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.

Gentle thermolyses of CpW(NO)(CH 2 CMe 3 )-(η 3 -allyl) complexes (Cp = η 5 -C 5 Me 5 (Cp*), η 5 -C 5 Me 4 H (Cp′)) in neat hydrocarbon solutions result in the loss of neopentane from the metal's coordination spheres and the transient formation of the 16-electron (16e) intermediate species CpW(NO)(η 2 -allene) and/or CpW(NO)(η 2 -diene). These transient intermediates can react with hydrocarbon substrates, RH (R = alkyl, aryl), to form three different types of organometallic products. The first products are the desired CpW(NO)(η 3 -allyl)(η 1 -R) complexes that result from the selective single activation of a C−H bond of RH. The second class of products involves CpW(NO)(H)[η 3 -(R)-allyl] complexes that are isomers of the CpW(NO)(η 3 -allyl)(η 1 -R) compounds resulting from an intramolecular R/allyl H exchange. Finally, the third type of products contains CpW(NO)(H)[η 3 -hydrocarbyl] species that result from three successive C−H activations of hydrocarbon substrates such as R′CH 2 CH 2 CH 3 and loss of the original allyl ligand. Just which organometallic products ultimately result from the reactions of the CpW(NO)(CH 2 CMe 3 )(η 3 -allyl) complexes with hydrocarbons depends on several factors, including the natures of the cyclopentadienyl and allyl ligands, the hydrocarbon substrates themselves, the electron density at the metal centers, and the experimental conditions employed. This article documents these dependences and identifies the optimum CpW(NO)(CH 2 CMe 3 )(η 3 -allyl) compounds and experimental conditions for effecting the selective single C−H bond activations of hydrocarbon substrates such as benzene as a representative arene and methylcyclohexane as a representative alkane. During the course of these investigations all new organometallic complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of several of them have been established by singlecrystal X-ray crystallographic analyses.

Gentle thermolysis of the bis(neopentyl) complex Cp*W(NO)(CH2CMe3)2 (1) at 70 °C in various substituted benzenes results in the loss of neopentane and the generation of the transient alkylidene complex Cp*W(NO)(CHCMe3) (A), which subsequently effects single C−H bond activations of the benzenes. These activations exhibit a pronounced selectivity for the C−H linkages ortho to the benzene substituents. Thus, thermal reactions of 1 with C6H5X lead to the preferential formation of the corresponding Cp*W(NO)(CH2CMe3)(o-C6H4X) complexes, the ortho-selectivity, i.e., X = F > OMe > Cl > Br > C⋮CPh, diminishing as the steric demands of the substituents increase. Consistently, thermolyses of 1 in o-C6H4X2 afford Cp*W(NO)(CH2CMe3)(2,3-C6H3X2) complexes with 98% selectivity when X = F and 82% selectivity when X = Cl. Similarly, the principal organometallic products resulting from the thermolyses of 1 in m-C6H4X2 are the ortho-para-activated isomers Cp*W(NO)(CH2CMe3)(2,4-C6H3X2) with 84% selectivity when X = F and 89% selectivity when X = Cl. Finally, thermolyses of 1 in para-disubstituted benzenes p-C6H4XY (X = F or OMe, Y = Cl or OMe) again reveal that the ortho-directing abilities of the substituents diminish in the order F > OMe > Cl. Some mechanistic insights into these activation processes have been obtained by monitoring of the early stages of the thermolysis of 1 in chlorobenzene by 1H NMR spectroscopy. This monitoring reveals that the selectivity of the alkylidene intermediate A for forming the ortho-activated isomer is thermodynamic rather than kinetic in nature. Thus, the meta- and para-activated isomers are formed initially, but then convert to the ortho-activated product. The principal organometallic complexes resulting from ortho-C−H activations are formally 16-electron species in which there are no interactions between the tungsten centers and the Lewis-basic benzene substituents. Instead, the Lewis-acidic tungsten centers engage in intramolecular agostic interactions with the methylene C−H bonds of their neopentyl ligands to acquire some additional electron density. Being coordinatively and electronically unsaturated, these tungsten complexes react readily with added Lewis bases. Thus, treatment of Cp*W(NO)(CH2CMe3)(o-C6H4F) with Et4NCN and CO produces [Et4N]+[Cp*W(NO)(CH2CMe3)(CN)(o-C6H4F)]- and Cp*W(NO)(η2-C(O)CH2CMe3)(o-C6H4F), respectively, and the solid-state molecular structure of the latter complex has also been established by a single-crystal X-ray crystallographic analysis.

A calorimetric study has been made of proton ionization in dilute aqueous solution from aliphatic carboxylic acids a t 10, 25, and 40" (13 acids) and at 25" (3 acids). Values of A S " are calculated by combining the resulting AH" values with AGO values obtained from the literature or determined from potentiometric o r calorimetric measurements. The trends in AGO, AH", and ASo are described by an electrostatic model, and deviations from this model are taken as a measure of nonelectrostatic substituent effects for carboxylic acids.his study was undertaken as part2 of a program