Theoretical Study of the Reactivities of Neutral Six-Membered Carbene Analogues of the Group 13 Elements

Abstract

The potential energy surfaces for the chemical reactions of group 13 carbenoids have been studied using density functional theory (B3LYP/LANL2DZ). Five six-membered group 13 carbenoid species, HC(CMeNPh)2X, where X = B, Al, Ga, In, and Tl, have been chosen as model reactants in this work. Also, three kinds of chemical reaction, C−H bond insertion, alkene cycloaddition, and dimerization, have been used to study the chemical reactivities of these group 13 carbenoids. The present theoretical investigations suggest that the relative carbenoidic reactivity decreases in the order B > Al ≫ Ga > In > Tl. That is, the heavier the group 13 atom (X), the more stable is its carbenoid toward chemical reactions. This may be the reason that so far no experimental evidence for the HC(CMeNPh)2B species has been reported, while the other group 13 carbenoids are isolable at room temperature, since they are quite inert to chemical reaction. Furthermore, the group 13 carbenoid singlet−triplet energy splitting, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made.

A Mechanistic Study on Reactions of Group 13 Diyls LM with Cp*SbX2: From Stibanyl Radicals to Antimony Hydrides

“…According to quantum chemical calculations, the singlet-triplet energy gap (Al 46 kcal mol À1 ; Ga 54 kcal mol À1 ; In 55 kcal mol À1 ) and HOMO-LUMO + 1 separation (Al 82.8 kcal mol À1 ; Ga 95.3 kcal mol À1 ; In 95.9 kcal mol À1 ) increase from Al to Ga, whereas those of Ga and In are virtually identical. [5] A monomeric alanediyl LAl [6] containing a sterically demanding N,N'-chelating b-diketiminate ligand was found to activate a large variety of main group element-hydrogen s-bonds (HÀX; X = H, B, C, Si, N, P, O) [7] as well as CÀF and CÀO s-bonds, [8] whereas the corresponding gallanediyl LGa [9] shows a remarkable activity toward insertion reactions into main group metal-X bonds of heavy group 13 (Ga, In), [10] 14 (Ge, Sn, Pb), [11] 15 (Bi), [12] and 16 elements (Te). [13] In contrast, LIn is less reactive due to the enhanced stability of In in the + I oxidation state.…”

“…Their reactivity in oxidative addition reactions originates from the M‐centered (M=Al, Ga, In) electron lone pair (HOMO) as well as from the formally vacant p ‐orbital (LUMO+1), which makes these monovalent species particularly useful as strong nucleophiles and moderate electrophiles. According to quantum chemical calculations, the singlet‐triplet energy gap (Al 46 kcal mol −1 ; Ga 54 kcal mol −1 ; In 55 kcal mol −1 ) and HOMO–LUMO+1 separation (Al 82.8 kcal mol −1 ; Ga 95.3 kcal mol −1 ; In 95.9 kcal mol −1 ) increase from Al to Ga, whereas those of Ga and In are virtually identical . A monomeric alanediyl LAl containing a sterically demanding N , N’ ‐chelating β‐diketiminate ligand was found to activate a large variety of main group element‐hydrogen σ‐bonds (H−X; X=H, B, C, Si, N, P, O) as well as C−F and C−O σ‐bonds, whereas the corresponding gallanediyl LGa shows a remarkable activity toward insertion reactions into main group metal‐X bonds of heavy group 13 (Ga, In), 14 (Ge, Sn, Pb), 15 (Bi), and 16 elements (Te) .…”

Te–Te and Te–C bond cleavage reactions using a monovalent gallanediyl

“…Computational calculations predicted that LGa is a good σ-donor but a poor π-acceptor due to the low energy and high s-character of the HOMO, and the large energy difference (95.3-110 kcal mol −1 ) between the HOMO and the rather diffuse acceptor 4p-orbital (LUMO+1). [2][3][4] The σ-donor capacity of LGa was experimentally demonstrated for instance with the synthesis of the Lewis acid-base adduct LGa→B(C 6 F 5 ) 3 5 and other p-or d-block metal complexes as well as with the synthesis of a large variety of (late) transition metal complexes. 6 The latter were shown to be promising reagents for the activation of small molecules such as ethylene and have been used as precursors for the formation of heterometallic clusters, 7,8 which in part can be described as molecular models for alloys.…”

“…16,3.82, 3.42, 1.04 ppm) with the integral ratios of 2 : 1 : 2 : 1, respectively. Integrals of 2 H belong to the i-Pr methine groups of the L ligand.…”

Mechanistic insights into the insertion and addition reactions of group 13 analogues of the six-membered N-heterocyclic carbenes: interplay of electrophilicity, basicity, and aromaticity governing the reactivity

“…[8][9][10][11][12][13][14][15] In this work, we devote our attention to the reactivity of the neutral six-membered NHC analogues featuring a group 13 element (G13-6-Rea). Although the understanding of the six-membered-ring G13-6-Rea molecules has certainly grown in recent years, [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] our knowledge concerning their relative chemical reactivity remains primitive compared to that of ve-membered-ring NHC analogues bearing a central group 14 element. [22][23][24][25] In this study, we thus chose two typical chemical reactions (insertion, eqn (1), and cycloaddition, eqn (2)) based on density functional theory (DFT) to investigate the origin of the activation barriers for group 13 analogs of the six-membered NHCs.…”