THE UNUSUAL ATTACHMENT OF AN ALKYNE ACROSS THE OPEN EDGE OF A RH2PD COMPLEX

A structurally interesting hetero-trinuclear complex of formula ):eta( 2):eta(2)-CF3C2CF3){eta(2)-Ph2P(CH2)(2)PPh2} (III) has been formed fro m the reaction between u-eta(1):eta(1)-CF3C2CF3){eta(1)-Ph2P(CH2)(2)PP h2} (II) and (eta(5)-C5H5)Ph(eta(3)-C3H5). Determination of the struct ure of (III) by X-ray crystallography has shown that there is an open Rh2Pd core with an unusual attachment of the alkyne. This is sigma-bon ded to the central rhodium and sits across the open Rh...Pd edge of th e core. Molecular modeling established that one CF3 is free to rotate but the other is restrained. The bisphosphine, which was initially att ached to rhodium, is chelated to palladium. In solution, a second isom er (IV) coexists with (III); spectroscopic results indicate that (IV) incorporates a Rh-C(O)-C(CF3)=CCF3 unit within a structure that has a closed Rh2Pd core. Variable temperature NMR data indicate that the mol ecular structures of both isomers are fluxional in solution. (C) 1998 Elsevier Science S.A. All rights reserved.