SHOP-type nickel complexes with alkyl substituents on phosphorus, synthesis and catalytic ethylene oligomerization

The beta-keto phosphorus ylides (n-Bu)3P=CHC(O)Ph 6, (t-Bu)2PhP=CHC(O)Ph 7, (t-Bu)Ph2P=CHC(O)Ph 8, (n-Bu)2PhP=CHC(O)Ph 9, (n-Bu)Ph2P=CHC(O)Ph 10, Me2PhP=CHC(O)Ph 11 and Ph3P=CHC(O)(o-OMe-C6H4) 12 have been synthesized in 80-96% yields. The Ni(II) complexes [NiPh{Ph2PCH...C(...O)(o-OMeC6H4)}(PPh3)] 13, [NiPh{Ph(t-Bu)PCHC(O)Ph}(PPh3)] 15, [NiPh{(n-Bu)2PCH...C(...O)Ph}(PPh3)] 16 and [NiPh{Ph(n-Bu)PCH...C(...O)Ph}(PPh3)] 17 have been prepared by reaction of equimolar amounts of [Ni(COD)2] and PPh3 with the beta-keto phosphorus ylides 12 or 8-10, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. NMR studies and the crystal structure determination of 13 indicated an interaction between the hydrogen atom of the C-H group alpha to phosphorus and the ether function. The complexes [NiPh{Ph2PCHC(O)Ph}(Py)] 18, [NiPh{Ph(t-Bu)PCHC(O)Ph}(Py)] 19, [NiPh{(n-Bu)2PCH...C(...O)Ph}(Py)] 20, [NiPh{Ph(n-Bu)PCH...C(...O)Ph}(Py)] 21 and [NiPh{Me2PCH...C(...O)Ph}(Py)] 22 have been isolated from the reactions of [Ni(COD)2] and an excess of pyridine with the -keto phosphorus ylides Ph3PCH=C(O)Ph 3 or 8-11, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. Ligands 3, 8, 10 and 12 have been used to prepare in situ oligomerization catalysts by reaction with one equiv. of [Ni(COD)2] and PPh3 under an ethylene pressure of 30 or 60 bar. The catalyst prepared in situ from 12, [Ni(COD)2] and PPh3 was the most active of the series with a TON of 12700 mol C2H4 (mol Ni)-1 under 30 bar ethylene. When the beta-keto phosphorus ylide 8 was reacted in situ with three equiv. of [Ni(COD)2] and one equiv. of PPh3 under 30 bar of ethylene, ethylene polymerization was observed with a TON of 5500 mol C2H4 (mol Ni)-1.     

Tuning haptotropic rearrangements of arene-chromium complexes: steric and electronic effects of phosphorus coligands

(Eta6-arene)tricarbonylchromium 2 was synthesised by [3+2+1] benzannulation of the Fischer carbene complex 1 and converted to the thermodynamically more favorable regioisomer 3 by haptotropic metal migration. Photo-induced ligand-exchange reactions in both regioisomers with triphenylphosphine, triphenylphosphite, trimethylphosphine, and trimethylphosphite afforded dicarbonyl(phosphine or phosphite)arene complexes 4-11. The regioisomers were separated by high-performance liquid chromatography (HPLC), and kinetic analyses of the thermo-induced haptotropic metal shift were performed with regioisomers 4, 6, 8, and 10. The kinetic parameters were compared with those obtained for the parent tricarbonyl complex 2 and were discussed in terms of the steric and electronic properties of the phosphorus ligands by applying a quantitative analysis of ligand effects (QALE). The molecular structures of regioisomeric PPh3 and P(OPh)3 complexes 4/5 and 6/7 as well as of P(OMe)3 complex 10 have been established by single-crystal X-ray analysis.     

Low-valent ene-amido iron complexes for the asymmetric transfer hydrogenation of acetophenone without base

Examination of the role of base in the activation of our previously reported iron(II) complexes having the general formula [Fe(CO)(Br)(PNNP)][BPh(4)] revealed a five-coordinate iron(II) complex in which the tetradentate PNNP ligand had been doubly deprotonated. The new iron(II) complexes were used in the transfer hydrogenation of acetophenone in isopropanol in the absence of added base, and certain analogues showed catalytic activity.     

The effect of substituents of immobilized Rh complexes on the asymmetric hydrogenation of acetophenone derivatives

Using a modified Augustine’s method variously substituted Rh complexes were anchored on Al₂O₃ support. The prepared catalysts were characterized by spectroscopic methods and were applied in the hydrogenation of several acetophenone derivatives (p-CF₃-acetophenone, acetophenone, p-NH₂-acetophenone). Enantioselective C=O hydrogenations were observed with reasonable activity and selectivity on all heterogenized complexes, e.e. up to 80%. At the same time the immobilized samples showed the advantages of the heterogeneous systems: easy handling and recyclability.      

Abstraction of iodine from aromatic iodides by alkyl radicals: steric and electronic effects

Abstraction of the iodine atom from aryl iodides by alkyl radicals takes place in some cases very efficiently despite the unfavorable difference in bond dissociation energies of C-I bonds in alkyl and aryl iodides. The abstraction is most efficient in iodobenzenes, ortho-substituted with bulky groups. The ease of abstraction can be explained by the release of steric strain during the elimination of the iodine atom. The rate of abstraction correlates fairly well with the strain energy, calculated by density functional theory (DFT) and Hartree-Fock (HF) methods as a difference in the total energy of ortho and para isomers. However, besides the steric bulk, the presence of some other functional groups in an ortho substituent also influences the rate. The stabilization of the transition state, resembling a 9-I-2 iodanyl radical, by electron-withdrawing groups seems to explain a positive sign of the Hammett rho value in the radical abstraction of halogen atoms.     

Synthesis of new boron complexes: application to transfer hydrogenation of acetophenone derivatives

Two new boron complexes were synthesized from N‐[3‐(methylmercapto)aniline]‐3,5‐di‐tert‐butylsalicylaldimine ( LH ) with boron reagent BPh₃ or BF₃.Et₂O. These boron complexes are stable and easily soluble in protic solvents such as ethanol (C₂H₅OH) but hardly soluble in nonprotic solvents such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂) and tetrahydrofuran (THF). All new boron complexes have been fully characterized by both analytical and spectroscopic methods. The catalytic activities of complexes [LBPh₂], 2 , and [LBF₂], 3 , in the transfer hydrogenation of acetophenone derivatives were tested. Stable boron complexes were found to be efficient catalysts in the transfer hydrogenation of aromatic ketones in good conversions up to 99% in the presence of iso‐PrOH/KOH. Copyright © 2011 John Wiley & Sons, Ltd.     

铱(I)联萘胺Schiff碱(BPMBNDI)配合物催化苯乙酮的不对称氢转移反应

用旋光活性2, 2'-(1, 1'-联萘)二胺和2-吡啶基甲醛缩合得到的Schiff碱BPMBNDI[N, N'-二(2-吡啶基亚甲基)-(1, 1'-联萘)-2, 2'-二亚胺]为配体与[Ir(COD)Cl]2(COD=1, 5-环辛二烯)反应, 生成了10个光学活性铱配合物。研究它们在异丙醇对苯乙酮不对称氢转移反应中的光学诱导活性时, 发现10个催化剂均具有较高的立体选择性,其中[Ir(COD)(BPMBNDI)I]催化的光学产率高达84%。     

Iron and cobalt salicylaldimine complexes as catalysts for epoxide and carbon dioxide coupling: effects of substituents on catalytic activity

The synthesis and characterization of substituted ONNO-donor salen-type Schiff base complexes of general formula [M^III(L)Cl] (L = Schiff base ligand, M = Fe, Co) is reported. The complexes have been applied as catalysts for the coupling of carbon dioxide and styrene oxide in the presence of tetrabutylammonium bromide as a co-catalyst. The reactions were carried out under relatively low-pressure and solvent-free conditions. The effects of the metal center, ligands, and various substituents on the peripheral sites of the ligand on the coupling reaction were investigated. The catalyst systems were found to be selective for the coupling of CO₂ and styrene oxide, resulting in cyclic styrene carbonate. The cobalt(III) complex with no substituents on the ligand showed higher activity (TON = 1297) than the corresponding iron(III) complex (TON = 814); however, the iron(III)-based catalysts bearing electron-withdrawing substituents on the salen ligands (NEt₃, TON = 1732) showed the highest catalytic activity under similar reaction conditions. The activity of one of the cobalt(III) complexes toward the coupling of 1-butene oxide, cyclohexene oxide and propylene oxide with CO₂ was evaluated, revealing a notable activity for the coupling of 1-butene oxide.     

Phosphorus-nitrogen-phosphorus ligands: cooperative effects between nitrogen and phosphorus substituents on catalytic activity

A new generation of PNP compounds bearing different diarylphosphine groups were prepared and used as ligands in palladium-catalysed Suzuki cross-coupling reactions. Rates of oxidative addition of iodobenzene to (PNP)Pd[0] complexes were measured using UV spectroscopy. Synergistic effects between the N- and P- substituents were identified and correlated in redox and catalytic chemistry.     

Optically active phenanthrolines in asymmetric catalysis II. Enantioselective transfer hydrogenation of acetophenone by rhodium/alkyl phenanthroline catalysts

Three new alkyl phenanthrolines containing a norpinanyl substituent as the common chiral target, have been synthesized and tested as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of acetophenone. A marked catalytic activity was observed, but the highest optical yield was 24% e.e.     

Crystal structure of chiral binaphthol lanthanide complexes and their catalysis in asymmetric transfer hydrogenation of acetophenone

Heterometallic [(THF)₂Na]₃[Ln(R‐Binolate)₃(H₂O)] [Ln = Sm ( 1 ) and Gd ( 2 )] has been synthesized by the reactions of either LnCl₃ or LnBr₃ with 3 equiv. Na(R‐HBinolate) and characterized by X‐ray crystallographic analysis. Structural analyses proposed that 1 and 2 are isomorphous complexes, crystallizing in the hexagonal space group P6₃ with C₃ symmetry. The coordination geometry of the lanthanide ions in 1 and 2 can be best approximated as a mono‐capped triangle antiprism. When complexes 1 and 2 were employed as catalysts in the Meerwein–Ponndorf–Verley (MPV) reactions of acetophenone, the S‐phenylethanol was separated in 94 and 85% enantiomeric excess (e.e.) for 1 and 2 , respectively. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of substituents on the GPx-like activity of ebselen: steric versus electronic

The direct oxidation of ebselen and several derivatives by hydrogen peroxide is investigated using the B3LYP/6-31G(d,p) method to elucidate the effects of substituents on GPx-like activity. While previous studies have attributed the differences in GPx activity of substituted ebselen compounds to the electronic nature of the substituents, the influence of functional groups is poorly understood. The effects of various solvents are incorporated by employing the CPCM method. It is shown that a substituent in the ortho position to the selenium atom sterically hinders attack of a nucleophile at selenium and thus increases the barrier to reaction. The observed increase in GPx-like activity of an ebselen derivative with an ortho substituent is explained by the fact that the steric hindrance prevents thiol exchange reactions.     

Effect of the structure of the diamine backbone of P-N-N-P ligands in iron(II) complexes on catalytic activity in the transfer hydrogenation of acetophenone

The asymmetric transfer hydrogenation of aromatic ketones can be efficiently accomplished using catalysts that are based on platinum group metals which are more toxic and less abundant than iron. For that reason the discovery of iron based catalysts for the use in this transformation is important. To address this issue, we synthesized a new series of iron(II)-based precatalysts trans-[Fe(Br)(CO)(PPh(2)CH(2)CH═NCHRCHRN═CHCH(2)PPh(2))]BPh(4) (5a-5d) containing P-N-N-P ligands with the diamines (R,R)-1,2-diaminocyclohexane (a), (R,R)-1,2-diphenyl-1,2-diaminoethane (b), (R,R)-1,2-di(4-methoxyphenyl)-1,2-diaminoethane (c), and ethylenediamine (d) incorporated in the backbone using a convenient one-pot synthesis using readily available starting materials. All of the complexes, when activated with a base, show a very high activity in the transfer hydrogenation catalysis of acetophenone, using 2-propanol as a reducing agent under mild conditions. A comparison of the TOF of complexes 5a-5d show that the catalytic activity of complexes increase as the size of the substituents in the backbone of ligands increases (d < a < b = c).     

Influence of steric and electronic effects of substituents on the molecular structures and conformational flexibility of 1,8-naphthalenedicarboximides

A series of 1,8-naphthalenedicarboximide derivatives containing substituents of different steric and electronic nature were studied by X-ray diffraction analysis.Ab initio quantumchemical calculations in the HF/3–21G approximation demonstrated the high conformational flexibility of the imide tetrahydro ring in the molecules of these compounds. The electronic nature of the substituents has no effect on the geometry and conformational flexibility of naphthalenedicarboximides due to weak conjugation between the imide and naphthalene fragments in the molecules. However, the steric effects of the bulky substituents noticeably affect the equilibrium geometry of the imide ring by increasing its conformational flexibility. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 68–73, January, 2000.     

Iron phthalocyanine as new efficient catalyst for catalytic transfer hydrogenation of simple aldehydes and ketones

Catalytic transfer hydrogenation (CTH) of various aldehydes and ketones was studied using iron phthalocyanine catalyst, in order to substitute the typically used rare transition metals (Ir, Rh, Ru) with an easily available and less expensive metal. Iron phthalocyanine was found to be an efficient hydrogenation catalyst and its immobilized version was successfully prepared. The immobilized iron phthalocyanine was also active in the CTH reaction of various carbonyl compounds, and it was easy to handle and possible to recycle. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of steric and electronic effects of substituents on the molecular structures and conformational flexibility of 1,8-naphthalenedicarboximides

A series of 1,8-naphthalenedicarboximide derivatives containing substituents of different steric and electronic nature were studied by X-ray diffraction analysis.Ab initio quantumchemical calculations in the HF/3–21G approximation demonstrated the high conformational flexibility of the imide tetrahydro ring in the molecules of these compounds. The electronic nature of the substituents has no effect on the geometry and conformational flexibility of naphthalenedicarboximides due to weak conjugation between the imide and naphthalene fragments in the molecules. However, the steric effects of the bulky substituents noticeably affect the equilibrium geometry of the imide ring by increasing its conformational flexibility. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 68–73, January, 2000.