What difference one double bond makes: Electronic structure of saturated and unsaturated n-heterocyclic carbene ligands in Grubbs 2nd generation-type catalysts

N-heterocyclic carbene (NHC) ligands are a versatile and useful class of ligands that have enjoyed much success over the past few decades in organometallic chemistry. This fact is exemplified most convincingly in Grubbs 2nd generation olefin metathesis catalysts. We explore the electronic impact of the NHC-ligand by decoupling electronic and steric effects through simplified model N-heterocyclic carbenes. Saturated and unsaturated N-heterocyclic carbene ligands give rise to fundamentally different frontier orbitals in these catalysts, suggesting a need to classify them as two electronically distinct ligand classes.

[1]  B. Honig,et al.  Accurate First Principles Calculation of Molecular Charge Distributions and Solvation Energies from Ab Initio Quantum Mechanics and Continuum Dielectric Theory , 1994 .

[2]  W. Lipscomb,et al.  The synchronous-transit method for determining reaction pathways and locating molecular transition states , 1977 .

[3]  R. Grubbs,et al.  Mechanism and activity of ruthenium olefin metathesis catalysts. , 2001, Journal of the American Chemical Society.

[4]  B. Straub.  Origin of the high activity of second-generation Grubbs catalysts. , 2005, Angewandte Chemie.

[5]  Bielawski,et al.  Highly Efficient Ring-Opening Metathesis Polymerization (ROMP) Using New Ruthenium Catalysts Containing N-Heterocyclic Carbene Ligands C.B. is grateful to the National Science Foundation for a pre-doctoral fellowship. The authors thank Dr. Matthias Scholl for providing catalysts 4 a and 4 c. , 2000, Angewandte Chemie.

[6]  Luigi Cavallo,et al.  A Combined Experimental and Theoretical Study Examining the Binding of N-Heterocyclic Carbenes (NHC) to the Cp*RuCl (Cp* = η5-C5Me5) Moiety: Insight into Stereoelectronic Differences between Unsaturated and Saturated NHC Ligands , 2003 .

[7]  R. Grubbs.  Olefin-metathesis catalysts for the preparation of molecules and materials (Nobel Lecture). , 2006, Angewandte Chemie.

[8]  L. Cavallo,et al.  Origin of enantioselectivity in the asymmetric Ru-catalyzed metathesis of olefins. , 2004, Journal of the American Chemical Society.

[9]  T. H. Dunning.  Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen , 1989 .

[10]  R. Grubbs,et al.  Synthesis and activity of a new generation of ruthenium-based olefin metathesis catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligands. , 1999, Organic letters.

[11]  H. Schlegel,et al.  Combining Synchronous Transit and Quasi-Newton Methods to Find Transition States , 1993 .

[12]  B. Straub,et al.  Mechanism of enyne metathesis catalyzed by Grubbs ruthenium-carbene complexes: a DFT study. , 2005, Journal of the American Chemical Society.

[13]  L. Cavallo,et al.  Steric and electronic properties of N-heterocyclic carbenes (NHC): a detailed study on their interaction with Ni(CO)4. , 2005, Journal of the American Chemical Society.

[14]  S. H. Vosko,et al.  Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis , 1980 .

[15]  Patricio E. Romero,et al.  Direct observation of a 14-electron ruthenacyclobutane relevant to olefin metathesis. , 2005, Journal of the American Chemical Society.

[16]  A. Becke,et al.  Density-functional exchange-energy approximation with correct asymptotic behavior. , 1988, Physical review. A, General physics.

[17]  Vidar R. Jensen,et al.  Quantitative Structure−Activity Relationships of Ruthenium Catalysts for Olefin Metathesis , 2006 .

[18]  Par Jean‐Louis Hérisson,et al.  Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques , 1971 .

[19]  R. Friesner,et al.  Computing Redox Potentials in Solution: Density Functional Theory as A Tool for Rational Design of Redox Agents , 2002 .

[20]  R. Grubbs,et al.  The development of L2X2Ru=CHR olefin metathesis catalysts: an organometallic success story. , 2001, Accounts of chemical research.

[21]  M. Baik,et al.  Diastereoselective intermolecular rhodium-catalyzed [4 + 2 + 2] carbocyclization reactions: computational and experimental evidence for the intermediacy of an alternative metallacycle intermediate. , 2005, Journal of the American Chemical Society.

[22]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[23]  R. Grubbs,et al.  New insights into the mechanism of ruthenium-catalyzed olefin metathesis reactions. , 2001, Journal of the American Chemical Society.

[24]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitals , 1985 .

[25]  Walter Thiel,et al.  Mechanism of olefin metathesis with catalysis by ruthenium carbene complexes: density functional studies on model systems. , 2002, Chemistry.

[26]  M. Baik,et al.  Alpha,beta-(C-C-C) agostic bonds in transition metal based olefin metathesis catalyses. , 2005, Dalton transactions.

[27]  A. Orpen,et al.  Substituent effects and the mechanism of alkene metathesis catalyzed by ruthenium dichloride catalysts. , 2005, Dalton transactions.

[28]  A. J. Arduengo,et al.  Electronic Structure of a Stable Nucleophilic Carbene , 1991 .

[29]  SonBinh T. Nguyen,et al.  Well-defined ruthenium olefin metathesis catalysts: Mechanism and activity , 1997 .

[30]  Parr,et al.  Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. , 1988, Physical review. B, Condensed matter.

[31]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations , 1984 .

[32]  A. J. Arduengo,et al.  Electronic stabilization of nucleophilic carbenes , 1992 .

[33]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations. Potentials for main group elements Na to Bi , 1985 .

[34]  Peter Chen,et al.  Comparing intrinsic reactivities of the first- and second-generation ruthenium metathesis catalysts in the gas phase , 2003 .

[35]  B. Honig,et al.  New Model for Calculation of Solvation Free Energies: Correction of Self-Consistent Reaction Field Continuum Dielectric Theory for Short-Range Hydrogen-Bonding Effects , 1996 .

[36]  Anthony J. Arduengo,et al.  Looking for Stable Carbenes: The Difficulty in Starting Anew , 1999 .

[37]  Richard L. Harlow,et al.  A stable crystalline carbene , 1991 .

[38]  N. Koga,et al.  Orbital Interactions in the Ruthenium Olefin Metathesis Catalysts , 2004 .

[39]  Peter Chen,et al.  Mechanism and activity of ruthenium olefin metathesis catalysts: the role of ligands and substrates from a theoretical perspective. , 2004, Journal of the American Chemical Society.