Wing-Chi Cheng

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.

tert-Butylhydroperoxide epoxidation of alkenes catalysed by ruthenium complex of 1,4,7-trimethyl-1,4,7-triazacyclononane

Abstract The complex [Ru III (Me 3 tacn)(OH 2 ) 2 (CF 3 CO 2 )](CF 3 CO 2 ) 2 (Me 3 tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, CF 3 CO 2 = trifluoroacetate) is an effective catalyst for the oxidation of organic substrates by tert-butylhydroperoxide. It exhibits high activity and selectivity for alkene epoxidation under mild conditions. A heterolytic OO cleavage mechanism and an alkylperoxoruthenium(VI) active intermediate are suggested for the catalytic alkene epoxidation.

SYNTHESIS AND REACTIVITY OF N,N‘-BIS O-(DIPHENYLPHOSPHINO)BENZYLIDENE-2,2‘-DIIMINO-1,1‘-BINAPHTHYLENE (BINAP-P2N2) - CRYSTAL-STRUCTURE OF AG(BINAP-P2N2) BF4

Abstract The condensation of a racemic mixture of 2,2′-diamino-1,1′-binaphthylene with two equivalents of o-(diphenylphosphino)benzaldehyde gives a racemic mixture of N,N′-bis[o-(diphenylphosphino)benzylidene-2,2′-diimino-1,1′-binaphthylene (Binap-P2N2) (I) in good yield. The coordination behaviour of I towards CuI and AgI has been explored. The interaction of I with one equivalent of Cu(Ph3P)2Br and [Cu(CH3CN)4][PF6] in CH2Cl2 gives Cu(Binap-P2N2)Br(II) and [Cu(Binap-P2N2)][PF6] (III) in 60% and 74% yield, respectively. In II the Binap-P2N2 ligand acts as a tridentate chelating agent, with the two phosphino groups and one of the two imino groups coordinated to the Cu, whereas in III it acts in tetradentate chelating mode. A variable temperature 31P{1H} NMR study of II reveals that the coordinated and the uncoordinated imino groups of the tridentate Binap-P2N2 ligand undergo a facile intramolecular exchange even at −55°C. The interaction of I with one equivalent of AgBF4 in CH2Cl2 gives [Ag(Binap-P2N2)][BF4] (IV) in 79% yield. In IV, the Binap-P2N2 ligand acts as a tridentate chelating agent, with the two phosphino groups and one of the two imino groups coordinated to the Ag. The structure of IV has been established by an X-ray diffraction study. The distance between Ag and N(2) is 2.56(1) A, and the non-bonding distance between Ag and N(1) is > 3.0 A.

A novel cis-dioxoruthenium(VI) complex of N,N′,N″-trimethyl-1,4,7-triazacyclononane (Me3tacn) for organic oxidation

The X-ray structure of [Ru(Me3tacn)O2(CF3CO2)]+ shows a cis-dioxoruthenium(VI) unit with the RuO distances and O–Ru–O angle being 1.717(9) and 1.715(9)A and 118.3(4)° respectively, this RuVI complex catalyses alkene epoxidation and alkane hydroxylation by PhIO and ButOOH.

Synthesis, redox properties and reactivities of ruthenium(II) complexes of 1,1′-biisoquinoline (BIQN) and X-ray crystal structure of [RuII(terpy)(BIQN)(Cl)]ClO4 (terpy = 2,2′:6′, 2″-terpyridine)

Abstract The syntheses of the complexes [RuII(terpy)(BIQN)Cl]ClO4 (1) and [RuII (terpy)(BIQN)(OH2)](ClO4)2 (2) are described. The structure of 1 has been established by X-ray crystallography. The dihedral angle between the two isoquinoline rings is 37.4°. In aqueous solution, [RuII(terpy)(BIQN)(OH2)](ClO4)2 shows two reversible/quasi-reversible oxidation couples assigned to the oxidation of ruthenium(II) to ruthenium(III) and ruthenium(III) to ruthenium(IV). [RuII(terpy)(BIQN)(OH2)](ClO4)2 is an active catalyst for the oxidation of alkenes by PhIO.

Enantioselective epoxidation of unfunctionalized alkenes by a chiral monooxoruthenium(IV) complex [RuL(bpy)O]2+{L = 2,6-bis[(4S,7R)-7,8,8-trimethyl-4,5,6,7-tetrahydro-4,7-methanoindazol-2-yl]pyridine; bpy = 2,2′-bipyridine}

A new chiral monooxoruthenium(IV) complex containing 2,6-bis[(4S, 7R)-7,8,8-trimethyl-4,5,6,7-tetrahydro-4,7-methanoindazol-2-yl]pyridine and 2,2′-bipyridine ligands is prepared and the X-ray crystal structure of its RuII–OH2 precusor determined; this RuIVO complex catalyses epoxidation of Unfunctionalized alkenes with promising enantioselectivity.

Preparation and reactivities of chiral manganese(III) and copper(II) complexes of binaphthyl Schiff bases

A series of chiral Schiff bases, 2,2′-bis(3-R1-5-R2-2-hydroxybenzylideneamino)-1,1′-binaphthyl H2L (R2= Cl, R1= Cl, Me, Et or NO2; R2= Me, R1= But; R2= NO2, R1= H, Me, Et, Pri, But or Cl), and their complexes [CuL1]1 and [Mn2L12(OMe)2]2(R1= R2= Cl) have been prepared. The crystal structure of the racemic form of 1 has been determined. Complex 1 is an active catalyst for the oxidation of alkenes by tert-butyl hydroperoxide. On the contrary, 2 is inert towards alkene epoxidation by PhIO. However, upon mixing Mn(O2CMe)3·xH2O and H2L in acetonitrile a green solution was obtained which could effect asymmetric epoxidation of alkenes by PhIO. The effects of the steric and electronic effects of the R1 and R2 substituents, temperature, and the addition of donors like N-methyl- and 2-methyl-imidazole and pyridine N-oxide on the catalytic activity of the MnIII+(S)-H2L systems towards alkene epoxidation have been investigated. When R1= Et and R2= NO2 the best enantiomeric excesses of 58 and 43% were found for epoxidation of cis-β-methylstyrene to (1S,2R)-cis-β-methylstyrene oxide and 4-chlorostyrene to 4-(S)-chlorostyrene oxide respectively.

Synthesis, characterization and electrochemistry of phenylimido-rhenium(V) complex of 1,4,7-triazacyclononane (TACN)

Abstract The complex [Re(NPh)(OH)(PPh3)(tacn)]2+ (1) was prepared by reacting [Re(NPh)Cl3(PPh3)2] with tacn (tacn = 1,4,7-triazacyclononane) in CH2Cl2 and has been characterized by X-ray crystal analysis. The ReNPh distance is 1.706(10) A and the ReNPh angle is 170.2(9)°. In acetonitrile, the cyclic voltammogram of 1 shows an irreversible reduction wave at −0.77 V assignable to the reduction of rhenium(V) to rhenium(IV). Complex 1 catalyses alkene oxidation by PhIO.

Synthesis, characterization and crystal structures of some half-sandwich ruthenium(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane containing π-acidic ancillary ligands

The synthesis of a series of ruthenium(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane L of type [RuL(X)Y(Z)]+ containing H, O2CCF3, CO, PPh3, dppe [1,2-bis(diphenylphosphino)ethane] or 2,6-Me2C6H3NC as auxiliary ligands are described where X = Y = CO, Z = Cl 1; X, Y = dppe, Z = Cl 2; X, Y = dppe, Z = H 3; X = CO, Y = PPh3, Z = H 4; X = Y = 2,6-Me2C6H3NC, Z = O2CCF35. All complexes were characterized by spectroscopic methods. The crystal structures of 1 and 4 as PF6– salts have been determined. The two CO groups in complex 1 are in cis-fashion with a OC–Ru–CO angle of 90.1(3)° and the Ru–C distances are 1.850(6) and 1.893(6)A. Complex 4 features one of the few ruthenium complexes containing three different piano-stool ligands, namely, CO, PPh3 and H. The measured Ru–CO and Ru–H distances in 4 are 1.785(9) and 1.54(9)A respectively.

Preparation and crystal structures of cationic dienehydrido and dienyl ruthenium complexes containing N,N′,N″-trimethyl-1,4,7-triazacyclononane

The reaction between [{Ru(cod)Cl2}n](cod = cycloocta-1,5-diene) and N,N′,N″-trimethyl-1,4,7-triazacyclononane (tacn) in ethanol–water gave [Ru(tacn)(1,2,5,6-η-cod)H]ClO41. When tert-butyl alcohol was used as the solvent, [Ru(tacn)(1,2,3,4,5-η-C8H11)]ClO42 was obtained. The Ru-H moiety in 1 is characterized by a 1H NMR signal at δ–6.11 and a ν(Ru–H) stretch at 2040 Cm–1. Crystal structure analysis shows that the co-ordinated cod of 1 is in the tub form, whereas complex 2 has an η5-cyclooctadienyl ligand.