Anabel Elduque

Self-assembly in helical columnar mesophases and luminescence of chiral 1H-pyrazoles.

Chiral polycatenar 1H-pyrazoles self-assemble to form columnar mesophases that are stable at room temperature. X-ray diffraction and CD studies in the mesophase indicate a supramolecular helical organization consisting of stacked H-bonded dimers. The liquid-crystalline compounds reported are 3,5-bis(dialkoxyphenyl)-1H-pyrazoles that incorporate two or four dihydrocitronellyl chiral tails. It can be observed that the grafting of these branched chiral substituents onto the 3,5-diphenyl-1H-pyrazole core has a beneficial role in inducing mesomorphism, because isomeric linear-chain compounds are not liquid crystalline; this is not the usual scheme of behavior. Furthermore, the molecular chirality is transferred to the columnar mesophase, because preferential helical arrangements are observed. Films of the compounds are luminescent at room temperature and constitute an example of the self-organization of nondiscoid units into columnar liquid-crystalline assemblies in which the functional molecular unit transfers its properties to a hierarchically built superstructure.

Evidence for a dinuclear mechanism in alkyne hydrogenations catalyzed by pyrazolate-bridged diiridium complexes

The products obtained from the sequential reaction of [Ir2(mu-H)(mu-Pz)2H3(NCCH3)(PiPr3)2] (1) with diphenylacetylene and their subsequent reactions with hydrogen have been investigated in order to deduce the mechanisms operating in the hydrogenation reactions catalyzed by 1. The reaction of 1 with an excess of diphenylacetylene gives cis-stilbene and [Ir2(mu-H)(mu-Pz)2-[eta1-C6H4-2-[eta1-(Z)-C=CHPh]]((Z)-C(Ph) =CHPh](NCCH3)(PiPr3)2] (2), the structure of which has been determined by X-ray diffraction. The formation of 2 involves the intermediate species [Ir2(mu-H)(mu-Pz)2H2((Z)-C(Ph)=CHPh](NCCH3)-(PiPr3)2](3),[Ir2(mu-H)(mu-Pz)2H[(Z)-C(Ph)=CHPh]2(NCCH3)(PiPr3)2] (4), and [Ir2(mu-H)(mu-Pz)2H[eta1-C6H4-2-[eta1-(Z)-C=CHPh](NCCH3)(PiPr3)2] (5), which have been isolated and characterized. These three complexes react with hydrogen to give cis-stilbene and 1 and are possible intermediates of the diphenylacetylene hydrogenation under catalytic conditions. Nevertheless, the rate of formation of 5 is very slow compared with the rate of catalytic hydrogenation, which excludes its participation during catalysis. Compound 2 also reacts with hydrogen in benzene, but in this case the hydrogenation gives 1,2-diphenylethane as the sole organic product. The course of this reaction in acetone has been investigated, and deuteration experiments were carried out. The formation of [Ir2(mu-H)(mu-Pz)2H[eta1-C6H4-2-[eta1-(Z)-C=CHPh]](OC(CD3)2)(PiPr3)2] (6) and [Ir2(mu-H)(mu-Pz)2H[eta1-C6H4-2-[eta1-(Z)-C-CHPh]](NCCH3)(PiPr3)2] (7) was observed under these conditions. The experimental evidence obtained supports two alternative mechanisms for the alkyne hydrogenation catalyzed by 1, one of them being dinuclear and the other mononuclear. The experimental data suggest that the former is favored.

Silver Pyrazolates as Coordination-Polymer Luminescent Metallomesogens

Silver pyrazolates with columnar liquid-crystal phases that are stable at room temperature have been prepared by reaction of silver nitrate with 3,5-diarylpyrazolates. The complexes consist of open-chain oligomers, despite the fact that the most common structural type for homoleptic coinage metal pyrazolates is the trimeric metallacycle [M(μ-pz)](3). The special characteristics of silver in forming reversible metal-ligand bonds in solution, evidenced experimentally, leads to supramolecular organizations in which the silver cations promote self-organization of the nonmesomorphic pyrazolates into helical 1D polymers that exhibit columnar mesophases. The materials are readily soluble in common organic solvents and are liquid-crystalline over a broader temperature range than their gold counterparts, which are known to form discrete cyclic trinuclear species. Thin films of the silver complexes show luminescence at room temperature. The compounds described here are the first examples of luminescent metallomesogens formed by a main-chain coordination polymer.

Hydroformylation of styrene using thiolato–pyrazolate bridge rhodium catalysts modified with phosphorous ligands

Abstract Catalytic precursor systems prepared using [Rh 2 ( μ -pz)( μ -SBu t )(COD) 2 ] in the presence of triphenylphosphine and chiral diphosphines are active in styrene hydroformylation. The effect of the pressure and the dependence on the P/Rh ratio are studied. When triphenylphosphine is used as phosphorous ligand complete conversion to aldehydes and regioselectivities as high as 90% in 2-phenylpropanal are obtained at very mild conditions. The use of (+)-(2 R ,4 R )(−)-(2 S ,4 S )-2,4-bis(diphenylphosphino)pentane ((+)-BDPP) or (−)-(2 S ,4 S ) ((−)-BDPP) as chiral diphosphine in a P/Rh ratio of 2 provides 95% regioselectivity and enantiomeric excess as high as 50%.

Oxidative addition of methyl iodide and iodine to new binuclear rhodium(I) and iridium(I) compounds containing diaminoanthraquinonate-bridging ligands. Crystal structure of [Rh2(μ-1,4-DA)(CO)2(PPh3)2] (1,4-H2DA = 1,4-diaminoanthraquinone)

The binuclear rhodium and irridum complexes containing the 1,4-diaminoanthraquinonate ligand (1,4-DA) [M2(μ-1,4-DA)L2] (L = COD, M = Rh (1), Ir (2); L = (CO)2, M = Rh (3), Ir (4) L = (CO)(PPh3), M = Rh (5), Ir, (6)) have been prepared and oxidative addition of the electrophiles MeI and I2 has been investigated. The molecular structure of an isomer of compound 5 has been determined by X-ray diffraction methods. Complex 5a crystallised in the triclinic space group P-1, with a = 9.711(5), b = 13.701(7), . a = 68.53(2), β = 76.98(3), γ = 79.72(3)°, and Z = 2. The molecule is binuclear with the metals bridged by an approximately planar tetradentate dianionic 1,4-DA ligand. Both rhodium centres exhibit slightly distorted square-planar coordinations with both phosphine groups rans disposed to the aminic nitrogen atoms. Addition of MeI to the rhodium complex 5 leads to the diacyl-dirhodium(III) derivative [Rh2(μ-1,4-DA)(COMe)2]2(PPh1)2] (7). However, addition MeI to the isoelectronic iridium compound 6 yields the dimethyldiiridium(III) compound [Ir2(μ-1,4-DA)]2(Me)2(CO)2(PPh3)2] (8). Reaction of iodine with compounds 5 and 6, in a molar ratio M/I2 = 1/1, yields the symmetrical complexes [M2(μ-1,4-DA)I4(CO)2(PPh4)2] (M = Rh (9, Ir(10)).

Synthesis of [Ir2(μ-Pz)2(CH3)(CO)2(PiPr3)2]+. A key intermediate in SN2 oxidative addition of halocarbons to dinuclear complexes

Abstract The unusual compound of formula [Ir2(μ-Pz)2(CH3)(CO)2(PiPr3)2](ClO4) (3) has been prepared. This complex is the proposed intermediate species for the SN2 oxidative addition of methyl iodide to the dinuclear compound [Ir(μ-Pz)(CO)(PiPr3)]2 (1). The spectroscopic and X-ray diffraction data obtained for 3, together with EHMO calculations and reactivity studies, indicate that the compound can be described as an Ir(III)–Ir(I) species containing a weak metal–metal bond. The implications of these electronic features in the regioselectivity of halocarbons oxidative additions to dinuclear complexes are discussed.

New dinuclear and heterotrinuclear complexes containing the M2(μ-az) (μ-PPh2) core (MRh or Ir; az = azolate)

Abstract The heterobridged dinuclear complexes [M 2 (μ-Pz)(μ-PPh 2 ) (COD) 2 ] (MRh; Pz = pyrazolate (pz) ( 1 ) or 3,5-dimethylpyrazolate (dmpz) ( 2 ) (MIr; Pz = pz ( 3 ) or dmpz ( 4 )) have been prepared by reaction of [M 2 (μ-Cl)(μ-Pz)(COD) 2 ] with LiPPh 2 . Substitution of the chloride bridge in [Rh 2 (μ-Cl)(μ-PPh 2 )(COD) 2 ] by an azolate on compound is a good method for preparing complexes [Rh 2 (μ-az)(μ-PPh 2 )(COD) 2 ] (az = 1,2,4-triazolate (tz) ( 5 ), or tetrazolate (ttz) ( 6 )). The prepared of the heterobridged heterotrinuclear complexes [{M(μ-pz)(μ-PPh 2 )(COD)} 2 Pd] (MRh ( 7 ) or Ir ( 8 )) is also reported.

Rhodium complexes of 4,5-dicyano-1,2,3-triazole

Abstract Neutral bi- and mono-nuclear dicyanotriazolate (DcTz) complexes of formulae [Rh2(μ-DcTz)2L2L′2] (L2 = L′2 = diolefin; L = CO, L′ = PPh3 or P(OPh)3; L = L′ = P(OPh)3; L2 = COD, L′ = P(OPh)3) and [Rh(DcTz)L2L′] (L2 = diolefin, L′ = PPh3; L = PPh3, L′ = CO) and the ionic derivative [Rh(dppe)2][DcTz] have been prepared. New heteroatom-bridged complexes of formula [Rh2(μ-DcTz)(μ-X)(COD)L2] (L2 = COD, L = CO) have been obtained by treating [Rh2(μ-DcTz)2(COD)2] with [Rh2(μ-Cl)2(L2)2] (X = Cl), or (X = N3) by subsequent treatment with NaN3. The properties of [Rh2 (μ-DcTz)(μ-N3)(COD)(CO)2] and the related derivative, [Rh2(μ-DcTz)(μ-N3)(CO)4] indicate the presence of intermolecular interactions. Some oxidative addition reactions of I2, IMe and HgCl2 to [Rh2[μ-DcTc)2(CO)2(PPh3)2] have been examined.

Oxidative-addition reactions on planar chloranilate rhodium systems. Crystal structure of [Rh2(µ-C6Cl2O4)Me2I2(CO)2(PPh3)2]

The binuclear chloranilate complexes [Rh2(µ-C6Cl2O4)L4]{L = CO 1 or CNR (R = toluene-p-sulfonylmethyl)2, L4=(CO)2(CNR)23, (CO)2(PPh3)24 or (CO)2[P(OMe)3]25} have been prepared and oxidative addition of the electrophiles MeI and I2 investigated. Addition of XI (X = Me or I) to compounds 4 and 5, in a Rh : XI = 1 : 1 molar ratio, led to the symmetrical complexes [Rh2(µ-C6Cl2O4)X2I2(CO2)(PR3)2](X = Me, R = Ph 6; X = I, R = Ph 7; X = I, R = OMe 8). Interaction of 4 and 5 with 1 mol of XI (X = Me or I) gave equimolecular mixtures of RhI2 and RhIII2 systems. The crystal structure of 6 has been determined by X-ray diffraction methods.

Oxidative-addition reactions of Mel or CH2I2 to [M2(µ-pz)(µ-SBut)(CO)2{P(OMe)3}2](M = Rh or Ir) complexes. X-Ray structure of [Ir2(µ-pz)(µ-SBut)(µ-CH2)I2(CO)2{P(OMe)3}2](pz = pyrazolate)

The heterobridged binuclear complexes of general formula [M2(µ-pz)(µ-SBut)(CO)2{P(OMe)3}2](pz = pyrazolate; M = Rh, 1; or Ir, 2) react with methyl iodide to give [M2(µ-pz)(µ-SBut)(Me)I(CO)2{P(OMe)3}2](M = Rh, 3; or Ir, 4). Reaction of the diiridium complexes 2 or [Ir2(µ-dmpz)(µ-SBut)(CO)2{P(OMe)3}2](dmpz = 3,5-dimethylpyrazolate) with diiodomethane give [Ir2(µ-pz)(µ-SBut)(µ-CH2)I2(CO)2{P(OMe)3}2]5 or [Ir2(µ-dmpz)(µ-SBut)(CH2I)I(CO)2{P(OMe)3}2] respectively. The crystal and molecular structure of 5 has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21/c, with a= 11.398(1), b= 16.571(2), c= 16.274(2)A, β= 106.87(1)°, and Z= 4. The molecule is binuclear, with the two metal centres bridged by a pyrazolate anion, a SBut group and a methylene carbon atom.