SYNTHESIS AND STRUCTURE OF BIS(TRIMETHYLSTANNYL) AND BIS(DIMETHYLHALOSTANNYL) AMINES - THE ROLE OF THE NITROGEN LONE PAIR

Monoaminostannanes RNH-SnMe3 (1) with substituents R = tBu, Mes, 2,6-iPr2C6H3 are obtained by transmetallation from Me3SnX and RNH-Li, the distannylamines RN(SnMe3)2 (2) by transamination of Et2N-SnMe3 with RNH2, and bis(dimethylhalostannyl)amines R-N(SnMe2X)2 (8) by stannazane cleavage of 2 with Me2SnX2 or by SnC cleavage with BX3 (8n,o). Me2Sn(NtBuH)2, prepared from tBuNHLi and Me2SnBr2, decomposes with tBuNH2 elimination into the diazadistannetidine 4 already below room temperature. Information from multinuclear NMR spectra of type 2, 4, and 8 compounds ascertain the proposed relation between the value of the geminal coupling constant 2J(Sn-119 Sn-117) of distannazanes and the Sn-N-Sn bond angle as determined by the X-ray structure analysis of 2c and of (8a)2 as well as the participation of the electron pair at the nitrogen atom in bonding. 2c has C2 symmetry, contains a planar nitrogen atom with SnN bond lengths of 2.044 angstrom and an Sn-N-Sn bond angle of 125.0-degrees. The aryl group stands perpendicular to the Sn2N plane. These data exclude any pi-interaction between the N atom and the substituents. 2c, therefore, represents an example of a tertiary amine with the lone electron pair at the nitrogen atom in a p-type orbital. The supposed distannylamine (ClMe2Sn)2NMe (8a) is actually a dimer, whose unexpected structure contains a diazadistannetidine unit bearing two Me2SnCl2 groups at its nitrogen atoms in cis-configuration. This arrangement allows the formation of weak intramolecular SnCl bonds.