Alma Arévalo

On the Catalytic Hydrodefluorination of Fluoroaromatics Using Nickel Complexes: The True Role of the Phosphine

Homogeneous catalytic hydrodefluorination (HDF) of fluoroaromatics under thermal conditions was achieved using nickel(0) compounds of the type [(dippe)Ni(η(2)-C6F6-nHn)] where n = 0-2, as the catalytic precursors. These complexes were prepared in situ by reacting the compound [(dippe)Ni(μ-H)]2 with the respective fluoroaromatic substrate. HDF seems to occur homogeneously, as tested by mercury drop experiments, producing the hydrodefluorinated products. However, despite previous findings by other groups, we found that these HDF reactions were actually the result of direct reaction of the alkylphosphine with the fluoroaromatic substrate. This metal- and silane-free system is the first reported example of a phosphine being able to hydrodefluorinate on its own.

Analysis of a hydrodesulfurization process— 2 [1]. The reactions of 2- and 3-methylthiophenes with tris(triethylphosphine)platinum(0)

Abstract The oxidative insertion reactions of 2-methylthiophene (2-MeT) and 3-methylthiopene (3-MeT) with Pt(PEt3)3 (1), were examined as models for the first step in a platinum catalysed hydrodesulfurization. 2-MeT gave a single isomer, 1-bis(triethylphosphine)platina-2-thia-3-methylcyclohexa-3,5-diene (2), characterized spectroscopically. 3-MeT gave two isomers (ratio 1:1.6), 1-bis(triethylphosphine)platina-2-thia-5-methylcyclohexa-3,5-diene (3b), dentified spectroscopically, and 1-bis(triethylphosphine)platina-2-thia-4-methylcyclohexa-3,5-diene (3a), identified spectroscopically and by an X-ray crystal structure determination. The thiophenes in the thiametallacycles can be displaced by free thiophenes and measurements show that the equilibrium constants decrease in the order [Pt(C,S-3-MeT)(PEt3)2]+T[Keqm(3/0) = 2.30 (after 7 h)] ; [Pt(C,S-3-MeT)(PEt3)2]+2-MeT [Keqm(3/2) = 2.20 (after 12 h)]; and [Pt(C,S-2-MeT)(PEt3)3]+T [Keqm(2/0) = 1.45 (after 20 h)]. The order of stability in the complexes is T > 2-MeT > 3-MeT. Equilibrium is attained more rapidly in the 3-MeT complexes than in those of 2-MeT. Details of the X-ray structure of the previously prepared complex 5, [Pt(PEt3)2{C,S-C12H8S}], derived from dibenzothiophene, are also given and these two structures are compared with that for complex 4, [Pt(PEt3)2{C,S-C8H6S}], derived from benzothiophene. Comple 3a, 4 and 5 share the common feature of a six-membered thiaplatinacycle, which is planar in 3a, nearly so in 4, but very severely distorted in 5; however, many of the bond lengths and angles are similar.

Oxidative insertion into the N–H bond of carbazole, indole and pyrrole with zerovalent metals

Abstract The reactions of carbazole (C12H8NH), indole (C8H6NH) and pyrrole (C4H4NH) with the zerovalent [Pt(PEt3)3], [Pd(PEt3)3] and [Ni(PEt3)3] gave oxidative insertion into the N–H bond, affording the corresponding hydrides of the type trans-[HM(LN)(PEt3)2], LN=de-protonated heterocyclic ligand; the isolated compounds for platinum were trans-[HPt(C8H6N)(PEt3)2] (1), trans-[HPt(C4H4N)(PEt3)2] (2), and for nickel trans-[HNi(C12H8N)(PEt3)2] (3), trans-[HNi(C8H6N)(PEt3)2] (4) and trans-[HNi(C4H4N)(PEt3)2] (5); on using palladium the corresponding hydrides were also detected in solution, however, after longer reaction time the double substituted compounds: trans-[Pd(C12H8N)2(PEt3)2] (6), trans-[Pd(C8H6N)2(PEt3)2] (7) and trans-[Pd(C4H4N)2(PEt3)2] (8) were obtained. A crystal structure is reported for 6.

Nickel(0) complexes with fluorinated alkyne ligands and their reactivity towards semihydrogenation and hydrodefluorination with water.

The current work describes the synthesis and full characterization of zerovalent nickel complexes of the type [(dippe)Ni(η(2)-C,C-F(n)-alkyne)] (dippe = 1,2-bis(di-isopropylphosphino-ethane), F(n)-alkyne = fluorinated aromatic alkyne, n = 1, 3, 5; 3a-c) and [{(dippe)Ni}(2)(μ(2)-C,C-F(n)-alkyne)] (4). Reactions with complexes 3a-c, and water as the hydrogen source, yield selective semihydrogenation of the bound alkyne to the corresponding alkene, accompanied by partial hydrodefluorination of the aromatic ring. Different alkynes were tested; on using the alkyne with five fluorine atoms over the aromatic ring, partial defluorination was achieved under the mildest reaction conditions, followed in reactivity by the alkyne with three fluorine atoms. The alkyne with only one fluorine atom was barely defluorinated. The use of triethylsilane as a sacrificial hydride source resulted in an overall increase in reactivity towards defluorination.

Binuclear pentamethylcyclopentadienyl rhodium(III) compounds with pyrazolate and thiolate bridging ligands

Abstract Binuclear thiolato-bridged complexes of general formula [( η 5 -C 5 Me 5 ) 2 Rh 2 ( μ -Pz)( μ -SR) 2 ]BF 4 (Pz=pyrazolate; R=C 6 F 5 ( 2a ), p -C 6 F 4 H ( 2b ), p -C 6 H 4 F ( 2c ) or C 6 H 5 ( 2d )) have been prepared by reacting the hydroxo–pyrazolato-bridged compound [( η 5 -C 5 Me 5 ) 2 Rh 2 ( μ -Pz) 2 ( μ -OH)] BF 4 with the corresponding thiol. Complexes 2a–d show two types of fluxionality: rotation around the thiol C–S bond and isomerization among the three possible isomers in which the thiols occupy axial and/or equatorial positions within the Rh 2 S 2 metallacycle. These processes are studied by 1 H and 19 F NMR spectroscopies. The crystal structures of 2b and 2d were established by X-ray crystallography. Compound 2b crystallises in the monoclinic space group P 2 1 /n, with lattice parameters a =14.368(2), b =18.252(2), c =15.268(2) A, β =109.79(1)° and Z =4. Complex 2d crystallises in a monoclinic lattice, space group C 2/c, with a =48.723(5), b =8.7503(8), c =40.334(4) A, β =112.620(5)° and Z =16. Both cationic dinuclear complexes exhibit very similar molecular structures with analogous pseudo -octahedral environments for the rhodium centres. Each metal is bonded to a terminal η 5 -C 5 Me 5 group and to three bridging ligands: two monodentate thiolates ( p -SC 6 F 4 H in 2b and SC 6 H 5 in 2d ) and a bidentate pyrazolate group. The main structural dissimilarity affects the relative configuration of the thiolate phenyl substituents giving rise to syn ( 2b ) or anti ( 2d ) structures.

Mn(I) organometallics containing the iPr2P(CH2)2PiPr2 ligand for the catalytic hydration of aromatic nitriles

The first example of a homogeneous hydration of aromatic nitriles catalyzed by manganese molecular compounds is reported. The Mn(I) organometallics fac-[(CO)3Mn(dippe)(Z)]1−nX1−n (n = 0, 1; Z = Br, OTf, PhCN; X = OTf) were synthesized and characterized, and their reactivity was studied. The species fac-[(CO)3Mn(dippe)(OTf)] (2) was used as a catalyst precursor for the selective hydration of benchmark benzonitrile (2 mol% 2, THF/H2O 1 : 2 v/v, 18 h, 100 °C) to produce benzamide in 90% isolated yield. A series of (hetero)aromatic nitriles were hydrated to synthesize the corresponding amides in very good to excellent yields (88–94%). Isotopic labeling studies accounted for a proton transfer as the rate-determining step.