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.