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-But3C6H2) 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)2C6H2But2]}], [Fe(CO)4(PH2R1)], and also the diphosphine R1PHPHR1. In addition to the synthetic and structural studies, extended Huckel molecular orbital calculations have been carried out on model phosphinidene complexes in an attempt to understand their electronic and structural features.