Very Large Changes in Bond Length and Bond Angle in a Heavy Group 14 Element Alkyne Analogue by Modification of a Remote Ligand Substituent

The synthesis and characterization of the compound Me3Si-4-Ar'SnSnAr'-4-SiMe3 (Ar'-4-SiMe3 = C6H2-2,6-(C6H3-2,6-i-Pr2)2-4-SiMe3) shows that it has a Sn-Sn bond length = 3.066(1) A and a Sn-Sn-C bending angle of 99.25(14) degrees . These parameters differ by about 0.4 A and about 26 degrees from those previously reported for the closely related Ar'SnSnAr' (Ar' = C6H3-2,6-(C6H3-2,6-i-Pr2)2). The results show that, in accordance with the theoretical predictions by Nagase and Takagi, very small amounts of energy (ca. 5 kcal mol-1) separate structural isomers of distannynes that have large differences in their bonding parameters.