N→Ge Coordinated Germylenes as Ligands for Monomeric Cu Complexes

Reactivity of Cyclic (Alkyl)(amino)germylene towards Copper(I) and Gold(I) Complexes

The reactions of cyclic (alkyl)(amino)germylenes (CAAGe) with copper(I) and gold(I) complexes were investigated. CAAGe (1) reacts with CuBr(SMe2 ) leading to a tetrameric germylene complex [CAAGeCuBr]4 (2), whereas CAAGe (3) undergoes Au-Cl bond insertion with LAuCl (L=phosphine or N-heterocyclic carbene) to afford germanium gold(I) complexes (5 and 6). Chlorine abstraction of 6 gives the cationic germylene gold(I) complex 7.

Ge-Cu-Complexes Ph(pyO)Ge(μ2-pyO)2CuCl and PhGe(μ2-pyO)4CuCl-Representatives of Cu(I)→Ge(IV) and Cu(II)→Ge(IV) Dative Bond Systems

Phenylgermaniumpyridine-2-olate PhGe(pyO)₃ (compound 1Ge) and CuCl react with the formation of the heteronuclear complex Ph(pyO)Ge(μ²-pyO)₂CuCl (2Ge') rather than forming the expected compound PhGe(μ²-pyO)₃CuCl (2Ge). Single-point calculations (at the B2T-PLYP level) of the optimized molecular structures confirmed the relative stability of isomer 2Ge' over 2Ge and, for the related silicon congeners, the relative stability of 2Si over 2Si'. Decomposition of a solution of 2Ge' upon access to air provided access to some crystals of the copper(II) compound PhGe(μ²-pyO)₄CuCl (3Ge). Compounds 2Ge' and 3Ge were characterized by single-crystal X-ray diffraction analyses, and the Ge-Cu bonds in these compounds were analyzed with the aid of quantum chemical calculations, e.g., Natural Bond Orbital analyses (NBO), Non-Covalent Interactions descriptor (NCI), and topology of the electron density at bond critical point using Quantum Theory of Atoms-In-Molecules (QTAIM) in conjunction with the related silicon compounds PhSi(μ²-pyO)₃CuCl (2Si), PhSi(μ²-pyO)₄CuCl (3Si), as well as the potential isomers Ph(pyO)Si(μ²-pyO)₂CuCl (2Si') and PhGe(μ²-pyO)₃CuCl (2Ge). Pronounced Cu→Ge (over Cu→Si) lone pair donation was found for the Cu(I) compounds, whereas in Cu(II) compounds 3Si and 3Ge, this σ-donation is less pronounced and only marginally enhanced in 3Ge over 3Si.

Reactions of Mesityl Azide with Ferrocene‐Based N‐Heterocyclic Germylenes, Stannylenes and Plumbylenes, Including PPh 2 ‐Functionalised Congeners

The reactivity of ferrocene‐based N‐heterocyclic tetrylenes [{Fe(η⁵−C₅H₄−NSitBuMe₂)₂}E] (E=Ge, Sn, Pb) towards mesityl azide (MesN₃) is compared with that of PPh₂‐functionalised congeners exhibiting two possible reaction sites, namely the E^II and P^III atom. For E=Ge and Sn the reaction occurs at the E^II atom, leading to the formation of N₂ and an E^IV=NMes unit. The germanimines are sufficiently stable for isolation. The stannanimines furnish follow‐up products, either by [2+3] cycloaddition with MesN₃ or, in the PPh₂‐substituted case, by NMes transfer from the Sn^IV to the P^III atom. Whereas [{Fe(η⁵−C₅H₄−NSitBuMe₂)₂}Pb] and other diaminoplumbylenes studied are inert even under forcing conditions, the PPh₂‐substituted congener forms an addition product with MesN₃, thus showing a behaviour similar to that of frustrated Lewis pairs. The germylenes of this study afford copper(I) complexes with CuCl, including the first structurally characterised linear dicoordinate halogenido complex [CuX(L)] with a heavier tetrylene ligand L.

Synthesis, Characterization, and Reaction of Digermylenes

A series of digermylenes R(EGeL)₂ (L=CH[C(Me)N(Ar)]₂, Ar=2,6‐iPr₂C₆H₃; E=O, R=1,3‐C₆H₄ (1), 1,4‐C₆H₄ (2), Me₂C(CH₂)₂ (3); E=NH, R=1,4‐C₆H₄ (4), 1,4‐C₆H₁₀ (5); E=C(O)O, R=1,3‐C₆H₄ (6)) were synthesized by the reactions of L′Ge (L′=HC[C(CH₂)N(Ar)]C(Me)N(Ar), Ar=2,6‐iPr₂C₆H₃) with selected diphenols, diol, diamines, and o‐/m‐phthalic acids, respectively. Treatment of digermylene 1,3‐C₆H₄(OGeL)₂ (1) with sulfur, selenium and CuX (X=Cl, Br, I) led to the formation of 1,3‐C₆H₄[OGe(S)L]₂ (8), 1,3‐C₆H₄[OGe(Se)L]₂ (9), and (CuX)₂[1,3‐C₆H₄(OGeL)₂]₂ (X=Cl (10), Br (11), I (12)), respectively. The obtained products were characterized by melting point, elemental analysis, FT‐IR, ¹H and ¹³C NMR spectroscopy, and single‐crystal X‐ray diffraction.

Coinage Metal Complexes of Germylene and Stannylene

Group 11 metal (M = Cu, Ag, Au) complexes of heavier tetrylenes (namely, germylene and stannylene) have been studied for several years now. However, the field is mainly unexplored for their potential application either in homogeneous catalysis or in photophysical properties regardless of how the current reports allude to the rich and fascinating chemistry of group 14 elements. In this mini-review, we attempted to summarize the recent advances of heavier tetrylene-stabilized coinage metal complexes, which are majorly dominated by structure elucidation studies. This comprehensive summary intends to help researchers design and fine-tune the tetrylene ligand framework that can lead to coinage metal complexes for future applications as photoemitters in organic light-emitting diode fabrication and efficient catalysts in homogeneous catalysis.