Theoretical Insights on the Interaction of N-Heterocyclic Carbenes with Tetravalent Silicon Reagents

Abstract

Lewis acid-base type interaction between N-heterocyclic carbene (NHC) and tetravalent silicon reagent (SiR) has been investigated computationally. This NHC-Si interaction is of fundamental importance to the understanding of variety of NHC catalyzed organic transformations involving silicon compounds such as cyanosilylation, trifluoromethylsilylation, etc. Geometries of 24 NHCs, 10 silicon reagents, and their 61 Lewis acid-base complexes have been optimized using the B3LYP/6-31+G(d,p) and M05-2X/6-31+G(d,p) level of theory. The strength of NHC-Si interaction has been assessed in terms of binding energy of the complexes, charge transfer (CT) and the length of Si-CNHC bond. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis at M052X/6-31+G(d,p) level of theory has been carried out to get a deeper understanding of the nature of bonding and charge delocalization. Proton affinity of the NHCs and fluoride affinity of the SiRs have been calculated and correlated with the binding energy of the resulting complexes.

Stretching the P–C Bond. Variations on Carbenes and Phosphanes

“…Carbenes (Carbthis notation will be used throughout) are divalent carbon compounds, stabilized mainly by heteroelements like nitrogen or sulfur, − yielding N-heterocyclic carbenes (NHCs) or cyclic aminocarbenes (CAACs) just to mention the most widely applied ligands of transition metals. − Moreover, as strong nucleophiles, these ligands can stabilize otherwise highly reactive molecules formed from p-block elements. , Furthermore, they react with weak Lewis acids as silanes − and phosphanes. − The NHC–silane adducts could apparently be described by dative bond formation, − ,, being stabilized by (i) electronegative substituents (e.g. halogens) at silicon and (ii) by the increased nucleophilicity of the carbenes. , The products from the reactions between different NHCs and phosphanes are more diverse (Figure : A–E ), depending on the reaction conditions and the nature of the starting materials. − ,,− ,− The parent H-phosphanes did not react with imidazol-2-ylidene ( 1 R:Dipp); however, imidazolidine-2-ylidene ( 2 R:Dipp) and CAAC ( 3 ) were activating the PH bond, yielding prima...…”

A promising class of luminescent derivatives of Silver(I) and Gold(I)‐N‐heterocyclic carbene

“…The nature of binding interaction in NHC–Ag‐Cl has been probed by post‐wave function analysis using the natural bond orbital (NBO) method. [ 30 ] As summarized in Table 6, the natural charges on the Ag and Au atoms were calculated to be +0.454, +0.508, +0.508, and + 0.604 in complexes 2 , 3 , 4 and 5 , respectively. Moreover, Wiberg Bond Index (WBI) calculations were consistent with the X‐ray data, which effectively explained by 2 and 3 ; each one showed distinct M–C bond distances and were consistent with reported values.…”

Electronic Tuning and Catalytic Activity of a Novel Pd(II) Complex Supported by a Tetracoordinate Ligand

“…However, the Pd–N distances were calculated to be slightly longer (2.10990‐2.13016 Å) than those measured in the aforementioned complexes containing pyrimidine (2.086(7) Å) . Natural Bond Orbital (NBO) analyses were also conducted to elucidate the bonding contributions found in 2 . As summarized in Table , the natural charge on the Pd center was calculated to be 0.41690, whereas the charge on the carbene bonded to the metal center was calculated to range from 0.26791 ‐ 0.24946.…”