Chalcogen Stabilized bis-Hydridoborate Complexes of Cobalt: Analogues of Tetracyclo[4.3.0.02,4 .03,5 ]nonane.

Treatment of Li[BH3 ER] (E=Se or Te, R=Ph; E=S, R=CH2 Ph) with [Cp*CoCl]2 led to the formation of hydridoborate complexes, [{CoCp*Ph}{Cp*Co}{μ-EPh}{μ-κ2 -E,H-EBH3 }], 1a and 1 b (1 a: E=Se; 1 b: E=Te) and a bis-hydridoborate species [Cp*Co{μ-κ2 -Se,H-SeBH3 }]2 , 2. All the complexes, 1 a, 1 b and 2 are stabilized by β-agostic type interaction in which 1 b represents a novel bimetallic borate complex with a rare B-Te bond. QTAIM analysis furnished direct proof for the existence of a shared and dative B-chalcogen and Co-chalcogen interactions, respectively. In parallel to the formation of the hydridoborate complexes, the reactions also yielded tetracyclic species, [Cp*Co{κ3 -E,H,H-E(BH2 )2 -C5 Me5 H3 }], 3 a and 3 b (3 a: E=Se and 3 b: E=S), wherein the bridgehead boron atoms are surrounded by one chalcogen, one cobalt and two carbon atoms of a cyclopentane ring. Molecules 3 a and 3 b are best described as the structural mimic of tetracyclo[4.3.0.02,4 .03,5 ]nonane having identical structure and similar valence electron counts.