Dialkylallenylidenekomplexe mit Pentacarbonylfragmenten der VIb Metalle/Dialkylallenylidene Complexes with Pentacarbonyl Fragments of VI b Metals

Abstract

Abstract In the context of the synthesis of allenylidene compounds, the reaction of methylpropiolate with a (OC)5CrO(C2H5)2 complex was investigated. The species pentacarbonyl- (methylpropiolate)chromium(0) (1), 2,4-bis(methoxycarbonyl)-cyclobut-2-en-1-yliden-1- pentacarbonylchromium(0) (2) and cis-2,4-dimethoxycarbonyl-1,3-butadien-1 -yliden-1 - pentacarbonylchromium (3) were isolated. Attempts to synthesize allenylidene complexes from 1 were unsuccessful. Di-iso-propyl or di-tert-butylallenylidene complexes with chromium or tungsten centers (4a, 4b, 5a, 5b) were finally obtained by the photochemical reaction of pentacarbonylpropargylates, (OC)5MC(O)C ≡ CCR2O2-, M = Cr, W, and subsequent desoxygenation. The complexes 4 a, b were characterized as triphenylphosphane adducts, di-iso-propylallenylidenetriphenylphosphorane complexes (6a und 6b). The structure of 6 a was determined by X-ray methods.