Structural chemistry of binuclear metal centres. Crystal and molecular structures of the µ-vinyl and µ-methylcarbene complexes [Fe2(CO)2(µ-CO)(µ-CHCH2)(η-C5H5)2][BF4] and [Fe2(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2]

Abstract

Protonation of [Fe₂(CO)(µ-CO){µ-C(O)C₂H₂}(η-C₅H₅)₂] with HBF₄·OEt₂ affords the µ-vinyl cation of [Fe₂(CO)₂(µ-CO)(µ-CHCH₂)(η-C₅H₅)₂][BF₄](1 ). Reaction of (1) with NaBH₄ yields the µ-carbene complex [Fe(CO)₂(µ-CO)(µ-CHMe)(η-C₅H₅)₂](2). Both (1) and (2) have been studied using X-ray diffraction methods. Complex (1) crystallizes in the orthorhombic space group Pnma(no. 62) with unit-cell dimensions a= 12.149(4), b= 10.745(3), c= 12.470(3)Å, and Z= 4. The structure has been refined to R 0.083 for 1 281 intensity data, and consists of isolated [Fe₂(CO)₂(µ-CO)(µ-CHCH₂)(µ-C₅H₅)]⁺ cations and [BF₄]^– anions, each lying on sites of crystallographic mirror symmetry. The cations show orientational disorder, with the methylene function of the µ-vinyl group occupying two sites of occupancy 0.5 related by the mirror plane. The iron atoms are singly bonded to one another and are separated by 2.595(2)Å, being bridged both by vinyl and carbonyl ligands. In addition each iron atom carries one terminal carbonyl ligand and an η⁵-cyclopentadienyl moiety. The molecular cation adopts a conformation which places the cyclopentadienyl ligands mutually cis with the vinylic methylene anti to these groups. Complex (2) crystallizes in the orthorhombic space group Pnma(no. 62) with unit-cell dimensions a= 15.096(9), b= 14.414(8), c= 6.336(4)Å, and Z= 4. The structure has been refined to R 0.046 for 1 631 intensity data, and consists of isolated molecules of [Fe₂(CO)₂(µ-CO)(µ-CHCH₃)(η-C₅H₅)2] each lying on sites of crystallographic mirror symmetry. The Fe–Fe distance is 2.520(2)Å and is indicative of a bond order of unity, the bond being bridged both by methylcarbene and carbonyl ligands. In addition each iron atom carries one terminal carbonyl ligand and an η⁵-bound cyclopentadienyl moiety. The conformation of the molecule of (2) is similar to that of (1) having mutually cis cyclopentadienyl groups and the methyl group oriented anti to these.