Intramolecular exchange of coordinated and dangling phosphines in pentacarbonyl group 6 complexes of 1,1,2-tris(diphenylphosphino)ethane

The linkage isomers, (OC)₅M[κ¹-PPh₂ CH₂CH(PPh₂)₂] 1 and (OC)₅M[κ¹-PPh₂ CH(PPh₂)CH₂PPh₂] 2 (M = Cr, Mo and W) exist in equilibrium at room temperature. Equilibrium constants for 1Cr ? 2Cr, 1Mo ? 2Mo and 1W ? 2W at 25 °C in CDCl₃ are 2.61, 5.0 and 4.74, respectively. Enthalpy favors the forward reaction (ΔH = −13.5, −12 and −12.2 kJ mol⁻¹, respectively) while entropy favors the reverse reaction (ΔS = −37.6, −28 and −28.2 J K⁻¹ mol⁻¹, respectively). Isomerization is much faster than chelation with 1Mo ? 2Mo ? 1W ? 2W > 1Cr ? 2Cr. Enthalpies of activation for 1Cr ? 2Cr and 1W ? 2W are 119.0 and 92.6 kJ mol⁻¹, respectively, and entropies of activation are 1.4 and −28.2 J K⁻¹ mol⁻¹, respectively. Isomerization is 10⁴ times faster for these complexes than for (OC)₅M[κ¹-PPh₂CH₂CH₂P(p-tolyl)₂]. A novel mechanism is proposed to account for the rate differences. The X-ray crystal structure of 2W shows that the phosphorus atom of the short phosphine arm lies very close to a carbon atom of the W(CO)₄ equatorial plane (3.40 Å) which could allow “through-space” coupling, accounting in part for the observation of long-range J_PC and J_PW coupling. The X-ray structure of (OC)₅W[κ¹-PPh₂ C(CH₂)PPh₂] 5W has been determined for comparison to 2W.     

Synthesis, reactivities and catalytic carbonylation of rhodium(I) carbonyl complexes containing isomeric acetylpyridine ligands

[Rh(CO)₂Cl]₂ reacts with two mole equivalent of 2-acetylpyridine (a), 3-acetylpyridine (b) and 4-acetylpyridine (c) to afford chelate [Rh(CO)Cl(η²-N∩O)] (1a) and non-chelate [Rh(CO)₂Cl(η¹-N∼O)] (1b, 1c) complexes, where, N∩O = a, N∼O = b, c. Oxidative addition (OA) of 1a-1c with CH₃I and C₂H₅I yields penta coordinate rhodium(III) complexes, [Rh(COR)ClI(η²-N∩O)] {R = -CH₃ (2a); -C₂H₅ (3a)} and [Rh(COR)(CO)ClI(η¹-N∼O)] {R = -CH₃ (2b, 2c); -C₂H₅ (3b, 3c)}. Kinetic study for the reaction of 1a-1c with CH₃I indicates a pseudo-first order reaction. The catalytic activity of 1a-1c for the carbonylation of methanol to acetic acid and its ester was evaluated at different initial CO pressures 5, 10 and 20 bar at ∼25 °C and higher turn over numbers (TON = 1581-1654) were obtained compared to commercial Monsanto’s species [Rh(CO)₂I₂]⁻ (TON = 1000) under the reaction conditions: temperature = 130 ± 1 °C, pressure = 15-32 bar, rpm = 450, time = 1 h and catalyst: substrate = 1: 1900.     

Reactions of the pentamethylcyclopentadienyl trisulfido tungsten with M′Cl2 (M′ = Zn, Cd, Hg): Isolation and structural characterization of [PPh4][(η-C5Me5)WS3(ZnCl2)] and [{(η-C5Me5)WS3}2Hg]

Reactions of [PPh₄][(η⁵-C₅Me₅)WS₃] with equimolar M′Cl₂ (M′ = Zn, Cd) in MeCN or 0.5 equiv. of HgCl₂ in DMF afforded two binuclear clusters [PPh₄][(η⁵-C₅Me₅)WS₃(M′Cl₂)] (1: M′ = Zn; 2: M′ = Cd) and one trinuclear cluster [{(η⁵-C₅Me₅)WS₃}₂Hg] (3). Compounds 1-3 were characterized by elemental analysis, IR, UV-Vis, ¹H NMR and X-ray crystallography. Compound 1 may be viewed as a 1:1 composite of [PPh₄][(η⁵-C₅Me₅)WS₃] and ZnCl₂, in which one [(η⁵-C₅Me₅)WS₃]⁻ anion binds a ZnCl₂ moiety via two μ-S atoms. In the structure of 3, two [(η⁵-C₅Me₅)WS₃]⁻ anions coordinate the central Hg atom via two μ-S atoms, forming an unique bent linear structure. In addition, internal redox reactions of [PPh₄][(η⁵-C₅Me₅)WS₃] under the presence of M′Cl₂ (M′ = Zn, Cd, Hg) in high concentrations were discussed.     

Synthesis of cyclopentadienyl ruthenium(II) complexes containing tethered functionalities

The reaction of [C₅H₄(CH₂)_nX]Tl (1: n = 2, X = NMe₂, OMe, CN; n = 3, X = NMe₂) with [(η⁶-C₆H₆)RuCl(μ-Cl)]₂, 2, afforded the sandwich compounds [{η⁵-C₅H₄(CH₂)_nX}Ru(η⁶-C₆H₆)]PF₆, 3, and [η⁵-C₅H₄(CH₂)_nX]₂Ru, 4. Photolytic cleavage of 3 in acetonitrile afforded the tethered products [{η⁵:κN-C₅H₄(CH₂)_nX}Ru(CH₃CN)₂]PF₆, 5.     

Synthesis and characterisation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes [Ti(IV), Zr(IV), Hf(IV), La(III), Ce(III), Yb(III), Sn(II) and Fe(II)]

The preparation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes is described. These are of formula [M{η⁵-C₅H₄(BX)}Cl₃] [M = Ti and X = CAT (2a), CAT^t (2b) or CAT^tt (2c); X = CAT^tt and M = Zr (4a) or Hf (4b)], [M{η⁵-C₅H₄(BX)}₂Cl₂] [M = Zr, X = CAT (3a) or CAT^t (3c); or M = Hf, X = CAT (3b) or CAT^t (3d)], [M{(μ-η⁵-C₅H₃BCAT)₂ SiMe₂}Cl₂] [M = Zr (5a) or Hf (5b)], [M{η⁵-C₅H₃(BCAT)₂}Cl₃] [M = Zr (6a) or Hf (6b)], [M{η⁵-C₅H₄BCAT}₃(THF)] [M = La (7a), Ce (7b) or Yb (7c)], [Sn{η⁵-C₅ H₄(BCAT^t)}Cl](8) and [Fe{η⁵-C₅H₄(BCAT^t)}₂] (9). The abbreviations refer to BO₂C₆H₄-1,2 (BCAT) and the 4-Bu^t (BCAT^t) and the (BCAT^tt) analogues. The compounds 2a-9 have been characterised by microanalysis, multinuclear NMR and mass spectra. The single crystal X-ray structure of the lanthanum compound 7a is presented.     

Synthesis of bimetallic fulvalene and bis(cyclopentadienyl)methane derivatives of niobium and tantalum tetracarbonyl

Ring coupled bimetallic derivatives (μ-η^5:5-C₅H₄C₅H₄)[Nb(CO)₄]₂ and [μ-CH₂(η⁵-C₅H₄)₂][M(CO)₄]₂, where M = Nb and Ta have been prepared. The molecular structures of the latter two compounds have been determined: , triclinic, , a = 8.028(2) Å, b = 11.414(1) Å, c = 12.711(2) Å, α = 75.020(8)°, β = 80.34(2)°, γ = 79.46(2)°, V = 1097.3(4) ų, Z = 2, R(F) = 2.79%; [μ-CH₂(η⁵-C₅H₄)₂][Ta(CO)₄]₂, triclinic, , a = 7.815(3) Å, b = 10.275(4) Å, c = 13.135(4) Å, α = 104.25(3)°, β = 100.26(4)°, γ = 96.86(3)°, V = 991.2(6) ų, Z = 2, R(F) = 3.00%.     

Adduct formation of [(η-C7H7)Zr(η-C5H5)] with phosphines and N-heterocyclic carbenes: An experimental and theoretical study

The reaction of [(η⁷-C₇H₇)Zr(η⁵-C₅H₅)] with two Lewis bases, tetramethylimidazolin-2-ylidene and PMe₃, is reported and their stability probed via spectroscopic and theoretical methods. The strongly σ-basic N-heterocyclic carbene forms a stable adduct which has been structurally characterised, whilst the PMe₃ ligand coordinates weakly to the metal centre. Variable temperature ³¹P NMR spectroscopy has been used to determine the activation energy for this process (ΔG^‡ = 40.5 ± 1.9 kJ mol⁻¹). DFT calculations have been performed on both complexes and the structures discussed. In addition, the enthalpies for the formation of these compounds have been calculated [ΔH⁰(Zr-IMe) = −56.3 kJ mol⁻¹; ΔH⁰(Zr-PMe₃) = −2.3 kJ mol⁻¹] and show that the N-heterocyclic carbene forms a thermodynamically much more stable adduct than that with PMe₃.     

Synthesis, molecular structure, substitution and C-C coupling reactions of ruthenium complexes containing (η-C9H7)Ru(PPh3) as a molecular unit

The 2-methallyl complex [(η⁵-C₉H₇)Ru(η³-2-MeC₃H₄)(PPh₃)] (3), prepared from [(η⁵-C₉H₇)Ru(PPh₃)₂Cl] (2) and 2-MeC₃H₄MgCl, reacts with HX (X = Cl, CF₃CO₂) in the presence of ethene to give the chiral-at-metal compounds [(η⁵-C₉H₇)Ru(C₂H₄)(PPh₃)X] (4, 5) in nearly quantitative yields. Treatment of 2 with AgPF₆ and ethene affords [(η⁵-C₉H₇)Ru(C₂H₄)(PPh₃)₂]PF₆ (6), which reacts with acetone to give the substitution product [(η⁵-C₉H₇)Ru(OCMe₂)(PPh₃)₂]PF₆ (7). The molecular structure of 7 has been determined crystallographically. Whereas treatment of 4 with CH(CO₂Et)N₂ yields the olefin complex [(η⁵-C₉H₇)Ru{η²-(Z)-C₂H₂(CO₂Et)₂}(PPh₃)Cl] (8), the reactions of 4 and 5 with Ph₂CN₂, PhCHN₂ and (Me₃Si)CHN₂ lead to the formation of the carbeneruthenium(II) derivatives [(η⁵-C₉H₇)Ru(CRR′)(PPh₃)Cl] (9-11) and [(η⁵-C₉H₇)Ru(CRR′)(PPh₃)(κ¹-O₂CCF₃)] (12-14), respectively. Treatment of 9 (R = R′ = Ph), 10 (R = H, R′ = Ph) and 11 (R = H, R′ = SiMe₃) with MeLi produces the hydrido(olefin) complexes [(η⁵-C₉H₇)RuH(η²-CH₂CPh₂)(PPh₃)] (15), [(η⁵-C₉H₇)RuH(η²-CH₂CHPh)(PPh₃)] (18a,b) and [(η⁵-C₉H₇)RuH(η²-CH₂CHSiMe₃)(PPh₃)] (19) via C-C coupling and β-hydride shift. The analogous reactions of 11 with PhLi gives the η³-benzyl compound [(η⁵-C₉H₇)Ru{η³-(Me₃Si)CHC₆H₅}(PPh₃)] (20). The η³-allyl complex [(η⁵-C₉H₇)Ru(η³-1-PhC₃H₄)(PPh₃)] (17) was prepared from 10 and CH₂CHMgBr by nucleophilic attack.     

An NMR study of some reactions of an arachno-molybdapentaborane: Formation of an unstable nido-molybdapentaborane

Photolysis of the molybdaborane [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-arachno-2-MoB₄H₇] (1) in benzene-d₆ gives ca. 60% conversion to the compound [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-nido-2-MoB₄H₅] (2). Compound 2 could not be isolated as a solid and is thermally unstable at 20 °C in solution with a half-life of 3-4 h. Repeated photolysis and thermolysis of 1 in the presence of BH₃ · thf gives a low yield of the known metallacarbaborane [(η⁵-C₅H₅)(η²:η³-C₃H₃)-closo-1-MoC₂B₉H₉] (3) suggesting that 3 is formed from 1 via 2. Reaction of 1 with PEt₃ gives initially [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-arachno-2-MoHB₄H₄PEt₃] (4). Longer reaction times (>10 min, 20 °C) give in addition [(η⁵-C₅H₅)(η⁵:η¹-C₅H₄)-arachno-1-MoHB₃H₃PEt₃] (5). Both 4 and 5 are unstable in solution or the solid state decomposing to the molybdacarbaborane [(η⁵-C₅H₅)(η³:η²- C₃H₃)-nido-1-MoC₂B₃H₅] (6), [Mo(η-C₅H₅)₂H₂] and BH₃ · PEt₃. Compound 1 is deprotonated cleanly by KH in thf at the Mo-H-B bridging proton to give (7).     

Oxidation of [Ir(η-C5Me5)(C8H4S8)] and crystal structures of [IrI(η-C5Me5)(C8H4S8)](I3) and [IrI(η-C5Me5)(C8H4S8)](I3)1/2(I7)1/2

[Ir(η⁵-C₅Me₅)(C₈H₄S₈)] (1) [ = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2−)] was reacted with iodine in dichloromethane to afford one-electron- and two-electron-oxidized species [IrI(η⁵-C₅Me₅)(C₈H₄S₈)] (2), [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₃) (3) and [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₅) (4). The oxidized species exhibit electrical conductivities of (1.1-5.0) × 10⁻⁶ S cm⁻¹ measured for compacted pellets at room temperature. The X-ray crystal structures of the two-electron-oxidized complexes 3 and 4 revealed the Ir-I bonds for both of them and the presence of for 3 and ions for 4 as the counter anions. They have many S-S and S-I non-bonding contacts to form two-dimensional molecular interaction sheets in the solid state.     

Synthesis, characterization and applications in ethylene polymerization of asymmetric ansa-titanocene complexes. Molecular structure of [Ti{Me2Si(η-C5Me4)(η-C5H3iPr)}Cl2]

The ansa-titanocene complexes, [Ti{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₃R)}Cl₂] (R = Me (5), iPr (6), tBu (7), SiMe₃ (8)), were obtained from the reaction of Li₂{Me₂Si(C₅Me₄)(C₅H₃R)} (R = Me (1), iPr (2), tBu (3), SiMe₃ (4)) with [TiCl₄(THF)₂], respectively. Compounds 5-8 have been tested as catalysts in the polymerization of ethylene and compared with the ansa-titanocene complexes [Ti{Me₂Si(η⁵-C₅H₄)₂}Cl₂] and [Ti{Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂]. The resulting polyethylene showed molecular weights of about 200 000 g mol⁻¹ and polydispersity values of approximately 3. In addition, the molecular structure of 6 has been determined by single crystal X-ray diffraction studies.     

C-ansa-zirconocene complexes with O/S donor ligands: Novel homoleptic six coordinate 4-mercaptophenolate complex of Zr(IV)

New C-ansa-zirconocene complexes containing methoxythiophenolate and mercaptophenolate ligands have been synthesized and characterized. The reaction of (HSC₆H₄-n-OMe) (n = 2, 3 or 4) with [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}Me₂] (1) led to the formation of monosubstituted complexes [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}Me(κ,S-SC₆H₄-n-OMe)] (n = 2 (2); n = 3 (3)) and the disubstituted complex [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}(κ,S-SC₆H₄-4-OMe)₂] (4). The complexes [Zr{(R)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}(κ,O-OC₆H₄-4-SH)₂] (R = t-Bu (6); R = CH₂CHCH₂ (7)) and [Zr(η⁵-C₅H₄)₂(OC₆H₄-n-SH)₂] (n = 3 (9); n = 4 (10)) have been synthesized using the corresponding dimethyl zirconocene and mercaptophenol. However, the reaction of [Zr{(t-Bu)HC(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (11) with 4-mercaptophenol in the presence of NEt₃ led to the formation of the first example of a homoleptic six-coordinate mercaptophenolate complex of zirconium, namely [HNEt₃]₂[Zr(κ,O-OC₆H₄-4-SH)₆] (12). Complex 12 can be obtained in higher yield by the reaction of ZrCl₄ with six equivalents of 4-mercaptophenol and NEt_3. The reaction of 12 with [Zr(η⁵-C₅H₄)₂Cl₂] gave the unexpected disubstituted complex [Zr(η⁵-C₅H₄)₂(OC₆H₄-4-SH)₂] (10). The molecular structures of 4 and 12 have been determined by single-crystal X-ray diffraction studies.     

Copper(II) complexes derived from tripodal tris[(2-ethyl-(1-pyrazolyl)]amine

Three mono-nuclear copper(II) complexes [Cu(tepza)X]ClO₄ (X = Cl, 1; X = NCS, 2; X = dca, 3) and two dinuclear bridging complexes [Cu₂(tepza)₂(μ-C₄O₄)](ClO₄)₂·H₂O(4) and [Cu₂(tepza)₂(μ-C₅O₅)](ClO₄)₂(5) where tepza = tris[2-ethyl(1-pyrazolyl)]amine, dca = dicyanamide, C₄O₄²⁻ = 3,4-dihydroxycyclobut-3-ene-1,2-dionate (squarate dianion) and C₅O₅²⁻ = 4,5-dihydroxycyclopent-4-ene-1,2,3-trionate (croconate dianion) were synthesized and structurally characterized by IR and UV-Vis spectroscopy as well as by single X-ray crystallography. In the solid state, the geometry of copper(II) centers in these complexes are as follows: close to SP in 2, distorted TBP in 3, predominant SP in 4, and distorted octahedral in 5, whereas in solution distorted SP geometry was generally found. The squarato and the croconato dianions in complexes 4 and 5 are bridging the two copper(II) centers in cis-bis-monodentate and bis-bidentate bonding modes, respectively. Magnetic susceptibility measurements at variable temperatures (2-300 K) reveal the weak antiferromagnetic coupling in the two bridging dinuclear complexes 4 (J = −24.9 cm⁻¹) and 5 (J = −3.1 cm⁻¹).     

Mechanistic studies on monodentate-ligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine

Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp₃)](BF₄) (pt = 1-propanethiolate, pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine), with I⁻ in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp₃)]⁺ + I⁻ ? [PtI(pt) (pp₃)], and the kinetic parameters for the chemical exchange were obtained as follows: , ΔH⁰ = − 10 ± 2.4 kJ mol⁻¹, ΔS⁰ = − 36 ± 10 J K⁻¹ mol⁻¹, , ΔH^‡ = 34 ± 4.7 kJ mol⁻¹, ΔS^‡ = − 50 ± 21 J K⁻¹ mol⁻¹. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp₃)]Cl with trans-[PtCl₂(NCC₆H₅)₂] in chloroform. From these facts, ligand substitution reactions of [PtX(pp₃)]⁺ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp₃)]⁺ with Br⁻ and I⁻ in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.     

Synthesis and structural investigation of vanadocene(IV) complexes of non-linear pseudohalides

Two series of vanadocene complexes of the type (Cp′ = η⁵-C₅H₅, η⁵-C₅H₄Me; X = dicyanamide, tricyanomethanide, dicyanonitrosomethanide) were prepared by the reaction of appropriate vanadocene dichloride complex with alkali salt of non-linear pseudohalide. The bonding mode of pseudohalide ligands was determined by spectroscopic measurements and X-ray diffraction analyses.     

Structural, spectroscopic and redox studies of a new ruthenium(III) complex with an imidazole-rich tripodal ligand

The present paper describes a new tripodal ligand containing imidazole and pyridine arms and its first cis-[Ru^III(L)(Cl)₂]ClO₄ complex (1). The crystal structure of 1 shows Ru^III in a distorted octahedral geometry, in which two chloride ions, cis-positioned to each other, are coordinated besides the four nitrogen atoms from the tetradentate ligand L. The cyclic voltammogram of 1 exhibits three redox processes at −67, +73 and +200 mV versus SCE, which are attributed to the Ru^III/Ru^II couple in the cis-[Ru^III(L)(Cl)₂]⁺, cis-[Ru^II(L)(H₂O)(Cl)]⁺ and cis-[Ru^II(L)(H₂O)₂]²⁺, respectively. After chemical reduction (Zn(Hg) or Eu^II) only the cis-[Ru^II(L)(H₂O)₂]²⁺ species is observed in the cyclic voltammetry. Complex 1 absorbs at 470 nm (ε=1.4×10³ mol⁻¹ L cm⁻¹), 335 nm (ε=7.9×10³ mol⁻¹ L cm⁻¹), 301 nm (ε=6.7×10³ mol⁻¹ L cm⁻¹) and 264 nm (ε=9.9×10³ mol⁻¹ L cm⁻¹), in water solution (CF₃COOH, 0.01 mol L⁻¹, μ=0.1 mol L⁻¹ with CF₃COONa). Spectroelectrochemical experiments show a decrease of the bands at 335 and 301 nm, which are attributed to LMCT transitions from the chloride to the Ru^III center and the appearance of a broad band at 402 nm ascribed to MLCT transition from the Ru^II center to the pyridine ligand. The lability of the water ligands in the cis-[Ru^II(L)(H₂O)₂]²⁺ species has been investigated using the auxiliary ligand pyrazine. Reactions in the presence of stoichiometric and excess of pyrazine yield the same species, cis-[Ru^II(L)(H₂O)(pz)]²⁺, which exhibits a reversible redox process at 493 mV versus SCE and absorbs at 438 nm (ε=5.1×10³ mol⁻¹ L cm⁻¹) and 394 nm (ε=4.2×10³ mol⁻¹ L cm⁻¹). Experiments performed with a large excess of pyrazine gave a specific rate constant k₁=(2.8±0.5)×10⁻² M⁻¹ s⁻¹, at 25 °C, in CF₃COOH, 0.01 mol L⁻¹, μ=0.1 mol L⁻¹ (with CF₃COONa).     

New molybdenum(V) complexes based on the {Mo2O4} structural core with esters or anions of malonic and succinic acid

A series of malonato complexes of molybdenum(V) was prepared by reacting (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ or (PyH)_n[MoOBr₄]_n with malonic acid (H₂mal) or a half-neutralized acid, hydrogen malonate (Hmal⁻), at ambient conditions: (PyH)₃[Mo₂O₄Cl₄(μ₂-Hmal)] · CH₃CN (1), (PyH)₃[Mo₂O₄Br₄(μ₂-Hmal)] · CH₃CN (2), (PyH)₂[Mo₂O₄Cl(η²-mal)(μ₂-Hmal)Py] (3), (3,5-LutH)₂(H₃O) [Mo₂O₄(η²-mal)₂(μ₂-Hmal)] (4), (PyH)[Mo₂O₄Cl₂(μ₂-Memal)Py₂] (5), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-Memal)(3,5-Lut)₂] (6), (PyH)[Mo₂O₄Cl₂(μ₂-Etmal)Py₂] (7), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-Prmal)(3,5-Lut)₂] (8) and [{Mo₂O₄(μ₂-Memal)Py₂}₂(μ₂-OCH₃)₂] (9) (where Py = pyridine, C₅H₅N; PyH⁺ = pyridinium cation, C₅H₅NH⁺; 3,5-Lut = 3,5-lutidine, C₇H₉N; 3,5-LutH⁺ = 3,5-lutidinium cation, C₇H₉NH⁺; mal²⁻ = malonate, ⁻OOCCH₂COO⁻; Memal⁻ = monomethyl malonate, ⁻OOCCH₂COOCH₃; Etmal⁻ = monoethyl malonate, ⁻OOCCH₂COOC₂H₅ and Prmal⁻ = monopropyl malonate, ⁻OOCCH₂COOC₃H₇). The complex anions of compounds 1-8 have a common structural feature: a dinuclear, singly metal-metal bonded {Mo₂O₄}²⁺ core with the carboxylate moiety of the malonato ligand coordinated in a syn-syn bidentate bridging manner to the pair of metal atoms. The remaining four coordination sites of the {Mo₂O₄}²⁺ core are occupied with halides in 1 and 2, with halides/pyridine ligands in 5-8, with a pair of bidentate malonate ions in 4 and with the combination of all in 3. The neutral molecules of 9 consist of two {Mo₂O₄}²⁺ cores linked with a pair of methoxide ions into a chain-like, tetranuclear cluster. An esterification of malonic acid was observed to take place in the reaction mixtures containing alcohols. Solvothermal reactions with malonic acid carried out at 115 °C produced anionic acetato complexes as found in (PyH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)Py₂] · Py (10), (PyH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)Py₂] (11), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)(3,5-Lut)₂] (12) and (4-MePyH)₃[Mo₂O₄Cl₂(μ₂-OOCCH₃)(4-MePy)₂]₂Cl (13) (4-MePy = 4-methylpyridine, C₆H₇N). The acetate coordinated in the syn-syn bidentate bridging mode in all. Reactions of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with succinic acid (H₂suc) at ambient conditions resulted in a complex with a half-neutralized acid, (PyH)[Mo₂O₄Cl₂(μ₂-Hsuc)Py₂] · Py (14) (Hsuc⁻ = hydrogen succinate, ⁻OOC(CH₂)₂COOH), while those carried out at 115 °C in a tetranuclear succinato complex, (4-MePyH)₂[{Mo₂O₄Cl₂(4-MePy)₂}₂(μ₄-suc)] (15) (suc²⁻ = succinate, ⁻OOC(CH₂)₂COO⁻). The tetranuclear anion of 15 consists of two {Mo₂O₄}²⁺ cores covalently linked with a tetradentate succinato ligand. The compounds were fully characterized by infrared vibrational spectroscopy, elemental analyses and X-ray diffraction studies.     

Phosphorus-carbon bond formation via reactions of triphenylphosphine with acetylene and pentamethylcyclopentadienyl coordinated to iridium(III)

Phosphorus-carbon bond is formed via: (i) the apparent HCCH insertion into Ir-P bond to produce Ir-CHCH-PPh₃ group and (ii) the activation of the ring-methyl group of the coordinated Cp^* (C₅Me₅ ⁻) to produce Ir(η⁵-C₅Me₄CH₂-PPh₃) group from reactions of iridium(III)-Cp^* complexes, [Cp^*IrL₃]ⁿ⁺ (n=1, 2); Cp^*=C₅Me₅ ⁻; L₃=Cl(PPh₃)₂ (3), (CH₃CN)₃ (5). The following new P-C bond containing iridium(III) complexes have been prepared: [Cp^*Ir(-CHCH-PPh₃)Cl(PPh₃)]⁺ (4) from 3 with HCCH; [Ir(η⁵-C₅Me₄CH₂-PPh₃)(H)(PPh₃)₂]²⁺ (6) from 5 with PPh₃; [Cp^*Ir(-CHCH-PPh₃)₂(PPh₃)]²⁺ (7) from 5 with HCCH and PPh₃; [Ir(η⁵-C₅Me₄CH₂-PPh₃)(-CHCH-PPh₃)Cl(PPh₃)]²⁺ (8) from [Ir(η⁵-C₅Me₄CH₂-PPh₃)(Cl)(PPh₃)₂]²⁺ (6-Cl) with HCCH; [Ir(η⁵-C₅Me₃(1,3-CH₂-PPh₃)₂(H)(PPh₃)₂)]³⁺ (10) from [Ir(η⁵-C₅Me₄CH₂-PPh₃)(NCCH₃)₂(PPh₃)]³⁺ (9) with PPh₃; [Ir(η⁵-C₅Me₄CH₂-PPh₃)(-CHCH-PPh₃)₂(PPh₃)]³⁺ (11) from 9 with HCCH and PPh₃.     

Synthesis and properties of new trinuclear Mo(II) complexes containing imidazole and benzimidazole ferrocene units

The reaction of FcCOCl (Fc = (C₅H₅)Fe(C₅H₄)) with benzimidazole or imidazole in 1:1 ratio gives the ferrocenyl derivatives FcCO(benzim) (L1) or FcCO(im) (L2), respectively. Two molecules of L1 or L2 can replace two nitrile ligands in [Mo(η³-C₃H₅)(CO)₂(CH₃CN)₂Br] or [Mo(η³- C₅H₅O)(CO)₂(CH₃CN)₂Br] leading to the new trinuclear complexes [Mo(η³-C₃H₅)(CO)₂(L)₂Br] (C1 for L = L1; C3 for L = L2) and [Mo(η³-C₅H₅O)(CO)₂(L)₂Br] (C2 for L = L1; C4 for L = L2) with L1 and L2 acting as N-monodentade ligands. L1, L2 and C2 were characterized by X-ray diffraction studies. [Mo(η³-C₅H₅O)(CO)₂(L1)₂Br] was shown to be a trinuclear species, with the two L1 molecules occupying one equatorial and one axial position in the coordination sphere of Mo(II). Cyclic voltammetric studies were performed for the two ligands L1 and L2, as well as for their molybdenum complexes, and kinetic and thermodynamic data for the corresponding redox processes obtained. In agreement with the nature of the frontier orbitals obtained from DFT calculations, L1 and L2 exhibit one oxidation process at the Fe(II) center, while C1, C3, and C4 display another oxidation wave at lower potentials, associated with the oxidation of Mo(II).     

Reduction chemistry of the mixed ligand metallocene [(C5Me5)(C8H8)U]2(μ-C8H8) with bipyridines

The U⁴⁺ cyclooctatetraenyl complex, [(C₅Me₅)(C₈H₈)U]₂(μ-C₈H₈), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me₂bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η⁵-C₅Me₅)(η⁸-C₈H₈)U(Me₂bipy-κ²N,N′) and (η⁵-C₅Me₅)(η⁸-C₈H₈)U(bipy-κ²N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U⁴⁺ complexes of bipyridyl radical anions. Hence, only one of the (C₈H₈)²⁻ ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C₈H₈)²⁻, Me₂bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.