Synthesis and Characterization of Linear Poly(dialkylstannane)s

A comprehensive study was made of the synthesis of a spectrum of poly(dialkylstannane)s by catalytic dehydropolymerization of dialkylstannanes (dialkyltin dihydrides, R 2 SnH 2, prepared by reduction of R 2 SnCl 2 ), with R = ethyl, propyl, butyl, pentyl, hexyl, octyl, and dodecyl. The polymerization reactions were followed by 1 H and 119 Sn NMR spectroscopy, IR spectroscopy (disappearance of the Sn−H vibration), and quantitative measurement of H 2 which evolved during the reaction. Among the numerous metal complexes employed as catalyst, [RhCl(PPh 3 ) 3 ] was found to be particularly suited for the preparation of these inorganic polymers. The reaction parameters temperature, solvent, R 2 SnH 2 concentration, and [RhCl(PPh 3 ) 3 ]/R 2 SnH 2 ratio were varied, with the most prominent influence on the monomer conversion being the temperature. The number-average molar masses of the polystannanes were in the range of 1 × 10 4 to 1 × 10 5 g/mol, depending on the reaction conditions. For the generic case of the polymerization of Bu 2 SnH 2 with [RhCl(PPh 3 ) 3 ] as catalyst, it was demonstrated that poly(dibutylstannane) did not form by a random polycondensation, but by growth at a rhodium complex, whereby only a minor part of [RhCl(PPh 3 ) 3 ] was converted to catalytically active species by reaction with tin hydrides. The polymers featured phase transitions into liquid-crystalline states, on occasion at remarkably low temperatures. A particularly high phase transition temperature was observed for poly(dipropylstannane), which also was characterized by a high density, indicative of a particularly favorable packing of the propyl groups.