Electrochemical illumination of intramolecular communication in ferrocene-containing tris-β-diketonato aluminum(III) complexes; cytotoxicity of Al(FcCOCHCOCF3)3

The series of ferrocene-containing tris-β-diketonato aluminum(III) complexes [Al(FcCOCHCOR)(3)] (R = CF(3), 1; CH(3), 2; C(6)H(5), 3; and Fc = ferrocenyl = Fe(η(5)-C(5)H(5))(η(5)-C(5)H(4)), 4) were synthesized and investigated structurally and electrochemically; complex 1 was subjected to cytotoxicity tests. (1)H NMR-spectroscopy distinguished between the mer and fac isomers of 2 and 3. Complex 1 existed only as the mer isomer. A single crystal X-ray crystallographic determination of the structure of a mer-isomer of Al(FcCOCHCOCF(3))(3), 1, (Z = 4, space group P2(1)2(1)2(1)) demonstrated extensive delocalization of all bonds which explained the pronounced electrochemically observed intramolecular communication between molecular fragments. In contrast to electrochemical studies in CH(2)Cl(2)/[N((n)Bu)(4)][PF(6)], the use of the supporting electrolyte [N((n)Bu)(4)][B(C(6)F(5))(4)] allowed identification of all Fc/Fc(+) electrochemical couples by cyclic and square wave voltammetry for 1-4. For R = Fc, formal reduction potentials of the six ferrocenyl groups were found to be E°' = 33, 123, 304, 432, 583, and 741 mV versus free ferrocene respectively. Complex 1 (IC(50) = 10.6 μmol dm(-3)) was less cytotoxic than the free FcCOCH(2)COCF(3) ligand having IC(50) = 6.8 μmol dm(-3) and approximately 2 orders of magnitude less toxic to human HeLa neoplastic cells than cisplatin (IC(50) = 0.19 μmol dm(-3)).     

Kinetics of ferrocenoylacetonato substitution from (1,5-cyclooctadiene)(ferrocenoylacetonato)rhodium(I) with 2,2′-dipyridyl and derivatives of 1,10-phenanthroline

Treatment of MeOH solutions of [Rh(cod)(fca)] (cod = 1,5-cyclooctadiene, fca = ferrocenoylacetonato) with seven derivatives of 1,10-phenanthroline (N,N), as well as with the (N,N) ligand 2,2-dipyridyl, gave [Rh(cod)(N,N)]⁺. The kinetics of these reactions follow the rate law: Rate = k[Rh(cod)(fca)[N,N] The temperature dependence of all the studied substitutions resulted in activation entropies, S , more negative than –100 J K^–1 mol^–1 which is indicative of associative mechanisms. The pK _a's of the incoming phenanthroline derivatives were between 3.03 and 6.31 but did not influence the reaction rate to any significant extent. This implies that the rate determining step during the substitution involves Rh—O bond breaking and not Rh—N bond formation. Substitution of fca with 2,2-dipyridyl was slightly faster (k = 118 dm³ mol^–1 s^–1) than with the 1,10-phenanthroline derivatives (k _average = 14.2 dm³ mol^–1 s^–1) and may be attributed to the free rotation capability of the two pyridyl rings about the 1-1 carbon–carbon axis in 2,2-dipyridyl. 1,10-Phenanthroline cannot rotate about the corresponding carbon axis.     

Vinylidene transition-metal complexes: I. Novel rhodium(I) and rhodium(III) complexes containing alkynes,alkynyls, and vinylidenes as ligands.Crystal structure of IC5H5Rh(CCHPh)(PPri3)

The syntheses of the novel cyclopentadienylphosphinevinylidenerhodium complexes C₅H₅Rh(CCHR)(PPrⁱ₃) (R = Ph, Me, H) and, for R = Ph, of the isomeric alkynyl hydrido compound C₅H₅ RhH(C₂Ph)(PPrⁱ₃) are reported. The square-planar complexes trans-[RhCl(RC₂H)(PPrⁱ₃)₂] (IIa, IIb), which in solution are in equi-librium with the five-coordinated pyridine to give the octahedral compounds RhHCl(C₂R)(PRrⁱ₃)₂(py) (VIa, VIb). Treatment of Via, VIb with NaC₅H₅ gives the vinylidene complexes IVa, IVb in good yield. C₅H₅Rh(CCH₂)(PPrⁱ₃) (IVc) is directly obtained from trans-[RhCl(C₂H₂)(PPrⁱ₃)₂] (IIc) and NaC₅H₅. Mechanistic studies confirm that the reaction of VIa, VIb with the cyclopentadienide anion primarily gives, by elimination of HCl, the rhodium(I) compounds trans-[Rh(C₂R)(py)(PPrⁱ₃)₂] (VIIIa, VIIIb), which react with cyclopentadiene, possibly via trans-[Rh(C₂R)(η²-C₅H₆)(PPrⁱ₃)₂](X) as an intermediate, to give C₅ VIIIa with cyclopentadiene in presence of water gives the complex C₅H₅RhH(C₂Ph)(PPrⁱ₃), which isomerizes only slowly to form IVa and, therefore, is not an intermediate in the reaction of VIIIa and C₅H₆ to give IVa. The crystal structure of IVa has been determined. The RhCC arrangement is almost linear. The RhC distance is significantly shorter than in carbenerhodium complexes, which, in agreement with ¹³C NMR data and MO calculations, indicates a high degree of multiple bonding.     

Synthesis of 2-picolyl functionalized η-cyclopentadienyl derivatives of rhodium(I) and iridium(I) and preliminary study of their reaction with ruthenium(II) for assembling hetero-bimetallic complexes

The 2-picolylcyclopentadienyl derivatives of rhodium(I) and iridium(I) of formula [M{η⁵-C₅H₄(2-CH₂C₅H₄N)}(η⁴-C₈H₁₂)] (3) (M = Rh) and (4) (M = Ir) are obtained in good yields by reacting 2-picolylcyclopentadienyllithium (7) with [RhCl(η⁴-C₈H₁₂)]₂ and [IrCl(η⁴-C₈H₁₂)]₂, respectively. The corresponding dicarbonyl derivatives, [M{η⁵-C₅H₄(2-CH₂C₅H₄N)}(CO)₂] (5) (M = Rh) and 6 (M = Ir), are obtained in good yields by reacting 2-picolylcyclopentadienylthallium(I) (8) with [RhCl(CO)₂]₂ and [IrCl(C₅H₅N)(CO)₂], respectively. 5 has already been reported in the literature. The new complexes were characterized by elemental analysis, mass spectrometry, ¹H NMR, FT-IR, and UV-Vis (210-330 nm) spectroscopy. The UV-Vis spectra indicate the existence of some electronic interaction between the 2-picolinic chromophore and the cyclopentadienyl-metal moiety. The study of the electrochemical behaviour of 3-6 by cyclic voltammetry (CV) allows the interpretation of the electrode processes and gives information about the location of the redox sites. Moreover, various synthetic strategies were tested in order to try to coordinate the complexes 3-6 to a ruthenium(II) centre, but most of them failed. Instead, the hetero-bimetallic complex bis(2,2′-bipyridine)[(η⁵-2-picolylcyclopentadienyl)(η⁴-cycloocta-1,5-diene)rhodium(I)]chlororuthenium(II)-(hexafluorophosphate) (13), was obtained, although in poor yields (10%), by reacting the nitrosyl complex [RuCl(bipy)₂(NO)][PF₆]₂14 (bipy = 2,2′-bipyridine) first with potassium azide and then with the rhodium(I) complex 3. The analogous complex bis(2,2′-bipyridine)(2-picoline)chlororuthenium(II)-(hexafluorophosphate) (15), that carries a ruthenium-bonded 2-picoline molecule instead of 3, has prepared in the same way. 13 and 15 were characterized by elemental analysis, mass spectrometry, and ¹H NMR.     

Ready formation of phosphonate complexes of rhodium and iridium from [M(P(OMe3)5]Cl compounds (M = Rh,Ir). Differences between reactions of dihydrogen with [Mp(O)(OMe)2(P(OMe)3)4] complexes (M = Co,Rh, Ir), including facile hydrogenolysis of a rhodiumphosphorus bond

The ease of formation of the phosphonate complexes [M(P(O)(OMe)₂(P(OMe)₃)₄] (M = Rh, Ir), from the pentakis-trimethylphosphite complexes [M(P(OMe)₃)₅]Cl is reported. Differences in the interaction of H₂ with the complexes [M′(P(O)(OMe)₂(P(OMe)₃)₄), (M′ = Co, Rh, Ir) are presented and discussed.     

Bridging alkyls in d-transition metal chemistry: reaction of (cod)2 RH2 (μ-R)2 with Lewis bases to give (cod)Rh(R)(L) and their reaction with aromatic hydrocarbons

Low temperatùre (−70°C) reaction of (cod)₂Rh₂2 (μ-Cl)₂ with two molar equivalents of RLi in diethyl ether gives (cod)₂Rh₂ (μ-R)₂ where R = Me, Me₃SiCH₂. Even though the bridging alkyls are air and moisture sensitive, they may be stored for prolonged periods at −30°C. The bridging alkyls are fluxional at + 20°C and the NMR spectra are consistent with a dimer of idealized D_2h symmetry. Low temperature NMR spectroscopic studies suggest that the dimers have idealized C_2v symmetry as found by X-ray studies described earlier. The bridging alkyls readily react with Lewis bases to give monomeric (cod)Rh(R)(L) where R = Me and L = PMe₃, PEt₃, P(NMe₂)₃, P(OMe)₃, py and R = Me₃SiCH₂, L = P(OMe)₃. The five coordinate, fluxional complex, (cod)RhMe(PMe₃)₂ also may be isolated. The four coordinate (cod)RhMe(PEt₃), slowly reacts with toluene to give (cod)Rh(m-tolyl)(PEt₃), (cod)Rh(p-tolyl)(PEt₃), and methane and (cod)RhMe(PMe₃) slowly reacts with benzene to give (cod)Rh(Ph)(PMe₃) and methane.     

Asymmetric hydroformylation of vinyl acetate with BINAP–rhodium(I) complexes

Complexes of (R)-BINAP (BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) derived from the available rhodium precursors Rh(acac)(CO)₂ and [Rh(μ-OMe)(cod)]₂ are used for the asymmetric hydroformylation of vinyl acetate. Enantiomeric excesses of up to 60% are achieved with regioselectivities of up to 99%. Only a BINAP/Rh ratio of 2 is required. Effects of pressure and temperature on catalyst stability, enantio- and chemoselectivity are discussed.     

Polyfluorothiolate derivatives of rhodium(I). Crystal and molecular structure of [Rh(μ-SC6HF4)(C8H12)]2

Summary The thiolato-bridged dinuclear compounds [Rh(-SR)-(COD)]₂, where R=p-C₆HF₄ (1),p-C₆H₄F (2) and CF₃ (3), are obtained from the chloro-bridged analogue by ligand exchange.Compound (1) crystallizes in the space group P₁ with a=9.740(3)Å, b=11.642(4)Å, c=13.997(6)Å, =103.87(3)°, =106.98(3)° and =105.10(2)°; z=2. In this dinuclear molecule both Rh atoms have a square planar coordination sharing one edge, namely the two sulphur bridging atoms. The Rh—Rh separation of 2.96 Å is consistent with at most a very weak metal-metal interaction. Upon addition of CO the dimeric [Rh(-SR)(CO)₂]₂ (4), (5) and (6) are obtained, but addition of PPh₃ affords the monomeric species [Rh(SR)(PPh₃)-(COD)] (7), (8) and (9). Reactions of the dimeric tetracarbonyl derivatives with PPh₃ vary with the nature of R; [Rh(-SR)(PPh₃)(CO)]₂ is obtained when R=p-C₆H₄F (10) and CF₃ (11) but monomeric [Rh(SR)-(PPh₃)(CO)₂] (12) is produced when R=p-C₆HF₄. The latter mononuclear compounds, with R=p-C₆H₄F (13) and CF₃ (14), are also formed by reaction of [Rh(SR)-(PPh₃)(COD)] with CO.     

Iodomethane oxidative addition to β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study

New rhodium(I)- and rhodium(III)-β-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh)₃)₂] and [Rh(FcCOCHCOR)(P(OPh)₃)₂(CH₃)(I)], with Fc = ferrocenyl and R = Fc, CH₃ and CF₃, have been synthesized. The reactivity of complexes of the type [Rh(β-diketonato)(P(OPh)₃)₂] increase in the order: β-diketonato = (CF₃COCHCOCF₃)⁻ < (CF₃COCHCOPh)⁻ < (CF₃COCHCOCH₃)⁻ < (PhCOCHCOPh)⁻ < (CF₃COCHCOFc)⁻ < (CH₃COCHCOPh)⁻ < (CH₃COCHCOCH₃)⁻ < (CH₃COCHCOFc)⁻ < (FcCOCHCOFc)⁻, giving linear relationships between the kinetic parameter ln k₂ and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the β-diketonato side groups (χ_R + χ_R′) and the pK_a of the uncoordinated β-diketone RCOCH₂COR′. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF₃)(P(OCH₃)₃)₂] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product.     

Relationship between the analytical properties of lanthanide(III) βdiketonates and the nature of ligands

The effect of the nature of β-diketones on the spectrochemical-luminescence properties of lanthanide complexes used as analytical forms for the highly sensitive determination of some rare-earth elements was examined. NMR spectroscopy, molecular mechanics, calculations, and an experimental evaluation of the hydrophobicity of the test β-diketones indicated that an increase in the intensity, quantum yield, and lifetime of luminescence of lanthanide (Ln) β-diketonates depends on the charge distribution in the chelate ring, on the spatial structure, and on the hydrophobicity of the coordinated ligand. These factors determine the efficiency of energy transfer from the β-diketone to the Ln⁺³ ion and the decrease in energy losses caused by the quenching action of water molecules.     

Fluorine-substituted β-diketonate PbII complexes, [Pb(phen)(TFPB)2] and [Pb(2,2′-bipy)(TFPB)2]

Lead(II) 4,4,4-trifluoro-1-phenyl-1,3-butandionate (TFPB^?) complexes with 1,10-phenanthroline (phen) and 2,2′-bipyridine (2,2′-bipy), [Pb(L)(TFPB)₂], have been synthesized and characterized by elemental analysis, IR-, ¹H NMR spectroscopy and studied by X-ray crystallography. The self-assembly of [Pb(L)(TFPB)₂] complexes, (L?=?phen or 2,2′-bipy) is caused by C–H?···?F–C, C–H?···?O–C and π–π stacking interactions. The thermal stabilities of compounds were studied by thermal gravimetric (TG) and differential thermal analyses (DTA).     

Crystal structure and properties of (1,5-cyclooctadiene) (η<Superscript>5</Superscript>-pentamethylcyclopentadienyl) iridium(I) [Ir(cod)Cp*]

Volatile iridium(I) complexes [Ir(cod)Cp^x] (Cp^x = pentamethylcyclopentadienyl Cp*, ethylcyclopentadienyl Cp^Et, cod = 1,5-cyclooctadiene) are synthesized and characterized by IR and NMR spectroscopy. The [Ir(cod)Cp*] complex is a solid and the [Ir(cod)Cp^Et] complex is a liquid (SATP). The XRD method is used to determine the structure of the [Ir(cod)Cp*] complex: chemical formula C₁₈H₂₇Ir, space group P2₁/c, a = 8,4418(2) Å, b = 9,4764(3) Å, c = 19.2682(5) Å, β = 96.128(1) °, V = 1532.61(7) ų, Z = 4, d _calc = 1.888 g/cm³, μ = 8.697 mm^–1. The cyclopentadienyl ligand is η⁵-type coordinated; 1,5-cyclooctadiene have a cis-cis conformation and is η⁴-type coordinated. The thermal properties of the complexes are studied by thermogravimetry.     

Dimeric and polymeric copper(I) complexes. Synthesis and characterization of copper(I) complexes of di-2-pyridyl ketone oxime (DPKox) and crystal structures of [Cu(DPKox)Cl]2·2H2O and [Cu(DPKox)(NCS)]n

Copper(I) complexes with di-2-pyridylketone oxime (DPKox) of the type CuLX·nH₂O, n=1 for X=Cl and Br, and n=0 for X=I and SCN, have been synthesized and characterized. The overall physical results suggest tridentate and bidentate DPKox ligand in the Cl, Br and I, SCN complexes, respectively, and terminal X in the former but bridging X in the later. These complexes display MLCT bands in the visible region, but they do not fluoresce at room temperature. The structure determination has shown the chloride complex (1) to have a centro-symmetrically related dimeric unit, in which each copper atom is coordinated by Cl(1), N(1), N(2) and N(3) (of the second ligand molecule) in a distorted tetrahedral environment. Hydrogen bonds are formed by the O(1) of the oxime group and a lattice water molecule, and between different lattice water molecules and Cl(1). The structure of the thiocyanate complex (2) features tetrahedral geometry around copper atoms, a chelating bidentate DPKox ligand coordinating via one of the two pyridyl nitrogens, N(1), and N(oxime) only and μ-1,3-thiocyanate group forming zigzag chains along the c-axis of the unit cell.     

Synthesis and characterisation of bite angle-dependent (η1-allyl)Rh and (η3-allyl)Rh complexes bearing diphosphine ligands. Implications for nucleophilic substitution reactions

Several novel rhodium allyl complexes have been prepared and their structures have been studied using NMR spectroscopy and X-ray crystallography. Depending on the bite angle of the ligand and the substitution pattern of the allyl group, two different coordination modes (η¹ and η³) have been observed for the allyl moiety. The activities of these Rh allyl complexes in the allylic alkylation reaction have been tested. We have shown that both coordination modes give active complexes in this reaction, but that the regioselectivity is dependent on the coordination mode of the allyl group.     

Palladium complexes with biological ligands—I. Equilibrium and reaction mechanism of Pd(II) complexes with ethionine

An equilibrium study has been carried out on the interaction of ethionine(eth) with Pd(II) in aqueous solution at I = 0.16 M (Cl⁻ and 25°C using potentiometic methods. It has been concluded that five complex species exist in the pH range 2.8–4.8. these species are: PdCl₃(Eth0H⁰₂, PdCl₂(Eth)⁻, PdClOH(Eth)⁻, Pd(Eth)₂(H)²⁺₂ and Pd(Eth)⁰₂. In addition, the stopped-flow method has been used to study the reaction kinetics of Pd(II) with Eth. Three kinetic steps were observed in the pH range 1–5.5. These steps are dependent on the total concentration of Eth (T_Eth) as well as the pH of the medium. The observed pseudo-first order rate constants for the three reaction kinetic steps at constant pH are expressed empirically by kⁱ_obs = m_i + m′_iT_Eth. The parameters m_i and m′_i are pH-dependent. It has been concluded that PdCl²⁻₄ and PdCl₂OH²⁻ species play an important role in the complex formation reactions with Eth. The data were interpreted in terms of the complex species obtained from the equilibrium study. cis-trans substitution reactions have been suggested to account for some kinetic steps.     

Electronic effect of β-diketonato ligands on the redox potential of fac and mer tris(β-diketonato) iron(III) complexes: A density functional theory study and molecular electrostatic potential analysis

Experimental redox potentials of 16 derivatives of tris(β-diketonato)iron(III) complexes (where β-diketonato(R₁COCHCOR₂)^─, with substituents R₁ and R₂ in different combinations of H, C₄H₃S, C₄H₃O, CH₃, Ph, CF₃, or C (CH₃)₃), and 11 additional isomers, were studied theoretically in terms of the electronic properties, substituent effects, electron affinity, and molecular electrostatic potential (MESP) analysis, using density functional theory methods. The computational methods reproduced the experimental reduction potential to a very high level of accuracy, especially when the M062X functional was used (with mean absolute deviation [MAD] = 0.054 and 0.093 and correlation R² = 0.978 and 0.981 obtained by application of two slightly different free energy cycles, respectively). The most negative computed reduction potential corresponds to the most negative reported experimental reductions, which is indicative of the least favorable reduction potential, also in most cases the most stable molecules energetically. The calculated reduction potentials of the fac isomers of the molecules were generally higher (less negative) than that of the mer isomers when one of the ligand substituents R₁ or R₂ was CF₃ (M062X results), indicating better ease of reduction, although in many cases, the experimental reduction potential agreed better with the calculated reduction potential of the mer isomer instead. The calculated reduction potentials were also affected by the substituents in the order of CF₃ > H > C₄H₃S > C₄H₃O > Ph > CH₃ > C(CH₃)₃ (the most negative value). The stronger the electron withdrawing tendency of the substituent, the more favorable (less negative value) the reduction potential becomes. In relation to the CH₃-substituted molecule 1 as a reference, the molecules with electron withdrawing substituents resulted in an electron-deficient MESP iso-surface, in both the neutral state and reduced state. All the molecules in their reduced state were characterized with an electron-deficient MESP iso-surface compared with the reduced CH₃-substituted molecule 1, with the deficiency increasing in mer compared with fac, for both the neutral and reduced molecules. The relative MESP values of ΔV_Fe in the reduced state of the molecules were able to predict the corresponding experimental reduction potential to a significant level of accuracy (with MAD = 0.091).     

Chelating alkoxy NHC–Rh(I) complexes and their applications in the arylation of aldehydes

In this study, new rhodium(I) complexes (5 and 6) have been prepared by the reaction of [RhCl(COD)]₂ with a series of imidazolium salts (3 and 4), which were obtained from a chiral amino alcohol. The catalytic activities of these complexes were tested in the arylation of aldehydes. It was found that the synthesized rhodium complexes were highly effective catalysts for the arylation of aldehydes in short reaction times (5 min, TOF = 1193 h⁻¹). However, the obtained ee values (up to 32% ee) remained low. We have proposed a mechanism for the arylation reaction of aldehydes, which is confirmed via ¹⁹F NMR spectroscopy.     

31P-NMR and X-ray studies of new rhodium(I) β-ketoiminato complexes Rh(R1C(O)CHC(NH)R2)(CO)(PZ3) where PZ3=PPh3, PCy3, P(OPh)3 or P(NC4H4)3

The substitution of the CO ligand in rhodium(I) β-ketoiminato complexes Rh(R₁{O,N}R₂)(CO)₂ ({O,N}=R₁C(O)CHC(NH)R₂; R₁, R₂=CF₃, Me, CMe₃ in several combinations) by phosphorus ligands PZ₃ (PZ₃=PCy₃, PPh₃, P(OPh)₃, P(NC₄H₄)₃) leads to Rh(R₁{O,N}R₂)(CO)(PZ₃) complexes characterised by ³¹P{¹H}-NMR and X-ray methods. The stronger σ-donor PZ₃ ligands (PZ₃=PCy₃, PPh₃) substitute almost exclusively the CO group trans to N, forming P-trans-to-N isomers. The complexes Rh(CF₃{O,N}Me)(CO)(PCy₃) (II), Rh(CF₃{O,N}CMe₃)(CO)(PCy₃) (III), Rh(CF₃{O,N}Me)(CO)(PPh₃) (IV) and Rh(CF₃{O,N}CMe)(CO)(PPh₃) (V) are of a square-planar geometry with a slight tetrahedral distortion around the rhodium atom in II, III and V. The RhP(PCy₃) bonds are slightly longer than the RhP(PPh₃) bonds. The reaction of stoichiometric amounts of the less basic P(OPh)₃ or P(NC₄H₄)₃ ligands leads to the formation of both isomers of the Rh(R₁{O,N}R₂)(CO)(P(OPh)₃) or Rh(R₁{O,N}R₂)(CO)(P(NC₄H₄)₃) complex in comparable yields. The RhP(P(OPh)₃) distance (2.195(2) Å) in the isomer of Rh(CF₃{O,N}CMe₃)(CO)(P(OPh)₃) with P(OPh)₃ coordinated trans to N (VI) is ca. 0.04 Å longer than in the isomer of that complex with P(OPh)₃ coordinated trans to O (VII). The CO substitution in Rh(R₁{O,N}R₂)(CO)₂ by PZ₃ ligands (PPh₃, PCy₃, P(OPh)₃) causes the shortening of the RhC(CO) bond by ca. 0.04 Å compared to Rh(CF₃{O,N}Me)(CO)₂ (I), making difficult the coordination of another PZ₃ ligand, especially one with stronger σ-donor properties. The more π-acceptor P(OPh)₃ ligands form bis-phosphito complexes and Rh(CF₃{O,N}CMe₃){P(OPh)₃}₂ (VIII) exhibits inequivalence of the two P(OPh)₃ ligands in solution (³¹P-NMR) as well as in solid form (X-ray).