Photoactivation of C-H bonds of iridium and rhodium complexes and the photochemistry of some dinuclear metal carbonyls : matrix isolation studies at ca.12k
Photoactivation of C-H bonds of iridium and rhodium complexes and the photochemistry of some dinuclear metal carbonyls : matrix isolation studies at ca.12k
Spectroscopic studies in a variety of frozen gas matrices (including Ar, CH4, CD4, N2, 12CO and 13CO) at cryogenic temperatures (ca.12K) have been pursued with the aim of identifying unstable intermediates in some proposed C-H photoactivation reactions and in the photochemical reactions of some dinuclear metal carbonyl complexes, which occur in room temperature solutions. Photoactivation of CH4 in a matrix is observed for [Ir(η5-C5H5)(CO)(H)2], affording [Ir(η5-C5H5)(CO)(CH3)(H)], probably via initial reductive elimination of H2 to form [Ir(η5-C5H5)(CO)], which is detected in Ar matrices. Photolysis of [Ir(η5-C5H5)(CO)(H)2] in N2 and CO matrices affords [Ir(η5-C5H5(CO)(N2)] and [Ir(η5-C5H5)(CO)2], respectively. The lack of evidence for HCO. in CO matrices, and the lack of isotopic scrambling in mixed isotope experiments, e.g. [Ir(η5-C5H5)(CO)(H)2] in CD4 and [Ir(η5-C5H5)(CO)(D)2] in CH4, confirms that the initial photoprocess is H2 ejection, which can be reversed photochemically by long wavelength irradiation. Irradiation of [Rh(HBPz3quad )(CO)2] and [Rh(H2BPz2 quad ] (Pz = 3,5-dimethylpyrazolyl) leads to the photoejection of CO and the detection of new monocarbonyl species in Ar and CH4 matrices. Additional dicarbonyl-containing photoproducts are probably the products of tridentate to bidentate and bidentate to unidentate conversions of the pyrazolylborate ligands. The lack of photoactivation of CH4 matrices by [Rh(HBPz3quad )(CO2],which activates alkane C-H bonds with high efficiency in room temperature solutions, points towards thermal contributions to C-H activation processes. Low energy irradiation of the metal-metal bonded dimers [(η5-C5H5)2M2(CO)4] (M= Fe or Ru) in gas matrices results in photoinduced CO-bridge opening to produce non-CO bridged isomers; this is the first report of the direct observation of such a dimer for iron. Irradiation into the electronic absorptions of the non-CO-bridged isomers produces small amounts of the radical species [(η5-C5H5)M(CO)2] via photoinduced cleavage of the metal-metal bonds. Photolysis also results in CO loss and the production of the novel CO-bridged dimers [(η5-C5H5)2M2(μ-CO)_3]. The observed photochemistry appears to be exclusive to the trans-isomers. Similar photolyses of CH_2[(η5-C_5H_4)Ru(CO)_2]_2, held in a cis-configuration, produces no reaction. However high energy irradiation of CH_2[(η5-C_5H_4)Ru(CO)_2]_2 does result in some CO ejection. Photolysis of [(η5C_5Me_5)_2Ru_2(CO)_4] results in no detectable bridge opening, although small amounts of the radical species, [(η5-C_5Me_5)Ru(CO)_2] are detected. Irradiation of CH_2[(η5-C_5H_4)Mn(CO)_3]_2, [(μ,η5:η5-C10H8)Mn2(CO)6], [(μ,η6:η6-C_12H_10)Cr_2(CO)_6], and [(μ,η6:η6-C14H14)Cr2(CO)6], which contain metal tricarbonyl fragments bridged by organic ligands but without metal-metal bonds, in Ar and CH4 results in CO ejection to afford dicarbonyl fragments, e.g. CH2[(η5-C5H4)Mn(CO)2][(η5-C5H4)Mn(CO)3]. In N2 matrices the new species react to give dinitrogen containing species, e.g. CH2[(η5-C5H4)Mn(CO)2(N2)] [(η5-C5H4)Mn(CO)3]. Annealing or secondary photolysis produces reversal, as for the majority of photoprocesses studied, but no coupling of the metal centres. The lack of coupling, which is seen in solution, demonstrates the rigidity of the low temperature matrix cages. (DX84122)
University of Southampton
1988
Bloyce, Peter Edward
(1988)
Photoactivation of C-H bonds of iridium and rhodium complexes and the photochemistry of some dinuclear metal carbonyls : matrix isolation studies at ca.12k.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Spectroscopic studies in a variety of frozen gas matrices (including Ar, CH4, CD4, N2, 12CO and 13CO) at cryogenic temperatures (ca.12K) have been pursued with the aim of identifying unstable intermediates in some proposed C-H photoactivation reactions and in the photochemical reactions of some dinuclear metal carbonyl complexes, which occur in room temperature solutions. Photoactivation of CH4 in a matrix is observed for [Ir(η5-C5H5)(CO)(H)2], affording [Ir(η5-C5H5)(CO)(CH3)(H)], probably via initial reductive elimination of H2 to form [Ir(η5-C5H5)(CO)], which is detected in Ar matrices. Photolysis of [Ir(η5-C5H5)(CO)(H)2] in N2 and CO matrices affords [Ir(η5-C5H5(CO)(N2)] and [Ir(η5-C5H5)(CO)2], respectively. The lack of evidence for HCO. in CO matrices, and the lack of isotopic scrambling in mixed isotope experiments, e.g. [Ir(η5-C5H5)(CO)(H)2] in CD4 and [Ir(η5-C5H5)(CO)(D)2] in CH4, confirms that the initial photoprocess is H2 ejection, which can be reversed photochemically by long wavelength irradiation. Irradiation of [Rh(HBPz3quad )(CO)2] and [Rh(H2BPz2 quad ] (Pz = 3,5-dimethylpyrazolyl) leads to the photoejection of CO and the detection of new monocarbonyl species in Ar and CH4 matrices. Additional dicarbonyl-containing photoproducts are probably the products of tridentate to bidentate and bidentate to unidentate conversions of the pyrazolylborate ligands. The lack of photoactivation of CH4 matrices by [Rh(HBPz3quad )(CO2],which activates alkane C-H bonds with high efficiency in room temperature solutions, points towards thermal contributions to C-H activation processes. Low energy irradiation of the metal-metal bonded dimers [(η5-C5H5)2M2(CO)4] (M= Fe or Ru) in gas matrices results in photoinduced CO-bridge opening to produce non-CO bridged isomers; this is the first report of the direct observation of such a dimer for iron. Irradiation into the electronic absorptions of the non-CO-bridged isomers produces small amounts of the radical species [(η5-C5H5)M(CO)2] via photoinduced cleavage of the metal-metal bonds. Photolysis also results in CO loss and the production of the novel CO-bridged dimers [(η5-C5H5)2M2(μ-CO)_3]. The observed photochemistry appears to be exclusive to the trans-isomers. Similar photolyses of CH_2[(η5-C_5H_4)Ru(CO)_2]_2, held in a cis-configuration, produces no reaction. However high energy irradiation of CH_2[(η5-C_5H_4)Ru(CO)_2]_2 does result in some CO ejection. Photolysis of [(η5C_5Me_5)_2Ru_2(CO)_4] results in no detectable bridge opening, although small amounts of the radical species, [(η5-C_5Me_5)Ru(CO)_2] are detected. Irradiation of CH_2[(η5-C_5H_4)Mn(CO)_3]_2, [(μ,η5:η5-C10H8)Mn2(CO)6], [(μ,η6:η6-C_12H_10)Cr_2(CO)_6], and [(μ,η6:η6-C14H14)Cr2(CO)6], which contain metal tricarbonyl fragments bridged by organic ligands but without metal-metal bonds, in Ar and CH4 results in CO ejection to afford dicarbonyl fragments, e.g. CH2[(η5-C5H4)Mn(CO)2][(η5-C5H4)Mn(CO)3]. In N2 matrices the new species react to give dinitrogen containing species, e.g. CH2[(η5-C5H4)Mn(CO)2(N2)] [(η5-C5H4)Mn(CO)3]. Annealing or secondary photolysis produces reversal, as for the majority of photoprocesses studied, but no coupling of the metal centres. The lack of coupling, which is seen in solution, demonstrates the rigidity of the low temperature matrix cages. (DX84122)
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Published date: 1988
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Local EPrints ID: 460747
URI: http://eprints.soton.ac.uk/id/eprint/460747
PURE UUID: 7cc03dc5-cfe9-4752-85b6-22e70f5f6f2e
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Last modified: 04 Jul 2022 18:29
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Peter Edward Bloyce
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