Simple route to new palladium-carbonyl-bis(diphenylphosphino)methane complexes

Abstract

The method of synthesizing metal-carbonyl-dppm complexes [dppm = bis(diphenylphosphino)methane) devised by Holah and Hughes has been extended to include palladium. Specifically, reductions of palladium salts by NaBH4 in the presence of dppm and CO lead to any one or more of five different palladium-dppm complexes. Two of these complexes, (see document) were identified spectroscopically and have been previously prepared by other less convenient routes. Three new palladium complexes are also reported. The hexameric Pd 6 ( µ- dppm) 3 ( µ- C0) 6 , 3, has been identified spectroscopically and crystallographically. The X-ray crystal structure of 3 shows that crystals of this complex lie in the space group Pna2 1 and are orthorhombic with unit cell dimensions of a, 39.836(13) A; b, 15.587(4) A; c, 12.1654 A. The other two unidentified complexes 4a and 5a were only partially characterized spectroscopically. Two possible structures, (see document) are proposed for 4a and these proposals are based largely on spectroscopic and analytical evidence. An X-ray quality crystal of 4a has been obtained very recently. It has been found to diffract satisfactorily and data are currently being collected as of this report. The unidentified complex 5a was characterized only partially. Complex 5a is a fluxional molecule at room temperature and is thought to contain at least 3 Pd trimeric units. The inter-relationships between 3, 4a and 5a are discussed.