Preliminary investigations on the chemistry of (η4-1-phosphabutadiene)tricarbonyliron complexes. Synthesis and X-ray crystal structure analysis of a (η4-2-phosphabutadiene)tricarbonyliron complex

Abstract

The reaction of the η²-complexed and half-masked dialdehyde [Fe(CO)₄{trans-(MeO)₂CHCHCHCHO}] with the ‘phospha-Wittig’ reagent [W(CO)₅{PHPhPO(OEt)₂}] yields, after unmasking of the second aldehyde functionality, the 1-phosphabutadiene complex [Fe(CO)₃{η⁴-OCHCHCHCHPPh[W(CO)₅]}], 4. The aldehyde functionality of 4 normally reacts with methyllithium, a phosphorus ylide, LiAlH₄, or a dimercaptan to give the expected products in high yield without destruction of the (η⁴-1-phosphadiene)tricarbonyliron moiety. Thus, Fe(CO)₃ is a convenient protecting group for the otherwise unstable 1-phosphadiene unit. Similarly, the reaction of isobutyraldehyde with the phospha-Wittig reagent [W(CO)₅{trans-PhCHCHPHPO(OEt)₂}] yields a (2- phosphabutadiene)pentacarbonyltungsten complex whose X-ray crystal structure analysis shows a planar, transoid but not delocalized 2-phosphadiene unit. Reaction of this complex with [Fe₂(CO)₉] gives a complex with a planar, cisoid and fully delocalized-2-phosphadiene unit according to the X-ray data.