Stabilization of Ethane‐Like Dianionic Diborane(6) in Monometallic Titanium Complexes and its Subsequent B(sp³)−B(sp³) Bond Cleavage

Abstract

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; 1a: E = S, 1b: 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 electron‐precise B(sp3)‐B(sp3) bond that yielded ĸ3‐hydridoborato complexes [(Cp*Ti)(ĸ3‐BH3R)(μ‐EPh)2{M(CO)4}] (2a‐c: R = H, 3a‐c: R = Ph). In an attempt to isolate the Te‐analogue of 1a‐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}] (2d: R = H, 3d: R = Ph) that are analogues of 2a‐c and 3a‐c, respectively. Formation of these species provide indirect evidence for existence of unstable [(Cp*Ti)(η4‐B2H4LL')] (L = C6H4Te; L' = C6H5Te; 1c).