Photolysis of [((~5-C5H,)Fe(CO)2}2] in CH4 (1 2 K) and polyvinyl chloride film (12-77 K) matrices leads to the formation of a novel species proposed, on the basis of i.r. evidence including I3CO enrichment and u.v.visible spectra, to be the CO-bridged dimerA recent flash photolysis study1 of the photochemistry of [ ((q5-C5H5)Fe(CO), >,I (1) provided evidence for two distinct

The photochemistry of [M,(q5-C,H,) ,(CO),][M = Fe, (1); or Ru, (2)] and [CH,{(q5-C,H,)M(C0), },] [M = Fe, (5); or Ru, ( 6)] has been studied in frozen-gas matrices (Ar, CH, , and N, ) at ca. 12 K and that of (2) in poly(viny1 chloride) (pvc) films at ca. 12 K. Low-energy photolysis of compounds (1) and (2) was found to induce opening of trans-carbonyl-bridged species affording terminal carbonyl species. Photolyses into the electronic absorption band maxima of these new terminal-carbonyl species yielded 17-electron radical species [ M(q5-C,H,) (CO),]' as well as small amounts of triply carbonyl-bridged species, [M,(q5-C5H5),(p-C0),1. At the corresponding maxima of trans-carbonyl-bridged complexes (1 ) and ( 2) photolysis yielded the triply-carbonyl-bridged species directly. Photolysis of (5), which is exclusively bridging and is constrained by the methylene linkage between the rings to be in a cis conformation, at a range of wavelengths showed no evidence for carbonyl-bridge opening. At its electronic absorption maxima photolysis resulted in carbonyl ejection and formation of a new species whose spectrum is consistent with its having three terminal carbonyl groups and an Fe-Fe double bond. Photolysis of compound (6) which exists in a cis-terminal conformation also resulted in carbonyl loss and formation of a species similar to that observed for (5). These results are discussed in terms of their relationship to previous photochemical studies of (1) and ( 2) and an overall model for the photochemical behaviour of (1) and (2) is presented.

Infrared spectroscopic evidence including 13C0 substitution and energy-factored force-field fitting is presented to show that photolysis of [M (q5-C5H5) (CO),CI] complexes (M = Mo or W) in argon, methane, nitrogen, carbon monoxide, and 5% C, H, -CH, matrices at ca. 12 K yields ejection of CO and formation of the 16-electron species [M(q5-C5H5) (CO),CI] as the primary process. This process is reversible. In nitrogen and 5% C, H, -CH, matrices the [ M (q5-C5H5) (CO),CI] species react with N, and C2H4 to give cis-[ Mo(q5-C5H5) (CO),( N, ) CI] and cis-[ M (q5-C5H5) (CO),( C, H, ) CI] (M = Mo or W) respectively. In carbon monoxide matrices the ejection of CO is suppressed and the photolysis products are proposed to be the species [ M (q5-C5H5) (CO),] 'CI-(M = Mo or W), indicative of metal-chlorine bond heterolysis. Irradiation of [M(q5-C5H5) (CO),CI] complexes (M = Fe or Ru) in methane, nitrogen, and carbon monoxide matrices and in poly(viny1 chloride) films at ca. 12 K produced only the 16-electron species [M (q5-C5H5) (CO)CI] and CO indicating that dissociation, rather than cleavage of the metal-chlorine bond, is the principal reaction pathway. The primary process can be reversed thermally in the polymer films by virtue of their wider working temperature range (ca. 12-298 K). For the iron complex reversal occurred by ca. 60 K, whereas the ruthenium complex needed a higher temperature of annealing (ca. 80 K). The results of the low-temperature studies are discussed in relation to the thermal and photochemical reactions of complexes of Mo, W, Fe, and Ru in solution at ambient temperatures.f Non-S.I. unit employed: Torr x 133 Pa.

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CO),] together with its mononuclear analogue [Cr(q6-C,H,) (CO),] in gas matrices at ca. 12 K results in CO ejection t o yield [M(CO),] molecular fragments rather than detachment of polyene rings or the formation of new M-M linkages via M-M bonding and/or CO bridging. The reactivity of the resultant [M(CO),] molecular fragments is demonstrated by the recombination with CO when matrices (Ar, CH,) were irradiated with light of a longer wavelength and b y the reactions with N, and 13C0 (5% in Ar or CH,) t o afford [ M (CO),( N,)] and [ M (12CO),(13CO),,] fragments, respectively. The failure to form new M-M linkages is attributed t o the isolation of the dimers in pseudo-trans configurations in the matrix cages such that even the excess photochemical energy is insufficient to both cleave M-CO bonds and supply the energies required to rotate the bulky fragments in the rigid matrix cages. These findings are discussed in relation to solution photochemical reactions.