Homoleptic low-valent polyazides of group 14 elements

Synthesis and Complexation of a Free Germanide Bearing a Tridentate N-Heterocyclic Substituent

The tris-N-heterocycle germanide (tmim)Ge^- (1) (tmimH₃ = tris(3-methylindol-2-yl)methane) was synthesized by nucleophilic substitution for the tmim^3- trianion on GeCl₂·dioxane. In combination with the previously reported (tmim)Si^- and (tmim)P analogues, it provides a convenient model for investigating the influence of the central atom on the properties of isoelectronic ligands. Complexation of the germanide (tmim)Ge^- to CuCl resulted in the dimeric chloro cuprate [(tmim)GeCu(μ-Cl)]₂ ^2-, which is prone to dissociation in MeCN to form the neutral, solvated germylcopper (tmim)GeCu(NCMe)₃. The reaction of 1 with Fe₂(CO)₉ afforded the germyl iron tetracarbonyl [(tmim)GeFe(CO)₄]^-. Analysis of the ν̃(CO) infrared absorption bands in this complex indicates that the combined electron donating and accepting properties of 1 are found in between those of (tmim)P and (tmim)Si^-. In contrast to (tmim)Si^-, (tmim)Ge^- is reluctant to coordinate to FeCl₂, likely because of its softer Lewis base character. Key structural features of the ligands and complexes reflect changes in their electronic properties. In particular, the N-Ge-N angles increase upon coordination to a metal fragment, suggesting increasing hybridization of the Ge s- and p-orbitals. These findings will be useful in further understanding low-valent heavier group 14 complexes in organometallic chemistry.

Labile Low-Valent Tin Azides: Syntheses, Structural Characterization, and Thermal Properties

The first two examples of the class of tetracoordinate low-valent, mixed-ligand tin azido complexes, Sn(N₃)₂(L)₂, are shown to form upon reaction of SnCl₂ with NaN₃ and SnF₂ with Me₃SiN₃ in either pyridine or 4-picoline (2, L = py; 3, L = pic). These adducts of Sn(N₃)₂ are shock- and friction-insensitive and stable at r.t. under an atmosphere of pyridine or picoline, respectively. A new, fast, and efficient method for the preparation of Sn(N₃)₂ (1) directly from SnF₂, and by the stepwise de-coordination of py from 2 at r.t., is reported that yields 1 in microcrystalline form, permitting powder X-ray diffraction studies. Reaction of 1 with a nonbulky cationic H-bond donor forms the salt-like compound {C(NH₂)₃}Sn(N₃)₃ (4) which is comparably stable despite its high nitrogen content (55%) and the absence of bulky weakly coordinating cations that are conventionally deemed essential in related systems of homoleptic azido metallates. The spectroscopic and crystallographic characterization of the polyazides 1-4 provides insight into azide-based H-bonded networks and unravels the previously unknown structure of 1 as an important lighter binary azide homologue of Pb(N₃)₂. The atomic coordinates for 1 and 2-4 were derived from powder and single crystal XRD data, respectively; those for 1 are consistent with predictions made by DFT-D calculations under periodic boundary conditions.