Chalcogen stabilized borate complexes of tantalum

In an attempt to isolate some electron precise early transition metal borate complexes, we have explored the reactions of [Cp*TaCl4] (Cp* = η5-C5Me5) with chalcogen-based borate ligand Li[BH3(SPh)]. The room-temperature reaction yielded bimetallic borate complex [(Cp*Ta)2(μ-SPh){S(BH3)}{SPh(BH3)}] (1) that present two types of borate ligands, i.e., {BH3(SPh)} and {BH3(S)} ligands having unique coordination with the tantalum atoms. Interestingly, the {BH3(S)} ligand is coordinated to both the Ta centers in µ-η1:η2 fashion. On the other hand, thermolysis of [Cp*TaCl4] in the presence of Li[BH3(SPh)] yielded a bimetallic borate species [(Cp*Ta)2(µ-η3:η3-B2H4S){µ-η2:η2-S(C6H4)BH3}] (2). Compound 2 contains a triborane analog and a borate ligand, which are coordinated to two Ta atoms. This can also be considered as a notable example of C[sbnd]H activated molecule, in which a B-C bond formation took place. Both the borate species have been characterized by mass spectrometry, IR spectroscopy, NMR spectroscopy, and single-crystal X-ray diffraction studies. The density functional theory (DFT) calculations further provided insights into the bonding and electronic structures of these bimetallic borate species.