Synthesis and Reactivity of Rhodium Complexes Bearing [E(o

Mar 14, 2012 - Reed , A. E.; Weinstock , R. B.; Weinhold , F. J. Chem. Phys. 1985, 83, 735. [Crossref], [CAS]. 15. Natural population analysis. Reed, ...
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Synthesis and Reactivity of Rhodium Complexes Bearing [E(oC6H4PPh2)3]-Type Tetradentate Ligands (E = Si, Ge, and Sn) Hajime Kameo, Sho Ishii, and Hiroshi Nakazawa* Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, 558-8585, Japan S Supporting Information *

ABSTRACT: Rhodium complexes {(Ph2P)C6H4}3ERh(CO) (1: E = Si; 2: E = Ge; 3: E = Sn) bearing EP3-type tetradentate ligands were synthesized by the reaction of the corresponding ligand precursors HE(o-C6H4PPh2)3 with tris(triphenylphosphine) carbonyl rhodium hydride RhH(CO)(PPh3)3. In these complexes, the group 14 elements E exhibited a high σ-electron donor ability and elongated the Rh−CO bond trans to E in the order (H ≪) Sn ≈ Ge < Si. The Rh−E strength has influence on the CO/P(OMe)3 substitution reactions. The substitution of 1 is remarkably slower than those of 2 and 3, and the relative ratios of the pseudo-first-order rate constants kobs for 1, 2, and 3 are 1:7.7:8.5. The kinetic study indicated that heavy group 14 elements E could induce the dissociation of a phosphine ligand cis to E, which eventually leads to CO/L substitution.

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INTRODUCTION Transition metal complexes with multidentate ligands containing a carbon atom featuring a σ-electron donor as part of the chelate architecture have attracted much attention owing to their notable reactivities.1 The strong electron-donating and trans-labilizing properties of a carbon donor play a crucial role in the reactivity. The replacement of a carbon atom ligand by a silicon atom ligand is of great interest, because it sometimes leads to a remarkable stoichiometric and catalytic reactivity.2−7 Stobart and co-workers8 have reported the synthesis of a fivecoordinate rhodium carbonyl complex, Rh(tripsi)(CO) [tripsi = (PPh2CH2CH2)3Si−], having a Rh−Si bond. This is an example of the pioneering work on the incorporation of a silyl group into a polydentate framework. The rhodium has a trigonal-bipyramidal (TBP) geometry in which the apical positions are occupied by the carbonyl and silyl ligands, and the silyl ligand is demonstrated to exhibit high trans-labilizing ability via the long rhodium−carbonyl distance (1.92 Å). Peters and co-workers have extended a similar ligand system, where the ethylene groups in Stobart’s tripsi ligand were displaced by o-phenylene groups. They have prepared several coordination complexes containing {(R2P)C6H4}3SiM− frameworks for several transition metals (M = Fe, Ru, Os, Ir, Ni, Co; R = Ph or iPr) and reported the dinitrogen silylation and N−N coupling of aryl azides using a trigonal-bipyramidal {(R2P)C6H4}3SiFe− scaffold (R = Ph, iPr).9 Other heavier group 14 elements, such as Ge and Sn, are also expected to serve as strong electron-donating and translabilizing ligands. However, to the best of our knowledge, multidentate ligands containing Ge or Sn in the chelate architecture have been extremely limited.10 Hence, we focus on the three complexes {(Ph2P)C6H4}3ERh(CO) (1: E = Si; 2: E = Ge; 3: E = Sn), having a tetradentate ligand containing a heavier group 14 element. These complexes have frameworks © 2012 American Chemical Society

similar to the well-known tris(triphenylphosphine) carbonyl rhodium hydride RhH(CO)(PPh3)3 (4) and correspond to complexes where the hydride in 4 is replaced by a group 14 element E. A comparison among them would provide important information on the σ-electron-donating and translabilizing abilities of group 14 elements.

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RESULTS AND DISCUSSION New ligand precursors {(Ph2P)C6H4}3EH (6: E = Ge; 7: E = Sn) were prepared (Scheme 1). Compound 6 was obtained by treating the o-lithiated-phenyldiphenylphosphine with 1/3 equiv of Ge(OMe)4 in the presence of TMEDA (TMEDA = tetramethylethylenediamine) and then with excess LiAlH4. The last alkoxy-hydride exchange process imparted high stability to the compound and allowed the isolation of 6 in 70% yield. The related stannane compound 7 was prepared in a manner similar to that of 6. Treatment of the o-lithiated-phenyldiphenylphosphine with 1/3 equiv of SnCl4 afforded {(Ph2P)C6H4}3SnCl with some contaminations. Therefore, adequate elemental analysis data for {(Ph2P)C6H4}3SnCl were not obtained. However, the structure was confirmed by X-ray diffraction analysis.11 Reduction of crude {(Ph2P)C6H4}3SnCl with excess LiAlH4 and a subsequent purification produced analytically pure 7 as a white powder in 52% yield. By allowing 59c to react with RhHCO(PPh3)3 (4) at 80 °C, the desired rhodium complex 1 was obtained in 92% yield. When the reaction in benzene-d6 was monitored by 1H and 31P NMR spectroscopy, the respective formation of free triphenylphosphine and dihydrogen was confirmed (PPh3: δ = −6.1 ppm in the 31P NMR spectrum; H2: δ = 4.47 ppm in the 1 H NMR spectrum). Complex 1 exhibits a single doublet in 31P Received: November 15, 2011 Published: March 14, 2012 2212

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Scheme 1. Synthetic Pathways for the Rhodium Complexes [{(Ph2P)C6H4}3E]Rh(CO)a

a

1: E = Si; 2: E = Ge; 3: E = Sn.

Figure 1. ORTEP drawings of 1 (left), 2 (center), and 3 (right) with 40% probability ellipsoids. Hydrogen atoms and phenyl groups (except for ipso-carbon) are omitted for clarity.

NMR spectroscopy (δ = 60.0 ppm, JRh−P = 150.7 Hz), which is consistent with the C3v symmetrical structure observed for a solid state (see below). The related germanium and tin analogues 2 and 3 were prepared according to a synthetic procedure similar to that used to produce 1. Upon reactions of 6 and 7 with RhHCO(PPh3)3 at 80 °C, the desired complexes 2 and 3 were isolated in 87% and 85% yields, respectively. A single doublet in each 31P NMR spectrum was observed at δ 63.8 (JRh−P = 147.1 Hz) and 62.3 ppm (JRh−P = 146.9 Hz), respectively, indicating the symmetric coordination of the three phosphorus atoms. The relatively small coupling constants of 2 and 3, compared to that of 1, might be attributable to the weaker coordination of the phosphorus ligands. The IR spectra of 1, 2, and 3 showed strong absorption bands at 1958, 1948, and 1946 cm−1, respectively, and these carbonyl stretching frequencies were significantly higher than that of 4 (1918 cm−1). These ν(CO) values show that the CO ligand in 1−3 coordinates more weakly to Rh than that in 4. This trend can also be observed in the X-ray analysis data. The structures of 1−3 were confirmed by X-ray diffraction analyses using single crystals obtained from the slow diffusion of n-hexane into the concentrated methylene dichloride solutions (Figure 1). Each structure had a TBP geometry, and the carbonyl and the group 14 element E (E = Si, Ge, and Sn) were located at the apical positions. The average E−Rh−P angles (1: 81.99°, 2: 80.21°; 3: 82.00°) were smaller than the average H−Rh−P angle (4: 84.60°),12 and the TBP geometries around the Rh centers were considerably distorted because of the constrained tetradentate frameworks. The Rh−P distances in 1−3 ranged from 2.3006 to 2.3367 Å. One of three P−Rh−P angles in 1 (109.97°) is considerably smaller than the other two (121.67° and 122.56°). In comparison, the deviations of three P−Rh−P angles are smaller in 2 and 3 than in 1. The Rh−E

distances as well as the sum of the three C−E−C angles increased down a group. It should be noted that the Rh−CO distances in 1−3 (1: 1.921 Å; 2: 1.888 Å; 3: 1.888 Å) are considerably longer than that in 4 (4: 1.829 Å).12 It is known that an electron-donating ligand such as an alkyl or a hydride ligand makes a central metal atom electron rich, resulting in a strong M−CO bond owing to π back-donation from M to CO. However, our system showed that all heavier group 14 element ligands, such as silyl, germyl, and stannyl groups, which are considered to be strong electron-donating ligands, weaken the Rh−CO bond.13 To rationalize our findings, we performed density functional theory (DFT) calculations for 1−3.14 The natural bond orbital (NBO) analysis data15 together with their spectroscopic data are listed in Table 1. The NBO analyses show that the Rh−E bond is highly polarized as Rh(δ−)−E(δ+) irrespective of the kind of E for 1−3 and that the NBO atomic charge values qRh are almost equal for 1−3, whereas qE changes considerably depending on the kind of E. As mentioned above, π backdonation is stronger for 2 and 3 relative to 1. The question raised here is why qRh values are the same for 1−3 whether the extent of Rh−CO π back-donation differs. Two explanations are conceivable: (i) the electron-donating ability of Si to Rh in 1 is weaker than that of Ge in 2 and that of Sn in 3, and (ii) although the electron-donating ability of Si to Rh in 1 is almost equal to that of Ge in 2 and that of Sn in 3, there is greater electron flow from Rh to P for 1 via π back-donation than for 2 or 3. The value of qE is larger in 1 than in 2 (qSi = 1.64, qGe = 1.49), and it is unlikely that its Si σ-donor ability is lower than that of Ge. Therefore, we consider (ii) to be the more probable explanation. In other words, the electron density resulting from Si σ donation would strengthen the Rh−P bond, whereas the electron density resulting from Ge and Sn σ donation would 2213

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Table 1. Spatial, Spectroscopic, and NBO Analysis Data Rh−C distance (Å) Rh−P1 distance (Å) Rh−P2 distance (Å) Rh−P3 distance (Å) E−Rh−P angle (deg) P1−Rh−P2 angle (deg) P1−Rh−P3 angle (deg) P2−Rh−P3 angle (deg) Rh−E distance (Å) Σ (C-E-C) (deg) ν(CO) 31 P NMR (ppm) JRh−P (Hz) NBO analysis (qRh)a NBO analysis (qE)a a

1 (E = Si)

2 (E = Ge)

3 (E = Sn)

4

1.921 (3) 2.3006 2.3150 2.3189 81.99 121.67 122.56 109.97 2.3308 324.0 1958 60.0 150.7 −1.74 1.64

1.888(4) 2.3118 2.3172 2.3012 80.21 115.03 115.88 120.58 2.3967 333.7 1948 63.8 147.1 −1.71 1.49

1.888(5) 2.3244 2.3161 2.3367 82.00 119.01 120.76 114.51 2.5419 338.7 1946 62.3 146.9 −1.77 1.77

1.82911 2.33611 2.31611 2.31511 84.6011 115.811 120.511 116.711

191811

−1.54 0.10

B3PW91 (SDD/Rh, Sn; 6-31G(d)/C, H, O, P, Si, Ge).

strengthen the Rh−CO bond. This hypothesis would be supported by molecular orbital analysis of Frontier orbitals. The highest occupied molecular orbital (HOMO) of 1 apparently involves the π interaction between Rh and two phosphorus atoms (Figure 2; frontier orbitals of 2 and 3 are given in the

Figure 3. Molecular structure of one of the two independent molecules of 9 (40% probability). Hydrogen atoms and phenyl groups (except for ipso-carbon) are omitted for clarity. Selected bond lengths (Å) and angles (deg): Rh1−Ge1, 2.3767(5); Rh1−P1, 2.3189(11), Rh1−P2, 2.3175(11); Rh1−P3, 2.3194(11); Rh1−P4, 2.2463(11); Ge1−Rh1−P1, 82.19(3); Ge1−Rh1−P2, 81.96(3); Ge1−Rh1−P3, 81.46(3).

reactions were demonstrated to be first-order in the corresponding carbonyl complexes. The rate constant of the reaction at 110 °C with 1 is remarkably smaller than those with 2 and 3 by factors of 1/7.7 and 1/8.5, respectively [kobs in the reactions with 2 equiv of P(OMe)3; 7.38 × 10−6 s−1 (for 1); 5.70 × 10−5 s−1 (for 2); 6.26 × 10−5 s−1 (for 3)]. Therefore, the observation that there is a longer Rh−CO bond in 1 than in 2 and 3 seems to be inconsistent with the reactivity of the CO/ P(OMe)3 substitution. In order to gain a better understanding of the mechanism of the substitution reactions of carbonyl ligands, kinetic studies were carried out by monitoring the reaction of 2 with trimethylphosphite. The reaction of 2 depends strongly on the concentration of the phosphite ligand, and the high negative value of entropy (ΔS‡ = −16.4 eu) suggests that the CO/P(OMe)3 substitution reaction does not proceed via the mechanism initialized by a CO dissociation. A plausible pathway for the substitution of carbonyl ligands is the dissociation of one arm of the triphos ligand (Scheme 2). This type of reaction has been observed in several organometallic and catalytic reactions.17 First, a vacant coordination site for an incoming substrate is created by the dissociation of one of the phosphine arms to give IA, featuring square-planar geometry (step A). Trimethylphosphite can access the rhodium atom from the opposite face of the dissociating phosphine arm with respect to the plane around the rhodium atom (step B); therefore, the CO ligand is pushed to the equatorial position to give IC (step C). Alternatively, a trimethylphosphite approaching the rhodium from the same face of the pendant phosphine ligand might be expected to form ID, followed by the site exchange between CO and P(OMe)3 to give IC. Finally, the dissociation of the carbonyl ligand in IC and the recoordination

Figure 2. Highest occupied molecular orbital (HOMO) of 1 (−4.50 eV).

Supporting Information), and this interaction is most probably strengthened by the small P2−Rh−P3 angle in 1 due to the relatively large overlap between the dx2−y2 orbital and the π* orbital of phosphorus atoms. The Rh−E bond strength is expected to influence the reactivities of 1−3. We examined the reactions of 1−3 with P(OMe)3 and found the formation of the corresponding CO/ P(OMe)3 exchange products (eq 1).16 The reactions were monitored by 1H and 31P NMR spectroscopy, and it was found that no intermediate was detected. Compounds 8−10 were characterized by 1H and 31P NMR spectroscopy, and the structure of 9 was confirmed by X-ray diffraction analysis (Figure 3). The disappearance of the carbonyl complexes 1−3 was monitored by 31P NMR spectroscopy, and the substitution 2214

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Scheme 2. Possible Mechanism for Substitution Reactions

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of the phosphine arm generate the final complex (step D). DFT calculation using model compounds [{o-(H2P)C6H4}3E]Rh(CO) (1A: E = Si; 2A: E = Ge; 3A: E = Sn) indicates that the dissociation of one arm of the triphos ligand proceeds smoothly in the order 1A(Si) < 2A(Ge) < 3A(Sn).18 The result supports somewhat the mechanism of the dissociation of one arm of the triphos ligand. However, the high negative value of entropy (ΔS‡ = −16.4 eu) observed in the kinetic study appears to be inconsistent with the hypothesis that the dissociation of one arm of the triphos ligand is the rate-determining step. These results might support the concerted mechanism involving the dissociation of one phosphine arm and the incorporation of a phosphite ligand. Neutral monocarbonyl complexes of rhodium(I) rarely show the CO replacement reaction because of strong back-donation from the metal center. For example, Baird and his co-worker reported that in the presence of a large excess of PMe3, RhMe(CO)[η3-MeC(CH2PPh2)3] produced a perceptible amount of RhMe(CO)(PMe3)[η2-MeC(CH2PPh2)3] by a process involving the dissociation of one arm of the triphos ligand; however they did not observe the dissociation of CO.19 Therefore, the CO dissociation in 1−3 is perhaps induced by the presence of group 14 elements.

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EXPERIMENTAL SECTION

General Procedures. The compounds described below were handled under a dinitrogen atmosphere, and air and water were removed completely using the Schlenk techniques. 2-(PPh2)C6H4Br,20 RhH(CO)(PPh3)3 (4),21 and {(Ph2P)C6H4}3SiH (5)9c were prepared according to literature procedures. Benzene-d6, tetrahydrofuran-d8, diethyl ether, and benzene were dried over sodium benzophenone ketyl and distilled under the dinitrogen atmosphere. Tetrahydrofuran, hexane, and toluene were purified using a two-column solid-state purification system. Chloroform-d, dichloromethane-d2, and dichloromethane were dried over P2O5 and stored over 4 Å molecular sieves. The other reagents used in this study were purchased from commercial sources and used without further purification. The 1H, 13C, and 31P NMR spectra were recorded on a JNM-AL-400 spectrometer. 1H and 13 C NMR data were referred to the residual peaks of the solvent, and 31 P NMR data were referred to the external standard. IR spectra were recorded on a Perkin-Elmer FTIR spectrometer. Mass spectra were obtained with a Jeol AX-500 or Jeol JMS-700T spectrometer. The elemental analyses were recorded on a Perkin-Elmer 2400 II elemental analyzer. Preparation of {(Ph2P)C6H4}3GeH (6). A 600 mg portion of oPPh2(C6H4)Br (1.76 mmol) was dissolved in 10 mL of dimethyl ether, and the solution was cooled to −78 °C. To the cold solution was slowly added 1.17 mL of n-BuLi (1.65 M in hexane, 1.93 mmol), and then the mixture was gradually warmed to room temperature. Additionally, the solution was stirred at room temperature for 1 h, and then the volatile materials were removed under vacuum. The white residue was washed with 1.5 mL of Et2O to afford 0.557 g of {oPPh2(C6H4)}Li·Et2O (1.63 mmol) as a white solid in 93% yield. After {o-PPh2(C6H4)}Li·Et2O (0.56 g, 1.63 mmol) was dissolved in THF (10 mL), TMEDA (0.27 mL, 1.79 mmol) was added to the solution. To the cold (−78 °C) THF solution of Ge(OMe)4 (80.5 μL, 0.542 mmol) was added the prepared reaction solution, and the mixture was allowed to warm to room temperature. Additionally, the reaction mixture was stirred at room temperature for 15 h. After removing the volatile materials under vacuum, the residue was extracted with benzene (15 mL). After removal of the volatile materials under vacuum, the residue was dissolved in THF (10 mL). The THF solution was cooled to −78 °C, and a suspension of LiAlH4 (26.4 mg, 0.70 mmol) in THF (5 mL) was added. After the mixture was allowed to warm to room temperature, the reaction mixture was stirred at room temperature for 12 h. To quench an excess amount of LiAlH4, 0.25 mL of H2O was added to the mixture at −78 °C. After the mixture was allowed to warm to room temperature, the reaction mixture was stirred at room temperature for 2 h. The resulting solution was filtered through a Celite pad, and the volatile materials were

SUMMARY

We report the synthesis of the first rhodium complexes featuring polydentate ligands containing σ-electron donating germyl and stannyl groups as a part of the chelate architecture. To the best of our knowledge, there is no preceding systematic study on the σ-electron donor abilities of group 14 elements E (E = Si, Ge, and Sn) in the TBP system. Group 14 elements E were found to exhibit a high σ-electron donor ability and to elongate the M−CO bond trans to E in the order (H ≪) Sn ≈ Ge < Si. Furthermore, the reactivity study indicates that heavy group 14 elements E can induce the dissociation of a phosphine ligand cis to E, which eventually leads to CO/L substitution. We are currently investigating a new catalytic process that takes full advantage of high σ-electron donor and strong transinfluencing abilities of group 14 elements. 2215

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removed in vacuo. The white residue was washed with Et2O (2 mL × 3) and dried under vacuum to afford 6 (0.325 g, 0.378 mmol) in 70% yield as a white powder. 1H NMR (400 MHz, C6D6): δ 6.94−7.05 (m, 25H), 7.19−7.40 (m, 15H), 7.61−7.62 (m, 3H). 31P{1H} NMR (163 MHz, C6D6): δ −10.3 (s). Anal. Calcd for C55H43P3Ge: C, 75.64; H, 5.05. Found: C, 75.33; H, 5.24. HRMS (FAB+): [M − H]+ calcd for C54H42P3Ge 857.1711, found 857.1714. Preparation of {(Ph2P)C6H4}3SnH (7). A 1.00 g portion of oPPh2(C6H4)Br (2.93 mmol) was dissolved in 15 mL of diethyl ether, and the solution was cooled to −78 °C. To the cold solution was slowly added 1.95 mL of n-BuLi (1.65 M in hexane, 3.22 mmol), and then the mixture was gradually warmed to room temperature. Additionally, the solution was stirred at room temperature for 1 h, and then the volatile materials were removed under vacuum. The white residue was washed with 3.0 mL of Et2O to afford 0.948 g of {oPPh2(C6H4)}Li·Et2O (2.77 mmol) as a white solid in 94% yield. The toluene solution (5 mL) of {o-PPh2(C6H4)}Li·Et2O (0.948 g, 2.77 mmol) was added dropwise to the cold (−78 °C) toluene solution of SnCl4 (1 M in toluene, 0.92 mL, 0.923 mmol), and the mixture was allowed to warm to room temperature. Additionally, the reaction mixture was stirred at room temperature for 15 h. After the resulting solution was filtered through a glass filter, the volatile materials were removed under vacuum to afford crude ClSn(o-C6H4PPh2)3 as a white solid. [The formation of ClSn(o-C6H4PPh2)3 was confirmed by 1H and 31P NMR spectroscopy. 1H NMR (400 MHz, C6D6): δ 6.86−7.13 (m, 30H), 7.36−7.43 (m, 9H), 8.21−8.24 (m, 3H). 31P{1H} NMR (163 MHz, C6D6): δ −1.4 (s, JP‑119Sn = 40.4 Hz).] After the white residue was dissolved in THF (10 mL), the solution was cooled to −78 °C. A suspension of LiAlH4 (52.6 mg, 1.39 mmol) in THF (5 mL) was added dropwise to the cold solution. After the mixture was allowed to warm to room temperature, the reaction mixture was stirred at room temperature for 12 h. To quench an excess amount of LiAlH4, a 0.25 mL portion of H2O was added to the mixture at −78 °C. After the mixture was allowed to warm to room temperature, the solution was stirred at room temperature for 2 h. The resulting solution was filtered through a Celite pad, and the volatile materials were removed in vacuo. The white residue was washed with hexane (2 mL) and Et2O (2 mL × 3) and dried under vacuum to afford 7 (0.458 g, 0.507 mmol) in 55% yield as a white powder. 1H NMR (400 MHz, C6D6): δ 7.00− 7.05 (m, 25H), 7.19−7.41 (m, 15H), 7.77−7.79 (m, 3H). 31P{1H} NMR (163 MHz, C6D6): δ −4.1 (s, JP‑119Sn = 84.4 Hz). HRMS (FAB +): [M − H]+ calcd for C54H42P3Sn 903.1521, found 903.1525. Preparation of {(Ph2P)C6H4}3SiRh(CO) (1). A Schlenk tube was charged with 164.5 mg of 5 (0.202 mmol), 186.0 mg of 4 (0.202 mmol), and 15 mL of toluene, and then the reaction mixture was stirred at 80 °C. After 12 h, the mixture was cooled to room temperature and filtered through a glass filter. After removal of the volatile materials under reduced pressure, the residue was washed with hexane (2 mL × 3) and dried under vacuum to afford 175.2 mg of 1 (0.186 mmol) as a yellow powder in 92% yield. 1H NMR (400 MHz, C6D6): δ 6.73−6.77 (m, 9H), 6.83−6.87 (m, 6H), 6.94−6.98 (m, 3H), 7.02−7.05 (m, 6H), 7.13−7.24 (m, 9H), 7.36−7.39 (m, 6H), 8.31− 8.33 (m, 3H). 13C{1H} NMR (100 MHz, C6D6): δ 128.3, 128.7, 129.0, 129.4, 132.4, 132.9, 134.3, 141.4, 148.2, 154.1, 207.3. 31P{1H} NMR (163 MHz, C6D6): δ 60.0 (d, JP−Rh = 150.7 Hz). IR (KBr, cm−1) ν(CO): 1958. Anal. Calcd for C55H42OP3RhSi: C, 70.00; H, 4.49. Found: C, 70.10; H, 4.73. Preparation of {(Ph2P)C6H4}3GeRh(CO) (2). A Schlenk tube was charged with 106.0 mg of 6 (0.124 mmol), 113.6 mg of 4 (0.127 mmol), and 10 mL of toluene, and then the reaction mixture was stirred at 100 °C. After 12 h, the mixture was cooled to room temperature, and the volatile materials were removed under reduced pressure. The residue was washed with Et2O (2 mL × 3) and dried under vacuum to afford 106.2 mg of 2 (0.108 mmol) as a yellow powder in 87% yield. 1H NMR (400 MHz, C6D6): δ 6.71−6.75 (m, 9H), 6.82−6.86 (m, 6H), 6.96−7.40 (m, 24H), 8.32−8.34 (m, 3H). 13 C{1H} NMR (100 MHz, C6D6): δ 128.7, 128.9, 129.1, 129.6, 132.4, 133.1, 134.2, 141.4, 145.7, 156.2, 207.7. 31P{1H} NMR (163 MHz, C6D6): δ 63.8 (d, JP−Rh = 147.1 Hz). IR (KBr, cm−1) ν(CO): 1948. Anal. Calcd for C55H42OP3RhGe: C, 66.90; H, 4.29. Found: C, 66.53;

H, 4.24. HRMS (m/z): [M]+ calcd for C55H42OP3RhGe 988.0715, found 988.0717. Preparation of {(Ph2P)C6H4}3SnRh(CO) (3). A Schlenk tube was charged with 243 mg of 7 (0.269 mmol), 247 mg of 4 (0.269 mmol), and 15 mL of toluene, and then the reaction mixture was stirred at 60 °C. After 12 h, the mixture was cooled to room temperature, and the volatile materials were removed under reduced pressure. The residue was washed with Et2O (2 mL × 3) and dried under vacuum to afford 236 mg of 3 (0.228 mmol) as a yellow powder in 85% yield. 1H NMR (400 MHz, C6D6): δ 6.70−6.73 (m, 9H), 6.80−6.84 (m, 6H), 6.92− 6.96 (m, 3H), 7.04−7.49 (m, 18H), 7.73−7.78 (m, 3H), 8.22−8.24 (m, 3H). 13C{1H} NMR (100 MHz, C6D6): δ 128.4, 128.6, 128.9, 129.3, 132.0, 132.2, 135.4, 141.4, 148.4, 154.6, 209.3. 31P{1H} NMR (163 MHz, C6D6): δ 62.3 (d, JP−Rh = 146.9 Hz, JP‑119Sn = 165.2 Hz). IR (KBr, cm−1) ν(CO): 1946. Anal. Calcd for C55H42OP3RhSn: C, 63.92; H, 4.42. Found: C, 63.51; H, 4.42. HRMS (FAB+): [M]+ calcd for C55H42OP3RhSn 1034.0526, found 1034.0522. Preparation of Rh(P(OMe)3)(Si(o-C6H4PPh2)3) (8). A Schlenk tube was filled with 1 (78.7 mg, 0.0835 mmol) and xylene (4 mL), trimethylphosphite (197 μL, 1.67 mmol) was added, and the reaction mixture was stirred at 140 °C. After 20 h, removal of the solvent under reduced pressure gave a pale yellow solid. The residue was washed with hexane (2 mL × 3) and dried under vacuum to afford 78.2 mg of 8 (0.0753 mmol) as a yellow powder in 90% yield. 1H NMR (400 MHz, C6D6): δ 2.85 (d, JH−P = 10.3 Hz, 9H, OMe), 6.75−7.04 (m, 18H, Ph), 7.16−7.36 (m, 21H, Ph), 8.27−8.29 (m, 3H, Ph). 31P{1H} NMR (163 MHz, C6D6): δ 51.7 (dd, JP−Rh = 157.9 Hz, JP−P = 51.4 Hz, Ph2P), 147.9 (qd, JP−Rh = 176.2 Hz, JP−P = 51.4 Hz, P(OMe)3). Anal. Calcd for C57H51O3P4RhSi: C, 65.90; H, 4.95. Found: C, 66.03; H, 5.22. HRMS (FAB+): [M]+ calcd for C57H51O3P4RhSi 1038.1613, found 1038.1619. Preparation of Rh(P(OMe)3)(Ge(o-C6H4PPh2)3) (9). A Schlenk tube was filled with 2 (65.8 mg, 0.0666 mmol), and toluene (4 mL). Trimethylphosphite (157 μL, 1.33 mmol) was added, and the reaction mixture was stirred at 110 °C. After 24 h, removal of the solvent under reduced pressure gave a pale yellow solid. The residue was washed with hexane (2 mL × 3) and dried under vacuum to afford 66.4 mg of 9 (0.0613 mmol) as a yellow powder in 92% yield. 1H NMR (400 MHz, C6D6): δ 2.86 (d, JH−P = 10.3 Hz, 9H, OMe), 6.72−6.96 (m, 18H, Ph), 7.20−7.33 (m, 21H, Ph), 8.33−8.35 (m, 3H, Ph). 31P{1H} NMR (163 MHz, C6D6): δ 56.7 (dd, JP−Rh = 154.2 Hz, JP−P = 47.7 Hz, Ph2P), 149.0 (qd, JP−Rh = 194.6 Hz, JP−P = 47.7 Hz, P(OMe)3). Anal. Calcd for C57H51O3P4RhGe: C, 63.19; H, 4.74. Found: C, 62.85; H, 5.01. HRMS (FAB+): [M]+ calcd for C57H51O3P4RhGe 1084.1055, found 1084.1045. Preparation of Rh(P(OMe)3)(Sn(o-C6H4PPh2)3) (10). A Schlenk tube was filled with 3 (53.0 mg, 0.0513 mmol) and touene (2.5 mL). Trimethylphosphite (12.1 μL, 0.103 mmol) was added, and the reaction was stirred at 110 °C. After 48 h, removal of the solvent under reduced pressure gave a pale yellow solid. The residue was washed with hexane (2 mL × 3) and dried under vacuum to afford 37.6 mg of 10 (0.0333 mmol) as a yellow powder in 65% yield. 1H NMR (400 MHz, C6D6): δ 2.82 (d, JH−P = 10.7 Hz, 9H, OMe), 6.69−6.95 (m, 18H, Ph), 7.19−7.36 (m, 21H, Ph), 8.21−8.22 (m, 3H, Ph). 31P{1H} NMR (163 MHz, C6D6): δ 55.7 (dd, JP−Rh = 150.5 Hz, JP−P = 47.7 Hz, JP‑119Sn = 179.9 Hz, Ph2P), 153.3 (qd, JP−Rh = 223.9 Hz, JP−P = 47.7 Hz, JP‑119Sn = 51.4 Hz, P(OMe)3). Anal. Calcd for C57H51O3P4RhSn: C, 60.61; H, 4.55. Found: C, 60.31; H, 4.47. HRMS (FAB+): [M]+ calcd for C57H51O3P4RhSn 1130.0866, found 1130.0868. Reactions of 8−10 with CO. A 50 mL Schlenk tube was filled with 8 (13.4 mg, 0.0142 mmol) and toluene (2 mL). After the solution was evacuated at −196 °C using a high-vacuum line, 1 atm of CO (about 2.0 mmol) was transferred into the tube. The reaction mixture was stirred at 60 °C. After 10 h, the mixture was cooled to room temperature, and the solvent was removed under reduced pressure. Washing the residual solid with hexane (2 mL × 1) afforded 1 as a pale yellow solid (13.7 mg, 0.0132, 93%). The P(OMe)3/CO substitution reactions of 9 and 10 with CO were similarly carried out by using 9 and 10 instead of 8, and the almost quantitative formation of 2 and 3 was confirmed. 2216

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Estimate of the Rate Constants Concerning the Reactions of 1−3 with 2 equiv of Trimethylphosphite. An NMR tube was charged with 1 (6.2 mg, 6.6 μmol), toluene-d8 (0.4 mL), trimethylphosphite (1.55 μL, 0.0132 mmol, 2 equiv), and triphenylphosphine oxide (5.5 mg) as an internal standard. The reactions were performed at 110 °C, and the reactions were monitored by 31P NMR spectroscopy. The reactions were demonstrated to be first-order at the initial step, and the rate constants were calculated on the basis of the time conversion of [1]: k = 7.38 × 10−6 s−1. The rate constants concerning the reactions of 2 and 3 with P(OMe)3 were calculated by using 6.5 mg of 2 (6.6 μmol) and 6.8 mg of 3 (6.6 μmol) instead of 1: k = 5.70 × 10−5 s−1 (for 2); 6.26 × 10−5 s−1 (for 3). Kinetic Experiments of the Reaction of 2 with Trimethylphosphite. A Schlenk tube was charged with 2 (26.0 mg, 0.0263 mmol), toluene-d8 (1.6 mL), and triphenylphosphine oxide (22.0 mg) as an internal standard. The solution was divided evenly into four NMR sample tubes. Different equivalents of trimethylphosphite (1.55 μL, 0.0132 mmol, 2 equiv; 6.20 μL, 0.0528 mmol, 8 equiv; 10.9 μL, 0.0924 mmol, 14 equiv; 15.5 μL, 0.132 mmol, 20 equiv) were introduced into each tube, and the reactions were performed at 110 °C. The reactions were monitored by 31P NMR spectroscopy, and the rate constants were calculated on the basis of the time conversion of [2]: k = 5.70 × 10−5 s−1 (2 equiv); 6.73 × 10−5 s−1 (8 equiv); 1.00 × 10−4 s−1 (14 equiv); 2.01 × 10−4 s−1 (20 equiv). Eyring Plot for the Reaction of 2 with Trimethylphosphite. A Schlenk tube was charged with 2 (26.0 mg, 0.0263 mmol), toluene-d8 (1.6 mL), and triphenylphosphine oxide (14.8 mg) as an internal standard. The solution was divided up evenly into four NMR sample tubes. Then 20 equiv of trimethylphosphite (14.5 μL, 0.132 mmol) was introduced into each tube, and the reactions were performed at appropriate temperature (80, 90, 100, and 110 °C). The reactions were monitored by 31P NMR spectroscopy. The rate constants were calculated on the basis of the time conversion of [2]: k = 1.46 × 10−5 s−1 (80 °C); 3.75 × 10−5 s−1 (90 °C); 9.09 × 10−5 s−1 (100 °C); 2.01 × 10−4 s−1 (110 °C). The temperature dependence of the rate constants yielded the following activation parameters (Eyring plot was shown in Figure S1): ΔH‡ = 22.8 ± 0.3 kcal mol−1 and ΔS‡ = −16.4 ± 0.7 cal mol−1 K−1. Structure Determination by X-ray Diffraction. Suitable single crystals of {(Ph2P)C6H4}3SnCl and 9 were obtained from slow diffusion of n-hexane into the CH2Cl2 solution of {(Ph2P)C6H4}3SnCl or the toluene solution of 9. Single crystals of 1, 2, and 3 were obtained from the preparations described above. The prepared single crystals were mounted on the CryoLoop with Palaton oil, and the Xray diffraction experiments were carried out using a Rigaku/MSC Mercury CCD diffractometer with a graphite-monochromated Mo Kα radiation source (λ = 0.71069 Å) at 200 K. Cell refinement and data reduction were carried out using the CrystalClear program.22 The intensity data were corrected for Lorentz−polarization effects and empirical absorption. The structures were determined by the direct method (SIR 97). All non-hydrogen atoms were found by a difference Fourier synthesis and were refined anisotropically. The refinement using the SHELXL-97 package23 was carried out by the least-squares methods based on F2 with all measured reflection data. The crystal data and results of the analyses are listed in Tables S2−S11. Density Functional Theory Calculation. DFT calculations were carried out at the B3PW91 level24 in conjunction with the Stuttgart/ Dresden ECP1925 and associated with triple-ξ basis sets for Rh and Sn. For H, C, O, P, Si, and Ge, 6-31G(d) was employed. Calculations utilizing the Gaussian09 program26 were performed on the actual structures of 1−3 by using the atomic coordinates determined from Xray diffraction analysis.

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available in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The present research is supported by Challenging Exploratory Research (No. 23655056) and a Grant-in-Aid for Young Scientists (B) (No. 23750064) from Japan Society of the Promotion of Science. H.K. acknowledges financial support from the Sasakawa Scientific Research Grant from the Japan Science Society.

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ASSOCIATED CONTENT

S Supporting Information *

Tables of atomic coordinates and parameters, bond lengths and angles, torsion angles, and structure refinement details and ORTEP drawings of 1, 2, 3, and 9; crystallographic data are also 2217

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