Metal-metal interactions as a function of bridging ligand topology: an electrochemical,spectroelectrochemical, and magnetic study on dinuclear Oxo-Mo(V) complexes with various isomers of dihydroxynaphthalene as bridging ligand

Reaction of [MoV(TpMe,Me)(O)Cl2] with 1,3-, 1,5-, 1,6-, 2,6-, and 2,7-dihydroxynaphthalene affords the dinuclear complexes [[Mo(TpMe,Me)(O)Cl]2(mu-C10H6O2)], abbreviated as 1,3-Mo2, 1,5-Mo2, 1,6-Mo2, 2,6-Mo2, and 2,7-Mo2, according to the substitution pattern of the bridging ligand. Electrochemical, UV-vis/NIR spectroscopic, and variable-temperature magnetic susceptibility studies have been used to probe the effects of the bridging-ligand topology on the metal-metal electronic and magnetic interactions. The complexes can be split into two classes according to the properties of the bridging ligands. Complexes 1,3-Mo2, 1,6-Mo2, and 2,7-Mo2 all have bridging ligands that are topologically equivalent to meta-substituted bridging ligands such as 1,3-dihydroxybenzene, in that (i) there is an odd number of C atoms separating the two oxygen atoms, regardless of the pathway that is taken through the ligand skeleton, and (ii) the doubly oxidized from of the bridging ligand is a diradical. These complexes are classified as being "T-meta" (= topologically equivalent to meta). Complexes 1,5-Mo2 and 2,6-Mo2 have bridging ligands that are topologically equivalent to para-substituted groups such as 1,4-dihydroxybenzene, in that (i) there is an even number of C atoms separating the two oxygen atoms, whichever pathway is taken through the ligand skeleton, and (ii) the doubly oxidized form of the bridging ligand is a diamagnetic quinone. These complexes are classified as "T-para". Electrochemical studies show that the comproportionation constants for the Mo(V)/Mo(IV) mixed-valence states of the T-meta complexes are smaller than those for the T-para complexes. Spectroelectrochemical studies show that the Mo(V)/Mo(IV) mixed-valence states of the T-para complexes show pronounced Mo(IV)-->Mo(V) IVCT transitions, whereas those of the T-meta complexes do not show these transitions. Magnetic susceptibility studies show that the T-meta complexes all display ferromagnetic exchange between the metal centers, whereas the T-para complexes all display antiferromagnetic exchange. Thus, both the electronic and the magnetic properties of these complexes show a clear demarcation into two sets according to the bridging-ligand topology.     

1,4-Bis(4-nitrosophenyl)piperazine: novel bridging ligand in dinuclear complexes of rhodium(III) and iridium(III)

The synthesis, spectroscopic characterization and crystal structures of the first 1,4-bis(4-nitrosophenyl)piperazine (BNPP) (4) bridged dinuclear complexes of rhodium(III) and iridium(III) are presented. The reaction of the μ(2)-halogenido-bridged dimers [(η(5)-C(5)Me(5))IrX(2)](2) [X = Cl (5a), Br (5b), I (5c)] and [(η(5)- C(5)Me(5))RhCl(2)](2) (6a) with 4 yields the dinuclear complexes [(η(5)-C(5)Me(5))IrX(2)](2)-BNPP (7a-c) and [(η(5)-C(5)Me(5))RhCl(2)](2)-BNPP (8a). All new compounds were characterized by their NMR, IR and mass spectra. The X-ray structure analyses of the obtained half-sandwich complexes revealed a slightly distorted pseudo-octahedral configuration ("three-legged pianostool") for the metal(III) centers. The bridging BNPP ligand is σ-N coordinated by both nitroso groups and shows different conformations of the piperazine ring depending on the solvent used for crystallization. Moreover the crystal structures of 1,4-bis(4-nitrosophenyl)piperazine (4) and its precursor 1,4-diphenylpiperazine (3) are reported.     

Stacking interaction in crystals of a dinuclear rhodium complex with a bridging phenylborole ligand

Russian Chemical Bulletin -     

Photoluminescent dinuclear lanthanide complexes with tris(2-pyridyl)carbinol acting as a new tetradentate bridging ligand

A tripodal ligand, tris(2-pyridyl)carbinol, affords a novel tetradentate coordination mode in homodinuclear lanthanide complexes, which exhibit remarkably short distances between metal ions. The strong luminescences of Eu(III) and Tb(III) complexes with the ligand demonstrate that the ligand has a suitable excited state for energy transfer from the ligand to the Eu(III) and Tb(III) centers, respectively.     

Platinum and rhodium complexes in which diphenylphosphino(methylthio)methane acts as a monodentate,chelated or bridging ligand

Reaction of [PtCl₂(cod)] with Ph₂PCH₂SCH₃ yields cis-[PtCl₂(Ph₂PCH₂-SCH₃)₂] which, on treatment with AgBF₄, is converted to [PtC](Ph₂PCH₂SCH₃)₂]-BF₄, in which one of the ligands is chelated. With [Pt(dba)₂], cis-[Pt(Cl₂(Ph₂PCH₂-SCH₃)₂] reacts to give the platinum(I) complex [Pt₂Cl₂(μ-Ph₂PCH₂SCH₃)₂], which contains a platinum-platinum bond. The terminal chlorides may be replaced by iodide, but the complex is cleaved by carbon monoxide. [Rh₂(μ-Cl)₂(CO)₄] reacts with Ph₂PCH₂SCH₃ to produce [Rh₂Cl₂(CO)₂(μ-Ph₂PCH₂SCH₃)₂], whereas with Ph₂PCH₂CH₂SCH₃ it yields [RhCl(CO)(Ph₂PCH₂CH₂SCH₃)]. A ligand exchange reaction occurs between cis-[PtCl₂(Ph₂SCH₃)₂] and [Rh₂(μ-Cl)₂(CO)₄] to give cis-[PtCl₂(CO)(Ph₂PCH₂SCH₃)] and [Rh₂Cl₂(CO)₂(μ-Ph₂PCH₂SCH₃)₂].     

Binuclear nickel(II) complexes with a bridging carbonato ligand

Three nickel(II) dinuclear carbonato-bridged complexes: (-CO3)[Ni(TAA)]2(ClO4)2·4H2O (1), (-CO3)[Ni(TTA)]2- (ClO4)2·2H2O (2), (-CO3)[Ni(cyclam)]2(ClO4)2 (3) [TAA =N(CH2CH2NH2)3,TTA=triethylenetetramine,cyclam = 1,4,8,11-tetraazacyclotetradecane] have been prepared. The temperature dependence of the magnetic susceptibility for (1), (2) and (3) were measured over the 77–300K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator (H= –2JS1S2), giving the exchange integral J=–7.75cm–1 for (1), J=–1.23 cm–1 for (2) and J=–40.26cm–1 for (3).     

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

A bisphosphine in which a PhP-PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes. Free trans-1, a more stable isomer having two phenyl groups on phosphorus centers mutually trans with respect to a naphthalene plane, was allowed to react with two equivalents of M(CO)₅(thf) (M = W, Mo, Cr) at room temperature to give dinuclear complexes (OC)₅M(μ-trans-1)M(CO)₅ (M = W (2a), Mo (2b), Cr (2c)). The preparation of the corresponding dinuclear complexes bridged by the cis isomer of 1 was also carried out starting from the free trans-1 in the following way. Mono-nuclear complexes M(trans-1)(CO)₅ (M = W (3a), Mo (3b), Cr (3c)) which had been prepared by a reaction of trans-1 with one equivalent of the corresponding M(CO)₅(thf) (M = W, Mo, Cr) complex, were heated in toluene, wherein a part of the trans-3a-c was converted to their respective cis isomer M(cis-1)(CO)₅. Each cis trans mixture of the mono-nuclear complexes 3a-c was treated with the corresponding M(CO)₅(thf) to give a cis trans mixture of the respective dinuclear complexes 2a-c. The cis isomer of the ditungsten complex 2a was isolated, and its molecular structure was confirmed by X-ray analysis, showing a shorter W?W distance of 5.1661(3) Å than that of 5.8317(2) Å in trans-2a.     

Influence of the bridging azine ligand on the rate of ligand substitution in a series of dinuclear platinum(II) complexes

A series of azine‐bridged dinuclear platinum(II) complexes of the type [{trans‐Pt(NH₃)₂(OH₂)}₂(μ‐azn)](ClO₄)₄ (where azn = pyrazine (pzn, Pt1 ), 2,3‐dimethylpyrazine (2,3‐pzn, Pt2 ), and 2,5‐dimethylpyrazine (2,5‐pzn, Pt3 )) were synthesized to investigate the influence of the bridging azine ligand on the reactivity of the platinum(II) centers. The pK_a values of the complexes were determined via acid–base titration, and the rate of substitution of the aqua moiety by a series of neutral nucleophiles, viz. thiourea (TU), 1,3‐dimethyl‐2‐thiourea (DMTU), and 1,1,3,3‐tetramethyl‐2‐thiourea (TMTU), was determined under pseudo‐first‐order conditions as a function of concentration and temperature using standard spectrophotometric techniques. The introduction of the methyl groups to the bridging azine linker in Pt2 and Pt3 leads to a moderate increase in the pK_a values obtained for the first and second deprotonation steps, respectively, as a result of the increased σ‐donor capacity of the bridging azine ligand trans to the aqua moiety. A comparison of the rate constants, k₁ and k₂, at 298 K, obtained for the substitution of the aqua moieties from Pt1 , Pt2 , and Pt3 by TU, shows that the introduction of the σ‐donating methyl groups on the bridging azine ligand in Pt2 and Pt3 results in a corresponding decrease in the reactivity, by ca. five times for the first substitution step and ca. 10 times for the second substitution step. Density functional theory calculations at the B3LYP/LACVP** level of theory for the complexes demonstrate that the introduction of electron‐donating methyl groups results in (i) increased steric hindrance over the metal centers and (ii) decreased the positive charge on the metal center and increases energy separation of the frontier molecular orbitals (E_HOMO – E_LUMO) of the ground‐state platinum(II) complexes, leading to a less‐reactive metal center. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 161–174, 2011     

Preparation of mononuclear and dinuclear Rh hydrotris(pyrazolyl)borato complexes containing arenethiolato ligands and conversion of the mononuclear complexes into dinuclear Rh-Rh and Rh-Ir complexes with bridging arenethiolato ligands

Reactions of [Tp*Rh(coe)(MeCN)](; Tp*= HB(3,5-dimethylpyrazol-1-yl)(3); coe = cyclooctene) with one equiv. of the organic disulfides, PhSSPh, TolSSTol (Tol = 4-MeC(6)H(4)), PySSPy (Py = 2-pyridyl), and tetraethylthiuram disulfide in THF at room temperature afforded the mononuclear Rh(III) complexes [Tp*Rh(SPh)(2)(MeCN)](3a), [Tp*Rh(STol)(2)(MeCN)](3b), [Tp*Rh(eta(2)-SPy)(eta(1)-SPy)](6), and [Tp*Rh(eta(2)-S(2)CNEt(2))(eta(1)-S(2)CNEt(2))](7), respectively, via the oxidative addition of the organic disulfides to the Rh(I) center in 1. For the Tp analogue [TpRh(coe)(MeCN)](2, Tp = HB(pyrazol-1-yl)(3)), the reaction with TolSSTol proceeded similarly to give the bis(thiolato) complex [TpRh(STol)(2)(MeCN)](4) as a major product but the dinuclear complex [[TpRh(STol)](2)(micro-STol)(2)](5) was also obtained in low yield. Complex 3 was treated further with the Rh(III) or Ir(III) complexes [(Cp*MCl)(2)(micro-Cl)(2)](Cp*=eta(5)-C(5)Me(5)) in THF at room temperature, yielding the thiolato-bridged dinuclear complexes [Tp*RhCl(micro-SPh)(2)MCp*Cl](8a: M = Rh, 8b: M = Ir). Dirhodium complex [TpRhCl(micro-STol)(2)RhCp*Cl](9) was obtained similarly from 4 and [(Cp*RhCl)(2)(micro-Cl)(2)]. Anion metathesis of 8a proceeds only at the Rh atom with the Cp* ligand to yield [Tp*RhCl(micro-SPh)(2)RhCp*(MeCN)][PF(6)](10), when treated with excess KPF(6) in CH(2)Cl(2)-MeCN. The X-ray analyses have been undertaken to determine the detailed structures of 3b, 4, 5, 6, 7, 8a, 9, and 10.     

New rhodium(II)-rhodium(III) dinuclear complexes with 2-aminopyridine bridges

Summary The syntheses of the complexes [Rh₂(ap)₄X] (ap = the heterocyclic anion of 2-aminopyridine; X = Cl or Br) are described. The complexes have been characterized on the basis of elemental analysis, i.r., e.s.r. and electronic absorption spectra, and magnetic susceptibility measurements. The 2-aminopyridine anion behaves as bridging ligand, coordinatingvia the pyridine and amine nitrogen atoms in a way analogous to that in the dinuclear rhodium(II) carboxylates.     

Preparation of polymer-anchored dinuclear rhodium(I) catalysts attached by the bridging groups

We describe a method to anchor dinuclear rhodium(I) complexes by substitution of the chlorine bridge in Rh₂(μ-Cl)₂L₄ with LiSR where R represents a polymeric chain. The catalytic activity of such complexes compares well with that observed in homogeneous phase.     

Photolysis of dicarbonyl(cyclopentadiene)rhodium complexes with a pendent alkyne unit

The syntheses of dicarbonyl[1-(5,5-dimethylhex-3-inyl)-3-phenylcyclopentadienyl]rhodium (7) and its congeners 8 and 9 are reported. Photolysis of 8 and 9 leads to a replacement of one CO ligand by the tethered alkyne unit, yielding 16, and to the dirhodium complexes 17 and 18. The structural assignment of 17 and 18 is based on X-ray studies. The photolysis of 9 leads to 19 and 20.     

Synthesis and NMR characterization of dinuclear Fe(II) organometallic complexes containing a non-equivalently bridging 5-aryl tetrazolate ligand

The synthetic routes to the formation of a wide range of dinuclear Fe(II) organometallic complexes of the general formula [Cp(CO)(L)Fe-N₄C-C₆H₄-CN-Fe(L)(CO)Cp][SO₃CF₃], in which the 4-cyanophenyl-tetrazolate anion N₄C-C₆H₄-CN acts as bridging ligand, are described. ¹H and ¹³C NMR characterization of the product complexes indicate the presence of a significant interannular conjugation effect involving the aromatic rings of the organic spacer, the extent of which can be chemically modified by addition of electrophiles such as and H⁺. Furthermore, the reversibility of protonation reaction entails the opportunity of modulating the conjugative properties of the title compounds by a proton addition-elimination mechanism.     

Modulating the M-M distance in dinuclear complexes. New ligand with a 2,2'-Biphenol fragment as key unit: synthesis, coordination behavior, and crystal structures of Cu(II) and Zn(II) dinuclear complexes

The synthesis and characterization of the new polyamino-phenolic ligand 3,3'-bis[N,N-bis(2-aminoethyl)aminomethyl]-2,2'-dihydroxybiphenyl (L) are reported. L contains two diethylenetriamine units linked by a 1,1'-bis(2-phenol) group (BPH) on the central nitrogen atom which allows two separate binding amino subunits in a noncyclic ligand. The basicity and binding properties of L toward Cu(II) and Zn(II) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm-3). L behaves as a pentaprotic base and as a monoprotic acid under the experimental conditions used, yielding the H5L5+ or H-1L- species, respectively. L forms both mono- and dinuclear species with both metal ions investigated; the dinuclear species are largely prevalent in aqueous solution with a L/M(II) molar ratio of 1:2 at pH higher than 7. L shows different behavior in Cu(II) and Zn(II) binding, affecting the dinuclear species formed and the distance between the two coordinated metal ions, which is greater in the Zn(II) than in the Cu(II) dinuclear species. This difference can be attributed to the different degree of protonation of BPH which influences the angle between the phenyl rings in the two systems. In this way, it is possible to modulate the M(II)-M(II) distance by the choice M(II) and to space the two M(II) farther away than was possible with the previously synthesized ligands. L does not saturate the coordination sphere of the coordinated M(II) ions in the dinuclear species, and thus, these latter species are prone to add guests. 1H and 13C NMR experiments carried out in aqueous solution, as well as the crystal structures of the dinuclear Cu(II) and Zn(II) species formed in aqueous solution, aided in elucidating the involvement of L and BPH in Zn(II) and Cu(II) stabilization.     

The first metallacarborane triple-decker complexes with a bridging borole ligand

The (borole)iodide complex [(η⁵-C₄H₄BPh)RhI]₄ reacts with the carborane anion [Carb′]⁻ (Carb′ = 9-SMe₂-7,8-C₂B₉H₁₀) giving (Carb′)Rh(η⁵-C₄H₄BPh) (2). Reactions of 2 with dicationic fragments [LM]²⁺ afford the μ-borole triple-decker complexes [(Carb′)Rh(μ-η⁵:η⁵-C₄H₄BPh)ML]²⁺ [LM = Cp^∗Ir (4), (Carb′)Rh (7)] or the arene-type complexes [(Carb′)Rh(μ-η⁵:η⁶-C₄H₄BPh)ML]²⁺ [LM = Cp^∗Rh (3), (Carb′)Ir (8)]. The structure of 4(BF₄)₂ was determined by X-ray diffraction.     

Solvent-dependent interconversions between Rh(I), Rh(II), and Rh(III) complexes of an aryl-monophosphine ligand

Reaction of the aryl-monophosphine ligand alpha(2)-(diisopropylphosphino)isodurene (1) with the Rh(I) precursor [Rh(coe)(2)(acetone)(2)]BF(4) (coe=cyclooctene) in different solvents yielded complexes of all three common oxidation states of rhodium, depending on the solvent used. When the reaction was carried out in methanol a cyclometalated, solvent-stabilized Rh(III) alkyl-hydride complex (2) was obtained. However, when the reaction was carried out in acetone or dichloromethane a dinuclear eta(6)-arene Rh(II) complex (5) was obtained in the absence of added redox reagents. Moreover, when acetonitrile was added to a solution of either the Rh(II) or Rh(III) complexes, a new solvent-stabilized, noncyclometalated Rh(I) complex (6) was obtained. In this report we describe the different complexes, which were fully characterized, and probe the processes behind the remarkable solvent effect observed.     

Polystyrene anchored rhodium (I) bidentate ligand complexes as catalysts for hydrogenation

Polystyrene supported Rh(I) AA′ (AA′ = anthranilic acid, 2,2′-bipyridine or 1,10-phenanthroline) complexes catalyse the hydrogenation of monoolefins (terminal, cyclic and internal) and dienes. Ethyl sorbate undergoes saturation via the monoene intermediate. Thiscis olefin reacts faster than thetrans isomer. The rate law for the reaction is: Rate α [catalyst] [substrate] [H₂].     

Extending the coordination capabilities of tertiary phosphines and arsines: preparation, molecular structure, and reactivity of dinuclear rhodium complexes with PR3 and AsR3 in a doubly bridging coordination mode

The reactions of [Rh2(kappa2-acac)2(mu-CPh2)2(mu-PR3)] (PR3= PMe34, PMe2Ph 7, PEt38) with an equimolar amount of Me3SiX (X = Cl, Br, I) afforded the unsymmetrical complexes [Rh2X(kappa2-acac)(mu-CPh2)2(mu-PR3)]5, 9-12, which contain the phosphine in a semi-bridging coordination mode. From 4 and excess Me3SiCl, the tetranuclear complex [[Rh2Cl(mu-Cl)(mu-CPh2)2(mu-PMe3)]2]6 was obtained. In contrast, the reaction of 4 with an excess of Me3SiX (X = Br, I) yielded the dinuclear complexes [Rh2X2(mu-CPh2)2(mu-PMe3)]13, 14 in which, as shown by the X-ray crystal structure analysis of 14, the bridging phosphine is coordinated in a truly symmetrical bonding mode. While related compounds with PEt3 and PMe2Ph as bridging ligands were prepared on a similar route, the complex [Rh2Cl2(mu-CPh2)2(mu-PiPr3)]19 was obtained from the mixed-valence species [(PiPr3)Rh(mu-CPh2)2Rh(kappa2-acac)2]17 and HCl. The reaction of [Rh2(kappa2-acac)2(mu-CPh2)2(mu-SbiPr3)]3 with AsMe3 gave the related Rh(mu-AsMe3)Rh compound 21. With Me3SiCl, the acac ligands of 21 can be replaced stepwise by chloride to give [Rh2Cl(kappa2-acac)(mu-CPh2)2(mu-AsMe3)]23 and [[Rh2Cl(mu-Cl)(mu-CPh2)2(mu-AsMe3)]2]24, the latter being isomorphous to the phosphine-bridged dimer 6.