Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2

Various Ru(L₁)(L₂) (1) complexes (L₁ = 2,2′-bipyridines, 2,2′:6′,2″-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl-2,2′-bipyridinyl or 2,2′-bipyridinyl-6-carboxylate; L₂ = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2′-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H₂O₂. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2′-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2′]bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed.     

Synthesis of copper(I) bis(3,5-dimethylpyrazolyl)methane olefin complexes and their reactivity towards carbon monoxide

The chemistry of bis(3,5-dimethylpyrazolyl)methane complexes of copper(I) has been investigated and a dinuclear copper(I) derivative of formula {Cu₂[μ-CH₂(3,5-Me₂Pz)₂]₂}(TfO)₂ [TfO = trifluoromethanesulphonate anion, ], characterized by an uncommon bridging coordination of the bis(pyrazolyl)methane ligands, has been isolated and characterized by X-ray diffraction methods. Moreover, new olefin derivatives of general formula [Cu[CH₂(3,5-Me₂Pz)₂](olefin)]TfO have been prepared (olefin: coe = cyclooctene, van = 4-vinylanisole, nbe = norbornene), their carbonylation reactions, {Cu[CH₂(3,5-Me₂Pz)₂](olefin)}TfO + CO ? {Cu[CH₂(3,5-Me₂Pz)₂](CO)}TfO + olefin, have been studied gas volumetrically and the thermodynamical parameters of the equilibria for the displacement of the coordinated olefin by carbon monoxide have been determined.     

EPR studies on regio-selective H-abstraction by “magic blue” reagent from polymers

The radical reactions of polyolefin and olefin copolymers (4-9), polydienes and diene coplymers (10-15), and polysiloxane (16) with “magic blue” reagent containing H-abstracting agent-bis{perfluoro-1-[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide [FSO₂CF₂CF₂OCF(CF₃)]₂N(O) (2)and spin trap-perfluoro-1-nitroso-[1-(2-fluoro-sulfonyl)ethoxy]ethane FSO₂CF₂CF₂OCF(CF₃)NO (3) were studied by EPR detection of the spin adducts of the corresponding polymeric radicals generated in the H-abstraction step to the spin trap 3, namely, the nitroxides FSO₂CF₂CF₂OCF(CF₃)N(O) (polymer-H) 17-29. EPR studies have provided information about the regio-selectivity of H-abstraction, the subsequent radical steps followed H-abstraction and grounded a possibility of employing “magic blue” reagent in polymer modification via H-abstraction-initiated grafting polymerization.     

Facile synthesis of [(NHC)(NHCewg)RuCl2(CHPh)] complexes

The utility of [(NHC)(PPh₃)RuCl₂(CHPh)] for the facile and efficient synthesis of ten complexes of the type [(NHC)(NHC_ewg)RuCl₂(CHR)] with saturated and unsaturated NHC ligands in 85-94% isolated yield via a simple one step synthesis utilizing [AgI(NHC_ewg)] as NHC_ewg transfer reagents was demonstrated.     

Latent ruthenium olefin metathesis catalysts featuring a phosphine or an N-heterocyclic carbene ligand

The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy₃)((^κN,O)-picolinate)₂RuCHPh (5) and (H₂IMes)((^κN,O)-picolinate)₂RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on l-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes.     

A convergent total synthesis of a new antiepileptic ceramide and its triacetyl derivative using olefin cross metathesis

A convergent total synthesis of a new antiepileptic ceramide 1b and its triacetyl derivative 1b′ was completed by using two important C-C bond forming reactions, Wittig methylenation and olefin cross metathesis as the key steps. The easily available 3,4,6-tri-O-benzyl-d-galactal was used as a chiral pool for the synthesis of highly functionalized amide 3 and the commercially available 1,12-dodecanediol for the long chain olefin counterpart 4. The long hydrocarbon chain of the new ceramide 1b was installed by using olefin cross metathesis between amide 3 and long chain terminal olefin 4 followed by hydrogenation.     

Convergent total synthesis of squamostolide

A convergent total synthesis of the Annonaceous acetogenin squamostolide, in a longest linear sequence of nine steps from d-mannitol, is reported. Central to the efficiency of the synthesis is a highly selective tandem ring-closing/cross metathesis step in which lactone formation and fragment coupling are accomplished.     

Cyclometalated group 4 complexes supported by tridentate pyridine-2-phenolate-6-(σ-aryl) ligands: Catalysts for ethylene polymerization and comparisons with fluorinated analogues

An adaptable synthetic methodology for the tridentate dianionic pyridine-2-phenolate-6-aryl [O,N,C] ligand framework, comprising the aromatic σ-carbanion moiety as a chelating component, has been developed. A series of non-fluorinated group 4 bis(benzyl) complexes supported by [O,N,C] auxiliaries, with halogen and alkyl groups at the ‘R¹’ position ortho to the metal-C(σ-aryl) bond, have been prepared by exploiting the cyclometalation of the ligand. All derivatives have been characterized by NMR spectroscopy, and the spectral features concerning the metal-bound diastereotopic methylene groups have been highlighted. The capabilities of these complexes as catalysts for olefin polymerization have been tested, and comparisons with the recently reported fluorine-containing Ti-[O,N,C] analogues and related Hf-[N,N,C] derivatives are discussed. The titanium catalysts, in conjunction with MAO, displayed moderate to high activities for ethylene polymerization (up to 200 g mmol⁻¹ h⁻¹).     

Some selected chapters from the (butadiene)zirconocene story

(Butadiene)zirconocene was the first mono-nuclear metal complex for which the s-trans-η⁴-conjugated diene coordination mode was established. Meanwhile a variety of additional examples from metals throughout the Periodic Table was found. The (butadiene)zirconocenes have found use as valuable reagents in organic and organometallic synthesis, for which various representative examples are described. They have also found extensive use as precursors for the generation of very active and sometimes very selective homogeneous metallocene Ziegler-Natta olefin polymerization catalysts. The employment of the dipolar zirconocene(butadiene)/B(C₆F₅)₃ addition products in mechanistic studies has revealed important aspects of the reaction course taken in the carbon-carbon coupling reaction sequences at this important class of catalysts. Several specific examples are described in this article.     

Studies on Diastereoselective Intramolecular meta-Cycloaddition of Arene to Olefin (Part Ⅱ)

Wththecapacityt0pr0duceuPt03newringsand6newstereogeniccentersinonestep,thearene-athenephotocycloadditionreactionprovidesaremarkablyeffectivemeansinthesynthesistowardspolyquinanesalldfenestranes.2-'Asfarastheregioselectivityisconcemed,itisbelievedthatsubstitUentsatthear0maticringandthenon-bondedinteractionsbetWeensuchsubstitUentsandthesidechaincontrolthemode0fthecycloadditi0n.Wehaverep0rted"'thatintramolecularhydrogenbondeffectcouldsignificantlyincreasethediastereoselectivityinsuchcycloadditio…