Cyclobutanone formation via in situ generated vinyl ketene complexes of chromium

Wulff, William D.; Kaesler, Ralph W.

doi:10.1021/om00127a028

Cited by 48 publications

(15 citation statements)

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“…Futhermore, the synthesis of the complexes 5 − 7 , which can be considered to be the acylimino analogs of the acyl intermediate in the formation of 4 , favors the first mechanism (Scheme ). Results reported by Van der Heiden and co-workers working with systems similar to ours also oppose this alternative mechanism 10b. When they reacted CO with the titanium neopentylidene complex [Ti(Cp)(CH- t- Bu)(PMe 2 CH 2 CO)(CMe 2 - o -C 6 H 4 CMe 2 )], which contains a bulky phosphinoalkoxide ancillary ligand, they obtained a mixture of two isomeric ketene complexes in which the CO bond of the carbonyl group is bonded in a “edge-on” fashion to the titanium center.…”

Section: Resultssupporting

confidence: 83%

“…This mechanism involves formation of a methylene intermediate via rearrangement of the metallacycle of 1 into an “alkylidene/olefin” intermediate and subsequent loss of the coordinated ethene as described earlier in the mechanism for the formation of the substituted tantalacyclobutanes 2 and 3 . A ketene intermediate is then formed through a reaction of this methylene intermediate with CO 10a…”

Section: Resultsmentioning

confidence: 99%

“…However, attempted reaction of this ketene complex with ethene does not give a monosubstituted oxytitanacyclopropane complex as would be expected when a mechanism similar to that shown in Scheme is operative. Instead they found that insertion of CO into the Ti-C bond takes place to afford a bis(alkoxide) complex which contains a 1-oxa-titanacyclopentane unit 10b 5 Postulated Mechanism for the Reaction of Tantalacyclobutane Complexes with CO via a Ketene Intermediate (*Ta = {Ta(CNN)(O- t- Bu) 2 }) a a Reaction conditions: i , −C 2 H 4 ; ii , +C 2 H 4 ; iii , +CO; iv , +C 2 H 4 . …”

Section: Resultsmentioning

confidence: 99%

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Tantalacyclobutane Complexes Containing the Potentially C,N,N‘-Coordinating Ligand [C₆H₄(CH₂N(Me)CH₂CH₂NMe₂)-2]^- (CNN) and Their Reactivity with Carbon Monoxide and tert-Butyl Isocyanide. X-ray Molecular Structures of [Ta{CH₂CH(Me)CH₂-1,3}(CNN)(O-t-Bu)₂], [Ta{CH₂CH(Ph)CH₂-1,3}(CNN)(O-t-Bu)₂], [Ta{C(O)((CH₂)₃-1,3)}(CN

et al. 1997

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From the reactions of the unsubstituted tantalacyclobutane complex [Ta{(CH 2 ) 3 -1,3}(CNN)-(O-t-Bu) 2 ] (CNN ) [C 6 H 4 (CH 2 N(Me)CH 2 CH 2 NMe 2 )-2] -) (1) with propene and styrene have been isolated in good yields the substituted tantalacyclobutane complexes [Ta{CH 2 CH(Me)-CH 2 -1,3}(CNN)(O-t-Bu) 2 ] (2) and [Ta{CH 2 CH(Ph)CH 2 -1,3}(CNN)(O-t-Bu) 2 ] (3), respectively. The X-ray molecular structures of 2 and 3 show them to be seven-coordinate pentagonal bipyramidal species in which the meridional ligation comprises C,N,N′-bonding of the aryldiamine ligand CNN and σ-bonding of two carbons of the metallacycle; the two alkoxide groups occupy the apical positions. The organyl substituent of the metallacycle is positioned on the -carbon. Complexes 2 and 3 can both be converted back into 1 by reacting them in Et 2 O with ethene. The reaction of 1 with carbon monoxide yields the oxytantalacyclopropane complex [Ta{C(O)((CH 2 ) 3 -1,3)}(CNN)(O-t-Bu) 2 ] (4), which has been isolated as an air-stable white solid in 59% yield. The X-ray molecular structure of 4 reveals that the carbon and oxygen atoms of the CdO function are ligated in the meridional plane with further η 3 -C,N,N′-ligation of CNN and the two alkoxides as found in 2 and 3. Reaction of the tantalacyclobutane complexes 2-4 with 1 equiv of t-BuNC affords the 1:1 insertion products [Ta{C(dN-t-Bu)-CH 2 CH(R)CH 2 -1,4}(CNN)(O-t-Bu) 2 ] (R ) H (5), Me (6), and Ph (7), respectively). Complexes 5 and 7 have been isolated as yellow solids (yields: 5, 62%; 7, 50%), while 6 has been prepared and characterized in situ. 1 H and 13 C NMR spectroscopy of 6 and 7 indicate for each complex the presence of two isomers in solution. The X-ray molecular structure of 7 shows η 2 -C,Nbonding of the CNN ligand through the aryl C ipso atom and the N(Me) donor atom and, most importantly, the presence of two tantalacyclic rings of different sizes that have a common Ta-C bond. The smaller three-membered ring comprises the metal center with the nitrogen and the R-carbon atom of the η 2 -bonded iminoacyl fragment, while the larger five-membered ring is a metallacylopentane system comprising the metal center and four carbon atoms.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Tantalacyclobutane Complexes Containing the Potentially C,N,N‘-Coordinating Ligand [C₆H₄(CH₂N(Me)CH₂CH₂NMe₂)-2]^- (CNN) and Their Reactivity with Carbon Monoxide and tert-Butyl Isocyanide. X-ray Molecular Structures of [Ta{CH₂CH(Me)CH₂-1,3}(CNN)(O-t-Bu)₂], [Ta{CH₂CH(Ph)CH₂-1,3}(CNN)(O-t-Bu)₂], [Ta{C(O)((CH₂)₃-1,3)}(CN

et al. 1997

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“…Alternatively, for chromium carbene complex 1e, Katz and Yang [36] have pointed out that cyclopropanes 74 can also be favoured by performing the reaction with the metal-carbene complex adsorbed on silica gel, while cyclobutanones 72 are the main products if the reaction is carried out in acetonitrile [36,37]; those bicyclo[3. 2.0]heptanones 72, which arise via intramolecular [2 + 2] cycloaddition, are prepared with high diastereoinduction when chiral enynes are used, with yields between 33% and 73%, which enhances their synthetic potential [38].…”

Section: Reactions With Ax-enynesmentioning

confidence: 99%

Group 6 Fischer carbene complexes: “chemical multitalents” for multi-component reactions

Barluenga

Fernández‐Rodríguez

Aguilar

2005

Journal of Organometallic Chemistry

125

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“…The chemistry of Fischer carbene complexes relevant to organic synthesis is dominated by reactions of chromium complexes . In comparison, use of tungsten complexes has been rather limited. 1d, The reason ascribed to this evident lack of popularity of the latter is the relatively high W−C bond strength, ,5g which does not permit ready decarbonylation.…”

Section: Introductionmentioning

confidence: 99%

Rearrangement of Fischer Carbene Complexes to Ketones: Stereochemistry and Mechanism

et al. 1996

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Fischer carbene complexes of general structure (CO)5MC(Ar)(OCHRAr‘), where M = Cr or W and R = H or Me, rearrange to ketones, ArC(O)CHRAr‘Cr(CO)3 or ArC(O)CHRAr‘ (for M = W), on heating. For M = W and Ar‘ = 2-furyl, the rearrangement is the most facile. A probable mechanism is proposed. Rearrangement also occurs with (CO)5WC(4-Me-C6H4)(OCH2CHCMe2) and (CO)5WC(Ph)(OCH2CHCHPh); the ketones do not result from a [3,3]-sigmatropic shift alone. Excellent diastereoselectivity is observed with (CO)5CrC(Ph){OCH(Me)(C6H4-2-OMe)}; that the product obtained is a result of kinetic control is established by an equilibration experiment. The structure of this product was determined by X-ray crystallography.

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Cyclobutanone formation via in situ generated vinyl ketene complexes of chromium

Cited by 48 publications

References 2 publications

Group 6 Fischer carbene complexes: “chemical multitalents” for multi-component reactions

Rearrangement of Fischer Carbene Complexes to Ketones: Stereochemistry and Mechanism

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