Synthesis and structural characterization of the first trialkylguanidinate and hexahydropyramidopyramidinate complexes of tin

The first guanidinate complexes of tin have been prepared using N,N',N"-trialkylguanidinates ([(RN)(2)C(NRH)](-); R = cyclohexyl; isopropyl) and 1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyramidinate (hpp(-)) as ligands. The direct reaction between triisopropylguanidine and SnCl4 provided the complex {[(PrN)-Pr-i](2)C[(NHPr)-Pr-i]}SnCl3 (1) along with concomitant formation of the guanidinium salt {C[(NHPr)-Pr-i](3)} (+) [SnCl5(THF)](-) (2). The Sn(II) guanidinate complexes {(C6H11N)(2)C[NH(C6H11)]}(2)Sn (3) and {CN[N(CH2)(3)](2)}(2)Sn (4) were prepared through metathesis reactions between 0.5 equiv. SnCl2 and (C6H11N)(2)C[NH(C6H11)]Li or hppLi, respectively. Complex 4 is the first reported mononuclear complex of this ligand. In contrast, the reaction of hppLi with I equiv. SnCl, afforded a bridging dinuclear species, {CN[N(CH2)(3)](2)SnCl}(2) (5). A second mononuclear complex of the hpp ligand, {CN[N(CH2)(3)](2)}(2)SnCl2 (6), was the product obtained from the reaction of 2 equiv. of hppLi with SnCl4. The full structural details of compounds I and 3 6 are reported. In the case of compounds I and 3 these results revealed a distinctly unsymmetrical bonding mode for the bidentate guanidinate ligand and suggest variable degrees of pi delocalization with the ligand. The geometries of the Sn centers in 3, 4 are derived from distorted trigonal bipyramidal coordination with a stereochemically active lone pair occupying one coordination site. In contrast, complex 5 displayed a geometry derived from a tetrahedral ligand array with one vertex occupied by a lone pair of electrons. Complex 6 is six coordinate and possesses 2 equiv. chelating bidentate hpp(-) ligands and two cis-chloro groups. (C) 2002 Elsevier Science Ltd. All rights reserved.