From Tetrahydroborate− to Aminoborylvinylidene−Osmium Complexes via Alkynyl−Aminoboryl Intermediates

The tetrahydroborate OsH(η2-H2BH2)(CO)(PiPr3)2 (1) reacts with aniline and p-toluidine to give the aminoboryl derivatives Os{B(NHC6H4R)NHCCHCHC(R)CHC}(CO)(PiPr3)2 (R = H (2), CH3 (3)) and four H2 molecules. Treatment of 2 and 3 with phenylacetylene gives Os{B(NHC6H4R)2}(CCPh)(CO)(PiPr3)2 (R = H (4), CH3 (5)), which react with HBF4 to afford the amino(fluoro)boryl species Os{BF(NHC6H4R)}(CCPh)(CO)(PiPr3)2 (R = H (6), CH3 (7)). In contrast to HBF4, the addition of acetic acid to 4 and 5 induces the release of phenylacetylene and the formation of the six-coordinate derivatives Os{B(NHC6H4R)2}(κ2-O2CCH3)(CO)(PiPr3)2 (R = H (8), CH3 (9)). The coordination number six for 4 and 5 can be also achieved by addition of CO. Under this gas Os{B(NHC6H4R)2}(CCPh)(CO)2(PiPr3)2 (R = H (10), CH3 (11)) are formed. In toluene, these alkynyl−aminoboryl compounds evolve into the aminoborylvinylidenes Os{CC(Ph)B(NHC6H4R)2}(CO)2(PiPr3)2 (R = H (12), CH3 (13)) via a unimolecular 1,3-boryl migration from the metal to the Cβ atom of the alkynyl ligand. Similarly to 4 and 5, complexes 6 and 7 coordinate CO to give Os{BF(NHC6H4R)}(CCPh)(CO)2(PiPr3)2 (R = H (15), CH3 (16)), which evolve to Os{CC(Ph)BF(NHC6H4R)}(CO)2(PiPr3)2 (R = H (17), CH3 (18)).