Although there is a great potential for Lewis acid to react with Lewis base, some unreacted Lewis pairs can still exist in the same system due to their special structures (Figure , the essential factor is the steric effect). In 2006, Welch et al reported compound (C6H2Me3)2PH(C6F4)BH(C6F5)2 (2) can lose H2 at temperatures above 100℃, forming (C6H2Me3)2P(C6F4)B(C6F5)2 (3). In addition, 3 can react with H2 (1 atm) at room temperature to reform 2 (Figure ). The regioselectivity for the formation of 1 can be attributed to steric effects. (C6H2Me3)2PH, acting as the Lewis base, fails to attack the Boron