Quaternization of the Bridgehead Nitrogen in Silatranylosmium(II) Complexes and Reestablishment of the Transannular N−Si Bond following Migratory Insertion of the Silatranyl Ligand

The Si−N distance in the five-coordinate silatranyl complex Os(Si{OCH 2 CH 2 } 3 N)Cl(CQ)(PPh 3 ) 2 ( 1a, Q = O) is very long, and the geometry about nitrogen is planar. Accordingly, the nitrogen atom readily undergoes methylation or protonation, and this increases the Si−N separation even further. On addition of CO to 1b (Q = S), the coordinated CS inserts into the Os−Si bond and the normal silatrane N−Si interaction is restored in the ( 4 ).