C−H Activation by AlCl Monomers: Characterization of HAl(Cl)CH₃ as the Product of the Photoactivated Reaction Between AlCl and CH₄ in a Solid Ar Matrix at 12 K

Abstract

In a solid Ar matrix at 12 K and upon photoactivation AlCl inserts into the C−H bond of CH 4 IntroductionSubvalent compounds of the general formula MX [M ϭ Al, Ga or In, and X ϭ F, Cl, I, or a cyclopentadienyl (Cp) derivative] react readily, when photoactivated, with a number of molecules.[1] Examples include the reaction of AlCl with H 2 to give H 2 AlCl, [2] with O atoms to give OAlCl, [3] with O 2 to give ClAlO 2 [4] or, when the concentration of O 2 is increased, ClAl(O 2 ) 2 , [5] and with HX (X ϭ F, Cl or Br) to give HAl(Cl)X. [6,7] With GaCl [8] and InCl, [9] reactions with H 2 and with HCl afford the hydrides H 2 MCl and HMCl 2 (M ϭ Ga or In), respectively. GaF reacts with O atoms to give OGaF.[10] Finally, matrix-isolated AlCp* reacts with H 2 upon photoactivation to yield H 2 AlCp*. [11] Although these species are generally highly reactive, there are some remarkable differences between AlX, GaX and InX with respect to their reactivities and the structures and composition of the end-products. Whereas AlCl reacts, as already mentioned, upon photoactivation with O 2 [Equation (1)], GaCl or InCl show no matrix reaction, photoactivated or not, with O 2 [Equation (2)]. [12] (1) (2) [a]

Chemistry in low-temperature matrices

“…Photoactivated AlCl also inserts into the C-H bond of CH 4 . 251 Here the novel monomeric hydride HAl(Cl)CH 3 is the primary product for which C s symmetry is indicated. With acetylene the corresponding reaction leads only to the acetylide, Cl(H)AlCCH, by C-H insertion and not to the metallocyclopropene derivative which would be formed by addition to the p-system.…”

Characterization of Oligomers of AlCl: Al–Cl versus Al–Al Bonding

“…[11] Only when O atoms are generated is reaction possible, which leads to OAlCl. [12] Photoactivated AlCl reacts, on the other hand, not only with O 2 , [11] but also readily with molecules such as CH 4 , [13] H 2 , [14] C 2 H 2 [15] and HX (X = F, Cl or Br). [16] The effect of photolysis has been shown to lead to excitation of an electron from a σ to a π orbital with strong p character localized mainly at the Al atom.…”