An inexpensive cyclodiphosphazane as an efficient ligand for the palladium-catalyzed amination of aryl bromides and chlorides

A chiral phosphazane reagent strategy for the determination of enantiomeric excess of amines

Methods for measuring enantiomeric excess (ee) of organic molecules by NMR spectroscopy provide rapid analysis using a standard technique that is readily available. Commonly this is accomplished by chiral derivatisation of the detector molecule (producing a chiral derivatisation agent, CDA), which is reacted with the mixture of enantiomers under investigation. However, these CDAs have almost exclusively been based on carbon frameworks, which are generally costly and/or difficult to prepare. In this work, a methodology based on the readily prepared inorganic cyclodiphosph(iii)azane CDA ClP(μ-N^tBu)₂POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be highly effective in the measurement of ee’s of chiral amines, involving in situ reaction of the chiral amines (R*NH₂) with the P–Cl bond of the CDA followed by quaternization of the phosphorus framework with methyl iodide. This results in sharp ³¹P NMR signals with distinct chemical shift differences between the diastereomers that are formed, which can be used to obtain the ee directly by integration. Spectroscopic, X-ray structural and DFT studies suggest that the NMR chemical shift differences between diastereomers is steric in origin, with the sharpness of these signals resulting from conformational locking of the bornyl group relative to the P₂N₂ ring induced by the presence of the P(v)-bonded amino group (R*NH). This study showcases cheap inorganic phosphazane CDAs as simple alternatives to organic variants for the rapid determination of ee.

The simple inorganic cyclodiphosph(iii)azane chiral derivatisation agent ClP(μ-^tBuN)₂POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be effective in the measurement of ee’s of chiral amines using ³¹P NMR spectroscopy.

Comparative study of aryl halides in Pd-mediated reactions: key factors beyond the oxidative addition step

The comparative experimental study of Ar–X (X = Cl, Br, I) reactivity and analysis reported herein suggest that oxidative addition cannot be considered the sole reason of the observed low reactivity of aryl chlorides.

Facile Buchwald-Hartwig coupling of sterically encumbered substrates effected by PNP ligands

The diphosphinoamine ligands [(Ph2P)2N(Ar); 1 (Ar = C6H5), 2 (Ar = 2,6-iPr2C6H3)] were effectively utilized in Buchwald-Hartwig coupling of a range of sterically demanding substrates. The reaction was carried out using conventional and microwave routes and the latter reduces the reaction time from 3 d to 15-30 min. A broad substrate scope was achieved in this protocol and most of the coupling products are isolated on a mutligram scale. DFT calculations were carried out to elucidate the reaction mechanism.

Manganese catalyzed N-alkylation of anilines with alcohols: ligand enabled selectivity

Ligand enabled earth-abundant manganese catalyzed N-alkylation of amines with alcohols via a hydrogen auto-transfer strategy is reported. The choice of the ligand plays a significant role in the alcohol reactivity (aliphatic or aromatic) toward N-alkylation reactions.

Cyclodiphosphazanes: options are endless

This short review describes the transition metal chemistry of cyclodiphosphazanes.

Chiral ditopic cyclophosphazane (CycloP) ligands: synthesis, coordination chemistry, and application in asymmetric catalysis

A series of dichlorocyclophosphazanes [{ClP(μ-NR)}2 ] containing chiral and achiral R groups was obtained from simple commercially available amines and PCl3 . Their condensation reactions with axially chiral biaryl diols yielded ansa-bridged chiral cyclophosphazane (CycloP) ligands. This highly modular methodology allows extensive elaboration of the ligand set, in which the chirality can be introduced at the diol bridge and/or the amido R group. This provides the possibility to observe match and mismatch effects in catalysis. A series of twenty CycloP ligands was synthesized and characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and in selected cases, single-crystal X-ray diffraction. These studies show that all of the ditopic CycloP ligands are C2 symmetric, rendering their metal coordination sites symmetry equivalent. Two well-established enantioselective reactions were explored by using late-transition metal CycloP complexes as catalysts; the gold-catalyzed hydroamination of γ-allenyl sulfonamides and the asymmetric nickel-catalyzed three-component coupling of a diene and an aldehyde. The steric demands of the CycloP ligands have a subtle influence on the reactivity and selectivity observed in both reactions. Good enantiomeric ratios (e.r.) as high as 89:11 in the gold-catalyzed reaction and 92:8 in the nickel-catalyzed bis-homoallylation reaction were observed.

The Phospha-Michael addition product {(t-BuNH)P(μ-N-t-Bu)(2)P(=N-t-Bu)-C(=CH(2))CH(p-CH(3)O-C(6)H(4))-P(O)[(OCH(2)C(CH(3))(2)CH(2)O)]}

The title compound, 2-{2-[1,3-di-tert-butyl-4-(tert-butyl-amino)-2-(tert-butyl-imino)-1,3,2λ(5),4-diaza-diphosphetidin-2-yl]-1-(4-meth-oxy-phen-yl)prop-2-en-1-yl}-5,5-dimethyl-1,3,2λ(5)-dioxaphosphinan-2-one, C(31)H(57)N(4)O(4)P(3), was synthesized from the Phospha-Michael addition reaction of cyclo-diphos-pha-zane [(t-BuNH)P(μ-Nt-Bu)](2) and allenyl-phospho-nate [(OCH(2)C(CH(3))(2)CH(2)O)P(O)C(p-CH(3)O-C(6)H(4))=C=CH(2)]. In the crystal, N-H⋯O and C-H⋯O hydrogen bonds link the mol-ecules. The structure exhibits pseudosymmetry but attempts to solve it in a higher (monoclinic) space group were unsuccessful.