ArF and KrF Laser-Induced Gas-Phase Photolysis of Selenophene and Tellurophene:  Extrusion of Te and Se and Intramolecular 1,3-H Shift Competing with β-C−C Cleavage in C₄H₄ Residue

Abstract

ArF (193 nm) and KrF (248 nm) laser-induced photolysis of gaseous selenophene and tellurophene (C4H4M, M=Se and Te) has been examined. It is shown that, unlike thiophene and furan, selenophene and tellurophene cleave both M-C bonds and yield the elemental heteroatom (Se, Te), 1-buten-3-yne, and ethyne. The proposed mechanism involves an intermediate .HC=CH-CH=CH. diradical that decomposes via two competitive pathways, namely, 1,3-H shift to 1-buten-3-yne and beta-cleavage to two molecules of ethyne. It is shown that the relative importance of the channels depends both on the energy of the photon and on the heteroatom. Specifically, the 1,3-H shift/beta-cleavage ratios are 2.3 (193 nm, M=Se), 3.6 (248 nm, M=Se), 1.4 (193 nm, M=Te), and 10.5 (248 nm, M=Te). The inertness of the Te residuum and the high preference for the 1,3-H shift in KrF laser photolysis of tellurophene suggest that this photolysis can serve as a source of the C4H4 diradical for mechanistic studies.

Laser powered homogeneous decomposition of selenophene and tellurophene

“…The mechanism of thermolysis of heterocyclopentadienes (C 4 H 4 M, M = O, S, Se, Te) has been comprehensively examined only for furan [1][2][3] and thiophene [3][4][5][6][7]. It was shown that the thermal decomposition of both C 4 H 4 M (M = O, S) yields primary stable products that reflect the cleavage of only one of the two C-M bonds.…”

“…The thermal decomposition of the congener rings containing Se and Te has not yet been studied and the only data on the decomposition of these compounds are those related to fragmentation upon electron impact [6] and UV laser photolysis [7].…”

“…The laser photolytic fragmentation of selenophene and tellurophene from electronically excited states involves fission of both C-M bonds and yields elemental heteroatom (Se, Te) together with 1-buten-3-yne and ethyne [7]. These hydrocarbons were proposed to arise from intermediate HC CH-CH CH diradical via 1,3-H shift and bcleavage, but the assumed preference of the 1,3-H shift over b-C-C-cleavage and its dependence on the excitation wavelength and the heteroatom could not be given simple explanation due to the uncertainty of the mode of electronic excitation and involvement of both laser-induced nonequilibrium and energy-randomized thermal processes.…”

“…These hydrocarbons were proposed to arise from intermediate HC CH-CH CH diradical via 1,3-H shift and bcleavage, but the assumed preference of the 1,3-H shift over b-C-C-cleavage and its dependence on the excitation wavelength and the heteroatom could not be given simple explanation due to the uncertainty of the mode of electronic excitation and involvement of both laser-induced nonequilibrium and energy-randomized thermal processes. We considered interesting to continue our studies [7] on selenophene and tellurophene by examining thermal decomposition of these compounds, which occurs from the vibrationally excited ground state. Here we present our results on examination of thermal decomposition of selenophene and tellurophene using the technique of IR laserpowered homogeneous decomposition (LPHD [8][9][10]) that was frequently applied to elucidate truly homogeneous decomposition of a number of organic compounds [11][12][13][14][15][16].…”

Atmospheric pressure chemical vapour deposition of selenium and tellurium films by UV laser photolysis of diethyl selenium and diethyl tellurium

“…[6][7][8] The KrF and ArF laser photolysis was disclosed to yield the ground state tellurium atoms and is presumed to involve homolysis of the Te-C bond. 6,7 We have recently reported on ArF and KrF laserinduced photolyses of gaseous selenophene and tellurophene 9 and demonstrated 10 that these photolyses are efficient methods for chemical vapour deposition of elemental selenium and tellurium. We have also shown 11 that the prevailing pathway of the KrF laser photolysis of gaseous (C 2 H 5 ) 2 M (M = Se, Te) molecules is not the M-C bond homolysis, but a four-centre molecular elimination of ethene into MH 2 molecules which decompose into elemental tellurium and selenium.…”