Kinetics and thermodynamics of intra- and intermolecular rearrangement in binaphtholate complexes of titanium(IV)

Boyle, Timothy J.; Barnes, Denise L.; Heppert, Joseph A.; Morales, Luis B.; Takusagawa, Fusao; Connolly, J.C.

doi:10.1021/om00039a017

Cited by 82 publications

(90 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…B and B), whereas complex II, recognized as a 2:1 dinuclear Ti 2 L*(O i Pr) 5 complex, was dominant in the presence of 15 eq of Ti(O i Pr) 4 (Figs. C and C) because of the equilibrium shifting from I to II driven by excess Ti(O i Pr) 4 , which was also observed previously for 1,1′‐bi‐2‐naphthol‐based ligands and Sharpless' tartrate esters . The aromatic proton signals and aromatic ipsocarbon signals for both species I and II were shifted to downfield with respect to free ligand 8 as a consequence of titanium complexation by oxygen or nitrogen donor ligands .…”

Section: Resultssupporting

confidence: 78%

The Syntheses of new Camphorsulfonylated Ligands Derived from 2‐Amino‐2′‐Hydroxy‐1,1′‐Binaphthyl and Their Enantioselectivities in the Addition of Dialkylzinc Reagents to Aldehydes

et al. 2012

View full text Add to dashboard Cite

A series of new camphorsulfonylated ligands derived from chiral 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) and (+)-camphorsulfonic acid were synthesized by a short and simple synthetic sequence, and their enantioselective catalytic activities were assessed in the nucleophilic addition reaction of dialkylzinc reagents to aldehydes in the presence of titanium tetraisopropoxide. The most efficient ligand, N-hydroxycamphorsulfonylated (S)-NOBIN, gave (S)-addition products with good yields and up to 87% of ee value. The (1)H nuclear magnetic resonance (NMR) and (13)C NMR results of the titanium titration experiments on this ligand indicate that the most likely catalytic reactive species involved in this catalytic asymmetric addition is a bimetallic titanium complex. A possible catalytic reaction mechanism is proposed.

show abstract

Section: Resultssupporting

confidence: 78%

The Syntheses of new Camphorsulfonylated Ligands Derived from 2‐Amino‐2′‐Hydroxy‐1,1′‐Binaphthyl and Their Enantioselectivities in the Addition of Dialkylzinc Reagents to Aldehydes

et al. 2012

View full text Add to dashboard Cite

show abstract

“…20 The lability of such complexes can be traced down to titanium(IV) oxophylicity, itself responsible of the tendency of titanium complexes to form homo or hetero aggregates, as well as of titanium reactivity towards oxygen donors such as water or alcohols, 21,22 not underscoring the capacity of titanium complexes to undergo inter or intramolecular rearrangements. 23 Accordingly, among the additional operational variables which need to be controlled at the optimization step of a titanium(IV)-catalyzed procedure, stoichiometry is a major factor to be adjusted, 24,25 as well as the presence of poisons or activators, 26,27 either chiral, 28 or achiral. 29 Moreover, other apparently trivial matters such as the order of addition of reactants, 30 the aging of the precatalytic mixture, 31 as well as other procedural issues such as the presence or absence of molecular sieves, 32 or even their drying procedure, 33 quite often affect the efficiency of titanium(IV)-catalyzed enantioselective chemistry.…”

Section: Introductionmentioning

confidence: 99%

“…These studies have in fact revealed a complex equilibrium network involving mononuclear M and dinuclear D (dimers and mixed dimers resulting from aggregation phenomena) species, each of which could be responsible for catalysis. In particular, Heppert and co-workers using X-ray crystallography, cryoscopy and NMR spectroscopy, 23 reported that a 1:1 mixture of 3,3'-disubstituted Binols and Ti(OiPr) 4 gives rise, after removal of iPrOH by evaporation, to either monomeric, mononuclear M M complexes (R 2 BINOLate)Ti(OiPr) 2 (when bulky R substituents such as SiMe 2 -t-Bu are seated at C 3 and C 3' ), or to dinuclear dimers D D 4 were found to be the major species (at low temperature) in equilibrium with C 2 symmetric, dinuclear, open mixed dimers D oMD (R 2 BINOLate)Ti 2 (OiPr) 6 , when 3,3'-disubstituted Binols reacted with Ti(OiPr) 4 in a 1:2 ratio followed by removal of iPrOH. Recently, Walsh and coworkers studied unsubstituted Binol:Ti(OiPr) 4 mixtures in a systematic manner, i.e.…”

Section: Introductionmentioning

confidence: 99%

Curtin–Hammett versus non-Curtin–Hammett frameworks in optimizing the enantioselective binolam/titanium(IV)-catalyzed cyanobenzoylation of aldehydes: Part 2

Saá

Baeza

Nájera

et al. 2011

Tetrahedron: Asymmetry

View full text Add to dashboard Cite

Graphical AbstractTo create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered. Leave this area blank for abstract info. Stereochemistry AbstractTo create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered. You may insert more abstracts by copying this box or by using the menu option to insert a stereochemistry abstract.Authors' names here --- * Corresponding author for additional computational details (J.M.S.) Tel.: +34-971173262; fax: +34-971173426; e-mail: jmsaa@uib.es IntroductionEvidences have been provided in support of the involvement of an LABB (Lewis Acid-Brønsted Base) cooperative, 1 dual action mechanism for "Binolam-AlCl"-catalyzed enantioselective cyanation reactions, the overall reaction taking place through an indirect route involving hydrocyanation followed by Ofunctionalization. In these reactions, according to the reported data, the aluminium atom of the in situ-generated catalyst plays the role of a Lewis acid (LA), while the N atom acts as a Brønsted base (BB) in catching the available HCN in the mixture (either present in the commercial samples, or being generated by induced hydrolysis of the cyanide reagent employed induced by trace amounts of water contained in the molecular sieves, or otherwise).2,3,4,5 Unfortunately, such a detailed knowledge of the mechanism of action of the analogous "Binolam-TiX 2 " catalysts is lacking, among other reasons because the structure of the titanium(IV) complexes initially formed (precatalysts), as well as that of the actual catalysts, is not well-known, 6 in spite of recent advances in the field. 7 In this work we will try to show that our "Binolam-TiX 2 " catalyzed cyanobenzoylations are particularly difficult to optimize because these reactions do not fit within the usual Curtin-Hammett (C-H) construction. 8 More on the contrary, as it will be shown below, "Binolam-TiX 2 " catalyzed cyanobenzoylations rather behave as a non-Curtin-Hammett framework. So, let us shed light upon the C-H principle prior to analyze and discuss the results.The basic Curtin-Hammett (C-H)/Winstein-Holness (W-H) kinetic system illustrated in Scheme 1 describes the relationship between two equilibrating molecules (or two conformations of a single molecule) and their reactivity.9 For our present purposes we can think of A and B as equilibrating catalysts involved in an asymmetric catalytic system. A R T I C L E I N F O ABSTRACT Article history: Received Received in revised form Accepted Available onlineExtensive experimental and computational studies have been carried out upon the enantioselective titanium(IV)-catalyzed cyanobenzoylation of aldehydes using 1:n Binolam:Ti(OiPr) 4 mixtures as precatalysts, with the purpose of identifying the key mechanistic aspects governing enantioselectivity. HCN and isopropyl benzoate were detected in the reacting mixtures. This, as well as the reaction response to the presence of an exog...

show abstract

“…[17] In our case, two observations call for the existence of an oligomeric titanium complex as well. An ESI(+) MS measurement of a mixture of Ti(OtBu) 4 , (R)-binol, and aniline (1:2.2:10), which had been prepared in CH 2 Cl 2 according to the general synthetic protocol, displayed a tetranuclear titanium cluster of the formal composition [Ti 4 (OtBu) 3 ((R)-binol) 6 ] (m/z = 2115) as a major component.…”

Section: Methodsmentioning

confidence: 55%

Titanium Binolate Catalyzed Aminolysis of meso Aziridines: A Highly Enantioselective and Direct Access to 1,2‐Diamines

2009

View full text Add to dashboard Cite

show abstract

Kinetics and thermodynamics of intra- and intermolecular rearrangement in binaphtholate complexes of titanium(IV)

Cited by 82 publications

References 2 publications

The Syntheses of new Camphorsulfonylated Ligands Derived from 2‐Amino‐2′‐Hydroxy‐1,1′‐Binaphthyl and Their Enantioselectivities in the Addition of Dialkylzinc Reagents to Aldehydes

The Syntheses of new Camphorsulfonylated Ligands Derived from 2‐Amino‐2′‐Hydroxy‐1,1′‐Binaphthyl and Their Enantioselectivities in the Addition of Dialkylzinc Reagents to Aldehydes

Curtin–Hammett versus non-Curtin–Hammett frameworks in optimizing the enantioselective binolam/titanium(IV)-catalyzed cyanobenzoylation of aldehydes: Part 2

Titanium Binolate Catalyzed Aminolysis of meso Aziridines: A Highly Enantioselective and Direct Access to 1,2‐Diamines

Contact Info

Product

Resources

About