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.