7.54 (dd, JH–P = 14.5 Hz, J = 1.8 Hz, 4H), 7.60–7.63 (m, 2H), 8.08 (d, JH–P = 475.5 Hz, 1H); 13C NMR (CDCl3, 98.5 MHz) δ 31.4 (12C), 35.2 (4C), 125.1 (d, JC–P = 12.2 Hz, 4C), 126.7 (2C), 130.8 (d, JC–P = 100.5 Hz, 2C), 151.6 (d, JC–P = 12.2 Hz, 4C); 31P NMR (CDCl3, 158.6 MHz) δ 23.2.
Synthesis of Bis(3,5-di-tert-butylphenyl)phosphine Borane Complex 6
Bis(3,5-di-tert-butylphenyl)phosphine oxide 5 (2.00 g, 4.7 mmol) was dissolved in 25 mL of THF at room temperature to obtain a colorless solution. To the resulting solution was slowly added 1.0 M THF solution of BH3·THF complex (10 mL, 9.4 mmol) by using a syringe pump over 8 h. After completion of the addition of BH3·THF complex, the suspension was concentrated in vacuo. The residue was dissolved in hexane, filtered with a pad of silica gel, and then concentrated in vacuo to obtain the crude product as a white oil. The crude product was dissolved in toluene and purified by silica-gel column chromatography (100% toluene) to obtain the title compound as a white solid (1.34 g, 67% yield). Rf = 0.51 (hexane/AcOEt = 19/1); IR (neat) 2965, 2869, 2389, 2355, 2316, 1592, 1478, 1462, 1424, 1395, 1362, 1319, 1248, 1203, 1141, 1060, 1023, 924, 906, 894, 878, 791, 781, 732, 695, 679 cm−1; m.p.: 119.0–120.5 °C; 1H NMR (CDCl3, 392 MHz) δ 0.6–1.7 (br d, 3H), 1.31 (s, 36H), 6.30 (dq, JH–P = 376.3 Hz, J = 6.9 Hz, 1H), 7.50 (dd, JH–P = 12.5 Hz, J = 2.0 Hz, 4H), 7.55–7.56 (m, 2H); 13C NMR (CDCl3, 98.5 MHz) δ 31.4 (12C), 35.2 (4C), 125.2 (d, JC–P = 57.3 Hz, 2C), 125.8 (d, JC–P = 1.9 Hz, 2C), 127.3 (d, JC–P = 10.3 Hz, 4C), 151.7 (d, JC-P = 10.3 Hz, 4C); 31P NMR (CDCl3, 158.6 MHz) δ 0.71; 11B NMR (CDCl3, 125.7 MHz) δ −40.4; Anal. calcd for C28H46BP C, 79.23; H, 10.92, found C, 79.28; H, 11.00.
Synthesis of 1,3-Bis{bis(3′,5′-di-tert-butylphenyl)phosphino}propane Diborane Complex (SciPROP-H·2BH3) 7-H
To a THF solution (15 mL) of bis(3,5-di-tert-butylphenyl)phosphine borane complex 6 (1.05 g, 2.5 mmol) was added BuLi (1.6 mL, 1.56 M in hexane, 2.5 mmol) at −78 °C. After stirring the solution at the same temperature for 0.5 h, 1,3-diiodopropane (0.292 g, 0.99 mmol) was added to the solution and it was stirred for 18 h at room temperature. After aqueous NH4Cl (saturated, 20 mL) was added, the mixture was extracted with AcOEt (30 mL, three times). The combined organic layers were dried over magnesium sulfate and concentrated in vacuo to obtain the crude product. The residue was purified by silica gel column chromatography (eluent: hexane/AcOEt = 20/1) and GPC (eluent: CHCl3) to obtain the title compound as a white solid (0.817 g, 93% yield). Rf = 0.44 (hexane/AcOEt = 19/1); IR (neat) 2956, 2904, 2891, 2870, 2388, 2374, 2367, 2359, 2345, 1591, 1477, 1462, 1423, 1394, 1363, 1321, 1248, 1203, 1144, 1060, 975, 963, 897, 878, 867, 831, 788, 735, 708, 670 cm−1; m.p.: 177.0–179.5 °C; 1H NMR (CDCl3, 392 MHz) δ 0.5–1.2 (br, 6H), 1.27 (s, 72H), 1.82–1.96 (m, 2H), 2.28 (dt, 4H, JH–P = 10.6 Hz, J = 7.8 Hz), 7.45–7.50 (m, 12H); 13C NMR (CDCl3, 98.5 MHz) δ 18.0, 28.4 (dd, JC–P = 35.7 Hz, J = 12.2 Hz, 2C), 31.5 (24C) 35.2 (8C), 125.4 (4C), 126.5 (d, JC–P = 9.5 Hz, 8C), 128.1 (d, JC-P = 55.5 Hz, 4C), 151.2 (d, JC–P = 9.5 Hz, 8C); 31P NMR (CDCl3, 158.6 MHz) δ 16.0; 11B NMR (CDCl3, 125.7 MHz) δ −39.8; HRMS (ESI-FT-ICR) m/z [M + Na]+ calcd for C59H96B2P2Na 911.70656; found 911.70966; Anal. calcd for C59H96B2P2 C, 79.71; H, 10.88, found C, 79.74; H, 11.03.
Synthesis of 2-Methyl-1,3-bis{bis(3′,5′-di-tert-butylphenyl)phosphino}propane Diborane Complex (SciPROP-M·2BH3) 7-M
To a THF solution (90 mL) of bis(3,5-di-tert-butylphenyl)phosphine borane complex 6 (10.66 g, 25 mmol) was added BuLi (15.4 mL, 1.62 M in hexane, 25 mmol) at −78 °C. After stirring the solution at the same temperature for 1 h, 2-methyl-1,3-diiodopropane (3.10 g, 10.0 mmol) was added to the solution and it was stirred for 6 h at room temperature. After NH4Cl aq (saturated, 50 mL) was added, the mixture was extracted with AcOEt (30 mL, three times). The combined organic layers were washed with brine (100 mL) and dried over magnesium sulfate and concentrated in vacuo to obtain the crude product (12.57 g). The crude product was purified by silica gel column chromatography (eluent: hexane/AcOEt = 19/1) and GPC (eluent: CHCl3) to obtain the title compound as a white solid (8.48 g, 94% yield). Rf = 0.29 (hexane/AcOEt = 19/5); IR (neat) 2961, 2905, 2869, 2379, 2343, 1592, 1476, 1462, 1422, 1394, 1363, 1248, 1203, 1144, 1062, 898, 876, 834, 813, 792, 784, 750, 707, 613, 475, 423 cm−1; m.p.: 185.1–187.1 °C; 1H NMR (CDCl3, 392 MHz) δ 0.82 (d, J = 6.3 Hz, 3H), 1.25 (s, 36H), 1.29 (s, 36H), 2.25–2.37 (m, 2H), 2.34–2.50 (m, 1H), 2.58 (ddd, JH–P = 10.2 Hz, J = 5.1 and 14.1 Hz, 2H), 7.43–7.62 (m, 12H); 13C NMR (CDCl3, 98.5 MHz) δ 23.2 (t, JC–P = 5.2 Hz, 1C), 27.1 (s, 1C), 31.48 (s, 12C), 31.51 (s, 12C), 35.17 (s, 4C), 35.21 (s, 4C), 35.8 (dd, JC–P = 8.5 and 33.8 Hz, 2C), 125.1 (d, JC–P = 1.9 Hz, 2C), 125.3 (d, JC–P = 1.9 Hz, 2C), 126.4 (d, JC–P = 10.3 Hz, 4C), 127.8 (d, JC–P = 9.4 Hz, 4C), 128.7 (d, JC–P = 54.5 Hz, 2C), 129.6 (d, JC–P = 54.5 Hz, 2C), 151.0 (d, JC–P = 10.3 Hz, 4C), 151.1 (d, JC–P = 9.5, 4C); 31P NMR (CDCl3, 158.6 MHz) δ 13.9; 11B NMR (CDCl3, 125.7 MHz) δ −38.8; HRMS (ESI-FT-ICR) m/z [M + Na]+ calcd for C60H98B2P2Na 925.72221; found 925.72635; Anal. calcd for C60H98B2P2 C, 79.81; H, 10.94, found C, 79.50; H, 10.99.
Synthesis of 2-Tert-butyl-1,3-bis{bis(3′,5′-di-tert-butylphenyl)phosphino}propane Diborane Complex (SciPROP-TB·2BH3) 7-TB
To a THF solution (80 mL) of bis(3,5-di-tert-butylphenyl)phosphine borane complex 6 (6.37 g, 15 mmol) was added BuLi (9.5 mL, 1.58 M in hexane, 15 mmol) at −78 °C. After stirring the solution at the same temperature for 1 h, 2-tert-butyl-1,3-diiodopropane (2.11 g, 6.0 mmol) was added to the solution and it was stirred for 18 h at room temperature. After aqueous NH4Cl (saturated, 60 mL) was added, the mixture was extracted with AcOEt (30 mL, three times). The combined organic layers were dried over magnesium sulfate and concentrated in vacuo to obtain the crude product. The residue was purified by silica gel column chromatography (eluent: hexane/AcOEt = 19/1) and GPC (eluent: CHCl3) to obtain the title compound as a white solid (4.80 g, 85% yield). Rf = 0.51 (hexane/AcOEt = 19/5); IR (neat) 2962, 2905, 2870, 2377, 1592, 1477, 1422, 1394, 1363, 1322, 1249, 1203, 1143, 1060, 1025, 988, 925, 897, 878, 836, 818, 784, 737, 707, 657 cm−1; m.p.: 98.0–101.5 °C; 1H NMR (CDCl3, 392 MHz) δ 0.40 (s, 9H), 1.29 (s, 72H), 2.02–2.18 (m, 1H), 2.60 (ddd, J = 3.9, 14.5 and 14.5 Hz, 2H), 2.85 (ddd, J = 6.3, 10.6 and 15.3 Hz, 2H), 7.46–7.50 (br, 4H), 7.60–7.60 (m, J = 11.0 Hz, 8H); 13C NMR (CDCl3, 98.5 MHz) δ 27.9 (3C), 28.9 (dd, J = 3.7 and 31.0 Hz, 2C), 31.5 (24C), 34.1 (t, J = 4.7 Hz, 1C), 35.2 (8C), 42.3 (1C), 124.8 (2C), 124.9 (2C), 127.2 (d, J = 8.5 Hz, 4C), 127.6 (d, J = 9.4 Hz, 4C), 129.3 (d, J = 55.4 Hz, 2C), 130.3 (d, J = 55.4 Hz, 2C), 150.80 (d, J = 4.6 Hz, 4C), 150.90 (d, J = 4.7 Hz, 4C); 31P NMR (CDCl3, 158.6 MHz) δ 17.9; 11B NMR (CDCl3, 125.7 MHz) δ −37.6; HRMS (ESI-FT-ICR) m/z [M + Na]+ calcd for C63H104B2P2Na 967.76916, found 967.77443; Anal. calcd for C63H104B2P2 C, 80.07; H, 11.09, found C, 80.23; H, 11.31.
Synthesis of 1,3-Bis{bis(3′,5′-di-tert-butylphenyl)phosphino}propane (SciPROP-H) 1-H
To a toluene solution (20 mL) of 1,3-bis(3′,5′-di-tert-butylphenyl)phosphino}propane diborane complex 7-H (1.70 g, 1.9 mmol) was added 1,4-diazabicyclo[2.2.2]octane (DABCO) (0.643 g, 5.7 mmol) at room temperature. After stirring the reaction mixture for 6 h at 50 °C, the solvent was removed in vacuo. The title compound (1.39 g, 85% yield) was obtained after silica gel column chromatography (eluent: hexane/AcOEt = 6/1) as a white solid. Rf = 0.44 (hexane/AcOEt = 97/3); IR (neat) 2955, 2902, 2867, 1587, 1578, 1476, 1462, 1420, 1392, 1361, 1287, 1248, 1201, 1183, 1131, 1022, 964, 895, 869, 791, 710 cm−1; m.p.: 57.1–58.6 °C; 1H NMR (CDCl3, 392 MHz) δ 1.25 (s, 72H), 1.70–1.81 (m, 2H), 2.18–2.24 (m, 4H), 7.22 (dd, J = 1.8 and 8.0 Hz, 8H), 7.33 (t, J = 1.80 Hz, 4H); 13C NMR (CDCl3, 98.5 MHz) δ 23.6 (t, JC–P = 18.3 Hz, 1C), 30.7 (t, JC–P = 12.2 Hz, 2C), 31.6 (24C), 35.0 (8C), 122.6 (4C), 127.0 (d, JC–P = 19.7 Hz, 8C), 137.4 (d, J = 12.2 Hz, 4C), 150.5 ((d, JC–P = 4.6 Hz, 8C); 31P NMR (CDCl3, 158.6 MHz) δ −15.1; HRMS (FAB) m/z [M + H]+ calcd for C59H91P2 861.6590, found 861.6600; Anal. calcd for C59H90P2 C, 82.28; H, 10.53, found C, 82.10; H, 10.74.
Synthesis of 2-Methyl-1,3-bis{bis(3′,5′-di-tert-butylphenyl)phosphino}propane (SciPROP-M) 1-M
To a toluene solution (43 mL) of 2-methyl-1,3-bis(3′,5′-di-tert-butylphenyl)propane diborane complex 7-M (7.76 g, 8.59 mmol) was added DABCO (2.89 g, 25.76 mmol) at room temperature. After stirring the reaction mixture for 12 h at 40 °C, the solvent was removed in vacuo. The title compound was obtained as a white solid after silica gel column chromatography (eluent: hexane/AcOEt = 95/5) (7.40 g, 98% yield). Rf = 0.68 (hexane/AcOEt = 10/1); IR (neat) 2962, 2903, 2868, 1578, 1477, 1458, 1419, 1392, 1362, 1247, 1013, 895, 869, 796, 709, 474 cm−1; m.p.: 124.0–125.5 °C; 1H NMR (CDCl3, 392 MHz) δ 1.21 (d, J = 6.7 Hz, 3H), 1.24 (s, 36H), 1.25 (s, 36H), 1.88–2.02 (m, 1H), 2.08 (dd, J = 7.8 and13.7 Hz, 2H), 2.44 (dd, J = 3.5 and 13.7 Hz, 2H), 7.20 (dd, J = 1.8 and 8.0 Hz, 4H), 7.25 (dd, J = 1.6 and 7.8 Hz, 4H), 7.30–7.34 (m, 4H); 13C NMR (CDCl3, 98.5 MHz) δ 23.1 (t, JC–P = 10.3 Hz, 1C), 30.5 (t, JC–P = 16.0 Hz, 1C), 31.6 (s, 24C), 35.0 (s, 8C), 39.3 (dd, JC–P = 9.4 and 14.1 Hz, 2C), 122.5 (d, JC–P = 16.8 Hz, 4C), 126.9 (d, J = 19.7, 4C), 127.2 (d, JC–P = 19.7 Hz, 4C), 137.6 (d, JC–P = 11.3 Hz, 2C), 138.3 (d, J = 11.3 Hz, 2C), 150.4 (d, JC–P = 5.6 Hz, 4C), 150.5 (d, JC–P = 5.7 Hz, 4C); 31P NMR (CDCl3, 158.6 MHz) δ −18.9; HRMS (ESI-FT-ICR) m/z [M + H]+ calcd for C60H93P2 875.67470; found 875.67175.
Synthesis of 2-Tert-butyl-1,3-bis{bis(3′,5′-di-tert-butylphenyl)phosphino}propane (SciPROP-TB) 1-TB
To a toluene solution (30 mL) of 2-tert-butyl-1,3-bis(3′,5′-di-tert-butylphenyl)propane diborane complex 7-TB (3.81 g, 4.03 mmol) was added DABCO (1.36 g, 12.1 mmol) at room temperature. After stirring the reaction mixture for 9 h at 40 °C, the solvent was removed in vacuo. The title compound was obtained as a white solid after silica gel column chromatography (eluent: 100% hexane) (3.59 g, 97% yield, >98% purity on GC analysis). Rf = 0.44 (hexane/AcOEt = 49/1); IR (neat) 2956, 2903, 2868, 1589, 1578, 1476, 1466, 1460, 1419, 1393, 1362, 1287, 1248, 1202, 1190, 1147, 1131, 1024, 924, 896, 873, 809, 792, 709, 664 cm−1; m.p.: 61.5–63.5 °C; 1H NMR (CDCl3, 392 MHz) δ 0.66 (s, 9H), 1.25 (s, 36H), 1.28 (s, 36H), 1.40–1.46 (br, 1H), 2.09 (dd, J = 8.5 and 13.9 Hz, 2H), 2.51 (d, J = 13.9 Hz, 2H), 7.31–7.36 (m, 12H); 13C NMR (CDCl3, 98.5 MHz) δ 27.8 (3C), 31.7 (24C), 33.2 (t, JC–P = 4.7 Hz, 2C), 34,7 (t, JC–P = 5.7 Hz, 1C), 35.0 (4C), 35.1 (4C), 43.6 (t, JC–P = 13.1 Hz, 1C), 122.1 (2C), 122.6 (2C), 127.1 (t, JC–P = 10.3 Hz, 4C), 128.5 (t, JC–P = 10.3, 4C), 137.8 (t, JC–P = 6.6 Hz, 2C), 139.7 (t, JC–P = 6.6 Hz, 2C), 150.3 (s, 8C); 31P NMR (CDCl3, 158.6 MHz) δ −17.4; HRMS (FAB) m/z [M]+ calcd for C63H98P2 916.7138; found 917.7107; Anal. calcd for C63H98P2 C, 82.48; H, 10.77, found C, 82.32; H, 10.85.
Synthesis of dichloro{1,3-bis[bis(3′,5′-di-tert-butylpheny)phosphine-κP]propane}iron(II) FeCl2(SciPROP-H) 2-H
To an EtOH solution (30 mL) of FeCl2·4H2O (0.128 g, 0.64 mmol) was added SciPROP-H 1-H (0.505 g, 0.59 mmol) at room temperature. After the mixture was stirred at 90 °C for 6 h, the solvent was removed in vacuo. The residue was washed with EtOH and hexane to obtain iron complex 2-H (0.410 g, 69% yield) as a white solid. IR (neat) 2958, 2902, 2869, 1592, 1582, 1477, 1464, 1421, 1394, 1363, 1322, 1289, 1250, 1203, 1142, 1049, 1024, 1000, 971, 924, 936, 924, 897, 876, 821, 791, 781, 751, 741, 707, 672 cm−1; mp: 135.2–137.8 °C; Magnetic susceptibility (THF-d8/benzene = 9/1, 293–338 K): μeff = 5.07–4.99; 1H NMR (CDCl3, 392 MHz) δ −17.45, −3.22, −1.86, 1.04, 23.14, 117.99; Anal. calcd for C59H90Cl2FeP2 C, 71.72; H, 9.18, found C, 71.89; H, 9.21.
Synthesis of dichloro{1,3-bis[bis(3′,5′-di-tert-butylpheny)phosphine-κP]-2-methylpropane}iron(II) FeCl2(SciPROP-M) 2-M
To an EtOH solution (10.0 mL) of FeCl2·4H2O (220.9 mg, 1.10 mmol) was added SciPROP-M 1-M (876.28 mg, 1.10 mmol) at room temperature. After the mixture was stirred at 80 °C for 6 h, the solvent was cooled to room temperature. The solution was filtered and the residue was washed with EtOH to obtain iron complex 2-M (832.9 mg, 83% yield) as a white powder. IR (neat) 2955, 2904, 2869, 1593, 1580, 1477, 1462, 1420, 1393, 1362, 1250, 1131, 874, 707, 587, 482, 438 cm−1; m.p.: 180.0–182.0 °C; 1H NMR (CDCl3, 392 MHz) δ −6.03, −5.74, −1.29, 0.28, 1.84, 2.15, 2.99, 8.42, 46.30, 191.97; Anal. calcd for C60H92Cl2FeP2 C, 71.92; H, 9.25, found C, 72.04; H, 9.43.
Synthesis of dichloro{1,3-bis[bis(3′,5′-di-tert-butylpheny)phosphine-κP]-2-tert-butylpropane}iron(II) FeCl2(SciPROP-TB) 2-TB
To an EtOH solution (2.5 mL) of FeCl2·4H2O(57.1 mg, 0.29 mmol) was added SciPROP-TB 1-TB (0.240 mg, 0.26 mmol) at room temperature. After the mixture was stirred at 80 °C for 11 h, the solvent was cooled to room temperature. The solution was filtered and the residue was washed with EtOH and hexane to obtain iron complex 2-TB (0.173 g, 64% yield) as a white solid. IR (neat) 2954, 2932, 2868, 1587, 1478, 1419, 1394, 1362, 1287, 1249, 1202, 1133, 1104, 1073, 1029, 976, 924, 896, 873, 839, 818, 793, 777, 721, 707, 682 cm−1; m.p.: 171.6–172.7 °C; Magnetic susceptibility (THF-d8/benzene = 9/1, 293–338 K): μeff = 5.04–4.98; 1H NMR (CDCl3, 392 MHz) δ −4.91, −1.26, −0.91, −0.34, 0.58, 1.41, 3.38, 13.07, 60.69, 162.39; Anal. calcd for C63H98Cl2FeP2 C, 72.47; H, 9.46, found C, 72.65; H, 9.76.
Procedure A; A representative procedure for the iron-catalyzed reaction shown in Table 3.
Reaction of 1-chlorodecane (8a) with lithium phenyl(tert-butyl)borate 9a prepared from (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene and tert-butyllithium
To a THF solution (2.0 mL) of (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (0.164 g, 0.80 mmol) was added tert-BuLi (0.490 mL, 1.53 M in pentane, 0.75 mmol) at −40 °C. The reaction mixture was stirred at the same temperature for 30 min, and then at 0 °C for 30 min. The solvent was removed in vacuo at 0 °C. To residual borate were added THF (2.0 mL), undecane (30.1 mg, 0.19 mmol), 8a (71.0 mg, 0.40 mmol), MgBr2 (0.80 mL, 0.100 M in THF, 80 µmol), 1-TB (36.2 mg, 39 µmol) and 2-TB (0.80 mL, 50.0 mM in THF, 40 µmol, 10 mol %) at 0 °C. The coupling reaction was carried out at 40 °C for 18 h. An aliquot of the reaction mixture was diluted with AcOEt and then filtered with a pad of Florisil. Product yields of 1-phenyldecane 10a, 1-decene, decane, and recovery of 8a were determined by GC analysis of the crude product using undecane as an internal standard. Screening of various iron catalyst precursors was also carried out under the similar conditions described above.
Procedure B; A representative procedure for the iron-catalyzed reaction shown in Table 4.
Synthesis of 4-(1-Methyl-1H-indol-5-yl)butyl Acetate (10j)
1-Methyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-indole (514.28 mg, 2.00 mmol) was added t-BuLi (1.150 mL, 1.65 M in pentane, 1.90 mmol) at −40 °C. The reaction mixture was stirred at the same temperature for 30 min, and then at 0 °C for 30 min. The solvent was removed in vacuo at 0 °C. To residual borate were added THF (3.0 mL), 4-chlorobutyl acetate (148.35 mg, 0.99 mmol), MgBr2 (1.00 mL, 0.200 M in THF, 0.20 mmol), SciPROP-TB 1-TB (0.500 mL, 0.100 M in THF, 0.050 mmol, 5 mol%) and FeCl2(SciPROP-TB) 2-TB (0.500 mL, 0.100 M in THF, 0.050 mmol, 5 mol%) at 0 °C. The coupling reaction was carried out at 40 °C for 4 h. After cooling to 0 °C, aqueous NH4Cl (saturated, 2.0 mL) was added. The aqueous layer was extracted three times with Et2O. The combined organic extracts were filtered with a pad of Florisil (100–200 mesh, Wako). GC analysis of the crude mixture showed, upon comparison with the area of an internal standard (undecane, 56.33 mg, 0.36 mmol), no starting alkyl chloride or byproducts such as alkene and alkane derived from alkyl chloride. After concentrated in vacuo, 1H NMR analysis of the crude product showed, upon comparison with the integration of an internal standard (tetrachloroethane, 60.96 mg, 0.36 mmol), that targeted coupling product was obtained in 98% yield. The title compound (215.39 mg, 89% yield) was obtained as a yellow oil after silica gel column chromatography (pentane:Et2O = 95:5). Rf = 0.14 (pentane:Et2O = 90:10); IR (neat) 2936, 2857, 1732 (C=O, st), 1513, 1492, 1446, 1423, 1386, 1364, 1337, 1300, 1238, 1155, 1080, 1039, 875, 793, 761, 716, 631, 606, 596, 473, 428 cm−1; 1H NMR (CDCl3, 300 MHz) δ 1.60–1.80 (m, 4H), 2.03 (s, 3H), 2.74 (t, J = 7.2 Hz, 2H), 3.77 (s, 3H), 4.08 (t, J = 6.3 Hz, 2H), 6.41 (dd, J = 0.8 and 3.3 Hz, 1H), 7.02 (d, J = 3.0 Hz, 1H), 7.05 (dd, J = 1.7 and 8.3 Hz, 1H), 7.24 (d, J = 8.7 Hz, 1H), 7.40–7.42 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 21.2, 28.3, 28.6, 33.0, 35.6, 64.7, 100.6, 109.1, 120.2, 122.6, 128.8, 129.1, 133.0, 135.5, 171.4; HRMS (FAB) m/z [M]+ calcd for C15H19NO2 245.1410; found 245.1416.
X-ray Absorption Spectroscopy (XAS) Measurement
XAS measurements were performed under standard beamline conditions of BL14B2 and BL27SU37 beamlines at SPring-8 in Japan and samples were prepared and manipulated in an Ar gas-filled glovebox. The Fe K-edge (7.11 keV) XAFS data were collected with transmission mode using a Si(111) double-crystal monochromator. All the spectra were recorded at room temperature with N2/Ar mixed gas-filled ionization chambers. The energy calibration was performed using an iron metal foil as a reference sample. For solution phase Fe K-edge XAS, air- and moisture-sensitive THF solutions of 2-R were transferred into a specially designed quartz solution cell with Teflon film windows (20 µm thickness). For solution-phase Fe L-edge XAS, fluorescence yield was recorded by using a silicon drift detector (SDD). The THF solution samples of 2-R were introduced into a specially designed flow cell equipped with Si3N4 window (100 nm thickness) which was embedded into the vacuum chamber (1.0 × 10−5). To avoid X-ray-induced sample damage, the sample liquid was continuously flowed into the cell at a flow rate of 150 µL/h. The XAS data-processing was carried out by using Athena and Artemis software.44
Comparison of the Coordination Abilities of SciPROP-R and SciOPP by 31P NMR
Coordination ability of SciPROP-R 1-R towards the iron center relative to SciOPP was estimated based on 31P NMR spectroscopy. To a 0.20 mL of THF-d8 solution of FeCl2(SciOPP) 3 (3.0 µmol), an equimolar amount of 1-R (3.0 µmol) was added, and 31P NMR measured (Figures S3–S5). The ratio of 31P signal areas of detached 3 and non-coordinating 1-R was calculated to determine the corresponding relative coordination ability of SciPROP-R versus SciOPP. It is noted that 31P NMR of iron-coordinating phosphorus is silent due to the paramagnetic tetrahedral iron(II) center.
Footnotes
Present address: Department of Applied Chemistry, Faculty of Engineering, Sanyo-Onoda City University, 1-1-1 Daigaku-Dori, Sanyo-Onoda, Yamaguchi 756-0884, Japan.
Present address: Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Present address: TSK corporation, 2-2-2 Hikaridai Seika-cho, Sorakugun, Kyoto 619-0288, Japan.
Present address: Department of Life & Health Science, Faculty of Life & Environmental Sciences, Teikyo University of Science, 2-2-1 Senju Sakuragi, Adachi-ku, Tokyo 120-0045, Japan.
Dedicated to Professor Shigeru Yamago on the occasion of his 60th birthday.
Acknowledgment
This work was supported by JSPS KAKENHI Grant Numbers 20675003, 15K13694, 20H02740, 23H01959, and Grant-in-Aid for Scientific Research on Innovative Areas “3D Active-Site Science (26105003)” from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and through the “Funding Program for Next generation World-Leading Researchers (Next Program)” initiated by the Council for Science and Technology Policy (CSTP), the CREST (11103784 and 1102545), ALCA from the Japan Science and Technology Agency (JST), Tosoh Finechem Corporation, Nissan Chemical Corporation. The synchrotron single-crystal X-ray analysis was performed at SPring-8 beam line BL02B1, BL14B2, BL27SU, BL38B1, BL40B2, and BL40XU with the approval of JASRI (BL02B1: 2016A0114, 2015B0114 and 2015A0114; BL14B2: 2016A0121, 2015B0121, 2015A0121, 2013A1798, and 2013A1601; BL27SU: 2016A0122, 2015B0122, 2015A0122, 2015A1916, 2014B1300, 2014A1740, 2013B1115, 2013A1685, and 2012B1797; BL38B1: 2010A1455; BL40XU: 2016B0123, 2016A0123, 2015B0123, 2015A0123, 2013A1705, and 2012B1815). FT-ICR-MS analyses were supported by the iJURC at ICR, Kyoto University. The authors thank Ms Toshiko Hirano (ICR, Kyoto Univ.) for elemental analyses. The authors also thank MANAC Inc. for the generous gift of 3,5-di-tert-butyl-1-bromobenzene. M.N. express sincere gratitude for the financial support from Nissan Chemical Industries Co. H.T. expresses his deepest gratitude to Dr. Yusuke Tamenori for his invaluable support and advise for soft-X-ray XAS experiments. K.I. expresses his special thanks to the MEXT project “Integrated Research on Chemical Synthesis”. S.N. expresses his special thanks to the JSPS project “Bilateral Joint Research Projects/Seminars”. S.N. expresses his deep gratitude to the Sumitomo Chemical Co. Fellowship program.
Supporting Information
Describe concisely what is in the material. This material is available on https://doi.org/10.1246/bcsj.20230180.
References
Metal-Catalyzed Cross-Coupling Reactions, 2nd ed. (Eds.: A. de Meijere, F. Diederich), Wiley-VCH, Weinheim, 2004.
Cross-Coupling Reactions: A Practical Guide (Ed.: N. Miyaura), Topics in Current Chemistry Series 219, Springer-Verlag, Heidelberg, 2002.
a)Handbook of Organopalladium Chemistry for Organic Synthesis (Ed.: E. Negishi), Wiley-Interscience, New York, 2002.
b)J. Tsuji, in Palladium Reagents and Catalysts: New Perspectives for the 21st Century, Wiley, Chichester, 2004.
c)B. M. Trost, T. R. Verhoeven, in Comprehensive Organometallic Chemistry, Vol. 8 (Eds.: G. Wilkinson, F. G. A. Stone, E. W. Abel), Pergamon, Oxford, 1982, pp. 799–938.
d)S. P. Nolan, O. Navarro, in Comprehensive Organometallic Chemistry III, Vol. 11 (Eds.: R. H. Crabtree; M. P. Mingos), Elsevier, Oxford, 2006, pp. 1.
a)C. Klein, M. Costa, H. Satoh in Handbook on the Toxicology of Metals, 3rd ed. (Eds.: G. F. Nordberg, B. A. Fowler, M. Nordberg, L. T. Friberg), Elsevier, Amsterdam, 2007, pp. 743.
b)Nickel and the skin: Absorption, Immunology, Epidemiology, and Metallurgy (Eds.: J. J. Hostynek, H. I. Maibach), CRC Press, New York, 2002.
c)
a)
c)A. Leitner, in Iron Catalysis in Organic Chemistry: Reaction and Applications (Ed.: B. Plietker), Wiley-VCH, Weinheim, 2008. pp. 147.
d)
b)
d)
e)
f)
g)
h)
j)
k)
m)
n)
p)
q)
s)
u)
v)
a)
b)
c)
d)
a)
c)
c)
d)
e)
f)
g)
b)
c)
d)
b)
d)
b)
c)
b)
d)
e)
f)
M. Nakamura, T. Hatakeyama, T. Hashimoto, S. Nakajima, N. Nakagawa, Jpn. Kokai Tokkyo Koho JP 2013180991, 2013.
b)
a)
b)
c)
a)
b)
b)
a)
b)
a)
b)
b)
c)
d)
e)
f)
g)
Masaharu Nakamura
Masaharu Nakamura received his B. Sc. in 1991 from Tokyo University of Science under the supervision of Prof. Teruaki Mukaiyama and his D. Sc. in 1996 from Tokyo Institute of Technology under the supervision of Prof. Eiichi Nakamura. He worked at Eiichi’s laboratory at The University of Tokyo as an assistant and associate professor during 1996–2005. Since 2006, he has been a professor of the Institute for Chemical Research at Kyoto University. His research interest pursues the best synthesis for the betterment of society and humanity.
