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1.
Chemistry ; 25(48): 11308-11317, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31293004

RESUMO

Synthetic challenges have significantly slowed the development of the catalytic asymmetric hydroarsination reaction despite it being a highly attractive C-As bond formation methodology. In addition, there is a poor understanding of the main reaction steps in such reactions which limit further development in the field. Herein, key intermediates of the hydroarsination reaction catalyzed by a PCP NiII -Cl pincer complex are presented upon investigating the reaction with DFT calculations, conductivity measurements, NMR spectroscopy, and catalytic screening. The novel Ni-Cl-As interaction proposed was then contrasted against known NiII -catalyzed hydrophosphination reactions to highlight dissimilarities between them even though P and As share a close group relationship. Lastly, the asymmetric hydroarsination of nitroolefins was further developed to furnish a library of chiral organoarsines in up to 99 % yield and 80 % ee under mild conditions (-20 °C to RT) between 5 to 210 mins.

2.
Dalton Trans ; 48(14): 4602-4610, 2019 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-30888384

RESUMO

Given the periodic relationship of phosphines and arsines, is remodeling the catalytic asymmetric hydrophosphination reaction an efficient manner to develop the corresponding hydroarsination reaction? Herein, a chiral PCP-Pd(ii) pincer complex adept at generating enantioenriched phosphines was examined in the asymmetric hydroarsination reaction. Under distinct conditions, tertiary phosphines and arsines were generated in excellent yields (P: 96%, As: 91%) and ees (P: 90%, As: 85%). While secondary arsine reagents were not direct substitutes for the analogous phosphines, important parameters were identified which increased yield and ee of the hydroarsination reaction. Unlike the PCP-PdOAc pincer complex commonly used for hydrophosphinations, hydroarsination reactions involved a PCP-PdCl catalyst with 10 equiv. of CsF for optimal performance. Notable differences between the two reactions and their workup procedures were highlighted to guide further developments in the field. Lastly, respective mechanisms were proposed and contrasted for the activation of HEPh2 (E = P, As).

3.
Chem Commun (Camb) ; 53(47): 6307-6310, 2017 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-28492693

RESUMO

A catalytic asymmetric hydroarsination reaction of an activated alkene viz. (E)-nitrostyrene was developed using chiral PCP Pt-, Pd- and Ni-pincer complexes as catalysts. The corresponding chiral tertiary arsine adduct was obtained in ees of up to 80% under mild reaction conditions using the PCP Ni-Cl pincer catalyst. The arsine adduct was furnished with catalyst loadings of 1-5 mol% and the reaction duration ranging from <5 min to 180 min. The subsequent coordination of the hydroarsination product to gold(i) chloride allowed for the confirmation of the stereochemistry of the arsine adduct via crystallographic analysis.

4.
Dalton Trans ; 46(4): 1311-1316, 2017 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-28070578

RESUMO

A chiral phosphine auxiliary was generated with excellent ee via catalytic asymmetric hydrophosphination of 3-(naphthalen-1-ylmethylene)pentane-2,4-dione. The subsequent metal complexation of the monophosphine yielded two different coordination complexes depending on the reaction conditions. The ortho-palladation of both coordination complexes resulted in the formation of a single dimeric phosphapalladacycle complex that could be further converted to the monomeric bisacetonitrile derivative. Moreover, the palladium complex exhibits interesting oxophilicity as the stable bisaquo derivative could be isolated and characterized crystallographically. The catalytic potential of the phosphapalladacycle was also demonstrated.

5.
Dalton Trans ; 45(34): 13449-55, 2016 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-27488728

RESUMO

The impact of the structural attributes of chiral PC- and PCP-palladium catalysts was investigated in the asymmetric hydrophosphination of various heterocycle-functionalized enone substrates. Due to the architecture of the catalysts, they are confronted with potential catalyst deactivation arising from the coordination of the electron-rich heteroatoms (P, O, N and S) to the metal center. A systematic variation of the location and identity of the heteroatoms demonstrated the impact of structural modifications on the substrates, which have a significant influence on both yields (16-99%) and enantioselectivities (0-99%). A detailed discussion on the distinct catalytic mechanisms (intra- vs. inter-molecular addition) provides important information to explain the results obtained.

6.
Chem Commun (Camb) ; 52(22): 4211-4, 2016 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-26912423

RESUMO

Cyclopalladation of the pyridyl-substituted chiral phosphine sulfide (N-P=S) and oxide (N-P=O) compounds afforded the asymmetric N-C(sp(3))*-S and N-C(sp(3))*-O pincer complexes. When applied as catalysts in asymmetric hydrophosphination, the newly developed aliphatic pincer catalyst could be recycled over three runs and obtained in large quantities via a one-pot "self-breeding" catalytic protocol.

7.
Dalton Trans ; 45(5): 2095-101, 2016 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-26483364

RESUMO

A (13)C{(1)H} NMR based investigation was conducted to examine the electronic properties of C(aryl)-M bonds and their trans influence in P-C(aryl)-P pincer complexes. A series of structurally related platinum pincer complexes were rationally designed and their corresponding (13)C-(195)Pt coupling constants were systematically examined. By methodical substitution of the ligand trans to the organometallic C(aryl)-Pt bond, this study revealed the significant influence of the ligands on the nature of the C(aryl)-M bonds. The single crystal X-ray analysis of the complexes and computational studies further confirmed the observations that the C-M bond exhibits significant π-character.

8.
Dalton Trans ; 44(3): 1258-63, 2015 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-25415079

RESUMO

Both PC-cyclometalated and PCP-pincer type palladium catalysts have recently been found to be robust and efficacious catalysts for the asymmetric P-H addition reaction involving activated olefins. Our studies on the asymmetric P-H addition of diphenylphosphine to malonate ester and α,ß,γ,δ-alkylidenemalonate ester revealed for the first time that the catalyst choice can have a dramatic impact in terms of reactivity as well as regio- and stereo-control for this asymmetric hydrofunctionalization reaction. Besides showing significantly contrasting reactivity and stereoselectivity in the hydrophosphination reaction involving malonate ester, in the case of α,ß,γ,δ-alkylidenemalonate ester, a novel regiodivergent method was developed with the 1,4-adduct being obtained exclusively with the PC-catalyst while the pincer catalyst produced only the 1,6-adduct.

9.
Inorg Chem ; 53(19): 10232-9, 2014 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-25248095

RESUMO

C-chirogenic diphosphine-based clusters with 8-membered "chairlike" Cu4Cl4L2 and 12-membered "drumlike" Cu6Cl6L3 (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, (1)H, (13)C, and (31)P{(1)H} NMR spectroscopy. The synthesized clusters were found to exhibit catalytic activity in the hydroboration reaction of α,ß-unsaturated enones with excellent yields albeit with low enantioselectivity.

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