Stabilization of Ethane-Like Dianionic Diborane(6) in Monometallic Titanium Complexes and its Subsequent B(sp)-B(sp) Bond Cleavage.

Treatment of [CpTiCl] with [LiBH ⋅ THF] followed by thermolysis with [PhE] (E=S or Se) resulted in the formation of classical diborane(6) complexes, [(CpTi)(η-BHLL')] (L=CHE; L'=CHE; 1 a: E=S, 1 b: E=Se), stabilized at titanium template. To the best of our knowledge, they are the first examples of mono-metallic classical diborane(6) complexes. The bonding analysis and theoretical studies suggest that the stabilization of these diborane(6) species is due to the presence of four bridging ligands in ĸ-fashion, where two of them are phenyl thiolates/selenolates that provide more electrons to the electron-deficient titanium center. Reactions of these diborane(6) species with [M(CO) ⋅ THF] (M=Mo, W) led to the cleavage of the electron-precise B(sp)-B(sp) bond that yielded ĸ-hydridoborato complexes [(CpTi)(ĸ-BHR)(μ-EPh){M(CO)}] (2 a-c: R=H, 3 a-c: R=Ph). In an attempt to isolate the Te-analogue of 1 a-b, a similar reaction was performed; however, the complex was too unstable to be isolated. Interestingly, the treatment of this unstable intermediate with [W(CO) ⋅ THF] yielded [(CpTi)(ĸ-BHR)(μ-TePh){W(CO)}] (2 d: R=H, 3 d: R=Ph) that are analogues of 2 a-c and 3 a-c, respectively. Formation of these species provide indirect evidence for the existence of unstable [(Cp*Ti)(η-BHLL')] (L=CHTe; L'=CHTe; 1 c).