Metallacarbenes from Diazoalkanes: An Experimental and Computational Study of the Reaction Mechanism
- 1 May 2003
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 125 (21), 6532-6546
- https://doi.org/10.1021/ja028923c
Abstract
PCP ligand (1,3-bis-[(diisopropyl-phosphanyl)-methyl]-benzene), and PCN ligand ({3-[(di-tert-butyl-phosphanyl)-methyl]-benzyl}-diethyl-amine) based rhodium dinitrogen complexes (1 and 2, respectively) react with phenyl diazomethane at room temperature to give PCP and PCN−Rh carbene complexes (3 and 5, respectively). At low temperature (−70 °C), PCP and PCN phenyl diazomethane complexes (4 and 6, respectively) are formed upon addition of phenyl diazomethane to 1 and 2. In these complexes, the diazo moiety is η1 coordinated through the terminal nitrogen atom. Decomposition of complexes 4 and 6 at low temperatures leads only to a relatively small amount of the corresponding carbene complexes, the major products of decomposition being the dinitrogen complexes 1 and 2 and stilbene. This and competition experiments (decomposition of 6 in the presence of 1) suggests that phenyl diazomethane can dissociate under the reaction conditions and attack the metal center through the diazo carbon producing a η1-C bound diazo complex. Computational studies based on a two-layer ONIOM model, using the mPW1K exchange-correlation functional and a variety of basis sets for PCP based systems, provide mechanistic insight. In the case of less bulky PCP ligand bearing H-substituents on the phosphines, a variety of mechanisms are possible, including both dissociative and nondissociative pathways. On the other hand, in the case of i-Pr substituents, the η1-C bound diazo complex appears to be a critical intermediate for carbene complex formation, in good agreement with the experimental results. Our results and the analysis of reported data suggest that the outcome of the reaction between a diazoalkane and a late transition metal complex can be anticipated considering steric requirements relevant to η1-C diazo complex formation.This publication has 71 references indexed in Scilit:
- Comparison of Steric and Electronic Requirements for C−C and C−H Bond Activation. Chelating vs Nonchelating CaseJournal of the American Chemical Society, 2001
- Exclusive C−C Activation in the Rhodium(I) PCN Pincer Complex. A Computational StudyOrganometallics, 2001
- Benchmark ab Initio Energy Profiles for the Gas-Phase SN2 Reactions Y- + CH3X → CH3Y + X- (X,Y = F,Cl,Br). Validation of Hybrid DFT MethodsThe Journal of Physical Chemistry A, 2001
- On the integration accuracy in molecular density functional theory calculations using Gaussian basis setsComputer Physics Communications, 2001
- Metal Insertion into C−C Bonds in SolutionAngewandte Chemie International Edition, 1999
- A New Family of Carbenerhodium(I) Complexes: Ligand Variation as The Key to SuccessChemistry – A European Journal, 1997
- Organometallic diazo compoundsChemical Reviews, 1993
- Identification of the active catalyst in the rhodium porphyrin-mediated cyclopropanation of alkenesJournal of the American Chemical Society, 1993
- Mechanism of the Rhodium Porphyrin-Catalyzed Cyclopropanation of AlkenesScience, 1992
- Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitalsThe Journal of Chemical Physics, 1985