Metal cluster nitrile derivatives

Article abstract of DOI:10.1021/om50003a001

Thermal and photochemical activation of Fe₃(μ₃-PC₆H₅) ₂(CO)₉ and Co₄(μ₄-PC₆H₅) ₂(CO)₁₀, in acetonitrile or propionitrile solutions, provided the reactive nitrile clusters: Fe₃(μ₃-PC₆H₅) ₂(CO)₈(NCR), Fe₃(μ₃-PC₆H₅) ₂(CO)₇(NCR)₂, and Co₄(μ₄-PC₆H₅) ₂(CO)₉(NCR). Using these nitrile derivatives, a series of substitution derivatives with PF₃, P(OR)₃, PR₃, and AsR₃ ligands were prepared in high yield. Interestingly, the bis(acetonitrile) derivative of the iron cluster had both nitrile groups on the same (basal) iron atom. X-ray crystallographic studies for single crystals of Fe₃(μ₃-PC₆H₅) ₂(CO)₇(NCCH₃)₂ established that they utilize the centrosymmetric orthorhombic space group Pnma - C_2h¹⁶ with a = 13.103 (2) A?, 6 = 16.972 (2) A?, c = 25.038 (5) A?, and Z = 8. The asymmetric unit contains two crystallographically independent molecules both of which possess rigorous C_s-m symmetry. The molecular structure of Fe₃(μ₃-PC₆H₅) ₂(CO)₇(NCCH₃)₂ is related to that of the parent Fe₃(μ₃-PC₆H₅) ₂(CO)₉ with two of the equatorial carbonyl ligands on a single basal Fe atom replaced by acetonitrile ligands. Basically, the stereochemistry of the phosphorus- and arsenic-based ligand derivatives of the iron cluster were analogous to that of the parent nitrile derivatives from which they were obtained. Conformationally, there were differences that can be rationalized in terms of steric and electronic factors and of fluxional features of the molecules. Studies of the temperature-dependent ¹³C spectra of the parent ion cluster and its derivatives established certain dominant mechanistic pathways for ligand site exchange in the cluster.