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 an o-Carborane-1,2-dithiolate Ligand with Ethyl Diazoacetate

The reaction of the 16-electron half-sandwich complex CpCo(S2C2B10H10) (1; Cp = cyclopentadienyl) with ethyl diazoacetate (EDA) at ambient temperature leads to compounds CpCo(S2C2B10H10)(CHCO2Et) (2), CpCo(S2C2B10H8)(CHCO2Et)(CH2CO2Et) [CH(CO2Et)(CH2CO2Et)] (3), CpCo(S2C2B10H9)(CH2CO2Et)(CHCO2Et)(2) (4), CpCo(S2C2B10H9)(CHCO2Et)(CH2CO2Et) (5), and CpCo(S2C2B10H9)(CHCO2Et)(2)(CH2CO2Et) (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(S2C2B9H9)(CHCO2Et)(CH2CO2Et)(2) (7) containing a nido-C2B9 unit. All of the new compounds 2-7 were characterized by NMR spectroscopy (H-1, B-11, and C-13), mass spectrometry, IR spectroscopy, and elemental analysis, and their solid-state structures were further characterized by X-ray structural analysis.