Synthesis of a Thiocarbamoyl Alkylidyne Complex and Caveats Associated with the Use of [Mo(CLi)(CO)₂(Tp*)] (Tp* = Hydrotris(3,5-dimethylpyrazol-1-yl)borate)

The successive reactions of [Mo(CBr)(CO)2(Tp*)] (1; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with nBuLi and N,N′-dimethylthiocarbamoyl chloride provides as intended, via formation of [Mo(CLi)(CO)2(Tp*)] (2a), the thiocarbamoyl alkylidyne complex [Mo{CC(S)NMe2}(CO)2(Tp*)] (3). Although the yields are poor, analysis of the side products obtained provides insights into caveats to be considered when employing the lithium/halogen exchange protocol in these systems: the 1-pentylidyne [Mo(CnBu)(CO)2{HB(pzMe2)3}] (4) would appear to arise from competition between nBuBr and the electrophile of choice, and Templeton’s nonclassical vinylidene [Mo2(μ-CCH2)(CO)4(Tp*)2] (5a) most likely arises under strictly anhydrous conditions from nBuBr acting as a proton donor (i.e., E2) rather than electrophile (SN2). The formation of the ethanediylidyne [Tp*(CO)2MoCCMo(CO)2(Tp*)] (6) may be accounted for by single-electron-transfer (outer-sphere) oxidation of 2 to provide the radical carbido complex [Mo(C•)(CO)2{HB(pzMe2)3}] (7), which dimerizes to provide 6. The dimer 6 is also formed alongside 5a in the reaction of 2 with [Fe(η-C5H5)2]PF6, supporting the intermediacy of 7 in the formation of 6.