Claude Moise

Memory effects in functionalized conducting polymer films: titanocene derivatized polypyrrole in contact with THF solutions

Abstract Films with a polypyrrole matrix and pendant titanocene dichloride centers, p(Tc3Py), have been obtained by potentiostatic electropolymerization of the titanocene-pyrrolyl derivative, Tc3Py=Tc(CH 2 ) 3 NC 4 H 4 (Tc=Cl 2 TiCpCp′, Cp=C 5 H 5 , Cp′=C 5 H 4 ), in acetonitrile (AN) solutions on a Pt surface. The redox activity has been studied after the transfer of the film-coated electrode into the monomer-free solution of the same electrolyte, TBAPF 6 , in THF. Contrary to the case of AN or dichloromethane solutions, one can achieve a stable redox activity of the immobilized Tc centers in THF solutions during a series of cycles. A parallel between the redox properties of the Tc complex in solution and inside the film for different solvents has been established. Various ‘memory’ effects have been observed, i.e. the dependence of the film response on the previous treatment of the film: (a) a prepeak at the onset of the polymer matrix oxidation (observed earlier for other functionalized conducting polymer films); (b) an ‘enhanced plateau’ within the range of the polymer matrix electroactivity; (c) a strong increase of the current within the reduction peak of titanocene centers after the previous passage through the range of the matrix electroactivity (compared to the response when the potential variation is limited to the titanocene potential range); (d) a shift of all oxidation waves in the positive direction as a result of the film exposure to sufficiently high negative potentials as well as their backward shift if the film is held at a potential in the ‘window’ between the two ranges of electroactivity. Possible interpretations of this phenomenon have been discussed. A non-equilibrium origin of this phenomenon has been proven. An attribution of the observed effects to redox processes in the polymer matrix and immobilized titanocene centers has been proposed.

Mono- and di-bridged heterobimetallic systems from group 5 hydride phosphido and hydride phosphino metalloligands. Crystal structure of Cp2Ta(H)( μ-H)( μ-PMe2)Cr(CO)4

The trihydrides Cp 2 MH 3 (M ue5fb Nb, Ta) react with chlorophosphines PR 2 Cl (R ue5fb Me, Ph) affording phosphonium salts [Cp 2 MH 2 (PR 2 H)] + , Cl − ( 2 (a, b) 2′ (a, b)) . Depending on the metal (Nb or Ta) and on the nature of the phosphine substituent (Me or Ph), deprotonation of these salts leads to hydride phosphino Cp 2 MH(PR 2 H) ( 3 (a, b) 3′a) or hydrided phosphido Cp 2 TaH 2 (PPh 2 ) ( 4′b ) metalloligands. These two kinds of complexes are able to bind [M′(CO) 5 ] or [M′(CO) 4 ] (M′ ue5fb Cr, Mo, W) organometallic fragments to give mono- or di-bridged heterobimetallic systems. The crystallographic analysis of Cp 2 Ta(H)(μ-H)(μ-PMe 2 )Cr(CO) 4 ( 7′aCr ) is reported and discussed.

First catalytic allyltitanation reactions

Catalytic allyltitanation reactions were accomplished from dienes and aldehydes with only 5% of titanocene complexes at the expense of employing stoichiometric amounts of PMHS.

Addition of Cr(CO)5 to the M(η2- S2) moiety of Cp2 M(S2H (Cp′ = tBuC5H4 : M = Ta; CpX = C5Me4Et: M = Nb) and crystal structures of Cp′2TaS2H · [Cr(CO)5]n (n = 1, 2)

Reaction of Cp′2TaS2H (Cp′ = tBuC5H4) or Cp2xNbS2H (Cpx = C5Me4Et) with an excess of Cr(CO)5THF gives the adducts Cp′2TaS2H · Cr(CO)5 1, Cp′2TaS2H · 2Cr(CO)5 2, and Cp2xNbS2H · Cr(CO)5 3 respectively. 1 and 2 are separated by fractional crystallisation. The crystal structures show the Cr(CO)5 fragment in 1 to be coordinated to the ‘outer’ sulfur, and in 2 both Cr(CO)5 fragments are coordinated to each sulfur of the S2 ligand in a trans fashion. In all cases approximate sp3 hybridisation of the S atoms is observed. The new compounds are thermally labile and give CO-free, trinuclear compounds of the type Cp4M2S4Cr upon heating their solutions.

Synthesis, X-ray crystal structure, NMR characterization and theoretical calculations on [Cp2Ta(η2-H2)(CO)]+, the first thermally stable group 5 dihydrogen complex

Protonation n of Cp2TaH(CO) (Cp xa0=xa0 C5H5, 1a; C5H4But, 1b) by HBF4·Et2O at −78xa0°C in CH2Cl2 affords [Cp2TaH2(CO)]BF4 n (2, n 3) as mixtures of 2 isomers. The minor ones (2a, 2b) contain the known trans-dihydride [Cp2TaH2(CO)]+ cations n whereas the major ones (3a, 3b) are [Cp2Ta(η2-H2)(CO)]BF4, the first group 5 dihydrogen complexes. The crystal n structure of the analogous complex 3a·BArf4 recorded at 120 K confirms the presence of the coordinated dihydrogen n ligand, which displays an H–H separation of 1.09(2) A in agreement with distances calculated from NMR data. n Protonation of Cp2TaH2(SiMe2Ph) by (Et2O)2 n·HBArf4 does not lead to an analogous silane derivative but to the new n dinuclear complex [(Cp2TaH2)2(μ-H)](BArf4). Variable temperature NMR studies were carried out on the dihydrogen n complex [Cp2Ta(H2)(CO)]+ (3) and its isotopomers. The high field signal of [Cp2Ta(HD)(CO)]+ (3-d) shows a decoalescence n at 208 K in both 1H and 2D NMR, which allows us to calculate the barrier to rotation of HD (9.6 kcal mol−1). The absence of decoalescence in the signal of 3 down to 173 K and the absence of a large kinetic isotope effect for n the classical rotation of H2 were demonstrated. These results are understood in terms of the presence of very n large exchange couplings in a non-rotating dihydrogen ligand. The large barrier of rotation for the dihydrogen ligand n in 3 was shown by DFT calculations to arise from a transition state in which the dihydrogen ligand is only coordinated n through σ-donation from the H–H bond. The analogous phosphite and phosphine complexes {Cp2TaH2[P(OMe)3]}+ n (4) and [Cp2TaH2(PMe2Ph)]+ (5) were shown to be cis dihydrides, in agreement with DFT calculations on n a model compound, to display exchange couplings in NMR and no isotope effect for the classical exchange n of the n hydride ligands.

Investigation into the reactivity of oxoniobocene complexes [Cp*2Nb(O)R] (Cp*=η5-C5Me5; R=H, OH, OMe) towards heterocumulenes: formation of carbamato and thiocarbamato complexes and catalytic cyclization of PhNCO

Abstract The reaction of [Cp*2NbCl2] (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*2Nb(ue605O)H] (1), the new compound [Cp*2Nb(ue605O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*2Nb(ue605O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*2Nb(ue605O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η1-S-thiocarbamato (3) or η1-O-carbamato ligand (4) along with a terminal Nbue605O group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*2NbH{OC(O)NPh}] (5) along with some 4. The molecular structure of 5 contains a niobocene unit comprising η2-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the Nbue605O group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess PhNCO gave a mixture of heterocycles (PhNCO)2 (6) and (PhNCO)3 (7) in the approximate ratio 3:2. By contrast, the reaction of [Cp*2Nb(ue605O)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7.

Reactivity of the actinoid–carbon σ bond: reaction of [(Me3Si)2N]2MCH2Si(Me)2NSiMe3 with acidic hydrogen, ready C–H activation

The metal-carbon bond of the four-membered metallacycles [(Me3Si)2N]2[graphic ommitted]SiMe3(M = U,Th) reacts under mild conditions with acidic hydrogen of alcohols, phenols, and alkynes, with pyridine to give the orthometallated products from sp2C–H activation, and with metal hydrides to five stable binuclear compounds with an isocarbonyl linkage, whereas cyclopentadienes cleave the metal–nitrogen bond providing biscyclopentadienyl four-membered metallacycles.

Insertion of isocyanides into actinoid–carbon bonds of tris-and bis-cyclopentadienyluranium mono-and di-alkyls

Isocyanides react readily with UCp3R and U(C5Me5)2RCl (Cp cyclopentadienyl, R alky) to give iminoalkyl insertion compounds; with U(C5Me5)2R2, only one insertion reaction occurs, the second metal–carbon bond does not react; i.r. spectra of the insertion compounds exhibit unusually low CN stretching frequencies indicatives of strong metal–nitrogen bonding which causes non-equivalence in the Cp groups in the n.m.r. spectrum of UCp3{η2-CN(C6H3Me2-2,6)Bun}

Syntheses and reactivity of oxo niobocene complexes Cp*2Nb(O)X (X=H, OCH3) and crystal structures of [Cp*2Nb(OH)F]BF4 and Cp*2Nb(O)OC(O)H (Cp*=η5-C5Me5)

Reaction of Cp* 2 NbCl 2 (Cp*= η 5 -C 5 Me 5 ) with KOH or Ba(OH) 2 ·8H 2 O in THF forms the complexes Cp* 2 Nb(ue605O)X (X=Cl: 2 , H: 3 ). The ratio of 2 and 3 depends on the stoichiometry. If NaOMe is added or MeOH in solution Cp* 2 Nb(ue605O)OMe 4 is formed in good yields. Reactivity studies with 3 and 4 show that the Nbue605O as well as the Nb–X unit behave as chemically active sites. Protonation of 3 or 4 with HBF 4 is followed by an attack of fluoride (from BF 4 − anion) to give [Cp* 2 Nb(OH)F]BF 4 6 and [Cp* 2 NbF 2 ]BF 4 7 . In contrast the reaction of 3 or 4 with HCO 2 H results in an exchange of X − by formate to give Cp* 2 Nb(ue605O)OC(O)H 8 . The crystal structures of 6 and 8 are reported. Electrochemical investigations of 2–4 and 7 , 8 reveal reaction pathways for the transformation of 1 into 3 .

Comparative studies in the Cp2M(η2-S2) H series (Cp = t-BuC5H4,C5Me Et; M = Nb, Ta) on the reactivity of hydrie and disulfide ligands

Reactions of Cp′2Ta(S2)H(1;′ =t-BuC5H4)and CP2xNb(S2)H(2;Cpx =C5Me4Et) with S8, I2, CH3 and CH3I are investigated Sulfur insertion into the MH bond of1 results in the formation of Cp′3Ta3S12 and Cp′4Ta4S13, where structures are known by analogy, and Cp′6Ta8S17, which is characterised spectroscopically. Complex2 gives in the analogous reaction Cp3xNb3 S12 as the only product. This compound desulfurises in boiling decane to give Cp3xNb3S7 (8). An X-ray diffraction analysis of8 revealed an unusual M3S7 core containing four monosulfide and one trisulfide ligand. The polysulfide ligand is arranged in such a way that its inner sulfur atom is at the top of the molecule in a noncoordinating fashion. Whereas reaction of1 or2 with I2 gives spectroscopically characterised Cp′2Ta(S2)I and Cp2xNb(S2)I by an H/I exchange, only the reaction of1 with CH3I leads to well defined products. At 0°C [Cp′2Ta(S2CH3)H]I is formed as an intermediate product which converts into Cp′2Ta(=S)I at higher temperatures. The attack of CH3I at the disulfide ligand gives rise to the formation of a chiral sulfur site as inferred from 1H NMR data.