In contrast to previous work on addition of E-H bonds (E = SiR(3), NR(2), OR, SR) to organoruthenium phosphine complexes, reactions of the latter with organoboranes, BRR’H, are dominated by B-C bond formation. Treatment of RuH(PMe(3))(3)(eta(2)-CH(2)PMe(2)) with thexylborane [{BH(CMe(2)CHMe(2))(mu-H)}(2)] and 9-H-BBN [9-borabicyclo-[3.3.1]nonane, {B(C8H14)(mu-H)}(2)], gives ruthenaheterocycles RuH(PMe(3))(3)[eta(1),eta(1)-PMe(2)CH(2)BRR’(mu-H)] (3a,b) via insertion of B-H into the Ru-C bond. Analogous Os complexes (3c,d) were prepared similarly. Activation energies for exchange of M-H and M-H-B moieties in 3a-c were estimated from H-1 and P-31 DNMR spectra. Benzyne complex Ru(PMe(3))(4)(eta(2)-C6H4) and thexylborane yield Me(3)P . BH2(thexyl) and Ru(PMe(3))(3)[eta(1),eta(2)-CH(2)CHMeCMe(2)BPh-(mu-H)(2)] (5) via B-C bond formation and C-H bond activation of the thexyl side chain. Reaction of Ru(PMe(3))(4)-(eta(2)-C2H4) with 9-H-BBN affords Me(3)P . BH(C8H14) and vinylborane complex RuH(PMe(3))(3)[eta(2),eta(1)-CH2=CHB(C8H14)(mu-H)] (7) which exists as a mixture of fac- and mer-isomers in solution. A competing pathway gives cis-RuH2(PMe(3))(4) and 9-vinyl-BBN. These reactions provide an alternative mechanistic pathway for the metal-mediated dehydrogenative borylation of alkenes reported previously. Molecular structures of 3b,d, 5, and fac-7 were determined by X-ray diffraction.