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Rhodium(I), tungsten(0), and molybdenum(0) carbonyl complexes of the N-heterocyclic-carbene-phosphinidene adducts IPr ·PR [ 1a, R = H; 1b, R = Ph; 1c, R = Mes; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene; Mes = 2,4,6-trimethylphenyl] were prepared. The reaction of 1b with [Rh(µ-Cl)(CO)2]2 afforded the dicarbonyl rhodium(I) complex cis-[(IPr ·PPh)RhCl(CO)2] ( 2) as the major product together with the tetranuclear complex [{µ-(IPr ·PPh)}2Rh4(µ-Cl)4(CO)4] ( 3). The latter was characterized by X-ray diffraction analysis. The tungsten pentacarbonyl complexes [(IPr ·PR)W(CO)5] ( 4a, R = H; 4b, R = Ph; 4c, R = Mes) were isolated from the reactions of 1a- 1c with [(Me3N)W(CO)5], whereas the reactions of 1a and 1b with [(thf)Mo(CO)5] (thf = tetrahydrofuran) gave the corresponding molybdenum complexes [(IPr ·PR)Mo(CO)5] ( 5a, R = H; 5b, R = Ph). The molecular structures of the five carbonyl complexes were established by X-ray diffraction analyses. The IR spectroscopic analysis of the CO stretching frequencies of the carbonyl complexes 2, 4, and 5 revealed the strong electron-donating abilities of the phosphorus(I) ligands. [ABSTRACT FROM AUTHOR]

Dehydrogenative oxidation of amines is a relevant process in metal-mediated catalysis, with the amines being either substrates or ligands. Transformation of amine- into imine-type ligands in the coordination sphere of a transition metal can be an important catalyst activation process. The behaviour of secondary pyridin-2-ylmethanamine (pma) ligands in the corresponding rhodium and iridium complexes upon N H deprotonation varies, depending on a number of factors. In this paper the behaviour of the Me-pma ligand [Me-pma = N-methyl-1-(pyridin-2-yl)methanamine] bound to [Rh(cod)]+ and [Ir(cod)]+ was studied. Whereas the iridium amido complex could be obtained upon N H deprotonation, the rhodium complex instantaneously disproportionated into a free pma ligand and an unusual dinuclear complex, adopting a structure with two RhI metal centres hosted by a dianionic (pma-2 H)2- ligand, and with the ligand coordinating to Rh2 as an 'aza-allyl' fragment. The study gives further proof for the effect of pyridine ligation on the previously observed charge-transfer from the ligand to the metal. Furthermore, the catalytic activity of both the Ir and the Rh species with Me-pma in carbene carbonylation reactions to generate ketenes was studied. [ABSTRACT FROM AUTHOR]

Rhodium(I) carbenes were generated from propargylic alcohol derivatives as the result of a dehydrative indole annulation. Depending on the choice of the electron-withdrawing group on the aniline nitrogen nucleophile, either a cyclopropanation product or dimerization product was obtained chemoselectively. Intramolecular hydroamidation occurred for the same type of propargylic alcohol derivatives when other transition-metal catalysts were employed. [ABSTRACT FROM AUTHOR]

Using a general synthetic procedure employing readily accessed terminal alkene-functionalized pro-ligands and macrocyclization by ring-closing olefin metathesis, rhodium carbonyl complexes have been prepared that contain lutidine (1a; n = 1) and pyridine (1b; n = 0) derived tridentate CNC macrocycles with dodecamethylene spacers. In solution, 1a shows temperature-invariant time-averaged C2 symmetry by ¹H NMR spectroscopy (CD2Cl2, 500 MHz), whereas in the solid-state, two polymorphs can be obtained showing different conformations of the alkyl spacer about the metal-carbonyl bond (asymmetric and symmetric). In contrast, time-averaged motion of alkyl spacer in 1b can be halted by cooling below 225 K (CD2Cl2, 500 MHz), and the complex crystallizes as a dimer with an interesting unsupported Rh···Rh bonding interaction (3.2758(6) Å). Oxidative addition reactions of 1a and 1b, using MeI and PhICl2, have been studied in situ by ¹H NMR spectroscopy, although pure Rh(III) adducts can be ultimately isolated only with the pyridine-based macrocyclic ligand. The lutidine backbone of 1a can be deprotonated by addition of K[N(SiMe3)2], and the resulting neutral dearomatized complex (5) has been fully characterized in solution, by variable-temperature ¹H NMR spectroscopy, and in the solid state, by X-ray diffraction. [ABSTRACT FROM AUTHOR]

Rhodium(I) complexes bearing amide-functionalised NHC ligands were synthesized in high yields through various synthetic routes and from different metal precursors, showing the versatility of such systems. By changing the ancillary ligands on the rhodium from cyclooctadiene to carbonyls the coordination behaviour of the NHC-amide ligand could be influenced. When a more basic precursor was employed for complexation, bidentate behaviour with the amide in an anionic mode was observed. All reported complexes are synthesized in high yields and under ambient conditions, which shows their robustness. The monodentate rhodium(I) biscarbonyl NHC complexes were shown to be able to activate iodomethane. [ABSTRACT FROM AUTHOR]

Herein we report robust methods for the preparation and full characterisation of a range of Ir(I) and Rh(I) fluoride and bifluoride complexes using N-heterocyclic carbenes (NHCs) as ancillary ligands. The processes that link the fluoride and the bifluoride species are investigated and reports of the first Ir-bifluoride and Ir(I)-NHC and Rh(I)-NHC trifluoromethyl complexes are revealed. [ABSTRACT FROM AUTHOR]

Copper(I) complexes with phenanthro-annulated N-heterocyclic carbene ligands were prepared by reaction of imidazolium salts with copper(I) oxide. Transmetalation of the copper complexes with [RhCl(cod)]2 in usual solvents like CH2Cl2 led to an equilibrium between the reactants and the products. For rhodium complexes 4 and 5 this equilibrium could be shifted to the product side by carrying out the reaction in acetonitrile. The ester functionalized rhodium complex 6 was prepared in a two phase mixture of chloroform and aqueous CaCl2 starting from copper complex 3c. The rhodium complexes were characterized by NMR and X-ray measurements. [ABSTRACT FROM AUTHOR]

The N-heterocyclic carbene NHC/thione ligand precursors 1-[(3-R-2-thioxo-2 H-imidazol-1-yl)methyl]-3-R-2 H-imidazol-2-ium hexafluorophosphate, [HCSR]PF6 (R = methyl, benzyl) have been prepared and used in the synthesis of the complexes [Rh(CSR)(cod)][PF6] (R = methyl, benzyl; cod = 1,5-cyclooctadiene). The coordination and structural features of the novel ditopic NHC/thione ligands have been explored. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of water-soluble Rh(I), Ir(I), and Ru(II) N-heterocyclic carbene complexes is described. These complexes are applied as catalysts for aqueous phase hydrogenation reactions. Good hydrogenation activities under ca. 40 atm pressure H2 at room temperature are observed. [Copyright &y& Elsevier]

Rh(III) complexes with a bidentate N-heterocyclic carbene ligand bearing flexible dendritic frameworks have been synthesized and fully characterized by X-ray crystallographic analysis, NMR measurements and theoretical calculations. [ABSTRACT FROM AUTHOR]