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[RhIII(*Cp)Cl(X,Y)] n+ complexes {X, Y = Cl, PTA, n = 0 ( 2); X, Y = en, n = 1 ( 3, Cl- salt; 4, PF6- salt); X, Y = acac, n = 0 ( 5); X, Y = cur, n = 0 ( 6), where *Cp = pentamethylcyclopentadienato, curH = curcumin; PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane; en = 1,2-ethanediamine; acac = acetylacetonato = 2,4-pentanedionato(1-)} were synthesized from [Rh(*Cp)(µ-Cl)Cl]2 ( 1). While 2- 5 were inactive against human epithelial A549 lung-cancer cells in assays of cytotoxicity, and antimetastatic and proapoptotic behaviors, 6 had a cytotoxic activity similar to that of curH over 72 h, but at 24 h in real-time cell migration assays, it was less active, showing slow release of curH. All complexes underwent ligand-exchange reactions with biomolecules and cells within the timeframes of the assays (X-ray absorption spectroscopy). Intracellular elemental distributions (X-ray fluorescence microscopy) showed that 6 effectively delivered curH to cells, where it was released. Other elemental distributions and caspase activities were consistent with preapoptotic activities. As such, 6 is a promising delivery agent for bioactive ligands, such as curH. However, pure curcumin itself showed a previously unrecognized ability to promote migration of A549 cells at subtoxic concentrations in the presence of endothelial growth factor, which may be a concern for its widespread use as a nutritional supplement and as a potential drug. This aspect warrants further research. [ABSTRACT FROM AUTHOR]

Treatment of the germyl complex [Rh(GePh3)(PEt3)3] ( 1) with CS2 afforded the rhodium thiocarbonyl complex trans-[Rh(SGePh3)(CS)(PEt3)2] ( 2) by phosphine dissociation and C-S bond activation. The analogous reaction with COS gave the structurally related carbonyl complex trans-[Rh(SGePh3)(CO)(PEt3)2] ( 3). Low-temperature NMR measurements revealed initial formation of the intermediates mer-[Rh(GePh3)(η2-CS2)(PEt3)3] ( 4) and mer-[Rh(GePh3)(η2-COS)(PEt3)3] ( 5). Reactions of 2 towards CO and HCl led to the replacement of the thiocarbonyl or germylthiolato ligand yielding complex 3 and trans-[Rh(Cl)(CS)(PEt3)2] ( 6), respectively. The germylthiolato complex trans-[Rh(SGePh3)(CS)(PEt3)2] ( 2) reacted with the boryl complex [Rh(Bpin)(PEt3)3] ( 7; pin = pinacolato) to afford the rhodium µ-carbido complex trans, trans-[{Rh(SBpin)(PEt3)2}(µ-C){Rh(SGePh3)(PEt3)2}] ( 8). Complex 8 is not stable in solution and rearranges to form the symmetrical µ-carbido complexes trans, trans-[Rh2(µ-C)(SGePh3)2(PEt3)4] ( 9) and trans, trans-[Rh2(µ-C)(SBpin)2(PEt3)4] ( 10). The molecular structures of 2 and 9 were determined by X-ray crystallography. [ABSTRACT FROM AUTHOR]

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]

The preparation and characterization of a dimeric RhIII complex containing two SSi ligands on each rhodium fragment is reported. {Rh[SiMe2( o-C6H4SMe)]2Cl}2 ( 1) was obtained by reaction of thioether-silane SiMe2H( o-C6H4SMe) ( L1) with [Rh(cod)Cl]2. Mixed-valent RhI/RhIII complex {(cod)Rh(μ-Cl)2Rh[SiMe2( o-C6H4SMe)]2} ( 2), which is an intermediate in the formation of 1, was isolated. Furthermore, 1H NMR spectroscopic monitoring revealed the formation of cyclooctenyl intermediates. The tridentate pincer proligand, SiMeH( o-C6H4SMe)2 ( L2), reacts with [Rh(cod)Cl]2 to yield a robust cyclooctenyl RhIII complex, {Rh(η3-cyclooctenyl)[SiMe( o-C6H4SMe)2]Cl} ( 3). Complexes 1- 3 were characterized by X-ray crystallography. [ABSTRACT FROM AUTHOR]

The stepwise in situ formation of neutral μ2-chloro-bridged dinuclear (diphosphine)rhodium complexes of the type [{Rh(PP)(μ2-Cl)}2] (PP = chelating diphosphine) following the reaction of [{Rh(COD)(μ2-Cl)}2] (COD = cyclooctadiene) with the ligands BINAP, SegPhos, DM-SegPhos and DiFluorPhos was investigated quantitatively by stopped-flow UV/Vis spectroscopy at 25.0 °C. The second-order rate constants of each step of the consecutive reactions were determined. The investigations were hindered by an unexpected equilibrium reaction between starting and target complex on one side and an intermediate species formed during the ligand-exchange process on the other. The rate constants of this equilibrium were also determined. The results reveal that the in situ formation of neutral μ2-chloro-bridged dinuclear (diphosphine)rhodium complexes, which are commonly applied in homogeneous catalysis as catalyst precursors, requires longer reaction times than is generally expected. [ABSTRACT FROM AUTHOR]

The (β-ketiminato)rhodium complex [Rh{κ2-( N, O)-( tBu)( O)CCHC( tBu) N(C6F5)}(cod)] ( 1) [cod = (1 Z,5 Z)-1,5-cyclooctadiene] and (β-diketiminato)rhodium complexes [Rh{κ2-( N, N)-(Ar) NC(Me)CHC(Me) N(Ar)}(L1)(L2)] [ 2: Ar = C6F5, (L1)(L2) = cod; 3: Ar = C6F5, L1 = L2 = C2H4; 4: Ar = C6F5, L1 = L2 = CN tBu; 5: Ar = 2,6-MeC6H3, L1 = L2 = CN tBu; 6a: Ar = C6F5, L1 = L2 = CO; 7a: Ar = C6F5, L1 = CO, L2 = NCMe; 8a: Ar = C6F5, L1 = CO, L2 = PEt3; 9a: Ar = C6F5, L1 = CO, L2 = NH3] were synthesized. Treatment of [Rh{κ2-( N, N)-(C6F5) NC(Me)CHC(Me) N(C6F5)}(CO)(NCMe)] ( 7a) with tertiary silanes HSiR3 gave the (β-diketiminato)(hydrido)(silyl)rhodium complexes [Rh{κ2-( N, N)-(C6F5) NC(Me)CHC(Me) N(C6F5)}(H)(SiR3)(CO)] ( 10a: R = Me; 11: R = Et; 12: R = iPr; 13: R = Ph; 14: R = OMe; 15: R = OEt). When using an excess amount of HSiMe3 the dihydridobis(silyl) complex [Rh{κ2-( N, N)-(C6F5) NC(Me)CHC(Me) N(C6F5)}(H)2(SiMe3)2] ( 16) was formed in addition to 10a. [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 addition of aminoalkyl-substituted 2,6-bis(imino)pyridine (or pyridine diimine, PDI) ligands to [(COD)RhCl]2 (COD = 1,5-cyclooctadiene) resulted in the formation of rhodium monochloride complexes with the general formula (NPDI)RhCl (NPDI = iPr2NEtPDI or Me2NPrPDI). The investigation of ( iPr2NEtPDI)RhCl and (Me2NPrPDI)RhCl by single-crystal X-ray diffraction verified the absence of amine arm coordination and a pseudo square-planar geometry about rhodium. Replacement of the chloride ligand with an outer-sphere anion was achieved by adding AgBF4 directly to ( iPr2NEtPDI)RhCl to form [( iPr2NEtPDI)Rh][BF4]. Alternatively, this complex was prepared by chelate addition following the salt metathesis reaction between AgBF4 and [(COD)RhCl]2. Using the latter method, both [(NPDI)Rh][BF4] complexes were isolated and found to exhibit κ4- N, N, N, N-PDI coordination regardless of arm length or steric bulk. In contrast, the metallation of PPDI chelates featuring alkylphosphane imine substituents (PPDI = Ph2PEtPDI or Ph2PPrPDI) resulted in the formation of cationic complexes featuring κ5- N, N, N, P, P-PDI coordination in all instances, [(PPDI)Rh][X] (X = Cl, BF4). Adjusting the metallation stoichiometry allowed the preparation of [(Ph2PPrPDI)Rh][(COD)RhCl2], as validated by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

A novel synthetic route based on [4+2] cycloaddition for dibromobenzobarrelene derivatives starting from in situ generated 3,5-dibromo-1,2-didehydrobenzene and mesitylene, 1,2,4,5-tetramethylbenzene, 1,2,3,5-tetramethylbenzene, pentamethylbenzene, 1,3-dimethoxybenzene, and 2,4,6-trimethylbromobenzene, respectively, was developed. Thus, six novel dibromobenzobarrelenes with diverse substitution patterns at the barrelene framework including chiral derivatives are reported. The benzobarrelene 6,8-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene ( 1a) was functionalized at the annulated benzene ring to give three novel carboxylic acids and two novel phosphonic acid esters. Selected benzobarrelene complexes with RhICl were tested for their catalytic activity in the 1,4-addition of phenylboronic acid towards cyclohex-2-enone. Turnover frequencies up to 3405 h-1 were observed, which are among the highest reported so far for Rh-diene complexes in this type of C-C coupling reaction. [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]

The design and synthesis of an intensely blue rhodium(III) complex [ 3]+ of a new N,N-donor ligand, 8-(quinolin-8-ylamino)pyrido[2,1- c][1,2,4]benzotriazin-11-ium, [ 2]+, which contains a planar pendant triazinium arm, is described. Structural characterization for [ 3]+ was carried out by using various spectroscopic techniques and single-crystal X-ray crystallography. The organometallic rhodium(III) compound shows a ligand-based reversible reduction at -0.65 V. The electrochemically reduced compound displays a single-line EPR spectrum that signifies the formation of ligand-based free radicals. Compound [ 3]+ shows a binding propensity to calf thymus DNA to give a Kapp value of 6.05 × 105 M-1. The parent triazinium salt, pyrido[2,1- c][1,2,4]benzotriazin-11-ium [ 1]+ and the ligand salt [ 2]+ exhibit photoinduced cleavage of DNA in UV-A light, whereas the reference Rh complex [ 3]+ photocleaves DNA with red light (647.1 nm). The compounds show photonuclease activities under both aerobic and anaerobic conditions. Mechanistic investigations under aerobic conditions with several inhibitors indicate the formation of hydroxyl radicals by means of a photoredox pathway. Under anaerobic conditions, it is believed that a photoinduced oxidation of DNA mechanism is operative. Compound [ 3]+ exhibits photocytotoxicity in HeLa cervical cancer cells to give IC50 values of (12 ± 0.9) μ M in UV-A light at 365 nm and (31.4 ± 1.1) μ M in the dark. [ABSTRACT FROM AUTHOR]