다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal-ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.

Strategies for the Construction of Supramolecular Compounds through Coordination Chemistry

Synthesis of Stereoregular Poly(phenylacetylene)s by Organorhodium Complexes in Aqueous Media

The synthesis of [Ru III (salen)(X)(Y)] n [n=1, (X)(Y)=(CN) 2 ; n=0, (X)(Y)=(PPh 3 )(PBu 3 ), (PPh 3 )(py); n=1, (X)(Y)=(PPh 3 )(N 3 ), (PPh 3 )(TsO) (TsO=tosylate anion) from [Ru III (salen)(PPh 3 )(Cl)] is described. These ruthenium(III) complexes are dark green air-stable solids. Their cyclic voltammograms display reversible Ru(IV)/Ru(III) and Ru(III)/Ru(II) couples. At room temperature, they catalyze oxidation of alkenes by PhIO. With norbornene and cyclooctene, epoides are formed. The mechanism of the catalytic oxidation is discussed

Oxidation chemistry of ruthenium-salen complexes

Oxidation of (Ru{sup II}(OEP)(CO)) (H{sub 2}OEP = octaethylporphyrin) by m-chloroperoxybenzoic acid in methanol gave (Ru{sup VI}(OEP)(O){sub 2}), isolated as air-stable diamagnetic purpose solid ({mu}{sub eff} {approximately} 0 {mu}{sub B}). (Ru{sup VI}(OEP)(O){sub 2}) shows one intense IR band at 821 cm{sup {minus}1} assignable to {nu}{sub as} (O{double bond}Ru{double bond}O) stretch. In CH{sub 2}Cl{sub 2}, it reacts with olefins to give epoxides and (Ru{sup IV}(OEP)(OH)){sub 2}O in quantitative yields. In alcohols (ROH), the epoxidation reactions give (Ru{sup IV}(OEP)O(ROH)), which readily dimerizes to (Ru{sup IV}(OEP)(OH)){sub 2}O in noncoordinating solvents. (Ru{sup IV}(OEP)O(ROH)) is paramagnetic with measured {mu}{sub eff} of 3.1 {mu}{sub B}. Its {sup 1}H NMR spectrum shows three broad singlets, the paramagnetic isotropic shifts of which vary inversely with temperature. The E{degree} for the (Ru{sup IV}(OEP)O(ROH))/(Ru{sup III}(OEP)O(ROH)){sup {minus}} couple in CH{sub 2}Cl{sub 2}/py (py = pyridine) is {minus}0.86 V vs Cp{sub 2}Fe{sup +/0}. In CH{sub 2}Cl{sub 2}/py solution, (Ru{sup IV}(OEP)O(ROH)) reacts with olefins to give (Ru{sup II}(OEP)(py){sub 2}) and epoxides.

High-valent ruthenium(IV) and -(VI) oxo complexes of octaethylporphyrin. Synthesis, spectroscopy, and reactivities

Chiral metal Schiff-base complexes [AlL(Et)], [TiLCl2], [VO(L)], [(FeL)2O], [CoL], [NiL], [CuL], [ZrLCl2], [RuL(CO)2] and trans-[RuL(NO)Cl]([H2L =(R,R)-(–)-N,N′-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine] were synthesized and characterized. The structures of [CoL] and trans-[RuL(NO)Cl] have been established by X-ray crystallography. The former has a pseudo-square-planar geometry with Co–N and Co–O distances of 1.88 and 1.84 A, respectively. The geometry around Ru in trans-[RuL(NO)Cl] is octahedral with Ru–N (nitrosyl) and Ru–Cl distances of 1.72(2) and 2.354(4)A, respectively, and Ru–N–O 175(2)°. The cyclic voltammograms for the metal Schiff-base complexes show reversible MIII–MII and ligand-centred oxidation couples. Treatment of NiL with AgBF4 afforded air-stable [NiL]BF4, which is formulated as a nickel(II) complex of the Schiff-base cation radical.

Wa-Hung Leung

Papers

Synthesis of Stereoregular Poly(phenylacetylene)s by Organorhodium Complexes in Aqueous Media

Oxidation chemistry of ruthenium-salen complexes

High-valent ruthenium(IV) and -(VI) oxo complexes of octaethylporphyrin. Synthesis, spectroscopy, and reactivities

Metal complexes of a chiral quadridentate Schiff base

Recent advances in the coordination chemistry of cerium(IV) complexes