This review surveys some aspects of the chemistry of [VCp2]. The high potential of vanadocene [VCp2] (and [V(CO)Cp2]) in organometallic chemistry is illustrated by new organometallic architectures. The rich redox chemistry of [VCp2] is shown by incorporation of this fragment into various C≡C and C≡N bonds. This molecular approach allows the connection of two (or more) paramagnetic centers through an organic linker in order to build magnetic nanoscopic organometallic wires. [VCp2] has also been studied in the field of materials such as vanadium carbide (VC) ceramics and in its role as a reducing agent toward elements of groups 8–10 to prepare Fe, Rh, and Pd colloids. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Intermolecular alkyne hydroamination with primary amines is catalyzed with group 5 (vanadium and tantalum) transition metal complexes and a new imido-Ti(IV) complex. The reaction is very regioselective. The scope of the reaction was investigated with a variety of alkynes and amines; 1-hexyne and anilines were found to be especially good substrates.

A Pd colloid prepared by reduction of the [Pd(η3-allyl)2Cl]2 precursor with Vcp2 (vanadocene) in presence of polyvinylpyrrolidone (PVP) as a protecting polymer was found to be an active and stable catalyst of methoxycarbonylation of iodobenzene carried out in an ionic liquid (IL) medium of [bmim]X and/or [bumepy]X (bmim=1-methyl-3-butyl imidazolium cation, bumepy=1-butyl-4-methyl pyridinium cation, X=Cl, BF4, PF6) or in the presence of ammonium salts of [R4N]X type (R=nBu, Et, Me; X=Cl, Br, I). The yield of benzoic acid methyl ester produced in methoxycarbonylation of iodobenzene in ionic liquids depends on their structure: those with the pyridinium cation are much more effective than those with the imidazolium one. At the optimal concentration of methanol, the yield of methoxycarbonylation reaction catalyzed by Pd colloid decreases in the order: [nBu4N]Br>[nBu4N]I>[nBu4N]Cl>[bumepy]PF6>[Et4N]Br>[bumepy]Cl>[bumepy]BF4>[Et4N]Cl>[bmim]PF6>[bmim]BF4>[bmim]Cl.

The reaction between [VCp2], BPh3, or BCl3 and the nitrile F3CC6H4C⋮N gives the borane adduct of vanada(IV)azirine complex [VCp2{η2:C,N-F3CC6H4CN·BR3}] (R = Ph (2), Cl (3)). Using B(C6F5)3 and dicyano compounds such as 1,4-benzene dicarbonitrile N⋮C(C6H4)C⋮N and adiponitrile N⋮C(CH2)4C⋮N, an access to homobimetallic vanadium complexes was obtained and complexes [(VCp2)2{η2:C,N-(C6F5)3B·NC(C6H4)CN·B(C6F5)3}] (6) and [(VCp2)2{η2:C,N-(C6F5)3B·NC(CH2)4CN·B(C6F5)3}] (8) are formed. Malononitrile N⋮CCH2C⋮N in the presence of 2 equiv of B(C6F5)3 and 1 or 2 equiv of [VCp2] gave the monometallic complex [(VCp2){η2:C,N-(C6F5)3B·NCCH2C⋮N·B(C6F5)3}] (7). Complexes 2, 3, 7, and 8 were characterized by X-ray structure determination. All these complexes are paramagnetic to one electron per vanadium.

The reactions between V(N-3)(2)(NMe2)(2) or V(OiPr)(4) and the chelating dianionic bis(phenoxy)amine ligand [ONNO]H-2 afford complexes formulated as [V(N-3)(2)(ONNO)] (1) and [V(OiPr)(2){ONNO}] (2). When refluxed in toluene with an excess of Me3SiCl, compound 2 leads to mono- or dichloro derivatives [V(Cl)(OiPr){ONNO}] (3) and [VCl2{ONNO}] (4) depending on the experimental conditions. The crystal structures of complexes 1-4 were solved and show in all cases an [ONNO] ligand that has phenolate groups in a trans configuration, with both amino-nitrogen donor atoms of the ligand coordinated to the octahedral vanadium center. Complexes 1-4 were further characterized by EPR spectroscopy and susceptibility measurement studies typical of d(1)-paramagnetic V-IV species. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).

The reaction of [Cp2Ti(CO)(2)] with borane adducts (CF3C6H4CNB)-B-.(C6F5)(3) and [(H2OB)-B-.(C6F5)(3)] has afforded the titanaazirine [CP2Ti(eta(2)-C,N-F3CC6H4CN)B-.(C6F5)(3)] (1) and the Ti-III salt [Cp2Ti][HOB(C6F5)(3)] (2), respectively. In both cases, a (TiF)-F-... interaction between the titanium centre and an orthofluorine atom of the tris(perfluorophenyl)borane is observed in the X-ray structure determination. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

The reaction of the vanadium(II) carbonyl [Cp2V(CO)] and B(C6F5)(3) resulted in formation of zwitterionic, ring-borylated vanadium(III) complexes [(Cp)(C5H4B(C6F5)(3))V] (3) and [(Cp)(C5H4B(C6F5)(3))V(CO)(2)] (4) and of the salt [Cp2V(CO)(2)][HB(C6F5)(3)] (5). All were characterized by crystallography. Formation of a hydride vanadium(IV) [(Cp)(C5H4B(C6F5)(3))VH(CO)] obtained by the electrophilic addition of the borane at the Cp-ring followed by redox and disproportionation reaction is suggested to account for these results.

[Pd(eta(3)-C3H5)(2)Cl](2) reacts in THF in the presence of poly(vinylpyrrolidone) (PVP), with the 15-electron complex vanadocene [V(C5H5)(2)], to give PVP-protected palladium particles. High resolution electron microscopy (HREM) and wide angle X-ray scattering (WAXS) experiments were carried out on the PVP-protected palladium particles as obtained when exposed to H-2 and O-2 and after hydrogenation catalysis. In each case, the particles display the fcc lattice of bulk palladium and a narrow size distribution centred near 2-3 nm. Catalytic hydrogenation reactions of nitrotoluene and 2,4-dinitrotoluene into their corresponding aniline and 2,4-diaminotoluene were performed in CH2Cl2 and in H2O/CH2Cl2 biphasic conditions. The catalytic reactions were found to be zero order with respect to the substrate and first order with respect to dihydrogen and catalyst.

The reaction between VO(OR)(3) (R = (i)()Pr, (t)()Bu, CH(2)CF(3)) and the chelating dianionic bis(phenoxy)amine ligand [ONNO]H(2) affords a mixture of two isomers (A and B in a ratio A:B approximately 3:1) formulated as VO(OR)[ONNO] (1a-c) (R = (i)()Pr (1a), (t)Bu (1b), CH(2)CF(3) (1c)). Multinuclear and NOESY NMR spectroscopy experiments were able to determine the structure in solution of the complexes. Both isomers have the symmetry-related phenolate groups in a trans configuration, the difference arising from the different configuration of the oxo and alkoxo ligands being located either cis (in isomer A) or trans (in isomer B) to the tripodal amino nitrogen donor atom and the (dimethylamino)ethyl sidearm respectively for the oxo and the alkoxo ligands. Crystals of isomer A (cis-1a) were obtained, and the structure determination confirms the arrangement of the ligands around the vanadium center. Analogue complexes VO(X)[ONNO] (X = Cl (2); X = N(3) (3)) were prepared by reacting equimolar amount of [ONNO]H(2) and VO(X)(n)(OR)(3-n) (X = Cl, R = Et, n = 1; X = N(3), R = (i)Pr, n = 2) at ambient temperature. Compounds 2 and 3 were further characterized by NMR spectroscopy experiments and X-ray structure determination. For both 2 and 3, a single isomer is obtained, having a trans-(O,O) configuration for the phenolate groups and a trans configuration of the oxo ligand in respect to the tripodal amino nitrogen donor atom. Finally, complex 2 could also be obtained by chlorination of 1a or 3 using a large excess of ClSiMe(3) in refluxing toluene.

The reaction of the imido precursor [V(NAr)Cl(2)](n)() (1) (Ar = 2,6-i-Pr(2)C(6)H(3)) with 3 equiv of PMe(2)Ph yields the monomeric complex [V(=NAr)Cl(2)(PMe(2)Ph)(2)] (2). Reacting 1 with 1.5 equiv of dmpe or 1 equiv of dppm affords the dimeric complexes [V(=NAr)Cl(2)(dmpe)](2)(mu-P,P'-dmpe) (3) and [V(=NAr)Cl(2)(dppm)](2) (4), respectively. Complexes 2-4 have been fully characterized by spectroscopic methods, magnetism studies, and X-ray crystallography.

Treatment of the oxovanadium(v) complex [VO(OCH2CF3)(3)](2) (3) with the Lewis acid B(C6F5)(3) leads to aryl/alkoxy group exchange and formation of the unexpected organometallic oxovanadium(v) [VO(mu-OCH2CF3)(OCH2CF3)(C6F5)](2) (1), while reaction of B(C6F5)(3) and [VO(NEt2)(3)] produces the Lewis acid adduct [(Et2N)(3)(VOB)-B-.(C6F5)(3)] (2). The crystal structures of 1, 2 and 3 were determined. V-51 NMR chemical shifts for complexes 1-3 and [VO(NEt2)(3)] are discussed. A concentration-dependant monomer-dimer equilibrium for 3 is observed in solution. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

The reaction of [CP2Ti(Cequivalent toCPh)(2)], [Cp2Zr(Cequivalent toCPh)(2)], [(C5H4SiMe3)(2)Zr(Cequivalent toCPh)(2)] and vanadocene in toluene was performed at room temperature and gave heterodimetallic complexes [Cp2V(mu-eta(2) : eta(4)-PhC4Ph) . MCp2'] (1, M=Ti, Cp'=C5H5; 2, M Zr, Cp' =C5H5; 3, M=Zr, Cp' C5H4SiMe3), respectively. These compounds, which have been characterized by elemental analysis mass spectrometry, H-1 NMR, IR and Raman spectroscopy, exhibit similar magnetic susceptibilities. According to an X-ray diffraction analysis of compound 3, the Cp2V and CP2'Zr metallocene moieties are bonded to a butadiene(or butadiyne) framework via the two internal carbon atoms for Cp2V, and via both the two internal carbon atoms and the two external carbon atoms for CP2'Zr. The distances and angles observed around the internal carbon atoms of the butadiene framework indicate that both internal carbon atoms of butadiene skeleton are planar and tetracoordinated.

The reaction of [Cp2Ti(C dropCPh)(2)], [Cp2Zr(C drop CPh)(2)] with vanadocene in toluene at room temperature gives heterodimetallic complexes [Cp2V(mu-eta(2) : eta(4)-butadiyne)MCp2] 1 (M = Ti), 2 (M = Zr), respectively. These compounds, which have been characterized by elemental analysis, mass spectrometry, IR and Raman spectroscopy, exhibit similar magnetic susceptibilities. According to an X-ray diffraction analysis of 2, the Cp2V and Cp2Zr metallocene moieties are bonded to a butadiene (or butadiyne) framework via the two internal carbon atoms for Cp2V, and via both the two internal carbon atoms and the two external carbon atoms for Cp2Zr. The distances and angles observed around the internal carbon atoms of the butadiene framework indicate that both internal carbon atoms of butadiene skeleton are planar and tetracoordinated.

Novel complexes of vanadium(III), chromium(111) and iron(II) containing the alkaloid (-)-sparteine as a bidentate ligand have been prepared. Two of them, [VCl3((-)-sparteine)] and [FeCl2((-)-sparteine)], were characterised by X-ray diffraction. Known cobalt(Ill) and nickel(II) analogue complexes were prepared using the same procedure. (C) 2002 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are reported. Reaction of V(NMe(2))(4) with anilines ArNH(2), where Ar = 2,6-i-Pr(2)-C(6)H(3), 2,6-Me(2)-C(6)H(3), Ph, 2,6-Cl(2)-C(6)H(3), and C(6)F(5), afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe(2))(2)](2) (1a-e). Chlorination of 1a-e with trimethylchlorosilane afforded complexes 2a-e formulated as [V(=NAr)Cl(2)(NHMe(2))(x)()](n)(). One-pot reaction of V(NMe(2))(4) with ArNH(2) in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(=NAr)Cl(2)(NHMe(2))(2)] (3a-e). Reaction of 3a-e with pyridine, bipyridine (bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(=NAr)Cl(2)(Py)(3)] (4a-e) or [V(=NAr)Cl(2)(Py)(2)(NHMe(2))] (5a), bipyridine complexes [V(=NAr)Cl(2)(bipy)(NHMe(2))] (5a-e) and [V(=NAr)Cl(2)(bipy)(Py)] (9a), and tmeda adduct [V(=NAr)Cl(2)(tmeda)(NHMe(2))] (10a). Moreover, five-coordinate complexes free of NHMe(2) ligands, such as [V(=NAr)Cl(2)(Py)(2)] (5a), [V(=NAr)Cl(2)(bipy)] (8a), and [V(=NAr)Cl(2)(tmeda)] (11a), were directly prepared starting from precursors 2a-e. All compounds were totally characterized by spectroscopic methods (IR, (1)H NMR for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.

The cationic vanadocene alkyl complex [Cp2VMe(CH3CN)](+) with [BPh4](-) counteranion was structurally established. The reaction of Cp2VMe2 in THF in the presence of B(C6F5)(3) is also described: EPR evidence of the intermediate formation of the [Cp2VMe(THF)](+) species, which gives, via a disproportionation redox reaction, the V-III species [Cp2V(THF)][Me B(C6F5)(3)], is demonstrated.

Reaction of vanadocene [V-Cp)(2)] with "activated" nitrile (RCN)-C-1.L (L: Lewis acid), obtained by the reaction of borane adducts (L = BR3, R = C6F5, 2,6-F2C6H3, 3,4,5-F3C6H2) with nitriles (CH3CN, F3CC6H4CN), yields the borane adduct of vanada(IV)azirine complexes [V(Cp)(2)(eta(2)-(RC)-C-1 = N.L)]. EPR studies of a fluid solution were conducted on these complexes. A doublet of octets due to the coupling of one unpaired electron of the vanadium with the V-51 (I = 7/2) nucleus and to an additional hyperfine coupling to the ortho-F atom borne by the phenyl ring of the borane was elucidated by means of the different Lewis acids used in this work. This EPR behaviour gives evidence for the presence of a C-F...V interaction in a fluid solution with L = B(C6F5)(3) and B(2,6-F2C6H3)(3). In contrast, the expected eight line EPR pattern is observed with L = B(3,4,5-F3C6H2)(3), in which no ortho-F atoms are present in the phenyl ring. A model can be drawn to take into account this flexibility and V...F distances between and ortho-F atoms are in the expected range for such an interaction.

A new set of criteria for quantitative analysis of molecular interactions is proposed resulted from the investigation of crystal structures of 808 picomplexes of rare-earth atoms (Ln).The set is based on the conceptions of atomic and molecular Voronoi-Dirichlet polyhedra and comprises: I.The criteria of existence of agostic and van der Waals contacts Ln...H-L between the complexing atom Ln and a ligand L. II.A set of criteria for ligands, namely: ligand total, valent and agostic solid angles, which are to be calculated with the faces of Voronoi-Dirichlet polyhedron of the Ln atom corresponding to all, only valent or only agostic Ln-L contacts, respectively; and ligand residual solid angle which is the difference between total and valent solid angles.III.A set of criteria for complexes as a whole including similar terms as the previous set, but relating to entire complex particle, to be calculated by summation of corresponding ligand solid angles for all ligands in a given complex.It is shown that the criteria of the first set allow one to improve the conclusions about existence or missing of agostic contacts.Seven different numerical combinations of the second and third sets of criteria were singled out, with which one can predict the composition and sterical stability of complex groups, the existence of intra-and intermolecular agostic and van der Waals interactions, and can judge about the capability of a ligand L to screen the central atom and to form the agostic contacts Ln...H-L.

Several N,N ' -bis(trialkylsilyl)-substituted diamines of the general formula [(SiR3)(2)-ABA]H-2 [ABA = 2-amidobenzylamido, SiR3 = SiMe3 (la), SiMePh2 (1b), SiMe(2)tBu (1c) Or SiiPr(3) (1d)], together with related compounds in which the substituents of the two nitrogen atoms are different, e.g. [(SiMePh2)(SiMe3)-ABA]H-2 (1g), have been synthesized. Their reaction with 2 equiv. of nBuLi afforded the dilithiated derivatives, which reacted with ZrCl4 to yield metallaspirocyclic complexes of the type Zr[(SiR3)(2)-ABA](2). Protonolysis of Zr(NMe2)(4) with 1 equiv. of the parent diamines led to the monosubstituted complexes Zr((SiR3)2-ABA](NMe2)2 [SiR3 = SiMe3 (4a), SiMePh2 (4b) or SiMe(2)tBu (4c)] and Zr[(SiMePh2)(SiMe3)-ABA](NMe2)(2) (4g) in high yield, and subsequent reaction with excess SiMe3Cl afforded the dichlorides Zr[(SiMe3)(2)-ABA]Cl-2 (5a), Zr[(SiMe(2)tBu)(2)-ABA]Cl-2 (5c), and Zr[(SiMePh2)(SiMe3)-ABA]Cl-2 (5g). The X-ray crystal structure of 5c shows that it forms dimers via two Zr-Cl bridges; moreover, a bonding interaction between the zirconium centre and the aryl ipso-carbon atom linked to the anilinic nitrogen atom is evident. A hydrochlorinated derivative of 5c, Zr[(SiMe(2)tBu)(2)(H)-ABA]Cl-3 (6c), was also analysed by X-ray diffraction and shown to exhibit analogous structural characteristics. Low-temperature NMR studies revealed all these complexes to be fluxional and permitted an insight into the molecular structures in solution. The ABA framework undergoes a rocking motion about the corresponding ZrN2 plane, whose activation energy is between 37 and 43 kJ mol(-1). Compounds 3 and 5 exist as several stereoisomers that interconvert by this process. On activation with MAO, the dichloride complexes of type 5 polymerize ethylene at both room temperature and pressure to yield linear high molecular mass polyethylenes with a broad molecular mass distribution.