Organometallic conformational equilibriums. X. Steric factors and their mechanistic implications in .pi.-allyl(amine)chloropalladium(II) complexes

Faller, J. W.; Thomsen, Maren; Mattina, Mary Jane Incorvia

doi:10.1021/ja00740a011

Cited by 146 publications

(42 citation statements)

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“…Pregosin and co-workers have investigated the dynamics of some 1,3-substituted allylpalladium complexes with (P, S) donors where the sulfur is a within a thioether linkage [25]. In that case, the allyl substituents effectively prevent the syn-anti exchange observed here, but do not necessarily prevent cis-trans exchange [26]. Of particular relevance is our previously published analysis of rearrangements of the BINAP(S) allyl analogue, 2c [16].…”

Section: [Pd(g 3 -C 3 H 5 )(Pp=s)][sbf 6 ] Complexes (2)mentioning

confidence: 81%

Hemilability and nonrigidity in metal complexes of bidentate P,PS donor ligands

Faller

Milheiro

Parr

2008

Journal of Organometallic Chemistry

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Section: [Pd(g 3 -C 3 H 5 )(Pp=s)][sbf 6 ] Complexes (2)mentioning

confidence: 81%

Hemilability and nonrigidity in metal complexes of bidentate P,PS donor ligands

Faller

Milheiro

Parr

2008

Journal of Organometallic Chemistry

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“…Intermolecular P-ligand exchange has been seen in many cases. Intermolecular exchange of both bidentate and monodentate ligands has also been indicated in analogous cases[17] [29][30]. Since one would anticipate differential rates for the breaking of PdÀP and PdÀN bonds in a hemilabile ligand, we believe that a three-coordinate intermediate is the most likely type of intermediate to be involved in the apparent rotation.…”

mentioning

confidence: 76%

Rearrangements in Allylpalladium Complexes with Hemilabile Chelating Ligands

Faller¹,

Stokes‐Huby²,

Albrizzio³

2001

HCA

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In memoriam Professor Luigi M. VenanziIn addition to h 3 -to h 1 -allyl rearrangement, h 2 -to h 1 -chelating-ligand rearrangements can affect the dynamic properties in allylpalladium complexes containing hemilabile ligands. These rearrangements have the potential of altering stereochemistry, which can ultimately affect the stereochemistry and regiochemistry of reactions upon the allyl group, e.g., allylic alkylation. Apparent rotation of an h 3 -allyl in four-coordinate Pd IIcomplexes can be the result of ligand exchange or intramolecular processes. NMR Studies indicate that the effects of h 2 -to h 1 -chelating-ligand stereochemistry and rearrangements may be hidden or subtle, and both intraand intermolecular processes may be important.Introduction. ± The synthetic utility of transition-metal-catalyzed alkylations involving allyl intermediates has been shown to be effective for the regio-and stereocontrolled formation of CÀC bonds over the past thirty years [1] [2]. Asymmetric variants have been developed more recently [3]. Early work focused on the use of bisphosphane ligands, such as chiraphos [3], where C 2 -symmetric ligands were considered to have special advantages [4]. More recently, however, some of the most impressive enantioselectivities have been obtained with asymmetric P,N ligands, e.g., phosphinoaryloxazolines [5 ± 13]. In general, the complexes show dynamic NMR spectra, which indicate that the complexes are rearranging rapidly. The stereodynamics in these systems can be important in enantioselective allylic alkylations and has been reviewed recently [14], but many of the principles were established previously [3] [15 ± 19]. A number of rearrangements are possible that can affect the geometry. In earlier work, there was a tendency to overemphasize the importance of a C 2 -symmetric ligand for obtaining high levels of asymmetric induction. However, the excellent levels of enantioselectivity obtained with P,N ligands has demonstrated that asymmetric bidentate ligands can be as effective as, if not superior to, C 2 -symmetric ligands [5 ± 13].With a C 2 -symmetric ligand, such as chiraphos [3], a rotation of the allyl group or the ligand will yield an equivalent structure; hence, the presence or absence of a rotation mechanism may be irrelevant. With a non-C 2 -symmetric ligand, however, a different isomer will be produced and this has the potential to have significant consequences with regard to the resulting stereochemistry of the allyl product (see Fig. 1). Although, regiochemistry has often been determined on the basis of substitution patterns of the termini of the allyl, Hayashi et al. have recently shown that the regiochemistry of nucleophilic attack in some cases can be determined by differences in trans influence of the phosphine and the other ligand [20].

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“…Thus, one can expect an increase of 4-12 kJ mol −1 in G ‡ per methyl substituent. 287 Two effects tend to produce a G ‡ for σ -bond formation at the different termini of ≈20 kJ mol −1 in 1,1-dimethyl-substituted allyls: (1) the stability order of 1 • > 2 • > 3 • M-C bond and (2) the decreased stability of π -M-C bonds on substitution. Hence, one would generally expect the ease of formation of the σ -bonded intermediate at the unsubstituted terminus to increase in the order 1,1-dimethylallyl < 1-methylallyl < allyl.…”

Section: Allyl Rearrangementsmentioning

confidence: 99%

Stereochemical Nonrigidity of Organometallic Complexes

Faller

2005

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Compounds that undergo intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges are described as stereochemically nonrigid. Analysis of 1D and 2D NMR spectra as a function of temperature often allow the rates, as well as the mechanisms of interconversion of conformers or isomers, to be determined. Examples were selected to illustrate the importance of stereochemical nonrigidity in reactivity and the potential for affecting stereochemistry in the products of reactions.

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Organometallic conformational equilibriums. X. Steric factors and their mechanistic implications in .pi.-allyl(amine)chloropalladium(II) complexes

Cited by 146 publications

References 0 publications

Hemilability and nonrigidity in metal complexes of bidentate P,PS donor ligands

Hemilability and nonrigidity in metal complexes of bidentate P,PS donor ligands

Rearrangements in Allylpalladium Complexes with Hemilabile Chelating Ligands

Stereochemical Nonrigidity of Organometallic Complexes

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