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Title
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A theoretical quest to identify the precedence between NHC side group (R′) and bridge group (R) in the formation of [NHC(R′)(M(di‑μ‑R) YR)] (M = Li, Na, K; Y = Zn, Cd; R = H, CH3, t‑Butyl, Si(CH3)3, C6H5; R′ = H, CH3, Dipp) complexes
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Abstract
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Latest developments in bimetallic chemistry confirm that the lethargic kinetic reactivity of organozinc reagents can be modified by pairing zinc reagents with group 1 organometallic compounds to form alkali-metal zincates. This study seeks to characterize the impact of NHC(R′) substituent and/or R bridge group on the formation mechanism of [NHC(R′)(M(di- μ-R)YR)] (M = Li, Na, K; Y = Zn, Cd; R = H, CH3, t-Butyl, Si(CH3)3, C6H5; R′ = H, CH3, Dipp) compounds. The nature of Ccarbene→ M bond in the complexes has been analyzed with the help of density functional theory methods. In this regard, CAM-B3LYP functional is the most appropriate DFT method for the well-studied complexes among seven selected DFT methods. The effect of R′ substituent and the R bridge group on the formation mechanism of the titled compounds and the amount of activation barriers show interesting consequences regarding the size effect of R groups. In this view, a formation mechanism is suggested. Besides, the nature of Ccarbene→ M bonds in all complexes is inspected through natural bond orbitals, atoms in molecules, energy decomposition analysis and extended transition state-natural orbitals for chemical valence analyses. Results confirmed that the contribution of electrostatic interaction in C→M bonds in present complexes is almost more than 70%.
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