Photoinduced N2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

Calladine, James A.; Torres, Olga; Anstey, Mitch; Ball, Graham E.; Bergman, Robert G.; Curley, John J.; Duckett, Simon B.; George, Michael W.; Gilson, Amy I.; Lawes, Douglas J.; Perutz, Robin N.; Sun, Xue-Zhong; Vollhardt, K. Peter C.

doi:10.1039/c0sc00311e

Cited by 43 publications

(48 citation statements)

References 49 publications

(91 reference statements)

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“…33 Precursor complexes for this type of alkane complex production necessitate the incorporation of stable leaving groups that are able to dissociate from the metal centre. Most commonly, carbon monoxide is the ligand of choice; however, dinitrogen,52 dihydride32 and ethylene53 groups have also been used to fulfil this purpose.…”

Section: Methods For Alkane Complex Generationmentioning

confidence: 99%

Characterisation of Alkane σ‐Complexes

Young

2014

Chemistry A European J

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Alkane σ-complexes have evolved from a curious phenomenon to an intermediate of intense interest, fuelling research into the area. Over the last fifteen years, metal alkane complex characterisation has evolved to incorporate reports employing UV/Vis, IR and NMR spectroscopy, and X-ray and neutron diffractometry. Previously, due to the sparse geometric characterisation of alkane σ-complexes, assumptions regarding bonding geometries and selectivities were made by comparison to related σ-complexes, or by analysis of C-H activation products. This minireview assembles relevant literature that illuminates the metrics of alkane-metal bonding, and critically analyses the binding mode, selectivity and stability of alkane complexes.

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Section: Methods For Alkane Complex Generationmentioning

confidence: 99%

Characterisation of Alkane σ‐Complexes

Young

2014

Chemistry A European J

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“…Indeed, as there is keen interest in using nitrogenase to reduce substrates other than N 2 , 48–50 it is of fundamental importance to test if E 4 (2H)* can react with other possible substrates (CO 2 ; C 2 H 2 , C 2 H 4 , etc), as occurs with the coordinatively unsaturated states produced by photo- re of single-metal complexes. 17,20,51 …”

Section: Summary and Prospectsmentioning

confidence: 99%

Reversible Photoinduced Reductive Elimination of H₂ from the Nitrogenase Dihydride State, the E₄(4H) Janus Intermediate

et al. 2016

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We recently demonstrated that N2 reduction by nitrogenase involves the obligatory release of one H2 per N2 reduced. These studies focused on the E4(4H) ‘Janus intermediate’, which has accumulated four reducing equivalents as two [Fe-H-Fe] bridging hydrides. E4(4H) is poised to bind and reduce N2 through reductive elimination (re) of the two hydrides as H2, coupled to the binding/reduction of N2. To obtain atomic-level details of the re activation process, we carried out in situ 450 nm photolysis of E4(4H) in an EPR cavity at temperatures below 20 K. ENDOR and EPR measurements show that photolysis generates a new FeMo-co state, denoted E4(2H)*, through the photoinduced re of the two bridging hydrides of E4(4H) as H2. During cryoannealing at temperatures above 175 K, E4(2H)* reverts to E4(4H) through the oxidative addition (oa) of the H2. The photolysis quantum yield is temperature invariant at liquid helium temperatures and shows a rather large kinetic isotope effect, KIE = 10. These observations imply that photoinduced release of H2 involves a barrier to the combination of the two nascent H atoms, in contrast to a barrierless process for mono-metallic inorganic complexes, and further suggest that H2 formation involves nuclear tunneling through that barrier. The oa recombination of E4(2H)* with the liberated H2 offers compelling evidence for the Janus intermediate as the point at which H2 is necessarily lost during N2 reduction; this mechanistically coupled loss must be gated by N2 addition that drives the re/oa equilibrium toward reductive elimination of H2 with N2 binding/reduction.

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“…46,47 Our aim is to use the same precursors, solvents, temperatures, and laser wavelengths for both the IR and the NMR studies. Roomtemperature TRIR or low-temperature FTIR spectroscopic studies provide information regarding the reactivity of the alkane complexes and their lifetime.…”

Section: ' Introductionmentioning

confidence: 99%

Manganese Alkane Complexes: An IR and NMR Spectroscopic Investigation

et al. 2011

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Manganese propane and manganese butane complexes derived from CpMn(CO)(3) were generated photochemically at 130-136 K with the alkane as solvent and characterized by FTIR spectroscopy and by (1)H NMR spectroscopy with in situ laser photolysis. Time-resolved IR spectroscopic measurements were performed at room temperature with the same laser wavelength. The ν(CO) bands in the IR spectra of the photoproducts in propane are shifted to low frequency with respect to CpMn(CO)(3), consistent with formation of CpMn(CO)(2)(propane). The (1)H NMR spectra conform to the criteria for alkane complexes: a high-field resonance for the η(2)-CH protons that shifts substantially on partial deuteration of the alkane and exhibits a coupling constant J(C-H) on (13)C-labeling of ca. 120 Hz. The NMR spectrum of each system exhibits two diagnostic product resonances in the high-field region for the η(2)-CH protons, corresponding to CpMn(CO)(2)(η(2)-C1-H-alkane) and CpMn(CO)(2)(η(2)-C2-H-alkane) isomers. Partial deuteration of the alkane at C1 results in characteristic strong isotopic perturbation of equilibrium of the η(2)-CH resonance of CpMn(CO)(2)(η(2)-C1-H-alkane). With propane-(13)C(1), the η(2)-CH resonance of CpMn(CO)(2)(η(2)-C1-H-alkane) isomer exhibits (13)C satellites with J(C-H) = 119 Hz. The corresponding resonance of CpMn(CO)(2)(η(2)-C2-H-alkane) is identified by use of propane-2,2-d(2). The lifetimes of the (η(2)-C1-H-alkane) isomers of the manganese complexes were determined by NMR spectroscopy as 22 ± 2 min at 134 K (propane) and 5.5 min at 136 K (butane). The corresponding spectra and lifetimes of the CpRe(CO)(2)(alkane) complexes were measured for reference (CpRe(CO)(2)(propane) lifetime ca. 60 min at 161 K; CpRe(CO)(2)(butane) 13 min at 171 K). The lifetimes determined by IR spectroscopy were similar to those determined by NMR spectroscopy, thereby supporting the assignments. These measurements extend the range of alkane complexes characterized by NMR spectroscopy from rhenium and rhodium derivatives to include less stable manganese derivatives.

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Photoinduced N2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

Cited by 43 publications

References 49 publications

Characterisation of Alkane σ‐Complexes

Characterisation of Alkane σ‐Complexes

Reversible Photoinduced Reductive Elimination of H₂ from the Nitrogenase Dihydride State, the E₄(4H) Janus Intermediate

Manganese Alkane Complexes: An IR and NMR Spectroscopic Investigation

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Photoinduced N2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

Cited by 43 publications

References 49 publications

Characterisation of Alkane σ‐Complexes

Characterisation of Alkane σ‐Complexes

Reversible Photoinduced Reductive Elimination of H2 from the Nitrogenase Dihydride State, the E4(4H) Janus Intermediate

Manganese Alkane Complexes: An IR and NMR Spectroscopic Investigation

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Reversible Photoinduced Reductive Elimination of H₂ from the Nitrogenase Dihydride State, the E₄(4H) Janus Intermediate