Monosilicon‐substituted cyanoacetylene: A computational study

Abstract

A detailed theoretical investigation of the [H,Si,C(2),N] potential energy surfaces including 28 minimum isomers and 65 interconversion transition states is reported at the Gaussian-3//B3LYP/6-31G(d) level. Generally, the triplet species lie energetically higher than the singlet ones. The former three low-lying isomers are linear HCCNSi 1 (0.00 kcal/mol), branched SiC(H)CN 12 (7.09 kcal/mol), and bent HNCCSi 7 (14.22 kcal/mol), which are separated by rather high barriers from each other and are kinetically very stable with the least conversion barriers of 32.6-70.5 kcal/mol. Two energetically high-lying isomers HCNCSi 3 (42.99 kcal/mol) and SiC(H)NC 13 (36.05 kcal/mol) are also kinetically stable with a barrier of 49.19 and 21.42 kcal/mol, respectively. Additionally, five high-lying isomers, that is, three chainlike isomers, HCCSiN 2 (55.17), HCSiNC 6 (47.80), HSiNCC 11 (78.83), and one three-membered ring isomer HN-cSiCC 19 (51.21), and one four-membered ring isomer cSiCN(H)C 27 (50.6 kcal/mol), are predicted to each have lower conversion barriers of 12-18 kcal/mol and can be considered as meta-stable species. All of the predicted 10 isomers could exist as stable or meta-stable intermediates under suitable conditions. Finally, the structural and bonding analysis indicate that the [H,Si,C(2),N] molecule contains various properties that are of chemical interest (e.g., silylene, SiC triple bonding, and conjugate SiN triple bonding and CC triple bonding, charge-transfer specie, planar aromatic specie, cumulate double bonding). This is the first detailed theoretical study on the potential energy surfaces of the series of hydrogenated Si,C,C,N-containing molecules. The knowledge of the present monohydrogenated SiC(2)N isomerism could provide useful information for more highly hydrogenated or larger Si,C(2),N-containing species.

Synthesis of the Silaisocyanoacetylene Molecule

“…Despite the tetravalent characters of carbon and silicon, the higher electronegativity difference between nitrogen (3.04) and silicon (1.90) compared to nitrogen (3.04) and carbon (2.55) is reflected in a preferential localization of the unpaired electron at the nitrogen atom in the silicon nitride radical. Further, the refractory nature of silicon nitrides such as the Si 3 N 4 parent compound has made investigations of gas phase reactions of the diatomic silicon nitride radical (SiN; X 2 Σ + ) fraught with difficulties with studies limited largely to theoretical examinations. − In contrast, the simplest closed-shell carbon- and nitrogen-bearing molecule, i.e., cyanogen C 2 N 2 , exists as a gas at room temperature. Also, reactions of the isoelectronic cyano radicals (CN; X 2 Σ + ) with simple hydrocarbons like acetylene have been extensively studied theoretically and experimentally utilizing the crossed molecular beam approach. , Under single collision conditions, these bimolecular gas phase reactions lead to the formation of nitriles (RCN), i.e., organic molecules carrying the cyano group (CN), which is connected with its carbon atom to the organic group R; the corresponding isonitrile isomers (RNC) were not synthesized under bimolecular collisions in the gas phase.…”

“…The silaisocyanide (HNSi, 10 ) was computed to be thermodynamically favored by 271 kJ mol –1 compared to the silahydrogencyanide isomer (HSiN, 9 ). Considering organic silanitriles and silaisonitriles, a single theoretical study suggested that the silaisocyanoacetylene (HCCNSi, 12 ) should be more stable by 230 kJ mol –1 compared to the silacyanoacetylene (HCCSiN, 11 ), i.e., the corresponding silicon-analogous molecules of cyanoacetylene (HCCCN, 13 ) and isocyanoacetylene (HCCNC, 14 , Scheme ). Nevertheless, the synthesis of any silanitrile or silaisonitrile has remained elusive so far.…”

Spectroscopic and structural characterization of three silaisocyanides: exploring an elusive class of reactive molecules at high resolution

“…HCCNSi and silaisocyanogen (NCNSi) are isovalent to the well-known compounds HCCCN 16 and NCCN, 17 but there is a paucity of information on their energetics and structures, and their spectroscopic properties are essentially unknown. For HCCNSi, in addition to some calculations accompanying the crossed molecular beam experiment, 13 there is only one other quantum chemical study, 18 in which extensive density functional theory calculations of the [H, Si, 2C, N] potential energy surface were undertaken, work that predicted this isomeric arrangement of atoms to be the global minimum. The situation is no better for NCNSi, it has not yet been detected experimentally, and there are only two computational studies, 19,20 but both identify NCNSi as the most stable isomer.…”