A. Antiñolo

Metallocene derivatives of early transition metals. Synthesis and characterization of new halo hydridobis(silylated cyclopentadienyl)niobium complexes

The reduction of the niobocene complexes Nb(η-C5H4SiMe3)2X2 (I: X = Br, II: X = I) with one equivalent of sodium amalgam gives the NbIII solids Nb(η5-C5H4SiMe3)2X (III: X = Br, IV: X = I). These complexes can also be obtained by treatment of Nb(η5-C5H4SiMe3)2H3 (V) with one equivalent of EtBr or MeI. Reactions of III and IV with CO, PhCCPh, P(OMe)3 and CN(2,6-Me2C6H3) give the solid 11 adducts Nb(η5-C5H4SiMe3)2XL (VI: X = Br, L = CO; VII: X = Br, L = PhCCPh; VIII: X = Br, L = P(OMe)3; IX: X = Br, L = CN(2,6-Me2C6H3); X: X = I, L = CO; XI: X = I, L = PhCCPh; XII: X = I, L = (P(OMe)3; XIII: X = I, L = CN(2,6-Me2C6H3). The carbenoid-like III reacts with cumulenes to give the complexes Nb(η5-C5H4SiMe3)2Br(XCY) (XIV: X = Y = S; XV: X = PhN, Y = O; XVI: X = PhN, Y = S). The hydride complexes Nb(η5-C5H3RR′)2HL (XVII: R = H, R′ = SiMe3; XVIII: R = R′ = SiMe3) have been prepared by treating the trihydride complexes Nb(η5-C5H3RR′)2H3 in the presence of CO. The related complexes Nb(η5-C5H3RR′)2HL(XIX: R = H, R′ = SiMe3, L = PhCCPh; XX: R = H, R′ = SiMe3, L = P(OMe)3) were made by reaction of Nb(η5-C5H4SiMe3)2XL with an excess of NaA1H2(OCH2CH2OMe)2.

Synthesis and reactivity of bis(trimethylsilylcyclopentadienyl)- niobium compounds with cumulene ligands

Abstract The reduction of Nb(η 5 -C 5 H 4 SiMe 3 ) 2 Cl2 (I) with Na/Hg in a 1/1 molar ratio gives Nb(η 5 -C 5 H 4 SiMe 3 ) 2 Cl (II). Reactions of II with some cumulenes give the corresponding niobocene derivatives with the functional groups anchored to the bis(trimethylsilylcyclopentadienyl)niobium unit, Nb(η 5 -C 5 H 4 SiMe 3 ) 2 Cl(CS 2 ), Nb(η 5 -C 5 H 4 SiMe 3 ) 2 Cl(PhNCX) (X = O or S) and Nb(η 3 -C 5 H 4 SiMe 3 ) 2 Cl(CyCN- Cy). The imido compound Nb(η 5 -C 5 H 4 SiMe 3 ) 2 Cl(NPh) has been prepared. The chemical properties and structural features of the compounds are described.

Preparation and structural characterization of new alkoxo- and (alkoxo)(amido)(imido)-niobium(V) compounds. Crystal structure of [NbCl(μ-OMe)[N(SiMe3)2](NSiMe3)]2

Abstract The reactions of NbCl 3 with Me 3 SiOMe in the appropriate molar ratios have given new alkoxoniobium(V) derivatives of the type NbCl 5− x (OMe) x ( x = 2 (I), 3 (II)). Reactions of I and II with various ligands afford the corresponding species NbCl 5− x (OMe) x L, x = 2, L = OPPh 3 (III); L = OAsPh 3 (IV); L = THF (V); L = Cl − (VI); x = 3, L = OPPh 3 (VII); L = Cl − (VIII). Similar hexacoordinate compounds NbCl 3 (OR) 2 (OPPh 3 ), (R = Me (III), R = Et (IX), R = Pr i (X)) have been obtained by reactions of NbCl 5 (OPPh 3 ) with the relevant Me 3 SiOR compounds. Compounds I and II also react with {[LiN(SiMe 3 ) 2 ]Et 2 O} 2 to give [NbCl(μ-OMe)[N(SiMe 3 ) 2 ](NSiMe 3 )] 2 (XI) and [Nb(OMe)(μ-OMe)[N(SiMe 3 ) 2 ](NSiMe 3 )] 2 (XII). All the compounds have been characterized by IR and NMR spectroscopy and the crystal structure of XI has been determined by X-ray diffraction. XI crystallizes in the monoclinic space group P 2 1 / c with a 10.236(1), b 9.789(1), c 21.201(3) A, β 102.67(1)° and D c 1.30 g cm −3 for Z = 4. A final R value of 0.042 ( R w = 0.052) based on 4272 reflections was obtained. The two metal atoms are asymmetrically bridged by the two methoxide ligands. Chloride, amido, and imido ligands complete the coordination spheres of both metal atoms.

Electrochemical studies on organometallic compounds XXXII. Pseudo-reversibility of the first reduction stage of Nb[η5-1,3-C5H3(SiMe3)2]2Cl2

Abstract The one-electron reduction of Nb[η5-1,3C5H3(SiMe3)2]2Cl2 yields the derivative Nb[η5-1,3C5H3(SiMe3)2]2Cl. Pseudo-reversible behaviour is observed due to a return of Cl− to the molecule. The effect of the disubstitution of the cyclopentadienyl ring is discussed.

Mixed halodicyclopentadienyl-niobium(V) and -tantalum(V)

We greatly appreciate the financial support received from the Comision Asesora de Investigacion Cientifica y Tecnica (Spain).

Dicyclopentadienyl-niobium(iii) and -niobium(iv) complexes

We greatly appreciate finantial support from Comision Asesora de Investigacion Cientifica y Tecnica (Spain).

Electrochemical studies on organometallic compounds: XXXIX. Electrochemical bahavior of bis-silylated cyclopentadienyl niobium trihydride. ESR spectroscopic characterization of the dimeric hydride niobium(IV) complex [Nb(η5-Me3SiC5H4)2H]2(μ-H)2

Abstract The one-electron oxidation of NbCp2′H3, 1 (Cp′ = Me3SiC5H4), has been found to give the dimeric niobium(IV) complex (NbCp2′H2)2, 3, which has been characterized by ESR spectroscopy. The cationic niobium(V) species [NbCp2′H2(THF)]+, 4, has been prepared through a two-electron oxidation of 1. 3 can also be obtained by one-electron reduction of 4. The same behaviour has been observed for Nb(η5-tBuC5H4)2H3.

New neutral and cationic dicyclopentadienylniobium complexes

Abstract (η 5 -C 5 H 5 ) 2 NbX(PMe 3 ) (X = Cl, Br) was prepared by reducing (η 5 -C 5 H 5 ) 2 NbX 2 with Na/Hg amalgam in the presence of PMe 3 . (η 5 C 5 H 4 Me) 2 TaCl(PMe 3 ) was obtained analogously. The reaction of (η 5 -C 5 H 5 ) 2 NbCl(PMe 3 ) with AgBF 4 gave metallic silver and cationic [η 5 -C 5 H 5 ) 2 NbCl(PMe 3 )] + , which reacts with OPPh 3 to give [(η 5 -C 5 H 5 ) 2 Nb(OPPh 3 )(PMe 3 )] 2+ Cationic halide complexes [(η 5 -C 5 H 5 ) 2 NbClL] + are also formed from (η 5 -C 5 H 5 ) 2 NbCl 2 by abstraction of chloride with AgBF 4 in the presence of the ligand, L = CH 3 CN or OPPh 3 . When L is acrylonitrile, the dinuclear species {[(η 5 -C 5 H 5 ) 2 NbCl] 2 (μ-CH 2 CHCN)} 2+ is obtained. Attempts to isolate alkylniobium(III) complexes by alkylation of the corresponding halide complexes or by reduction of the haloalkylniobium(IV) derivatives were unsuccessful; no (η 5 -C 5 H 5 ) 2 NbCl(CH 2 C 6 H 5 ) was obtained and treatment of (η 5 -C 5 H 5 ) 2 Nb(CH 2 C 6 H 5 ) 2 with halogen gave (η 5 -C 5 H 5 ) 2 NbI 2 , (η 5 -C 5 H 5 ) 2 NbBr 3 and (η 5 -C 5 H 5 ) 2 NbX 2 + X 3 − (X = Br, I).

Etude électrochimique de complexes organométalliques: XXVII. Électrogénération du complexe anionique Nb(η5-C5H4SiMe3)2Cl2−☆

Abstract The one-electron reduction of Nb(η5-C5H4SiMe3)2Cl2 at −30°C yields the corresponding stable anion wich slowly decomposes at room temperature to give [Nb(η5C5H4SiMe3)Cl]2.

Metallocene derivatives of early transition metals. Reactions of bis(silylated cyclopentadienyl)niobium complexes with organic halides

Abstract The reactions of the complexes Nb(η 5 -C 5 H 3 RR′) 2 H 3 and Nb(η 5 -C 5 H 3 -RR′) 2 X (X = Br, I; R = H, R′ = SiMe 3 ; R = R′ = SiMe 3 ) with ethyl bromide and methyl iodide afford the new niobium(IV) complexes, Nb(η 5 -C 5 H 3 RR′) 2 X 2 (X = Br, R = H, R′ = SiMe 3 (I); R = R′ = SiMe 3 (II); X = I, R = H, R′ = SiMe 3 (III); R = R′ = SiMe 3 (IV)) in high yields. The formation of these complexes is explained in terms of an initial oxidative addition of the organic halide. The reaction of complex Nb(η 5 -C 5 H 4 SiMe 3 ) 2 Cl with benzyl chloride has also been investigated.