A New Family of Mixed-Valence Dinuclear Rhodium Complexes Containing the Two Metal Centers in Different Stereochemical enviironments

摘要

A series of dinuclear chelate complexes of the general composition [Rh_2(k~2-L)_2(#mu#-CR_2)_2(#mu#-SbiPr_3)] (R = Ph, p-Tol; L = CF_3CO_2~-, acac~-, acac-f_3~-) and [Rh_2Cl(k~2-L)_2(#mu#-CR_2)_2(#mu#-SbiPr_3)] (R = Ph, p-Tol; L = acac~-, acac-f_3~-) has been prepared by replacement of the chloro ligands in the precursors [Rh_2Cl_2(#mu#-CR_2)_2(#mu#-SbiPr_3)] by anionic chelates. The lability of the SbiPr_3 bridge in the rhodium dimmers is illustrate by the reactions of [Rh_2(k~2-acac)_2(#mu#-CR_2)_2(#mu#-SbiPr_3)] (7,8) with Lewis bases such as CO, CntBu, and SbEt_3 which lead to the formation of the substitution products [Rh_2(k~2-acac)_2(#mu#-CR_2)_2(#mu#-L')] (13-16) in excellent yields. Treatment of 7 and 8 with sterically demanding tertiary phosphanes PR_3 (R_3 = iPr_3, iPr_2Ph, iPrPh_2, Ph_3) affords the mixed-valence Rh~0-Rh~(II) complexes [Rh_2(k~2-acac)_2(#mu#-CPh_2)_2Rh(PR_3)] (21-24) and [Rh_2(k~2-acac)_2Rh{#mu#-C(p-Tol)_2}_2Rh(PiPr_3)] (25) for which there is no precedence. The terminal PiPr_3 ligand of 21 is easily displaced by alkynes, CNtBu, and CO to give, by preserving the [k~2-acac]_2Rh{#mu#-CPh_2}_2Rh} molecular core, the related dinuclear compounds 26-31 in which the coordination number of the Rh~0 center is 3, 4, or 5. The molecular structures of [Rh_2Cl(k~2-acac){#mu#-CPh_2}_2(#mu#-SbiPr_3)] (5), [Rh_2(k~2-acac)_2{#mu#-CPh_2}_2(#mu#-CO (13), [(k~2-acac)_2Rh(#mu#-CPh_2)_2Rh(PiPr_3)] (21), and [(k~2-acac)_2Rh{#mu#-CPh_2}_2Rh(CntBu)_2] (30) have been determined crystallographically.