Abstract
One-electron reduction of the carbene-stabilized borane (Me(2)-cAAC)B(Cl)(2)Si(SiMe(3))(3), 1, with potassium naphthalenide gave the radical (Me(2)-cAAC)B(Cl)Si(SiMe(3))(3), 2. A subsequent one-electron reduction of 2 yielded the dicoordinate borylene (Me(2)-cAAC)BSi(SiMe(3))(3), 3, which rapidly underwent intramolecular C-H activation to give cyclo-(Me(2)-cAAC)B(H)Si(SiMe(3))(3), 4, irrespective of the employed reaction conditions. Compound 3 could be stabilized as the carbonyl complex (Me(2)-cAAC)B(CO)Si(SiMe(3))(3), 5, that gave 4 upon irradiation with a UV light under a CO(2) atmosphere. In contrast, the two-electron reduction of 1 under an atmosphere of CO(2) yielded a mixture of products of which (Me(2)-cAAC)B(Cl)(H)C(O)OSi(SiMe(3))(3), 6, could be separated and structurally characterized. Compound 6 is a rare example of CO(2) insertion into a B-E (E = heavier main group element) bond in which boron functions as a nucleophile, thereby mimicking transition metal-mediated carboxylation. The mechanism for the formation of 6 from the purported boryl anion intermediate [(Me(2)-cAAC)B(Cl)Si(SiMe(3))(3)](-), 2 (-), was analyzed computationally.