@article {328,
	title = {C-H activation of substituted arenes by tungsten alkylidene complexes: Products, selectivity, and mechanism},
	journal = {Organometallics},
	volume = {21},
	number = {7},
	year = {2002},
	note = {ISI Document Delivery No.: 534QZTimes Cited: 18Cited Reference Count: 35},
	month = {Apr},
	pages = {1474-1486},
	type = {Article},
	abstract = {Thermolyses (70 degreesC, 40 h) of Cp*W(NO)(CH2CMe3)(2) (1) and Cp*W(NO)(CH2CMe3)(CH2C6H5) (2) in xylenes, mesitylene, and a,a,(x-trifluorotoluene generate mixtures of the corresponding aryl and/or benzyl products derived from aromatic sp(2) and benzylic sp(3) C-H bond activations of the solvent molecules by the intermediate alkylidene complexes Cp*W(NO)(=CHCMe3)(sigma-CMe4) (sigma-A) and Cp*W(NO)(=CHC6H5)(sigma-CMe4) (sigma-B), respectively. For instance, the thermolysis of 1 in p-xylene affords products resulting from the activation of one and two molecules of p-xylene. The two products derived from the activation of one solvent molecule are Cp*W(NO)(CH2CMe3)(C6H3-2,5-Me-2) (10) and CP*W(NO)(CH2CMe3)(CH2C6H4-4-Me)(2) (11). The other two complexes derived from the activation of two solvent molecules are Cp*W(NO)(CH2C6H4-4-Me)(C6H4-2,5-Me-2) (12) and Cp*W(NO)(CH2C6H4-4Me)(2) (13). The ratio of the four products in the final reaction mixture is 10:11:12:13 = 1.81 +/- 0.09:0.44 +/- 0.05:1.0:0.15 +/- 0.02. All new complexes prepared have been characterized as fully as possible by conventional spectroscopic methods, and the solid-state molecular structures of Cp*W(NO)(CH2C6H5)(C6H3-3,5-Me-2) (7) and Cp*W(NO)(CH2C6H5)(CH2C6H3-3,5-Me-2) (9) have been established by X-ray diffraction methods. Analyses of the product distributions resulting from the various thermolyses indicate that the benzyl products are increasingly favored over the aryl products as the number of methyl substituents on the solvent molecule increases. Likewise, the movement of the methyl groups from the ortho to meta to para position in the xylenes shifts the aryl vs benzyl product distribution toward the benzyl products. With respect to the aryl product regioselectivities, only the least sterically congested aryl regioisomers are formed in the activations of o- and m-xylene, while the meta and para aryl products are formed preferentially for (x,(x,(x-trifluorotoluene. Finally, the distributions obtained from sigma-B are more abundant in the aryl products than are those obtained from a-A. However, despite these general trends, it is also apparent that the origin of the observed product selectivities is highly dependent on the nature of the substrate, the nature of the C-H activation products, and the intermediate alkylidene complex.},
	keywords = {1, 2-RH-ELIMINATION, ARYL, BOND ACTIVATION, CARBON-HYDROGEN, FUNCTIONALIZATION, HYDROCARBON ACTIVATION, METHANE, MOLYBDENUM, ORGANOMETALLIC NITROSYL CHEMISTRY, REVERSIBLE, THERMOLYSIS},
	isbn = {0276-7333},
	url = {<Go to ISI>://000174599400020},
	author = {Adams, C. S. and Legzdins,Peter and Tran, E.}
}
@article {4996,
	title = {Thermal activation of hydrocarbon C-H bonds by tungsten alkylidene complexes},
	journal = {Journal of the American Chemical Society},
	volume = {123},
	number = {4},
	year = {2001},
	note = {ISI Document Delivery No.: 396RTTimes Cited: 32Cited Reference Count: 80},
	month = {Jan},
	pages = {612-624},
	type = {Article},
	abstract = {Thermal activation of Cp*W(NO)(CH2CMe3)(2) (1) in neat hydrocarbon solutions transiently generates the neopentylidene complex, Cp*W(NO)(=CHCMe3) (A), which subsequently activates solvent C-H bonds. For example, the thermolysis of 1 in tetramethylsilane and perdeuteriotetramethylsilane results in the clean formation of Cp*W(NO)(CH2CMe3)(CH2SiMe3) (2) and Cp*W(NO)(CHDCMe3)[CD2Si(CD3)(3)] (2-d(12)), respectively, in virtually quantitative yields. The neopentylidene intermediate A can be trapped by PMe3 to obtain Cp*W(NO)(=CHCMe3)(PMe3) in two isomeric forms (4a-b), and in benzene, 1 cleanly forms the phenyl complex Cp*W(NO)(CH2CMe3)(C6H5) (5). Kinetic and mechanistic studies indicate that the C-H activation chemistry derived from 1 proceeds through two distinct steps, namely, (1) rate-determining intramolecular alpha -H elimination of neopentane from 1 to form A and (2) 1,2-cis addition of a substrate C-H bond across the W=C linkage in A. The thermolysis of 1 in cyclohexane in the presence; of PMe3 yields 4a-b as well as the olefin complex Cp*W(NO)(eta (2)-cyclohexene)(PMe3) (6). In contrast, methylcyclohexane and ethylcyclohexane afford principally the allyl hydride complexes Cp*W(NO)(eta (3)-C7H11)(H) (7a-b) and Cp*W(NO)(eta (3)-C8H13)(H) (8a-b), respectively, under identical experimental conditions. The thermolysis of 1 in toluene affords a surprisingly complex mixture of six products. The two major products are the neopentyl aryl complexes, Cp*W(NO)(CH2CMe3)(C6H4-3-Me) (9a) and Cp*W(NO)(CH2CMe3)(C6H4-4-Me) (9b), in approximately 47 and 33\% yields. Of the other four products, one is the aryl isomer of 9a-b, namely, Cp*W(NO)(CH2CMe3)(C6H4-2-Me) (9c) (similar to1\%). The remaining three products all arise from the incorporation of two molecules of toluene; namely, Cp*W(NO)(CH2C6H5)(C6H4-3-Me) (11a; similar to 12\%), Cp*W(NO)(CH2C6H5)(C6H4-4-Me) (11b; similar to6\%), and Cp*W(NO)(CH2C6H5)(2) (10; similar to1\%). It has been demonstrated that the formation of complexes 10 and 11a-b involves the transient formation of Cp*W(NO)(CH2CMe3)(CH2C6H5) (12), the product of toluene activation at the methyl position, which reductively eliminates neopentane to generate the C-H activating benzylidene complex Cp*W(NO)(=CHC6H5) (B). Consistently, the thermolysis of independently prepared 12 in benzene and benzene-d(6) affords Cp*W(NO)(CH2C6H5)(C6H5) (13) and Cp*W(NO)(CHDC6H5)(C6D5) (13-d(6)), respectively, in addition to free neopentane. Intermediate B can also be trapped by PMe3 to obtain the adducts Cp*W(NO)(=CHC6H5)(PMe3) (14a-b) in two rotameric forms. From their reactions with toluene, it can be deduced that both alkylidene intermediates A and B exhibit a preference for activating the stronger aryl sp(2) C-H bonds. The C-H activating ability of B also encompasses aliphatic substrates as well as it reacts with tetramethylsilane and cyclohexanes in a manner similar to that summarized above for A. All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 4a, 6, 7a, 8a, and 14a have been established by X-ray diffraction methods.},
	keywords = {2-RH-ELIMINATION, INSERTION REACTIONS, LIGANDS, {1},
	isbn = {0002-7863},
	url = {<Go to ISI>://000166650900011},
	author = {Adams, C. S. and Legzdins,Peter and Tran, E.}
}
