Unusually slow photodissociation of CO from (η6-C 6H6)Cr(CO)3 (M= Cr or Mo): A time-resolved Infrared, Matrix Isolation, and DFT investigation

Mohammed A.H. Alamiry, Nicola M. Boyle, Christopher M. Brookes, Michael W. George, Long Conor, Peter Portius, Mary T. Pryce, Kate L. Ronayne, Xue Zhong Sun, Michael Towrie, Q. Vuong Khuong

Research output: Journal PublicationArticlepeer-review

33 Citations (Scopus)

Abstract

The photochemistry of η6-C6H6)M(CO) 3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λEXC. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C 6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm-1) that decays over 150 ps to (η6-C6H6)Cr(CO) 2(n-heptane) (70%) and (η6-C6H 6)Cr(CO)6 (30%). Pulsed photolysis (λexc. = 266 nm) of (eta;6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H 6)Cr(CO)6(n-heptane) (1930 and 1870 cm-1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of( η6-C 6H6)Cr(CO)6. Photolysis of (η6- C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm-1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.

Original languageEnglish
Pages (from-to)1461-1468
Number of pages8
JournalOrganometallics
Volume28
Issue number5
DOIs
Publication statusPublished - 9 Mar 2009
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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