Divinyldisiloxane and divinylsilane complexes of rhodium(I)

Reaction of the tetrakis(cyclooctene)rhodium(I) complex [{Rh(C8H14-c)(2)(mu-Cl)}(2)] with the appropriate divinyldisiloxane molecules (ViSiR(2))(2)O (R = Me or Ph) yields, by displacement of the cycloctene ligands, the complexes [{Rh(ViSiR(2))(2)O(mu-Cl)}(2)] (R = Me (1) or Ph (2)). These react further with a tertiary phosphine PR3 to give cis-[Rh{(ViSiR(2))(2)O}(PR3')Cl] (R' = Ph or C6H4Me-p). The complex cis-[{Rh(Vi(2)SiMe(2))(mu-Cl)}(2)] (7) was similarly prepared by the displacement of ethylene from [{Rh(C2H4)(2)(mu-Cl)}(2)] by the divinyldimethylsilane Vi(2)SiMe(2). X-ray molecular structures of the crystalline complexes 1, 2 and 7 show a distorted square planar Rh(I) environment, the CH2=CH groups being orthogonal to this plane; 1 and 2 have the Rh-(ViSiR(2))(2)O metallacycle in the chair conformation, but differ in the nature of the central Rh(Cl)RhCl core, which is planar for 1 and puckered for 2, but each of 1 and 2 is the rac-diastereoisomer, whereas 7 has the meso-configuration. In solution 1 and 2 exist as a mixture of isomers, probably the rac- and meso-pairs as established by multinuclear NMR spectral studies. A series of saturation transfer NMR spectroscopic experiments showed that the divinyldisiloxane ligands in [{Rh(ViSiPh(2))(2)O(mu-Cl)}(2)] underwent a dynamic process involving the dissociation, rotation and then reassociation of the vinyl groups. (C) 1999 Elsevier Science S.A. All rights reserved.