Matrix Isolation Fourier Transform Infrared Spectroscopic and Density Functional Theoretical Studies of the Reactions of Chromium Atoms and Acetylene

Abstract

The reactions between chromium atoms and acetylene have been investigated in solid argon with infrared absorption spectroscopy. It is found that the ground-state chromium atoms reacted with acetylene to form the metallocyclopropene Cr(C2H2) molecule spontaneously on annealing. The Cr(C2H2) molecule underwent photochemical rearrangement to the alkynyl hydride HCrCCH molecule upon ultraviolet−visible irradiation. The two products were identified on the basis of isotopic IR studies with 13C2H2 and C2D2, and density functional theory calculations.

Chemistry in low-temperature matrices

“…176 The reactions between Cr atoms and acetylene have been explored. 177 Ground state Cr atoms react with acetylene in Ar matrices to form the metallocyclopropane molecule Cr(C 2 H 2 ) spontaneously on annealing. Photolysis of this cyclic species affords the alkynyl hydride HCrCCH.…”

Photoelectron Spectroscopy of CoC2H2– and Density Functional Study of ConC2H2 (n = 1–3) Anion and Neutral Clusters

“…Therefore, the interactions of transition metals with the typical and simplest unsaturated hydrocarbons like acetylene have received considerable attention from both experimental and theoretical points of view. Four kinds of transition metal–acetylene complexes have been addressed via the reactions of transition metals with acetylene, including the side-on M-(η 2 -C 2 H 2 ), the vinyl M–C 2 H 2 , the inserted HM–CCH, and the vinylidene MCCH 2 . − Zhou and co-wokers found that the ground-state Cr atoms reacted with acetylene to form metallocylcopropene, which will rearrange into the inserted product upon ultraviolet–visible irradiation . Recently, using matrix isolation infrared spectroscopy and density functional theory (DFT) calculations, Andrews and co-workers have reported that the reactions of laser-ablated transition metals (Sc, Y, La, Cr, Mo, W) with acetylene produce the π and the inserted complexes. , Xu and co-workers have identified the products of the side-on M-(η 2 -C 2 H 2 ) (M = Y, Ge, Sn), the inserted HYCCH (M = Y, Ge, Sn, Pb), anionic HScCCH – , HScScCCH – , and the vinylidene Sn 2 CCH 2 . , Duncan and co-workers investigated the cationic M + (C 2 H 2 ) complexes (M = Ca, V, Fe, Co, and Ni) by using infrared photodissociation spectroscopy and theoretical calculations. − Ramsvik et al studied the chemisorption and decomposition of acetylene on the Co single-crystal surface using the near-edge X-ray absorption fine structure (NEXAFS) technique and observed that the dehydrogenated fragment C 2 H was adsorbed on the Co crystal surface in the temperature range of 200–300 K.…”

Infrared Spectra of M-η2-C2H2 and HM-C≡CH Produced in Reactions of Laser-Ablated Group 6 Metal Atoms with Acetylene

“…[1][2][3][4][5][6][7][8][9]11 On the basis of the C−C bond lengths and observed stretching frequencies, the Group 4 metals form remarkably strong π complexes due to effective back-donations to the π* orbitals in M-η 2 -(C 2 H 2 ). 4 Group 3 and 5 metals also generate strong π complexes but slightly weaker than the Group 4 metal analogues. 4 In contrast, the main group and late transition metals produce much weaker π complexes.…”

“…Huang et al have recently reported the observation of the two and three vibration bands of the Cr π and insertion complexes in reaction with acetylene. 4 In this article, we report reactions of Group 6 metals with C 2 H 2 and their products identified in the matrix IR spectra. The backdonation to the π system continuously decreases from the Group 4 to 6 metal systems; the absence of the vinylidene products is consistent with the high activation energies, and the insertion complexes have bent structures.…”

“…It is generally believed that coordination of the metal atom to the acetylene π system (M-η 2 -C 2 H 2 with C 2 v symmetry) occurs first, and the excess reaction energy or photon energy leads to C–H bond insertion by the metal atom to form the insertion complex (HM-CCH). − The vinylidene complex (H 2 CCM) is supposedly produced through conversion of either HM-CCH (migration of H from M to β-C) or M-η 2 -C 2 H 2 (migration of H from one C to the other). A previous investigation reveals that production of the vinylidene product via the insertion complex is energetically more favorable (requiring smaller activation energy) than the direct conversion from the π complex .…”