Synthesis, structure, and dynamic behaviour of (p-quinone)copper(I) complexes. Crystal structure determination of a copper p-benzoquinone complex stabilized by a tridentate oxygen ligand

Abstract

The quinonecopper(I) complexes [Cu(olefin)L][olefin =p-benzoquinone (bq), methyl-p-benzoquinone, or 1,4-naphthoquinone] of the tridentate oxygen ligand L^–=[(C₅H₅)Co{P(O)(OCH₃)₂}₃]^– have been prepared by the reaction of NaL and the appropriate quinone with [Cu(CH₃CN)₄]PF₆ and by carbon monoxide substitution from [Cu(CO)L]. The complex [Cu(bq)L] crystallizes in space group P(Z= 2) with a= 11.358(6), b= 12.138(7), c= 12.465(6)Å, α= 92.18(2), β= 134.24(2), γ= 99.49(4)°, and its X-ray crystal structure was refined to R= 0.056 for 4 140 reflections [|F_o| > 2.5σ(F_o)]. The co-ordination about the copper atom is distorted tetrahedral with one long [2.184(2)Å] and two short [1.966(2), 2.001 (2)Å] copper–oxygen contacts. p-Benzoquinone co-ordinates through one olefinic double bond to the copper atom. The complex dismutates in solution according to the equilibrium 2 [Cu(bq)L]⇌[LCu(µ-bq)CuL]+ bq. In addition, it exhibits several other dynamic processes, the lowest-energy of which is olefin rotation. The intramolecular exchange of the free and the co-ordinated double bond gives rise to a coalescence temperature of about 305 K in the ¹H n.m.r. spectrum, corresponding to an activation barrier of ca. 60 kJ mol^–1. Intermolecular exchange of co-ordinated and non-co-ordinated bq becomes rapid on the n.m.r. time-scale above ca. 370 K.