Heterodinuclear Cu(i)/Mo(vi) chemistry with bifunctional dibenzobarrelene ligands
Abstract
Bifunctional dibenzobarrelene ligands combining diphosphine with diol or other potentially bidentate functionalities are well-known mononucleating ligands for middle and late transition metals. These ligands generally exhibit tetradentate coordination, in which a metal is coordinated by [PC(sp3)P] 3-dimensional pincer and an additional alkoxide donor. These ligands can also be envisioned as heterodinucleating ligands, which coordinate a soft, late metal (via the diphospine) and a hard, early metal (via the diolate); the heterodinucleating reactivity of these ligands has not been studied. Herein we describe our initial studies on Cu(I)/Mo(VI) chemistry of the diphosphine/diol ligand L1H2; it is compared with the dibenzobarrelene ligand combining diphosphine with diester (L2). Both ligands led to stable Cu(I) complexes in which the ligand coordinates as a bidentate diphosphine. Spectroscopic characterization (carried out in CD2Cl2) revealed an AB system for the diastereotopic phosphine groups in 31P {1H} NMR spectrum. The phosphorus signals appear as an AB system due to the large values of 2JP–P, 120–150 Hz. 63Cu NMR spectroscopy (conducted in concentrated CD3CN solutions) revealed broad Cu signals at, or below, room temperature. The observation of a quadrupolar 63Cu (I = 3/2) signal was accompanied by the broadening of the 31P signals, which now appear as a single broad peak. The reaction of both ligands with (Et4N)2[MoO4] failed to form well-defined products. Treatment of [Cu(NCMe)2(L1H2)](PF6) with (Et4N)2[MoO4], followed by recrystallization from DMSO/ether, revealed the structure of a trinuclear complex [MoO2(μ2-O)2{Cu(DMSO)(L1H2)}2] in which one Mo(VI) center is linked with two Cu(I) centers via oxo bridging ligands. In DMSO solution, the trinuclear complex likely forms discrete ionic species [Cu(DMSO)2(L1H2)]2[MoO4] or [Cu(DMSO)2(L1H2)][Et4N][MoO4].