Heterocarbenoids of germanium and tin and their polyhedral oxidation products: The case for thermodynamic product control in Group 14 chalcogenides

The polycyclic Group 14 amides [P(μ-NtBu)2P(tBuN)2]M, M = Ge (4), Sn (5) were synthesized from cis-[P(μ-NtBu)2P(tBuNLi · THF)2] and GeCl2 · dioxane or SnCl2, respectively. Oxidation of these heterocarbenoids or of the analogous diazastannylene [MeSi(μ-tBuN)2SiMe(tBuN)2]Sn with O2, S8 and Sen furnished the chalcogenides {[P(μ-NtBu)2P(tBuN)2]GeO}2 (6), {[P(μ-NtBu)2P(tBuN)2]SnE}2, E = O (7), S (8), Se (9), {[SP(μ-NtBu)2P(tBuN)2]SnS}2 (10), and {[MeSi(μ-tBuN)2SiMe(tBuN)2]SnE}2, E = S (11), Se (12), respectively. All products (6–12) were shown by single-crystal X-ray methods to consist of dimeric molecules with central (M–E)2 rings, M = Group 14 element, E = chalcogen. The exclusive formation of dimeric compounds with bridging M–E–M bonds, vs. alternative monomeric structures with terminal Mdouble bond; length as m-dashE bonds, is rationalized in terms of the thermodynamic favorability of the dimers. The case is made that most, if not all, currently known Group 14 chalcogenides, even those labeled “kinetically stabilized”, are really thermodynamic products.