Diakylhaloboranes reduce benzaldehyde at a rate much faster than does trialkylboranes. Whereas IpQBCl reduces 2 equiv of benzaldehyde at room temperature almost instantaneously, the related trialkylborane Ipc2B-n-Hex requires approximately 6 days. Sia2BC1, 2-MeCpnzBC1, CarzBCl and IpczBBr also reduce benzaldehyde rapidly, but 2- MeChx2BC1 reacts relatively slowly. A cyclic mechanism with a" boat-like" transition state ...
