Abstract: A gold(III)-catalyzed carbon−carbon bond formation reaction between arenes and electron-deficient alkynes or alkenes is described. Electron-rich arenes can be efficiently functionalized with the alkyne or alkene substrates. This reaction can be run with neat reactants at ambient temperature. Under the “solventless” conditions, clean product was obtained from a reaction of equal molar amounts of arene and alkyne substrates. The mild conditions and potential tolerance to different functional groups make this method practical for arene functionalization and for constructing complicated molecules. Efficient preparation of various coumarins from aryl alkynoates was demonstrated. Preliminary mechanistic studies were performed to probe the pathway of this reaction.

Abstract: The asymmetric Heck reaction is a powerful method for the synthesis of both tertiary and quaternary chiral carbon centers, with an enantiomeric excess often greater than 80%, and in some cases much higher (up to 99% ee). A variety of carbocyclic and heterocyclic systems can be constructed, including spirocyclic systems. The scope of the reaction with respect to the product alkene isomerization is somewhat limited by problems of regioselectivity, however, these problems are surmountable, and a new generation of ligands that dissociate more rapidly from the products, might improve both enantio- and regiocontrol. A variety of chiral compounds prepared by the asymmetric Heck reaction were successfully utilized in the enantioselective syntheses of complex natural products.

Abstract: The reaction mechanism of olefin metathesis by ruthenium carbene catalysts is studied by gradient-corrected density functional calculations (BP86). Alternative reaction mechanisms for the reaction of the “first-generation” Grubbs-type catalyst (PCy3)2Cl2RuCH2 (1) for the reaction with ethylene are studied. The most likely dissociative mechanism with trans olefin coordination is investigated for the metathesis reaction between the “first-” and the “second-generation” Grubbs-type catalysts 1 and (H2IMes)(PCy3)Cl2RuCH2 (2) with different substrates, ethylene, ethyl vinyl ether, and norbornene, and a profound influence of the substrate is found. In contrast to the degenerate reaction with ethylene, the reactions with ethyl vinyl ether and norbornene are strongly exergonic by 8−15 kcal/mol, and this excess energy is released after passing through the metallacyclobutane structure. While the metallacyclobutane is in a deep potential minimum for degenerate metathesis reactions, the energy barrier for the [2+2] cy...

Abstract: Preface- Acknowledgements- 1: Introduction- 11 Catalysis 12 Homogeneous catalysis 13 Historical notes on homogeneous catalysis 14 Characterization of the catalyst 15 Ligand effects 16 Ligands according to donor atoms 2: Elementary Steps- 21 Creation of a 'vacant' site and co-ordination of the substrate 22 Insertion versus migration 23 beta-Elimination and de-insertion 24 Oxidative addition 25 Reductive elimination 26 alpha-Elimination reactions 27 Cycloaddition reactions involving a metal 28 Activation of a substrate toward nucleophilic attack 29 sigma-Bond metathesis 210 Dihydrogen activation 211 Activation by Lewis acids 212 Carbon-to-phosphorus bond breaking 213 Carbon-to-sulfur bond breaking 214 Radical reactions 3: Kinetics- 31 Introduction 32 Two-step reaction scheme 33 Simplifications of the rate equation and the rete-determining step 34 Determining the selectivity 35 Collection of rate data 36 Irregularities in catalysis 4: Hydrogenation- 41 Wilkinson's catalyst 42 Asymmetric hydrogenation 43 Overview of chiral bidentate ligands 44 Monodentate ligands 45 Non-linear effects 46 Hydrogen transfer 5: Isomerisation- 51 Hydrogen shifts 52 Asymmetric isomerisation 53 Oxygen shifts 6: Carbonylation of Methanol and Methyl Acetate- 61 Acetic acid 62 Process scheme Monsanto process 63 Acetic anhydride 64 Other systems 7: Cobalt Catalysed Hydroformylation- 71 Introduction 72 Thermodynamics 73 Cobalt catalysed processes 74 Cobalt catalysed processes for higher alkenes 75 Kuhlmann cobalt hydroformylation process 76 Phosphine modified cobalt catalysts: the shell process 77 Cobalt carbonyl phosphine complexes 8: Rhodium Catalysed Hydroformylation- 81 Introduction 82 Triphenylphosphine asthe ligand 83 Diphosphines as ligands 84 Phosphites as ligands 85 Diphosphites 86 Asymmetric hydroformylation 9: Alkene Oligomerisation- 91 Introduction 92 Shell-higher-olefins-process 93 Ethene trimerisation 94 Other alkene oligomerisation reactions 10: Propene Polymerisation- 101 Introduction to polymer chemistry 102 Mechanistic investigations 103 Analysis by 13CNMR spectroscopy 104 The development of metallocene catalysts 105 Agostic interactions 106 The effect of dihydrogen 107 Further work using propene and other alkenes 108 Non-metallocene ETM catalysts 109 Late transition metal catalysts 11: Hydrocyanation of Alkenes- 111 The adiponitrile process 112 Ligand effects 12: Palladium Catalysed Carbonylations of Alkenes- 121 Introduction 122 Polyketone 123 Ligand effects on chain length 124 Ethene/propene/CO terpolymers 125 Stereoselective styrene/CO terpolymers 13: Palladium Catalysed Cross-Coupling Reactions- 131 Introduction 132 Allylic reaction 133 Heck reaction 134 Cross-coupling reaction 135 Heteroatom-carbon bond formation 136 Suzuki reaction 14: Epoxidation- 141 Ethene and propene oxide 142 Asymmetric epoxidation 143 Asymmetric hydroxilation of alkenes with osmium tetroxide 144 Jacobsen asymmetric ring-opening of epoxides 145 Epoxidations with dioxygen 15: Oxydation with Dioxygen- 151 Introduction 152 The Wacker reaction 153 Wacker type reactions 154 Terephthalic acid 155 PPO 16: Alkene Metathesis- 161 Introduction 162 The mechanism 163 Reaction overview 164 Well-characterised tungsten and molybdenum catalysts 165 Ruthenium catalysts 166 Stereochemistry 167 Catalyst decomposition 168 Alkynes 169 Industrial applications 17: Enantioselective Cyclopropanation-

Abstract: The title concept involves the use of structurally modified RCM substrates that contain extender arms, terminating in a remote reactive alkene. Initiation of an RCM sequence at that reactive alkene is followed by rapid intramolecular relay of the metal center to an initially less reactive alkene in the parent substrate. This permits one to control the relative timing (or direction) of a metathesis sequence. For example, one can reverse the inherent tendency of an unsymmetrical alpha,omega-diene substrate to close, say, left-to-right, to that of right-to-left. Four distinct types of application of the RRCM concept are demonstrated. Among other things, they show the preparation of tetrasubstituted electron-deficient alkenes using G1 [(Cy3P)2(Cl2)Ru=CHPh], complementary control of directionality (endedness), auxiliary benefits (enzyme specificity) from the incorporation of additional steric bulk, the activation of otherwise ineffective substrates for RCM closure, the use of unorthodox alkenes as initiation sites for ring closure, and control of product olefin geometry.

Abstract: A symmetrical α,ω-substituted sexithiophene derivative containing thermally removable branched ester solubilizing groups has been prepared. These oligomers can be solution cast into thin films and then thermolyzed to remove the solubilizing group, leaving short pendant alkene groups on the oligomer. Device testing of thin film transistors shows an increase in hole mobility from 1 × 10-5 cm2/(V s) with on/off ratios of ∼100 before thermolysis to 5 × 10-2 cm2/(V s) with on/off ratios >105 after thermolysis. This method offers an attractive route to easily processed and highly performing thiophene oligomers.

Abstract: In the asymmetric hydrogenation of unfunctionalized olefins with cationic iridium-PHOX catalysts, the reaction kinetics and, as a consequence, catalyst activity and productivity depend heavily on the counterion. A strong decrease in the reaction rate is observed in the series [Al[OC(CF3)3]4]- >BArF- >[B(C6F5)4]- >PF6- >>BF4- >CF3SO3-. With the first two anions, high rates, turnover frequencies (TOF >5000 h(-1) at 4 degrees C), and turnover numbers (TONs) of 2000-5000 are routinely achieved. The hexafluorophosphate salt reacts with lower rates, although they are still respectable; however, this salt suffers from deactivation during the reaction and extreme water-sensitivity, especially at low catalyst loading. Triflate and tetrafluoroborate almost completely inhibit the catalyst. In contrast to the hexafluorophosphate salt, catalysts with [Al[OC(CF3)3]4]-, BArF-, and [B(C6F5)4]- as counterions do not lose activity during the reaction and remain active, even after all the substrate has been consumed. In addition they are much less sensitive to moisture and, in general, rigorous exclusion of water and oxygen is not necessary. A first-order rate dependence on the hydrogen pressure was determined for the BArF- and the PF6- salts. At low catalyst loading, the rate dependence on catalyst concentration was also first order. The rate dependence on the alkene concentration was strikingly different for the two salts. While the reaction rate observed for the BArF- salt slightly decreased with increasing alkene concentration (rate order -0.2), a rate order of approximately 1 was determined for the corresponding hexafluorophosphate at low alkene concentrations.

Abstract: Although catalytic hydrogenation has been practiced for over a century, use of hydrogen as a terminal reductant in catalytic C-C bond formation has been restricted to processes involving migratory insertion of carbon monoxide, e.g., alkene hydroformylation and related Fischer-Tropsch-type reactions. In an effort to develop hydrogenation as a new method for catalytic cross-coupling, a catalytic system enabling capture of hydrogenation intermediates was recently developed in our lab. These results support the feasibility of developing a broad new family of hydrogen-mediated C-C bond formations.

Abstract: More than 70 million tons of polyethylene and polypropylene are produced annually. The majority is prepared by catalytic polymerization employing Ziegler or Phillips catalysts based on early transition metals. More recently, olefin polymerization by complexes of late transition metals has also received increasing attention. A major motivation is their higher tolerance towards polar reagents due to a reduced oxophilicity by comparison to early transition-metal catalysts. Thus, ethylene and 1-olefins can be copolymerized with acrylates in a random fashion, and ethylene homoand copolymerizations can be carried out in aqueous emulsion to afford polymer latexes (i.e., aqueous dispersions of polymer particles of about 50–1000 nm size). The discovery by Brookhart and co-workers of the unique catalytic properties of cationic nickel and palladium diimine catalysts in olefin polymerization has given a strong impulse to the field. As a result, polymerization with neutral Ni complexes has received renewed interest, as these catalysts are expected to be more functional-group tolerant than their cationic Ni counterparts. However, catalyst activity and stability over time and the capability to form polymers with higher molecular weights at the same time are critical issues, particularly if the effort for catalyst synthesis is also considered. By analogy with the influence of bulky alkyl or aryl groups in cationic diimine complexes, in neutral Ni kN,O salicylaldiminato complexes bulky isopropyl groups on theN-aryl moiety retard chain transfer, which is supported by computational studies by Ziegler and co-workers. Introduction of electron-withdrawing substituents in the ortho or para position of the O donor in neutral nickel(ii) complexes has been reported to increase catalytic activities substantially, again in accordance with theoretical calculations. Most specifically for this class of catalysts, Grubbs and co-workers have shown that bulky groups in the C3 position of the Ocoordinating phenolate moiety of salicylaldimine ligands substantially increase polymerization activity. While these ligands afford highly active catalysts, their syntheses require multistep procedures with very low yields. Our particular interest in the design of novel Ni salicylaldiminato complexes stems from the recent finding that the known isopropyl-substituted complexes enable the synthesis of latexes of high-molecular-weight polyethylene, which are, to date, inaccessible by other techniques. Such polyolefin latexes can provide environmentally friendly and economically attractive coatings, which, for example, can be stable towards UV light and hydrolysis at the same time in contrast to current commodity coatings. In view of applications, a very active catalyst based on conveniently accessible ligands, and that is suited to polymerization in emulsion to higher-molecular-weight polyethylene is a prerequisite. Such a system is equally attractive for fundamental studies of catalytic polymerization in emulsion, in which well-defined catalyst precursors are also desirable. Our investigations subject to this report were initiated by the reasoning that an aryl substituent with strongly electron-withdrawing groups could provide steric bulk and electron withdrawing properties at the same time. Suzuki coupling provided a convenient synthetic method for the introduction of electron-withdrawing substituted aryl groups in the C2 and C6 position of the aniline aryl ring (Scheme 1). A series of salicylaldimine ligands with systematically varied electronic properties, 1a–e, resulted from the condensation of the corresponding substituted anilines with 3,5-diiodo-salicylaldehyde. The C NMR resonances of the compounds were fully assigned by H–H COSY, heteronuclear H-C 2D NMR and H–C 2D longrange-coupling NMR spectroscopy. The chemical shifts of the carbon atom para to the imine function in 1a–e (atom labeled p in Scheme 1) are d= 126.90, 126.96, 126.55, 126.48, and 126.56 ppm, respectively, and for the imine carbon atom, C= N, d= 168.42, 168.05, 166.99, 166.23, and 166.26 ppm were observed. Although the differences in chemical shifts are moderate, this trend follows the electron withdrawing/donating character of the R group and indicates that the electronic character of the substituents R in 1 indeed affects the electronic properties of the neighboring aryl ring and the imine function. Reaction of 1a–e in diethylether with [(tmeda)Ni(CH3)2] [12] (tmeda=N,N,N’,N’-tetramethylethylenediamine) in the presence of excess pyridine afforded the neutral methylnickel(ii) complexes 2a–e in high yield (Scheme 1). The molecular structure of 2a and 2c was determined by single-crystal X-ray crystallography (Figure 1). 14] To our knowledge, these are the first examples of structurally characterized neutral methylnickel complexes, which are precursors to very active olefin polymerization catalysts. Such methyl complexes are of particular interest, in comparison to the more frequent phenyl complexes [*] Dr. M. A. Zuideveld, Dipl. Chem. P. Wehrmann, Priv.-Doz. Dr. S. Mecking Institut f$r Makromolekulare Chemie und Freiburger Materialforschungszentrum der Albert-Ludwigs-Universit*t Freiburg Stefan-Meier-Strasse 31, 79104 Freiburg (Germany) Fax: (+49)761-203-6319 E-mail: stefan.mecking@makro.uni-freiburg.de

Abstract: Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.

Abstract: We have explored the scope of the palladium-catalyzed nucleophilic ring opening methodology. New highly selective and highly active catalysts have been found for the ring opening of oxabenzonorbornadienes. Employing these catalysts, the addition of various alkyl nucleophiles to oxabenzonorbornadiene has been achieved. In addition, reaction of diethylzinc with [3.2.1] oxabicyclic alkenes has been accomplished to yield ring-opened products as well as functionalized alkene addition products.

Abstract: Enhanced activity, lower catalyst loading, shorter reaction time, and expanded substrate scope are the advantages of [Mn(dpm)3] over Co catalysts in the hydrohydrazination reaction of alkenes. Thus, sterically hindered alkenes, including tetrasubstituted alkenes, can now also readily undergo this reaction. [on SciFinder (R)]

Abstract: Dependent on the selection of the light sources employed, the photoinduced iodoperfluoroalkylation of a variety of unsaturated compounds takes place efficiently via a radical mechanism. Upon irradiation with a xenon lamp through Pyrex (hν >300 nm), terminal alkenes (R−CHCH2) and alkynes (R−C⋮CH) undergo iodoperfluoroalkylation with perfluoroalkyl iodides (RF-I) regioselectively, providing R−CH(I)−CH2−RF and R−C(I)CH−RF, respectively. In the case of terminal allenes (R−CHCCH2), the photoinduced iodoperfluoroalkylation occurs selectively at the terminal double bond, giving the corresponding β-perfluoroalkylated vinylic iodides (R−CHC(I)−CH2−RF) in good yields. The photoinitiated reaction of vinylcyclopropanes (c-C3H5−C(R)CH2) with RF-I proceeds via the rearrangement of cyclopropylcarbinyl radical intermediates to the homoallylic radical intermediates, and the corresponding 1,5-iodoperfluoroalkylated products (I−(CH2)2CHC(R)−CH2−RF) are obtained in high yields. Isocyanides (R−NC), as C−N unsaturated compound...

Abstract: Highly selective epoxidation (>95%) of unfunctionalized alkenes was performed by tetrabutylammonium periodate in the presence of six different phenyl substituted manganese(III) meso-tetraphenylporphyrins [Mn(Por)] and imidazole in CH2Cl2. Electron-withdrawing and bulky substituents on the phenyl groups lowered the catalytic activities of the corresponding Mn(Por). Less bulky alkenes with electron -rich double bonds showed greater reactivity in the epoxidation. Co-catalytic activities of four different classes of axial nitrogen donors are compared in the presence of various Mn(Por). In general no direct correlation was found between co-catalytic activities and the pKa values of the nitrogen donors. Strong σ-donor amines (pKa = 10.6 to 11.123) and weak π-donor pyridines (pKa = 5.25 to 6.65) showed comparable co-catalytic activities. Strong π-donor aminopyridines (pKa = 7 to 9.71) and imidazoles (pKa = 6.95 to 7.86) are generally much better co-catalysts than pure σ-donors, suggesting the importance of π-bonding interactions of the nitrogenous donors. N–H imidazoles with the possibility for N–H⋯B hydrogen bonding are much more effective co-catalysts than 1-methylimidazole. Methylpyridines and aminopyridines with substituents at the 2 or 2,6 positions showed particularly high co-catalytic activities toward manganese(III) meso-tetrakis(pentafluorophenylporphyrin) acetate. This “unusual” observation suggests the occurrence of some attractive hydrogen bonding interactions between ortho-fluorines of the manganese porphyrin and the substituents of these donors. A simple qualitative molecular orbital diagram is presented to describe the possible π-interactions of (dxz, dyz) metal orbitals with axially coordinated ImH and periodate in six-coordinate Mn(Por)(ImH)(IO4), as the active oxidizing species. A catalytic cycle is postulated in which the intermediate involves complexation of an alkene to the coordinated periodate, and attempts have been made to visualize the orbital interactions for this intermediate species.

Abstract: A new hydroformylation of alkenes using carbon dioxide as a reactant is shown to take place in the presence of ruthenium cluster complexes and halide salts. Similar or even better yields of alcohols were formed as compared to the conventional hydroformylation with CO under the same reaction conditions. The reaction proceeded in three steps: CO2 is first converted to CO; then it is used as a reagent for hydroformylation to give aldehyde; subsequently, it is hydrogenated to alcohol. ESI-mass spectrometric analyses of the reaction solutions indicated formation of four kinds of ruthenium anionic complexes including tetra-, tri-, and mononuclear species. On the basis of experimental findings, possible roles of these complexes are discussed.

Abstract: Direct oxidative cyclization of (η2:η2-CH2CHCH2C6H4CHO)Ni(PR3) to form the nickelacycle and drastic acceleration of the cyclization by the addition of Me3SiOTf were observed. (η2-PhCHO)Ni(PCy3)2 also reacted with Me3SiOTf to give (η1:η1-Me3SiOCH(Ph))Ni(PCy3)OTf.

Abstract: Monomeric imidozirconocene complexes of the type Cp2(L)ZrNCMe3 (Cp = cyclopentadienyl, L = Lewis base) have been shown to activate the carbon−hydrogen bonds of benzene, but not the C−H bonds of saturated hydrocarbons. To our knowledge, this singularly important class of C−H activation reactions has heretofore not been observed in imidometallocene systems. The MNR bond formed on heating the racemic ethylenebis(tetrahydro)indenyl methyl tert-butyl amide complex, however, cleanly and quantitatively activates a wide range of n-alkane, alkene, and arene C−H bonds. Mechanistic experiments support the proposal of intramolecular elimination of methane followed by a concerted addition of the hydrocarbon C−H bond. Products formed by activation of sp2 C−H bonds are generally more thermodynamically stable than those formed by activation of sp3 C−H bonds, and those resulting from reaction at primary C−H bonds are preferred over secondary sp3 C−H activation products. There is also evidence that thermodynamic selectivit...

Abstract: The effect of the chemical structure on the reactivity of alkenes used in thiol–ene photopolymerizations has been investigated with real-time infrared spectroscopy. Model studies of thiol–ene photoreactions with various monofunctional hydrocarbon alkenes and the monofunctional thiol ethyl-3-mercaptopropionate have been performed to identify and understand structure–reactivity relationships. The results demonstrate that terminal enes react very rapidly with thiol, achieve complete conversion, and are independent of the aliphatic hydrocarbon substituent length. Disubstitution on a single carbon of a terminal ene significantly reduces the reactivity, whereas substitution on the carbon α to the terminal ene has a minimal influence on the reactivity. Internal trans enes display reduced reactivity and a lower overall conversion and deviate from the standard thiol–ene reaction mechanism because of steric strain induced by 1,3-interactions. The reactivity and conversion of internal trans enes decrease as the substituents on the ene become larger, reaching a minimum when the substituent size is greater than or equal to that of propyl groups. Internal cis enes react rapidly with thiol; however, they undergo a fast isomerization–elimination reaction sequence generating the trans ene, which proceeds to react at a reduced rate with thiol. The reactivity of cyclic enes is dictated by ring strain, stereoelectronic effects, and hydrogen abstractability. The reactivity trends in the model studies have been used to explain the photopolymerization mechanism and kinetics of a series of multifunctional thiol–ene systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6283–6298, 2004

Abstract: Catalytic hydrogenation of carbon-, nitrogen- and oxygen-tethered 1,6-diynes 1a-9a and 1,6-enynes 10a-18a using cationic Rh(I) precatalysts at ambient temperature and pressure enables reductive carbocyclization to afford 1,2-dialkylidene cyclopentanes 1b-9b and monoalkylidene cyclopentanes 10b-18b, respectively, in good to excellent yields and as single alkene stereoisomers. Notably, the 1,3-diene and alkene containing cyclization products 1b-9b and 10b-18b are not subject to over-reduction under the conditions of catalytic hydrogenation in which they are formed. Reductive cyclization 1,6-diyne 1a and 1,6-enyne 10a performed under an atmosphere of D(2) provides the carbocyclization products deuterio-1b and deuterio-10b, respectively, which incorporate two deuterium atoms. The collective data are consistent with a catalytic mechanism involving heterolytic activation of elemental hydrogen (H(2) + Rh(+)X(-) --> Rh-H + HX) followed by Rh(I)-mediated oxidative cyclization of the 1,6-diyne or 1,6-enyne substrates to afford (hydrido)Rh(III)-based metallocyclopentadiene and metallocyclopentene intermediates, respectively. These transformations represent the first examples of metal-catalyzed reductive carbocyclization mediated by hydrogen.

Abstract: Nickel-catalyzed reductive couplings of aldehydes with alkynes that contain tethered olefins are described, in which the degree and sense of regioselectivity are controlled by the length of the tether and the presence or absence of an additive. When the alkyne and alkene are separated by four bonds, very high (>95:5) regioselectivities are observed. Use of a monodentate phosphine as an additive leads to formation of the opposite regioisomer in equal and opposite selectivity (5: >95). These results provide strong evidence for an interaction between the remote alkene and the metal center during the regioselectivity-determining step and suggest that reactions with and without an additive proceed via fundamentally distinct mechanisms.

Abstract: Among a large variety of fine-tuning parameters for homogeneous catalysts the net charge of transition-metal complexes appear to be an interesting factor that considerably affects activation of substrates and catalytic activity in general. The electrophilicity of coordinated alkenes in transition-metal complexes can be strongly enhanced by increasing the positive net charge, resulting in strong carbocationic properties. Theoretical and experimental studies have shown that the alkene in cationic complexes is kinetically and thermodynamically more activated towards nucleophilic addition than in neutral complexes. The concept of increasing the positive complex charge is thought to be useful for the development of new catalysts for reactions in which alkenes or other unsaturated substrates are involved.