Synthesis of diphosphine-substituted selenido carbonyl iron clusters: Progressive deformation of the fe3se2 core in the nido clusters [fe3se2(co)7{μ-(ph2p)2r}] by widening the bite of the bridging ligand

Article abstract of DOI:10.1016/S0022-328X(96)06754-X

The reactions of [Fe₃(CO)₁₂] with three diphosphine diselenides, dppmSe₂, dppeSe₂ and dppfcSe₂, produce the disubstituted clusters [Fe₃(μ₃-Se)₂(CO)₇{(Ph₂P)₂R}] (R = CH₂ (dppm) 3; R = CH₂CH₂ (dppe) 7; R = (C₅H₄)₂Fe (dppfc) 8) as the main products. Other products are [Fe₃(μ₃Se)₂(CO)₉] 1, [Fe(CO)₄(dppm)] 2, [Fe₂(μ-Se₂)(CO)₄(dppm)] 4 in the case of dppm and [{Fe₃(μ₃-Se)₂(CO)₈}₂(dppe)] 5 in the case of dppe. Clusters 1, 3, 5, 7 and 8 have a square-pyramidal structure with two iron and two selenium atoms alternating in the basal plane and the third iron atom (Fe_ap) at the apex of the pyramid, and should be regarded as nido-clusters with seven skeletal electron pairs. The phosphine substitution is regioselective, occurring only on the two basal iron atoms. ¹H and ³¹P NMR data in solution suggest a fluxional behaviour for 3 and 7 in solution due to the migration of a metal-metal bond to link the two iron atoms bound to the bidentate ligand. This is probably related to the deformation of the Fe₃Se₂ core induced by the steric demand of the diphosphines in such a way that the Fe ... Fe non-bonding distance decreases as the bite of the ligand shortens. The crystal structures of 3, 4, 5, 7 and 8 are described.