Cobalt-Mediated Selective B−H Activation and Formation of a Co−B Bond in the Reaction of the 16-Electron CpCo Half-Sandwich Complex Containing ano-Carborane-1,2-dithiolate Ligand with Ethyl Diazoacetate

Abstract

The reaction of the 16-electron half-sandwich complex CpCo(S(2)C(2)B(10)H(10)) (1; Cp = cyclopentadienyl) with ethyl diazoacetate (EDA) at ambient temperature leads to compounds CpCo(S(2)C(2)B(10)H(10))(CHCO(2)Et) (2), CpCo(S(2)C(2)B(10)H(8))(CHCO(2)Et)(CH(2)CO(2)Et)[CH(CO(2)Et)(CH(2)CO(2)Et)] (3), CpCo(S(2)C(2)B(10)H(9))(CH(2)CO(2)Et)(CHCO(2)Et)(2) (4), CpCo(S(2)C(2)B(10)H(9))(CHCO(2)Et)(CH(2)CO(2)Et) (5), and CpCo(S(2)C(2)B(10)H(9))(CHCO(2)Et)(2)(CH(2)CO(2)Et) (6). In 2, the EDA molecule has been inserted into one Co-S bond in 1 with the loss of N(2) to form an 18-electron compound containing a three-membered metallacyclic ring. In 3, two B-H bonds of the carborane cage have been activated and the unusual B4-H bond activation leads to the formation of a stable Co-B bond. Two EDA molecules are inserted into the Co-B3 bond to generate an unexpected six-membered heterocyclic ring Co-B-B-C-C-O. In 4, a stable Co-B bond is present as well but in the position B3/B6, and two EDA molecules are inserted into one Co-S bond to produce a five-membered heterocyclic ring Co-C-C-C-O. In 5, one EDA is inserted into the Co-B bond with the formation of a C-B bond in the position B3/B6. One more EDA is inserted into the Co-S bond in 5 to generate 6. Upon heating, 6 loses the BH vertex close to the two carbon atoms to lead to CpCo(S(2)C(2)B(9)H(9))(CHCO(2)Et)(CH(2)CO(2)Et)(2) (7) containing a nido-C(2)B(9) unit. All of the new compounds 2-7 were characterized by NMR spectroscopy ((1)H, (11)B, and (13)C), mass spectrometry, IR spectroscopy, and elemental analysis, and their solid-state structures were further characterized by X-ray structural analysis.