Formation of Boron-Main-Group Element Bonds by Reactions with a Tricoordinate Organoboron L2PhB: (L = Oxazol-2-ylidene).

The reactivity of L2PhB: (1; L = oxazol-2-ylidene) as well as its transition-metal (chromium and iron) complexes toward main-group substrates have been systematically examined, which led to the construction of B-E (E = C, Ga, Cl, H, F, N) bonds. The combination of 1 and triethylborane smoothly captured carbon dioxide concomitant with the formation of B-C and B-O bonds. The soft basic boron center in 1 readily reacted with soft acidic gallium trichloride (GaCl3) to afford the extremely stable adduct 4 involving a B-Ga dative bond. Electrophilic alkylation of a neutral tricoordinate organoboron was first achieved by the treatment of 1 with dichloromethane and methyl trifluoromethanesulfonate (MeOTf), both of which afforded ionic species featuring an additional B-C bond. Comparatively, redox reactions took place when halides of heavier elements such as germanium dichloride, dichlorophenylphosphine, and chlorodiphenylbismuth were employed as substrates, from which cationic species 7 bearing a B-Cl bond was obtained. In addition, reactions of metal complexes [2, Cr(1)(CO)5; 8, Fe(1)(CO)4] with cationic electrophiles were investigated. With HOTf and FN(SO2Ph)2, the corresponding ionic species featuring a B-H bond (9) and a B-F bond (10) were formed via a formal electrophilic substitution reaction, whereas the reaction of 1 with F·Py-BF4 resulted in the formation of a dicationic boron species 11 with a newly formed B-N bond.