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

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Abstract
A series of dinuclear chelate complexes of the general composition [Rh2(κ2‐L)2(μ‐CR2)2(μ‐SbiPr3)] (R=Ph, p‐Tol; L=CF3CO2−, acac−, acac‐f3−) and [Rh2Cl(κ2‐L)(μ‐CR2)2(μ‐SbiPr3)] (R=Ph, p‐Tol; L=acac−, acac‐f3−) has been prepared by replacement of the chloro ligands in the precursors [Rh2Cl2(μ‐CR2)2(μ‐SbiPr3)] by anionic chelates. The lability of the SbiPr3 bridge in the rhodium dimers is illustrated by the reactions of [Rh2(κ2‐acac)2(μ‐CR2)2(μ‐SbiPr3)] (7, 8) with Lewis bases such as CO, CNtBu, and SbEt3 which lead to the formation of the substitution products [Rh2(κ2‐acac)2(μ‐CR2)2(μ‐L′)] (13–16) in excellent yields. Treatment of 7 and 8 with sterically demanding tertiary phosphanes PR3 (R3=iPr3, iPr2Ph, iPrPh2, Ph3) affords the mixed‐valence Rh0–RhII complexes [(κ2‐acac)2Rh(μ‐CPh2)2Rh(PR3)] (21–24) and [(κ2‐acac)2Rh{μ‐C(p‐Tol)2}2Rh(PiPr3)] (25) for which there is no precedence. The terminal PiPr3 ligand of 21 is easily displaced by alkynes, CNtBu, and CO to give, by preserving the {(κ2‐acac)2Rh(μ‐CPh2)2Rh} molecular core, the related dinuclear compounds 26–31 in which the coordination number of the Rh0 center is 3, 4, or 5. The molecular structures of [Rh2Cl(κ2‐acac)(μ‐CPh2)2(μ‐SbiPr3)] (5), [Rh2(κ2‐acac)2(μ‐CPh2)2(μ‐CO)] (13), [(κ2‐acac)2Rh(μ‐CPh2)2Rh(PiPr3)] (21), and [(κ2‐acac)2Rh(μ‐CPh2)2Rh(CNtBu)2] (30) have been determined crystallographically.