SYNTHESIS AND CHEMISTRY OF NOVEL 2,2'-BINAPHTHYL-SUBSTITUTED ORGANOTIN LEWIS-ACIDS

The synthesis and chemistry of novel Lewis acids containing neutral tin-centered Lewis acidic groups at the 2- and 2'-positions of 1,1'-binaphthyl are described. (+/-)-2,2'-Dibromo-1,1'-binaphthyl (3) was converted to the dilithio derivative, which was treated with trimethyltin chloride to yield 2,2'-bis(trimethylstannyl)-1,1'-binaphthyl (4) in excellent yield. Compound 4 then underwent highly selective methyl-Sn cleavage in the redistribution reactions with methyltin trichloride and tin tetrachloride to afford 2,2'-bis(monochlorodimethylstannyl)- and 2,2'-bis(dichloromethylstannyl)-1,1'-binaphthyl, 2a and 2b, respectively. The chlorotins were then converted into the organotin triflates, 2c and 2d, by metathetic reactions with silver triflate. Interaction of the bis(dichlorotin) 2b and DMSO afforded a mono-DMSO (12) whose X-ray crystal structure revealed that coordination of DMSO occurred to one tin center and a chloride ligand from this tin had bridging interaction with the other tin moiety. An estimation of the equilibrium constant for the formation of 12 was obtained by Sn-119 NMR spectroscopy.