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

Abstract

The tris-N-heterocycle germanide (tmim)Ge– (1) (tmimH3 = tris(3-methylindol-2-yl)methane) was synthesized by nucleophilic substitution for the tmim3– 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)]22–, 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.

A crystalline T-shaped planar group 14 anion

“…Upon reduction, the endocyclic N–Ge–N bond angles (78.23(7)° and 76.56(7)°) in 4 become more acute with respect to those (80.34(8)° and 79.59(9)°) of 3, thus reflecting the elongation of both the equatorial Ge1–N3 bond (1.9039(19) Å) and axial Ge1–N1/N2 bonds (2.0578(18) and 2.1633(18) Å) in 4. Additionally, the equatorial Ge1–N3 bond distance is shorter than those (1.925(7)–1.970(4) Å) in trinitrogen substituted germanides in pyramidal geometries, 10 and the axial Ge1–N1/N2 bonds are longer, which are in good agreement with the calculated results reported by Arduengo and co-workers. 7 Moreover, it is noteworthy that the average C–N (1.376(3) Å) and C–C (1.421(3) Å) bond distances in two C 2 N 2 Ge rings are between corresponding single and double bonds, implying that 4 is best viewed as a resonance of canonical forms 4A and 4B ( Scheme 2 ), which represents an analogue of T-shaped bismuth( i / iii ) triamide 3 h and a rare example of valence tautomerism of p -block element compounds.…”