Oxidative addition to M(II) (M = Ge, Sn) amidinate complexes: routes to group 14 chalcogenolates with hypervalent coordination environments

Abstract

Oxidative addition of diphenyl dichalcogenides, PhE–EPh (E = S, Se) to Ge(II) and Sn(II) amidinate complexes is reported. In the case of the bis(alkylamidinato)Ge complexes, Ge(CyNC(R′)NCy) (Cy = cyclohexyl; R′ = Me, ^tBu), six coordinate Ge(IV) compounds were isolated and the structure of (PhS)₂Ge(CyNC(Me)NCy) (10) was confirmed by single crystal X-ray diffraction analysis. Mixed amidinato–amido species, M(CyNC(R′)NCy)[N(SiMe₃)₂] (M = Ge, Sn; R = Me, ^tBu), react in a similar manner to yield novel bis(phenylchalcogenolate) complexes of Sn and Ge. Spectroscopic features and, in the case of (PhSe)₂Ge(CyNC(Me)NCy)[N(SiMe₃)₂] (13), a single crystal structural analysis indicate that this ligand environment appears to favor Ge(IV) complexes with a strong disposition towards a tetrahedral geometry. In these cases, a five coordinate environment for the metal center is avoided by one of the amidinate ligands exhibiting a monodentate coordination mode, which preserves the pseudo-tetrahedral metal coordination geometry. These observations contrast with the Sn(II/IV) analogues which exhibit no such tendency. For example the single crystal structure of (PhS)₂Sn(CyNC(Me)NCy)[N(SiMe₃)₂] (14) displays a bidentate ligand and a five coordinate metal coordination geometry. Complex 13 reacts with elemental Se to generate the terminal germanium selenide and regenerate PhSeSePh. Concomitant with this reaction is a rearrangement of the previously monodentate amidinate ligand to a bidentate coordination mode.