Guanidinate stabilized germanium(II) and tin(II) amide complexes and their catalytic activity for aryl isocyanate cyclization

Abstract

Two different synthetic routes for the preparation of guanidinate stabilized germanium(II) and tin(II) amide complexes have been established. First, the reaction of one equiv of bulky guanidine ligand either L1H or L2H [L1 = {ArNC (NiPr2)NAr} (Ar = 2,6-Me2–C6H3) and L2 = {Ar′NC (NiPr2) NAr′}(Ar′ = 2,6-iPr2-C6H3)] with two equiv of KN(SiMe3)2 and one equiv of metal dihalide i.e., MCl2{M = Ge(dioxane) and Sn} led to the formation of guanidinate supported germanium(II) amide, i.e., L1GeN(SiMe3)2 (1) and tin amide, i.e., L1SnN(SiMe3)2 (2) and L2SnN(SiMe3)2 (3) complexes, respectively. Second, deprotonation of L1H upon treatment with M[N(SiMe3)2]2 (M = Ge and Sn) in C6D6 at 80 °C for 12 h, afforded the compounds L1MN(SiMe3)2 M = Ge(1) and Sn(2), respectively. X-ray crystal structures of 1 and 2 revealed that both are in monomeric and metal centers in distorted tetrahedral environments with one vertex occupied by a stereo chemically active lone pair of electrons. Furthermore, compounds 1, 2 and 3 were tested for the catalytic activity in the cyclotrimerization of arylisocyanates, which are exhibiting as excellent catalysts.