sp-Hybridized Seesaw Ge0 Complexes via Germylone-to-Seesaw Isomerization in a Four-Electron Cyclic N2Ge2 Ligand

Abstract

We report the first examples of two linear trigermanium complexes (μ-Ge)(κ²-N₂Ge₂^Ar) (Ar = 2,4,6-Me₃C₆H₂ (4), 2,6-Et₂C₆H₃ (5)), in which each central Ge⁰ atom displays a seesaw geometry enforced by a four-electron cyclic N₂Ge₂^Ar ligand. The pyridine-stabilized sp-hybridized Ge⁰ center is a four-electron donor and two terminal germylenes are electron-acceptors. Comparative studies show that the N₂Ge₂ scaffold uniquely stabilizes the Ge⁰ atom. This work not only introduces a new class of main-group seesaw complexes but also demonstrates ligand-driven control over hybridization and donor-acceptor dynamics. Compound 5 underwent one-electron reduction, followed by ligand rearrangement and dimerization, to afford a novel hexanuclear homounivalent germanium cluster, 10, featuring a snake-like Ge₆ core. In 10, each Ge atom in the central Ge^I-Ge^I unit is solely stabilized one amido ligand, while each of the remaining four Ge atoms is supported by one amido and one pyridyl donor. The isolation of a bulkier analogue (11) and a heteronuclear Ge₄Sn₂ cluster (16) further underscores the crucial role of ligand sterics in stabilizing these assemblies. These findings expand the structural diversity of low-valent group 14 compounds and establish a new paradigm for constructing multinuclear tetrel clusters.

1

Characterized germylones supported by (a) N-heterocyclic carbenes (NHCs), (b) N-donors and imine-NHCs, (c) bis­(DSSi) (DSSi = donor-stabilized silylene), and (d) bis­(germylene), and their Lewis adducts (C, H, G and K). (e) Present work.

2

A cyclic four-electron dipyridyl-digermylene ligand (N ₂ Ge ₂ ^Dipp ) is used to support a Ge⁰ atom, where the ligand is derived from 1 (bis­(DSGe^Dipp)) via decoordination of two pyridyl N-donors from the two Ge atoms.

1. Synthesis of Two Germylone-Stabilized Linear Trigermanium Compounds 4 and 5, and Lewis Acid–Base Coupling of 5 with InCl₃ to Afford Indium Adduct 6

3

(a) The solid-state molecular structure of 5 with thermal ellipsoids at 50% probability. The hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°) Ge1–Ge2, 2.5042(4); Ge2–Ge3, 2.4986(4); Ge1–N1, 2.023(2); Ge1–N6, 1.965(2); Ge2–N2, 1.968(2); Ge2–N5, 1.965(2); Ge3–N3, 1.966(3); Ge3–N4, 2.026(3); Ge1–Ge2–Ge3, 176.609(19); N1–Ge1–N6, 100.11(10); N2–Ge2–N5, 101.00(10); N3–Ge3–N4, 99.37(11); Ge2–Ge1–N1, 80.61(7); Ge2–Ge1–N6, 84.14(7); N3–Ge3–Ge2, 84.07(7); N4–Ge3–Ge2, 80.65(7). (b) ELF plots of 5. The ELF function of η­(r) = 0.8 is shown around Ge.

4

Energy profile for 5A undergoing intramolecular rearrangement via an intermediate 5B to give the product 5C. All free energies in kcal/mol are relative to 5A at 1 atm and 298.15 K.

5

Solid-state molecular structure of 6·Et ₂ O with thermal ellipsoids at 30% probability. Hydrogen atoms and Et₂O were omitted for the sake of clarity. Selected bond lengths (Å) and angles (°): Ge1–Ge2, 2.3987(5); Ge2–Ge3, 2.5031(5); In1–Ge1, 2.6217(4); In1–Cl1, 2.4018(9); In1–Cl2, 2.3580(10); In1–Cl3, 2.3805(10); Ge1–N1, 1.915(3); Ge1–N6, 1.893(3); Ge2–N2, 1.976(3); Ge2–N5, 1.989(3); Ge2′···Cl1, 3.4091(10); Ge2′···Cl3, 3.3514(11); Ge3–N3, 1.973(3); Ge3–N4, 2.043(3); Ge1–Ge2–Ge3, 178.77(2); In1–Ge1–Ge2, 134.405(18); N1–Ge1–N6, 104.69(12); N2–Ge2–N5, 98.92(11); N3–Ge3–N4, 99.18(11); Ge2–Ge3–N3, 83.40(8); Ge2–Ge3–N4, 79.60(7).

2. Preparation of the Trigermanium Compounds 4 and 5, Cyclic Tetagermanium Compounds 7–9, and Hexagermanium Compounds 10, 11 and 16

6

(a) The solid-state molecular structure of 11 with thermal ellipsoids at 30% probability. The hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Ge1–Ge2, 2.4446(4); Ge2–Ge3, 2.4734(4); Ge3–Ge3′, 2.7634(5); Ge1···K1, 3.1870(8); K1···C24′, 3.233(4); K1···C25′, 3.063(4); K1···C26′, 3.388(4); K1–O1, 2.563(3); Ge2–N2, 1.9671(19); Ge2–N4, 1.960(2); Ge1–N1, 1.993(2); Ge1–N5, 2.016(2); Ge3–N3, 2.059(2); K1–N6, 2.683(3); Ge2–Ge3–Ge3′, 77.609(12); Ge1–Ge2–Ge3, 141.969(14); Ge2–Ge1–K1, 136.68(2); Ge1–K1–O1, 155.82(9); N3–Ge3–Ge3′, 98.34­(6); N1–Ge1–N5, 98.27(8); N2–Ge2–N4, 99.46(9). (b) ELF plots of 11m. The ELF function of η­(r) = 0.7 is shown around Ge.

7

Solid-state molecular structure of 16 with thermal ellipsoids at 30% probability where the hydrogen atoms were omitted for the sake of clarity. Selected bond lengths (Å) and angles (°): Sn1–Sn1′, 2.9718(9); Sn1–Ge1, 2.5865(7); Ge1–Ge2, 2.4473(8); Ge2···K1, 3.2605(18); Sn1···Ge1′, 3.3944(8); Sn1–N1, 2.195(5); 2.021(5); K1···C7′, 3.194(8); K1···C6′, 3.285(7), K1–O1, 2.669(6); K1–N4, 2.729(6); K1–O1 2.669(6); Ge1–N2, 1.984(4); Ge1–N6, 1.953(5); Ge2–N3, 1.996(5); Ge2–N5, Sn1′–Sn1–Ge1, 74.93(2); Sn1–Ge1–Ge2, 142.21(3); Ge1–Ge2–K1, 137.51(4); Sn1′–Sn1–N1, 93.71­(13); Ge1–Sn1–N1, 80.38(12); N2–Ge1–N6, 103.7(2); N3–Ge2–N5, 97.0(2).