Organotin cations stabilized by π coordination – synthesis and NMR studies in solution and in the solid state

The organoboration of tetraalkynyltin compounds [Sn‐(CCR 1 ) 4 ( 1 ): R 1 = Me ( a ), Et ( b ), Pr ( c ), i Pr ( d ), t Bu ( e )] with triethylborane ( 2 ) proceeds stepwise. Intermediates with a cationic triorganotin ( 3, 5 ) and a dicationic diorganotin fragment ( 4 ), stabilized by intramolecular coordination of one and two alkynyl moieties, respectively, were isolated ( 3e, 4a ) and/or identified by multinuclear NMR in solution ( 1 H, 11 B, 13 C, 119 Sn) and in the solid state ( 13 C and 119 Sn CP/MAS) ( 3e, 4a ). The magnitude of 1 J ( 13 C 13 C) in 4a (101.0 Hz) is significantly smaller than that for sodium triethyl‐1‐propynylborate ( 7 ) (119.2 Hz), proving the weak coordination of the CC bond to the dicationic tin fragment. The final products of the organoboration, 1,4,6,9‐tetraalkyl‐2,7‐bis(diethylboryl)‐3,8‐diethyl‐5‐stannaspiro[4.4]nona‐1,3,6,8‐tetraenes ( 6b–6e ) were obtained in high yield.