21 research outputs found
A One-Pot Diastereoselective Self Assembly of CāStereogenic Copper(I) Diphosphine Clusters
C-chirogenic
diphosphine-based clusters with 8-membered āchairlikeā
Cu<sub>4</sub>Cl<sub>4</sub>L<sub>2</sub> and 12-membered ādrumlikeā
Cu<sub>6</sub>Cl<sub>6</sub>L<sub>3</sub> (L = diphosphine) frameworks
were prepared in one-pot syntheses from chiral diphosphines, which
were generated in situ via the double hydrophosphination reaction
in excellent enantio- and diastereoselectivity. Excellent control
over the final molecular architecture of the cluster (drum vs chair)
could be achieved by the judicious selection of the source of the
copper atoms employed in the synthetic protocol. Each cluster was
characterized by single-crystal X-ray crystallography, <sup>1</sup>H, <sup>13</sup>C, and <sup>31</sup>PĀ{<sup>1</sup>H} NMR spectroscopy.
The synthesized clusters were found to exhibit catalytic activity
in the hydroboration reaction of Ī±,Ī²-unsaturated enones
with excellent yields albeit with low enantioselectivity
Palladacycle-Catalyzed Asymmetric Hydrophosphination of Enones for Synthesis of C*- and P*-Chiral Tertiary Phosphines
A highly reactive and stereoselective hydrophosphination
of enones
catalyzed by palladacycles for the synthesis of C*- and P*-chiral
tertiary phosphines has been developed. When Ph<sub>2</sub>PH was
employed as the hydrophosphinating reagent, a series of C*-chiral
tertiary phosphines were synthesized (C*āP bond formation)
in high yields with excellent enantioselectivities, and a single recrystallization
provides access to their enantiomerically pure forms. When racemic
secondary phosphines <i>rac</i>-R<sup>3</sup>(R<sup>4</sup>)ĀPH were utilized, a series of tertiary phosphines containing both
C*- and P*-chiral centers were generated (C*āP* bond formation)
in high yields with good diastereo- and enantioselectivities. The
stereoelectronic factors involved in the catalytic cycle have been
revealed
Asymmetric Construction of a Ferrocenyl Phosphapalladacycle from Achiral Enones and a Demonstration of Its Catalytic Potential
A new
approach toward ferrocenyl phosphapalladacycle construction from achiral
enones via asymmetric hydrophosphination and subsequent diastereoselective
CāH activation is described. Its catalytic efficacy toward
CāC bond formation is subsequently illustrated
Asymmetric Construction of a Ferrocenyl Phosphapalladacycle from Achiral Enones and a Demonstration of Its Catalytic Potential
A new
approach toward ferrocenyl phosphapalladacycle construction from achiral
enones via asymmetric hydrophosphination and subsequent diastereoselective
CāH activation is described. Its catalytic efficacy toward
CāC bond formation is subsequently illustrated
Metal Effects on the Asymmetric Cycloaddition Reaction between 3,4-Dimethyl-1-phenylphosphole and Sulfoxide
The
orthometalated [1-(dimethylamino)Āethyl]Ānaphthalene platinumĀ(II) complex
has been used successfully to promote the asymmetric cycloaddition
reaction between 3,4-dimethyl-1-phenylphosphole and sulfoxide in high
selectivity. The <i>exo</i>-cycloadduct coordinated to the
platinum template as bidentate chelates via their phosphorus and sulfur
atoms. The dichloro platinum complexes could be crystallized and were
stable in the solid state as well as in solution. Optically pure PāS
bidentate ligands could be liberated from these dichloro complexes
by treatment with aqueous potassium cyanide. The study also highlights
the difference in reactivity and mode of substrate activation between
an earlier study involving a Pd analogue of the template and the current
results
Asymmetric Synthesis of Enaminophosphines via Palladacycle-Catalyzed Addition of Ph<sub>2</sub>PH to Ī±,Ī²-Unsaturated Imines
A highly reactive, chemo- and enantioselective addition
of diphenylphosphine to Ī±,Ī²-unsaturated imines catalyzed
by a palladacycle has been developed, thus providing the access to
a series of chiral tertiary enaminophosphines in high yields. A putative
catalytic cycle has also been proposed
Asymmetric Synthesis of Enaminophosphines via Palladacycle-Catalyzed Addition of Ph<sub>2</sub>PH to Ī±,Ī²-Unsaturated Imines
A highly reactive, chemo- and enantioselective addition
of diphenylphosphine to Ī±,Ī²-unsaturated imines catalyzed
by a palladacycle has been developed, thus providing the access to
a series of chiral tertiary enaminophosphines in high yields. A putative
catalytic cycle has also been proposed
Stereogenic Lock in 1āNaphthylethanamine Complexes for Catalyst and Auxiliary Design: Structural and Reactivity Analysis for Cycloiridated Pseudotetrahedral Complexes
A series of optically
active pseudo-tetrahedral five-membered cyclometalated
1-naphthylethanamine iridiumĀ(III) complexes were prepared and characterized
to analyze the efficacy of the stereogenic conformational lock in
both solid and solution phases. The synthesis of the iridacycles was
diastereoselective, and the compounds were found to be conformationally
rigid. In comparison to its phenyl derivative, the structural lock
prevented oxidation of the amine moiety within the five-membered organometallic
ring during its synthesis. With up to three stereogenic centers in
one of the naphthalene complexes, the stereochemistry of the metallacycle
remained stable to both thermal and chemical changes. In terms of
catalytic performance, the complexes displayed excellent activity
for the asymmetric hydrogen transfer reaction, albeit with modest
enantioselectivities
Asymmetric 1,4-Conjugate Addition of Diarylphosphines to Ī±,Ī²,Ī³,Ī“-Unsaturated Ketones Catalyzed by Transition-Metal Pincer Complexes
An
enantioselective asymmetric 1,4-addition of diarylphosphines
to linear Ī±,Ī²,Ī³,Ī“-unsaturated dienones was
developed. A series of chiral PCP- and PCN-transition-metal (Pd, Pt
and Ni) pincers, themselves prepared catalytically via asymmetric
hydrophosphination, were sequentially screened to reveal the roles
of backbone architecture and metal ion in catalyst design. The selected
ester-functionalized PCP-palladium pincer afforded the chiral 1,4-phosphine
adducts in excellent yields with up to >99% <i>ee</i>. The
same catalyst when utilized for the hydrophosphination of an Ī±,Ī²,Ī³,Ī“-unsaturated
malonate ester also revealed the critical role played by the ester
functionality on the ligand backbone in dictating the enantioselectivity
of the 1,6-adduct
Synthesis of Stereoprojecting, Chiral NāC(sp<sup>3</sup>)āE Type Pincer Complexes
A synthetic strategy
to generate chiral N-CĀ(sp<sup>3</sup>)-E (E
= S, O) pincer complexes incorporating enhanced stereoprojecting groups
at the N-arm site has been established. The synthesis of the tridentate
pincer ligand was carried out via palladacycle-catalyzed asymmetric
hydrophosphination of N-chelating enones. The chelation properties
of the substrates were initially demonstrated on CĀ(sp<sup>2</sup>)-N
type palladacycles. The extended substrate scope allows versatile
structural modifications on the ligand backbone. Subsequent cyclometalation
provided N-CĀ(sp<sup>3</sup>)-E complexes in a diastereoselective reaction