Synthesis, X-Ray Structures, and Fluxional Properties of Symmetrical, Asymmetrical Binuclear and Cubane Type Copper(I) Complexes Bearing the Pyrrole-Based P, N-Hetero Donor Ligand

The 1 : 1 reaction between 2-(3,5-dimethylpyrazolylmethyl)-5-(diphenylphosphinomethyl)pyrrole L and CuX (X=Cl, and Br) in THF afforded the symmetrical binuclear copper(I) complexes [Cu(mu-X){mu-C4H2NH-2-(CH2PPh2)-5-(CH(2)Me(2)pz)-kappa P-2,N}](2), having one type of copper environment. When X=I, the asymmetrical complex having two copper environments was isolated, in addition to the symmetrical complex as crystals. Interestingly, the 1 : 2 ratio reaction between L and CuCl gave a distorted cubane type complex [Cu4Cl4{mu-C4H2NH-2-(CH2PPh2)-5-(CH(2)Me(2)pz)-kappa P-2,N}(2)], while the CuBr and CuI reactions did not give similar cubane complexes. Conversely, the 2 : 1 (L : Cu) ratio reactions using CuX (X=Cl, Br and I) in THF suggest the formation of four coordinate bis-chelated copper(I) complex of the type [CuL2](+) in solution, in addition to the binuclear complexes. The X-ray solid state structures of [CuL2X2] (X=Br and I) are retained in solution, in contrast to its chloride derivative giving two signals in P-31{H-1} NMR spectrum. The formation of the binuclear complexes from [CuL2](+) and their equilibria were shown by variable temperature NMR, P-31{H-1} 2D NOESY and HRMS studies. In addition, the reaction of L with [Cu(CH3CN)(4)]BF4 gave yet another binuclear complex [Cu2L2][BF4](2) which was characterized by spectroscopic methods. This study lends support for the hemilability of L.