Francisco Estevan

Tandem β-Boration/Arylation of α,β-Unsaturated Carbonyl Compounds by Using a Single Palladium Complex To Catalyse Both Steps

Diphenyl(3-methyl-2-indolyl)phosphine (C(9)H(8)NPPh(2), 1) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N-bridging coordination mode. On treating 1 with [Pd(O(2)CCH(3))(2)], the new complexes [Pd(mu-C(9)H(7)NPPh(2))(NCCH(3))](2) (2) or [Pd(mu-C(9)H(7)NPPh(2))(mu-O(2)CCH(3))](2) (3) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(mu-C(9)H(7)NPPh(2))(3)(mu-O(2)CCH(3))] (4), in which the bimetallic unit is bonded by three C(9)H(7)NPPh(2)(-) moieties and one carboxylate group. Using this methodology, [Pd(2)(mu-C(6)H(4)PPh(2))(2)(mu-C(9)H(7)NPPh(2))(mu-O(2)CCX(3))] (X=H (7); X=F (8)) were synthesised from the ortho-metalated compounds [Pd(C(6)H(4)PPh(2))(mu-O(2)CCX(3))](2) (X=H (5); X=F (6)). Complexes 3, 4, 7, and 8 have been found to be active in the catalytic beta-boration of alpha,beta-unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive beta-boration/cross-coupling reaction with dimethyl acrylamide as the substrate (99% conversion, 89% isolated yield).

High yield synthesis of trinuclear [M3S4X3(diphos)3]+ (M=Mo, W; X=Cl, Br and diphos=dmpe, dppe) molecular clusters from solid state materials. Synthesis and structure of [W3S4H3(dppe)3](BPh4)

The excision of polymeric {M 3 S 7 X 4 } x (M=Mo, W; X=Cl, Br) cluster phases with diphosphines (dmpe, dppe) in acetonitrile affords a one step general synthetic route for the preparation of trinuclear molecular clusters with formula [M 3 S 4 X 3 (diphos) 3 ] + (M=Mo, W; X=Cl, Br and diphos=dmpe, dppe) in high yields. Following this strategy, the cluster cations [Mo 3 S 4 Br 3 (dmpe) 3 ] + and [W 3 S 4 Br 3 (dppe) 3 ] + have been prepared for the first time. This last tungsten cluster has proved to be a useful synthon for the synthesis of the hydride derivative [W 3 S 4 H 3 (dppe) 3 ] + in moderate yields. The crystal structure of [W 3 S 4 H 3 (dppe) 3 ](BPh 4 ) consists of a equilateral tungsten triangle with one capping and three bridging sulfur atoms defining a incomplete W 3 S 4 cuboidal unit in which the tungsten and the sulfur atoms occupy adjacent vertex of a cube with a metal atom missing. The hydride ligand occupies the outer position of the metal in a pseudo-octahedral environment. The other two outer positions on each metal are occupied by the diphosphine phosphorus atoms, located one above and one bellow the M 3 plane resulting in two different 31 P{ 1 H} NMR signals. Electrochemical studies for all trinuclear clusters reported show one quasi reversible and one irreversible reduction process.

Orthometalation reactions in trifluoroacetate dirhodium(II) compounds. Molecular structure of Rh2(O2CCF3)2[(C6H4)PPh2]2·(PPh3)2·2(C7H8)

Abstract Rh 2 (O 2 CCF 3 ) 3 [(C 6 H 4 )PPh 2 ]·(HO 2 CCF 3 ) 2 reacts with PPh 3 yielding the doubly metalated compound Rh 2 (O 2 CCH 3 ) 2− [(C 6 H 4 )PPh 2 ] 2 ·(HO 2 CCF 3 ) 2 . The reaction proceeds via a reactive intermediate with an equatorial phosphine, Rh 2 (η 2 -O 2 CCF 3 )(μ-O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ](PPh 3 )·(HO 2 CCF 3 ), which can also be generated in moderate yield under photochemical conditions. The structure of the PPh 3 bis-adduct Rh 2 (O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ] 2 ·(PPh 3 ) 2 ·2(C 7 H 8 ) has been determined by X-ray diffraction. M r =1663.27, orthorhombic, space group Fdd 2, a =41.748(9), b =21.620(5), c =17.375(5) A, V =15683(6) A 3 , Z =8, D x =1.41 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.71073 A), μ(Mo Kα)=5.57 cm −1 , F (000)=6800, T =293 K. Final conventional R factor=0.035 for 2789 ‘observed’ reflections and 422 variables. The molecule shows crystallographic two-fold axis symmetry through the RhRh bond. One toluene solvent molecule slightly disordered is present in the asymmetric unit.

Synthesis and structure of the incomplete cuboidal clusters [W3Se4H3(dmpe)3]+, [W3Se4H3−x(OH)x(dmpe)3]+ and [W3Se4(OH)3(dmpe)3]+, and the mechanism of the acid-assisted substitution of the coordinated hydrides

The novel incomplete cuboidal cluster [W3Se4H3(dmpe)3](PF6), [1](PF6), has been prepared by reduction of [W3Se4Br3(dmpe)3](PF6) with LiBH4 in THF solution. The trihydroxo complex [W3Se4(OH)3(dmpe)3](PF6), [2](PF6), was obtained by reacting [W3Se4Br3(dmpe)3](PF6) with NaOH in MeCN-H2O solution. The complexes [1](PF6) and [2](PF6) were converted to their BPh4- salts by treatment with NaBPh4. Recrystallisation of [1](BPh4) in the presence of traces of water affords the mixed dihydride hydroxo complex [W3Se4H2(OH)(dmpe)3](BPh4). The crystal structures of [1](BPh4), [2](BPh4) and [W3Se4H2(OH)(dmpe)3](BPh4) have been resolved. Although the [1]+ trihydride does not react with an excess of halide salts, reaction with HX leads to [W3Se4X3(dmpe)3]+ (X = Cl, Br). The kinetics of this reaction has been studied at 25 degrees C in MeCN-H2O solution (1:1, v/v) and found to occur with two consecutive kinetic steps. The first step is independent of the nature and concentration of the X(-) anion but shows a first order dependence on the concentration of acid (k1 = 12.0 mol(-1) dm(3) s(-1)), whereas the second one is independent of the nature and concentration of both the acid and added salts (k2 = 0.024 s(-1)). In contrast, the reaction of [2]+ with acids occurs in a single step with kobs = 0.63 s(-1)(HCl) and 0.17 s(-1)(HBr). These kinetic results are discussed on the basis of the mechanism previously proposed for the reactions of the analogous [W3S4H3(dmpe)3]+ cluster, with special emphasis on the effects caused by the change of S by Se on the rate constants for the different processes involved.

A unified mechanistic view obtained from the temperature and pressure dependence of the spontaneous, acid-, and base-assisted cyclometallation reactions of dirhodium(II) complexes

The reaction of compounds [Rh2(O2CMe)(µ-O2CMe)2{µ-(XC6H3)P(C6H4X-p)2}{P(C6H4X′-p)3}](X = H, X′= H or Me; X = Me, X′= H or Me), having a metallated and an equatorial phosphine in a head-to-tail cisoid configuration, to produce the corresponding doubly metallated compounds [Rh2(µ-O2CMe)2{µ-(XC6H3)P(C6H4X-p)2}2], has been studied in detail. The thermal, acid-, and base-assisted conditions include toluene solution, neat acetic acid, and different bases [PPh3, P(C6H4Me-p)3 or pyridine] in toluene solution and as a function of temperature, pressure and base concentration (when applicable). The doubly metallated compounds always show retention of the head-to-tail cisoid configuration according to 31P NMR spectroscopy. The reported activation parameters allow a clear differentiation between the spontaneous, acid-assisted and base-assisted processes, some of which had been previously studied (ΔH‡= 80 ± 5, 68 ± 1, 38 ± 3 kJ mol–1; ΔS‡=–105 ± 15, –85 ± 3, –150 ± 30 J K–1 mol–1; ΔV‡=–22.7 ± 0.2, –15.3 ± 0.2, –35.0 ± 0.5 cm3 mol–1 respectively, for the compound with X, X′= H). For the reactions under baseassisted conditions, when long reaction times and/or high added Lewis-base concentrations were applied, the non-metallated phosphine was displaced from equatorial to axial co-ordination. Under these conditions a mixture of the bis adducts of the monometallated [Rh2(µ-O2CMe)3{µ-(XC6H3)P(C6H4X-p)2}], and the doubly-metallated compounds was detected by 31P NMR spectroscopy. The activation parameters obtained for this slower process agree with those expected for substitution reactions and are interpreted in terms of the steric demands of the mono and bis adducts formed immediately on mixing the reaction solutions.

Electrochemical study of dinuclear ruthenium(II)—arene compounds: Electrogeneration of Ru(II)—Ru(I) species

Abstract The preparation and characterization of Ru(II)—arene compounds [{RuCl2(p-cym)}2(μ-L-L)] where p-cym = p-MeC6H4CHMe2; and L-L = diphenylphosphinomethane (I), 1,1′-bisdiphenylphosphinoferrocene (II), pyrazine (III) and 4,4′-bipyridine (IV), are described. Electrochemical data for these compounds obtained by cyclic voltammetry and coulometry are reported. The electrochemical reduction of compounds I or II yields ruthenium(O) species. However, compounds III or IV containing ligands with delocalized Π orbitals undergo one-electron reduction. The ESR signal detected during the electrolysis of compounds III or IV is consistent with one delocalized electron through the whole dinuclear unit.

Synthesis and electrochemical studies of new ferrocene-labelled dinuclear rhodium(II) complexes. Crystal structures of [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]Fe(C5H5)}2(HO2CMe)2] and [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]2Fe}(HO2CMe)]·CH2Cl2

The reaction of diphenylphosphinoferrocene and 1,1′-bis(diphenylphosphino)ferrocene with [Rh2(O2CMe)4(MeOH)2](1:1 and 1:2 molar ratio respectively) yields the monoadducts [Rh2(O2CMe)4{(Ph2PC5H4)Fe(C5H5)}]1 and [{Rh2(O2CMe)4(MeOH)}2{(Ph2PC5H4)2Fe}]2. By thermal treatment of 1 in refluxing toluene–acetic acid (10:3) the monometallated product [Rh2(O2CMe)3{[(C6H4)PhP(C5H4)]Fe(C5H5)}(HO2CMe)2]3 was obtained in practically quantitative yield. Compound 3 reacts with [Fe(C5H5)(C5H4PPh2)](1:1 molar ratio) giving the adduct [Rh2(O2CMe)3{[(C6H4)PhP(C5H4)]Fe(C5H5)}{(Ph2PC5H4)Fe(C5H5)}]4, which reacts thermally in toluene–acetic acid (10:3) yielding the doubly metallated product [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]Fe(C5H5)}2(HO2CMe)2]5 as a mixture of conformational isomers. An X-ray determination of 5 has been carried out: space group Pbca(orthorhombic), a= 18.065(3), b= 20.606(4), c= 26.242(5)A, Z= 8, and R= 0.038. The crystal structure shows that the two metallated phosphines are in a head-to-tail configuration. Thermal treatment of a mixture of [Rh2(O2CMe)4(MeOH)2] and [Fe(C5H4PPh2)2](1:1 molar ratio) in acetic acid yields the compound [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]2Fe}(HO2CMe)]·CH2Cl26 after purification and crystallization from a CH2Cl2–hexane–acetic acid mixture. An X-ray diffraction investigation showed that this compound crystallizes in space group P21/c(monoclinic) with a= 12.735(4), b= 16.811(5), c= 20.161(8)A, β= 95.17(4)°, Z= 4 and R= 0.089. The two PPh2 fragments of the ferrocene ligand act as bridging orthometallated ligands in a head-to-head configuration. Two well defined oxidation processes were detected by cyclic voltammetry for all the complexes in CH2Cl2 solution: the first one, in the range 0.6–0.7 V, is due to the couple Fe2+–Fe3+ while the second one, in the range 0.9–1.32 V, is due to the couple Rh24+–Rh25+.

Reaction of Rh2(μ2-O2CCH3)3[μ2-(C6H4)PMePh](HO2CCH3)2 with triphenylphosphine: rearrangement of the metalated PMePh2 ligand and formation of a compound with a diphenylphosphinomethanide group in (P,C) coordination; crystal structure of [Rh2(μ2-O2CCH3)2{μ2-(CH2)PPh2}- {μ2-(C6H4)PPh2}(PPh3)]·2CH2Cl2☆

The reaction of [Rh2(μ2-O2CCH3)3{μ2-(C6H4)PMePh}] (1) in CHCl3 with one mole of PPh3 gives the two phosphine monoadducts, which are in rapid equilibrium above −40 °C. After 6 h at room temperature this mixture gives [Rh2(μ2-O2CCH32{μ2-(C6H4)PMePh}{μ2-(C6H4)PPh2}](HO2CCH3)2 (3), a doubly metalated compound with a head-to-head configuration. 1 reacts with two moles of PPh3, forming the bis-adduct 1.P2, which at 10 °C gives a mixture 3, in the form of its phosphine adduct 3.P, and [Rh2(μ2-O2CCH3)2{μ2-(CH2)PPh2}{μ2- (C6H4) PPh2}(PPh3)] (2). It is confirmed that 3.P is not the kinetic product in the reaction from 1.P2 to 2. The structure of [Rh2(μ2-O2CCH3)2{μ2-(CH2)PPh2}{μ2-(CP6H4) PPh2} (PPh3)]·2CH2Cl2 has been determined by X-ray diffraction: Mr = 1216.55, monoclinic, space group P21/c, a=19.930(8), b=15.29(2), c=16.84(2) A, β=90.14(9)°, V=5129(9) A3, Z=4, Dc=1.58 g cm−3, Mo Kα radiation (graphite monochromator, λ=0.71073 A), μ (Mo Kα)=9.80 cm−1, F(000)=2464, T=200 K. The final conventional R factor was 0.061 for 4749 ‘observed’ reflections. The compound contains an orthometalated triphenylphosphine and a diphenylphosphinomethanide group bridging the two rhodium atoms. The two ligands are in a head-to-head configuration. Two bridging acetate groups and one axial PPh3 complete the coordination around the rhodium atoms. The RhRh bond distance is 2.532(2) A.

Zinc complexation to N-substituted sulfonamide ligands.: Preparation, properties and crystal structure of copper(II) doped {[Zn(sulfamethizolate)2(py)]·H2O}∞

Abstract The single crystal structure and spectroscopic properties of the copper(II) doped {[Zn(sulfamethizolate) 2 (py)]·H 2 O} ∞ are reported. The complex is a polymer where the Zn(II) ions are coordinated by four N atoms in a very distorted tetrahedral environment. The sulfamethizolate anion acts as a monodentate ligand through the thiadiazole N atom and as a bridging ligand via the amino and thiadiazole N atoms. The compound is studied by EPR, by 13 C NMR in solid state and by 1 H and 13 C NMR in DMSO-d 6 solution. The similarity between the 13 C NMR spectrum in solution and the solid 13 C NMR spectrum indicates that the structure of the compound remains in solution. The EPR spectrum shows the presence of two different environments for the Cu(II) ions.

Photo-assisted formation of a chelating diphos ligand from PPh3 and a cyclometallated [P(C6H4)(C6H5)2]− ligand. Crystal structure of Pd{η2-o-[P(C6H5)2]2(C6H4)}Br2

Abstract The cyclometallated palladium compound, Pd[η2-(C6H4)P(C6H5)2]Br[P(C6H5)3] (1), in the solid state by action of light, evolves to give Pd{η2-o-[P(C6H5)2]2(C6H4)}Br2 (2). This compound contains the diphosphine, o-[P(C6H5)2]2(C6H4), as chelated ligand that is formed by a couple reaction of the metallated ligand η2-[(C6H4)P(C6H5)2]− and the coordinated arylphosphine. A study by NMR spectroscopy confirms that the o-phenylene bridge in the diphosphine ligand in 2 comes from the metallated phosphine ligand in 1.