SYNTHESIS AND PROPERTIES OF NEW TRIS(CYANOETHYL)PHOSPHINE COMPLEXES OF PLATINUM(0,II), PALLADIUM(0,II), IRIDIUM(I) AND RHODIUM(I) - CONFORMATIONAL-ANALYSIS OF TRIS(CYANOETHYL)PHOSPHINE LIGANDS

The tris(cyanoethyl)phosphine (tcep) complexes trans-[PtCl2(tcep)(2)], cis-[PtMe2(tcep)(2)] and trans-[PtMeCl(tcep)(2)] are prepared by trea tment of the corresponding [PtXY(cod)] (cod = 1,5-cyclooctadiene) with tcep. Reduction of trans-[PtCl2(tcep)(2)] with NaBH4 gives trans-[PtH Cl(tcep)(2)] which, in the presence of tcep and NEt3, gives the coordi natively unsaturated platinum(0) complex [Pt(tcep)(3)]. This coordinat ively unsaturated species is also formed when [Pt(norbornene),] reacts with tcep. [Pt(tcep),] is very unreactive compared to its PEt3 analog ue: it is air-stable and does not react with further tcep to form an 1 8-electron species. It is protonated by HBF4 . OEt2 to form [PtH(tcep) (3)]BF4. The complex trans-[PdCl2(tcep)(2)] is made from [PdCl2(NCPh)( 2)] and tcep and the derivatives trans-[PdX2(tcep)(2)] (X = Br or I) a re made by metathesis of the dichloro complex. Reduction of trans-[PdC l2(tcep)(2)] with LiOMe in the presence of tcep gave the palladium(0) complex [Pd(tcep)(3)] which, like its platinum(0) analogue, undergoes exchange with free tcep on the NMR timescale. The palladium complex re acts with dibenzylideneacetone (dba) to form [Pd(eta(2)-dba)(tcep)(2)] ; the same product is formed in the reaction of [Pd(eta(2)-dba)(2)] an d tcep. Reaction of [Pd2Cl2(eta(3)-C3H3)(2)] and tcep gives [PdCl(tcep )(eta(3)-C3H3)] or [Pd(tcep)(2)(eta(2)-C3H3)]Cl depending on stoichiom etry. The rhodium(I) and iridium(I) complexes trans-[MCl(CO)(tcep)(2)] , [MCl(tcep)(cod)] and [MCl(tcep)(3)] are all readily made from tcep a nd an appropriate precursor. All new compounds have been fully charact erised by a combination of elemental analysis, IR, P-31, C-13, H-1 and Pt-195 NMR spectroscopy. The crystal structure of [IrCl(tcep)(3)] as a MeCN solvate shows a distorted square planar coordination geometry ( trans angles at Ir(I) ca. 164 degrees, cia P-Ir-P av. 96 degrees, cis P-Ir-Cl av. 85 degrees). Analysis of the conformations of tcep ligands in this and other published tcep complexes shows there is a preferenc e for conformations in which aaa, aag or g(+)g(-) (a = anti, g = gauch e) arrangements of the three M-P-C-C chains are avoided. (C) 1998 Else vier Science S.A.