Insertion of Difluorovinylidene into Hydrogen and Methane

Abstract

Insertion reactions of difluorovinylidene 1b into H2, CH4, and CD4 have been observed in argon matrixes at 20−40 K. These reactions are controlled by diffusion of trapped species rather than by activation barriers, indicating that the activation barriers are very small (<1 kcal/mol) or absent. In contrast, no insertion was observed into CF4 or C2H4. With C2H4, addition to the double bond to give (difluoromethylene)cyclopropane (5) is the only pathway. This was rationalized by ab initio (MP2/6-31G(d,p)) and DFT (B3LYP/6-311++G(d,p)) calculations, which predict activation barriers of essentially zero for the H2 and CH4 insertion, but 40 and 3 kcal/mol for the insertion into CF4 and C2H4, respectively.

Super-electrophilic carbenes and the concept of Philicity

“…This is in agreement with DFT calculations [B3LYP/6-311G(d,p)] of the insertions of 2 into H 2 and CH 4 , which predict zero barriers for both reactions and reaction energies of À113 and À101 kcal mol À1 , respectively (Scheme 1). 17 With À91 and À79 kcal mol À1 [B3LYP/6-31G(d,p)] the insertion of 3 into H 2 and CH 4 is about 20 kcal mol À1 less exothermic (Scheme 2). The addition of carbenes 2 and 3 to ethene to give the corresponding cyclopropane is much less dependent on the nature of the carbene and exothermic by 89 and 85 kcal mol À1 , respectively.…”

“…For the insertion of 2 into the CH bond of ethene an activation barrier of 3 kcal mol À1 has been calculated, while the addition reaction proceeds without barrier. 17 The activation barrier for insertions into H 2 and CH clearly depends on the electrophilicity of the carbene, while the spin state seem to be less important. Insertion reactions into H 2 and hydrocarbons at cryogenic temperatures can thus serve as a qualitative measure for the carbene philicity.…”

CN radical hydrogenation from solid H2 reactions, an alternative way of HCN formation in the interstellar medium

“…In these particles various molecules are embedded, and at temperatures between 3 and 15 K, reactive molecules are kinetically stabilised. Conditions similar to that in the CHIMPs can be simulated in the laboratory by cryogenic matrix isolation experiments where solid H 2 is A&A 598, A22 (2017) used as a matrix (Norman & Porter 1954;Whittle et al 1954;Kötting & Sander 1999;Zuev & Sheridan 2001;Hoshina et al 2004;Henkel et al 2014). Momose et al (1998) studied the reaction of H 2 with a photoinduced radical CD 3 .…”

Silylenes and germylenes: The activation of H–H bond in hydrogen molecule

“…The reversible activation reactions of H 2 with boron and phosphorus centers are regarded as Lewis acid-base adduct reactions, in which the Lewis acidic B center and Lewis basic P center interact with H 2 synchronously [13]. Recently, H 2 was demonstrated to be split by nucleophilic activation at a single carbon center in the carbenes [20][21][22][23][24][25][26]. Theoretical calculations with the density functional theory (DFT) at the B3LYP/ 6-311G ** level displayed that the hydrogen bounds to the carbon center irreversibly, generating a hydride-like hydrogen, which subsequently reacts with the positively polarized carbon atom [23].…”

“…In fact, activation of O-H of water molecule can also proceed with silylenes [67,95,96,103]. Similar mechanism exists for carbenes as well [20][21][22][23][24][25][26]. The isodesmic reactions of silylenes and germylenes with dihydrogen were employed to discuss the relative stability of cyclic silylenes and germylenes at the level of Hartree-Fock (HF) [27,71].…”