Rafael Ruiz

Coordination chemistry of N,N′-bis(coordinating group substituted)oxamides: a rational design of nuclearity tailored polynuclear complexes

Abstract The coordinating properties of N , N ′-bis(coordinating group substituted)oxamides have been thoroughly investigated both in aqueous solution and in the solid state. The easy cis – trans isomerization equilibria that they exhibit together with the great variety of N , N ′-substituents which can be used to play on the overall charge, complexing ability and polarity, make them very suitable ligands in designing homo- and heterometallic species. The knowledge of their complex formation in aqueous solution by potentiometry and using the hydrogen ion concentration as a probe, allowed us to settle the basis of a rational design of oxamidate-containing polynuclear species whose nuclearity can be easily tuned. Concerning their electronic properties, the strong basicity of the deprotonated amide–nitrogen atoms stabilizes high oxidation states of late first-row transition metal ions. Finally, one of the most appealing aspects of this type of ligands is the remarkable efficiency they exhibit to mediate strong antiferromagnetic interactions between paramagnetic centres when acting as bridges but in order to maintain the present work within a rational length, we have omitted this last point which deserves a further review.

Significant antiferromagnetic coupling in a terephthalate (ta)-bridged manganese(II) compound: preparation, crystal structure and magnetic properties of the chain [Mn2(bipy)4(ta)][ClO4]2(bipy = 2,2′-bipyridine)

A new manganese(II) compound [Mn2(bipy)4(ta)][ClO4]21(bipy = 2,2′-bipyridme, ta = terephthalate dianion) has been synthesised and its crystal structure determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P, with a= 9.516(2), b= 11.613(3), c= 11.615(3)A, α= 70.92(2), β= 80.16(2), γ= 76.64(2)° and Z= 1. The structure consists of canonic terephthalate-bridged [Mn2(bipy)4(ta)]2+ chains and non-co-ordinated perchlorate anions. Each terephthalate is bound to four manganese atoms through carboxylate oxygens with the sym-sym bridging mode, affording manganese(II) pairs which are linked by the terephthalate group to yield a one-dimensional chain running along the a axis. The intrachain Mn ⋯ Mn separations through the double carboxylate and terephthalate bridges are 4.643(1) and 9.637(2)A, respectively The manganese(II) ion displays a severely distorted octahedral co-ordination being linked to four nitrogen atoms of two bipy ligands and to two oxygen atoms of two carboxylate groups from two terephthalate ligands. The magnetic susceptibility of 1 as a function of temperature (4.2–290 K) exhibits a sharp maximum at 6.0 K which is consistent with a significant antiferromagnetic coupling between the metal centres. This magnetic behaviour has been interpreted in terms of a dimer with a molecular field approximation, the values obtained for J, g and zJ′ being –1.35 cm–1,1.97 and –0.04cm–1, respectively. In the light of the structural data, it can be concluded that the double-carboxylate bridge between the manganese(II) pairs provides a more efficient exchange pathway than that of terephthalate and most likely is responsible for the observed J value.

Variation of the exchange interaction in oximato-bridged CuIIMII dimers (MCu, Ni, Mn). Crystal structure of [Cu(pdmg)Cu(bipy)(H2O)2] (ClO4)2· H2O

Abstract Three new dinuclear complexes of formula [Cu(pdmg)Cu(bipy)(H 2 O) 2 ](ClO 4 ) 2 ·H 2 O ( 1 ), [Cu(pdmg)Cu(terpy)]-(CIO 4 ) 2 ( 2 ) and [Cu(pdmg)Ni(cyclam)](ClO 4 ) 2 ·H 2 O (3) (H 2 pdmg=3,3′-aminopropylenedinitrilobis(2-butanoneoxime); bipy=2,2′-bipyridyl; terpy=2,2′:6′,2″-terpyridyl; cyclam=1,4,8,11-tetraazacyclotetradecane) have been synthesized. The structure of 1 has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P 2 1 / a , with a =14.160(3), b =21.300(2), c =10.208(2) A, β=95.44(2)°, V =3065(2) A 3 , Z =4, D x =1.68 g cm −3 , μ(Mo Kα)=16.3 cm −1 , F(000)=1584 and T =291 K. A total of 5263 reflections was measured over the range 1 ⩽θ⩽25°; of these, 2057 (independent and with I ⩾2σ( I )) were used in the structural analysis. The final R and R w residuals were 0.062 and 0.064, respectively. The structure of 1 is made up of cationic [Cu(pdmg)Cu(bipy) 2 (H 2 O) 2 ] 2+ units, non-coordinated perchlorate anions and water of crystallization. The [Cu(pdmg)] fragment coordinates to the second copper(II) ion through its deprotonated oximate oxygens to afford a binuclear structure doubly bridged by the oximate groups in the cis arrangement. The Cu(NO) 2 Cu bridging network is bent, the dihedral angle being 151°. The intramolecular metal-metal distance is 3.691(2) A. The magnetic behavior of 1 – 3 was investigated in the temperature range 50–300 K. The values of the exchange coupling constant J (the spin Hamiltonian being Ĥ=- J Ŝ A ·Ŝ B ) for 1 – 3 were −674, −174 and −204 cm −1 , respectively. The influence on the exchange coupling of the orientation of the magnetic orbitals and the number of unpaired electrons involved in the oximato-bridged Cu II M II dimers (M=Cu, Ni, Mn) are analyzed and discussed.

A study of the exchange interaction through phenolato, oximato and oxamidato bridges in MnIICuII dimers. Crystal structure of [Cu(salen)Mn(hfa)2]

Abstract Three new heterodinuclear CuIIMnII complexes of formula [Cu(salen)Mn(hfa)2] (1), [Cu(pdmg)Mn(phen)2](ClO4)2·2.5H2O (2) and [Cu(apox)Mn(bpy)2](ClO4]2·0.5H2O (3) (salen=N,N′-ethylenebis(salicylideneiminate), hfa=hexafluoroacetylacetonate, pdmg=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioximate, phen=1,10- phenanthroline, apox=N,N′-bis(3-aminopropyl)oxamidate and bipy=2,2′-bipyridyl) have been synthesized. The crystal and molecular structure of 1 has been determined by X-ray diffraction methods. It crystallizes in the triclinic system, space group P 1 with cell constants a=15.584(4), b=12.039(3), c=9.470(2) A, α=113.83(2), β=107.17(3), γ=84.28(3)°; V=1552(1) A3, D (calc., Z=2)=1.708 g cm−3, Mr=798.89, F(000)=792, λ (Mo Kα)=0.71069 A, μ=12.63 cm−1 and T=298 K. A total of 3129 reflections was collected over the range 2≤θ≤25; of these, 2584 (independent and with I≥2.5σ(I)) were used in the structural analysis. The final value of R and Rw residuals was 0.069. The structure of 1 is made up of neutral [Cu(salen)Mn(hfa)2] units. Imine-nitrogen and phenolate-oxygen atoms from salen are bound to the copper atom forming a four-folding surrounding slightly deviating from planarity whereas six oxygen atoms (two from salen and four from the two hfa ligands) define a distorted octahedral environment around the manganese atom. The CuO2Mn bridging network is bent, the dihedral angle being 14.6°. The magnetic properties of 1–3 have been investigated in the 4.2–300 K temperature range. They correspond to what is expected for an antiferromagnetically coupled CuIIMnII pair with SCu=1/2 and SMn=5/2 local spins. Based on the spin Hamiltonian Ĥ−JŜCu·ŜMn, the coupling constant J was evaluated as −22.4, −50.3 and −24.5 cm−1 for 1–3, respectively. The larger value of |J| for 2 confirms the great efficiency of the oximate bridge to transmit the electronic effects between metal centers separated by more than 3.5 A.

Alcohol Oxidation by Dioxygen and Aldehydes Catalysed by Square-Planar Cobalt(III) Complexes of Disubstituted Oxamides and Related Ligands

The square-planar cobalt(III) complexes of o-phenylenebis(N′-methyloxamidate) (Me2opba) and related oxamate (Meopba) and bis(oxamate) (opba) ligands catalyse the selective oxidation, by dioxygen and pivalaldehyde, of a wide range of secondary alcohols to the corresponding ketones, in good yields and under mild conditions in acetonitrile at room temperature. Thus, the oxidation of the series of α-alkylbenzyl alcohols PhCH(OH)R (R = Me, Et, iPr, tBu) results in the exclusive formation of ketones as a product of C−H bond cleavage, and no C−C bond cleavage products are observed in any case. The modulation of catalytic activity by ligand substituents among this series of cobalt catalysts highlights the role of oxocobalt(IV) species as the putative intermediates in these aerobic alcohol oxidation reactions. Relative reactivities for the oxidation of 1-phenylethanol increase in the order Me2opba < Meopba < opba, which correlates with the oxidising power of the postulated CoIV=O intermediate. In contrast, competitive reaction studies on the oxidation of the series of para-substituted 1-phenylethanol derivatives XPhCH(OH)CH3 (X = H, OMe, Br, CF3, NO2) show little variation in relative rate (kX/kH) with the para substituent and no correlation with Hammett σ parameters. Overall, these results are more in line with a mechanism involving concerted hydride transfer in the oxidation of alcohols by high-valent oxocobalt species (rather than a hydrogen atom transfer or an electron transfer mechanism).

Aerobic epoxidation of olefins catalysed by square-planar nickel(II) complexes of bis-N,N′-disubstituted oxamides and related ligands

The new square-planar nickel(II) complexes of o-phenylenebis(N′-methyloxamidate) and related ligands catalyse the aerobic epoxidation of olefins with co-oxidation of pivalaldehyde; the modulation of catalytic activity by substituents along this series of metal complexes points out the role of high-valent nicke(IV)-oxo species as the putative intermediate in these oxygen atom transfer reactions.

Oximato complexes. Part 1. Solution study, synthesis, structure, spectroscopic and magnetic properties of polynuclear copper(II) complexes containing dimethylglyoxime

Copper(II) complexes of composition [Cu2(Hdmg)2(H2dmg)(H2O)2][ClO4]2·H2O 1, [Cu2(dmg)(Hdmg)(H2dmg)]ClO4·1.5H2O 2 and [Cu3(dmg)2(H2dmg)2][ClO4]2·2H2O 3(H2dmg = dimethylglyoxime) were obtained. The crystal structure of complex 1 was solved by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P21/n, with a= 15.991(3), b= 11.682(1), c= 14.363(4)A, β= 90.82(5)° and Z= 4. The structure consists of cationic dinuclear [Cu2(Hdmg)2(H2dmg)(H2O)2]2+ units, unco-ordinated perchlorate anions and lattice water. The Cu(H2dmg)2+ fragment co-ordinates to the second copper(II) ion through the depronated oximate oxygens of Cu(Hdmg)2 to afford a dinuclear structure doubly bridged by the oximate groups in a cis arrangement. The intramolecular Cu(1)⋯ Cu(2) separation is 3.526(4)A. The configuration about the copper atoms is a distorted square pyramid: the basal plane for Cu(1) comprises two nitrogens of H2dmg and two oximate oxygens whereas that of Cu(2) is formed by four nitrogens of two Hdmg– groups; a water molecule occupies the apical position in both cases. Variable-temperature magnetic susceptibility measurements (50–300 K) on complexes 1–3 revealed the occurrence of a very strong intramolecular antiferromagnetic interaction through the oximate bridges. The formation of mononuclear, dinuclear and trinuclear copper(II) dimethylglyoxime complexes have been observed by spectrophotometry in ethanolic solutions of copper(II) perchlorate and [Cu(Hdmg)2]. A rational scheme accounting for the nature of the existing species has been proposed in the light of the coupled solution–solid state studies.

Structure and magnetic properties of a linear oximato-bridged tetranuclear copper(II) complex

Abstract The tetranuclear copper(II) complex of formula [Cu2(dmg)(Hdmg)(terpy)]2(ClO4)2 (1) (H2dmg = dimethylglyoxime and terpy = 2,2′:6′,2″-terpyridine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the triclinic system, space group P(−1), with a = 14.382(3), b = 13.728(3), c = 8.979(2) A, α = 96.99(2), β = 111.85(2), γ = 111.22(3)°, V = 1465.0(9) A3, Z = 1, Dc = 1.607 g cm−3, Mr = 1418.0, F(000) = 719, λ(Mo Kα) = 0.71073 A, μ(Mo Kα) = 16.61 cm−1 and T = 298 K. A total of 4891 reflections were measured over the range 2 ≤ θ ≤ 25° and 4393 of them were unique (I > 2.5σ(I) and used in the structural analysis. The structure of 1 may be described as two dimeric [Cu2(dmg)(Hdmg)(terpy)]+ units linked by relatively long out-of-plane oxime bonds building a cationic centrosymmetric tetrameric entity with a linear Cu4(NO)8 core, and uncoordinated perchlorate anions. Within each dinuclear unit, the partially deprotonated [Cu(dmg)(Hdmg)]− complex unit coordinates to the [Cu(terpy)]2+ fragment through in-plane oxime bonds in an asymmetric fashion. The coordination geometry around both copper atoms is square pyramidal. The intra- and interdimer copper separations within the tetranuclear complex are 3.674(5) and 3.994(6) A, respectively. Variable-temperature magnetic susceptibility measurements (4.2–300 K) have been interpreted on the basis of the tetranuclear nature of the compound. The nature and magnitude of the magnetic couplings are discussed on the basis of the structural features and compared with that of related oximato-bridged copper(II) dinuclear complexes.

A Square‐Planar Dinickel(II) Complex with a Noninnocent Dinucleating Oxamate Ligand: Evidence for a Ligand Radical Species

The new bimetallic nickel(II) compound (PPh4)4[Ni2(2)]·6H2O (3), where H8[2] stands for N,N′,N′′,N′′′-1,2,4,5-benzene-tetrayltetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of [Ni2(η4:η4-2)]4– anions, tetraphenylphosphonium cations, and water molecules. Facile one-electron oxidation of the square-planar diamagnetic dinickel(II) complex [Ni2(η4:η4-2)]4– generates the metallo-radical species [Ni2(η4:η4-2·+)]3– with characteristic intra-ligand π-cation radical transitions in the visible region (475–550 nm) as well as a typical quasi-isotropic EPR signal at g ≈ 2.0.

Oximato complexes. Part 2. Dinuclear dimethylglyoximato complexes of copper(II) with a new co-ordination mode of the oximate ligand

There new dinuclear copper(II) complexes of formula [Cu2(dmg)(Hdmg)(H2dmg)]Cl·H2O 1, [Cu2(dmg)(Hdmg)(H2dmg)]ClO42 and [{Cu2(dmg)(Hdmg)(H2dmg)}2(SO4)]·2.52O 3(H2dmg = dimethylglyoxime) have been synthesised. The crystal structure of 3 was solved by single-crystal X-ray diffraction methods: monoclinic, space group C2/c, a= 22.736(2), b= 21.367(12), c= 11.781(7)A, β= 122.97(5)° and Z= 4. The structure consists of two cationic binuclear [Cu2(dmg)(Hdmg)(H2dmg)]+ units bridged by a sulfate anion, leading to a neutral tetrameric entity, and lattice water. In the dinuclear cation the copper(II) ions are bridged by two oximate groups, one through the nitrogen and oxygen atoms and the other only through the oxygen atom. The intramolecular Cu(1)⋯ Cu(2) distance is 3.266(2)A. The geometry around the copper atoms is a distorted square pyramid: the basal plane for Cu(1) comprises three nitrogen and one oxygen atom of the Hdmg– and dmg2– groups, whereas that of Cu(2) is formed by two nitrogens of H2dmg and two oximate oxygens; two oxygen atoms from a sulfate ion occupy the apical position of each copper atom. The temperature dependence of the molar magnetic susceptibility (100–300 K) for 1–3 reveals a very strong intramolecular antiferromagnetic coupling between copper(II) ions (J ca.–950 cm–1).