Chung-Kwong Poon

Chiral ruthenium(IV)-oxo complexes. Structure, reactivities of [Ru(terpy)(N∩N)O]2+ (N∩N = N,N,N′,N′-tetramethyl-1,2-diaminocyclohexane) and [Ru(Me3tacn)(cbpy)O]2+ (cbpy = (−)-3,3′-[(4S-trans)-1,3-dioxolane-4,5-dimethyl]-2,2′-bipyridine)☆

Abstract The Complexes [RuIV(terpy)(cxhn)O](ClO4)2 (cxhn = N,N,N′,N′-tetramethyl-1,2-diaminocyclohexane, terpy = 2,2′:6′,2′′(terpyridine) and RunIV(Me3tacn)(cbpy)O](ClO4)2 (cbpy = (−)-3,3′-[(4S-trans)-1,3-dioxolane-4,5-dimethyl]-2,2′-bipyridine and Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) have been prepared and crystal structures of [RuIV(terpy)(cxhn)O](ClO4)2 and [RuII(Me3tacn)(3,3′Me2bpy)(OH2)](ClO4)2 have been determined [RuIV(terpy)(cxhn)O](ClO4)2 H2O, C25H35Cl2N5O10Ru, Mr=737.68, space group P2 1 n , monoclinic, a = 8.215(5), b = 14.650(7), c = 24.261(10) A , β = 94 78(4)°, Z = 4 , [RuII(Me3tacn)(3,3′-Me2bpy)(OH2)](ClO4)2, C21H35C12N5O9Ru, Mr=673.52, space group P2 1 n , monoclinic, a = 8.463(1), b = 10.751(1), c = 30.192(3) A , β = 91.77(1)°, Z = 4 . The RuO distance in [RuIV(terpy)(cxhn)O](ClO4)2 is 1.827(14) A. All the ruthenium-oxo complexes react with alkenes to give the corresponding epoxides. Stoichiometric oxidation of styrene and 4-chlorostyrene by [RuIV(terpy)(1R,2R-cxhn)O](ClO4)2 gave the corresponding epoxide with no enantiomeric excess. Using [RuIV(Me3tacn)(cbpy)O](ClO4)2, a 9% enantiomeric excess of R-styrene oxide and R-4-chlorostyrene oxide were found in the oxidation of both styrene and 4-chlorostyrene, respectively.

Novel luminescent platinum(II) complexes. Photophysics and photochemistry of Pt(5,5′-Me2bpy)(CN)2(5,5′-Me2bpy=5,5′-dimethyl-2,2′-bipyridine)

The Pt(5,5′-Me2bpy)(CN)2 complex (5,5′-Me2bpy = 5,5′-dimethyl-2,2′-bipyridine) displays intense photoluminescence in fluid solution (emission maximum, 502 nm; τ0, 6.3 µs) at room temperature; the excited ππ* triplet of Pt(5,5′-Me2bpy)(CN)2 is a powerful one-electron oxidant (E∘, ∼1.0V) and reductant (E∘≤–1.5V vs. AgNO3/Ag) which undergoes oxidative and reductive quenching with inorganic and organic substrates.

The infrared spectra of some cis- and trans- isomers of octahedral cobalt(III) complexes with a cyclic quadridentate secondary amine☆

Abstract The infrared spectra of 22 different complex cations with a variety of anions of mononuclear cobalt(III) and binuclear peroxo-bridge cobalt(III) complexes with 1,4,8,11-tetraazacyclotetradecane (cyclam) have been examined. Consistent differences between the spectra of cis- and trans- isomers have been found in the region 800–910 cm−1. Deuteration studies suggest that the vibrational modes of both the secondary amine and methylene groups which occur in this region are useful in differentiating between the two geometric isomers of cobalt(III) cyclam complexes.

A simple synthetic route to N,N′-dialkyl-2,11-diaza[3.3](2,6)-pyridinophanes. Crystal structures of N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane and its copper(II) complex

Abstract Reaction of 2,6-bis9bromomethyl)pyridine with primary amines gave the 12-membered N,N′-dialkyl-2,11-diaza[3.3](2,6)pyridinophanes. The structures of N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (4) and its copper(II) derivative [Cu(4)Cl2] (7) have been characterized by X-ray crystal analysis. The average axial CuN (tertiary amine) distance of 2.490 A in 7 is appreciably longer than the related value of 2.347 A in Cu(6)Cl2·H2O.4 In 4, the two planar pyridyl rings are not in the same plane, but roughly parallel and the 12 atoms of the macrocyclic ring constitute a syn chair-chair conformation. In complex 7, the copper(II) ion adopts a distorted octahedral geometry, in which the tertiary amine nitrogen atoms span axial positions approximately normal to the square plane formed by the two pyridine nitrogens and the chloro ligands. The average Cu—N (tertiary amine), Cu—N(pyridine) and Cu—Cl distances are 2.49(2), 2.03(2) and 2.287(7) A, respectively.

Oxidation of organic substrates catalysed by trans-[RuIII(phen)2(OH)(OH2)][ClO4]2 and trans-[RuIII(bpy)2(OH)(OH2)][ClO4]2(phen = 1,10-phenanthroline; bpy = 2,2′-bipyridine)

trans-[RuIII(phen)2(OH)(OH2)][ClO 4]2 and trans-[RuIII(bpy)2(OH)(OH2)][ClO4]2(bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline) are active catalysts for the PhlO and aerobic oxidation of organic substrates; a modified electrode, through adsorption oftrans-[RuIII(phen)2(OH)(OH2)][ClO 4]2, was active in the oxidation of alcohol to give aldehyde (or ketone).

Ruthenium catalysed oxidation of alkanes with alkylhydroperoxides

The cis-[RuII(L)2(OH2)2]2+ complexes (L = substituted 2,2′-bipyridines or 1,10-phenanthrolines) catalyse oxidation of saturated hydrocarbons to alcohols and ketones by t-butylhydroperoxide; the low values of kinetic isotope effect (kH/kD= 3.5 for cyclohexane) and tertiary of secondary C–H bond relative reactivities (ktert/ksecca. 6.5 for adamantane) are in a range expected for hydrogen atom abstraction by radical species.

Spectroscopy and redox properties of the luminescent excited state of [Au2(dppm)2]2+(dppm = Ph2PCH2PPh2)

The electronic absorption spectrum of [Au2(dppm)2]2+[dppm = bis(diphenylphosphino)methane] in acetonitrile exhibits an absorption band at 290 nm, attributable to a pσâ†�dσ* transition. A much weaker band in the region 300–370 nm is assigned to a pσâ†�dδ* transition. Excitation of [Au2(dppm)2]2+ in degassed acetonitrile at 310–390 nm at room temperature results in phosphorescence centred at 575 nm, which is most likely to be derived from the 3B1u[(dδ*)1(pσ)1] state. The phosphorescence of [Au2(dppm)2]2+* is found to be quenched by a number of electron acceptors and donors, as well as energy-transfer acceptors. The powerful reducing nature of [Au2(dppm)2]2+* is revealed by its excited-state redox potential E°[Au2(dppm)23+/2+*] of –1.6(1) V vs. a saturated sodium chloride calomel electrode (s.s.c.e.) which was determined through studies of quenching by a series of pyridinium acceptors.

Synthesis, reactivities and electrochemistry of trans-dioxoruthenium(VI) complexes of π-aromatic diimines

The synthesis and electrochemistry of trans-[RuIII(L)2(OH)(H2O)][CIO4]2[L = 1,10-phenanthroline (phen) or 5,5′-dimethyl-2,2′-bipyridine(dmbipy)] are described. Oxidation of trans-[RuIII(L)2(OH)(H2O)]2+ by CeIV in water gave trans-[RuVI(L)2O2]2+ which were isolated as the yellow perchlorate salts. The complex trans-[RuVI(dmbipy)2O2][CIO4]2 is a powerful oxidant with E°(RuVI–RuIV)= 1.0 V vs. saturated calomel electrode at pH 1.0. In acetonitrile or acetone, it oxidizes alcohols to ketones/aldehydes, tetrahydrofuran to γ-butyrolactone, alkenes to epoxides and saturated or aromatic hydrocarbons to alcohols/ketones. Oxidation of saturated alkanes occurs preferentially at the tertiary C–H bond. In the presence of CCl4, cyclohexane is oxidized to cyclohexyl chloride instead of cyclohexanone. The mechanisms of alcohol and cyclohexane oxidation were investigated by kinetic experiments and by isotope labelling studies.

Syntheses, electrochemistry and reactivities of pyridine amide complexes of chromium(III) and manganese(III)

Reactions of anhydrous CrCl3 with H2bpb and H2bpc [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; H2bpc = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene] in dimethylformamide and manganese(III) acetate with H2bpc in methanol, yielded the respective [CrIII(bpb)Cl]·xH2O, [CrIII(bpc)Cl]·H2O and [MnIII(bpc)(O2CMe)] complexes. The electrochemistry of the chromium(III) amide complexes has been studied by cyclic voltammetry. They exhibit reversible oxidation couples with E° values ranging from 0.28 to 0.80 V vs. ferrocenium–ferrocene. Except for [CrIII(bpb)(CN)2]– which has a quasireversible reduction couple at –1.97 V, the electrochemical reductions are irreversible. The complexes [CrIII(bpb)(H2O)2]ClO4, [CrIII(bpb)Cl(MeOH)] and [MnIII(bpc)(O2CMe)] have been shown to catalyse olefin epoxidation by iodosobenzene. With [Mn(bpc)(O2CMe)], catalytic oxidation of alkanes by PhIO has also been observed. An oxygen-rebound mechanism involving a MnvO or a CrvO intermediate is proposed for the PhIO oxidation reactions.

Synthesis and characterization of a ruthenyl (RuIVO) complex with a saturated macrocyclic tetramine

The synthesis and characteriaztion of a novel mono-oxo-ruthenium(IV)(ruthenyl) species of 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (tmc)are described; this ruthenyl cation, together with another high-valent RuIV–NCS species of tmc, can also be generated electrochemically from trans-[Ru(tmc)Cl2]+.