Photochemistry of Alkyltricarbonyl(η5-cyclopentadienyl)tungsten (alkyl = Et, Prn, Pri, Bun, or CH2Ph), Tricarbonyl(η5-cyclopentadienyl)(phenyl)tungsten, Tricarbonyl(η5-pentamethylcyclopentadienyl)(n-propyl)tungsten, and Tricarbonyl(η5-cyclopentadienyl)(ethyl)-...
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Source and publish data:
Journal of the Chemical Society, Dalton Transactions p. 175 - 186 (1984)
Update date:2022-08-05
Topics:
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Authors:
Mahmoud, Khalil A.
Rest, Anthony J.
Alt, Helmut G.
Eichner, Manfred E.
Jansen, Brigitte M.
Article abstract of DOI:10.1039/DT9840000175
The photoreaction of 5-C5R'5)> complexes (M = Mo,or W; R = Et, Prn, Pri, Bun, Ph, or CH2Ph; R'= H or Me) have been studied in solution (-30 to 20 deg C) and in gas matrices (12-30 K).In alkane solutions in the absence of ligands the alkyl complexes that contain β-hydrogens initially undergo β-photoelimination at -30 deg C to give 5-C5R'5)> complexes of which only the trans isomers colud be detected, isolated, and characterised (i.r., n.m.r., and mass spectra).Intramolecular rotation of the olefin ligands about the tungsten-olefin bond axis was observed by low-temperature (-80 deg C) n.m.r. spectroscopy; asymetric olefins gave rotamers in different proportions.Prolonged photolysis of 5-C5R'5)> complexes in alkane solutions gave 5-C5R'5)> complexes and ultimately <5-C5R'5)>2>.The dimer <5-C5H5)>2> was the only metal-containing photoproduct when 5-C5H5)> was photolysed alone in pentane at -30 deg C, while for 5-C5H5)> the major photoproduct was 3-CH2Ph)(η5-C5H5)>.In the presence of C2H4, the phenyl and benzyl complexes gave the new monosubstitution products 5-C5H5)> (R = Ph or CH2Ph) whereas the alkyl complexes all gave 5-C5R'5)> as the main metal-containing product.In CH4 and CO gas matrices at 12 K the primary photolysis step was shown to be photo-ejection of a CO ligand and the formation of the 16-electron species 5-C5R'5)> (R = alkyl or aryl).The identity of the co-ordinatively unsaturated species was confirmed by (13)CO-labelling in 5-C5H5)> and fitting the terminal CO stretching bands using an energy-factored force-field program.For the alkyl complexes with β-hydrogens, thermal and photochemical reactions led to the conversion of 5-C5R'5)> species into the olefin-hydride complexes 5-C5R'5)>.Gas matrix studies for the W complexes at 12 K showed the presence of both cis and trans isomers together with intramolecular cis <*> trans isomerisation whereas in a previous paraffin-wax disc study of 5-C5R'5)> complexes (M = Mo or W; R = Et or n-C5H11; R'= H or Me) at 77 K only trans isomers were observed.Photolysis of the benzyl complex, 5-C5H5)>, led to the formation of the η3-bonded benzyl complex, 3-CH2Ph)(η5-C5H5)> in CH4, Ar, and CO matrices.The olefin-hydride species with asymmetric olefins, 5-C5H5)>, were found to be formed and to exist as rotamers in gas matrices at 12 K.Prolonged photolysis of the alkyl complexes resulted in the formation of 5-C5R'5)> complexes.In the presence of ligands L (L = C2H4 or N2) the 16-electron intermediate 5-C5H5)> gave addition products 5-C5H5)> at 12 k but no such products were observed for 5-C5H5)>.The combination of solution and matrix isolation studies established that the primary photolysis ...
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Full text of DOI:10.1039/DT9840000175
