Aluminum-catalyzed selective hydroboration of carbonyls and dehydrocoupling of alcohols, phenols, amines, thiol, selenol, silanols with HBpin

Abstract

A popular N, N’-chelated NacNac analogue, i.e., conjugated bis-guanidinate (CBG) stabilized aluminum dihydride LAlH2(1) [L = {(ArHN)(ArN)–CN–C=(NAr)(NHAr)}; Ar = 2,6-Et2-C6H3], demonstrates excellent catalytic hydroboration of a wide array of carbonyls with pinacolborane (HBpin) under neat conditions with good tolerance of reducible functional groups such as alkyl, alkene, halide, nitrile, nitro, ester, amide, and heteroaryl. In addition, we investigated complex 1 catalyzed cross-dehydrocoupling (CDC) of alcohols, phenols, amines, thiol, selenol, and silanols with HBpin under mild reaction conditions. Furthermore, several control experiments have been performed to understand the mechanisms in hydroboration and CDC reactions. All corresponding catalytic intermediates have been identified and characterized by 1H and 13C{1H} NMR spectroscopic methods. In contrast to several reports on metal-catalyzed hydroboration of carbonyls, this is the second report for the molecular aluminum catalyzed CDC of organic substrates with HBpin.