Synthesis and reactions of nickel and palladium carbon-bound enolate complexes

Burkhardt, Elizabeth R.; Bergman, Robert G.; Heathcock, Clayton H.

doi:10.1021/om00115a007

Cited by 126 publications

(62 citation statements)

References 1 publication

(3 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The latter compounds are known to exist in the s-bound form c, in equilibrium with the nickel enolate form c' as well as with the p-oxo allyl complex c''. [28] It is important to note that this type of mechanism has been already proposed in the isomerization of allylic alcohols, mediated by ruthenium and rhodium complexes. [29, 11d] This type c intermediate reacts with another molecule of allylic alcohol to regenerate the corresponding alcoholate a and to liberate the free enol e. The latter key intermediate can either tautomerize to the saturated carbonyl compound h or react with the aldehyde to afford the aldol product g. The different lines of evidence in favor of such a mechanistic proposal are the following: * The nickel enolates, which could be considered as alternative intermediates in this reaction, have been clearly excluded.…”

Section: Introductionmentioning

confidence: 87%

“…The nickel enolate derived from ketone 40 was prepared following literature procedure for similar compounds. [28] In the presence of benzaldehyde (with or without MgBr 2 ), no reaction was obtained and only the starting materials were recovered (Scheme 14). [30] This result is in agreement with the literature data indicating that the nickel enolates derived from ketones have a very low reactivity, affording very small amount of the expected aldol products.…”

Section: Introductionmentioning

confidence: 99%

“…[30] This result is in agreement with the literature data indicating that the nickel enolates derived from ketones have a very low reactivity, affording very small amount of the expected aldol products. [28] * The magnesium enolates, which could be also considered as possible intermediates by metal exchange from the nickel enolates, were unambiguously excluded as well.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

From Allylic Alcohols to Aldols through a New Nickel‐Mediated Tandem Reaction: Synthetic and Mechanistic Studies

Cuperly

Petrignet

Crévisy

et al. 2006

Chemistry A European J

View full text Add to dashboard Cite

Nickel hydride type complexes have been successfully developed as catalysts for the tandem isomerization-aldolization reaction of allylic alcohols with aldehydes. Optimization of the reaction conditions has shown that a cocatalyst, such as MgBr2, has a very positive effect on the kinetics of the reaction and in the yields of aldols. Under such optimized conditions {[NiHCl(dppe)] + MgBr(2) at 3-5 mol %)}, this reaction affords the aldols in good to excellent yields. It is a full-atom-economy-type reaction that occurs under mild conditions. Furthermore, it has a broad scope for the allylic alcohols and it is compatible with a wide range of aldehydes, including very bulky derivatives. The reaction is completely regioselective, but it exhibits a low stereoselectivity, except for allylic alcohols with a bulky substituent at the carbinol center. The use of chiral nonracemic catalysts was not successful, affording only racemic compounds. However, it was possible to use asymmetric synthesis for the preparation of optically active aldols. Various mechanistic studies have been performed using, for instance, a deuterated alcohol or a deuterated catalyst. They gave strong support to a mechanism involving first a transition-metal-mediated isomerization of the allylic alcohol into the free enol, followed by the addition of the latter intermediate onto the aldehyde in an "hydroxyl-carbonyl-ene" type reaction. These results confirm that allylic alcohols can be considered as new and useful partners in the development of the aldol reaction.

show abstract

Section: Introductionmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

From Allylic Alcohols to Aldols through a New Nickel‐Mediated Tandem Reaction: Synthetic and Mechanistic Studies

Cuperly

Petrignet

Crévisy

et al. 2006

Chemistry A European J

View full text Add to dashboard Cite

show abstract

“…12 The metal -cage carbon distances (M-C cage ) between 1.95 and 2.01 Å for 4-8 are comparable to the 1.998(9)-2.013(9) Å in [Ni{(C 2 B 10 H 10 ) 2 } 2 ] 2-, 13 17 and to the 2.134(1) Å in Cp*Ni(PPh 3 )(CH 2 COt-Bu). 18 …”

Section: Synthesis and Structurementioning

confidence: 99%

Synthesis, structural characterization, and reactivity of late transition-metal complexes bearing linked cyclopentadienyl–carboranyl ligands

et al. 2012

View full text Add to dashboard Cite

Late transition-metal complexes bearing linked cyclopentadienyl/indenyl-carboranyl ligands were synthesized and their reactivities were examined. Reaction of Li2[Me2C(L)(C2B10H10)] (L = C5H4, C9H6, Me2NCH2CH2C5H3) with MCl2(PPh3)2 in Et2O afforded [h 5 :s-Me2C(C5H4)(C2B10H10)]M(PPh3) (M = Co (4), Ni (5)), [h 5 :s-Me2C(C9H6)(C2B10H10)]M(PPh3) (M = Co (6), Ni (7)), and [h 5 :s-Me2C(Me2NCH2CH2C5H3)(C2B10H10)]Ni(PPh3) (8). Treatment of 4 or 5 with 2,6-dimethylphenylisocyanide, N-heterocyclic carbene (NHC), PCy3, or 1,2-bis(diphenylphosphino)ethane (dppe) gave the corresponding PPh3 displacement complexes [h 5 :s-Me2C(C5H4)(C2B10H10)]M(2,6-Me2C6H3NC) (M = Co (9), Ni (10)), [h 5 :s-Me2C(C5H4)(C2B10H10)]M[1,3-(2,6-i-Pr2C6H3)2C3N2H2] (M = Co (11), Ni (12)), [h 5 :s-Me2C(C5H4)(C2B10H10)]Ni(PCy3) (13), or {[h 5 :s-Me2C(C5H4)(C2B10H10)]Co}2(dppe) (14), respectively. These complexes were characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 4-14 were further confirmed by singlecrystal X-ray analyses.

show abstract

“…[9] We have reported recently the synthesis and structural characteristics [10] of metallacyclic, O-bound nickel enolates 1-3, which are stabilized by the diphosphine iPr 2 PCH 2 CH 2 PiPr 2 (dippe). The metallacyclic nature of these compounds disfavors the acid-base process and, therefore, converts them into suitable candidates for the above purpose.…”

Section: Introductionmentioning

confidence: 99%

Conjugate Additions of Cyclic Oxygen‐Bound Nickel Enolates to α,β‐Unsaturated Ketones

Maya¹,

Cámpora²,

Carmona³

et al. 2007

Chemistry A European J

View full text Add to dashboard Cite

The reaction of nickel enolates displaying a metallacyclic structure with the alpha,beta-unsaturated ketones methyl vinyl ketone (MVK) or methyl propenyl ketone (MPK) takes place in two stages, affording initially bicyclic adducts, which subsequently isomerize to the corresponding open-chain products. The former are generated with high stereoselectivity and can be considered as the products of the [2+4] cycloaddition of the enolate to the enone. The ring opening process involves a prototropic rearrangement that can be catalyzed by water. In the case of the reaction of the parent nickel enolate complex 1 (which displays an unsubstituted Ni-O=C(R)CH2 arrangement) with MVK, a double-addition process has been observed, consisting of two successive cycloaddition/isomerization reactions. The carbonylation of the different cyclic and noncyclic products affords the corresponding lactones that retain the stereochemistry of the organometallic precursors. This methodology allowed trapping the primary product of the reaction of 1 with MPK as the corresponding organic lactone, demonstrating that the cycloaddition process takes place with exo selectivity. DFT modeling of the latter reaction provides further support for a quasi-concerted cycloaddition mechanism, displaying a nonsymmetric transition state in which the C-C and the C-O bond are formed in an asynchronous manner.

show abstract

Synthesis and reactions of nickel and palladium carbon-bound enolate complexes

Cited by 126 publications

References 1 publication

From Allylic Alcohols to Aldols through a New Nickel‐Mediated Tandem Reaction: Synthetic and Mechanistic Studies

From Allylic Alcohols to Aldols through a New Nickel‐Mediated Tandem Reaction: Synthetic and Mechanistic Studies

Synthesis, structural characterization, and reactivity of late transition-metal complexes bearing linked cyclopentadienyl–carboranyl ligands

Conjugate Additions of Cyclic Oxygen‐Bound Nickel Enolates to α,β‐Unsaturated Ketones

Contact Info

Product

Resources

About