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The slow addition of NO to a CCl4 solution of VCl4 forms the polymer [V(NO)(sub 3)Cl2](sub n) as a dark brown powder. The polymer is characterized by conventional spectroscopic methods and the solid state structures have been established by single-crystal X-ray diffraction analyses.

The monomeric trinitrosyl complex, W[(NO).sub.3][Cl.sub.3], can be prepared by the treatment of W[Cl.sub.6] in C[H.sub.2][Cl.sub.2] with NO gas, and its identity has been unambiguously confirmed by a single-crystal X-ray diffraction analysis. The complex crystallizes in the space group Pmn[2.sub.1] as a three-component twin (a = 10.4280(4) [Angstrom], b = 6.3289(2) [Angstrom], c = 5.6854(2) [Angstrom], Z = 2, [R.sub.1] = 0.065, w[R.sub.2] = 0.176). Its solid-state molecular structure consists of a tungsten centre bound to three chloride ligands and three linear nitrosyl ligands in a fac-octahedral stereochemistry. In addition, the structure contains a crystallographically imposed mirror plane. The two independent W--N linkages are 1.88(2) and 1.92(1) A long, while the two corresponding N--O bond lengths are 1.13(2) and 1.16(2) [Angstrom]. DFT calculations on fac-W[(NO).sub.3] [Cl.sub.3] at the B3LYP/LANL2DZ level of theory afford optimized intramolecular metrical parameters that match the X-ray crystallographically determined bond lengths and bond angles quite well. In addition, they provide a rationale for the nearly linear W-N-O linkages extant in the complex. Solutions of fac-W[(NO).sub.3] [Cl.sub.3] in C[H.sub.2] [Cl.sub.2] lose CINO under ambient conditions and deposit the well-known [W[(NO).sub.2][[Cl.sub.2]].sub.2] polymer, and this conversion is fully reversible. Key words: nitrosyl, tungsten, structure, bonding.

An investigation into the system of isolating several Lewis-base adducts of the acidic Fe(NO)(sub 3)(super +) species disclosed that they exhibit distinctly bent Fe-N-O linkages. Experiments carried out show that the bending of the NO ligands results in an increase in the energy of the HOMO relative to the linear case, but at the same time causes a decrease in energy of the HOMO-1 and the HOMO-2 molecular orbitals.

Research has been conducted on the (trimpsi)M(CO) (sub)2 (NO) complexes, where M is V, Nb, Ta and trimpsi is (super)t BuSi(CH (sub)2 PMe (sub)2) (sub)3. The reactions of these complexes with halogens and halogen sources have been investigated and are described.

Research has been conducted on the (trimpsi)M(CO) (sub)2 (NO) complexes [M= V, Nb, Ta; trimpsi= (super)t BuSi(CH (sub)2 PMe (sub)2) (sub)3]. The synthesis and characterization of these complexes have been carried out and the preparation of the (trimpsi)V(CO) (sub)2 (NO) is described.

The authors discuss the publications on transition metal- nitric oxide complex chemistry. The topics of interest include the effect of electron-withdrawing nitric oxide ligands on nitrosyl complexes' physical and chemical properties.

Reaction of CpMo(NO)(C[H.sub.2]Ph)Cl with [Me.sub.2]Mg, [Ph.sub.2]Mg, or PhCCLi reagents in THF affords the corresponding alkyl, aryl, or alkynyl CpMo(NO)(C[H.sub.2]Ph)R (R = hydrocarbyl) complexes as orange powders in good yields. Unlike related 16-electron CpMo(NO)[R.sub.2] complexes, these 18-electron species exhibit good thermal stability due to their [[eta].sup.2]. benzyl-Mo interactions. Treatment of CpMo(NO)(C[H.sub.2]Ph)Cl with Na(DME)Cp provides dark green [Cp.sub.2]Mo(NO)(C[H.sub.2]Ph), whose solid-state molecular structure has been established by a single-crystal X-ray crystallographic analysis. The two Cp rings display different binding modes to the Mo atom, while the benzyl ligand is coordinated to the metal centre in an [[eta].sup.1] fashion. The triflate complex, CpMo(NO)(C[H.sub.2]Ph) (OTf), is obtained by addition of AgOTf to the benzyl chloride precursor. The covalent Mo--OTf bond in this compound can be disrupted by the addition of Lewis bases (L) such as P[Ph.sub.3] or pyridine, leading to the corresponding [CpMo(NO)(C[H.sub.2]Ph)(L)][OTf] salts. Attempts to generate neutral benzylidene complexes by deprotonation of [CpMo(NO)(C[H.sub.2]Ph)(P[Ph.sub.3])][OTf] have not yet been successful. Key words: nitrosyl, molybdenum, benzyl, hydrocarbyl, triflate.

Anionic and paramagnetic [CpCr(NO)X2]- complexes were synthesized by the reaction of [NBu4]I with [CpCr(NO)I]2. The CpCr(NO)X2 anions exhibited single strong nitrosyl-stretching absorption that was generated by a linear nitrosyl group. The formation of CpCr(NO)Cl2 from the oxidation of [CpCr(NO)Cl2]- also involved the formation of an initial oxidation product that was unstable due to the loss of the NO unit. Furthermore, the stability of the anionic and paramagnetic complexes were dependent on pi-donation from alkoxide or amide ligands which reinforced the low-spin state.

The ligand L's nature and the chromium center's valence-electron count regulate the stability of CpCr(NO)L2 compounds. The compound is stable as an 18-electron material in the presence of pi-acidic ligands such as CO, and the compound is stable as a 17-electron complex when the ligands are sigma-base. The ESR spectra and magnetic moments of the resulting compounds are discussed.

The complexes (Cp*MoR)2(mu-NO)2 (R = CH2CMe3 -1-, CH2CMePh -2-, Cp* = eta to the fifth power-C5Me5), and (Cp*Mo-CH2SiMe3-)(mu-NO)2(Cp*W-CH2SiMe3-) (3) are prepared. The complexes 1, 2 and 3 on isomerization yield (Cp*Mo-NO-R)(mu-N)(Cp*Mo-O-R) (R = CH2CMe3 -4-, CH2CMe2Ph -5-) and a 60:40 (M1 = W:M1 =Mo) mixture of (Cp*M1-NO--CH2SiMe3-)(mu-N)(Cp*M2-O--CH2SiM3-) (6) respectively. The Mo-Mo bond distance of 1 is short than that in 6. In 6 a linear M-N-M' multiply bonded arrangement of 157.3(4) is present.

The key step in the formation of CpCr(NO)(PPh3)(CH2SiMe3) from an alkyl-for-iodide metathesis reaction between CpCr(NO)(PPh3)I and Me3SiCH2MgCl involves removal of phosphine ligand. IR and ESR spectroscopic studies help identify four intermediate complexes. Mechanistic studies of this reaction help synthesize 17-valence-electron CpCr(NO)(L)R complexes, where L is a ligand from the chromium coordination sphere.

A reaction involving the [[eta].sup.5]-[C.sub.5][Me.sub.4]H analogue has produced only the phenyl complexes during the first 24 h, thereby providing their isolation in good yields. The difference in reactivity in the C-H activation of benzene and the above reaction is attributed to the lesser steric demands of the [[eta].sup.5]-[C.sub.5][Me.sub.4]H ligand that has resulted in its complexes reacting at a slower rate.

Thermolysis of Cp*W(NO)(C[H.sub.2]C[Me.sub.3])([[eta].sup.3]-C[H.sub.2]CHCHMe) at ambient temperatures has led to the loss of neopentane and the formation of the [[eta].sup.2]-diene intermediate, which is isolated as its 18e P[Me.sub.3] adduct. The newly formed alkyl ligands is liberated from the tungsten centers in the product complexes by treatment with iodine and the exposure of a CD[Cl.sub.3] solution of the n-pentyl allyl complex to [I.sub.2] has produced n-[C.sub.5][H.sub.11]I in moderate yields.

The unprecedented intramolecular C-H activations of molybdenacyclobutanes that eventually produce coupled organic products are described. These complexes have differed from previously reported metallacyclobutanes in that they show no propensity for metathesis processes, favoring instead C-H activation routes.

The isolation and characterization of three different types of organometallic products resulting from the transformations of cyclohexene effected at the Cp(super *)W(NO) fragment is described. The three transformations are initiated by coordination of cyclohexene to the tungsten center and formally involve intramolecular C-H activation of cyclohexene to form an eta(super 3)-cyclohexenyl hydrido complex.

The first definitive demonstration of the C-H bond-activating ability of a transition-metal allene complex is constituted. The results indicate the concurrent generation of a diene reactive species, which is evidently been responsible for the C-H bond-activating chemistry.

Cp*Mo(NO)(CH2CMe3)(sub 2), a complex with Alpha-agostic C-H[...]Mo interactions, evolves neopentane in neat hydrocarbon solutions at room temperature and forms the transient 16-electron alkylidene complex, Cp*Mo(NO)(=CHCMe3), which subsequently activates solvent C-H bonds. Density functional theory calculations indicate that better agreement with experimental observations is obtained when the actual neopentyl ligand is used in the model complexes.

This article describes thermal reactivity of the pseudooctahedral 16-electron Cp(sup)*M(NO)R(sub)2 systems of molybdenum and tungsten to form a wide range of reactive 16e nitrosyl complexes, which mediate intermolecular single, double, or triple activation of hydrocarbone C-H bonds. Results discuss kinetics and mechanistic aspects of the above thermal activation reactions.

A unique tungsten allyl nitrosyl complex is discovered that has selectively activated the terminal C-H bond of n-alkanes under ambient conditions and has formed thermally stable n-alkyl complexes. The analysis has indicated that this tungsten complex can initiate similar C-H bond activations and functionalizations even in the presence of functional groups containing N and O heteratoms.

The effect of allyl nitrosyl complexes on the concurrent activation of N-H and [alpha]-C-H bonds of pyrrolidine and piperidine under ambient conditions is examined. The results have shown that these reactions of the saturated cyclic amines constitute the first unambiguous examples of concurrent N-H and C-H bond activations of organic substrates by transition-metal complexes.

An investigation with Cp*Mo(NO)(CH2CMe3)(sub 2) complex is made since the related CpMo(NO)(CH2Me3)2 complex forms a dimeric molybdenum alkylidene complex in CH2CI2 below room temperature. Results of the investigation show that the thermal chemistry of this molybdenum complex, which reveals parallel C-H bond activation chemistry, mediated not only transient alkylidene complex but also by transient benzyne complexes under mild conditions.

Generation of a reactive 16e allene complex by the gentle thermolysis of an alkyl-alkyl precursor is discussed. Reactivity differences suggest that new avenues of alkane activation chemistry may well be accessible through alkyl-alkyl complexes.

It has been possible to obtain the first definitively characterized examples of O-protonated terminal nitrosyl ligands. This research identified the changes to the metal-NO bonding interactions that arise within the resulting eta-1-hydroxylimido-metal linkages

NO is a strong pi-acceptor ligand and M-NO back-bonding is important in determining the chemistry exhibited by transition-metal nitrosyl complexes. There are no well-characterized niobium or tantalum nitrosyl complexes for group 5 elements. The synthesis and characterization of (trimpsi)M(NO)-(CO)(sub2) nitrosyls of such elements is now reported.

The monosubstitution of a deuterium atom at the alpha carbon of the neopentyl ligand was established by the presence of a broad singlet for one proton at sigma 3.19 in its 1HNMR spectrum. The evidence for the synthesis of a highly reactive alkyldiene species which mediates the transformation even in the presence of excess trimethylphosphine was described. The transition-metal alkyldiene complex cab influence the addition of C-H bonds of alkanes across the metal-carbon double bond.

A new synthetic route to complexes containing the 16-electron pi-donating fragment Cp*W(NO)(PPh3) is introduced. It is based on the facile ligand-induced reductive elimination of arene in the phosphine Cp*W(NO)(H)(eta2-PPh2C6H4) in the presence of isocyanides or carbonyls at room temperature. When the phosphine is reacted with acetone and PMe3, the rate rises linearly as the concentration of the incoming ligand increases.