Promotion of tetrahedral copper(I) dimers by chelation of 1,1′-bis(diphenylphosphino)ferrocene (dppf). Crystal structures of [{CU(µ-X)(dppf-P,P′)}2](X = O2CH, I or NO3)

Abstract

Treatment of Cu(NO₃)₂ with 1,1′-bis(diphenylphosphino)ferrocene (dppf) gave [{Cu(µ-NO₃-O)(dppf-P,P′)}₂] which readily exchanged with NaO₂CH or KI to give [{Cu(µ-O₂CH-O,O′)(dppf-P,P′)}₂] or [{Cu(µ-I)(dppf-P,P′)}₂]. X-Ray structural analysis of the complexes revealed three tetrahedral copper(I) dimers with nitrate, iodide or formate preferentially in bridging and dppf consistently in chelating modes. The P–Cu–P chelate angle in the nitrate [11 7.8(1)°] is the largest of known dppf chelates in all geometries. These structures are different from their triphenylphosphine analogues which are all monomers. Exchanges of the nitrate complex with other carboxylates gave [{Cu(µ-O₂CR)(dppf-P,P′)}_n](R = Me, CF₃, Et, Prⁿ or Ph). It also reacted with a stoichiometric amount of dppf to give [Cu₂(NO₃-O)₂(µ-dppf )(dppf-P,P′)₂]. The geometrical influence of PPh₃, Ph₂PCH₂PPh₂ and dppf, and their preferred bonding modes to Cu¹ in relation to the complex nuclearity, are discussed.