The unusual attachment of an alkyne across the open edge of a Rh2Pd complex

A structurally interesting hetero-trinuclear complex of formula (eta(5)-C5H5),Rh2Pd(mu(3)-CO)(mu-eta(1):eta(2):eta(2)-CF3C2CF3){eta(2)-Ph2P(CH2)(2)PPh2} (III) has been formed from the reaction between (eta(5)-C5H5)2Rh(2)(CO)(mu-eta(1):eta(1)-CF3C2CF3){eta(1)-Ph2P(CH2)(2)PPh2} (II) and (eta(5)-C5H5)Ph(eta(3)-C3H5). Determination of the structure 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-bonded to the central rhodium and sits across the open Rh...Pd edge of the core. Molecular modeling established that one CF3 is free to rotate but the other is restrained. The bisphosphine, which was initially attached to rhodium, is chelated to palladium. In solution, a second isomer (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 molecular structures of both isomers are fluxional in solution. (C) 1998 Elsevier Science S.A. All rights reserved.