Synthesis and characterization of tungsten oxo alkylidene complexes via the reaction of WCl 2(O)[PX 3] 3 (PX 3  P(OMe) 3, PMe 2Ph, PMePh 2) with 4,8-dioxaspiro[2,5]oct-1-ene (ketalcyclopropene)

Abstract

This paper describes the synthesis and characterization of the first tungsten oxo ketalvinyl alkylidene complexes via the reaction of WCl 2 (O)[PX 3] 3 (PX 3  P(OMe) 3 1, PMe 2Ph 2, PMePh 2 3 4,8-dioxaspiro[2,5]oct-1-ene (ketalcyclopropene). Complex 1 reacts with ketalcyclopropene affording almost quantitatively the corresponding s- cis-vinyl alkylidene complex W(CHCHCR(Cl 2(O)[P(OMe) 3] 4 (RCOCH 2CH 2CH 2O−). NMR data for this complex support a pseudo octahedral structure where the oxygen ligand occupies an axial position. In order to maximize π-bonding the alkylidene ligand must be cis to the oxo ligand and the chelating ketal functionality is placed trans to the oxo ligand. The P(OMe) 3 and chloride ligands lie in the equatorial plane with the P(OMe) 3 ligand situated cis to the alkylidene ligand. Complexes 2 and 3 also react with a slight excess of ketalcyclopropene affording vinyl alkylidene complexes that adopt different coordination modes. The two chloride ligands in complex 4 can be exchanged by reaction with different lithium alkoxides yielding tungsten oxo alkoxo ketalvinyl alkylidene complexes that present different geometry depending on the alkoxide ligands.