Search

The reaction of (C5H4SiMe3)2NbH3 with Au[N(SiMe3)2]PPh3 produces the novel raft cluster [NbAuH2{C5H4(SiMe3)}2]3 in high yield; the structure consists of a gold triangle surrounded by 3 Cp′2Nb groups (Cp′= C5H4SiMe3) and 6 bridging hydrides [Au–Au 2.7635(20), 2.7571(18), and 2.7801(25)A; Nb–Au 3.0321(25), 3.0326(25), and 2.9891(18)A], MO calculations indicate a striking electronic stabilization of this geometry which may be of importance in other gold hydrides.

The reduction of the niobocene complexes Nb(η 5 -C 5 H 3 RR′) 2 Cl 2 (R  H, R′  SiMe 3 (I); R  R′  SiMe 3 (II)) with one equivalent of (1%) sodium amalgam in the presence of an isocyanide ligand R″NC yields Nb(η 5 - 5 H 3 RR′) 2 Cl(CNR″) (R  H, R′  SiMe 3 , R″  Cy  cyclohexyl (III); t Bu (IV); Ph (V); 2,6-Me 2 C 6 H 3 (VI), and R  R′  SiMe 3 , R″  Cy (VII), t Bu (VIII)). Reactions of III and V with LiMe and LiCH 2 SiMe 3 give the thermally stable iminoacyl compounds [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 -(CRNR′)] n (R  Me, R′  Cy (IX); R  CH 2 SiMe 3 , R′  Cy (X) and R  Me, R′  Ph (XII)), through spontaneous insertion of the isocyanide ligand into the alkyl-niobium bond. Insertion of t-BuNC into the metal-alkyl bond in IV was not observed, and only the alkyl isocyanide derivative Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (Me)(CN t Bu) (XI) was isolated. The compounds were characterized by IR and NMR spectroscopy.

[Nb(η-C5H4R)Cl4][R = H (1) or SiMe3(2)] are easily hydrolysed to give [{Nb(η-C5H4R)Cl2}2(µ-O)-(µ-Cl)2][R = H (3) or SiMe3(4)] and finally [{Nb(η-C5H4R)Cl3(OH2)}2(µ-O)][R = H (5) or SiMe3(6)]. The reduction of (1) and (2) with sodium amalgam in the presence of ligands allows isolation of [Nb(η-C5H4R)Cl3L2] and [Nb(η-C5H4R)Cl2(CO)L2](R = H or SiMe3; L2= 2PMe3,2PMe2Ph, or Ph2PCH2CH2PPh2) which have been characterized by magnetic measurements and i.r. and n.m.r. spectroscopy. The crystal structure of (4) has been determined: monoclinic, space group P21/n with a= 26.805(7), b= 7.310(2), c= 13.400(3)A, β= 91.42(2)°, and Z= 4. The structure was refined to R= 0.063 for 2 539 observed reflections.

The new compounds {(η-C 5 H 5 WX)[μ-(σ, η-C 5 H 4 )]} 2 , where X = Cl, Br or I are described. The known hydride X = H, protonates and rearranges giving the new cation {(η-C 5 H 5 )WH} 2 , (μ-H)[μ-C 5 (η-C 5 H 4 -η-C 5 H 4 )] + .

(C5Me5)RuH3PCy3(1)(Cy = cyclohexyl) reacts smoothly with 1/n[CuCl]n in toluene and with 1 or 1/2 equivalent of [Cu(MeCN)4]PF6 in tetrahydrofuran (THF) to give (C5Me5)RuH3PCy3CuCl (2) and {(C5Me5)RuH3PCy3)2Cu}PF6(3) respectively, and the anomalous n.m.r. behaviour of (1) characterized in particular by the observation of AB2 spectra showing large temperature dependent AB coupling constants is preserved in (2) whereas in (3) a disymmety is observed in agreement with the presence of one hydride and one dihydrogen molecule; an interpretation is given and a model taking into account these data is proposed for the structure of the ‘trihydrogen’ derivatives.

(C6Cl5)3Sb and (C6Cl5)3Bi have been isolated from SbCl3 or BiCl3 and C6Cl5Li. AsCl3 gives only (C6Cl5)2AsCl even with a large excess of C6Cl5Li. Treatment of (C6Cl5)3Sb with halogens gives (C6Cl5)3SbX2 (X  Cl, Br). Br2 does not react with (C6Cl5)2AsCl whereas Cl2 gives an intractable residue which is rapidly hydrolysed to [(C6Cl5)2As]2O. Treatment of (C6Cl5)3Bi with halogens cleaves the CBi bonds to give C6Cl5X and unidentified oxohalobismuth(III) derivatives.

Alcoholysis with catechol or substitution reactions with NaOPh on Nb(η 5 -C 5 H 4 R)Cl 4 (R  H, SiMe 3 ) have given new alkoxoniobium(V) derivatives of the type Nb(η 5 -C 5 H 4 R)Cl 3 (OPh) (R  H, SiMe 3 ) Nb(η 5 -C 6 H 5 )Cl 2 (O 2 C 6 H 4 ) and {[Nb(η 5 -C 5 H 4 SiMe 3 )Cl] 2 (μ-O)(μ-O 2 C 6 H 4 ) 2 }. The crystal structure of the last species has been studied. The two metal atoms, 3.079(1) A apart, are symmetrically bridged by the oxo and the two catechol ligands. The two oxygen atoms of each catecholate group are coordinated to the metal atoms, one of them to one Nb atom and the other bridging the two Nb atoms. Chloride and CpSiMe 3 ligands complete the coordination sphere of both metal atoms.

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

{[(η 5 -C 5 H 4 Me)NbCl 2 ] 2 (μ-O)(μ-Cl) 2 } (I) has been obtained by hydrolysis of complex Nb(η 5 -C 5 H 4 Me)Cl 4 . The reactions of {[(η 5 -C 5 H 4 R)NbCl 2 )] 2 (μ-O)(μ-Cl) 2 } (I: R = Me; II: R = H; III: R = SiMe 3 with an 0.5 molar proportions of the nitrogen donor ligands 2,2′-bipyridine (bipy) or 1,10-phenanthroline ( o -phen) give the complexes {[(η 5 -C 5 H 4 R)NbCl 3 (NN)] 2 -(μ-O)} (IV: R = CH 3 , NN = bipy; V: R = CH 3 , NN = o -phen: VI: R = H, NN-bipy; VII: R = H, NN = o -phen; VIII: R = SiMe 3 , NN-bipy; IX: R = SiMe 3 , NN = o -phen), whereas the similar reactions of complex III with the phosphorus donor ligands dppe and dppm give the complexes {[(η 5 -C 5 H 4 SiMe 3 )NbCl 3 ] 2 (PP)(μ-O)} (X: PP = dppe; XI: PP = dppm). The complexes have been characterized by IR and 1 H NMR spectroscopy.

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.

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.

Oxidation of (η5-C5H5)2MCl (M = Nb, Ta) with 1 mol of Cl2, Br2 or I2 gives (η5-C5H5)2MClX2 whereas the reaction with an excess of the halogen gives the cationic complexes [η5-C5H5)2MClX]+ X3− (X = Br, I). Similar oxidation of (η5-C5H5)2MCl2 with 0.5 mol of halogen gives (η5-C5H5)2MCl2X complexes, but if the halogen is used in excess cationic [η5-C5H5)2MCl2]+ X3− (X = Br, I; M = Ta and X = I, M = Nb) are obtained. All these complexes can also be obtained simultaneously by oxidizing (η5-C5H5)4M2Cl3, and the separation is fairly easy in most cases. Conductivity and IR and NMR data are discussed., We greatly appreciate the financial support received from the Comisión Asesora de Investigación Cientifica y Tecnica (Spain).

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.

The complexes [Nb(cp)2Cl2][cp =η-C5H5, η-C5H4SiMe3, or η-C5H3(SiMe3)2-1,3] are reduced with Na–Hg in the presence of CO to give the carbonylniobium(III) complexes [Nb(cp)2Cl(CO)]. The alkylation of these compounds using LiR, MgRX, or MgR2 leads to the alkyl derivatives [Nb(cp)2R(CO)](cp =η-C5H5 or η-C5H4SiMe3; R = Me, CH2CMe3, CH2SiMe3, CH2Ph, or C6F5). These alkyl carbonyl niobium(III) complexes react with oxygen to produce an unresolved mixture of compounds when cp =η-C5H5 whereas the complex [Nb(cp)2(O2)Me] is obtained in the reaction of [Nb(cp)2Me(PMe3)](cp =η-C5H4SiMe3) with oxygen. Similar reactions of [Nb(cp)2Cl(CO)] with O2 lead to the oxo-halogenoniobium(V) derivatives [Nb(cp)2(O)Cl][cp =η-C5H5, η-C5H4SiMe3, or η-C5H3(SiMe3)2-1,3]. However, the corresponding peroxo-chloro complex [Nb(cp)2(O2)Cl](cp =η-C5H4SiMe3) results from the reaction with oxygen of the chloro(alkyl isocyanide) niobium(III) complex and can be preparated alternatively by reaction of the dichloride with H2O2. The oxo-chloro niobium(V) complex [Nb(η-C5H4SiMe3)2(O)Cl] can be easily alkylated in reactions with LiR (R = Me, Bun, CH2CMe3, or CH2SiMe3). All these complexes were characterised by i.r., 1H and 13C n.m.r. spectroscopy and the chloro-carbonyl niobium(III) and oxo niobium(V) complexes were studied by cyclic voltammetry. The crystal structures of [Nb(η-C5H4SiMe3)2Cl2](2), [Nb(η-C5H4SiMe3)2(C6F5)(CO)](2f), and [Nb(η-C5H4SiMe3)2(O)Me](2h) have been determined by X-ray diffraction methods. Compound (2) crystallizes in the triclinic space group P1, with a= 12.680(5), b= 12.923(5), c= 6.806(3)A, α= 97.82(2), β= 104.18(3), γ= 67.79(2)°, and Z= 2; (2h) crystallizes in the monoclinic space group P21/n, with a= 8.842(4), b= 37.108(10), c= 6.331(3)A, β= 108.03(4)°, and Z= 4; (2f) crystallizes in the triclinic space group P, with a= 9.781(4), b= 14.440(6), c= 8.765(4)A, α= 90.84(2), β= 85.86(2), γ= 93.90(2)°, and Z= 2. All the structures were solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares methods to R= 0.0377 for 2 889 observed reflections [(2)], R= 0.0441 for 2 269 observed reflections [(2f)], and R= 0.0385 for 1 466 observed reflections [(2h)]. All structures contain a niobium atom bonded to two cyclopentadienyl rings in a η5 fashion; the co-ordination of the metal is completed by two Cl atoms in (2), by a terminal carbonyl group and a carbon atom from the C6F5 ligand in (2f), and by an oxygen atom and a carbon atom from a methyl group in (2h).

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.

The new title complexes of tantalum are true hydrides whereas the niobium complexes have bonding interactions among the three hydrogen atoms, as evidenced by short n.m.r. T1 values and unusual couplings 1J(H,H) which vary with temperature from less than 3 to about 100 Hz.

The cationic NbV species Nb(η5-Me3SiC5H4)2I2+, has been shown to be an effective catalyst for the electrochemical oxidation of triphenylphosphine. Indirect anodic oxidation in the presence of water gives triphenylphosphine oxide in good yield.

The reactions of Nb(η5-C5H5)Cl2(CO)L2 ( PMe3, PMe2Ph) with α-diketones RCOCOR (R Me, Ph) and 3,5-di-t-butyl-o-quinone have been studied. When L PMe2Ph and R Ph the reaction in a molar ratio 1 1 gives Nb(η5-C5H5)Cl2(O2C2Ph2)(PMe2Ph)2 (I) whereas the same reaction for R Me gives the phosphonium salt [P{C(OH)MeC(O)Me}Me2Ph]Cl (VII). When L PMe3 only the phosphonium salts [P{C(OH)RC(O)R}Me3]Cl are obtained for R Me (V) and Ph (VI), but the complex Nb(η5-C5H5)Cl2(O2C2Ph2)PMe3 (II) can be isolated by previous addition of MeI. Similar reactions with 3,5-di-t-butyl-o-quinone give Nb(η5-C5H5)Cl2(o-O2C6H2But)L, L PMe3 (III), PMe2Ph (IV). All the compounds have been characterized by IR, 1H, 13C, 31P NMR spectroscopy and the crystal structure of VII has been determined by X-ray diffraction. VII crystallizes in the monoclinic space group P21/c with a 7.440(2), b 10.377(3), c 17.644(4) Å, β 96.94(2)° and Dcal 1.039 g cm-3 for Z = 4. A final R value of 0.046 (Rw = 0.049) based on 2309 observed reflections was obtained. The geometry around the P atom is tetrahedral. © 1987., The authors gratefully acknowledge financial support from Comision Asesora de Investigation Cientifica y Técnica. (2001-83) Spain.

New niobium(IV) complexes, Nb(η-C5H3RR′)2X2, R = H, R′ = SiMe3, X = Br (1), X = I (3); R = R′= SiMe3, X = Br (2), X = I (4), have been isolated in high yields from the reactions of Nb(η-C5H3RR′)2H3 and Nb(η-C5H3RR′)2X with EtBr and MeI. Both chemical and electrochemical oxidation processes of these niobium(IV) complexes produce the cationic niobium(V) compounds, [Nb(η-C5H4SiMe3)2X2]+, X = Cl (5), Br (6), I (7), which exhibit an acidic character towards nucleophilic reagents, such as Me2SiOR, to give new niobium(V) alkoxo complexes, [Nb(η-C5H4SiMe3)2Cl(OR)]+, R = CH3 (8), CH2CH3(9), CH(CH3)2 (10). Spectroscopic IR, ESR and NMR data are available for these compounds.

This review discusses the study we have carried out towards the synthesis, structure and reactivity of (imido)niobium complexes, which contain at least one cyclopentadienyl ligand. The following families of niobium complexes are described: (i) half-sandwich imido complexes; (ii) metallocene imido compounds; (iii) imido complexes containing ansa-cyclopentadienyl ligands; (iv) dinuclear imido complexes such as [{Nb(η5-C5H4SiMe3)2Cl}2(μ-1,3-N2C6H4)]. In addition we describe spectroscopic and structural features of the (imido)niobium complexes. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

The reaction of alkyne-containing niobium(III) complexes [NbCl3(dme)(RCCR′)] (dme = 1,2-dimethoxyethane) with the appropriate Na(S2CNR″2) reagents, in a 1∶3 molar ratio, afforded the corresponding dialkyldithiocarbamato complexes [Nb(RCCR′)(S2CNR″2)3] (R = R′ = Ph, R″ = Me 1; R = R′ = Ph, R″ = Et 2; R = R′ = R″ = Me 3; R = R′ = Me, R″ = Et 4; R = R′ = Et, R″ = Me 5; R = R′ = R″ = Et 6; R = R′ = SiMe3, R″ = Me 7; R = R′ = SiMe3, R″ = Et 8; R = Ph, R′ = Me, R″ = Me 9). The same complexes were also prepared from the reaction of the appropriate [NbCl3(bpzm)(RCCR′)] [bpzm = bis(pyrazol-1-yl)methane] complexes with the corresponding sodium dialkyldithiocarbamates. All complexes were spectroscopically characterized and the dynamic behaviour of some of them was studied by variable-temperature NMR techniques. The molecular structure of complex 9 was also established.

A new methane partial oxidation (MPO) catalyst has been prepared by grafting MoO2(acac)2 (acac: acetylacetonate ligand) onto the surface of dried HZSM-5 zeolite. This reaction was performed in an organic solvent under an inert atmosphere with the exclusion of water from the reaction. It was shown by FT-IR spectroscopy that the reaction takes place between the acidic hydroxyl groups of the zeolite and the acetylacetonate ligands of the complex. After the grafting reaction, the solid was washed, dried and calcined in air, to afford the final [S]O2MoO2, Mo(VI), highly dispersed, surface species. The catalytic activity of this new material in the MPO reaction is enhanced in comparison with the classical Mo,W/HZSM-5 impregnation catalysts., A.A., F.C., J.F.B., F.J.F. and A.O. acknowledge financial support from DGES (Dirección General de Enseñanza Superior e Investigación Cientı́fica, Grant No. PB 95-0023-CO1-CO2) of Spain. P.C., A.L., L.R. and J.L.V. acknowledge financial support from DGES (Dirección General de Enseñanza Superior e Investigación Cientı́fica, Grant No. PB92-521) of Spain.

The reaction of CS2 with Cp‘2Nb(H)(η2-CH2CH2) or Cp‘2Nb(H)(η2-CH2CHPh) (Cp‘ = η5-C5H4SiMe3) affords the alkylniobocene complexes Cp‘2Nb(Et)(η2-CS2-C,S) (2) and Cp‘2Nb(CH2CH2Ph)(η2-CS2-C,S) (3), respectively. The interaction of η2-CS2-containing complexes Cp‘2NbCl(η2-CS2-C,S) with alkynes bearing electron-withdrawing groups gives rise to a new family of 1,3-dithiol-2-ylidene niobocene species, Cp‘2NbX(CS(R)CC(R)S) (6, X = Cl, R = CF3; 7, X = Cl, R = COOMe; 8, X = Cl, R = COOtBu; 9, X = Et, R = COOMe; 10, X = Et, R = COOtBu; 11, X = CH2CH2Ph, R = COOMe; 12, X = CH2CH2Ph, R = COOtBu). In a similar way, with the carboxylate complexes Cp‘2Nb(OC(O)H-O)(η2-CS2-C,S) (4) and Cp‘2Nb(OC(O)CH3-O)(η2-CS2-C,S) (5) as starting materials, other 1,3-dithiol-2-ylidene species have been isolated Cp‘2Nb(OC(O)Y−O)(CS(R)CC(R)S) (13, Y = H, R = COOMe; 14, Y = H, R = COOtBu; 15, Y = CH3, R = COOMe; 16, Y = CH3, R = COOtBu). The structures of all complexes have been determined by spectroscopic methods. The structure of 2 was esta...

The multistep syntheses of the novel functionalized bis(pyrazol-1-yl)methane ligands, bis(5-diphenylphosphinopyrazol-1-yl)methane (bppzm) 1, bis(5-diphenylphosphinopyrazol-1-yl)trimethylsilylmethane (bppztm) 2 and bis(2-diphenylphosphinoimidazol-1-yl)methane (bpizm) 3, have been studied. The coordinative capacity of the bppzm ligand towards a variety of early and late metal fragments was evaluated and seven metallacycles were isolated. The complex [{NbCl3(dme)}n] (dme = 1,2-dimethoxyethane) reacted with an excess of bppzm to give the binuclear complex [{NbCl3(bppzm)}2] 4, and in the same way the reaction of the mononuclear species [NbCl3(dme)(RCCR′)] with 1 gave the appropriate [NbCl3(bppzm)(RCCR′)] complexes (R = R′ = Ph 5; R = R′ = SiMe3 6; R = Ph, R′ = Me 7; R = Ph, R′ = SiMe3 8). In all these niobium complexes, 1 behaves as an N,N chelate ligand. Compound 1 reacts with [MCl2(PhCN)2] (M = Pd, Pt) to yield the complexes [MCl2(bppzm)] (M = Pd 9, Pt 10), where a P,P chelate behaviour for 1 was observed. A dynamic conformation of the six- and eight-membered metallacycles formed in the complexes was observed and variable-temperature NMR studies were carried out. Finally, the molecular structure of complex 10 was determined crystallographically and a distorted square-planar geometry was found in which a proton (Hendo) of the bridging methylene is in close proximity to the metal centre in the boat–boat conformation of the metallacycle.

The reaction of the hydride niobocene complexes, Nb( η 5 -C 5 H 4 SiMe 3 ) 2 (H)(CNR) (R=2,6-dimethylphenyl (Xyiyl) orcyclohexyl (Cy)) and Nb( η 5 -C 5 H 4 SiMe 3 ) 2 ( H )( CO ) with the heterocumulenes PhN=C=X (X=0 or S) affords the new formamido and thioformamido complexes Nb(( η 5 -C 5 H 4 SiMe 3 ) 2 ) 2 (CNR)(η 1 -XC(H)NPh) (R=Xylyl, X=0 (1); R=Xylyl, X=S (2); R=Cy, X =O (3); R-Cy, X=S (4)) and Nb(( η 5 -C 5 H 4 SiMe 3 ) 2 ) 2(CO) (η1-XC(H) NPh) (X=0 (5); X=S (6) ). The protonation of these derivatives using HCF3COO yields the trifluoroacetato complexes Nb(( η 5 - C 5 H 4 SiMe 3 ) 2 2(CNR) ( η 1 -OOCCF 3 ) (R=Xylyl (7); R =Cy (8)) and Nb(( η 5 -C 5 H 4 SiMe 3 ) 2 )2(CO) ( η 1 -000CF 3 ) ( 9 ) and the imine derivatives HOC(H)=NPh and HSC(H)=NPh. Thermal treatment of 5 gives the η 2 -formamido, complex Nb( η 5 -C 5 H 4 SiMe 3 ) 2 ( η 2 -OC(H)NPh) (10). All these complexes have been characterised by spectroscopic methods.

The trihydride complex [Nb(η5-C5H4SiMe3)2(H)3] (1) reacts with diphenylphosphane to afford the monohydride [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3). The synthesis of complex 3 has also been achieved from the initial formation of the phosphonium salt [Nb(η5-C5H4SiMe3)2(H)2(PHPh2)]Cl (2) by reaction of the trihydride complex [Nb(η5-C5H4SiMe3)2(H)3] (1) with chlorodiphenylphosphane, followed by deprotonation of this salt in aqueous NaOH. Protonation of complex 3 at low temperature with a slight excess of CF3COOH or CF3COOD leads to the η2-dihydrogen complex [Nb(η5-C5H4SiMe3)2(η2-H2)(PHPh2)]CF3CO2(4) or its monodeuterated isotopomer [Nb(η5-C5H4SiMe3)2(η2-HD)(PHPh2)]CF3CO2(5). When the temperature is increased to room temperature, complexes 4 and 5 transform into the transoid dihydrides [Nb(η5-C5H4SiMe3)2(H)2(PHPh2)]CF3CO2(6) and [Nb(η5-C5H4SiMe3)2(H)2(PDPh2)]CF3CO2(7), respectively. Complex 3 undergoes an insertion of CS2 into the niobium−hydrogen bond to give the η1-dithioformato complex [Nb(η5-C5H4SiMe3)2(PHPh2)(η1-S-S(S)CH)] (8). This complex could be detected by NMR spectroscopy but could not be isolated due to rapid conversion into the η2-dithioformato complex [Nb(η5-C5H4SiMe3)2(η2-S,S-SSCH)] (9) by loss of the phosphane molecule. Complex 3 also reacts with CO2 to give the η2-formato complex [Nb(η5-C5H4SiMe3)2(η2-O,O-OOCH)] (10); in this case the η1-formato complex could not be detected. The reagent ClPPh2 very smoothly inserts into the Nb−H bond of the complexes [Nb(η5-C5H4SiMe3)2(H)(L)] [L = PHPh2, CN(xylyl), CO; xylyl = 2,6-dimethylphenyl], yielding the new ionic complexes [Nb(η5-C5H4SiMe3)2(PHPh2)(L)]Cl [L = PHPh2(11), CN(xylyl) (12), CO (13)]. All the complexes described have been characterized by analytical and spectroscopic methods.