An Experimental and Theoretical (DFT) Investigation of the Coordination Mode of 2,4‐Dithiouracil (2,4‐dtucH2) in Copper(I) Complexes with1,2‐Bis(diphenylphosphanyl)benzene (dppbz): The Crystal Structures of [Cu(μ‐Br)(dppbz)]2 and [CuBr(dppbz)(2,4‐dtucH2)

Abstract

AbstractNovel copper(I) mixed‐ligand complexes containing 1,2‐bis(diphenylphosphanyl)benzene (dppbz) and 2,4‐dithiouracil (2,4‐dtucH2) ligands have been synthesised by addition of the thione ligand to the dinuclear [Cu(μ‐X)(dppbz)]2 intermediate in acetonitrile/methanol or acetone solution. The molecular structures of both the precursor [Cu(μ‐Br)(dppbz)]2 and the [CuBr(dppbz)(2,4‐dtucH2)] complexes were established by single‐crystal X‐ray diffraction. Interestingly, the structure of the thione‐free dimer involves two diphosphane‐chelated CuI centres bridged by two bromide ligands, thus forming a non‐planar Cu2Br2 core. The structure of [CuBr(dppbz)(2,4‐dtucH2)] corresponds to a four‐coordinate CuI centre in a tetrahedral coordination environment with the heterocyclic dithione ligand being coordinated to the metal centre in a unidentate fashion through its exocyclic sulfur donor atom. The structural, bonding and electronic properties of the model complexes [Cu(μ‐X)(dppbz)]2 and [CuX(dppbz)(2,4‐dtucH2)] (X = Cl, Br, or I) are adequately described by DFT/B3LYP computational techniques. All model dinuclear [Cu(μ‐X)(dppbz)]2 complexes exhibit π‐type MOs delocalised over the entire four‐membered Cu(μ‐X)2Cu ring, thereby accounting for the near equivalency of the Cu–X bonds. Moreover, the [Cu(μ‐X)(dppbz)]2 dimers possess a σ‐type MO corresponding to weak Cu···Cu bonding interactions, which further stabilize the Cu(μ‐X)2Cu ring. According to our calculations, the interaction energies of the 2,4‐dtucH2 ligand with the CuI centre are predicted to be about 13–16 kcal mol–1. The coordination of the 2,4‐dtucH2 ligand is further stabilized by an X···H–N hydrogen bond that is perpendicular to the plane of the dppbz ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)