Synthesis and structures of phosphinidene and phosphido complexes of iron and cobalt

Abstract

Treatment of Na[Co₂(CO)₂(η-C₅H₅)₂] with R¹PCl₂(R¹= 2,4,6-Bu^t₃C₆H₂) results in a dicobalt phosphinidene complex, [Co₂(CO)₂(η-C₅H₅)₂(µ-PR¹)], of the ‘open’ type containing a trigonal-planar phosphorus, no metal–metal bond, and some degree of Co–P multiple bonding as established by an X-ray diffraction study. The attempted synthesis of di-iron phosphinidene complexes via the reaction of [NEt₄]₂[Fe₂(CO)₈] with dichlorophosphines RPCl₂ failed to produce an isolable species containing the desired phosphinidene fragment. For R =(Me₃Si)₂CH a large number of products were formed, two of which were isolated and identified within the same crystal structure by X-ray crystallography. Both complexes were found to contain a di-iron centre bridged by a phosphido ligand: [Fe₂(CO)₆(µ-OH){µ-PH[CH(SiMe₃)₂]}] and [Fe₂(CO)₇(µ-H){µ-P(OH)[CH(SiMe₃)₂]}]. In contrast, for R = R¹, a mixture of mono- and di-nuclear iron species were observed by ³¹P n.m.r. spectroscopy, these being [Fe₂(CO)₆(µ-PHR¹)₂], [Fe(CO)₄{PH[CH₂C(Me)₂C₆H₂Bu^t₂]}], [Fe(CO)₄(PH₂R¹)], and also the diphosphine R¹PHPHR¹. In addition to the synthetic and structural studies, extended Hückel molecular orbital calculations have been carried out on model phosphinidene complexes in an attempt to understand their electronic and structural features.