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The possibility of thermally reducing formic acid to formaldehyde selectively has been probed using metallic zinc. Good selectivity (over 80%) was obtained with low concentrations of formic acid, with methanol and methyl formate as secondary products. The selectivity can be tuned by changing the carrier gas flow, temperature, and zinc amount. Zinc was oxidized to zinc oxide during this process.Key words: formic acid reduction, formaldehyde, methanol.Nous avons explore la possibilite de reduire par voie thermique l'acide formique en formaldehyde en utilisant le zinc metallique. Nous avons obtenu une bonne selectivite (plus de 80%) en employant des concentrations faibles d'acide formique; les produits secondaires observes etaient le methanol et le formate de methyle. Il est possible de faire varier la selectivite en modifiant le debit du gaz vecteur, la temperature et la quantite de zinc. Au cours de ce processus, le zinc a ete oxyde en oxyde de zinc. [Traduit par la Redaction]Mots-cles : acide formique reduction, formaldehyde, methanol., IntroductionFormaldehyde is a commonly used industrial reagent for numerous materials such as plastics and resins, with a production capacity of over 30 million tons per year. (1) We have previously [...]

The capability of tripyrrolide ligand system to support dinitrogen fixation and activation in vanadium chemistry is described. The ligand system exhibit interesting flexibility to interchange [sigma]- to [pi]-bonding mode for the central alkylated ring depending on the metal oxidation state.

A study is conducted which aims to understand the chemistry of the Fe-C functionality in the bis-iminopyridine Fe catalyst. The results of the alkylation of the bis-iminopyridine-FeCl2 catalyst with R-LI are described.

Reactions of the in-situ-generated potassium salts of the dipyrroles [([C.sub.4][H.sub.3]NH).sub.2]C[(C[H.sub.3]).sub.2] and of [([C.sub.4][H.sub.3]NH).sub.2]C(C[H.sub.3])([C.sub.6][H.sub.5]) with Th[Cl.sub.4][(DME).sub.2] has afforded the corresponding homoleptic [({[[[([C.sub.4][H.sub.3]N).sub.2] C[(C[H.sub.3]).sub.2]].sub.3]Th}[[K.sub.2](DME )]).sub.n] (1) and {[[[([C.sub.4][H.sub.3]N).sub.2]C(C[H.sub.3]) ([C.sub.6][H.sub.5])].sub.3]Th}[[K.sub.2](DME)] (2). In the case of 1, the solid state polymeric structure was elucidated by X-ray diffraction analysis. Preliminary attempts to reduce these species have so far afforded only intractable materials. Just in the case of 2, it was possible to isolate the corresponding ligand dipotassium salt [{[([C.sub.4][H.sub.3]NH).sub.2] C(C[H.sub.3])([C.sub.6][H.sub.5])[[K(DME)].sub.2]}.sub.n] (3) as the only characterizable material. This species possesses an unprecedented inversed-sandwich type of structure. Key words: thorium, homoleptic, dipyrrolide. Les reactions du Th[Cl.sub.4][(DME).sub.2] avec des sels de potassium generes in situ des pyrroles [([C.sub.4][H.sub.3]NH).sub.2]C[(C[H.sub.3]).sub.2] et [([C.sub.4][H.sub.3]NH).sub.2]C(C[H.sub.3])([C.sub.6][H.sub.5]) conduit a la formation des composes homoleptiques correspondants [({[[[C.sub.4][H.sub.3]N).sub.2]C[(C[H.sub.3]).sub.2]].sub.3]Th} [[K.sub.2][(DME)]).sub.n] (1) et {[[[[C.sub.4][H.sub.3]N).sub.2] C(C[H.sub.3]) ([C.sub.6][H.sub.5])].sub.3]Th}[[K.sub.2](DME)] (2). Dans le cas du compose 1, on a elucide la structure polymere de l'etat solide par diffraction des rayons X. Des essais preliminaires en vue de reduire ces especes n'ont fourni que des produits intraitables. Dans le cas du compose 2, il a toutefois ete possible d'isoler le sel dipotassique du ligand [{[([C.sub.4][H.sub.3]NH).sub.2]C (C[H.sub.3]) ([C.sub.6][H.sub.5])[[K(DME)].sub.2]}.sub.n] (3) comme seul produit pouvant etre caracterise. Cette espece possede une structure de type sandwich inverse, inconnue jusqu'a maintenant. Mots cles : thorium, homoleptique, dipyrrolure. [Traduit par la Redaction]

Reaction of the bis-aminopyridine dianion {[2,e-[2,e-[(i-Pr).sub.2] PhN-C=[(C[H.sub.2])].sub.2]([C.sub.5][H.sub.3]N)]Li(THF)} {Li[(THF).sub.4]} with Co[Cl.sub.2][(THF).sub.1.5] under Ar afforded the dinuclear complex {[2,e-[(i-Pr).sub.2]PhN-C=[(C[H.sub.2])].sub.2] ([C.sub.5][H.sub.3]N)[2,e-(iPr)2PhN=C[(C[H.sub.2])]}.sub.2] [Co([micro]-Cl)Li[(THF).sub.3]2]*4(THF) (1) in which the ligand is coupled to a second identical unit at a terminal methylene carbon. In turn, the C--C bond formation caused reduction of the Co(II) center to the monovalent state. The same reaction performed under a nitrogen atmosphere afforded the double dinitrogen complex {[2,e-(iPr)2PhN-C= (C[H.sub.2])]([C.sub.5][H.sub.3]N)[2,e-(i-Pr)2PhN= C[(C[H.sub.2])]}.sub.2] [Co[([N.sub.2])].sub.2](toluene) (2). Key words: low-valent Co, diiminopyridinato, dinitrogen fixation. Resume : La reaction du dianion bis-aminopyridine {[2,e-[2,e-[(i-Pr).sub.2]PhN-C=[(C[H.sub.2])].sub.2]([C.sub.5] [H.sub.3]N)]Li(THF) } { Li[(THF).sub.4]} avec le Co[Cl.sub.2] [(THF).sub.1,5], sous atmosphere d'argon, conduit a la formation du complexe dinucleaire {[2,e-[(i-Pr).sub.2]PhNC=(C[H.sub.2])]([C.sub.5] [H.sub.3]N)[2,e-[(i-Pr).sub.2]PhN=C[(C[H.sub.2])]}.sub.2] [Co([micro]-C1)Li[(THF).sub.3]2]*4(THF) (1) dans lequel le ligand est couple a une deuxieme unite identique au niveau d'un carbone methylenique terminal. Par ailleurs, la formation d'une liaison C--C provoque une reduction du Co(II) vers l'etat monovalent. La meme reaction realisee sous atmosphere d'azote conduit au complexe double de diazote {[2,e-[(i-Pr).sub.2]PhN-C=(C[H.sub.2])]([C.sub.5][H.sub.3]N) [2,e-[(i-Pr).sub.2]PhN=C[(C[H.sub.2]).sub.]}2][Co[([N.sub.2])].sub.2]*2 (toluene) (2). Mots cles : cobalt de basse valence, diiminopyridinato, fixation de diazote. [Traduit par la Redaction]

The preparation and characterization of a NdI(sub 2) adduct of the 2,6-{[2,6-(i-Pr)C6H5]N=C(CH3)}(sub 2)(C5H3N) ligand, together with a modification of the ligand system and the results of further reduction reactions of the corresponding Nd and La complexes are described. The magnetic behavior indicates that the ligand acts as a spin carrier magnetically coupled to a Nd(III) cation.

The isolation and characterization of a monovalent manganese compound whose structure sheds some light on the intriguing behavior of the complexes of the remarkable ligand system are reported. The reduction of the metal center is particularly eloquent and reiterates that destabilization of higher-valent metal alkyl occurs in favor of lower oxidation states.

The preparation and characterization of a trivalent vanadium diimine/pyridine complex and an evaluation of its activity as a Ziegler-Natta precatalyst are described. It is shown that the ligand transformed into an anionic amide, the metal center eliminated one chloride atom and the vanadium coordination number decrease by one unit. The possible role of the ligand in chain termination and catalyst deactivation is also investigated.

Chemical research has established a method of creating the novel lithium amide LiN(SiMe2CH2NMe2)2 using NH3, silylamine Me2NSiMe2CH2NMe2 and butyllithium. The lithium amide dimer reacts with a series of group four starting halides, MCL4, to produce the complexes MCl3[N(SiMe2CH2NMe2)2]. Each trihalide structure is described.

The dinuclear and diamagnetic complex {[(Me3Si)2N]2V}2(mu-S)2 was synthesized through the reaction of [(Me3Si)2N]2VCl(THF) with S8. The amide complex's connectivity was highlighted via an X-ray crystal structure. Ab initio theoretical calculations carried out on the complex and the isostructural oxo-bridged dimer indicated a determinant participation of the bridging atoms in the formation of the V-V bonds.

The dinuclear and diamagnetic {[(Me3Si)2N]2V}2(mu-S)2 complex was synthesized from the reaction of [(Me3Si)2N]2VCl(THF) with S8 in toluene at room temperature. The isostructural {[(Me3Si)2N]2V}2(mu-S)2 complex was formed by ligand scrambling and oxidation of the metal center. Spectral analysis of the dinuclear and diamagnetic complex also indicated the presence of identical {(Me3Si)2N]2V units that were bridged by one pair of sulfur atoms. Furthermore, the vanadium atom exhibited a distorted tetrahedral coordination geometry.

The research aimed to prepare a complex that might be used to study Ti-Ti interaction. The new diamagnetic complex created has a short Ti-Ti distance and could have a Ti-Ti bonding interaction. The complex, (CyNC(H)NCy)4Ti2Cl2*2THF, has been crystallographically characterized. The Ti-Ti bond is suggested by Hartree-Fock calculations. The singlet state was seen as the most reasonable assumption for the calculation, and the singlet state was shown to be more stable than the triplet.

Homoleptic vanadium complex ((3,5-Me2Ph)AdN)3V was synthesized and characterized by X-ray crystallography and nuclear magnetic resonance spectroscopy. The complex was made to react with chalcogens to yield diamagnetic terminal chalcogenide derivatives of formula ((3,5-Me2Ph)AdN)3V=E, where E is either S or Se. The derivatives were similarly characterized.

A novel series of samarium(II) amides are synthesized from the reaction of SmCl3(THF)3 (THF = tetrahydrofuran) with anionic dialkylamides R2N- (R = Cy cyclohexyl, 1-Pr isopropyl, Ph phenyl) to give the corresponding product. The resultant Sm(II) complexes are unstable toward disproportionation to higher oxidation state. The stability of the divalent oxidation state of samarium is attributed to the absence of alpha-H in the amide ligand. Suggestively, combined electronic and steric factors are requisites in stability studies of the complexes.

N2O deoxinizes with the divalent chromium macrocyclic complex Cr(ORPG)Li2(THF)4 (ORPG = octaalkylporphyrinogen R = Et, n-Pr) in toluene to give Cr(IV) complex (THF)(ORPG)Cr(O)(LiTHF)2, 1. One-electron transfer to N2O in THF, produces the Cr(III) complex Cr(ORPG)(THF)2 Li(THF)4, 2. The 2e-deoxygenation of N2O in the first reaction, represents a direct synthesis of a unique paramagnetic Cr(IV) chromyl species.

The 1H-NMR spectroscopic analysis shows that (OEC-4-P)Li4 retains the alkyllithium and other lithiated functions even after the original (OEC-4-P)Li4(t-BuLi)2 was refluxed and dissoluted. The high Lewis acidity of the alkali cation mediates the coordination geometry of the carbon atom of (OEC-4-P)Li4(t-BuLi)2 complex. The synthesis of (OEC-4-P)Li4(t-BuLi)2 and (cyclohexyl2NLi)4 is discussed.

Preparation of neutral V(II) aryloxides can be done through ligand-replacement reactions on three V(II) complexes (Mz2V(Py)2)(mu-N2), Mz2V(py)2 and VCl2(TMEDA)2, where Mz = o-Me2NCH2C6H4, TMEDA = N,N,N',N'-tetramethylethylenediamine with several phenols or their corresponding alkali salts. It was possible to separate and characterize monomeric and neutral V(II) aryloxides with several coordination geometries.

The preparation and structural characterization of bis(benzamidinato)titanium(III) chloride and its transformation into the corresponding borohydride and allyl derivatives were reported. The reaction of TiCl3(THF)3 with PhC((Me3Si)N)2Li(TMEDA) in THF formed crystals of (PhC((Me3Si)N)2)2Ti(micro-Cl)2Li(TMEDA) (1). Further reaction of (1) with LiBH4 in toluene formed crystals of (PhC((Me3Si)N)2)2Ti(BH4). (PhC((Me3Si)N)2)2Ti(eta3-allyl) was obtained from the reaction of (1) with (allyl)MgBr in THF.

Trivalent titanium aryloxides derived from the ligand-replacement reactions of Ti(II) and Ti(III) halides were investigated. The reactions of trans-Ti(N,N,N',N'-tetramethylethylenediamine) with 2 equiv of RONa, where R = Ph and 3,5-(t-Bu)2C6H3, produced the trimeric complex (Ti TMEDA PhO 2)2(Ti PhO)(mu-OPh)4 and the dimeric complex (Ti TMEDA Cl)2(mu-OR)2. The steric hindrance of the aryloxide resulted in the stabilization of the trivalent oxidation state.

The reactions of the Fe complex with MAO and R3Al [R= Me, Et] are studied by examining the reaction of LFeCl2 (L={2,6-[2,6-(Pr2PhN=C(CH3]2(C5H3N)}) with the Al alkylating agents. It seems that the lower stability of an Fe-Et containing moiety doe not provide a lifetime long enough to enable its migration from the ligand system, leading to the arrest of the ligand transmetalation halfway, with the Fe atom remaining pi-coordinated to the ligand.

The preparation and characterization of a diamagnetic [7-azaindolyl)Nb](sub 2) compound is described. The axial ligation of LiCl is obtained at the expenses of one of the Nb-Nb bonds and nicely accounts for paramagnetism.

The dimeric (TAA Cr)2 was recrystallized from pyridine to form a low-spin monomeric complex (TAA Cr py2).py, indicating that molecular restructuring has occurred in the pyridine solution. The complex redissolved in hot toluene or THF to give the dimer, suggesting that chemical equilibrium exists between the two species. Cocrystallization also occurred when a pyridine solution of the dimer was mixed with THF/hexane. The crystal structure revealed one dimeric (TAA Cr)2 and two monomeric octahedral (TAA)Cr(py)2 molecules. The Cr-Cr multiple bond energy cannot be more than twice that of the Cr-py bond.

The reaction of U[Cl.sub.4][(THF).sub.4] with 1,3-[[2,5-[(i-Pr).sub.2]PhNC(-C[H.sub.2])].sub.2][C.sub.6][H.sub.4][Li.sub.2] produced a complex formulated as [{1,3-[[2,5-[(i-Pr).sub.2]PhNC(-C[H.sub.2])].sub.2][C.sub.6][H.sub.4]}U[Cl.sub.3]][Li[(THF).sub.4]] that exhibited a nonagostic interaction between one of the carbon atoms of the central phenyl ring and the U metal center is reported. The results from the density functional theory calculations indicated that the studied species contain additional spin density on the ligand system with the metal center in its more standard trivalent state.

The formation of an unusual diamagnetic, monovalent, vanadium complex with a short V...V contact is described. The studies have shown the presence of only a weak V-V bond in spite of the very short V-V distance.

The reduction of the bis(iminopyridine) Fe[Cl.sub.2] complex is described by using NaH as a reducing agent. The ideal situation for [N.sub.2] activation has involved the bimetallic attack of the associated dinitrogen moiety.

The formation of a bridging chromium-dinitrogen complex, its partial reduction and hydrogenation, and eventual cleavage to an imide product is reported. Results show that the electron-storage capabilities of the diiminepyridine ligand play an important role in the sequence of reactions.

The reaction of the highly selective [CySC[H.sub.2]C[H.sub.2]N(H)C[H.sub.2]C[H.sub.2]SCy]Cr[Cl.sub.3] catalyst precursor with alkyl aluminum activators is examined in order to isolate the reactive intermediates and assess both activity and selectivity. The effect of the deprotonation of the ligand system is also investigated.

Reduction of the two trivalent 2,6-{[2,6-(i-Pr)2C6H5]N=C(CH3)}2-(C5H3N)VCI3 and {[2,6-{[2,6-(i-Pr)2C6H3]N-C=(CH2)}2(C5H3N)-VCI(THF) complexes with excess NaH afforded two corresponding end-on dinitrogen bridged complexes [2,6-{[2,6-(i-Pr)2C6-H3]N-C=(CH2)}2(C5H3N)]V]2(m-2)-(hexane). Structural analysis and DFT calculations have indicated that partial reduction of the bridging nitrogen occurred for both complexes while substantial metal-to-ligand electron transfer also occured.

The dipyrrolide ligand system is discussed, which gave a rare example of a paramagnetic divalent dimolybenum. It has very short Mo-Mo distance and a staggering angle of 45 (degree) between the two Mo-containing moieties.

The nature of the solvent controls the nuclearity of the divalent Mn complexes of the dipyrrolide dianion, which in turns affects the extent of magnetic coupling between Mn centers. A structural and magnetic study was to test the hypothesis that dipyrrolide dianions might be promising ligands for the purpose of preparing reactive hydrolysis resisitant clusters.

Extreme chemical reactivity is the primary characteristic of the few low-valent Nb and Ta compounds that has been reported till date. A mixed-valence Nb(II)/(III) tetranuclear and diamagnetic cluster has been obtained by reacting the tetravalent NbCl4(THF)(sub 2) compound with Cy2NLi.

The development of synthetic pathways to medium-valent tantalum-amide derivatives through the use of precursor complexes of the type (R2N)nTaCl(5-n) is discussed. Specifically, the formation of bright yellow needles of the isotructural and isomorphous (Cy2N)2TaCl (CyNC6H10) and the dimeric (Cy2N)2TaCl through proton abstraction and reductive elimination of hydrazine, respectively, is reported.

Synthesis and analysis of stabilities of various vanadium(II) amidinates help analyze the influence of ligand steric bulk on stability and nuclearity of d(3)V(II) complexes. Formamidinate ligands produce dinuclear and diamagnetic complexes irrespective of the metal oxidation states. Bulky silylamidinate ligands do not form dimers but stabilize divalent vanadium and facilitate reversible dinitrogen fixation.

VCl3(THF)3 reacts with R2NLi to produce stable deep-green crystals of monomeric, paramagnetic (Ph2N)3V(THF). Cyclohexyl and isopropyl derivatives on solvent replacement produce diamagnetic brown crystals of ((R2N)3V)2(mu-N2). Elemental analysis and X-ray diffraction techniques reveal the presence of a dinitrogen molecule which connects two vanadium atoms in an end-on fashion. The heating of a reaction mixture of VCl3(THF) and LDA produces metallacycles.

Diminishing the quantity of THF available for the isolation of vanadium(II) ynolate complex helps examine the role of THF in the process. The method is arranged in a such a way that VCl3(THF)3 is the only available source of THF to tetralithium salt of the octaethyl porphyrinogen (Li4OEPG). This reaction gives red crystals of a complex that has all the three THF molecules available from VCl3(THF)3. Various possibilities for the presence of butyl group in the resultant complex are examined.

Recrystallization of a low-valent Sm macrocyclic complex from THF under nitrogen gives air-stable orange crystals of ((THF)2Li(OEPG)Sm)2(N2Li4). The molecule has an aggregation of two (THF)2Li(OEPG)Sm units containing Sm(III) with an N2Li4 unit. The large N-N distance is consistent with N-N single bond character and a four-electron reduction of dinitrogen. Formal reduction of N2 to N(super 4-)(sub 2) involves four different metal centers and some unknown products in the mixture.

Transitions metal compounds of polyaza ligands are examined using the synthesis of a vanadium(III) complex of the octaethylporphyrinogen ligand. The reaction of VCl3(THF)3 with the tetralithium salt of the octaethylporphyrinogen macrocyclic ligand (Et8N4Li4(THF)4), at room temperature, progressed in an unprecedented fashion to yield the vanadium ynolate complex (Et8N4)VLi2(O-C triple bond CH). The reaction is synthetically advantageous as it can be performed on a large scale.

Monomeric high-spin Me4CrLi2 species may be generated from the reversible cleavage of (Me8Cr2)(Li(L))4, where L = THF or Et2O. The cleavage proceeds via the substitution of the Lewis base coordinated to the alkali cation. The reaction of (Me8Cr2)(Li(Et2O))4 with TMEDA gives (Me4Cr)(Li(TMEDA))2, which consists of molecules having a square-planar central monomeric Me4Cr core. The replacement of the Lewis base coordinated to the alkali cation indicates that the alkali cation is a major factor in the stability of the Cr-Cr interaction in the precursor.