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 n BuLi and N,N ′-dimethylthiocarbamoyl chloride provides as intended, via formation of [Mo(≡CLi)(CO) 2 (Tp*)] ( 2a ), the thiocarbamoyl alkylidyne complex [Mo{≡CC(═S)NMe 2 }(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(≡C n Bu)(CO) 2 {HB(pzMe 2 ) 3 }] ( 4 ) would appear to arise from competition between n BuBr and the electrophile of choice, and Templeton’s nonclassical vinylidene [Mo 2 (μ-CCH 2 )(CO) 4 (Tp*) 2 ] ( 5a ) most likely arises under strictly anhydrous conditions from n BuBr acting as a proton donor (i.e., E 2 ) rather than electrophile (S N 2). The formation of the ethanediylidyne [Tp*(CO) 2 Mo≡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(pzMe 2 ) 3 }] ( 7 ), which dimerizes to provide 6 . The dimer 6 is also formed alongside 5a in the reaction of 2 with [Fe(η-C 5 H 5 ) 2 ]PF 6, supporting the intermediacy of 7 in the formation of 6 .