Matrix Photochemistry of trans-[CpFe(CO)]2(.mu.-CO)(.mu.-CH2): Generation of the Cis Isomer and of a Double-CO-Loss Photoproduct

Spooner, Yvonne H.; Mitchell, Ellen M.; Bursten, Bruce E.

doi:10.1021/om00011a048

Cited by 11 publications

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“…Reaction of Cp 2 Ru 2 ( μ -CH 2 )( μ -CO)(CO)(MeCN) (4) with Hydrosilanes Leading to Silylated μ -Methylene Species Cp 2 Ru 2 ( μ -CH 2 )(X)(SiR 3 )(CO) [5 (X = H), 6 (X = SiR 3 ]. In order to investigate participation of initial CO dissociation, we examined reactivity of the labile MeCN adduct ( 4 ) 5j of the coordinatively unsaturated species “Cp 2 Ru 2 (μ-CH 2 )(μ-CO)(CO)” arising from decarbonylation of 1 (Scheme ). As a result, 4 readily reacted with hydrosilane at ambient temperature to give hydrido−silyl−μ-methylene Cp 2 Ru 2 (μ-CH 2 )(H)(SiR 3 )(CO) 2 ( 5 ) and disilyl−μ-methylene species Cp 2 Ru 2 (μ-CH 2 )(SiR 3 ) 2 (CO) 2 ( 6 ) successively.…”

Section: Resultsmentioning

confidence: 99%

Conversion of a Diruthenium μ-Methylene Complex, Cp₂Ru₂(μ-CH₂)(μ-CO)(CO)₂, into Methane through Reduction with Hydrosilane: Reactivity of Silyl−μ-Methylene Intermediates Cp₂Ru₂(μ-CH₂)(SiR₃)(X)(CO)₂(X = H, SiR₃) Relevant to Catalytic CO Hydrogenation and Activation of Si−H, C−H, and C−Si Bonds

et al. 1996

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Thermolysis (170 °C, 3 days) of a diruthenium µ-methylene complex, Cp 2 Ru 2 (µ-CH 2 )(µ-CO)(CO) 2 (1), in the presence of HSiMe 3 produces methane along with methylsilane (SiMe 4 ) and mononuclear organometallic products, CpRu(H)(SiR 3 ) 2 (CO) (2) and CpRu(CO) 2 (SiMe 3 ) (3). The reaction mechanism involving initial CO dissociation has been investigated by using a labile µ-methylene species, Cp 2 Ru 2 (µ-CH 2 )(µ-CO)(CO)(MeCN) (4), the MeCN adduct of the coordinatively unsaturated species resulting from decarbonylation of 1. Treatment of 4 with HSiR 3 produces the hydrido-silyl-µ-methylene intermediate Cp 2 Ru 2 (µ-CH 2 )(H)(SiR 3 )(CO) 2 (5) and the disilyl-µ-methylene complex Cp 2 Ru 2 (µ-CH 2 )(SiR 3 ) 2 (CO) 2 (6) successively. Further reaction of 5 and 6 with HSiR 3 affords methane under milder conditions (120 °C, 12 h) compared to the methane formation from 1. Meanwhile complicated exchange processes are observed for the silylated µ-methylene species 5 and 6. The dynamic behavior of the hydrido-silyl species 5 giving a 1 H-NMR spectrum consistent with an apparent C s structure at ambient temperature has been analyzed in terms of a mechanism involving intramolecular H-and R 3 Si-group migration between the two ruthenium centers. It is also revealed that intramolecular exchange reaction of the hydride and µ-CH 2 atoms in 5 proceeds via the coordinatively unsaturated methyl intermediate Cp 2 Ru 2 (CH 3 )(SiR 3 )(CO) 2 (9). In addition to these intramolecular processes, the hydride, µ-CH 2 , and SiR 3 groups in 5 and 6 exchange with external HSiR 3 via replacement of the η 2 -bonded H 2 or HSiR 3 ligand in µ-methylene or µ-silylmethylene intermediates Cp 2 Ru 2 (µ-CHX)(µ-CO)(CO)(η 2 -H-Y) [X, Y ) H, SiR 3 (7), SiR 3 , H (18), SiR 3 , SiR 3 (16)] as confirmed by trapping experiments of 7 with L (CO, PPh 3 ) giving Cp 2 Ru 2 (µ-CHX)(µ-CO)(CO)(L) [X, L ) H, CO (1), H, PPh 3 (11), SiR 3 , CO (12), SiR 3 , PPh 3 (13)]. Hydrostannanes (HSnR 3 ) also react with 4, in a manner similar to the reaction with HSiR 3 , to give the hydrido-stannyl-µ-methylene intermediate Cp 2 Ru 2 (µ-CH 2 )(H)(SnR 3 )(CO) 2 ( 20) and the distannyl-µ-methylene complex Cp 2 Ru 2 (µ-CH 2 )(SnR 3 ) 2 (CO) 2 ( 21) successively (the stannyl analogues of 5 and 6, respectively). The intramolecular exchange processes (H T SnR 3 , H T µ-CH 2 ) are also observed for 20. But the HSnPh 3 adduct 20c is further converted to a mixture containing the µ-η 1 :η 2 -phenyl complex Cp 2 Ru 2 (µ-Ph)(SnCH 3 Ph 2 )(CO) 2 ( 22) and the bis(µ-stannylene) complex Cp 2 Ru 2 (µ-SnPh 2 ) 2 (CO) 2 ( 23) instead of 21c. The isolation of 22 supports viability of the methyl species (9). These results suggest that methane formation from 1 follows (i) CO dissociation, (ii) H-SiR 3 oxidative addition giving the hydrido-silyl-µ-methylene intermediate 5, (iii) equilibrium with the methyl intermediate 9, (iv) a second oxidative addition of H-SiR 3 , and (v) elimination of methane repeating reductive elimination from mono-and dinuclear hydrido-methyl intermediates 27 and 28. The...

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Section: Resultsmentioning

confidence: 99%

Conversion of a Diruthenium μ-Methylene Complex, Cp₂Ru₂(μ-CH₂)(μ-CO)(CO)₂, into Methane through Reduction with Hydrosilane: Reactivity of Silyl−μ-Methylene Intermediates Cp₂Ru₂(μ-CH₂)(SiR₃)(X)(CO)₂(X = H, SiR₃) Relevant to Catalytic CO Hydrogenation and Activation of Si−H, C−H, and C−Si Bonds

et al. 1996

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“…In the case of the Hi‐2 → Lo‐2 conversion, one attractive hypothesis is that the distinctive, possibly partially bridging, CO becomes totally bridging when the adjacent terminal CO is photodissociated (Scheme ). One example of conversion from terminal to bridged CO involves the photolytic and thermal reactions of trans ‐[Cp*Fe(CO)] 2 (μ‐CO)(μ‐CH 2 ), where loss of one terminal CO from the trans ‐species led to the remaining terminal CO assuming a bridging orientation 32…”

Section: Discussionmentioning

confidence: 99%

Photolysis of Hi‐CO Nitrogenase – Observation of a Plethora of Distinct CO Species Using Infrared Spectroscopy

Yan¹,

Dapper

George

et al. 2011

Eur J Inorg Chem

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Fourier transform infrared spectroscopy (FT-IR) was used to study the photochemistry of CO-inhibited Azotobacter vinelandii nitrogenase using visible light at cryogenic temperatures. The FT-IR difference spectrum of photolyzed hi-CO at 4 K comprises negative bands at 1973 cm−1 and 1679 cm−1 together with positive bands at 1711 cm−1, 2135 and 2123 cm−1. The negative bands are assigned to a hi-CO state that comprises 2 metal-bound CO ligands, one terminally bound, and one bridged and/or protonated species. The positive band at 1711 cm−1 is assigned to a lo-CO product with a single bridged and/or protonated metal-CO group. We term these species ‘Hi-1’ and ‘Lo-1’ respectively. The high-energy bands are assigned to a liberated CO trapped in the protein pocket. Warming results in CO recombination, and the temperature dependence of the recombination rate yields an activation energy of 4 kJ mol−1. Two α-H195 variant enzymes yielded additional signals. Asparagine substitution, α-H195N, gives a spectrum containing 2 negative ‘Hi-2’ bands at 1936 and 1858 cm−1 with a positive ‘Lo-2’ band at 1780 cm−1, while glutamine substitution, α-H195Q, produces a complex spectrum that includes a third CO species, with negative ‘Hi-3’ bands at 1938 and 1911 cm−1 and a positive feature ‘Lo-3’ band at 1921 cm−1. These species can be assigned to a combination of terminal, bridged, and possibly protonated CO groups bound to the FeMo-cofactor active site. The proposed structures are discussed in terms of both CO inhibition and the mechanism nitrogenase catalysis. Given the intractability of observing nitrogenase intermediates by crystallographic methods, IR-monitored photolysis appears to be a promising and information-rich probe of nitrogenase structure and chemistry.

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“…We believe that we have observed such an effect in the photochemistry of the lower-symmetry precursor [{Cp*Fe(CO)} 2 (m-CO)(m-CH 2 )], which forms a double-CO-loss product with a bridging or semibridging CO ligand. 12 We will continue to explore this interplay between spin state and structure in the photochemistry of other DOCs.…”

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confidence: 98%

Theoretical and experimental studies of the unprecedented spin-dependent structures of [Cp2Fe2(CO)2], the double-CO-loss product of [Cp2Fe2(CO)4]

Vitale¹

1998

Chem. Commun.

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Matrix Photochemistry of trans-[CpFe(CO)]2(.mu.-CO)(.mu.-CH2): Generation of the Cis Isomer and of a Double-CO-Loss Photoproduct

Cited by 11 publications

References 0 publications

Photolysis of Hi‐CO Nitrogenase – Observation of a Plethora of Distinct CO Species Using Infrared Spectroscopy

Theoretical and experimental studies of the unprecedented spin-dependent structures of [Cp2Fe2(CO)2], the double-CO-loss product of [Cp2Fe2(CO)4]

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