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

Treatment of [Cp*TiCl₃] with [LiBH₄ ⋅ THF] followed by thermolysis with [Ph₂E₂] (E=S or Se) resulted in the formation of classical diborane(6) complexes, [(Cp*Ti)(η⁴-B₂H₄LL')] (L=C₆H₄E; L'=C₆H₅E; 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 ĸ⁴-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)₅ ⋅ THF] (M=Mo, W) led to the cleavage of the electron-precise B(sp³)-B(sp³) bond that yielded ĸ³-hydridoborato complexes [(Cp*Ti)(ĸ³-BH₃R)(μ-EPh)₂{M(CO)₄}] (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)₅ ⋅ THF] yielded [(Cp*Ti)(ĸ³-BH₃R)(μ-TePh)₂{W(CO)₄}] (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)(η⁴-B₂H₄LL')] (L=C₆H₄Te; L'=C₆H₅Te; 1 c).