Distorted copper(II) radicals with sterically hindered salens: electronic structure and aerobic oxidation of alcohols.

The sterically hindered salen ligands featuring biphenyl and tetramethyl putrescine linkers were synthesized and chelated to copper. The resulting complexes CuLbp,tBu, CuLbp,OMe, CuLpu,tBu and CuLpu,OMe were structurally characterized, showing a significanty tetrahedrally distorted metal center. The complexes show two reversible oxidation waves in the range 0.2 to 0.8 V vs. Fc+/Fc. A further reduction wave is detected in the range -1.4 to -1.7 V vs. Fc+/Fc. It is reversible for CuLbp,tBu and CuLbp,OMe and assigned to the CuII/CuI redox couple. One-electron oxidation of CuLbp,OMe, CuLpu,tBu and CuLpu,OMe was performed chemically and electrochemically. It is accompanied by a quenching of the EPR resonances. Phenoxyl radical formation was established by X-Ray diffraction on the cations [CuLbp,OMe]+ and [CuLpu,OMe]+, whereby the coordination sphere is elongated upon oxidation with quinoidal distributions of bond distances. The cations exhibit a NIR band of moderate intensity in their optical spectrum, supporting their classification as class II mixed-valent radical species according to the Robin Day classification. The proposed electronic structures are supported by DFT calculations. The cations [CuLbp,OMe]+, [CuLpu,tBu]+ and [CuLpu,OMe]+ were active towards aerobic oxidation of the unactivated alcohol 2-phenylethanol, with TON numbers up to 58 within 3 h.

[1]  C. Philouze,et al.  Structural and spectroscopic investigations of nine-coordinate redox active lanthanide complexes with a pincer O,N,O ligand. , 2020, Dalton transactions.

[2]  C. Philouze,et al.  Effect of Distortions on the Geometric and Electronic Structures of One-Electron Oxidized Vanadium(IV), Copper(II), and Cobalt(II)/(III) Salen Complexes. , 2020, Inorganic chemistry.

[3]  Y. Shimazaki,et al.  Recent Advances in One-electron Oxidized CuII-Diphenoxide Complexes as Models of Galactose Oxidase: Importance of the Structural Flexibility in the Active Site. , 2020, Chemistry.

[4]  F. Thomas,et al.  Luminescent pro-nitroxide lanthanide complexes for the detection of reactive oxygen species. , 2019, Chemical communications.

[5]  C. Limberg,et al.  Oxygen‐Depleted Calixarenes as Ligands for Molecular Models of Galactose Oxidase , 2019, Chemistry.

[6]  F. Tani,et al.  π-π Stacking Interaction in an Oxidized CuII -Salen Complex with a Side-Chain Indole Ring: An Approach to the Function of the Tryptophan in the Active Site of Galactose Oxidase. , 2019, Chemistry.

[7]  C. Philouze,et al.  Structural and spectroscopic investigations of redox active seven coordinate luminescent lanthanide complexes , 2018, Inorganica Chimica Acta.

[8]  T. Storr,et al.  Preface for the Forum on Applications of Metal Complexes with Ligand-Centered Radicals. , 2018, Inorganic chemistry.

[9]  C. Philouze,et al.  Seven-coordinate lanthanide complexes with a tripodal redox active ligand: structural, electrochemical and spectroscopic investigations. , 2018, Dalton transactions.

[10]  C. Philouze,et al.  Electronic Structure and Reactivity of One-Electron-Oxidized Copper(II) Bis(phenolate)-Dipyrrin Complexes. , 2018, Inorganic Chemistry.

[11]  Yong‐Ill Lee,et al.  A Novel Copper Complex of Proline‐Based Mono(phenol) Amine Ligand (Hlpro) Immobilized in SBA‐15 as a Model Catalyst of Galactose Oxidase , 2017 .

[12]  T. Storr,et al.  Electronic structure elucidation in oxidized metal–salen complexes , 2017 .

[13]  C. Philouze,et al.  A Structurally Characterized CuIII Complex Supported by a Bis(anilido) Ligand and Its Oxidative Catalytic Activity. , 2017, Chemistry.

[14]  W. Kaim,et al.  Interacting metal and ligand based open shell systems: Challenges for experiment and theory , 2017 .

[15]  J. Worrall,et al.  Tyrosine or Tryptophan? Modifying a Metalloradical Catalytic Site by Removal of the Cys-Tyr Cross-Link in the Galactose 6-Oxidase Homologue GlxA. , 2017, Angewandte Chemie.

[16]  Z. Jagličić,et al.  Copper(II) complex of new non-innocent O-aminophenol-based ligand as biomimetic model for galactose oxidase enzyme in aerobic oxidation of alcohols , 2017 .

[17]  C. Philouze,et al.  A redox active switch for lanthanide luminescence in phenolate complexes. , 2017, Chemical communications.

[18]  A. Wojtczak,et al.  TEMPO-mediated aerobic oxidation of alcohols using copper(II) complex of bis(phenol) di-amine ligand as biomimetic model for Galactose oxidase enzyme , 2016 .

[19]  Daniël L J Broere,et al.  New avenues for ligand-mediated processes--expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands. , 2015, Chemical Society reviews.

[20]  M. Orio,et al.  Redox noninnocence of the bridge in copper(II) salophen and bis(oxamato) complexes. , 2015, Inorganic chemistry.

[21]  R. Sheldon.  Recent advances in green catalytic oxidations of alcohols in aqueous media , 2015 .

[22]  Changhua Mu,et al.  A Copper Complex of a Noninnocent Iminophenol-Amidopyridine Hybrid Ligand: Synthesis, Characterization, and Aerobic Alcohol Oxidation , 2014 .

[23]  T. Kohzuma,et al.  Characterization of one-electron oxidized copper(II)-salophen-type complexes; effects of electronic and geometrical structures on reactivities. , 2014, Dalton transactions.

[24]  Y. Shimazaki.  Properties of the one-electron oxidized copper(II) salen-type complexes: relationship between electronic structures and reactivities , 2014 .

[25]  Michael T. Green,et al.  Iron(IV)hydroxide pKa and the Role of Thiolate Ligation in C–H Bond Activation by Cytochrome P450 , 2013, Science.

[26]  A. Pombeiro,et al.  Marked stabilization of redox states and enhanced catalytic activity in galactose oxidase models based on transition metal S-methylisothiosemicarbazonates with -SR group in ortho position to the phenolic oxygen. , 2013, Inorganic chemistry.

[27]  Y. Shimazaki.  Recent Advances in X-Ray Structures of Metal-Phenoxyl Radical Complexes , 2013 .

[28]  R. Crabtree,et al.  Redox-active ligands in catalysis. , 2013, Chemical Society reviews.

[29]  C. T. Lyons,et al.  Recent advances in phenoxyl radical complexes of salen-type ligands as mixed-valent galactose oxidase models. , 2013, Coordination chemistry reviews.

[30]  F. Thomas,et al.  New insights into the electronic structure and reactivity of one-electron oxidized copper(II)-(disalicylidene)diamine complexes. , 2012, Inorganic chemistry.

[31]  C. T. Lyons,et al.  Electrochemical and spectroscopic effects of mixed substituents in bis(phenolate)-copper(II) galactose oxidase model complexes. , 2012, Journal of the American Chemical Society.

[32]  D. Dooley,et al.  Role of the Tyr-Cys cross-link to the active site properties of galactose oxidase. , 2012, Inorganic chemistry.

[33]  M. Orio,et al.  One-electron oxidized copper(II) salophen complexes: phenoxyl versus diiminobenzene radical species. , 2012, Chemistry.

[34]  T. Storr,et al.  Sulfanyl stabilization of copper-bonded phenoxyls in model complexes and galactose oxidase , 2011, Proceedings of the National Academy of Sciences.

[35]  P. Chirik.  Preface: Forum on redox-active ligands. , 2011, Inorganic chemistry.

[36]  A. Spek,et al.  Spectro-electrochemical and DFT studies of a planar Cu(II)-phenolate complex active in the aerobic oxidation of primary alcohols , 2011 .

[37]  Michael T. Green,et al.  Cytochrome P450 Compound I: Capture, Characterization, and C-H Bond Activation Kinetics , 2010, Science.

[38]  M. Orio,et al.  X-ray structures of copper(II) and nickel(II) radical salen complexes: the preference of galactose oxidase for copper(II). , 2010, Angewandte Chemie.

[39]  Karl Wieghardt,et al.  Radical Ligands Confer Nobility on Base-Metal Catalysts , 2010, Science.

[40]  P. R. Montellano.  Hydrocarbon hydroxylation by cytochrome P450 enzymes. , 2010 .

[41]  Meiyan Wang,et al.  Theoretical studies on the reaction mechanism of oxidation of primary alcohols by Zn/Cu(ii)-phenoxyl radical catalyst. , 2009, Dalton transactions.

[42]  Judith P Klinman,et al.  Galactose oxidase as a model for reactivity at a copper superoxide center. , 2009, Journal of the American Chemical Society.

[43]  Richard J. Gildea,et al.  OLEX2: a complete structure solution, refinement and analysis program , 2009 .

[44]  T. Storr,et al.  Defining the electronic and geometric structure of one-electron oxidized copper-bis-phenoxide complexes. , 2008, Journal of the American Chemical Society.

[45]  T. Weyhermüller,et al.  Targeted oxidase reactivity with a new redox-active ligand incorporating N2O2 donor atoms. Complexes of Cu(II), Ni(II), Pd(II), Fe(III), and V(V). , 2008, Inorganic chemistry.

[46]  E. Bill,et al.  Ligand-derived oxidase activity. Catalytic aerial oxidation of alcohols (including methanol) by Cu(II)-diradical complexes. , 2008, Inorganic chemistry.

[47]  J. W. Whittaker,et al.  The electronic structure of the Cys-Tyr(*) free radical in galactose oxidase determined by EPR spectroscopy. , 2008, Biochemistry.

[48]  P. Ghosh,et al.  Structural and functional mimic of galactose oxidase by a copper complex of a sterically demanding [N2O2] ligand. , 2008, Dalton transactions.

[49]  F. Thomas.  Ten years of a biomimetic approach to the copper(II) radical site of Galactose oxidase , 2007 .

[50]  D. Powell,et al.  Structural variation in copper(I) complexes with pyridylmethylamide ligands: structural analysis with a new four-coordinate geometry index, tau4. , 2007, Dalton transactions.

[51]  K. Wieghardt,et al.  Biomimetic metal-radical reactivity: aerial oxidation of alcohols, amines, aminophenols and catechols catalyzed by transition metal complexes , 2005, Biological chemistry.

[52]  T. D. Stack,et al.  Mechanistic insights from reactions between copper(II)-phenoxyl complexes and substrates with activated C-H bonds. , 2005, Inorganic chemistry.

[53]  J. W. Whittaker,et al.  Stereoselective hydrogen abstraction by galactose oxidase. , 2004, Biochemistry.

[54]  C. Philouze,et al.  Intramolecularly hydrogen-bonded versus copper(II) coordinated mono- and bis-phenoxyl radicals. , 2004, Dalton transactions.

[55]  C. Philouze,et al.  Galactose oxidase models: tuning the properties of CuII-phenoxyl radicals. , 2003, Chemistry.

[56]  T. D. Stack,et al.  Intramolecular charge transfer and biomimetic reaction kinetics in galactose oxidase model complexes. , 2003, Journal of the American Chemical Society.

[57]  J. W. Whittaker,et al.  Free radical catalysis by galactose oxidase. , 2003, Chemical reviews.

[58]  J. Koehne,et al.  The X-ray structures of a series of copper(II) complexes with tetradentate Schiff base ligands derived from salicylaldehyde and polymethylenediamines of varying chain length , 2003 .

[59]  Patrick L. Holland,et al.  Copper(I)-phenolate complexes as models of the reduced active site of galactose oxidase: synthesis, characterization, and O2 reactivity , 2003, JBIC Journal of Biological Inorganic Chemistry.

[60]  F. Thomas,et al.  A structural and functional model of galactose oxidase: control of the one-electron oxidized active form through two differentiated phenolic arms in a tripodal ligand. , 2002, Angewandte Chemie.

[61]  B. Nair,et al.  An e.p.r. study of tetradentate Schiff base copper complexes with an N–(CH2)n–N, n = 3–6 backbone , 2001 .

[62]  Y. Kitagawa,et al.  Ab initio computations of effective exchange integrals for H–H, H–He–H and Mn2O2 complex: comparison of broken-symmetry approaches , 2000 .

[63]  T. Omura,et al.  Forty years of cytochrome P450. , 1999, Biochemical and biophysical research communications.

[64]  Eckhard Bill,et al.  Aerobic Oxidation of Primary Alcohols (Including Methanol) by Copper(II)− and Zinc(II)−Phenoxyl Radical Catalysts , 1999 .

[65]  K. Wieghardt,et al.  Aerobic Oxidation of Primary Alcohols by a New Mononuclear Cu(II) -Radical Catalyst. , 1999, Angewandte Chemie.

[66]  K. Wieghardt,et al.  From Structural Models of Galactose Oxidase to Homogeneous Catalysis: Efficient Aerobic Oxidation of Alcohols. , 1998, Angewandte Chemie.

[67]  K. Hodgson,et al.  Catalytic galactose oxidase models: biomimetic Cu(II)-phenoxyl-radical reactivity. , 1998, Science.

[68]  S. H. Koenig,et al.  SPECTROSCOPIC STUDIES OF THE ACTIVE SITE OF GALACTOSE OXIDASE , 1995 .

[69]  A. Schäfer,et al.  Fully optimized contracted Gaussian basis sets of triple zeta valence quality for atoms Li to Kr , 1994 .

[70]  M. McPherson,et al.  Novel thioether bond revealed by a 1.7 Å crystal structure of galactose oxidase , 1994, Nature.

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

[72]  G. A. Petersson,et al.  A complete basis set model chemistry. II. Open‐shell systems and the total energies of the first‐row atoms , 1991 .

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

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

[75]  J. Tomasi,et al.  Electrostatic interaction of a solute with a continuum. A direct utilizaion of AB initio molecular potentials for the prevision of solvent effects , 1981 .

[76]  H. Yokoi,et al.  Spectroscopic and redox properties of pseudotetrahedral copper(II) complexes. Their relation to copper proteins , 1977 .

[77]  R. H. Holm,et al.  Structural and electronic effects on the polarographic half-wave potentials of copper (II) chelate complexes. , 1975, Bioinorganic chemistry.

[78]  F. Lions,et al.  A Four-coördinated Copper(II) Complex with a Tetrahedral Disposition of the Copper Valences , 1957 .

[79]  T. Günther,et al.  Redox chemistry of copper complexes with various salen type ligands , 2013 .

[80]  B. Bruin,et al.  Cooperative & Redox Non-Innocent Ligands in Directing Organometallic Reactivity (Eur. J. Inorg. Chem. 3/2012) , 2012 .

[81]  P. Ortiz de Montellano,et al.  Hydrocarbon hydroxylation by cytochrome P450 enzymes. , 2010, Chemical reviews.

[82]  J. W. Whittaker.  The radical chemistry of galactose oxidase. , 2005, Archives of biochemistry and biophysics.

[83]  James W Whittaker.  Galactose oxidase. , 2002, Advances in protein chemistry.

[84]  D. Hall,et al.  The colour isomerism and structure of some copper co-ordination compounds. Part XII. The crystal structure of NN′-(2,2′-biphenyl)bis(salicylaldiminato)copper(II) , 1966 .

[85]  D. F. Evans.  400. The determination of the paramagnetic susceptibility of substances in solution by nuclear magnetic resonance , 1959 .