Thermal Si-C bond cleavage of LRhH(SiAr3)(mu-H)(mu-Cl)RhH(SiAr3)L (Ar = C6H5, C6H4F-p; L = P(i-Pr)(3)) to give LRhH(mu-SiAr3)(mu-SiAr2)(mu-Cl)RhHL containing symmetrically bridging triarylsilyl and diarylsilylene ligands

The reaction of dinuclear rhodium complex LRhH(SiPh3)(mu-H)(mu-Cl)RhH(SiPh3 )L (1; L = P(i-Pr)(3)) with excess HSi(C6H4F-p)(3) leads to replacement of the SiPh3 ligands with the Si(C6H4F-p)(3) group to give LRhH[Si(C6H4F-p)(3) ](mu-H)(mu-Cl)RhH[Si(C6H4F-p)(3)]L (2) at room temperature. HSiPh2(C6H4F-p) and HSiPh(C6H4F-p)(2) also react with 1 to give LRhH[SiPh2(C6H4F-p)(mu-H)( mu-Cl)RhH[SiPh2(C6H4F-p)]L (3) and LRhH[SiPh(C6H4F-p)(2)](mu-H)(mu-Cl)RhH[S iPh(C6H4F-p)(2)]L (4), respectively. Heating of benzene or toluene solution of 1 and 2 at 60 degrees C results in Si-C bond cleavage of a triarylsilyl ligand and affords LRhH(mu-SiAr3)(mu-SiAr2)(mu-Cl)RhHL (7, Ar = Ph; 8, Ar = C6H4F-p) accompanied by liberation of benzene and fluorobenzene, respecti vely. The NMR (H-1 and P-31) spectra of 7 and 8 indicate symmetrical coordi nation of the bridging triarylsilyl and diarylsilylene groups to two Rh cen ters. The reaction of I to form 7 at 55-70 degrees C obeys first-order kine tics with the kinetic parameters: Delta G double dagger = 112 kJ mol(-1), D elta H double dagger =129 kJ mol(-1), and Delta S double dagger = 58 J mol( -1) deg(-1) at 298 K. Complexes 2-4 also undergo thermal Si-C bond cleavage of a triarylsilyl Ligand to Liberate fluorobenzene as the organic product. The rate constants of the reaction increase in the order 2 < 4 < 3 < 1.