Cu(I) Complexes Comprising tetrahedral Mo₂ E₂ or Mo₂ PE units (E=P, As, Sb) as Chelating Ligands

Novel isomorphous tetranuclear complexes, [(dppf)Cu(μ₃ ,η^{2 : 2 : 2} -E₂ {CpMo(CO)₂ }₂ ]BF₄ [E=P (1), As (4), Sb (5), (dppf=1,1'-bis-(diphenylphosphino)-ferrocene)] and [(dppf)Cu(μ₃ ,η^{2 : 2 : 2} -PE{CpMo(CO)₂ }₂ ]BF₄ [E=As (2), Sb(3)] were synthesized from the reactions between [(dppf)Cu(MeCN)₂ ][BF₄ ] and tetrahedral molybdenum complexes containing unsubstituted homo- and hetero-diatomic group-15 elements [(μ,η^2 : 2 -E₂ {CpMo(CO)₂ }₂ ] [E=P (A), As (D), Sb (E)] and [(μ,η^2 : 2 -PE{CpMo(CO)₂ }₂ ] [E=As (B), Sb (C)], respectively. In all these products, the {Mo₂ E₂ } or {Mo₂ PE} moieties coordinate the Cu(I) center via a rare side-on η² -coordination mode. The X-ray structure analyses of [(dppf)Cu(μ₃ ,η^{2 : 2 : 1} -PSb{CpMo(CO)₂ }₂ ][BF₄ ] demonstrate, for the first time, the utilization of an η¹ -coordination mode for the ligand complex C to coordinate to the Cu(I) center. All the products were characterized by X-ray crystallography, NMR and IR spectroscopy, mass spectrometry and elemental analysis. Electrochemical studies also revealed the formation of 1-5, and, further, to understand the structure and bonding of the products, theoretical calculations using density functional theory (DFT) were conducted.