RUTHENIUM-CATALYZED HYDROBORATIONS OF ALKENES

The complexes RuCl2(PPh3)4 (1), RuCl3(PPh3)2(MeOH) (2), RuHCl(PPh3)3 (3), RuH4(PPh3)3 (4), and RuHCl(DIOP)2 are shown to be catalysts for addition of catecholborane and 3-methyl-1,3,2-oxazaborolane (7) to unhindered alkenes and alkynes. These reactions are slower than the corresponding reactions mediated by rhodium(+1) complexes. Competing hydrogenation reactions occur, just as with hydroborations catalyzed by RhCl(PPh3)3. Analyses of the hydroboration of cyclohexene mediated by complex 2 reveal that the reaction occurs predominantly via addition of catecholborane, but a small amount of disproportionation of catecholborane to BH3 and conventional (uncatalyzed) hydroboration also occurs.