Synthesis and reactivity of cyclopentadienyl chloro, imido and alkylidene tungsten (VI) complexes

Mata, F. Javier de la; Gómez, Jesús Gómez; Royo, Pascual

doi:10.1016/s0022-328x(98)00639-1

Cited by 12 publications

(5 citation statements)

References 29 publications

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“…The reactions reported here are (fortunately) photochemical, which allows tungstacycles to be prepared and isolated in the dark and mechanistic studies to be carried out, usually in the absence of any olefins and metathesis reactions. Sensitivity of d 0 transition metal alkyls to light has been noted for several decades. − Light was found to accelerate the background (dark) α hydrogen abstraction in the first studies of α abstraction reactions in 14e SP CpTa(CH 2 – t -Bu) 2 Cl 2 and Cp*Ta(CH 2 – t -Bu) 2 Cl 2 complexes . α Hydrogen abstraction reactions that give d 0 alkylidene complexes from complexes that contain two or more alkyls usually do not require light, but some do require light (e.g., formation of Re(NAr) 2 (CH 2 SiMe 3 )(CHSiMe 3 ) from Re(NAr) 2 (CH 2 SiMe 3 ) 3 ) .…”

Section: Discussionmentioning

confidence: 99%

Syntheses of β,β′-Disubstituted Tungstacyclopentanes from Terminal Olefins and Their Conversions to Alkylidenes

et al. 2023

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Disubstituted tungstacyclopentane complexes have been prepared through addition of propylene, 1-heptene, 1,6heptadiene, 1,7-octadiene, or diallylaniline to unsubstituted tungstacyclopentane complexes, W(NR)(OR′) 2 (C 4 H 8 ); tungstabicycloalkanes are formed from the dienes. Several tungstacyclopentanes have been prepared from W(NR)(OR′) 2 Cl 2 complexes through alkylation and reduction with diethylzinc in the presence of the olefin. The synthesized complexes include those in which NR = NPh, NCPh 3 , or N-2,6-i-Pr 2 C 6 H 3 and OR′ = OSiPh 3 or OCMe 2 (CF 3 ). The tungstacyclopentane complexes are stable in the dark, but upon exposure to violet (405 λ max ) or blue (445 nm λ max ) LED light, they form alkylidenes, largely through α hydrogen abstraction; ring-contraction to give a tungstacyclobutane is a minor reaction pathway only for the β,β′-dimethyltungstacyclopentane. Preliminary DFT calculations suggest that one electron is promoted from the HOMO (composed of the two W−C σ bonds) into an empty d xy orbital to give what could be viewed as a W(V)CH 2 CHRCHRCH 2 • complex. Abstraction of an H α by the radical chain end yields an alkylidene, while abstraction of an H γ leads to ring-contraction to give a tungstacyclobutane. The rates of the photochemical reactions for the β,β′-disubstituted tungstacyclopentanes do not vary dramatically with solvent (toluene, THF, CDCl 3 ). Twelve compounds were characterized through single crystal X-ray diffraction studies.

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Section: Discussionmentioning

confidence: 99%

Syntheses of β,β′-Disubstituted Tungstacyclopentanes from Terminal Olefins and Their Conversions to Alkylidenes

et al. 2023

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“…Tungsten Cp* benzylidene and trimethylsilylmethylene complexes could be prepared as shown in eq 70. 161 Photolysis of isolated WCp*(NPh)Me 3 yielded unstable WCp*(NPh)(CH 2 )Me that could be identified only in solution (11.45 and 9.49 ppm). Other Cp* tungsten imidotrialkyl complexes could be prepared readily from the corresponding trichlorides, even when the alkyl contained β protons (e.g., Et or Pr).…”

Section: Tungstenmentioning

confidence: 99%

“…Tungsten Cp* benzylidene and trimethylsilylmethylene complexes could be prepared as shown in eq 70 . Photolysis of isolated WCp*(NPh)Me 3 yielded unstable WCp*(NPh)(CH 2 )Me that could be identified only in solution (11.45 and 9.49 ppm).…”

Section: 33 Tungstenmentioning

confidence: 99%

High Oxidation State Multiple Metal−Carbon Bonds

2001

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Richard R. Schrock received his Ph.D. degree in inorganic chemistry from Harvard in 1971 under the tutelage of John Osborn. After spending 1 year as an NSF postdoctoral fellow at Cambridge University working for Lord Jack Lewis and 3 years at the Central Research and Development Department of E. I. duPont de Nemours and Company, he moved to Massachusetts Institute of Technology in 1975. He became full professor in 1980 and the Frederick G. Keyes Professor of Chemistry in 1989. His interests include the inorganic and organometallic chemistry of high oxidation state, early metal complexes (especially those that contain an alkylidene or alkylidyne ligand), catalysis and mechanisms, the chemistry of high oxidation state dinitrogen and related complexes, and the controlled polymerization of olefins and acetylenes. He has received the ACS Award in Organometallic Chemistry (1985), the Harrison Howe Award of the Rochester ACS section (1990), the ACS Award in Inorganic Chemistry (1996), and an ACS Cope Scholar Award (2001). He has been elected to the American Academy of Arts and Sciences and the National Academy of Sciences. He was Associate Editor of Organometallics for 8 years, has published more than 370 research papers, and has supervised over 100 Ph.D. students and postdocs. (Photograph is reprinted with permission from Richard R. Schrock and L. Barry Hetherington.

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“…Photolysis has been known for some time to promote α hydrogen abstraction and other types of CH cleavage reactions in the main group and early transition metal d 0 alkyl chemistry, especially in crowded five-coordinate complexes, and, in alkylidene chemistry, to establish equilibrium mixtures of syn and anti alkylidene isomers. − In some of the earliest studies of α hydrogen abstraction in Cp tantalum neopentyl complexes to give neopentylidene complexes, the sensitivity of neopentyl complexes such as CpTa(CH 2 - t -Bu) 2 Br 2 toward light, especially sunlight, was noted . It was suggested that deprotonation of a neighboring alkyl in the α position by a nucleophilic alkyl and M–C bond cleavage followed by an α H atom abstraction from a neighboring alkyl were likely to be essentially indistinguishable.…”

Section: Discussionmentioning

confidence: 99%

Tungstacyclopentane Ring Contraction Yields Olefin Metathesis Catalysts

et al. 2022

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Exposure of a solution of the square pyramidal tungstacyclopentane complex W(NAr)(OSiPh3)2(C4H8) (Ar = 2,6-i-Pr2C6H3) to ethylene at 22 °C in ambient (fluorescent) light slowly leads to the formation of propylene and the square pyramidal tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). No reaction takes place in the dark, but the reaction is >90% complete in ∼15 min under blue LED light (∼450 nm λmax). The intermediates are proposed to be (first) an α methyl tungstacyclobutane complex (W(NAr)(OSiPh3)2(αMeC3H5)), and then from it, a β methyl version. The TBP versions of each can lose propylene and form a methylene complex, and in the presence of ethylene, the unsubstituted tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). The W–Cα bond in an unobservable TBP W(NAr)(OSiPh3)2(C4H8) isomer in which the C4H8 ring is equatorial is proposed to be cleaved homolytically by light. A hydrogen atom moves or is moved from C3 to the terminal C4 carbon in the butyl chain as the bond between W and C3 forms to give the TBP α methyl tungstacyclobutane complex. Essentially, the same behavior is observed for W(NCPh3)(OSiPh3)2(C4H8) as for W(NAr)(OSiPh3)2(C4H8), except that the rate of consumption of W(NCPh3)(OSiPh3)2(C4H8) is about half that of W(NAr)(OSiPh3)2(C4H8). In this case, an α methyl-substituted tungstacyclobutane intermediate is observed, and the overall rate of formation of W(NCPh3)(OSiPh3)2(C3H6) and propylene from W(NCPh3)(OSiPh3)2(C4H8) is ∼20 times slower than in the NAr system. These results constitute the first experimentally documented examples of forming a metallacyclobutane ring from a metallacyclopentane ring (ring contraction) and establish how metathesis-active methylene and metallacyclobutane complexes can be formed and reformed in the presence of ethylene. They also raise the possibility that ambient light could play a role in some metathesis reactions that involve ethylene and tungsten-based imido alkylidene olefin metathesis catalysts, if not others.

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Synthesis and reactivity of cyclopentadienyl chloro, imido and alkylidene tungsten (VI) complexes

Cited by 12 publications

References 29 publications

Syntheses of β,β′-Disubstituted Tungstacyclopentanes from Terminal Olefins and Their Conversions to Alkylidenes

Syntheses of β,β′-Disubstituted Tungstacyclopentanes from Terminal Olefins and Their Conversions to Alkylidenes

High Oxidation State Multiple Metal−Carbon Bonds

Tungstacyclopentane Ring Contraction Yields Olefin Metathesis Catalysts

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