The Ullmann coupling reaction: A new approach to tetraarylstannanes

Several iodobenzenes form tetraarylstannanes, in addition to other products, under reaction conditions typically employed for the Ullmann reaction, i.e., activated copper bronze (a copper-tin alloy) and 7 days at 230°C. The isolated yields of the tetraarylstannanes were low to good (8-58%). Significantly higher yields (54-64%) of tetraphenylstannane were obtained by the direct reaction of iodobenzene with an excess of tin powder (iodobenzene: tin = 1:1 w/w) under the same conditions. Crystal structure analysis reveals that tetrakis(4-carbomethoxyphenyl)stannane crystallizes in a tetragonal space group and has 4̄ symmetry, which is the case for many symmetrical tetraarylstannanes. However, tetrakis(2,4-dichlorophenyl)stannane, tetrakis(3,4-dichlorophenyl)stannane, and tetrakis(2,4-dimethylphenyl)stannane do not crystallize in a tetragonal space group and do not have real 4̄ symmetry.