THE COORDINATION OF ALKYNES TO FOUR METAL ATOMS IN SQUARE PLANAR CLUSTERS. CRYSTAL STRUCTURE AND CLUSTER CONTRACTION AND EXPANSION REACTIONS OF (η5-C5H5)2NiFe2(CO)6(μ4,η2-C2Ph2)

Article abstract of DOI:10.1016/0022-328X(85)80131-5

The structure of the tetranuclear cluster (η⁵-C5H5)2NiFe2(CO)6(μ₄,η²-C2Ph2) (Ia) has been determined by X-ray methods.Crystals of Ia are othorhombic, space group Pbca, with a 24.774(21), b 29.509(19), c 14.677(7) Angstroem, Z = 16; R = 0.063 for 3626 observed reflections.In the crystal structure of Ia two crystallographically independent but almost identical heteronuclear clusters are present, in which two Fe atoms and two Ni atoms are in slightly distorted square planar arrangement with the alkyne interacting with all four metals, through ? bonds to the Ni and ? bonds to the Fe atoms.The structural features of Ia are compared with those of related compounds, and a discussion is presented of the square planar and flattened butterfly clusters reported to date, some of which are formally unsaturated.The reactions of Ia (a formally 62 electron cluster which can be described in skeletal electron counting terms as a 6-vertex 8-skeletal pair nido-pentagonal bipyramid) with donor ligands (CO, PR3, alkynes) and metal fragments have been examined.No evidence of Lewis acidity normally associated with unsaturation was found, but cluster expansion reactions generating pentametallic complexes from Ia via completion of the pentagonal bipyramid have been observed.The synthesis and spectroscopic characterization of these new complexes are described.