Chemistry of fluorenylidene at low temperatures

Moss, Robert A.; Joyce, Martin

doi:10.1021/ja00482a027

Cited by 40 publications

(5 citation statements)

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“…Second, photolysis of 1 at 77 K in a 2:1 (v/v) 2-MeTHF: EG glass does not yield a g ) 2 radical species that can be detected under our experimental conditions. This observation is consistent with the previously described reactivity of fluorenylidene at low temperatures, [72][73][74][75] which has shown that the radical pair derived from the reaction with matrix is not stable at T < 130 K. 75 The absence of observable hyperfine coupling on the radical signal at g ) 2.0019 infers a structure with the radical primarily localized on the carbon at the 9-position of the fluorene ring. [17][18][19][20]76,77 The absence of hyperfine coupling to N 2 , which is commonly observed in one-electron oxidized diaryl diazo compounds, [17][18][19][20]76,77 confirms photoinduced N 2 loss along with reduction of the Cu(II) center and concomitant appearance of the monoradical signal.…”

Section: Resultssupporting

confidence: 90%

Cu(II)-Mediated Intramolecular Carbene Cation Radical Formation: Relevance to Unimolecular Metal−Ligand Radical Intermediates

et al. 2001

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We report the syntheses of the photochemically labile 9-diazo-4,5-diazafluorene (1) framework and the corresponding Cu(9-diazo-4,5-diazafluorene)(2)(NO(3))(2) compound (2). The X-ray structure of 2 reveals a 6-coordinate, tetragonal geometry with one nitrogen donor of an asymmetrically chelated diazafluorene in the equatorial position and the other defining the weak Jahn-Teller axis. The nitrate counterions bind in a monodentate fashion in the equatorial plane to complete the coordination sphere. Extended Hückel calculations reveal that the unusual solid-state structure derives from the enlarged bite angle of the fluorene skeleton and steric interactions between the adjacent hydrogen atoms in the higher energy (0.45 eV) symmetrically coordinated state. This is in contrast to Cu(py)(4)(NO(3))(2) which is 1.3 eV more stable with the nitrate counterions bound along the Jahn-Teller axis. Electron paramagnetic resonance (EPR) studies in solution reveal that the nitrates dissociate to yield 6-coordinate CuN(2)X(2)N(2)' structures with either a bound chloride ion (g(x) = 2.10, g(y) = 2.04, g(z) = 2.23, A(z) = 177 x 10(-4) cm(-1)) or a mixture of counterion and solvent (g(x)(a) = 2.05, g(y)(a) = 2.06, g(z)(a) = 2.29, A(z)(a) = 170 x 10(-4) cm(-1); g(x)(b) = 2.07, g(y)(b) = 2.08, g(z)(b) = 2.34, A(z)(b) = 155 x 10(-4) cm(-1)). Photolyses of 1 and 2 indicate loss of N(2) and formation of either carbene ([D/hc] = 0.408 cm(-1), [E/hc] = 0.0292 cm(-1)) or Cu(I)-L(*)(+) (S = (1)/(2), g = 2.0019) intermediates, which are identified by EPR, UV-vis, and time-dependent density functional theory methods. The results illustrate the important role redox active transition metals play in determining the nature of fundamental metal-ligand radical intermediates.

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Section: Resultssupporting

confidence: 90%

Cu(II)-Mediated Intramolecular Carbene Cation Radical Formation: Relevance to Unimolecular Metal−Ligand Radical Intermediates

et al. 2001

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“…All solvents were degassed with argon and kept in the glovebox over 4 Å molecular sieves. The ligand 2,6-bis(di- tert -butylphosphinomethyl)pyridine ( t Bu-PNP), RuCl 2 (PPh 3 ) 3 , and 9-dizaofluorene were prepared according to literature procedures.…”

Section: Methodsmentioning

confidence: 99%

Stable Carbene and Diazoalkane Complexes of the Same Complex System. Synthesis, Structure, and Reactivity of PNP−Ru(II) Fluorenylidene and Diazofluorene Complexes

et al. 2008

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The choice of synthetic methodology leads to either carbene or diazoalkane complexes of the same system. Thus, treatment of RuCl 2 (PPh 3 ) 3 with 9-diazofluorene followed t Bu-PNP ( t Bu-PNP ) 2,6-bis(ditert-butylphosphinomethyl)pyridine) resulted in loss of dinitrogen and formation of the Ru(II) fluorenylidene complex 1. On the other hand, treatment of the t Bu-PNP Ru(II) dinitrogen complex 4 with 9-diazofluorene resulted in the formation of η 1 -dizaofluorene Ru(II) complex 5, in which the diazo unit remains intact. The cationic Ru(II) carbene complex 2 was obtained by the reaction of 1 with 1 equiv of AgBF 4 or HBF 4 . Chloride dissociation to form a 16-e cationic carbene complex 3 took place also upon refluxing of 1 in toluene. The five-coordinated, unsaturated, charge-neutral diiodide Ru(II) complex 6 was obtained by reaction of 4 with NaI. Complex 6 is stabilized by a C-H agostic interaction, as observed by X-ray crystallography. Reaction of 4 with NaBEt 3 H followed by 9-dizaofluorene resulted in a novel η 1 -diazenofluorene Ru(II) complex 7, accompanied by the migration of one hydrogen atom from the metal center to the coordinated nitrogen atom of the diazenofluorene unit. Heating complex 7 at 65 °C resulted in sp 2 C-H activation followed by elimination of dihydrogen to form the chelated, β-carbon coordinated diazenofluorene ruthenium complex 8. Complexes 1, 2, 5, 6, and 8 were structurally characterized by X-ray crystallography.

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“…The precursor of DPM, diphenyldiazomethane (DPDM), was prepared by the method reported previously . The T 0 state of DPM was generated by photodissociation of DPDM (2 × 10 -3 M) in degassed methylcyclohexane (MCH) upon excitation by a Nd:YAG laser (third harmonics, 355 nm) at low temperature.…”

mentioning

confidence: 99%

Direct Detection of the Excited Triplet State of Diphenylmethylene by Time-Resolved EPR Spectroscopy

1998

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Chemistry of fluorenylidene at low temperatures

Cited by 40 publications

References 5 publications

Cu(II)-Mediated Intramolecular Carbene Cation Radical Formation: Relevance to Unimolecular Metal−Ligand Radical Intermediates

Cu(II)-Mediated Intramolecular Carbene Cation Radical Formation: Relevance to Unimolecular Metal−Ligand Radical Intermediates

Stable Carbene and Diazoalkane Complexes of the Same Complex System. Synthesis, Structure, and Reactivity of PNP−Ru(II) Fluorenylidene and Diazofluorene Complexes

Direct Detection of the Excited Triplet State of Diphenylmethylene by Time-Resolved EPR Spectroscopy

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