AbstractThe cover picture shows the molecular structure of a dinuclear ruthenium complex, which was obtained by an arene displacement reaction in a microwave oven. Although microwave heating has been used extensively in organic synthesis, there are relatively few reports about its application in preparative organometallic chemistry. On p. 1003 ff, K. Severin et al. describe that [(arene)Ru(μ‐Cl)3RuCl(L?L′)] complexes with a diverse set of chelate ligands L?L′ are easily accessible by microwave heating. It should be mentioned, though, that the instrument used for their experiments was slightly more sophisticated than the one shown on the cover.

Complex Ru(CO)(2)(PPh3)(3), 1, is a suitable starting compound for the generation of N-heterocyclic carbene complexes of Ru(0). Although inonodentate NHCs are totally unrcactive toward 1, phosphine- or o1cfin-functionalized N-heterocyclic carbenes, as well as their irnidazolium precursors, react with 1 under chelation assistance where the phosphine or the olefin is acting as a directing group. Reactions of 1-mesityl-3-(2-dipjenylphosphinoeth-1-yl)imidazolium bromide [HL1a]Br-+(-), 1-mesityl-3-(2-diphenyl-phosphinoeth-1-yl)imidazolium tetrafluoroborate, [HL1a]+BF4-, and 1-(2,6-diisopropylphenyl)-3-(2-diphenylphosphinoeth-1-yl)imidazolium bromide [HL1b]+Br-, with 1 give cationic hydrido species formulated as [RuH{L*(1a,b)} (CO)(2)(PPh3)]X-+(-) [2a,b]X-+(-) (a, Ar = mesityl; b, Ar = 2,6 which abnormal activation (symbolized by the asterisk) at the C(4) position of the heterocycle has taken place to yield the bidentate ligands L*(1a,b). Deprotonation of [HL1b](+) with KO'Bu gives the corresponding NHC/phosphinc bidentate ligand, which reacts with I to give the chelated NHC/phosphine complex Ru {L-1b)(CO)(2)PPh3) (3b), the first analogue of Roper's complex incorporating an NHC moiety. The olefin-functionalized irnidazoliurn ligand 3-(bLit-3-ciiyl)-i-iiiesitylimid izoliLli-n bromide, [HL2a](+) Br-, reacts with 1via chelation-assisted C-H activation and H transfer to the olefin, giving Ru{Ar-(N2C3H2)CH2C(H)(CH2CH3)}(CO)(2)(PPh3)Br (4a). Deprotonation of [HL2a]Br-+(-) gives L-2a which reacts with 1 to give Ru{L-2a}(CO)(2)(PPh3) (5a). Its protonation with HBF4 at -80 degrees C gives a cationic NHC/olefin-hydrido complex, [RuH{L-2a} (CO)(2)(PPh3)]+BF4-, [6a]+BF4-. NMR data indicate the occurrence of a dynamic process involving a fast exchange between the hydride and the two terminal hydrogen atoms of the coordinated olefin, which can be rationalized in terms of the transient generation of an elusive higher energy NFIC/alkyl intermediate, [Ru{Ar(N2C3H2)CH2CH2C(H)CH3)}(CO)(2)-(PPh3)]+BF4-,[7a]+BF4-.At temperatures above-20 degrees C,[6a]'BF4 is irreversibly converted into the isomerized NHC/olefin-hydrido complex [RuH Ar(N2C3H,)CH2CH=C(H)CH3}(CO)(2)(PPh3)]+BF4-, [8a]+BF4-. Hereagain, NMR data remil a dynamic process involving fast exchange between the hydride and the terminal hydrogen atom of the coordinated olefin, now through the intermediacy of the elusive cationic NHC/alkyl species [Ru{Ar(N2C3H2)CH2C(H)CH2CH3)(CO)(2)(PPh3)]+BF4-, [9a]+BF4-. Although neither ofthe above unsaturated cationic alkyl interniediates [7a]' or [9a]' was observed, their occurrence could be inferred from trapping experiments.Indeed, the addition of [PPN]Cl to the above Mixture after equilibration at 25 degrees C leads to the formation of the chloride analogue of 4a. Protonation with HCl instead of HBF4 allows capture of the first elusive intermediate [7a](+) by the halide, which quenches the isornerization process and prornotes a migratory CO insertion yielding the NHC/alkyl derivative Ru{Ar(N2C3H2)CH2C(H)CH2CH3)C=O}(CO)(PPh3), 10a. The X-ray structure analyses for 4and 5 are included.

Microwave heating was employed to promote arene displacement in reactions of [{(p-cymene)RuCl2}(2)] or [{(1,3,5-C-6,H(3)iPr(3))RuCl2}(2)] with neutral chelate ligands L-L' [L-L': 1,1'-bis(diphenylphosphanyl)methane, 1,1'- bis(diphenylphosphanyl)ferrocene, (S)-BINAP, (S,S)-DIOP, N,N'-bis(2,4,6- trimethylphenyl)-1,2-ethanediylidenediamine], (R)-Ph-PHOX, and 3-(phenylsulfanylpropyl)diphenylphosphane. The reactions gave complexes of the general formula [(arene)Ru(mu-Cl)(3)- RuCl(L-L')] in good yield. The synthesis of [(p-cymene)Ru(mu-Cl)(3)RuCl{PPh2(CH2)(3)NH2} (22) was accomplished in two steps via the intermediate [{(p-cymene)RuCl2}(2){mu- PPh2(CH2)(3)-NH2}] (21). The structures of [(1,3,5-C(6)H(3)iPr(3))Ru(mu-Cl)(3)RuCl- (dppf)] (16), [(1,3,5-C(6)H(3)iPr(3))Ru(mu-Cl)(3)RuCl{(S)-BINAP]} (17), and [(p- cymene)Ru(mu-Cl)(3)RuCl(MesNCHCHNMes)] (18) were determined by single- crystal X-ray diffraction. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The complexes [(p-cymene)Ru(mu-Cl)(3)RuCl(C2H4)(PR3)] (PR3 = PPh3, Pn-Bu-3) were synthesized by reaction of [(p-cymene)RuCl(mu-Cl)](2) with the respective phosphine ligand in the presence of ethylene. Structurally related complexes containing the tricyclopentylphosphine (PCyp(3)) or the isobutylphobane ligand (phobane = 9-phosphabicyclo[3.3.1]nonane) were obtained by reaction of [(arene)RuCl(mu-Cl)](2) (arene = p-cymene, 1,3,5-i-Pr3C6H3) with 2 equiv of [(arene)RuCl2(PCyp(3))] or [(arene)RuCl2(isobutylphobane)] in the presence of ethylene. The structures of the dinuclear complexes [(p-cymene)Ru(mu-Cl)(3)RuCl-(C2H4)(PPh3)] and [(1,3,5-i-Pr3C6H3)Ru(mu-Cl)(3)RuCl(C2H4)(isobutylpliobane)] as well as of the mononuclear precursors [(p-cymene)RuCl2(isobutylphobane)], [(1,3,5-i-Pr3C6H3)RuCl2(isobutylphobane)], and [(p-cymene)RuCl2(PCyp(3))] were determined by single-crystal X-ray analyses. Kinetic analyses of the atom transfer radical addition reaction of CCl4 to styrene revealed that the catalytic activity of the dinuclear complexes was strongly dependent on the nature of the phosphine ligand but only slightly affected by the nature of the arene ligand. Addition of Mg to the reaction mixture was found to increase the lifetime of the catalyst significantly. With Mg as the cocatalyst, mixed-valence Ru(II)-Ru(III) complexes of the general formula [(arene)Ru(mu-Cl)(3)RuCl2(PR3)] were found to be equally potent catalyst precursors when compared to the Ru(II)-Ru(II) complexes [(arene)Ru(mu-Cl)(3)RuCl(C2H4)(PR3)].

The unusual reactivity of chelating phosphane-imidazolium salts MesImEtPPh(2)(+)Br(-), DIPP-ImEtPPh(2)(+)Br(-), and MesImEtPPh(2)(+)BF(4)(-) towards the low-oxidation-state iridium complex [Ir(COD)(mu-Cl)](2) was studied. In the absence of a base, the C-H insertion at the C5 position of the imidazolium ring was the only reaction that occurred, with no normal NHC observed, leading to hydridoiridium(III) complexes. This reactivity was independent of the nature of the imidazolium counteranion and of the substitution pattern of the aryl group. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The unique structural features and chemical stabilities of bis(phenyl) tetracarboxamidatodirhodium(III) are reported, and their electronic structures are mapped through XPS, electrochemical, and computational methods. Comparison with the structures of dirhodium(II,II) and dirhodium(II,III) oxidative precursors portrays the diphenyl dirhodium(III) compounds as two square-pyramidal rhodium units that have undergone conrotatory motion in order to optimize metal−ligand bonding. Axial phenyl ligands are severely distorted from their expected Rh−Rh−C linear array. XPS data for this series of dirhodium compounds are consistent with the absence of a rhodium−rhodium bond for the diphenyl dirhodium(III) compounds, and electrochemical measurement shows a single reversible Rh26+/Rh27+ redox couple. Notably, they exhibit high thermal stability, and Bronsted acid removal of carboxamidate ligands precedes the formation of benzene. The ability of a phenyl group to impart unusual stability to rhodium(III) compounds is exp...

The first unambiguous characterization of a stable dirhodium(III) paddlewheel complex 1 is reported. Complex 1 is prepared via the copper-catalyzed aerobic oxidation of 2 in 77% isolated yield. Comparison of the X-ray crystal structure, visible, and X-ray photoelectron spectroscopy of 1, 2, and 3 indicate a cleavage of the Rh−Rh bond in 1. The oxidation of 2 to 1 is proposed to occur through the intermediacy of 3 with the Cu(II)/Cu(I) couple with oxygen as a terminal oxidant and NaBPh4 as a phenyl transfer agent.

Five new, bifunctional imidazolium-thioether ligands of the general formula RS(CH2)(n)(imidazolium)+ArBr- (n = 2 or 3, R = Et or tBu, Ar = 2,4,6-trimethylphenyl or 2,6-diisopropylphenyl) have been synthesised in good overall yields by a general method and used as N-heterocyclic carbene precursors for complexation studies on various transition metals (Ni-II, Pd-II and Rh-I). Sulfur does not coordinate the nickel centre, whereas the two functional groups bind the palladium centre to form a dinuclear compound. Cationic rhodium(l) complexes have also been prepared and preliminary catalytic tests show that they have good activity for the hydrosilylation of ketones. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).

Two new zwitterionic nickel(II) complexes, bearing phosphine/imidazolium ligands, have been prepared. Their catalytic activity, and the activity of an analogous Ni(II) complex, previously described by us, has been evaluated with a range of aryl chlorides, an aryl bromide and arylmagnesium halides. The catalytic activity is related to the length of the tether between the carbene and phosphine moieties. Thus the catalysts possessing a six-membered metallacycle are more active than that having a seven-membered metallacycle. Changing from a mesityl (Mes) to a 2,6-diisopropylphenyl (DIP) on the imidazole ring does not strongly influence the activity. The three complexes show moderate to very good activities with most substrates, and enhanced selectivities compared to previously published Ni(II)/N-heterocyclic carbene systems. The low activity observed with 4-chlorobenzotrifluoride seems to be related to the presence of a phosphine on the ligands. (c) 2006 Elsevier B.V. All rights reserved.

Zwitterionic Ni(II) complexes of type NiX3(NCN+), (NCN+ = 1-(2-diphenylphosphinoethyl)-3-(2,4,6-trimethylphenyl)imidazolium and X = Cl, 6; Br, 7), have been prepared by addition of NCN+ bromide (1a) or tetrafluoroborate (1b) to NiX2L, and characterised by X-ray crystallography. They have been used as catalytic precursors in the Kumada-Corriu coupling reaction between phenylmagnesium chloride and 4-chloroanisole, yielding high catalytic activities. Stoechiometric deprotonation investigations did not provide clear evidence for the formation of coordinated carbene species. (c) 2005 Elsevier B.V. All rights reserved.