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(trimethyl-stannyl)-1,1′-binaphthyl (4) in excellent yield. Compound 4 then underwent highly selective methyl-Sncleavage 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 ¹¹⁹Sn NMR spectroscopy.