Pulsed laser flash photolysis with IR diode laser detection: the reaction of photogenerated trans-[(n-C 7H 16)(P(OPr i) 3)W(CO) 4] with piperidine

Abstract

Pulsed laser flash photolysis with IR detection apparatus in which the analyzing source is an IR diode laser has been used to study ligand-exchange reactions of metal carbonyl transients in solution. The apparatus is described and the advantages of the IR diode laser analyzing source over the ‘globar’ and line-tuneable CO laser sources previously employed in such studies are discussed. It has been employed to monitor the thermal reaction with pip of trans-[(n-C 7H 16)(L)W(CO) 4], (L = tri(isopropyl) phosphite) produced via pulsed laser flash photolysis of cis-(pip)(L)W(CO) 4 in n-heptane. This reaction obeys a mixed order rate law interpreted in terms of bimolecular ‘trapping’ of the photogenerated intermediate with pip to afford trans-(pip)(L)W(CO) 4 and a competing unimolecular pathway tentatively ascribed to slow isomerization of trans-[(L)W(CO) 4] to its cis analogue. This isomer then is rapidly trapped by pip to afford the cis-(pip)(L)W(CO) 4 photolysis precursor.