Structure and Chemical Properties of Chlorohydrido(diarylsilyl)rhodium(III) Complexes,mer-RhCl(H)(SiHAr₂)(PMe₃)₃. Thermally Induced Chloro Transfer from Rhodium to Silicon in the Complexes and Silane Exchange

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Abstract

Reactions of the diarylsilanes H2SiPh2, H2Si(C6H4Me-p)2, H2Si(C6H4OMe-p)2, H2Si(C6H4F-p)2, and H2Si(C6H4CF3-p)2 with [Rh(PMe3)4]Cl involve oxidative addition of an Si−H bond of the substrates to give mer-RhCl(H)[SiH(C6H4X-p)2](PMe3)3 (1, X = H; 2, X = Me; 3, X = OMe; 4, X = F; 5, X = CF3). X-ray crystallography of 1, 3, 4, and 5 shows a distorted-octahedral coordination around the Rh center with three meridional PMe3 ligands and with the chloro and diarylsilyl ligands at mutually trans positions. The Rh−Si bond distances of the complexes are in the range 2.311−2.319 Å. Addition of H2Si(C6H4Me-p)2 to a toluene solution of 1 results in partial conversion of the complex into 2 accompanied by liberation of H2SiPh2. The exchange of the diphenylsilyl ligand of 1 on addition of the other diarylsilanes proceeds reversibly at 10−50 °C with the thermodynamic parameters of the reactions 1 + H2Si(C6H4X-p)2 = mer-RhCl(H)[SiH(C6H4X-p)2](PMe3)3 + H2SiPh2 as ΔH° = 4.16 kJ mol-1 and ΔS° = 8.2 J mol-1 K-1 for X = Me, ΔH° = 6.51 kJ mol-1 and ΔS° = 11.7 J mol-1 K-1 for X = OMe, and ΔH° = −2.33 kJ mol-1 and ΔS° = −5.3 J mol-1 K-1 for X = F, respectively. Enthalpy of the reactions of 1 with H2Si(C6H4X-p)2 (X = Me, OMe, and F) decreases with increase in the σp value of X. Heating a toluene solution of 1 at 50 °C and at 110 °C gives mixtures of fac-Rh(H)2(SiClPh2)(PMe3)3 (6) and RhCl(H)(SiClPh2)(PMe3)3 (7). The structure of 6 has been determined by X-ray crystallography, while 7 was characterized by comparison of the NMR (1H, 31P{1H}, 13C{1H}, and 29Si{1H}) peaks with those of the complex prepared independently from the reaction of HSiClPh2 with [Rh(PMe3)4]Cl.

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