Wa-Hung Leung

Molecular sieves promoted regioselective ring opening of N-tosylaziridines catalyzed by imidochromium complexes

Cr(NBut)Cl3(dme) catalyzes ring-opening of N-tosylaziridines with trimethylsilyl azide; the yield and selectivity of which was found to be enhanced by molecular sieves.

Tetravalent Titanium, Zirconium, and Cerium Oxo and Peroxo Complexes Containing an Imidodiphosphinate Ligand

Dinuclear Ti(IV), Zr(IV), and Ce(IV) oxo and peroxo complexes containing the imidodiphosphinate ligand [N(i-Pr(2)PO)(2)](-) have been synthesized and structurally characterized. Treatment of Ti(O-i-Pr)(2)Cl(2) with KN(i-Pr(2)PO)(2) afforded the Ti(IV) di-μ-oxo complex [Ti{N(i-Pr(2)PO)(2)}(2)](2)(μ-O)(2) (1) that reacted with 35% H(2)O(2) to give the peroxo complex Ti[N(i-Pr(2)PO)(2)](2)(η(2)-O(2)) (2). Treatment of HN(i-Pr(2)PO)(2) with Zr(O-t-Bu)(4) and Ce(2)(O-i-Pr)(8)(i-PrOH)(2) afforded the di-μ-peroxo-bridged dimers [M{N(i-Pr(2)PO)(2)}(2)](2)(μ-O(2))(2) [M = Zr (3), Ce (4)]. 4 was also obtained from the reaction of Ce[N(i-Pr(2)PO)(2)](3) with 35% H(2)O(2). Treatment of (Et(4)N)(2)[CeCl(6)] with 3 equiv of KN(i-Pr(2)PO)(2) afforded Ce[N(i-Pr(2)PO)(2)](3)Cl (5). Reaction of (Et(4)N)(2)[CeCl(6)] with 2 equiv of KN(i-Pr(2)PO)(2) in acetonitrile, followed by treatment with Ag(2)O, afforded the μ-oxo-bridged complex [Ce{N(i-Pr(2)PO)(2)}Cl](2)[μ-N(i-Pr(2)PO)(2)](2)(μ-O) (6). 6 undergoes ligand redistribution in CH(2)Cl(2) in air to give 5. The solid-state structures of [K(2){N(i-Pr(2)PO)(2)}(2)(H(2)O)(8)](n) and complexes 1-6 have been determined.

A Tetravalent Cerium Complex Containing a CeO Bond

Whereas terminal oxo complexes of transition and actinide elements are well documented, analogous lanthanide complexes have not been reported to date. Herein, we report the synthesis and structure of a cerium(IV) oxo complex, [CeO(LOEt )2 (H2 O)]⋅MeC(O)NH2 (1; LOEt (-) =[Co(η(5) -C5 H5 ){P(O)(OEt)2 }3 ](-) ), featuring a short CeO bond (1.857(3) Å). DFT calculations indicate that the hydrogen bond to cocrystallized acetamide plays a key role in stabilizing the CeO moiety of 1 in the solid state. Complex 1 exhibits oxidizing and nucleophilic reactivity.

Kinetics of C–H bond and alkene oxidation by trans-dioxoruthenium(VI) porphyrins

A. Series of [RuVILO2] complexes (H2L =Para-substituted tetraphenylporphyrins) have been synthesised and characterized, and the kinetics and mechanism of oxidation of the C–H bond and alkenes investigated. The complexes were selective towards tertiary C–H bonds in saturated alkanes but were almost inactive towards secondary C–H bonds. However, they were reactive towards aromatic hydrocarbons and the second-order rate constants (k2) for the oxidation of ethylbenzene and cumene by [Ru(tpp)O2](tpp = 5, 10, 15, 20-tetraphenylporphyrinate) were 2.21 × 10–4 and 3.16 × 10–4dm3 mol–1 s–1 respectively. A kinetic isotope effect (KH/KD) of 11.7 was found for the allylic oxidation of cyclohexene by [Ru(tpp)O2]. The major organic products of the oxidation of alkenes in CH2Cl2–MeOH mixtures were epoxides and [Ru(tpp)O2] gave a monomeric product formulated as [RuIV(tpp)O]·EtOH. or [RuIV(tpp)(OH)2·]EtOH. Similar reactions with [RuVI(oep)O2](oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate) gave [{RuVI(oep)(OH)}2O] in non-co-ordinating solvents. The observed rate law for alkene oxidation was rate =K2[RuVI][alkene]. There exists an almost linerar free-energy relationship between log k2 and E½(one-electron oxidation potentials of alkenes) with slope =–1.1 V–1 for the [Ru(tpp)O2] system. Activation parameters have been determined for the oxidation of styrene, norbornene and cyclooctene by [RuVILO2]. Non-linear and U-shaped Hammett plots were observed for the oxidation of substituted styrenes. The mechanism of alkene oxidation is proposed to involve a continum of transition states, the structures of which may change and be stabilized by defferent substituents.

Heteroselenometallic cluster compounds with tetraselenometalates

Abstract The coordination cluster compounds of tetraselenomolybdate and tetraselenotungstate anions with metal ions are reviewed. New heteroselenometallic cluster compounds are primarily of interest regarding their structures and reactivities, and their potential as non-linear optical (NLO) materials. This article focuses from a synthetic and structural point of view on coordination cluster compounds with tetraseleno-molybdate and -tungstate anions as polydentate ligands. A comprehensive survey is presented of the heteroselenometallic clusters known to date according to the number of center [MSe 4 ] 2− (M=Mo, W) anions. Representative spectroscopic and NLO properties of these clusters are also discussed.

Synthesis and reactivity of dihydroxoruthenium(IV) complex of tetramesitylporphyrin. Aerobic epoxidation of norbornene by ruthenium porphyrins

Abstract Treatment of Ru(TMP)(CO) with m-CPBA in CH2Cl2/EtOH afforded Ru (TMP)(OH)2, isolated as air-stable violet crystals. Ru(TMP)(OH)2 in paramagnetic (μeff ca 2.7 B.M.) and displays broad 1H NMR signals with paramagnetic isotropic shifts. The IR spectrum shows a band at 760 cm−1 assignable to the RuO stretch. Ru(TMP)(OH)2 is capable of catalysing aerobic epoxidation of alkenes under mild conditions.

Low-spin iron(III) complexes of a tetradentate bis-amide ligand and X-ray crystal structure of trans-[Fe(bpc)(1-MeIm)2]ClO4 (H2bpc=4, 5-dichloro-1, 2-bis(2-pyridinecarboxamido)benzene; 1-MeIm=1-methylimidazole)

A series of low-spin iron(III) complexes [Fe(bpc)(L) 2 ] + (H 2 bpc=4,5-dichloro-1,2-bis(2-pyridinecarboxamido)- benzene; LBu 3 P, Im, 1-MeIm, t Bupy) have been synthesized. These iron complexes display reversible one-electron oxidation and reduction couples. The stable one-electron-oxidized species [Fe(bpc)(Bu 3 P) 2 ] 2+ has been generated electrochemically. The complex trans -[Fe(bpc)(1-MeIm) 2 ](ClO 4 ) has been characterized by X-ray crystallography: space group P ; a =8.425(1), b =9.512(1), c =18.413(19) A; α=96.91(4), β=95.83(4), γ=90.44(1)°; V =1457(2) A 3 ; Z =2.

Organoimido complexes as a new class of Lewis acid catalysts for regioselective ring-opening of epoxides

Abstract Organoimido complexes of Group-VI transition metals were found to catalyze ring-opening of epoxides by trimethylsilyl azide and amines with good regioselectivities.

Ruthenium complexes with tetraphenylimidodiphosphinate: Syntheses, structures, and applications to catalytic organic oxidation

Treatment of Ru(PPh3)3Cl2 with K(tpip) (tpip(-)=[N(Ph2PO)2](-)) afforded Ru(tpip)(PPh3)2Cl (1), which reacted with 4- t-Bu-C6H4CN, SO2(g), and NH 3(g) to give Ru(tpip)(PPh3)2Cl(4- t-BuC6H4CN) (2), Ru(tpip)(PPh3)2Cl(SO2) (3), and fac-[Ru(NH3)3(PPh3)2Cl][tpip] (4), respectively. Reaction of [Ru(CO)2Cl2] x with K(tpip) in refluxing tetrahydrofuran (THF) led to isolation of the K/Ru bimetallic compound K 2Ru2(tpip)4(CO)4Cl2 (5). Photolysis of cis-Ru(tpip) 2(NO)Cl in MeCN and wet CH 2Cl 2 afforded cis-Ru(tpip) 2(MeCN)Cl ( 6) and cis-Ru(tpip)2(H2O)Cl (7), respectively. Refluxing 6 in neat THF yielded Ru(tpip) 2(THF)Cl (8). Treatment of Ru(CHR)Cl2(PCy3)2 (Cy=cyclohexyl) with [Ag(tpip)] 4 afforded cis-Ru(tpip)2(CHR)(PCy3) [R=Ph (9), OEt (10)]. Complex 9 is capable of catalyzing oxidation of alcohols and olefins with N-methylmorpholine N-oxide and iodosylbenzene, respectively. The crystal structures of 2-7 and 9 were determined.

Formation of a dinuclear imido complex from the reaction of a ruthenium(VI) nitride with a ruthenium(II) hydride.

The treatment of [Ru(L(OEt))(N)Cl(2)] (1; L(OEt)(-) = [Co(η(5)-C(5)H(5)){P(O)(OEt)(2)}(3)](-)) with Et(3)SiH affords [Ru(L(OEt))Cl(2)(NH(3))] (2), whereas that with [Ru(L(OEt))(H)(CO)(PPh(3))] (3) gives the dinuclear imido complex [(L(OEt))Cl(2)Ru(μ-NH)Ru(CO)(PPh(3))(L(OEt))] (4). The imido group in 4 binds to the two ruthenium atoms unsymmetrically with Ru-N distances of 1.818(6) and 1.952(6) Å. The reaction between 1 and 3 at 25 °C in a toluene solution is first order in both complexes with a second-order rate constant determined to be (7.2 ± 0.4) × 10(-5) M(-1) s(-1).