Isocyanide complexes of rhodium,part 41,2). η5-pentamethylcyclopentadienyl-rhodium (III) compounds

Summary The complexes Rh(⁵-C₅Me₅)(CNR)Cl₂, [Rh(⁵ - C₅Me₅)(CNR)₂Cl][PF₆], (R = Me, Et, i-Pr, t-Bu, C₆H₁₁, , p-CIC6H4 and 1-naphthyl), and [Rh(⁵-C⁵Me⁵)(CNR)₃][PF₆] (R = Et, i-Pr and t-Bu)] have been prepared by treatment of [Rh(⁵-C₅Me₅)Cl₂]₂ with RNC in the presence of [PF₆]^– (as appropriate). These complexes do not react with alcohols or amines to yield carbenes, but withm-MeC₆H₄SNa and NaS₂CNR₂, the species Rh(⁵-C₅H₅)(CNEt)(SC₆M₄Me-m)₂ and [Rh(⁵-C₅Me₅)(CNR)(S₂CNR₂)][PF₆] (R = Me, R¹ = Me or Et; R =p-ClC₆H₄, R¹ = Me) are formed. Treatment of [Rh(⁵-C₅H₅)(CNR)₂Cl][PF₆] with NaBH₄ gave low yields of compounds tentatively formulated as [Rh(⁵-C₅Me₅)(CNR)₂(BH₄)][PF₆] (R = Me or Et).Reprints of this article are not available.     

E.s.r. and electrochemical studies of four- and five-coordinate copper(II) complexes containing mixed ligands

Heterocyclic base adducts of salicylaldehyde N(4)- cyclohexylthiosemicarbazone(H2L) copper(II) complexes have been synthesized and characterized. I.r., electronic and e.s.r. spectra of the complexes, as well as i.r., electronic and 1H- and 13C-n.m.r. spectra of the thiosemicarbazone have been obtained. Based on e.s.r. studies, all possible parameters have been calculated. The g values, calculated for all the complexes in frozen solution, indicate the presence of the unpaired electron in the dx2−y2 orbital. The metal–ligand bonding parameters evaluated showed strong in-plane σ- and in-plane π-bonding. The magnetic and spectroscopic data indicate a square-planar geometry for the four-coordinate and a distorted square-pyramidal structure for the five-coordinate complexes. From cyclic voltammetric data quasireversible copper(II)/copper(I) couples are observed for the complexes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Temperature-dependent coordination of phosphine to five-coordinate alkenylruthenium complexes

The red, five-coordinate complexes Ru(CO)Cl(PPh(3))2(CH=CHPh) and [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHC(6)H(4)CH=CH) undergo reversible coordination of PPh(3) at low temperature to produce the pale yellow, six-coordinate complexes Ru(CO)Cl(PPh(3))3(CH=CHPh) and [Ru(CO)Cl(PPh(3))3]2(mu-CH=CHC(6)H(4)CH=CH). X-ray crystal structures of the latter complex and of the hydride complex RuH(CO)Cl(PPh(3))3 were obtained. 1H and 31P NMR spectra between 20 and -70 degrees C exhibit large changes in both equilibrium constants and dynamic effects. Thermodynamic parameters, DeltaH = -17.5 +/- 2.0 kcal/mol and DeltaS = -57.5 +/- 7.6 eu, were obtained for PPh(3) coordination to the monoruthenium complex, and activation parameters, DeltaH = 20.6 +/- 0.7 kcal/mol and DeltaS = 41.6 +/- 2.0 eu, were obtained for the reverse decoordination. Coordination of PPh(3) was not observed upon cooling of the shorter bridged complex, [Ru(CO)Cl(PPh(3))2]2(mu-CH=CHCH=CH).     

Theoretical investigations of uranyl-ligand bonding: four- and five-coordinate uranyl cyanide, isocyanide, carbonyl, and hydroxide complexes

The coordination and bonding of equatorial hydroxide, carbonyl, cyanide (CN-), and isocyanide (NC-) ligands with uranyl dication, [UO2]2+, has been studied using density functional theory with relativistic effective core potentials. Good agreement is seen between experimental and calculated geometries of [UO2(OH)4]2-. Newly predicted ground-state structures of [UO2(OH)5]3-, [UO2(CO)4]2+, [UO2(CO)5]2+, [UO2(CN)4]2-, [UO2(CN)5]3-, [UO2(NC)4]2-, and [UO2(NC)5]3- are reported. Four-coordinate uranyl isocyanide complexes are the predicted gas-phase species while five-coordinate uranyl cyanide complexes are energetically favorable in aqueous solution. Small energy differences between cyanide and isocyanide complexes indicate the energetic feasibility of mixed cyanide and isocyanide complexes. A D2d uranyl tetrahydroxide is the dominant gas-phase and aqueous species, but formation of uranyl carbonyl complexes is seen to be exothermic in the gas-phase and endothermic in aqueous solution.     

C-H Activation by dinuclear phosphine bridged complexes of rhodium,iridium, and ruthenium

The possibility of activation of the C-H bond by dinuclear phosphine bridged complexes of rhodium, iridium, and ruthenium is considered.This work was reported at the conference Modern Problems of Organometallic Chemistry (8–13 May, 1994, Moscow).Institut fer Technische Chemie und Petrolchemie der RWTH Aachen Worringerweg 1, 52074 Aachen, Deutschland.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 589–593, April, 1994.     

Four- and five-coordinate copper(II) complexes containing mixed ligands

New copper(II) complexes of general formula, Cu(ONS)B (ONS = the di-negatively charged Schiff base, S-benzyl-β-N-(2-hydroxyphenyl) methylendithiocarbazate; B = pyridine, 2,2′-dipyridyl or 1,10-phenanthroline) have been synthesized and characterised by magnetic and spectroscopic measurements. The complex, Cu(ONS)py is four-coordinate and square-planar. Magnetic and spectroscopic data support a five-coordinate, presumably, a trigonal-bipyramidal structure for the [Cu(ONS)dipy] and (Cu(ONS)phen] complexes     

New water-soluble platinum(II) phenanthroline complexes tested as cisplatin analogues: First-time comparison of cytotoxic activity between analogous four- and five-coordinate species

Four- and five-coordinate platinum(II) complexes, cis-[PtCl2(A2)] (1) and [PtCl2(A2)(eta2-ethylene)] (2) {A2 = 4,7-diphenyl-1,10-phenanthroline disulfonic acid disodium salt, BPS (mixture of isomers) (a); 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline disulfonic acid disodium salt, BCS (mixture of isomers) (b)} have been synthesized and characterized by 1H, 13C, and 195Pt NMR spectroscopy. The stability and high water solubility of complexes 1a, 1b and 2b, due to the presence of the polar SO3- groups on the ligands skeleton, allowed to test their in vitro cytotoxicity on HeLa tumour cells in a wide range of drug concentration. At low and medium incubation doses (<200 microM) 1a, 1b and 2b all showed similar in vitro cytotoxicity, negligible or much lower with respect to cisplatin. At doses higher than 200 microM their activity increased and 1b, the most active among the new complexes, exhibited a cytotoxicity comparable, although still lower, with respect to cisplatin. GFAAS Platinum analytical data showed that the tested compounds 1a, 1b and 2b, although carrying sulfonate charged groups, may undergo cellular uptake, which, in the case of 1b and 2b, is even higher with respect to cisplatin. Furthermore, in the case of 1b and 2b it has been possible to compare, for the first time, the cytotoxic activity for square-planar four-coordinate and trigonal-bipyramidal five-coordinate platinum(II) complexes having the same carrier ligand. The tendency of the five-coordinate species 2b to give at longer incubation time similar cytotoxicity with respect to the square-planar compound 1b suggests a possible use of the trigonal-bipyramidal five-coordinate complexes as prodrugs.     

The thermal behaviour of some rhodium complexes

The thermal behaviour of several complexes of rhodium has been investigated. Complexes containing nitrogen ligands readily decompose to the oxide, Rh₂O_3^? Complexes with phosphorus and arsenic ligands decompose to the same oxide of rhodium, although difficulty is encountered in removing all the phosphorus and arsenic. The suitability of the decomposition to Rh₂O₃ as an analytical technique for rhodium is discussed.     

Nickel complexes of a bis(benzimidazolin-2-ylidene)pyridine pincer ligand with four- and five-coordinate geometries

The four- and five-coordinate complexes [(CNC)NiX(2)] (X = Cl, Br, I), [(CNC)NiX]PF(6) (X = Cl, Br) and [(CNC)NiCl]Cl·H(2)O have been isolated, where CNC is the bis(N-butylbenzimidazolin-2-ylidene)-2,6-pyridine pincer ligand. A five-coordinate geometry is rare for this class of complex. Where amenable, the complexes have been structurally characterised by single crystal X-ray diffraction studies and in solution by NMR, UV-vis and MS studies. The five-coordinate dibromo complex [(CNC)NiBr(2)] is readily prepared on the gram-scale from the benzimidazolium salt precursor and Ni(OAc)(2)·4H(2)O in DMSO without the exclusion of air. Halide exchange and salt metathesis reactions using [(CNC)NiBr(2)] afford the other four- and five-coordinate complexes. [(CNC)NiBr(2)] displays very low solubility, and upon dissolution affords solutions of the four-coordinate [(CNC)NiBr](+). Factors that influence the formation of four- or five-coordinate complexes with this ligand class are discussed.     

Pentamethylcyclopentadienyl rhodium(III) trifluorovinyl phosphine complexes and attempted intramolecular dehydrofluorinative coupling of pentamethylcyclopentadienyl and trifluorovinyl phosphine ligands

The trifluorovinyl phosphine complexes [Cp*RhCl₂{PR_3−x(CFCF₂)_x}] (1x = 1, a R = Ph, b Prⁱ, c Et; 2x = 2, R = Ph) have been prepared by treatment of [Cp*RhCl(μ-Cl)]₂ with the relevant phosphine. The salt [Cp*RhCl(CNBu^t){PPh₂(CFCF₂)}]BF₄, 3, was prepared by addition of Bu^tNC to 1a in the presence of NaBF₄. The salt [Cp*RhCl{κP,κS-(CF₂CF)PPh(C₆H₄SMe-2)}]BF₄ was prepared as a mixture of cis (5a) and trans (5b) isomers by treatment of [Cp*RhCl(μ-Cl)]₂ with the phosphine-thioether (CF₂CF)PPh(C₆H₄SMe-2), 4, in the presence of NaBF₄. The structures of 1a-c and 5a have been determined by single-crystal X-ray diffraction. Intramolecular dehydrofluorinative carbon-carbon coupling between pentamethylcyclopentadienyl and trifluorovinylphosphine ligands of 1a, 3 and 5 has been attempted. No reaction was observed on treatment of the neutral complex [Cp*RhCl₂{PPh₂(CFCF₂)}], 1a, with proton sponge, however, 5a underwent dehydrofluorinative coupling to yield [{η⁵,κP,κS-(C₅Me₄CH₂CFCF)PPh(C₆H₄SMe-2)}RhCl]BF₄, 6. Other reactions, in particular addition of HF across the vinyl bonds of 5, occurred leading to a mixture of products. The cation of 3 underwent similar reactions.     

Hydroformylation of alkenes employing rhodium(i) complexes and a phosphine oxide ligand

Following the facile synthesis of a novel phosphine oxide compound, (diphenylphosphinoyl)phenylmethanol (1), this compound was employed as a ligand in the rhodium-catalyzed hydroformylation of alkenes, with good conversions and regioselectivities. This ligand was partially resolved using an enzyme, and enantioselective hydroformylation was carried out with the addition of a rhodium(I) complex. The rhodium(I) complex containing ligand 1 was not isolated, although it was subjected to low-temperature NMR studies.     

Intramolecular alkyl phosphine dehydrogenation in cationic rhodium complexes of tris(cyclopentylphosphine)

[Rh(nbd)(PCyp(3))(2)][BAr(F) (4)] (1) [nbd = norbornadiene, Ar(F) = C(6)H(3)(CF(3))(2), PCyp(3) = tris(cyclopentylphosphine)] spontaneously undergoes dehydrogenation of each PCyp(3) ligand in CH(2)Cl(2) solution to form an equilibrium mixture of cis-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(2)][BAr(F) (4)] (2 a) and trans-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(2)][BAr(F) (4)] (2 b), which have hybrid phosphine-alkene ligands. In this reaction nbd acts as a sequential acceptor of hydrogen to eventually give norbornane. Complex 2 b is distorted in the solid-state away from square planar. DFT calculations have been used to rationalise this distortion. Addition of H(2) to 2 a/b hydrogenates the phosphine-alkene ligand and forms the bisdihydrogen/dihydride complex [Rh(PCyp(3))(2)(H)(2)(eta(2)-H(2))(2)][BAr(F) (4)] (5) which has been identified spectroscopically. Addition of the hydrogen acceptor tert-butylethene (tbe) to 5 eventually regenerates 2 a/b, passing through an intermediate which has undergone dehydrogenation of only one PCyp(3) ligand, which can be trapped by addition of MeCN to form trans-[Rh{PCyp(2)(eta(2)-C(5)H(7))}(PCyp(3))(NCMe)][BAr(F) (4)] (6). Dehydrogenation of a PCyp(3) ligand also occurs on addition of Na[BAr(F) (4)] to [RhCl(nbd)(PCyp(3))] in presence of arene (benzene, fluorobenzene) to give [Rh(eta(6)-C(6)H(5)X){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (7: X = F, 8: X = H). The related complex [Rh(nbd){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] 9 is also reported. Rapid ( approximately 5 minutes) acceptorless dehydrogenation occurs on treatment of [RhCl(dppe)(PCyp(3))] with Na[BAr(F) (4)] to give [Rh(dppe){PCyp(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (10), which reacts with H(2) to afford the dihydride/dihydrogen complex [Rh(dppe)(PCyp(3))(H)(2)(eta(2)-H(2))][BAr(F) (4)] (11). Competition experiments using the new mixed alkyl phosphine ligand PCy(2)(Cyp) show that [RhCl(nbd){PCy(2)(Cyp)}] undergoes dehydrogenation exclusively at the cyclopentyl group to give [Rh(eta(6)-C(6)H(5)X){PCy(2)(eta(2)-C(5)H(7))}][BAr(F) (4)] (17: X = F, 18: X = H). The underlying reasons behind this preference have been probed using DFT calculations. All the complexes have been characterised by multinuclear NMR spectroscopy, and for 2 a/b, 4, 6, 7, 8, 9 and 17 also by single crystal X-ray diffraction.     

Hydrogenation of ketones and olefins via hydrogen transfer catalyzed by rhodium and iridium phosphine complexes

The reduction of ketones and olefins by hydrogen transfer from isopropanol is catalyzed by tertiary phosphine complexes of rhodium and iridium. The influence of the nature of the ligands and of the reaction conditions on the catalytic activity has been investigated. The reduction of the carbonyl group in the presence of olefins is also reported.     

Novel palladium complexes employing mixed phosphine phosphonates and phosphine phosphinates as anionic chelating [P,O] ligands

A route to various substituted phosphine phosphonic acid compounds of the general form Ar(2)PC(6)H(4)PO(OH)(2) (Ar = Ph, o-MeC(6)H(4), o-MeOC(6)H(4)) has been investigated. These compounds were employed as bidentate anionic [P,O] ligands in neutral palladium complexes. The [P,O] chelating coordination was determined by X-ray crystallography of a representative palladium complex. Furthermore, the bifunctional ligand Ph(2)PC(6)H(4)PO(OH)Ph represents the first example of a chelating anionic [P,O] ligand resulting from the combination of a phosphine and a phosphinate moiety.     

Effect of free phosphine on the reactivity of phosphine-containing rhodium(I) complexes

The photolysis products of SO₂-pentane-NO mixtures are N₂O, H₂O and a compound designated as RNO. Kinetic data obtained by OC method confirm the previously proposed scheme of photolysis. Also studied was the photolysis of SO₂, NO and cyclohexane mixtures. From comparison of spectral characteristics of RNO and its analog 2-methyl-2-nitrosopropane, the probable structure of RNO is suggested.

---

SO₂--NO N₂O, H₂O , RNO. , , . SO₂ NO . RNO 2--2- RNO.

     

Selective cleavage of P-N bonds and the conversion of rhodium N-pyrrolyl phosphine complexes into diphosphoxane-bridged dimers

Rhodium(I) complexes trans-[RhCl(CO)(PR(2)[NC(4)H(3)C(O)Me-2])(2)] (R = Ph, NC(4)H(4)) react with water to give the diphosphoxane-bridged dimers [Rh(2)Cl(2)(CO)(2)(mu-PR(2)OPR(2))(2)] following cleavage of the P-N bonds to the 2-acetyl-N-pyrrolyl groups. The two dimers have been crystallographically characterized and show a number of structural differences, with the PPh(2)OPPh(2) compound possessing semibridging chloride and carbonyl ligands whereas the P(NC(4)H(4))(2)OP(NC(4)H(4))(2) compound contains only terminal chlorides and carbonyls. No evidence for cleavage of the P-N bonds involving the unfunctionalized N-pyrrolyl groups in trans-[RhCl(CO)(P[NC(4)H(4)](2)[NC(4)H(3)C(O)Me-2])(2)] was observed.     

Rhodium phosphine complexes as homogeneous catalysts. part 3. Homogeneous ssymmetric hydrogenation of schiffs bases

Summary Complexes formed from [Rh(norbornadiene)Cl]₂ and tertiary phosphines under hydrogen are active catalysts for the homogeneous hydrogenation of Schiff bases at 30–80° and 1-70 bars. Using chiral phosphines some optical induction can be achieved, but the optical yields are rather low.     

Metal complexes in inorganic matrices,Part II. CO reactions of chloro(carbonyl)(phosphine)rhodium complexes in a silica gel matrix

Summary Materials obtained by polycondensation of [Rh(CO)ClL₂] [L=PPh₂CH₂CH₂Si(OEt)₃] with tetraethoxysilane (TEOS) irreversibly take up CO to give monomeric or dimeric [cis-Rh(CO)₂ClL']: (L'=PPh₂CH₂CH₂SiO_3/2·xSiO₂) (2). The polymeric metal complex (2) is also obtained by CO treatment of [Rh₂(CO)₂Cl₂L'₂] (4) or by polycondensation ofin-situ prepared (monomeric or dimeric) [Rh(CO)₂ClL] with TEOS. Unlike comparable complexes in solution,(2) is extremely stable in respect to CO loss, even at higher temperatures andin vacuo.Part I of this series, ref. (1).     

Hydroformylation of 1-hexene by soluble and zeolite-supported rhodium species part II

The hydroformylation of 1-hexene at 50 and 125°C and 300 psig CO:H₂ (1:1) using soluble and zeolite-supported rhodium species is reported. The presence of excess phosphine during homogeneous catalysis in shown to inhibit isomerization of 1-hexene and thus give high normal/branched aldehyde ratios for all levels of conversion. However, the absence of phosphine allows significant isomerization, causing the normal/branched ratio to vary with conversion. The activity of the immobilized catalysts is affected by the type and amount of phosphine. The homogeneous and heterogeneous catalysts can be poisoned by mercaptans, provided an excess of phosphine is not present. The data from the immobilized catalysts suggest that claims of intrazeolitic hydroformylation with rhodium-containing faujasites must be taken with caution.