Jacques Amaudrut

Niobium organometallic chemistry : IX. CS2 complexes: synthesis, reactivity and their use as ligand; crystal structure of (n-C4H9)(ν5-C5H5)2Nb(μ-CS2)W(CO)5

Abstract Carbon disulphide reacts with niobium complexes [Nb(η-C5H5)2(Me)2] and [Nb(η-C5H5)2H (CH2CHC2H5)] to produce the new η2-CS2 derivatives [Nb(η-C5H5)2(Me)(η2-CS2)] (1) and [Nb(η-C5H5)2(Bu) (η2-CS2)] (2) respectively. Treatment of 1 and 2 with methyl iodide affords the respective cationic η2- dithioalkyl ester complexes [Nb(η-C5H5)2(Me) {η2-C(S)SMe}] I (3) and [Nb(η-C5H5)2(Bu) {η2-C(S)SMe}] I (4). Hetero-dinuclear complexes [(Bu)-(η-C5H5)2Nb(η-CS2)M(CO)n] (M  Cr, Mo, W; n  5. M  Fe; n  4) and [(Bu)-(η-C5H5)2Nb(μ-CS2)Mn(CO)2(η-CH3C5H4)] and an homodinuclear complex [(Bu)(η-C5H5)2Nb(μ-CS2)Nb(η-C5H5)2(Bu)] have been synthesized. The structure of the niobium—tungsten derivative has been determined by single-crystal X-ray diffraction. Crystal data are space group P21/c, a 12.935(4), b 12.742(4), c 14.565(4) A, β 103.27(3)°, Z  4. The Nb(μ-CS2)W unit is planar within ±0.06 A. The CS2 group is η2-bonded to niobium through a CS linkage and σ-bonded to manganese through the other sulfur atom. The 13C NMR spectra indicate that 2 has a larger σ-donor/π-acceptor ratio than CO.

Chimie organométallique du niobium VIII. Etude détaillée de la réaction d'acétyléniques perfluorés avec (η5C5H5)2NbH3: Mise en evídence de la coupure de liaison C-F, de la formation de liaison Nb-F et de la reduction du niobium. Structure cristalline d'un dérivé niobiacyclopentadiène

Abstract Hexafluorobutyne (CF3CCCF3 = Hfb) reacts with Cp2NbH3 (Cp = η5-C5H5) affording five new complexes I–V, whose structures have been studied by mass, Ir, ESR and NMR spectroscopy. The X-ray study of II shows the presence of a planar NbC4 ring Nb—C(1): 2.25(5); C(1)—C(2): 1.31(7); C(2)—C(3): 1.53(8); C(3)—(4): 1.34(7); C(4)—Nb: 2.23(5) A. With trifluoropropyne (CF3CCH = tfp), only the analog of III, i.e. Cp2NbFf(tfpH), has been isolated.

Insertion of activated acetylenes into the metal-hydride bond of [(η5-C5H5)2M(CO)H] (M = Nb, Ta)

Abstract Reactions of [Cp 2 M(CO)H] (M = Nb, Ta; Cp = η 5 -C 5 H 5 ) with various acetylenes RCCR having electron-withdrawing groups were investigated. They give the σ-al- kenyl complexes [Cp 2 M(CO)(CRCHR)] via insertion of the alkyne into the MH bond. On the basis of 1 H and 19 F NMR data the reactions were shown to be: (i) regioselective, monosubstituted alkynes giving only the α-R metallated complex; (ii) stereoselective, exclusive formation of the Z -isomer being observed with hexafluorobut-2-yne. The Z isomer has been shown to exist as two conformers, the steric requirements of the ligands creating a barrier to rotation of the alkenyl group around the MC σ bond.

Syntheses and electrochemical behaviour of novel dithiolatoniobium-(IV) and -(V) complexes with two η5-cyclopentadienyl rings

Abstract Novel niobium(IV) complexes with two cyclopentadienyl rings and dmit, dmio or dddt were synthesized, and their voltammometric behaviour was investigated in acetonitrile and dichloromethane. These complexes in acetonitrile solution exhibited a reversible one-electron oxidation and a reversible one-electron reduction step, corresponding to niobium(V) and niobium(III) respectively, without any complicating side- or subsequent reactions. Among the three niobium(IV) complexes, the reduction potential of the complex with dddt was notably less negative than those of the complexes with dmit or dmio. This fact allows the preparation of the charge-transfer complexes with TCNQ. The niobium(V) dmit and dmio complexes with two cyclopentadienyl rings were also isolated as iodide salts by the oxidation of the corresponding niobium(IV) complex. These Nb V complexes gave two one-electron reduction steps whose potentials were identical to those of Nb IV and Nb III for niobium(IV) dmit and dmio complexes.

Synthese et etude electrochimique de complexes dithiolenes du dicyclopentadienyl niobium

Abstract Dithiolene complexes (Cp2NbvS2C2R2)+ are synthesized and characterized by spectroscopic data. They show two reversible monoelectronic reduction steps. A controlled potential reduction on the plateau of the first wave leads to stable niobium(IV) complexes Cp2NbS2C2R2.

Niobium organometallic chemistry: XIII. Alkylation of η2-CS2 derivatives and reaction with NaBH4. Evidence for a η2-CH(S)SR ligand☆

Abstract The cationic complexes 2 [Nb(η-C5H5)2(Bu)(η2-C(S)SR]]X are formed from [Nb(η-C5H5)2(Bu)[η2-CS2]] (1) and RX (R = Me, Et, i-Pr, CH2COOEt; X = I. R = CH2C6H5, CH2CH2CH2Cl, CH2CHCH2; X = Br). They react with NaBH4 in THF giving complexes 4. These decompose in solution and give, after column chromatography, neutral complexes 3 of the type [Nb(η-C5H5)2(Bu)[η-CH(S)SR]]. The conversion of 2 into 3, which corresponds to nucleophilic attack by the hydride ion on the CS2 carbon atom, seems to proceed via formation of intermediate derivatives 4 containing a niobium-coordinated BH4 group. Reaction of 1 with diiodomethane as alkylating reagent results in the formation of a dimeric niobium compound containing the NbC(S )SCH2S( S)CN b unit, which reacts further with NaBH4.

Niobium organometallic chemistry. Part III. Reaction of bis(cyclopentadienyl)niobium dichloride with tetraphosphorus decasulphide. E.S.R. and N.M.R. Studies of some niobium(IV) and niobium(V) O,O′-dialkyldithiophosphates☆

Abstract The reaction of (η 5 -C 5 H 5 ) 2 NbCl 2 with P 4 S 10 in an alcohol ROH affords two types of compounds: 1. paramagnetic niobium(IV) complexes formulated as [(η 5 -C 5 H 5 ) 2 Nb[S 2 P(OR) 2 ]] + PF − 6 . The e.s.r. spectra correspond to the interaction of the unpaired electron with the 93 Nb and 31 P nuclei. They show a significant delocalization over the phosphorus and indicate the unpaired electron lies in the d x 2 − y 2 orbital; 2. diamagnetic niobium(V) complexes [(η 5 C 5 H 5 ) 2 NbS 2 [SP(S)(OR) 2 ]] containing a NbS 2 ring, for which 1 H, 13 C and 31 P n.m.r. data are given.

Niobium organometallic chemistry ☆: XI. Diels-Alder reaction of a η1-cyclopentadienyl group. Crystal structure of a niobium derivative containing a η1-substituted norbornadienyl unit

Abstract Hexafluorobutyne (CF3CCCF3, HFB) reacts with tetracyclopentadienylniobium [Nb(η5-C5H5)2(η1-C5H5)2] to give a diamagnetic niobium derivative, the structure of which has been determined by single-crystal X-ray diffraction. Crystal data are space group P21/n, a 7.983(2) A, b 27.600(7) A, c 8.689(2) A, β 113.22(2)°, Z = 4. A terminal oxygen atom (NbO 1.63(3) A) and a η1-substituted norbornadienyl unit (arising from a Diels-Alder addition of HFB on a η1-C5H5 group) are bonded to a bent [Nb(η5-C5H5)2] system.

Electrochemical and chemical reduction of niobocene dichlorides in the presence of carbon dioxide

Abstract The chemical and electrochemical reduction of the niobocene dichlorides [Nb(η5-C5H4SiMe3)2Cl2]1, [Nb(η5-C5Me5)2Cl2] 2 and [Nb(η5-C5Me4Et)2Cl2] 3, in the presence of carbon dioxide has been investigated. Formation of compounds of the type [Cp2Nb(CO2)] and [Cp2(∗)NbCl(CO2))] 1 has been established by means of IR, ESR and/or NMR spectroscopy. They contain a labile η2-CO2. The order of stability increases with the degree of substitution the Cp. Less stable intermediates in the reduction of the system [Cp2NbCl2]/CO2 are discussed on the basis of cyclovoltammetric and coulometric data.

Niobium organometallic chemistry

Abstract The 17-electron species (η-C 5 H 5 ) 2 NbMe 2 reacts with cyclooctasulfur and with carbon disulfide to give, the 18-electron species (η-C 5 H 5 ) 2 NbS 2 Me (III) and (η-C 5 H 5 ) 2 Nb(CS 2 )Me (IV), respectively. Addition of methyl iodide to IV gives [(η-C 5 H 5 ) 2 Nb{C(S)SMe}MeI]. With sodium diethyldithiocarbamate and M′X (NH 4 PF 6 , NaBF 4 ), (η-C 5 H 5 ) 2 NbCl 2 yields the compounds [(η-C 5 H 5 ) 2 Nb(S 2 CNEt 2 )] + X − .