Photochemistry of pyridine-, 3-bromopyridine-, and hydrogen sulphide-pentacarbonyltungsten in frozen gas matrices at 10 K. Infrared spectroscopic evidence for reversible detachment of bulky ligands

Abstract

Infrared spectroscopic evidence is presented to show, for the first time, that photodetachment of bulky ligands with relatively high molecular weights can take place in gas matrices at 10 K. Ultraviolet photolysis of [W(CO)₅L][L = pyridine (py), 3-bromopyridine, or hydrogen sulphide] isolated at high dilution in methane and argon matrices produces new i.r. absorptions associated with [W(CO)₅] and ‘free’ L. The reaction is shown to be photochromic since subsequent irradiation with visible light regenerates [W(CO)₅L]. Additional evidence for photodetachment of L is obtained from experiments on [W(CO)₅(py)] in carbon monoxide and nitrogen matrices when u.v. photolysis produces [W(CO)₆] and [W(CO)₅(N₂)] respectively. The results are related to solution studies of the photochemical substitution reactions of [W(CO)₅L] complexes and to luminescence studies in organic glasses at 77 K. The work considerably extends the scope of the matrix-isolation technique as a means of studying the mechanisms of photochemical processes.