Formation of Formic Acid Derivatives through Activation and Hydroboration of CO₂ by Low-Valent Group 14 (Si, Ge, Sn, Pb) Catalysts

Abstract

The chemistry of low-valent main group elements has attracted much attention in the past decade. These species are relevant because they have been able to mimic transition metal behavior in catalytic applications, with decreased material costs and diminished toxicity. In this contribution, we study the L 1 EH catalysts (E = Si(II), Ge(II), Sn(II), and Pb(II); L 1 = [ArNC(Me)CHC(Me)NAr] with Ar = 2,6-iPr 2 C 6 H 3 ) for the formation of formic acid derivatives through hydroboration of CO 2 . Detailed characterization of relevant structures on the potential energy surface enabled us to rationalize different paths for the hydroboration of CO 2 . Interestingly, it was found that according to the activation energies for the whole catalytic cycle, the process of transformation of CO 2 becomes more favored going down group 14. However, an effective energetic decrease for the process (taking as the reference the uncatalyzed reaction between CO 2 and HBpin) is evidenced just from the germanium analogue. The trend in reactivity found in the present study is a direct consequence of the change in the central main group element, enabling enhanced polar character of the E−H (L 1 EH in the CO 2 activation step) and E−O (metal formates in the hydroboration step) bonds as the atomic radius increases. The transient stabilization of reaction intermediates found in the hydroboration step was rationalized through the non-covalent interaction index (NCI) and symmetry-adapted perturbation theory (SAPT). This computational study highlights the reactivity trends in group-14based hydride catalysts in hydrometalation and posterior hydroboration to form formic acid intermediates. We hope that this study will motivate further experimental work in low-valent lead chemistry.

Structural Characterization, DFT Calculation, NCI, Scan-Rate Analysis and Antifungal Activity against Botrytis cinerea of (E)-2-{[(2-Aminopyridin-2-yl)imino]-methyl}-4,6-di-tert-butylphenol (Pyridine Schiff Base)

“…To reveal possible noncovalent interactions, such as hydrogen bonds, steric repulsion, van der Waals interactions, noncovalent interaction index (NCI) was performed. NCI is based on the electron density and its derivatives, which enables the identification of noncovalent interactions on the reduced density gradient (S) at low-density regions (ρ) [ 52 , 78 , 79 , 80 ]. This analysis provides a graphical index (2D plot), which allows the characterization of the interactions mentioned before.…”

Low‐Valent Germanylidene Anions: Efficient Single‐Site Nucleophiles for Activation of Small Molecules

“…The only other crystallographically characterised example for germanium is a [4+2] cycloadduct of 1,4‐digermabenzene with CO 2 in which the two metalloid centres work in tandem as a Lewis acid and a base [67] . Germanium mediated CO 2 transformations typically involve insertion to a Ge−H bond to give Ge−O bound formic acid derivatives [68–72] . Other reported examples include the conversion of heavy Group 14 ketones to κ 2 O,O′ bound carbonates in the presence of CO 2 [36,73] and side‐on insertion of CO 2 to the Ge−Ge single bond of a digermyne to give a bis(germylene) oxide after CO release [74] .…”

“… [67] Germanium mediated CO 2 transformations typically involve insertion to a Ge−H bond to give Ge−O bound formic acid derivatives. [ 68 , 69 , 70 , 71 , 72 ] Other reported examples include the conversion of heavy Group 14 ketones to κ 2 O,O′ bound carbonates in the presence of CO 2 [ 36 , 73 ] and side‐on insertion of CO 2 to the Ge−Ge single bond of a digermyne to give a bis(germylene) oxide after CO release. [74] The high nucleophilic character of germanium in 4 and 5 is highlighted by comparison with germylones A that have not been reported to react with CO 2 .…”

Aluminum Amidinates: Insights into Alkyne Hydroboration

“… 6 Over the past decade, main-group systems have been shown to efficiently catalyze a host of hydroboration reactions. 1 , 7 − 10 The first example of aluminum-mediated hydroboration dates back to 2000, where a combination of LiAlH 4 , 1,1′-bi-2-naphthol (BINOL), and methanol was found to stoichiometrically reduce acetophenone with HBcat. 11 However, it was not until 2015 that Roesky, Parameswaran, and Yang reported the first example of aluminum-catalyzed hydroboration.…”