First Insertions of Carbene Ligands into Ge−N and Si−N Bonds

Abstract

The insertion of carbene ligands into Ge-N (three examples) and Si-N (one example) bonds has been achieved for the first time by treating Fischer carbene complexes (M=W, Cr) with bulky amidinatotetrylenes (E=Ge, Si). These reactions, which start with a nucleophilic attack of the amidinatotetrylene heavier group 14 atom to the carbene C atom, proceed through a stereoselective insertion of the carbene fragment into an E-N bond of the amidinatotetrylene ENCN four-membered ring, leading to [M(CO) L] derivatives in which L belongs to a novel family of tetrylene ligands comprising an ECNCN five-membered ring.

Reversible Carbene Insertion into a Ge−N Bond and Insights into CO and Carbene Substitution Reactions Involving Amidinatogermylenes and Fischer Carbene Complexes

“…The IR ν CO absorptions and the 1 H and 13 C{ 1 H} NMR spectra of the new complexes 5′ Cr and 5′ W are similar to those of 3 Cr and 3 W , respectively, in agreement with their structural similarities (the latter were crystallographically characterized). The stereochemistries of 5′ Cr , 5′ W , and 5 W (Scheme ) were established by NOE 1 H NMR measurements, which indicate that the Me and CH 2 SiMe 3 groups are close to each other ( syn arrangement) in 5′ Cr and 5′ W but not in 5 W .…”

“…This work demonstrates that the insertion of a carbene ligand into a Ge−N bond, a process that was observed for the first time by studying the room temperature reactions of the amidinatogermylene 1 t Bu with the electrophilic Fischer carbenes 2 M (M=Cr, W), can be reversible. The existence of an equilibrium between the inserted germylene complexes [M(CO) 5 {Ge( t Bu 2 bzamC(OEt)Me) t Bu}] ( 3 M ), germylene 1 t Bu and the corresponding Fischer carbene 2 M explains the epimerization of the former in solution (at 60 °C) and the unexpected thermally induced transformation of compounds 3 Cr and 3′ Cr to the mixed germylene–Fischer carbene complexes [Cr(CO) 4 {C(OEt)Me}{Ge( t Bu 2 bzam) t Bu}] ( cis ‐ 4 Cr and trans ‐ 4 Cr ).…”

“…Scheme displays a simple mechanistic proposal that, in accordance with the previous statement, accounts for a) the thermally induced transformation of 3 M (M=Cr, W) into an equilibrium mixture of the epimers 3 M and 3′ M and b) the final formation of the tetracarbonyl derivatives cis ‐ 4 Cr and trans ‐ 4 Cr in the case of the chromium system. If 1 t Bu and 2 M are present to some extent in solutions of 3 M (and 3′ M ), the Fischer carbene complexes 2 M can react with 1 t Bu to reform 3 M at room temperature, or give both 3 M and 3′ M at higher temperatures (the formation of both epimers is indeed possible at 60 °C). In the case of the thermolysis of 3 Cr , the Fischer carbene complex 2 Cr can alternatively undergo a thermally induced decarbonylation to give a transient tetracarbonyl species that rapidly alleviates its unsaturation by reacting with 1 t Bu to give the tetracarbonyl derivatives cis ‐ 4 Cr and trans ‐ 4 as the final products.…”

“…All reactions were carried out under argon in a drybox. The germylenes 1 t Bu and 1 tmsm , the Fischer carbene complexes 2 M (M=Cr, W), the ring‐expanded products 3 M , and the germylene complex 6 Cr were prepared following reported procedures. All these reagents and all reaction products were stored at −20 °C under argon in a dry box.…”

“…− Group 6 metal Fischer carbene complexes have been extensively used for this purpose as the carbene sources, although they require high temperatures or catalysis to transfer their carbene fragment. In this regard, we have communicated unprecedented room‐temperature insertions of Fischer carbene ligands into a Ge−N bond of an amidinatogermylene (Scheme ) . Remarkably, the final products ( 3 M ), despite containing two stereogenic atoms, were obtained as single diastereoisomers.…”