Reactivity patterns of thermally stable, terminal, electrophilic phosphinidene complexes towards diazoalkanes: oxidation at the phosphorus centre and formation of P-bound eta1-phosphaazine, eta1-phosphaalkene and eta3-diazaphosphaallene complexes

The thermally stable, terminal phosphinidene complexes [CpM(CO)2(eta1-PNiPr2)]AlCl4(Cp= Cp, Cp*; M = Fe) and [Cp*M(CO)3(eta1-PNiPr2)]AlCl4 (M = Cr, Mo, W) react with Ph2C=N=N to form terminal P-coordinated eta1-phosphaazine and eta3-diazaphosphaallene ligands, respectively, whereas [CpFe(CO)2(eta1-PNiPr2)]AlCl4 reacts with Me3SiCHN2 affording a terminal phosphorus bound eta1-phosphaalkene complex.     

Reaction of a terminal phosphinidene complex with azulenes: eta1-complexes, C--H bond insertions, and 1,4-adducts

Reaction of an in situ generated phosphinidene complex [PhPW(CO)(5)] with the aromatic azulene and guaiazulene leads to unexpected 1,4-adducts of the seven-membered ring and to C--H bond insertion of the five-membered ring. A DFT analysis suggests that the reaction is initiated by formation of a eta(1)-complex between the phosphinidene and the five-membered ring of the aromatic substrate. Four conformations of this complex were identified. Two convert without barrier to the slightly more stable syn- and anti-1,2-adducts. These undergo pericyclic 1,7-sigmatropic rearrangements with remarkably low barriers to give 1,4-adducts, with an inverted configuration at the phosphorus center. An X-ray crystal structure is presented for one of the 1,4-adducts of guaiazulene. The other two eta(1)-complexes insert with modest barriers into a C--H bond of the five-membered ring.     

Redox-associated eta(1) to eta(2) conversion of disulfide ligands in dinuclear ruthenium complexes

Disulfide-bridged dinuclear ruthenium complexes [[Ru(MeCN)(P(OMe)(3))(2)](2)(mu-X)(mu,eta(2)-S(2))][ZnX(3)(MeCN)] (X = Cl (2), Br (4)), [[Ru(MeCN)(P(OMe)(3))(2)](2)(mu-Cl)(2)(mu,eta(1)-S(2))](CF(3)SO(3)) (5), [[Ru(MeCN)(P(OMe)(3))(2)](2)(mu-Cl)(mu,eta(2)-S(2))](BF(4)) (6), and [[Ru(MeCN)(2)(P(OMe)(3))(2)](2)(mu-Cl)(mu,eta(1)-S(2))](CF(3)SO(3))(3) (7) were synthesized, and the crystal structures of 2 and 4 were determined. Crystal data: 2, triclinic, P1, a = 15.921(4) A, b = 17.484(4) A, c = 8.774(2) A, alpha = 103.14(2) degrees, beta = 102.30(2) degrees, gamma = 109.68(2) degrees, V = 2124(1) A(3), Z = 2, R (R(w)) = 0.055 (0.074); 4, triclinic, P1 a = 15.943(4) A, b = 17.703(4) A, c = 8.883(1) A, alpha = 102.96(2) degrees, beta = 102.02(2) degrees, gamma = 109.10(2) degrees, V = 2198.4(9) A(3), Z = 2, R (R(w)) = 0.048 (0.067). Complexes 2 and 4 were obtained by reduction of the disulfide-bridged ruthenium complexes [[RuX(P(OMe)(3))(2)](2)(mu-X)(2)(mu,eta(1)-S(2))] (X = Cl (1), Br (3)) with zinc, respectively. Complex 5 was synthesized by oxidation of 2 with AgCF(3)SO(3). Through these redox steps, the coordination mode of the disulfide ligand was converted from mu,eta(1) in 1 and 3 to mu,eta(2) in 2 and 4 and further reverted to mu,eta(1) in 5. Electrochemical studies of 6 indicated that similar conversion of the coordination mode occurs also in electrochemical redox reactions.     

A dicoordinate palladium(0) complex with an unusual intramolecular eta(1)-arene coordination

The reaction of (tmeda)PdMe2 with dcpBiph gives (dcpBiph)2Pd in high yield. The solid-state structure of (dcpBiph)2Pd reveals a bent P-Pd-P framework and an unusual eta1-arene interaction between the palladium and the distal ring of one of the biphenyl substituents. In solution, an additional conformer exists which does not show a pi-interaction with a biphenyl ring. The low-coordinate complex, (dcpBiph)2Pd, undergoes C-X oxidative addition reactions with PhX (X = I, Br, Cl). A minor product resulting from metalation of the biphenyl ring is also observed.     

Stable ion and electrophilic chemistry of the sterically crowded stilbene 1,1'-Bi(benzocyclobutenylidene) and its derivatives

Generation and NMR studies of novel carbocations and carboxonium ions are reported from sterically hindered stilbene 1,1'-bi(benzocyclobutenylidene) 1, its dimethoxy derivative 5, and from their skeletally rearranged derivatives, namely, the spirocyclic ketone 6, diastereomeric alcohols 7 and isomeric diols 8. Quenching experiments on the carbocations under various conditions resulted in the formation/isolation of several novel covalent adducts. Acid-catalyzed isomerization of the diols 8 produced a remarkable dimeric molecule, whose structure was confirmed by X-ray analysis. Reactions of hindered stilbenes 1 and 5 with Br 2/CDCl 3 were examined via NMR experiments. The experimentally observed carbocations were also studied computationally by GIAO-DFT and by NICS.     

Synthesis and characterization of an iron(II) eta(2)-hydrazine complex

The iron phosphine complex cis-[Fe(DMeOPrPE)2(eta2-N2H4)][BPh4]2 {DMeOPrPE = 1,2-bis[bis(methoxypropyl)phosphino]ethane} was synthesized and structurally characterized. The structure exhibits the first eta2 coordination of hydrazine to iron, which may be relevant to intermediates trapped during nitrogenase turnover. The reaction of I with acid results in the formation of ammonia via a disproportionation reaction.     

The synthesis of a sterically hindered samarium(II) bis(amidinate) and conversion to its homoleptic trivalent congener

The first divalent samarium bis(amidinate) has been prepared and aspects of its novel chemistry, including the preparation of a sterically hindered homoleptic Sm(III) tris(amidinate), explored.     

Dynamic equilibration of eta 1-carbene and eta 2-alkyne moieties within an alkynylcarbene dimanganese complex

The coordination of an additional [Cp(CO)2Mn] fragment to the alkyne linkage of an alkynylcarbene complex of the type Cp(CO)2Mn=C(R')C identical to CR" yields a highly fluxional molecule, in which the [eta 1-carbene] and [eta 2-alkyne] moieties are seen to exchange rapidly on the NMR time scale.     

Determination of cobalt at ng ml(-1) level in water using the electrophilic substiution complexation between co(II) and chlorophosphonazo-p-CL-Cu(II) complex

The chromophore chlorophosphonazo-p-Cl (PCCPA) was used to complex Co(II) and Cu(II) at pH 9.18. The formation of Co(PCCPA)2 and Cu(PCCPA)2 complexes were characterized by the spectral correction technique. Co(II) could competitively substitute Cu(II) from the Cu(II)-PCCPA complex via electrophilic effect. With the assistance of the light-absorption ratio variation approach, the electrophilic substitution complexation showed a high selectivity and good sensitivity with 1.9 ng mL(-1) of LOD. The proposed method has been applied to the direct detection of Co(II) in surface water and wastewater with good percent of recovery.     

(eta 5-Cyclopentadienyl)(eta 4-di- and tetra-phosphorylcyclobutadiene)cobalt(I): synthesis,structure, and formation of 1-D coordination polymer

(eta 5-Cyclopentadienyl)(eta 4-di- and tetra-phosphorylcyclobutadiene)cobalt(I) complexes were synthesized by the reaction of mono- and diphosphorylacetylenes with CpCo(CO)2, respectively. The tetraphosphoryl derivative has proved to work as a bis-bidentate ligand affording a one-dimensional coordination polymer with Ce(III).     

Wavelength-dependent photofragmentation and photoionization of gaseous (eta4-cycloocta-1,5-diene)(eta5-cyclopentadienyl)cobalt

Gas-phase photoreactions and photoproducts of the mixed-ligand compound (eta(4)-cycloocta-1,5-diene)(eta(5)-cyclopentadienyl)cobalt are reported. Significant amounts of the monoligated complexes CoCOD and CoCp are produced, and the relative amounts are wavelength dependent. The COD ligand (with the weakest metal-ligand bonds) is always preferentially labilized as expected, but the relative amounts of the CoCOD and CoCp fragments change by 1 order of magnitude as the excitation wavelength is changed. The gas-phase photoreactions exhibit other surprising features that are uncommon in the photoreactions of organometallic compounds in the gas phase. Significant amounts of the intact cation are formed, in contrast to most reported reactions where fragmentation of the weak metal-ligand bonds precedes ionization. Most surprisingly, fragmentation of the ligands occurs while the ligands are still coordinated. The resulting metal complexes contain ligand fragments that remain coordinated to the metal. Breaking several carbon-carbon bonds with retention of weaker metal-ligand bonds is unexpected. For example, C(5)H(5) undergoes fragmentation while still coordinated to the cobalt, yielding smaller compounds such as Co(CH)(+), Co(C(2)H(2))(+), Co(C(3)H(3))(+), and Co(C(4)H(6))(+). Correspondingly, coordinated COD yields Co(C(6)H(6))(+), Co(C(5)H(5))(+), Co(C(4)H(6))(+), Co(C(3)H(3))(+), Co(C(2)H(2))(+), and Co(CH)(+). The wavelength dependence of the ligand labilization is examined by utilizing mass-selected resonance enhanced multiphoton ionization spectroscopy. Both broad bands and sharp lines are observed in the mass-selected excitation spectra. The action spectra obtained in the gas phase while monitoring the cobalt ion follow the absorption onset found in solution. The changes in fragmentation pathways are interpreted in terms of the initially accessed excited state.     

Unprecedented syndioselectivity and syndiotactic polyolefin melting temperature: polypropylene and poly(4-methyl-1-pentene) from a highly active, sterically expanded eta1-fluorenyl-eta1-amido zirconium complex

The structurally unique, sterically expanded eta1-fluorenyl-eta1-amido single-site precatalyst, Me2Si(eta1-N-tBu)(eta1-C29H36)ZrCl2.OEt2 (3), upon activation with methylaluminoxane (MAO), is remarkably active and constitutes the most syndioselective alpha-olefin polymerization catalyst system yet reported. 3/MAO affords as-prepared syndiotactic polypropylene with [rrrr] > 99% and unprecedented melting temperatures for the unannealed (165 degrees C) and annealed (174 degrees C) polymers. The activity of this system is 4 times that of the prototypical syndioselective catalyst Me2C(eta5-C5H4)(eta5-C13H8)ZrCl2/MAO. The high activity and syndioselectivity of 3/MAO can be extended to the production of syndiotactic poly(4-methyl-1-pentene) with a record melting temperature of 215 degrees C and [rrrr] = 97%.     

Hydrotris(pyrazolyl)borate metallacycles: conversion of a late-metal metallacyclopentene to a stable metallacyclopentadiene-alkene complex

The bis(ethene) complex [(Tp)Ir(C(2)H(4))(2)] (3) undergoes reaction with dimethyl acetylenedicarboxylate (DMAD) in acetonitrile solvent at 60 degrees C to give the trispyrazolylborate metallacyclopent-2-ene complex [(Tp)Ir (CH(2)CH(2)C(CO(2)Me)=C(CO(2)Me))(NCMe)] (4). Spectroscopic analysis of a room-temperature reaction between 3 and DMAD in acetonitrile-d(3) provides evidence for the formation of an eta(2)-alkene/eta(2)-alkyne intermediate on the path to 4. The reaction of 3 with DMAD in THF solvent leads to the formation of the THF-ligated metallacyclopent-2-ene complex [(Tp)Ir(CH(2)CH(2)C(CO(2)Me)=C(CO(2)Me))(THF)] (5), which undergoes further reaction with DMAD at 60 degrees C in benzene to give [(Tp)Ir(C(CO(2)Me)=C(CO(2)Me)C(CO(2)Me)=C(CO(2)Me))(eta(2)-CH(2)=CH(2))] (6). Complex 4 was structurally characterized by X-ray crystallography.     

The electrophilic reactions of pentacyanonitrosylferrate(II) with hydrazine and substituted derivatives. Catalytic reduction of nitrite and theoretical prediction of eta(1)-, eta(2)-N(2)O bound intermediates

The electrophilic reactivity of the pentacyanonitrosylferrate(II) ion, [Fe(CN)(5)NO](2)(-), toward hydrazine (Hz) and substituted hydrazines (MeHz, 1,1-Me(2)Hz, and 1,2-Me(2)Hz) has been studied by means of stoichiometric and kinetic experiments (pH 6-10). The reaction of Hz led to N(2)O and NH(3), with similar paths for MeHz and 1,1-Me(2)Hz, which form the corresponding amines. A parallel path has been found for MeHz, leading to N(2)O, N(2), and MeOH. The reaction of 1,2-Me(2)Hz follows a different route, characterized by azomethane formation (MeNNMe), full reduction of nitrosyl to NH(3), and intermediate detection of [Fe(CN)(5)NO](3)(-). In the above reactions, [Fe(CN)(5)H(2)O](3)(-) was always a product, allowing the system to proceed catalytically for nitrite reduction, an issue relevant in relation to the behavior of the nitrite and nitric oxide reductase enzymes. The mechanism comprises initial reversible adduct formation through the binding of the nucleophile to the N-atom of nitrosyl. The adducts decompose through OH(-) attack giving the final products, without intermediate detection. Rate constants for the adduct-formation steps (k = 0.43 M(-)(1) s(-)(1), 25 degrees C for Hz) decrease with methylation by about an order of magnitude. Among the different systems studied, one-, two-, and multielectron reductions of bound NO(+) are analyzed comparatively, with consideration of the role of NO, HNO (nitroxyl), and hydroxylamine as bound intermediates. A DFT study (B3LYP) of the reaction profile allows one to characterize intermediates in the potential hypersurface. These are the initial adducts, as well as their decomposition products, the eta(1)- and eta(2)-linkage isomers of N(2)O.     

A stabilized mu-eta(2):eta(2) peroxodicopper(II) complex with a secondary diamine ligand and its tyrosinase-like reactivity

The activation of dioxygen (O(2)) by Cu(I) complexes is an ubiquitous process in biology and industrial applications. In tyrosinase, a binuclear copper enzyme, a mu-eta(2):eta(2)-peroxodicopper(II) species is generally accepted to be the active oxidant. Reported here is the characterization and reactivity of a stable mu-eta(2):eta(2)-peroxodicopper(II) complex at -80 degrees C using a secondary diamine ligand, N,N'-di-tert-butyl-ethylenediamine (DBED). The spectroscopic characteristics of this complex (UV-vis, resonance Raman) prove to be strongly dependent on the counteranion employed and not on the solvent, suggesting an intimate interaction of the counteranions with the Cu-O(2) cores. This interaction is also supported by solution EXAFS data. This new complex exhibits hydroxylation reactivity by converting phenolates to catechols, proving to be a functional model of tyrosinase. Additional interest in this Cu/O(2) species results from the use of Cu(I)-DBED as a polymerization catalyst of phenols to polyphenylene oxide (PPO) with O(2) as the terminal oxidant.     

Ring-opening reaction of phosphorus-bridged [1]ferrocenophane via ring slippage from eta(5)- to eta(1)-Cp

A reaction mechanism was investigated for a ring-opening reaction of RP(E)-bridged [1]ferrocenophane, where RP(E) = PhP(S) (3a), PhP (3b), and MesP (3c) (Mes = 2,4,6-trimethylphenyl). Irradiation of UV-vis light in the presence of an excess amount of P(OMe)(3) transformed 3a to [Fe(PhP(S)(eta(5)-C(5)H(4))(eta(1)-C(5)H(4)))(P(OMe)(3))(2)] (4a), in which one of the two cyclopentadienyl (Cp) rings of 3a changed its coordination mode from eta(5) to eta(1) and vacant coordination sites thus formed on the iron center were occupied by two P(OMe)(3) ligands. The molecular structure of 4a was determined by X-ray analysis, in which eta(1)-Cp adopted a 1-Fe-2-P-1,3-cyclopentadiene structure. Under the same reaction conditions, 3b and 3c also gave similar ring-slipped products 4b and 4c, respectively. Photolysis of 3a using more strongly coordinating PMe(3) in place of P(OMe)(3) led to complete dissociation of a Cp ligand from the iron center to form [Fe(PhP(S)(eta(5)-C(5)H(4))(C(5)H(4)))(PMe(3))(3)] (5). The formation of the ring-slipped and -dissociated products on the photolysis of 3 strongly supports the view that photolytic ring-opening polymerization of 3 proceeds via an unprecedented Fe-Cp bond cleavage mechanism.