SUCCESS AND SERENDIPITY DURING STUDIES AIMED AT PREPARING CARBENERHODIUM(I) COMPLEXES

The preparation of a series of new square-planar and half-sandwich type carbenerhodium(I) complexes will be described. The key to success is the use of the bis(stibane)rhodium compound trans-[RhCl(C2H4)(SbiPr(3))(2)] as starting material from which in a stepwise manner the complexes trans-[RhCl(=CRR')(SbiPr(3))(2)], trans-[RhCl(=CRR')L(2)] (L = PiPr(3), AsiPr(3), SbEt(3)) and [C5H5Rh(=CCR')L] (L = SbiPr(3), PiPr(3), PMe(3), CO, CNtBu) have been obtained. Displacement of the carbene ligand in either trans-[RhCl(=CPh(2))L(2)] (L = SbiPr(3), PiPr(3) or [C5H5Rh(= CPh(2))(PiPr(3))] by CO or CNtBu leads to the formation of the corresponding carbonyl- or isocyanidrhodium compounds and the C-C coupling products Ph(2)C=C=O and Ph(2)C=C=NtBu, respectively. The carbene ligand is also involved in the selective formation of the isomeric olefins CH2=CHCPh(2)H and Ph(2)C=CHCH3 on treatment of trans[RhCl(=CPh(2))(SbiPr(3))(2)] and trans-[RhCl(= CPh(2))(PiPr(3))(2)] with ethene. The most spectacular reaction of the bis(triisopropylstibane) complexes, however, occurs on warming of trans-[RhCl(=CRR')(SbiPr(3))(2)] in the absence of any substrate which yields the first representatives of dinuclear transition-metal compounds containing a tertiary stibane ligand in a bridging position. Some exploratory studies on the reactivity of the Rh-2(mu-SbiPr(3)) complexes indicate that the triisopropylstibane can be replaced by SbMe(3), SbEt(3) or CNtBu without destroying the dimetallic core of the molecule.