Organoborierung von Tetrakis(trimethylsilylethinyl)stannan – Röntgenstrukturanalyse eines 5‐Stannaspiro[4.4]nona‐1,3,6,8‐tetraen‐Derivates[1]

Organoboration of Tetrakis(trimethylsilylethynyl)stannane – X‐ray Structure of a 5‐Stannaspiro[4.4]nona‐1,3,6,8‐tetraene Derivative Tetrakis(trimethylsilylethynyl)stannane ( 1 ) reacts with non‐cyclic trialkylboranes BR 3 [ 2 , R = Me ( a ), Et ( b ), Pr ( c ), i Pr ( d )] and 9‐alkyl‐9‐borabicyclo[3.3.1]nonanes[ 2e (alkyl = Et), 2f (alkyl = neopentyl)] to give the 3,8‐dialkyl‐2,7‐bis(dialkylboryl)‐1,4,6,9‐tetrakis(trimethylsilyl)‐5‐stannaspiro[4.4]nona‐1,3,6,8‐tetraenes 5a to f in high yield. The reaction proceeds stepwise, and intermediates as well as final products were characterized by 1 H, 11 B, 13 C, 29 Si, 119 Sn NMR spectroscopy. According to an X‐ray structure analysis of 5f · 0.5 CH 2 Cl 2 (space group P 2/c) the endocyclic CSnC bond angles are small [84.9(2) and 84.2(2)°] and the two five‐membered rings are not exactly planar. Steric crowding causes a strong twist of the skeleton of the other ring systems. The agreement between solid‐state and liquid‐phase NMR data shows that main structural features are retained in solution.