Synthesis and Reactivity of the Monocarbon Molybdenacarborane Anion [1,2-<i>μ</i>-NHBu<i>^t</i>-2,2,2-(CO)₃-c<i>loso</i>-2,1-MoCB₁₀H₁₀]^-

The reagent Li[7-NHBut-nido-7-CB10H12] reacts with [Mo(CO)6] in NCMe at reflux temperatures, followed by addition of [N(PPh3)2]Cl, to give [N(PPh3)2][1,2-μ-NHBut-2,2,2-(CO)3-closo-2,1-MoCB10H10] (1). The tungsten (2) and chromium (3) analogues were similarly obtained, but the latter is unstable and was isolated in low yield. An X-ray diffraction study of 2 confirmed that the exo-polyhedral NHBut group forms a bridge between the cage-carbon atom and the tungsten. For 1, this intramolecular donor bond is lifted on protonation in the presence of donor molecules L (CO, PPh3, PMe3, PEt3, PMe2Ph) when zwitterionic complexes [1-NH2But-2,2,2-(CO)3-2-L-closo-2,1-MoCB10H10] (4) are formed. In contrast, protonation with HCl gives a salt [N(PPh3)2][1-NH2But-2,2,2-(CO)3-2-Cl-closo-2,1-MoCB10H10] (5). Complex 1 in CH2Cl2 with CNBut is oxidized by iodine, affording [1,2-μ-NHBut-2,2,2-(CNBut)3-2-I-closo-2,1-MoCB10H10] (6a). Treatment of 1 with [CuCl(PPh3)]4 in the presence of Tl[PF6] yields the bimetallic compound [exo-{Cu(PPh3)}-1,2-μ-NHBut-2,2,2-(CO)3-closo-2,1-MoCB10H10] (8), whereas reaction with [AuCl(PPh3)] and Tl[PF6] affords a mixture of [1,2-μ-NHBut-2-{Au(PPh3)}-2,2,2-(CO)3-closo-2,1-MoCB10H10] (9) and [Au(PPh3)2][2,2‘-μ-Au-{1,2-μ-NHBut-2,2,2-(CO)3-closo-2,1-MoCB10H10}2] (10a). In solution, 9 disproportionates, giving 10a. The [N(PPh3)2]+ salt (10b) is readily prepared by treating 1 with [AuCl(THT)] (THT = tetrahydrothiophene) and Tl[PF6], and its structure was determined by X-ray diffraction.