Synthesis and characterization of cationic rhodium(I) dicarbonyl complexes

Treatment of Rh(acac)(CO)₂ (acac = acetoacetonate) with perchloric acid followed by addition of an α-diimine (α-diimine = 1,4-bis(Ar)-2,3-dimethyl-1,4-diaza-1,3-butadiene, Ar = 3,5-dimethylphenyl, 1; 3,5-di-tert-butylphenyl, 2; and 3,4,5-trimethoxyphenyl, 3; phenyl, 4; and 4-chlorophenyl, 5) generates a series of complexes of the type [Rh(α-diimine)(CO)₂][ClO₄] 6-10 with varying electronic properties of the supporting diimine ligand. X-ray crystal structures have been determined for the α-diimine ligands 1-5, and complexes 6, 8, and 10.     

Synthesis of new cationic rhodium(I) complexes with diolefins and isoquinoline N-oxide as ligands

The preparation of cationic rhodium complexes of the types [RhL(IQNO)₂]ClO₄ (L  COD, COT and NBD) and [Rh(COD)(IQNO)L′]ClO₄ (L′ = 4-NH₂py, 4-NMe₂py and PPh₃) and the reactions of [Rh(COD)(IQNO)₂]ClO₄ with N- and P-donor ligands are described.     

Platinum(IV) isocyanide complexes

Neutral and cationic platinum(IV) isocyanide complexes of the type [PtCl₄(CNR)₂], [PtCl₄(CNR) (PMe₂Ph)], [PtCl₃(CNR)(PMe₂Ph)₂]⁺, [PtCl₂(CNR)₂ (PMe₂Ph)₂]²⁺, where R = methyl, t-butyl, cyclohexyl, p-tolyl, have been prepared by chlorine addition to the corresponding platinum(II) derivatives. The complexes [PtCl₂(CN)₂(CNR)₂] and [PtCl₂(CN)(CNR) (PMe₂Ph)₂]⁺ (R = t-butyl), are also reported. The cationic t-butylisocyanide derivatives are noteworthy in the way they readily lose the t-butyl cation at room temperature to give the corresponding cyano complexes. The compounds have been characterized by elemental analysis, molecular weights and conductivity measurements, and their i.r. and n.m.r. data are discussed in relation to structures and to the nature of the platinum-isocyanide bond.     

Synthesis of mixed ligand cationic rhodium(I) complexes with diolefin and substituted quinoline N-oxides as ligands

The mixed ligand cationic rhodium(I) complexes of the type [Rh(COD)LL′]C10₄ (L=QNO, 2-Me- QNO, 4-MeQNO, 4-C1QNO, 2-PhQNO; L′=4-NH2py, 4-NMe₂py, Im, PPh₃) have been prepared and characterized. The reactions of [Rh(COD)(4-MeQNO)₂]- C10₄ with various ligands are also reported.     

Synthesis and characterization of new cationic hydride complexes of rhodium(III)

New cationic hydride complexes of rhodium(III) with PR₃ and R-DAB ligands have been prepared and characterised. The tertiary phosphines employed were PPh₃, PMePh₂, PEt₃ and the R-DAB ligands, (RN:CR′CR′:NR), c-Hex-DAB, Ph-DAB, NH2-DAB-(CH₃,CH₃). Hexacoordinate-dihydride complexes, characterized by ¹H and ³¹P NMR, with stoichiometry [RhH₂(R-DAB)(PR₃)₂]X were obtained. Compounds with other stoichiometries (R-DAB/PR₃=1 or 2) are also possible. Preliminary studies of the catalytic activity in hydrogenation of olefins have been carried out.     

Secondary ion mass spectrometry of nonvolatile isocyanide complexes of silver(I) and copper(I)

A series of silver and copper coordination complexes has been studied using secondary ion mass spectrometry (SIMS). Results are presented for the monomeric silver(I) complexes [Ag(CNR)₄]X, where R = cyclohexyl for X  ClO₄⁻, and R = methyl or t-butyl for X  PF₆⁻. Likewise, Cu(I) complexes [Cu(CNR)₄]PF₆, where R =methyl, t-butyl, or cyclohexyl, were examined. The presence of AgL₂⁺ (L represents the intact RNC ligand) and the absence of AgL₃⁺ and AgL₄⁺ species attests to the gas phase stability of two-coordinate silver(I). Similar results to these were obtained for the Cu(I) complexes, with the exception of [Cu(CNCH₃)₄]PF₆ whose spectrum contains CuL₄⁺, CuL₃⁺, CuL₂⁺, CuL⁺, and Cu⁺ ions. The latter result reflects the enhanced stability of the tetrahedral Cu(I) geometry compared to Ag(I) in the gas phase. Cross labeling experiments and isotopic labeling studies have provided insights into fragmentation mechanisms. Ligand exchange occurs when mixtures are examined. These exchange reactions provide evidence for extensive molecular mixing which can accompany SIMS even under low primary ion dose conditions. Cluster ion formation as well as the observation of α-cleavage of the NC bonds of RNC ligands have been observed and these results are discussed. Granulated graphite and ammonium chloride were employed to study matrix effects. Granulated graphite enhanced NC cleavage for the silver complexes but had little effect on the relative abundance of silver cluster ions. On the other hand, copper cluster ions were more sensitive to matrix effects.     

Kinetics and mechanism of the reactions of ozone with superoxo, hydroperoxo, and hydrido complexes of rhodium(III)

Oxidation of the title complexes with ozone takes place by hydrogen atom, hydride, and electron transfer mechanisms. The reaction with (NH₃)₄(H₂O)RhH²⁺ is a two electron process, believed to involve hydride transfer with a rate constant k = (2.2 ± 0.2) × 10⁵ M⁻¹ s⁻¹ and an isotope effect k_H/k_D = 2. The oxidation of (NH₃)₄(H₂O)RhOOH²⁺ to (NH₃)₄(H₂O)RhOO²⁺ by an apparent hydrogen atom transfer is quantitative and fast, k = (6.9 ± 0.3) × 10³ M⁻¹ s⁻¹, and constitutes a useful route for the preparation of the superoxo complex. The latter is also oxidized by ozone, but more slowly, k = 480 ± 50 M⁻¹ s⁻¹.     

Synthesis and characterisation of ferrocene-containing β-diketonato complexes of rhodium(I) and rhodium(III)

The synthesis of new β-diketonato rhodium(I) complexes of the type [Rh(FcCOCHCOR)(CO)₂] and [Rh(FcCOCHCOR)(CO)(PPh₃)] with Fc=ferrocenyl and R=Fc, C₆H₅, CH₃ and CF₃ are described. ¹H, ¹³C and ³¹P NMR data showed that for each of the non-symmetric β-diketonato mono-carbonyl rhodium(I) complexes, two isomers exist in solution. The equilibrium constant, K_c, which relates these two isomers in an equilibrium reaction, are concentration independent but temperature and solvent dependent. Δ_rG, Δ_rH and Δ_rS values for this equilibrium have been determined and a linear relationship between solvent polarity on the Dimroth scale and K_c exists. The relationship between RhP bond lengths, d(RhP), and ³¹P NMR peak positions as well as coupling constants ¹J(³¹P¹⁰³Rh) has been quantified to allow calculation of approximate d(RhP) values. Variations in d(RhP) for [Rh(RCOCHCOR′)(CO)(PPh₃)] complexes have also been related to the group electronegativities (Gordy scale) of the terminal β-diketonato R groups trans to PPh₃. A measure of the electron density on the rhodium centre of [Rh(RCOCHCOR′)(CO)(PPh₃)] may be expressed in terms of the IR carbonyl stretching wave number, ν(CO), the sum of the group electronegativities of the R and R′ groups, (χ_R+χ_R′), or the observed pK_a^′ values of the free β-diketones RCOCH₂COR^′. An empirical relationship between ν(CO) and either pK_a^′ or (χ_R+χ_R′) has also been quantified.     

Antitumour action of planar, organometallic rhodium(I) complexes

Four cis-, square planar rhodium(I) organometallic complexes have been tested for antineoplastic properties. Their activity varies depending on the tumour system employed. They cause little or no effect on the growth of solid S180, and only one of them is effective on LI210 leukemia. Their activity on Ehrlich ascites is more pronounced, with low T/C ratios, two derivatives in particular causing some regressions. This greater activity on ascites carcinoma has been correlated with the oxidability and the lability of the leaving groups of these complexes. The most active compound on Ehrlich ascites, when tested for effects on the incorporation of labelled precursors in macromolecules shows a selective inhibition of leucine incorporation into proteins at therapeutically active doses. It is pointed out that these rhodium derivatives, in contrast to platinum complexes, are characterized by π carbon-metal bonds instead of nitrogen donor ligands for the non-leaving groups.     

Solid-gas carbonylation of aryloxide rhodium(I) complexes: stepwise reaction forming Vaska-type complexes

Aryloxide rhodium(I) complexes Rh(OAr)(PPh₃)₃ (1a: Ar=C₆Cl₅, 1b: Ar=C₆F₅, 1c: Ar=C₆H₄-NO₂-4) react with CO in toluene solutions to produce Vaska-type complexes trans-Rh(OAr)(CO)(PPh₃)₂ (2a: Ar=C₆Cl₅, 2b: Ar=C₆F₅, 2c: Ar=C₆H₄-NO₂-4). Carbonylation of a similar complex with PMe₃ ligands, Rh(OC₆H₄-NO₂-4)(PMe₃)₃ (3c), also forms trans-Rh(OC₆H₄-NO₂-4)(CO)(PMe₃)₂ (4c). Molecular structures of the complexes are determined by X-ray crystallography and NMR spectroscopy. Complex 1a reacts with CO in the absence of solvent to produce a mixture of 2a and complex A, the latter of which shows the IR and ¹³C{¹H} signals due to the carbonyl ligand at different positions from those of 2a. Addition of Et₂O to the above mixture turns it into analytically pure 2a. Carbonylation of 1b and 1c under the solvent-free conditions produces complexes B and C as the respective products of the solid-gas reaction. Recrystallization of B and C turns them into 2b and 2c, respectively. Complex 3c also reacts with CO in the solid state to form a mixture of 4c and complex D, although the latter complex is converted slowly into 4c even in the solid state.     

Diether functionalized rhodium(I)-N-heterocyclic carbene complexes and their catalytic application for transfer hydrogenation reactions

N-heterocyclic carbene (NHC) complexes of rhodium(I) (3 and 4) bearing one diether (MeOCH₂CH₂OCH₂CH₂-NHC) functionality on N¹ and bulky benzyl groups (CH₂-C₆H₂(CH₃)₃-2,4,6 and CH₂-C₆(CH₃)₅) on N³ of (5,6-dimethyl)benzimidazole were synthesized by deprotonation of the corresponding benzimidazolium salt with [Rh(μ-OMe)(1,5-cod)]₂ in dichloromethane at ambient temperature. All compounds have been fully characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. X-ray diffraction studies on single crystals of 3a and 3b confirm the cis square planar geometry. All of the new benzimidazol-2-ylidene rhodium(I) complexes were found to be effective catalysts for the transfer hydrogenation reaction.     

Chemistry of tris(2,4,6-trimethoxyphenyl)phosphine with rhodium(I) and iridium(I) olefin complexes

Rh(I) and Ir(I) complexes of the type [Rh(cod)(η²-TMPP)]¹⁺ (1) and M(cod)(η²-TMPP-O) (M = Rh (2), Ir (3); cod = cyclooctadiene; TMPP = tris(2,4,6-trimethoxyphenyl)phosphine; TMPP-O = mono-demethylated form of TMPP) have been isolated from reactions of [M(cod)Cl]₂ with M′BF₄ (M′ = Ag⁺, K⁺, Na⁺) followed by addition of the tertiary phosphine ligand. This chemistry is dependent on the identity of the metal, as both the cationic phosphine complex and the neutral phosphino-phenoxide compound are stable for Rh(I), whereas only the latter is stable for Ir(I). The three complexes have been characterized by IR and NMR (¹H and ³¹P) spectroscopies as well as by cyclic voltammetry. The ¹H NMR spectrum of [Rh(cod)(η²-TMPP)]¹⁺ (1) is in accord with the formula and reveals that the TMPP phenyl rings are undergoing rapid exchange between coordinated and non-coordinated modes; the corresponding spectra of 2 and 3 support free rotation about the P---C bonds of the unbound phenyl rings with no fluxionality of the bound demethylated ring. The ³¹P{¹H} NMR spectrum of the neutral species 2 exhibits a significant upfield shift with respect to the analogous cationic compound 1. This shielding is the result of improved electron donation to the metal from a phenoxide group as compared to an ether substituent. In situ addition of CO to the reaction between TMPP and [Rh(cod)Cl]₂ or [Ir(cod)Cl]₂ in the presence of M′BF₄ results in the isolation of the monocarbonyl species [Rh(TMPP)(η²-TMPP)(CO)][BF₄] (5) and the stable dicarbonyl compound [Ir(TMPP)₂(CO)₂][BF₄] (4), respectively. Single crystal X-ray data for

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. The geometry of 4 is square planar, with essentially ideal angles for the mutually trans disposed phosphine and carbonyl ligands, as found in earlier studies for the analogous Rh dicarbonyl compound. The ¹H NMR spectrum of 4 supports the assignment of magnetically equivalent phosphorus nuclei in solution. The results of this study indicate that cyclooctadiene is a particularly strong ligand for monovalent late transition metals ligated by TMPP, to the extent that it is inert with respect to substitution in the absence of π-acceptor ligands such as carbon monoxide.     

The oxidative addition of iodomethane to acetylacetonatocarbonylphosphinerhodium(I) complexes

The kinetics and mechanism of the oxidative addition of CH₃I to [Rh(acac)(CO)(PX₃)], where X = p-chlorophenyl, phenyl and p-methoxyphenyl, were studied with the aid of IR and visible spectrophotometry in 1,2-dichloroethane. The reaction proceeds through an initial ionic intermediate followed by two consecutive equilibrium steps, the first involving acetyl formation followed by acyl → alkyl rearrangement to give [Rh(acac)(CO)(CH₃)- (I)(PX₃)] as final product. Equilibrium and rate constants are correlated with phosphine basicity.     

Reactions of rhodium(II) and iridium(III) complexes bearing a P,O-coordination with tetracyanoethylene in the presence of KPF6

Reactions of Cp*M(MDMPP-P,O)Cl (1a: M=Rh, 1b: M=Ir; MDMPP-P,O=PPh₂(2-O-6-MeOC₆H₃)) with tetracyanoethylene (tcne) in the presence of KPF₆ gave Cp*MCl[PPh₂{2-O-3-(C(CN)₂CH(CN)₂)-6-MeOC₆H₂}] (2), [{Cp*MPPh₂{2-O-3-(C(CN)C(CN)₂)-6-MeOC₆H₂}}₂(CN)](PF₆) (3), [{Cp*IrPPh₂{2-O-3-(C(CN)C(CN)₂)-6-MeOC₆H₂}}(CN){Cp*Ir(MDMPP-P,O)}](PF₆) (4b) and [{Cp*Ir(MDMPP-P,O)}₂(CN)](PF₆) (5b), depending on the reaction conditions. Reaction of 2 with KPF₆ or AgOTf in the absence and presence of xylyl isocyanide (XylNC) gave 3 or [Cp*MCl{PPh₂(2-O-3-(C(CN)₂-CH(CN)₂)-6-MeOC₆H₂)}(XylNC)](OTf) (6). The structure of 3a (M=Rh) was confirmed by X-ray crystal analysis.     

Supported organometallic complexes. Part 27: novel sol-gel processed rhodium(I) complexes: synthesis, characterization, and catalytic reactions in interphases

A novel T-silyl functionalized cationic (COD)(dppp)rhodium(I) complex was sol-gel processed with various amounts of the co-condensing agents MeSi(OMe)₂(CH₂)₆(OMe)₂SiMe and MeSi(OMe)₂(CH₂)₃(C₆H₄)(CH₂)₃(OMe)₂SiMe to give novel stationary phases for ‘Chemistry in Interphases’. The polysiloxane matrices and the integrity of the rhodium(I) complex centers were investigated by means of multinuclear solid-state NMR (¹³C, ²⁹Si, ³¹P) and EXAFS spectroscopies. Dynamic NMR measurements show an increasing mobility of the matrix and the reactive centers with a higher amount of the co-condensing component. The accessibility of the anchored rhodium(I) centers was scrutinized by the metal catalyzed hydrogenation of 1-hexene. All applied xerogels show remarkable activities and selectivities. An enhancement of the activities is achieved when polar solvents are used. SEM micrographs reveal the morphology of the hybrid materials and energy dispersive X-ray spectroscopy (EDX) suggests that the distribution of the elements is in satisfying agreement with the applied composition.     

Structure and catalytic activity of rhodium(I) carbene complexes in polymerization of phenylacetylene

Rh(I) carbene complexes of [RhX(bmim)(η⁴-1,5-cod)] type (bmim = 1-butyl-3-methyl imidazolium cation, X = Cl 2, Br 3, I 4), obtained in the reaction of [Rh(OMe)(η⁴-1,5-cod)]₂ (1) with [bmim]X ionic liquids, catalyzed polymerization of phenylacetylene (PA) to cis-polyphenylacetylene (PPA) in CH₂Cl₂ and in ionic liquids. The yield of PPA increased and molecular weight (M_w) decreased after addition of phosphorus ligands PPh₃ or P(OPh)₃. Complex 4 reacted with P(OPh)₃ giving cis-[RhI(bmim)(P(OPh)₃)₂] (5) complex which catalyzed oligomerization but not polymerization of PA.     

Synthesis, immobilization and catalytic activity of some silylated cyclopentadienyl rhodium(I) complexes

The mixture of isomers of silylated cyclopentadiene derivative C₅H₅CH₂CH₂Si(OMe)₃ (1) has been used for the syntheses of the mononuclear Rh(I) complexes [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(CO)₂ (3). [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(COD) (4) and [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(CO)(PPh₃) (5). Upon entrapment of 3–5 in silica sol-gel matrices, air stable, leach-proof and recyclable catalysts 6–8 resulted. Their catalytic activities in some hydrogenation processes were compared with those of the non-immobilized complexes 3–5, as well as with those of homogeneous and heterogenized non-silylated analogs, 9–14.     

Five-coordinated rhodium(I) carbonyl compounds

The title compounds were synthesised by the replacement of chlorine in Rh(CO)(PPh₃)₂Cl with monobasic bidentate chelating ligands such as salicylaldehyde, acetylacetone, benzoylacetone, dibenzoylmethane, 8-hydroxyquinoline, benzoylphenyl hydroxylamine, 2-hydroxyacetophenone and 2-hydroxybenzophenone. IR spectral evidence points out that these compounds have a trigonal bipyramidal geometry around rhodium in the solid state. However, in benzene solutions, except for the 8-hydroxyquinoline and 2-hydroxybenzophenone derivatives they all take a square planar structure, as seen from their electronic spectra.     

Structural criteria for the activity of rhodium(I) phosphine complexes in the catalytic dehydrocoupling of di-n-hexylsilane

The activity of several neutral, rhodium(I) bis(phosphine) complexes for the dehydrogenative coupling of di-n-hexylsilane to two- and three-silicon chains was investigated and discussed in the context of the coordination numbers and geometries likely to be critical to catalyst activity. Wilkinson’s dimer, [Rh(μ-Cl)(PPh₃)₂]₂, shows the highest activity, while [Rh(μ-Cl)(dppe)]₂, with its rigidly cis-chelating diphosphine ligand, shows negligible activity for the dehydrocoupling reaction, even when the reaction is carried out in methylene chloride, in which both catalyst and silane are soluble. A dramatic decrease in the activity of Wilkinson’s dimer when the reaction is carried out in toluene or methylene chloride solution instead of neat silane is attributed to rate-limiting escape of the product hydrogen gas away from the solvated active catalyst.