Multimodal study of secondary interactions in Cp*Ir complexes of imidazolylphosphines bearing an NH group.

Hydrogen bonding phenomena are explored using a combination of X-ray diffraction, NMR and IR spectroscopy, and DFT calculations. Three imidazolylphosphines R(2)PImH (ImH = imidazol-2-yl, R = t-butyl, i-propyl, phenyl, 1a-1c) and control phosphine (i-Pr)(2)PhP (1d) lacking an imidazole were used to make a series of complexes of the form Cp*Ir(L(1))(L(2))(phosphine). In addition, in order to suppress intermolecular interactions with either imidazole nitrogen, 1e, a di(isopropyl)imidazolyl analogue of 1b was made along with its doubly (15)N-labeled isotopomer to explore bonding interactions at each imidazole nitrogen. A modest enhancement of transfer hydrogenation rate was seen when an imidazolylphosphine ligand 1b was used. Dichloro complexes (L(1) = L(2) = Cl, 2a-2c,2e) showed intramolecular hydrogen bonding as revealed by four X-ray structures and various NMR and IR data. Significantly, hydride chloride complexes [L(1) = H, L(2) = Cl, 3a-3c and 3e-((15)N)(2)] showed stronger hydrogen bonding to chloride than hydride, though the solid-state structure of 3b evinced intramolecular Ir-H...H-N bonding reinforced by intermolecular N...H-N bonding between unhindered imidazoles. These results are compared to literature examples, which show variations in preferred hydrogen bonding to hydride, halide, CO, and NO ligands. Surprising differences were seen between the dichloro complex 2b with isopropyl groups on phosphorus, which appeared to exist as a mixture of two conformers, and related complex 2a with tert-butyl groups on phosphorus, which exists in chlorinated solvents as a mixture of conformer 2a-endo and chelate 5a-Cl, the product of ionization of one chloride ligand. This difference became apparent only through a series of experiments, especially (15)N chemical shift data from 2D (1)H-(15)N correlation. The results highlight the difficulty of characterizing hemilabile, bifunctional complexes and the importance of innocent ligand substituents in determining structure and dynamics.

[1]  Samuel A. Delp,et al.  Combined experimental and computational study of W(II), Ru(II), Pt(IV) and Cu(I) amine and amido complexes using 15N NMR spectroscopy , 2009 .

[2]  A. Lledós,et al.  Protonation of transition-metal hydrides: a not so simple process. , 2009, Chemical Society reviews.

[3]  D. Grotjahn.  Bifunctional catalysts and related complexes: structures and properties. , 2008, Dalton transactions.

[4]  M. Pruski,et al.  Easily prepared chiral scorpionates: tris(2-oxazolinyl)boratoiridium(i) compounds and their interactions with MeOTf. , 2008, Inorganic chemistry.

[5]  N. Belkova,et al.  On the peculiarities of hydrogen bonding and proton transfer equilibria for organic vs organometallic bases , 2008 .

[6]  A. Cooksy,et al.  Finding the proton in a key intermediate of anti-Markovnikov alkyne hydration by a bifunctional catalyst. , 2008, Journal of the American Chemical Society.

[7]  P. Dutton,et al.  Hydrogen bond-free flavin redox properties: managing flavins in extreme aprotic solvents. , 2008, Organic & biomolecular chemistry.

[8]  H. Jacobsen.  Hydrogen and dihydrogen bonding of transition metal hydrides , 2008 .

[9]  Jianliang Xiao,et al.  Half-sandwich iridium complexes—Synthesis and applications in catalysis , 2008 .

[10]  K. Fujita,et al.  Cp*Ir-catalyzed N-alkylation of amines with alcohols. A versatile and atom economical method for the synthesis of amines , 2008 .

[11]  S. Bachrach.  The gem-dimethyl effect revisited. , 2008, The Journal of organic chemistry.

[12]  H. Amouri,et al.  Supramolecular assemblies based on organometallic quinonoid linkers: a new class of coordination networks. , 2008, Angewandte Chemie.

[13]  D. Natale,et al.  The combination of transition metal ions and hydrogen-bonding interactions. , 2008, Chemical communications.

[14]  G. Brudvig,et al.  Molecular recognition in homogeneous transition metal catalysis: a biomimetic strategy for high selectivity. , 2008, Chemical communications.

[15]  A. Cooksy,et al.  Hydrogen-bond acceptance of bifunctional ligands in an alkyne-metal pi complex. , 2008, Journal of the American Chemical Society.

[16]  Zilu Chen,et al.  NH-functionalized tungsten complexes of 2-(dimethylphosphino)imidazole , 2007 .

[17]  A. Lyčka,et al.  15N NMR Spectroscopy in Structural Analysis: An Update(2001-2005) , 2007 .

[18]  J. Leszczynski,et al.  Wide spectrum of H···H interactions : van der Waals contacts, dihydrogen bonds and covalency , 2007 .

[19]  D. Grotjahn,et al.  Extensive isomerization of alkenes using a bifunctional catalyst: an alkene zipper. , 2007, Journal of the American Chemical Society.

[20]  S. Bellemin‐Laponnaz,et al.  Using a tripod as a chiral chelating ligand: chemical exchange between equivalent molecular structures in palladium catalysis with 1,1,1-tris(oxazolinyl)ethane ("trisox"). , 2007, Chemistry.

[21]  A. Katritzky,et al.  NMR spectra, GIAO and charge density calculations of five‐membered aromatic heterocycles , 2007, Magnetic resonance in chemistry : MRC.

[22]  A. Cooksy,et al.  Experimental and Computational Study of the Transformation of Terminal Alkynes to Vinylidene Ligands on trans-(Chloro)bis(phosphine)Rh Fragments and Effects of Phosphine Substituents , 2007 .

[23]  E. Peris,et al.  “Cp*Ir(III)” Complexes with Hemicleaveable Ligands of the Type N-Alkenyl Imidazolin-2-ylidene. Reactivity and Catalytic Properties , 2007 .

[24]  Lukas Hintermann,et al.  Highly active in situ catalysts for anti-Markovnikov hydration of terminal alkynes. , 2006, Organic letters.

[25]  L. Zakharov,et al.  Bifunctional Imidazolylphosphine Ligands as Hydrogen Bond Donors Promote N−H and O−H Activation on Platinum , 2006 .

[26]  D. Andreeva,et al.  Geometrical features of hydrogen bonded complexes involving sterically hindered pyridines. , 2006, The journal of physical chemistry. A.

[27]  F. Lahoz,et al.  Effects of the heterocycle and its substituents on structure and fluxionality in rhodium(I) and iridium(I) complexes with the hindered thiolates 6-tert-butylpyridine-2-thiolate and 1-alkyl-4-tert-butylimidazole-2-thiolate (alkyl = methyl and tert-butyl) , 2006 .

[28]  P. Mastrorilli,et al.  Chelating versus bridging bonding modes of N-substituted bis(diphenylphosphanyl)amine ligands in Pt complexes and Co2Pt clusters. , 2006, Dalton transactions.

[29]  E. Szłyk,et al.  Experimental and quantum‐chemical studies of 15N NMR coordination shifts in palladium and platinum chloride complexes with pyridine, 2,2′‐bipyridine and 1,10‐phenanthroline , 2006, Magnetic resonance in chemistry : MRC.

[30]  T. Ikariya,et al.  Bifunctional transition metal-based molecular catalysts for asymmetric syntheses. , 2006, Organic & biomolecular chemistry.

[31]  L. Zakharov,et al.  Changes in coordination of sterically demanding hybrid imidazolylphosphine ligands on Pd(0) and Pd(II). , 2006, Journal of the American Chemical Society.

[32]  D. Grotjahn.  Bifunctional organometallic catalysts involving proton transfer or hydrogen bonding. , 2005, Chemistry.

[33]  K. I. Goldberg,et al.  The gem-Dialkyl Effect as a Test for Preliminary Diphosphine Chelate Opening in a Reductive Elimination Reaction† , 2005 .

[34]  M. Jung,et al.  gem-disubstituent effect: theoretical basis and synthetic applications. , 2005, Chemical reviews.

[35]  V. Bakhmutov.  Proton Transfer to Hydride Ligands with Formation of Dihydrogen Complexes: A Physicochemical View , 2005 .

[36]  R. Morris,et al.  Mechanisms of the H2-hydrogenation and transfer hydrogenation of polar bonds catalyzed by ruthenium hydride complexes , 2004 .

[37]  D. Grotjahn,et al.  A general bifunctional catalyst for the anti-Markovnikov hydration of terminal alkynes to aldehydes gives enzyme-like rate and selectivity enhancements. , 2004, Journal of the American Chemical Society.

[38]  Jason D. Masuda,et al.  Anionic Phosphinimine-Chelate Complexes of Rhodium and Iridium: Steric and Electronic Influences on Oxidative Addition of CH2Cl2 , 2004 .

[39]  R. Crabtree,et al.  Hydrogen Transfer Reduction of Aldehydes with Alkali-Metal Carbonates and Iridium NHC Complexes , 2004 .

[40]  J. Gallucci,et al.  M2(hpp)4Cl2 and M2(hpp)4, where M = Mo and W: preparations, structure and bonding, and comparisons with C2, C2H2, and C2Cl2 and the hypothetical molecules M2(hpp)4(H)2. , 2003, Journal of the American Chemical Society.

[41]  D. Stephan,et al.  Pyridine− and Imidazole−Phosphinimine Bidentate Ligand Complexes: Considerations for Ethylene Oligomerization Catalysts , 2003 .

[42]  A. Lledós,et al.  Influence of media and homoconjugate pairing on transition metal hydride protonation. An IR and DFT study on proton transfer to CpRuH(CO)(PCy3). , 2003, Journal of the American Chemical Society.

[43]  W. Marshall,et al.  Is fluoride bonded to two Pd acceptors still basic? Three CH2Cl2 molecules encapsulating a Pd2(mu-F)2 square and new implications for catalysis. , 2002, Angewandte Chemie.

[44]  R. Bergman,et al.  Cationic Ir(III) alkyl and hydride complexes: stoichiometric and catalytic CH activation by Cp∗(PMe3)Ir(R)(X) in homogeneous solution , 2002 .

[45]  Elena S. Shubina,et al.  New types of hydrogen bonding in organometallic chemistry , 2002 .

[46]  A. Lyčka,et al.  15N NMR Spectroscopy in Structural Analysis , 2002 .

[47]  W. E. Hill,et al.  Coordination Chemistry of Silver(I) with the Nitrogen-Bridged Ligands (C6H5)2PN(H)P(C6H5)2 and (C6H5)2PN(CH3)P(C6H5)2: The Effect of Alkylating the Nitrogen Bridge on Ligand Bridging versus Chelating Behavior , 2002 .

[48]  S. Gruendemann,et al.  Proton Transfer to CpRuH(CO)(PCy3) Studied by Low-Temperature IR and NMR Spectroscopy , 2001 .

[49]  J. E. Jackson,et al.  Dihydrogen bonding: structures, energetics, and dynamics. , 2001, Chemical reviews.

[50]  M. Peruzzini,et al.  In-depth NMR and IR study of the proton transfer equilibrium between ({(MeC(CH 2 PPh 2 ) 3 }Ru(CO)H 2 ) and hexafluoroisopropanol , 2001 .

[51]  G. Rowlands.  Ambifunctional Cooperative Catalysts , 2001 .

[52]  I. Eremenko,et al.  Structural and energetic aspects of hydrogen bonding and proton transfer to ReH2(CO)(NO)(PR3)2 and ReHCl(CO)(NO)(PMe3)2 by IR and X-ray studies , 2000 .

[53]  C. Bertozzi,et al.  A "traceless" Staudinger ligation for the chemoselective synthesis of amide bonds. , 2000, Organic letters.

[54]  R. Bergman,et al.  Mechanistic Investigation of the Reaction of Iridium Dihydride Complexes with Organic Acid Chlorides , 2000 .

[55]  Dmitry V. Khoroshun,et al.  Diminishing π-Stabilization of an Unsaturated Metal Center: Hydrogen Bonding to OsHCl(CO)(PtBu2Me)2 , 1998 .

[56]  B. Feringa,et al.  Bimetallic catalysis by late transition metal complexes , 1998 .

[57]  R. Bergman,et al.  A Useful Method for Preparing Iridium Alkoxides and a Study of Their Catalytic Decomposition by Iridium Cations: A New Mode of β-Hydride Elimination for Coordinatively Saturated Metal Alkoxides , 1998 .

[58]  A. Scrivanti,et al.  Mechanism of the Alkoxycarbonylation of Alkynes in the Presence of the Pd(OAc)2/PPh2Py/CH3SO3H Catalytic System , 1998 .

[59]  H. Berke,et al.  Spectroscopic Evidence for Intermolecular M−H···H−OR Hydrogen Bonding: Interaction of WH(CO)2(NO)L2 Hydrides with Acidic Alcohols , 1996 .

[60]  T. Koetzle,et al.  A new intermolecular interaction: unconventional hydrogen bonds with element-hydride bonds as proton acceptor. , 1996, Accounts of chemical research.

[61]  R. Crabtree,et al.  Factors Affecting the Strength of N-H.cntdot..cntdot..cntdot.H-Ir Hydrogen Bonds , 1995 .

[62]  W. Bachovchin,et al.  Direct observation of the tautomeric forms of histidine in nitrogen-15 NMR spectra at low temperatures. Comments on intramolecular hydrogen bonding and on tautomeric equilibrium constants , 1993 .

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

[64]  I. Padilla-Martínez,et al.  NMR Study of isolobal N‐CH3+, N‐BH3 and N‐BF3 imidazole derivatives , 1993 .

[65]  P. Jessop,et al.  Reactions of transition metal dihydrogen complexes , 1992 .

[66]  Harold Basch,et al.  Relativistic compact effective potentials and efficient, shared-exponent basis sets for the third-, fourth-, and fifth-row atoms , 1992 .

[67]  R. Bergman,et al.  Iridium alkoxide and amide hydride complexes. Synthesis, reactivity, and the mechanism of oxygen-hydrogen and nitrogen-hydrogen reductive elimination , 1991 .

[68]  R. Bergman.  A physical organic road to organometallic CH oxidative addition reactions , 1990 .

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

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

[71]  R. Bergman,et al.  Synthesis, insertion and reductive elimination reactions of a hydrido(alkoxy)iridium complex , 1985 .

[72]  A. Janowicz,et al.  Activation of carbon-hydrogen bonds in saturated hydrocarbons on photolysis of (.eta.5-C5Me5)(PMe3)IrH2. Relative rates of reaction of the intermediate with different types of carbon-hydrogen bonds and functionalization of the metal-bound alkyl groups , 1983 .

[73]  P. Maitlis.  New types of reactions involving rhodium and iridium compounds , 1982 .

[74]  J. Pople,et al.  Calculation of one‐electron properties using limited configuration interaction techniques , 1981 .

[75]  R. Taft,et al.  Linear solvation energy relationship. Part 11. An analysis of nitrogen-15 solvent shifts in amides , 1981 .

[76]  B. Shaw.  Some steric, conformational and entropy effects of tertiary phosphine ligands , 1980 .

[77]  R. Taft,et al.  Linear solvation energy relationships. Part 3. Some reinterpretations of solvent effects based on correlations with solvent π* and α values , 1979 .

[78]  H. Yeh,et al.  Adjacent lone pair (ALP) effects in heteroaromatic systems. 1. Isotope exchange of ring hydrogens in alkylimidazoles , 1978 .

[79]  P. Maitlis,et al.  Pentamethylcyclopentadienyl-rhodium and -iridium complexes : VIII. Di-μ-hydridobis[chloro(pentamethylcyclopentadienyl)iridium] and related compounds☆ , 1975 .

[80]  W. Gordy.  Spectroscopic Evidence of Hydrogen Bonds: Aniline and Some Substituted Phenols , 1939 .