Reactivity of Heavier Vinyl Anions [(CH₃)₂EE′(CH₃)]⁻ (E, E′ = C, Si, Ge) toward Carbon Monoxide: A Computational Study

The structures of heavier vinyl anions [(CH₃)₂EE′(CH₃)]⁻ (E, E′ = C, Si, Ge) and their abilities to activate carbon monoxide were investigated by DFT. Particularly, heteronuclear species exhibit a strong influence of the position of the heavier of the two group 14 elements (E or E′) with strongly differing singlet–triplet gaps as a measure of tetrylene character. The reactions of <b>CSi</b> and <b>CGe</b> (E′ = Si, Ge) with CO proceed in a concerted manner via [1 + 2] or [2 + 2] cycloadditions to a variety of potential products, whereas those of positional isomers as well as digerma and sila-germa analogues occur in a stepwise fashion. The three-membered rings derived from tetrylene-like vinyl anions (E′ = Si, Ge and E = C) are dominated by keto resonance structures, while an enol structure is observed for the product obtained from <b>SiC</b>. Allene-like isomers could only be optimized in case of E = Si, Ge

Reactivity of Heavier Vinyl Anions [(CH₃)₂EE′(CH₃)]⁻ (E, E′ = C, Si, Ge) toward Carbon Monoxide: A Computational Study

The structures of heavier vinyl anions [(CH₃)₂EE′(CH₃)]⁻ (E, E′ = C, Si, Ge) and their abilities to activate carbon monoxide were investigated by DFT. Particularly, heteronuclear species exhibit a strong influence of the position of the heavier of the two group 14 elements (E or E′) with strongly differing singlet–triplet gaps as a measure of tetrylene character. The reactions of <b>CSi</b> and <b>CGe</b> (E′ = Si, Ge) with CO proceed in a concerted manner via [1 + 2] or [2 + 2] cycloadditions to a variety of potential products, whereas those of positional isomers as well as digerma and sila-germa analogues occur in a stepwise fashion. The three-membered rings derived from tetrylene-like vinyl anions (E′ = Si, Ge and E = C) are dominated by keto resonance structures, while an enol structure is observed for the product obtained from <b>SiC</b>. Allene-like isomers could only be optimized in case of E = Si, Ge

A Molecular Complex with a Formally Neutral Iron Germanide Motif (Fe₂Ge₂)

We report the synthesis and isolation of a stable complex containing the formally neutral Fe₂Ge₂ motif, which is stabilized by the coordination of an N-heterocyclic carbene to the germanium and of carbon monoxide to the iron center. [(NHC^{<i>i</i>Pr₂Me₂})­GeFe­(CO)₄]₂ is obtained by reduction of the NHC^{<i>i</i>Pr₂Me₂}-coordinated dichlorogermylene adduct of Fe­(CO)₄, which in turn is obtained from the reaction of Fe₂(CO)₉ with GeCl₂·NHC^{<i>i</i>Pr₂Me₂} (NHC^{<i>i</i>Pr₂Me₂} = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The solid-state structure of the title compound reveals two distinct coordination modes for the Fe­(CO)₄ fragments: bridging (π-type) and terminal (σ-type). In solution, the rapid equilibrium between the two modes was resolved by NMR at −35 °C. Reaction with propylene sulfide at room temperature affords the sulfide-bridged digermanium complex with two terminal Fe­(CO)₄ moieties

Isolation and Reactivity of a Digerma Analogue of Vinyllithiums: a Lithium Digermenide

The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the SiSi moiety. The corresponding germanium analogue, digermenide Tip₂GeGe­(Tip)­Li·dme₂ (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip₂GeCl₂ with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at −70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the GeGe motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip₂GeGe­(Tip)­SiR₃

Isolation and Reactivity of a Digerma Analogue of Vinyllithiums: a Lithium Digermenide

The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the SiSi moiety. The corresponding germanium analogue, digermenide Tip₂GeGe­(Tip)­Li·dme₂ (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip₂GeCl₂ with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at −70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the GeGe motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip₂GeGe­(Tip)­SiR₃

A Molecular Complex with a Formally Neutral Iron Germanide Motif (Fe₂Ge₂)

We report the synthesis and isolation of a stable complex containing the formally neutral Fe₂Ge₂ motif, which is stabilized by the coordination of an N-heterocyclic carbene to the germanium and of carbon monoxide to the iron center. [(NHC^{<i>i</i>Pr₂Me₂})­GeFe­(CO)₄]₂ is obtained by reduction of the NHC^{<i>i</i>Pr₂Me₂}-coordinated dichlorogermylene adduct of Fe­(CO)₄, which in turn is obtained from the reaction of Fe₂(CO)₉ with GeCl₂·NHC^{<i>i</i>Pr₂Me₂} (NHC^{<i>i</i>Pr₂Me₂} = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The solid-state structure of the title compound reveals two distinct coordination modes for the Fe­(CO)₄ fragments: bridging (π-type) and terminal (σ-type). In solution, the rapid equilibrium between the two modes was resolved by NMR at −35 °C. Reaction with propylene sulfide at room temperature affords the sulfide-bridged digermanium complex with two terminal Fe­(CO)₄ moieties

Potential Protecting Group Strategy for Disila Analogues of Vinyllithiums: Synthesis and Reactivity of a 2,4,6-Trimethoxyphenyl-Substituted Disilene

Proof of concept for the protection of the nucleophilic functionality of disilenidesdisila analogues of vinyllithiumwith preservation of the SiSi bond is reported. 1-Iodo-2,4,6-trimethoxybenzene (TMOP-I) reacts with lithium tris­(2,4,6-triisopropylphenyl)­disilenide (<b>1</b>), affording the disilene Tip₂SiSi­(Tip)­TMOP (<b>2</b>) in high yield. The presence of the TMOP group in disilene <b>2</b> enables the regioselective addition of polar substrates to the SiSi double bond, including water, ammonia, acetylenes, and isocyanides. NMR spectroscopic analysis of the reductive cleavage of the TMOP group and subsequent trapping of the corresponding disilenides with Me₃SiCl reveals KC₈ as a highly appropriate reducing agent for the selective deprotection

Potential Protecting Group Strategy for Disila Analogues of Vinyllithiums: Synthesis and Reactivity of a 2,4,6-Trimethoxyphenyl-Substituted Disilene

Proof of concept for the protection of the nucleophilic functionality of disilenidesdisila analogues of vinyllithiumwith preservation of the SiSi bond is reported. 1-Iodo-2,4,6-trimethoxybenzene (TMOP-I) reacts with lithium tris­(2,4,6-triisopropylphenyl)­disilenide (<b>1</b>), affording the disilene Tip₂SiSi­(Tip)­TMOP (<b>2</b>) in high yield. The presence of the TMOP group in disilene <b>2</b> enables the regioselective addition of polar substrates to the SiSi double bond, including water, ammonia, acetylenes, and isocyanides. NMR spectroscopic analysis of the reductive cleavage of the TMOP group and subsequent trapping of the corresponding disilenides with Me₃SiCl reveals KC₈ as a highly appropriate reducing agent for the selective deprotection

Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

The reaction of cyclotrisilenes <b>1</b> with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes <b>2</b> with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of <b>1</b>. Minor quantities of the iminotrisilabicyclo[1.1.0]­butanes <b>3</b> are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of <b>1</b>. The bicyclo[1.1.0]­butanes <b>3</b> become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]­pentanes <b>4</b>

Functionalized Cyclic Disilenes via Ring Expansion of Cyclotrisilenes with Isocyanides

The reaction of cyclotrisilenes <b>1</b> with 1 equiv of alkyl and aryl isocyanides at 25 °C affords the four-membered trisilacyclobutenes <b>2</b> with an exocyclic imine functionality as the major products of formal insertion into one of the Si–Si single bonds of <b>1</b>. Minor quantities of the iminotrisilabicyclo[1.1.0]­butanes <b>3</b> are obtained as side products, formally resulting from [1 + 2] cycloaddition of the isocyanides to the Si–Si double bond of <b>1</b>. The bicyclo[1.1.0]­butanes <b>3</b> become dominant at lower temperatures and may react with an additional 1 equiv of isonitriles to give the diiminotrisilabicyclo[1.1.1]­pentanes <b>4</b>