Bridging Pyrazolate Research Articles

Combining organometallic and Werner-type coordination sites in highly preorganized heterobimetallic systems

A first example of a novel class of preorganized bimetallic complexes is reported, in which both an organometallic CpMn(CO) 2 fragment and a classical Werner-type coordination site are arranged in close proximity by means of a bridging pyrazolate. The synthetic route starts from N-protected bis(chloromethyl)pyrazole and involves sequential attachment of the manganese part and the chelating N-donor compartment, bis(pyridylmethyl)amine, at the different sides of the ligand backbone. Pyrazole binding to the manganese(I) is achieved by photoinduced substitution of CO, and the adjacent N 4-coordination pocket is suited to accommodate a second metal ion. The heterodinuclear MnZn complex 4 is characterized crystallographically and its redox chemistry investigated by spectroelectrochemical methods.

X-ray Structure, Magnetic and Catalytic Properties of a Cyclic Trinuclear CoII/CoIII/CoIII Complex with a μ3-Hydroxy Anion

The mixed-valent cyclic trinuclear cobalt(II)/cobalt(III)/cobalt(III) complex tris(dibenzoylmethanato-1κ2O,O′;2κ2O,O′;3κ2O,O′)(μ3-hydroxo-1:2κ2O;1:3κ2O;2:3κ2O)tetrakis(μ-pyrazolato-1:2κ4N1N2;1:3κ2N1N2;2:3κ2N1N2)-1,2-dicobalt(III)-3-cobalt(II) with four bridging pyrazolate anions and a μ3-hydroxy anion has been synthesized and its molecular structure has been elucidated on the basis of X-ray crystallographic, magnetic, NMR, and EPR studies. The remaining coordination sites of the pentacoordinate cobalt(II) and hexacoordinate cobalt(III) centers are occupied by oxygen donor atoms of dibenzoylmethanate anions, rendering the complex soluble in most organic solvents. The complex has been found to effectively catalyze the decomposition of tert-butyl hydroperoxide (TBHP) in chlorobenzene with a short induction period and a half-life of 80 min and to catalyze the oxidation of cyclohexene to 2-cyclohexen-1-one with oxygen and to 2-cyclohexen-1-ol with TBHP.

A linear trinuclear mixed oxidation state cobalt(III/II/III) complex with pyrazolate bridging ligands

A linear, trinuclear cobalt complex with pyrazolate bridges has been prepared and structurally characterised. The outer cobalt centre is low spin, octahedral cobalt(III) and is coordinated by a tetra-anionic tetradentate ligand. Two of these outer cobalt(III) complexes act as bidentate chelating ligands to the central cobalt(II) ion, which adopts a distorted, flattened, tetrahedral geometry.

Synthesis and characterization of heterodinuclear RuPt and IrPt complexes containing pyrazolate bridging ligands. Crystal structure of [(η 5-C 5Me 5)Ir(μ-pz) 3PtMe 3] (pz=pyrazolate)

The reaction of the metallo–ligand [Ru(η 6- p-cymene)(pz) 2(Hpz)] with the platinum complex [{PtIMe 3} 4] affords mixtures of the heterodinuclear complexes [(η 6- p-cymene)Ru(μ-pz) 3PtMe 3] ( 1) and [(η 6- p-cymene)Ru(μ-pz) 2(μ-I)PtMe 3] ( 2). The reaction of the iridium derivative [Ir(η 5-C 5Me 5)(pz) 2(Hpz)] with [{PtIMe 3} 4] gives [(η 5-C 5Me 5)Ir(μ-pz) 2(μ-I)PtMe 3] ( 3). Both [Ru(η 6- p-cymene)(pz) 2(Hpz)] and [Ir(η 5-C 5Me 5)(pz) 2(Hpz)] react with [{PtIMe 3} 4] in the presence of NaOH yielding 1 and [(η 5-C 5Me 5)Ir(μ-pz) 3PtMe 3] ( 4), respectively. While [Ru(η 6- p-cymene)(pz) 2(Hpz)] reacts with [PtBr 2Me 2S x ] to give mixtures of [(η 6- p-cymene)Ru(μ-pz) 3PtBrMe 2] ( 5) and [(η 6- p-cymene)Ru(μ-pz) 2(μ-Br)PtBrMe 2] ( 6), the reaction of [Ir(η 5-C 5Me 5)(pz) 2(Hpz)] with [PtBr 2Me 2S x ] gives [(η 5-C 5Me 5)Ir(μ-pz) 2(μ-Br)PtBrMe 2] ( 7) as the sole product. All species were characterized in solution by 1H-NMR spectroscopy. The crystal structure of complex 4 has been determined by single-crystal X-ray diffraction.

Ligand Exchange on Pyrazolate-κN-μ-pyrazolate and Pyrazole-κN-μ-pyrazolate Binuclear Nickel Complexes

Compounds containing bridging pyrazolate and terminal pyrazolate or pyrazole ligands of type Ni2(PMe3)2(L-κN)(μ2-η1:η3-CH2-o-C6H4)(μ2-L-κN,N‘) (L = 3,5-dimethylpyrazolate (Pz‘ ‘), 3b, or 3,5-di-tert-butylpyrazolate (Pz**), 3c); Ni2(PMe3)2(Pz**-κN)(μ2-η1:η3-CH2-o-C6H4)(μ2-Pz‘ ‘-κN,N‘), 4, and [Ni2(PMe3)2(HPz‘ ‘-κN)(μ2-η1:η3-CH2-o-C6H4)(μ2-Pz-κNN‘)](X) (X = Br, 5, or BPh4, 6) have been prepared. Spin saturation transfer experiments reveal a slow motion of the terminal pyrazolate ligand of 3b and 4, consisting of a combination of N,N-metallotropic shift and rotation around the Ni−N bond, but did not show any exchange of the bridging and terminal pyrazolate ligands. However, the mixed ligand derivative 4 can be obtained by conproportionation of 3b and 3c. This reaction reveals a slow intermolecular bridging−terminal as well as intermolecular pyrazolate exchange. In contrast with complexes of type 3 and 4, the formally cationic 5 and 6 display dynamic NMR spectra at room temperature due to their occurrence in solution as a mixture of rapidly exchanging isomers. Variable-temperature NMR experiments have shown that 5 also undergoes a highly stereoselective HPz/Br- exchange.

Tetranuclear grid-like copper(II) complexes with pyrazolate bridges: syntheses, structures, magnetic and EPR spectroscopic properties

Reaction of 3-(2-pyridyl)pyrazole (HL1) and 6-(3-pyrazolyl)-2,2′-bipyridine (HL2) with nickel(II) and zinc(II) salts afforded the simple mononuclear pseudo-octahedral complexes [M(HL1)3][PF6]2 and [M(HL2)2][PF6]2 respectively (M = Ni or Zn) in which the ligands co-ordinate as neutral mononucleating chelates in the same manner as e.g. 2,2′-bipyridine or 2,2′∶6′,2″-terpyridine respectively. However with CuII the complexes [Cu4(L1)6(solv)2][PF6]2 (solv = dmf or MeOH) and [Cu4(L2)4(dmf)4][PF6]4 were isolated and crystallographically characterised, in all cases containing four tetragonally elongated square-pyramidal copper(II) ions which are linked by pyrazolate bridges from the now deprotonated ligands L1 and L2. The approximate orthogonality of the different ligands within each complex and the approximately square array of metal ions result in a grid-like structure. In [Cu4(L1)6(solv)2][PF6]2 there are successively two, one, two and one pyrazolate bridges between adjacent copper(II) ions around the Cu4 square resulting in two clearly different magnetic coupling pathways; in [Cu4(L2)4(dmf)4][PF6]4 however, which has approximate S4 symmetry, each Cu· · ·Cu edge has a single pyrazolate bridge and the coupling pathways are all virtually equivalent. Prolonged drying of these compounds resulted in loss of the axial dmf ligands to give [Cu4(L1)6][PF6]2 and [Cu4(L2)4][PF6]4. Magnetic susceptibility studies on these showed the presence of two antiferromagnetic exchange pathways for [Cu4(L1)6][PF6]2 with J > 172 cm–1 and J′ < 155 cm–1 (strong correlation between the parameters precludes a more precise determination), but only one antiferromagnetic exchange pathway for [Cu4(L2)4][PF6]4 with J = 63.5 cm–1, consistent with the crystal structures of the dmf adducts. The EPR spectra of [Cu4(L1)6][PF6]2 and [Cu4(L2)4][PF6]4 at a variety of frequencies and temperatures can be well simulated as arising from triplet species; however the spectrum of [Cu4(L1)6][PF6]2 also contains a feature which may be ascribed to the expected thermally populated quintet state.

Magnetic properties of dinuclear copper(II) complexes with simple pyrazolate bridges

Three new copper(II) complexes with simple pyrazolate bridges have been prepared, [Cu2(pz)2(dpa)2(H2O)Cl]Cl·H2O 1, [Cu2(pz)2(phen)2Cl2]·2C2H5OH 2 and [Cu2(pz)(phen)2Cl3]·2H2O 3 (Hpz = pyrazole, dpa = di(2-pyridyl)amine, phen = 1,10-phenanthroline) and their crystal and molecular structures determined. The copper centres in the binuclear cation in 1 have a square pyramidal geometry at Cu1 and a distorted octahedral geometry at Cu2. The neutral complexes 2 and 3 have the copper atoms in a distorted square pyramidal geometry. Complexes 1 and 2 are bibridged by pyrazolate while 3 is monobridged by this ligand. Variable temperature magnetic studies on all three complexes indicate the existence of antiferromagnetic exchange phenomena (–2J = 191, 169, 42 cm–1 for 1, 2 and 3 respectively). Extended Huckel calculations showed a HOMO/LUMO gap which is in agreement with the experimental data.

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

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%.

Transition metal azolates from metallocenes. Part 3: Polymeric manganese(II) and nickel(II) pyrazolates; synthesis, characterization, and magnetochemistry

Direct reactions of nickelocene and manganocene with molten pyrazoles in an inert atmosphere or under vacuum have led to the isolation of the following metal pyrazolate compounds: [Ni(4-Xpz)2]x (where X = H, Cl and pz = pyrazolate); [M(4-Xdmpz)2]x (where X = H, CH3, Cl, Br and M = Ni, Mn anddmpz = 3,5-dimethylpyazolate); and [Mn(4-Xpz)2(4-XpzH)]x (where X = Cl, Br and pzH = pyrazole). On the basis of indirect evidence all compounds are considered to have extended chain structures with metal ions linked in chains by double bridging pyrazolates. The two [Ni(4-Xpz)2]x compounds are diamagnetic while all others are paramagnetic. Variable temperature magnetic susceptibility studies on the paramagnetic compounds reveal antiferromagnetic coupling between neighbouring metal ions. Analysis of the magnetic data (Hamiltonian of the form H = -2J sum Si·Sj) yields values of the exchange coupling constant J of -14 to -17 cm -1for the [Ni(4-Xdmpz)2]x compounds, -1.2 to -2.1 cm-1 for the [Mn(4-Xdmpz)2]x compounds, and -0.41 cm-1 for the [Mn(4-Xpz)2(4-XpzH)]x compounds.Key words: nickel, manganese, manganocene, nickelocene, pyrazolates, antiferromagnetic exchange.

Reactions of Pyrazole with Unsaturated Triangular Clusters of Rhenium. Solid-State and Solution Characterization of an Intramolecular N−H···π Hydrogen Bond

The reaction of the unsaturated anion [Re3(μ-H)4(CO)10]- with pyrazole (used as solvent at 80 °C) proceeds in a stepwise manner, at first giving the [Re3(μ-H)3(μ-η2-pz)(CO)10]- anion (2, pz = pyrazolate), with H2 evolution. Spectroscopic characterization has shown that 2 contains a pz ligand bridging through the two N atoms, one edge of the triangular cluster. At longer times, CO is evolved and 2 transforms into the novel species [Re3(μ-H)3(μ-η2-pz)(CO)9(Hpz)]- (3), containing one pz ligand bridging a cluster edge and a second pyrazole molecule terminally bonded on the third vertex of the triangle, replacing an axial carbonyl of 2. The treatment with CO (atmospheric pressure, room temperature) slowly restores 2. A single-crystal X-ray analysis of 3 has revealed the syn coordination of the two heterocycles with respect to the metal triangle plane and an intramolecular hydrogen bond between the N−H proton of the pyrazole ligand and the aromatic π-electrons of the bridging pyrazolate. There is NMR evidence t...

Characterization of a Dinuclear (&mgr;-Hydroxo)(&mgr;-pyrazolato)dimanganese(II) Complex and Hydrolytic Equilibrium of the Bridging Pyrazolate Ligand.

Reaction of the dinuclear bis(μ-hydroxo) complex 2 with 3,5-diisopropylpyrazole yielded a dinuclear (μ-hydroxo)(μ-pyrazolato)dimanganese(II) complex 4, which reacted with H2O2 in the absence of excess pyrazole to give the mononuclear Mn(III) side-on peroxo complex containing a neutral pyrazole ligand. However, hydrolytic equilibrium of the bridging pyrazolate ligand of the (μ-hydroxo)(μ-pyrazolato)dimanganese(II) complex was observed in the presence of H2O.

A Dinuclear Indium(III) Complex with Two Pyrazolate Bridging Ligands

The crystal structure of bis[μ-3-(2-pyridyl)-1H-pyrazolato]-1κ 2 N', N 2 :2κN 1 ;1κN 1 :2κN',N 2 -bis[dichloro(dimethylformamide-O)indium]-dimethylformamide (1/2), [In 2 Cl 4 L 2 (dmf) 2 ].2dmf [where HL is 3-(2-pyridyl)-pyrazole, C 8 H 7 N 3 , and dmf is dimethylformamide, C 3 H 7 NO], contains pairs of [InCl 2 (dmf)] fragments linked by two pyrazolate bridges from the deprotonated bridging ligand 3-(2-pyridyl)pyrazolate (L-). This ligand acts as a bidentate N-donor chelate to one metal centre using the pyridyl N and pyrazolyl N 2 atoms, and bridges to the other metal using the (deprotonated) pyrazolyl N 1 atom. Each In III centre, therefore, has an N 3 Cl 2 O donor set.

Unsymmetrically substituted pyrazolates: nickel(II) complexes of a novel dinucleating ligand providing both N- and S-rich co-ordination spheres ‡

An unsymmetric pyrazolate ligand with different chelating side arms in the 3 and 5 positions of the heterocycle {3-[(EtSCH2CH2)2NCH2]-5-[(Et2NCH2CH2)2NCH2]C3N2H2 (HL1)} and its symmetrical analogue {3,5-[(EtSCH2CH2)2NCH2]2C3N2H2(HL2)} have been prepared. Upon reaction with NiCl2·6H2O they afforded dinuclear complexes [Ni2L1Cl3] 2 and [Ni2L2Cl3] 1 that contain both a bridging pyrazolate and a bridging chlorine atom. While all nickel(II) ions within the N2S2 compartments of the primary ligands are six-co-ordinate, one of the amino side arms of L1 in the former complex is non-co-ordinating, leaving the respective nickel centre in a square-pyramidal environment. This dangling arm is co-ordinated to the metal ion upon treatment of 2 with NaBPh4 due to substitution of the terminal chlorine atom to form [Ni2L1Cl2][BPh4] 3. All new complexes were characterised by means of X-ray crystallography; 2 and 3 represent rare examples of dinuclear complexes exhibiting various kinds of asymmetry. The electrochemical and magnetic properties of the complexes are reported.

Preparation of the new podand ligand SP(pzpy) 3 [pzpy = 3-(2-pyridyl)-pyrazol-1-yl], and the syntheses and crystal structures of copper(II) and copper(I) complexes of its hydrolysis product [OSP(pzpy) 2] −, and a double helical copper(I) complex of [O 2P(pzpy) 2] −

The new podand ligand SP(pzpy) 3 [L 1; pzypy = 3-(2-pyridyl)-pyrazol-1-yl], containing three bidentate pyrazolyl-pyridine arms linked to an apical PS group via the pyrazolyl N 1 atoms, was prepared and crystallographically characterised. Reaction with Cu(II) or Cu(I) resulted in complexes of the partially-hydrolysed ligand [OSP(pzpy) 2] − (L 2), containing two bidentate chelating arms linked by a thiophosphinate fragment. [Cu 2(L 2) 2(μ-pzpy) 2] contains a planar dinuclear copper(II) core with two pyrazolate bridges linking the metal centres, and one L 2 ligand attached to each metal by one bidentate arm with the other arm pendant. In [Cu 2(L 2) 2] each ligand L 2 acts as an N, N-donor to one metal ion and an N, S-donor to the other with a non-coordinated pyridyl group, such that each metal ion has an N 3 S donor set; this complex is achiral with a “side-by-side” disposition of bridging ligands. For comparison purposes we also crystallographically characterised [Cu 2(L 3) 2], where L 3 is [O 2P(pzpy) 2] −, an analogue of L 2 but with a phosphinate rather than thiophosphinate group. This complex is a dinuclear double helicate in which each ligand acts as an N, N-bidentate chelate to each metal ion. Comparison of this with the structure of [Cu 2(L 2) 2] shows that it is the involvement of the thiophosphinate S atom of L 2 in coordination that prevents helication from occurring.

Transition metal azolates from metallocenes. Part 3: Polymeric manganese(II) and nickel(II) pyrazolates; synthesis, characterization, and magnetochemistry

Direct reactions of nickelocene and manganocene with molten pyrazoles in an inert atmosphere or under vacuum have led to the isolation of the following metal pyrazolate compounds: [Ni(4-Xpz)2]x (where X = H, Cl and pz = pyrazolate); [M(4-Xdmpz)2]x (where X = H, CH3, Cl, Br and M = Ni, Mn anddmpz = 3,5-dimethylpyazolate); and [Mn(4-Xpz)2(4-XpzH)]x (where X = Cl, Br and pzH = pyrazole). On the basis of indirect evidence all compounds are considered to have extended chain structures with metal ions linked in chains by double bridging pyrazolates. The two [Ni(4-Xpz)2]x compounds are diamagnetic while all others are paramagnetic. Variable temperature magnetic susceptibility studies on the paramagnetic compounds reveal antiferromagnetic coupling between neighbouring metal ions. Analysis of the magnetic data (Hamiltonian of the form H = -2J sum Si·Sj) yields values of the exchange coupling constant J of -14 to -17 cm -1for the [Ni(4-Xdmpz)2]x compounds, -1.2 to -2.1 cm-1 for the [Mn(4-Xdmpz)2]x compounds, and -0.41 cm-1 for the [Mn(4-Xpz)2(4-XpzH)]x compounds.Key words: nickel, manganese, manganocene, nickelocene, pyrazolates, antiferromagnetic exchange.

A novel one-dimensional nickel(II) alternating chain from discrete pyrazolate-based dinuclear complexes

Hexadentate dinucleating ligands that are based on a bridging pyrazolate bearing chelating side arms [3,5-(R2NCH2)2C3N2H2; R2N = Me2N(CH2)3NMe (HL1), Me2N(CH2)2NMe (HL2)] reacted with NiCl2·6H2O to yield complexes ClNi(µ-Cl)(µ-L1)NiCl 1 (Ni2L1Cl3) and ClNi(µ-Cl)(µ-L2)NiCl 2 (Ni2L2Cl3), respectively. Depending on the side-arm chain length and the solvent used for crystallisation these complexes either crystallised as dicrete bimetallic units (1) or were assembled via di-µ-chloro linkages to form a tetranuclear compound [ClNi(µ-Cl)(µ-L2)Ni(µ-Cl)2Ni(µ-Cl)(µ-L2)NiCl] 2a ([Ni2L2Cl3]2) or a novel bridge-alternating one-dimensional chain [Ni(µ-Cl)(µ-L1)Ni(µ-Cl)2]∞ 2b ([Ni2L2Cl3]∞) in the solid state. Variable-temperature magnetic susceptibility measurements revealed antiferromagnetic coupling within the basic µ-chloro-µ-pyrazolato bridged bimetallic framework in all cases and also suggested antiferromagnetic superexchange propagated by the di-µ-chloro linkage in 2b. The latter result is rationalised on the basis of the specific geometric findings for this di-µ-chloro linkage, in particular the unusually large Ni–Cl–Ni angle [101.37(4)°].

Pyrazolate‐Based Oligonuclear Copper and Silver Complexes with N/S Coordination Spheres

AbstractA series of pyrazole‐based potential ligands bearing thioether substituents in 3‐ and 5‐positions of the heterocycle was synthesized [3,5‐bis(RSCH2)‐pyzH R=Ph (1aH), PhCH2 (1bH), iPr (1cH), tBu (1dH)]. These ligands afford oligonuclear Cu1 and Ag1 coordination compounds [LCu]x (2a–c, L = 1a ‐ c) and [LAg]x (3a‐d, L = 1a‐d), respectively. The single crystal X‐ray analysis of 3c shows the presence of trimeric planar arrays of N,N′‐bridging pyrazolates and linear coordinated silver ions, with each two of the trinuclear moieties being linked by two unsupported short intermolecular Ag…Ag contacts [3.041(1) Å]. Molecular‐weight determinations for 2a (THF) and 3c (toluene) indicate that hexanuclear entities are preserved in solution. Starting from 1bH the CuII complex [(1b)2Cu2](BF4)2 (4) was synthesized. According to an X‐ray crystal structure analysis it consists of dinuclear molecules with two bridging pyrazolates, distorted square planar N2S2 coordination spheres for Cu11 and an axially bridging tetrafluoroborate. Magnetic susceptibility data reveal an antiferromagnetic exchange (J = ‐206 cm−1) that is among the highest found for doubly pyrazolate bridged dicopper(II) complexes, which is rationalized on the basis of the rather symmetric dinuclear core of 4. The irreversibility of the electrochemical reduction and oxidation processes for the CuII and CuI compounds, respectively, is explained by the inability of the respective coordination framework to adapt to different geometric preferences.

Organoamido‐ and aryloxo‐lanthanoids. XIII [1]. Organometallic compounds of the lanthanoids. CV [2]. New Lanthanoid(III) Complexes with Pyrazolate Ligands

AbstractThe complexes Er(Me2pz)3(thf) and Ln(Ph2pz)3(thf)n (Ln = Sc, Y, Gd, Er, n = 2; Ln = Lu, n = 3) (Me2pz− = 3,5‐dimethylpyrazolate, thf = tetrahydrofuran, Ph2pz− = 3,5‐diphenylpyrazolate) have been prepared by reaction of the lanthanoid metal with bis(pentafluorophenyl)mercury and the pyrazole in thf. The Ln(Ph2pz)3(thf)2 complexes are considered to be eight coordinate with three η2‐Ph2pz ligands. Other lanthanoid pyrazolate complexes, Y(pz)3(thf)2, La(Me2pz)3(thf), Cp2Ln(Me2pz)(thf)n (Ln = Y, Lu, n = 0; Ln = Lu, n = 1), (C5Me5)2Y(pz)(thf), (C5Me5)2Y(Mepz)(thf), (C5Me5)2Y(Me2pz)(thf)2 (pz− = pyrazolate, Mepz− = 3‐methylpyrazolate, Cp = cyclopentadienyl) have been synthesized by reaction of LnCl3, Cp2LnCl, or (C5Me5)2LnCl with the appropriate sodium pyrazolate in thf. The structure of Ln(Me2pz)3(thf) (Ln = La or Er) is considered to be a symmetrical dimer with four chelating and two bridging Me2pz groups, and two bridging thf ligands, whereas the cyclopentadienyl complexes are most likely dimers with bridging pyrazolate groups, and lattice thf of solvation.

Crystal structure, magnetic properties and spectroscopic studies of bis[1,3-bis(pyrazol-3-yl)triazenido]dicopper(II) trihydrate: a dinuclear complex with an asymmetric double pyrazolate bridge

The crystal and molecular structure of [{Cu(bpzt)}2]·3H2O [H2bpzt = 1,3-bis(pyrazol-3-yl)triazene] was determined by X-ray diffraction methods. The complex has a quasi-planar dinuclear structure with an asymmetric double pyrazolate bridge. The asymmetry results from the presence, on the C3 of each bridging pyrazolate, of a pyrazolyltriazenide chelating arm which completes the equatorial CuN4 co-ordination. The centrosymmetric dinuclear units have intramolecular Cu ⋯ Cu distances of 3.852(5) and 3.839(4)A respectively. The units are stacked in columns along the b axis. The cell also contains crossing channels filled with water molecules. The complex was characterized by spectroscopic and magnetic measurements. Magnetic susceptibility data show antiferromagnetic behaviour with an exchange parameter |J|= 151 cm–1 significantly decreased with respect to symmetric doubly bridged complexes (|J|=≈200 cm–1). The X-band powder EPR spectrum recorded at 77 K is typical of a triplet spin state lying above the singlet ground state. The results obtained for this complex are compared to recent literature data on other planar doubly bridged pyrazolate dicopper(II) complexes. A correlation, valid for symmetric as well as asymmetric systems, is described between the exchange parameter J and the deviation of the Cu–N–N bridge angle from the optimum value corresponding to the highest |J|.

Syntheses and characterization of binuclear Rh2, Ir2 and RhIr complexes containing dimethyl phosphonate and pyrazolate bridging ligands

The reaction of [Ir(η5-C5Me5)I{PO(OMe)2}{P(OH)(OMe)2}] with pyrazole (Hpz) in the presence of AgPF6 gave [Ir(η5-C5Me5){PO(OMe)2}{P(OH)(OMe)2}(Hpz)]PF61. Deprotonation of 1 with sodium carbonate afforded the neutral compound [Ir(η5-C5Me5){PO(OMe)2}2(Hpz)]2 which, in turn, can be deprotonated to [(η5-C5Me5)Ir{PO(OMe)2}2(pz)M′](M′= Tl 3 or Na 4) by Tl(acac)(acac = acetylacetonate) or NaH, respectively. The complex [Ir(η5-C5Me5)I2{P(OH)(OMe)2}]5, prepared by cleaving the iodide bridges in [{Ir(η5-C5Me5)I}2(µ-I)2] with HPO(OMe)2, reacted with Hpz in the presence of AgPF6 to give [Ir(η5-C5Me5){PO(OMe)2}(Hpz)2]PF66. Complexes of formulae [(η5-C5Me5)Ir{PO(OMe)2}2(pz)M″L2][M″L2= Rh(CO)27, Rh(cod)8 or Ir(cod)9] were prepared from 2 and [Rh(acac)(CO)2] or from 3′ and the appropriate [{M″(cod)}2(µ-Cl)2] dimer (cod = cycloocta-1,5-diene). Complex 6 reacted with [{Rh(cod)}2(µ-Cl)2] in basic medium to give [(η5-C5Me5)Ir{PO(OMe)2}(pz)2Rh(cod)]10. The rhodium–thallium compound [(η5-C5Me5)Rh{PO(OMe)2(pz)Tl] or the in situ prepared sodium derivative [(η5-C5Me5)Rh{PO(OMe)2}(pz)2Na] reacted with the dimers [{M″(diolefin)}2(µ-Cl)2] affording [(η5-C5Me5)Rh{PO(OMe)2}2(pz)M″(diolefin)][M″(diolefin)= Ir(cod)11 or Rh(nbd)12] or [(η5-C5Me5){PO(OMe)2}Rh(pz)2M″(diolefin)][M″(diolefin)= Rh(cod)13, Ir(cod)14 or Rh(nbd)15], respectively (nbd = bicyclo[2.2.1]hepta-2,5-diene). Related heterovalent complexes of general formula [I(η5-C5Me5)M{PO(OMe)2}2M″(diolefin)][M = Ir, M′(diolefin)= Rh(cod)16 or Ir(cod)17; M = Rh, M″(diolefin)= Rh(cod)18, Ir(cod)19, or Rh(nbd)20] have been prepared starting from the mononuclear complexes [M(η5-C5Me5I{PO(OMe)2}{P(OH)(OMe)2}](M = Ir or Rh). All the complexes have been characterized by spectroscopic means and the fluxional behaviour of 7–9, 11 and 12, in solution, has been studied. The protonation of 8 by toluene-p-sulfonic acid is reported. The structures of 8 and 16 have been determined by X-ray diffraction methods. Both complexes consist of doubly bridged binuclear (C5Me5)Ir–Rh(cod) species, where the Ir atoms exhibit pseudo-octahedral coordination and the rhodium square planar. The bridging system in 16 is formed by two identical P,O-bonded phosphonate groups, while in 8 a pyrazolate and a phosphonate ligand are bridging the metals. The intermetallic separations are 4.0445(9)(8) and 4.0928(9)A(16).