ON TITANIUM-PROMOTED HYDROBORATIONS OF ALKENES BY BOROHYDRIDE AND BY CATECHOLBORANE

Some literature reports of ''catalyzed'' hydroborations of alkenes by the borohydride anion and by catecholborane were investigated to probe the actual mode of hydroboration. Reactions involving both TiCl3 and Ti((OPr)-Pr-i)(4) seems to involve predominantly formation of BH3 in s itu, although there is some evidence that the metal may be directly in volved in a few cases. Ambiguity arises because it is shown that alkyl boronate esters can be formed by exchange between catecholborane and alkylboranes, so formation of these esters is not firm evidence of cat alysis.