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

Reactions of the diarylsilanes H 2 SiPh 2, H 2 Si(C 6 H 4 Me- p ) 2, H 2 Si(C 6 H 4 OMe- p ) 2, H 2 Si(C 6 H 4 F- p ) 2, and H 2 Si(C 6 H 4 CF 3 - p ) 2 with [Rh(PMe 3 ) 4 ]Cl involve oxidative addition of an Si−H bond of the substrates to give mer -RhCl(H)[SiH(C 6 H 4 X- p ) 2 ](PMe 3 ) 3 ( 1, X = H; 2, X = Me; 3, X = OMe; 4, X = F; 5, X = CF 3 ). X-ray crystallography of 1, 3, 4, and 5 shows a distorted-octahedral coordination around the Rh center with three meridional PMe 3 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 H 2 Si(C 6 H 4 Me- p ) 2 to a toluene solution of 1 results in partial conversion of the complex into 2 accompanied by liberation of H 2 SiPh 2 . 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 + H 2 Si(C 6 H 4 X- p ) 2 = mer -RhCl(H)[SiH(C 6 H 4 X- p ) 2 ](PMe 3 ) 3 + H 2 SiPh 2 as Δ H ° = 4.16 kJ mol - 1 and Δ S ° = 8.2 J mol - 1 K - 1 for X = Me, Δ H ° = 6.51 kJ mol - 1 and Δ S ° = 11.7 J mol - 1 K - 1 for X = OMe, and Δ H ° = −2.33 kJ mol - 1 and Δ S ° = −5.3 J mol - 1 K - 1 for X = F, respectively. Enthalpy of the reactions of 1 with H 2 Si(C 6 H 4 X- p ) 2 (X = Me, OMe, and F) decreases with increase in the σ p value of X. Heating a toluene solution of 1 at 50 °C and at 110 °C gives mixtures of fac -Rh(H) 2 (SiClPh 2 )(PMe 3 ) 3 ( 6 ) and RhCl(H)(SiClPh 2 )(PMe 3 ) 3 ( 7 ). The structure of 6 has been determined by X-ray crystallography, while 7 was characterized by comparison of the NMR ( 1 H, 31 P{ 1 H}, 13 C{ 1 H}, and 29 Si{ 1 H}) peaks with those of the complex prepared independently from the reaction of HSiClPh 2 with [Rh(PMe 3 ) 4 ]Cl.