Antony J. Rest

Matrix isolation studies of organometallic intermediates

Bonne methode pour la caracterisation des especes instables. Cas de complexes de metaux carbonyles ou non

Photolysis of Group VI metal carbonyls, (η6-C6H6)Cr(CO)3, (η5-C5H5)Mn(CO)3, (η5-CH3C5H4)Mn(CO)3 and (η5-C5H5)Re(CO)3 in Nujol at 77 K

Abstract Photolysis of M(CO) 6 , where M = Cr,Mo, and W, in Nujol mulls at 77K resulted in the formation of “free” CO and C 4 v M(CO) 5 photoproducts. This reaction was found to be photochemically and thermally reversible. Similarly, the photolysis of the metal “half-sandwich” complexes (η 6 -C 6 H 6 )Cr(CO) 3 , (η 5 -C 5 H 5 )Mn(CO) 3 , (η 5 -CH 3 C 5 H 4 )Mn(CO) 3 and (η 5 -C 5 H 5 )Re(CO) 3 in Nujol at 77 K was found to form the corresponding dicarbonyl photoproducts and “free” CO. These reactions were found to be photochemically reversible. (η 6 -C 6 H 6 )Cr(CO) 3 and (η 5 -C 5 )Re(CO) 3 were also found to produce small amounts of dinuclear products directly upon photolysis, while (η 5 -C 5 H 5 )Mn(CO) 3 and (η 5 -CH 3 C 5 H 4 )Mn(CO) 3 formed similar species upon annealing.

Photochemistry of tris(dimethylpyrazolyl)-boratorhodium dicarbonyl and bis(dimethylpyrazolyl)-boratorhodium dicarbonyl complexes in low temperature media at 12–298 K: some insights into CH activation processes

Abstract IR and electronic spectroscopic evidence, including a study of 13 CO enrichment pathways, is presented to show that photolysis of tris (dimethylpyrazolyl)-boratorhodium dicarbonyl and bis(dimethylpyrazolyl)-boratorhodium dicarbonyl complexes in argon and methane matrices at ca. 12 K produces CO loss and ligand dechelation products. No evidence was found for photochemical CH bond activation in methane matrices but the facile tridentate α bidentate interconversion for tris(dimethylpyrazolyl)-boratorhodium dicarbonyl provides support for the proposal that such a process could be the key step in the highly efficient CH photoactivation reaction of this complex at 298 K. In dinitrogen matrices the new CO loss products reacted to form monodinitrogen complexes. In an attempt to investigate whether additional thermal energy is needed for the photoactivation processes, the tris(dimethylpyrazolyl)-boratorhodium dicarbonyl and bis(dimethylpyrazolyl)-boratorhodium dicarbonyl complexes were photolysed in perfluorokerosine and Nujol mulls which could be warmed from ca. 12 K to 298 K. No CH bond photoactivation was observed in Nujol mulls at 12 K or 77 K but at 298 K photoactivation of Nujol by tris(dimethylpyrazolyl)-boratorhodium dicarbonyl was observed, i.e. there appears to be a thermal contribution to the photochemical CH activation process for this particular complex. The results of the low temperature studies are related to photochemical reactions observed in solutions at 298 K.

Photochemistry of the group VI metal hexacarbonyls in polyvinyl-chloride film matrices at 12-298 K. The reactivity of the species M(CO)5 and M(CO)5(THF)

Abstract The photochemistry of the metal hexacarbonyls M(CO) 6 (M = Cr, Mo, W) in polyvinyl chloride (PVC) film matrices over a wide temperature range (12–98 K) has been studied. Infrared spectroscopic evidence for the formation of the species M(CO) 5 and M(CO) 5 (THF) is presented. The effect of temperature and the influence of the polymeric medium on the observed photoreactions is discussed and the results are compared with those obtained using the following matrix materials: paraffin wax discs, frozen gases and hydrocarbon glasses.

NMR study of the photochemical reaction of (η5-C5H5)Fe(CO)2Me with P, As, Sb, S and N donor ligands

Abstract The photochemical reaction of (η5-C5H5)Fe(CO)2Me with E(C6H5)3 (E = P, As, Sb) has been studied quantitatively in situ by NMR spectroscopy and the rate of reaction, as monitored by η5-C5H5 and Me resonances, determined as a function of ligand, ligand concentration, solvent, wavelength and likely competing reactions. The product at temperatures above 27°C was found to be (η5-C5H5)Fe(CO)(Me)E(C6H5)3 in all cases and rate plots showed that the rate-determining step did not involve the ligand E(C6H5)3 and also that an acetyl complex was not involved as an intermediate. The photoreaction may be considered as: Qualitative NMR studies showed that C5H5N, (C2H5)2S, and o-phenylenebis(dimethylarsine) gave products of the type (η5-C5H5)Fe(CO)(Me)L in photochemical reactions.

Photoactivation of methane by η5-cyclopentadienyl and substituted η5-cyclopentadienyl Group 8 metal dicarbonyl complexes, [M(η5-C5R5)(CO)2](M = Rh or Ir, R = H or Me), and dicarbonyl(η5-indenyl)iridium: a matrix isolation study

Infrared spectroscopic evidence, including deuterium labelling, is presented to show that photolysis of [M(η5-C5R5)(CO)2](M = Rh or Ir, R = H or Me) complexes in CH4 matrices at ca. 12 K leads primarily to [M(η5-C5R5)(CO)(Me)(H)] complexes. Comparative photolysis experiments in CH4, Ar, and 13CO-doped (5%) matrices provided evidence that the initial step is the loss of CO to form the ‘naked’ 16-electron species, [M(η5-C5R5)(CO)]. Additional photoproducts in CH4 matrices are tentatively assigned as the CH4 complexes [M(η5-C5R5)(CO)⋯ CH4]. Cobalt analogues failed to activate CH4 but did afford very weak bands which could possibly be assigned to the CH4 complexes [Co(η5-C5R5)(CO)⋯ CH4](R = H or Me). The indenyl complex, [Ir(η5-C9H7)(CO)2], behaves similarly to the cyclopentadienyl complexes. The mechanism of CH4 activation in matrices in discussed and related to the activation of CH4 in solution at ambient temperatures. The lack of CH4 activation by Co analogues seems to be best rationalised on thermodynamic grounds.

Photochemistry of (η-cyclopentadienyl)nitrosylnickel in frozen gas matrices at 20 K. Infrared spectroscopic evidence for mono- and di-carbonyl(η-cyclopentadienyl)nickel in carbon monoxide matrices and for a species formed by photoionisation or photoelectron transfer in inert matrices

Infrared evidence, including 13CO data, is presented for the formation of [Ni(η-C5H5)(CO)], [Ni(η-C5H5)(CO)2], and ultimately [Ni(CO)4] on the u.v. photolysis of [Ni(η-C5H5)(NO)] in CO or mixed CO and ‘inert’(nitrogen, argon) matrices at 20 K. Infrared evidence, including 15NO data, is also presented for the formation of a species [Ni(η-C5H5)(NO*)][the asterisk denotes a nitrosyl group with an unusually low value of ν(NO)] on photolysis of [Ni(η-C5H5)(NO)] in argon, methane, and nitrogen matrices at 20 K. The significance of the low value of ν(NO) for [Ni(η-C5H5)(NO*)] is discussed in terms of either photoionisation, i.e. formation of an ion pair [Ni(η-C5H5)]+NO–, or photoelectron transfer, i.e. the nitrosyl group acting as a one- or two-electron ligand instead of a three-electron ligand. It is concluded that [Ni(η-C5H5)(NO*)] belongs to a class of complexes in which electron transfer from the metal to the nitrosyl ligand is particularly extensive and bending of the M–N–O group may be involved. A convenient photochemical synthesis of [Ni(η-C5H5)(15NO)] is described.

Photochemistry of (η-benzene)tricarbonylchromium, tricarbonyl-(η-cyclopentadienyl)manganese, and (η-cyclobutadiene)- and (tris-methylenemethane)-tricarbonyliron in frozen gas matrices at 12 K. Infrared spectroscopic evidence for dicarbonylmetal and dicarbonyl-(dinitrogen)metai complexes

Infrared evidence is presented for the formation of co-ordinatively unsaturated species [ML(CO)2][ML = Cr-(η-C6H6), Mn(η-C5H5), or Fe(η-C4H4), or Fe{C(CH2)H3}] on the u.v. photolysis of [ML(CO)3] complexes in argon and methane matrices, and dinitrogen complexes [ML(CO)2(N2)] in nitrogen matrices at 12 K. The primary photolysis step is readily reversed by visible light for [ML(CO)2] species of Cr and Fe, but not for Mn. The results are discussed in relation to the postulate of co-ordinatively unsaturated species as intermediates in the solution-phase substitution reactions.

Photochemistry of some iron and ruthenium (η5-cyclopentadienyl) carbonyl dimers in frozen gas matrices at ca. 12 K

The photochemistry of [M2(η5-C5H5)2(CO)4][M = Fe, (1); or Ru, (2)] and [CH2{(η5-C5H4)M(CO)2}2][M = Fe, (5); or Ru, (6)] has been studied in frozen-gas matrices (Ar, CH4, and N2) at ca. 12 K and that of (2) in poly (vinyl 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(η5-C5H5)(CO)2]˙ as well as small amounts of triply carbonyl-bridged species, [M2(η5-C5H5)2(µ-CO)3]. 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.

Photo-activation of methane at 12 K by (η5-cyclopentadienyl)- and (η5-pentamethylcyclopentadienyl)-dicarbonyl-rhodium and -iridium complexes

I. r. spectroscopic evidence, including 2H labeling, is presented to show that photolysis of [(η6C6R6)M(CO)2] complexes (M = Rh, R = Me; M = Ir, R = H, Me) in CH4 matrices at 12 K leads primarily to [(η6-C6R6)M(CO)(H)(Me)] species whereas in Ar and N2 matrices only small yields of [(η5-C5R5)M(CO)] species are observed.