Metathesis reactions between Cp*W(NO)(CH 2 EMe 3 )Cl (E ) C or Si) and a variety of bis(allyl)magnesium reagents lead to the formation of 18e Cp*W(NO)(alkyl)(η 3 -allyl) complexes. The compounds 5), and Cp*W(NO)(CH 2 CMe 3 )(η 3 -CH 2 CHCH 2 ) (6) have thus been synthesized in moderate yields. The solid-state molecular structures of 3, 4, 5, and 6 feature σ-π distorted allyl ligands in the endo conformation. Complex 1 effects the concurrent N-H and R-C-H activations of pyrrolidine and piperidine under ambient conditions and forms the alkyl amido complexes Cp*W(NO)(CH 2 CMe 3 )(NC 4 H 7 -2-CMe 2 CHdCH 2 ) (7) and Cp*W(NO)(CH 2 CMe 3 )(NC 5 H 9 -2-CMe 2 CHdCH 2 ) (8), respectively. Complexes 2-5 react with pyrrolidine in a similar manner, but the reaction of 3 to produce Cp*W(NO)(CH 2 CMe 3 )(NC 4 H 7 -2-CH 2 CMedCH 2 ) (10) is not as clean since 3 is thermally unstable at 20 °C. Unfortunately, the concurrent N-H and R-C-H activation transformation encompasses only a very limited range of substrates, namely cyclic amines. Complex 6, which contains an unsubstituted allyl ligand, exhibits a unique mode of reactivity with pyrrolidine and piperidine, incorporating 2 equiv of the amines and forming Cp*W-(NO)(NC 4 H 8 )(CHMeCH 2 NC 4 H 8 ) (13) and Cp*W(NO)(NC 5 H 10 )(CHMeCH 2 NC 5 H 10 ) ( 14), respectively. Plausible mechanisms are suggested to account for the different modes of reactivity of the Cp*W(NO)(alkyl)(η 3allyl) compounds with the cyclic amines. All new complexes have been characterized by conventional spectroscopic methods, and representative compounds have also been subjected to single-crystal X-ray crystallographic analyses.

Thermolysis of Cp*W(NO)(CH2CMe3)(eta(3)-CH2CHCHMe) (1) at ambient temperatures leads to the loss of neopentane and the formation of the eta(2)-diene intermediate, Cp*W(NO)(eta(2)-CH2=CHCH=CH2) (A), which has been isolated as its 18e PMe3 adduct. In the presence of linear alkanes, A effects C-H activations of the hydrocarbons exclusively at their terminal carbons and forms 18e Cp*W(NO)(n-alkyl)(eta(3)-CH2CHCHMe) complexes. Similarly, treatments of 1 with methylcyclohexane, chloropentane, diethyl ether, and triethylamine all lead to the corresponding terminal C-H activation products. Furthermore, a judicious choice of solvents permits the C-H activation of gaseous hydrocarbons (i.e., propane, ethane, and methane) at ambient temperatures under moderately elevated pressures. However, reactions between intermediate A and cyclohexene, acetone, 3-pentanone, and 2-butyne lead to coupling between the eta(2)-diene ligand and the site of unsaturation on the organic molecule. For example, Cp*W(NO)(eta(3),eta(1)-CH2CHCHCH2C(CH2CH3)2O) is formed exclusively in 3-pentanone. When the site of unsaturation is sufficiently sterically hindered, as in the case of 2,3-dimethyl-2-butene, C-H activation again becomes dominant, and so the C-H activation product, Cp*W(NO)(eta(1)-CH2CMe=CMe2)(eta(3)-CH2CHCHMe), is formed exclusively from the alkene and 1. All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by X-ray crystallographic analyses. Finally, the newly formed alkyl ligands may be liberated from the tungsten centers in the product complexes by treatment with iodine. Thus, exposure of a CDCl3 solution of the n-pentyl allyl complex, Cp*W(NO)(n-C5H11)(eta(3)-CH2CHCHMe), to I2 at -60 degrees C produces n-C5H11I in moderate yields.

Cp*W(NO)(n-alkyl)(η3-allyl) complexes result from the selective activations of the terminal C−H bonds of alkanes. Consequently, the reactions of prototypical members of this family of complexes with a range of electrophiles and nucleophiles have been explored with a view to developing methods for functionalizing the newly formed alkyl ligands. The two principal complexes investigated in this regard have been Cp*W(NO)(CH2SiMe3)(η3-CH2CHCHMe) (1) and Cp*W(NO)(CH2C6H5)(η3-CH2CHCHMe) (2). It has been found that treatment of 1 and 2 with the oxidant I2 at −60 °C produces Cp*W(NO)I2 and terminally functionalized ICH2SiMe3 and ICH2C6H5, respectively. Oxidation of 1 by H2O2 also results in the loss of the allyl ligand and production of the known oxo peroxo complex Cp*W(O)(η2-O2)(CH2SiMe3). Treatment of 1 and 2 with electrophiles affords the products resulting from addition of the electrophile to the electron-rich terminus of the σ−π distorted allyl ligands in the reactants. Thus, reagents of the type E-X (E = triphenylcarbenium, H, catecholborane; X = Cl, BF4) liberate CH3CHCHCH2E and form the organometallic products Cp*W(NO)(X)(CH2SiMe3) and Cp*W(NO)(X)(CH2C6H5), respectively. Exposure of the tungsten alkyl allyl complexes to isocyanide reagents leads to the formation of complexes bearing β,γ-unsaturated η2-iminoacyl ligands that apparently arise from the migratory insertion of isocyanide into the tungsten−allyl linkages. For instance, reaction of 1 with 2,6-xylylisocyanide produces Cp*W(NO)(CH2SiMe3)(η2-CH3CHCHCH2CNC6H3Me2) (4a). Interestingly, gentle heating or chromatography of 4a causes isomerization of the olefin and conversion to the conjugated product Cp*W(NO)(CH2SiMe3)(η2-CH3CH2CHCHCNC6H3Me2) (4b). A similar reaction of 2 with 2,6-xylylisocyanide affords both unconjugated and conjugated isocyanide insertion products, while treatment of 2 with n-butylisocyanide produces primarily the conjugated product. Finally, exposure of these tungsten alkyl allyl complexes to 1000 psi of CO gas generally results in the desired migratory insertion of the CO into the metal−alkyl linkages to form acyl compounds. Hence, 1 is first converted into Cp*W(NO)(C(O)CH2SiMe3)(η3-CH2CHCHMe), which then subsequently transforms into isolable Cp*W(NO)(C(O)CH3)(η3-CH2CHCHMe) (7). Interestingly, 2 does not react with CO under these experimental conditions. Nevertheless, the generality of this mode of reactivity is established by the fact that similar treatment of four other Cp*(W)(NO)(CH2CMe3)(η3-allyl) complexes with CO gas at elevated pressures does afford the corresponding acyl products (8−11). All new organometallic complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of several compounds have been established by X-ray crystallographic analyses.

A potential catalytic cycle for the formation of new C-C and C-O linkages from hydrocarbon feedstocks and readily available olefin and ketone substrates mediated by Cp′M(NO)(L) (M ) Mo, W; Cp′ ) Cp*, Cp; L ) Lewis base) fragments has been investigated. The cycle is based on three steps: (1) oxidative addition of the hydrocarbon substrate to the metal center, (2) subsequent hydrometalation of the olefin or the ketone, and (3) final reductive elimination of the coupled product. Of the various Cp′M-(NO)(L) groups examined, the Cp*W(NO)(PPh 3 ) fragment has been found to be the best candidate for mediating these catalytic steps since it is not prone to form unreactive Cp*W(NO)(PPh 3 ) 2 as are some of the other fragments that readily decompose to 18e Cp′M(NO)L 2 complexes. Hence, Cp*W(NO)(PPh 3 ) has been utilized to determine if the oxidative addition and hydrometalation steps can occur sequentially under one-pot experimental conditions. However, olefins are too π-acidic and readily form stable 18e Cp*W(NO)(PPh 3 )(η 2 -olefin) adducts, which prevent oxidative addition of the hydrocarbon substrate to the tungsten center. Similarly, benzophenone, Ph 2 CO, and diisopropyl ketone, i Pr 2 CO, also form 1:1 η 2 -CdO adducts with the π-basic tungsten center in the 16e fragment. Nevertheless, oxidative addition and hydrometalation do occur sequentially to form the desired aryl alkoxide complex, Cp*W(NO)(OCH i -Pr 2 )(Ph), in addition to the Cp*W(NO)(η 2 -OC i Pr 2 )(PPh 3 ) adduct, when benzene and diisopropyl ketone are employed as the two substrates. The solid-state molecular structures of cis-Cp*W(NO)[η 2 -(CH 2 -NMe)P(NMe 2 ) 2 ](H), Cp*W(NO)(OCH i Pr 2 )(Ph), and Cp*W(NO)(η 2 -OC i Pr 2 )(PPh 3 ) have been established by single-crystal X-ray crystallographic analyses.

Reactions of a variety of cyclic and acyclic olefins with the title alkylidene complex (formed spontaneously by loss of neopentane from Cp*Mo(NO)(CH2CMe3)2 under ambient conditions) result in the initial formation of molybdenacyclobutane complexes (Cp* = C5Me5). These molybdenacyclobutane complexes do not react via olefin metathesis or cyclopropanation pathways, but instead via C−H activation. Thus, when cyclopentene is the olefinic substrate, the direct result of C−H activation at the β-position of the metallacyclobutane affords a thermally stable allyl hydrido complex that can be isolated. Such an allyl hydride intermediate is not isolable for larger cyclic olefins (cyclohexene, cycloheptene, and cyclooctene) or acyclic olefins (allylbenzene and 1-hexene). Instead, those complexes react further, undergoing a second C−H activation at the allylic position to produce η4-trans-diene complexes concomitant with the loss of dihydrogen. Upon heating, these η4-trans-diene complexes liberate diene, thereby enabling the 14e Cp*Mo(NO) metal fragment to catalyze the oligomerization of cyclic olefins and dienes including cyclohexene and 1,4-cyclohexadiene. In the case of the acyclic olefin allylbenzene, the metal fragment catalyzes a dimerization to (E)-(4-methylpent-1-ene-1,5-diyl)dibenzene under ambient conditions.