Donor–acceptor-stabilised germanium analogues of acid chloride, ester, and acyl pyrrole compounds: synthesis and reactivity

Abstract

Hitherto unknown germaacid chloride (1), germaester (2), and Ngermaacyl pyrrole (3) compounds are stabilised as Lewis acid complexes. Reactivity studies on them yielded compounds such as germaynone (4) and germaacyl thioester (10).

N-Heterocyclic Carbene-Stabilized Germa-acylium Ion: Reactivity and Utility in Catalytic CO2 Functionalizations

“…The molecular structure of complex 3­[BArF] was unambiguously confirmed by SC-XRD analysis (Figure a), which revealed a distorted tetrahedral geometry at the germanium center. The Ge–O bond in complex 3­[BArF] is 1.697(3) Å, which is shorter than a tetracoordinate Ge–O single bond (1.76–1.82 Å) and falls within the range of donor/acceptor stabilized germanones (1.673–1.718 Å). − This bond is relatively elongated compared to three coordinate germanone 1.646(5) Å . In the solid-state IR spectrum, compound 3 displays a strong absorption at 807 cm –1 which is assigned as GeO.…”

“…The Ge-O bond in complex 3[BArF] is 1.697(3) Å, which is shorter than a tetracoordinate Ge-O single bond (1.76-1.82 Å) and falls within the range of donor/acceptor stabilized germanones (1.673-1.718 Å). [49][50][51][52][53] This bond is relatively elongated compared to three coordinate germanone 1.646(5) Å. 21 In the solid-state-IR spectrum compound 3 displays a strong absorption at 807 cm -1 which is assigned as Ge=O.…”

“…Inspection of the frontier orbitals show the HOMO-1 and HOMO in 3 + comprise of the lone pair orbitals on the O atom, whereas the LUMO consists of the vacant p π orbital on the carbene carbons (Figure 3b). In order to examine a relationship to classical acyl transfer, we treated compound 3 with Ph 3 SiOH, this resulted in the first example of an acceptor free stable germanium ester, compound 49,52 Expectedly, the Ge1-O2 bond length (1.802(18) Å) is longer than Ge1-O1 bond and is more in line with typical Ge-O single bond values. [52][53] Theoretical studies suggest the formation of 4 proceeds via a stable intermediate which contains a strong hydrogen bond from the hydroxyl proton in Ph 3 SiOH to the O1 center in 3M + .…”

“…In order to examine a relationship to classical acyl transfer, we treated compound 3 with Ph 3 SiOH, this resulted in the first example of an acceptor free stable germanium ester, compound 49,52 Expectedly, the Ge1-O2 bond length (1.802(18) Å) is longer than Ge1-O1 bond and is more in line with typical Ge-O single bond values. [52][53] Theoretical studies suggest the formation of 4 proceeds via a stable intermediate which contains a strong hydrogen bond from the hydroxyl proton in Ph 3 SiOH to the O1 center in 3M + . Proton transfer to O1 then occurs, followed by de-coordination of IMe 4 which then allows for proton abstraction from O1 to deliver the desired germanium ester (Figure S52).…”

Acid–Base Free Main Group Carbonyl Analogues

“…Treating the dimer with Lewis acids affords acid–base stabilized germanones 52( i Pr)‐LA (LA=B(C 6 F 5 ) 3 /GeCl 2 /SnCl 2 /ZnCl 2 ). In 2019, the same group elaborated on this chemistry by varying the X substituent on the germylene P52(X) (X= i Pr, Cl, OSiPh 3 , NC 4 H 4 ) to access a series of isolable Lewis acid–base stabilized germacarbonyls with significantly elongated Ge=O double bonds (1.695(3)–1.728(5) Å) [41d] …”