An efficient procedure is presented for the alkoxycarbonylation of industrially important amines using environmentally friendly alkyl carbonates as reagents and Zn4O(OAc)6 as catalyst. Aromatic ...amines in particular (thirteen examples) consistently give high yields (up to 98%), regardless of the electronic properties of the substituents or the ring substitution pattern.
Iridium(I) complexes of enantiomerically pure phosphine-phosphite ligands (Ir(Cl)(cod)(POP)) efficiently catalyze the enantioselective hydrogenation of diverse CN-containing heterocyclic compounds ...(benzoxazines, benzoxazinones, benzothiazinones, and quinoxalinones; 25 examples, up to 99% ee). A substrate-to-catalyst ratio as high as 2000:1 was reached.
Enantiopure
P
-stereogenic methylphosphane-boranes (
S
P
)-P(BH
3
)PhArMe (
ArMe
; Ar = 1-naphthyl (
NpMe
), and 2-biphenylyl (
BiphMe
)) have been used to prepare diphosphanes of the type ArPhPCH
2
...PR
2
(R = Ph, iPr or
t
Bu;
ArR
). The ligands have been reacted with Rh(COD)
2
BF
4
to furnish the corresponding six monochelated Rh(COD)(
ArR
)BF
4
organometallic compounds (
RhArR
) or, depending on the reaction conditions, the bis(chelated) coordination compound Rh(
BiphiPr
)
2
BF
4
as a mixture of
cis
and
trans
isomers. The crystal structure of
cis
-Rh(
BiphiPr
)
2
BF
4
was obtained. The coordination of the
BiphR
with RuCl(μ-Cl)(η
6
-
p
-cymene)
2
2
under different conditions produced cationic chelated complexes of the type RuCl(η
6
-
p
-cymene)(κ
2
-
BiphR
)PF
6
(
RuBiphR
) and the neutral monocoordinated complex RuCl
2
(η
6
-
p
-cymene)(κ
1
-
BiphPh
) (
RuBiphPh′
) with the uncoordinated
P
-stereogenic moiety. The Rh(
i
) complexes were used in the catalytic hydrogenation of functionalized olefins and the Ru(
ii
) complexes were tested in the transfer hydrogenation of acetophenone. Both precursors displayed good activities with moderate enantioselectivities.
P
-stereogenic, methylene-bridged unsymmetrical diphosphanes coordinate to Rh(
i
) and Ru(
ii
), forming different complexes. The complexes are active in catalytic reductions.
We describe an efficient methodology for the preparation of new chiral zinc complexes by assembling dynamically racemic biphenol derivatives and chiral 1,2-diamines with suitable zinc(II) precursors. ...Mononuclear and dinuclear zinc(II) complexes were formed from differently substituted biphenols. The solid-state and solution structural characterization of the resulting compounds allowed us to demonstrate a preferential sense of induced axial chirality for mononuclear complexes, a phenomenon that was not observed for the dinuclear ones.
The role of the counterion in metal-catalyzed reactions can be crucial as this often-unconsidered component of the catalyst can modify the performance of the catalyst and influence the reaction rate ...and/or selectivity of the transformation under study. Herein, we disclose the effects of counterion variation in cationic halogen bond-assembled Rh(I) catalysts in the hydroboration reaction of terminal alkynes, which leads to rather elusive branched (or internal) hydroboration products. Our studies showed that the higher the coordination ability of the counterion, the higher the activity and selectivity toward the hydroboration products. This observation was demonstrated by catalytic and spectroscopic (NMR, IR and X-ray) studies. An array of structurally diverse alkynes was efficiently transformed into the corresponding hydroboration products employing the highest performing catalyst XBphos-Rh-OTf. The practicality of our synthetic method was demonstrated by developing one-pot hydroboration/Csp2-Csp2 coupling processes.
The structural optimization of a family of modular, enantiopure β-amino alcohol ligands with a common 2-amino-2-aryl-1,1-diphenylethanol skeleton, whose stereogenicity was introduced through the ...Jacobsen epoxidation of 1,1-diphenyl-2-arylethylenes, has led to the identification of a small set of optimal catalysts with enhanced activity and enantioselectivity in the addition of alkylzinc and arylzinc reagents to aldehydes. Criteria for the discrimination between apparently analogous, highly enantioselective ligands are proposed.
Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for ...industrial-scale purification due to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture, and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here, we disclose a porous, robust homochiral metal–organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural l-histidine. TAMOF-1 has shown to be able to separate a variety of model racemic mixtures, including drugs, in a wide range of solvents of different polarity, outperforming several commercial chiral columns for HPLC separations. Although not exploited in the present article, it is worthy to mention that the preparation of this new material is scalable to the multikilogram scale, opening unprecedented possibilities for low-energy chiral separation at the industrial scale.
Progress reaction profiles are affected by both catalyst activation and deactivation processes occurring alongside the main reaction. These processes complicate the kinetic analysis of reactions, ...often directing researchers toward incorrect conclusions. We report the application of two kinetic treatments, based on variable time normalization analysis, to reactions involving catalyst activation and deactivation processes. The first kinetic treatment allows the removal of induction periods or the effect of rate perturbations associated with catalyst deactivation from kinetic profiles when the quantity of active catalyst can be measured. The second treatment allows the estimation of the activation or deactivation profile of the catalyst when the order of the reactants for the main reaction is known. Both treatments facilitate kinetic analysis of reactions suffering catalyst activation or deactivation processes.
Mit der Zeit gehen: Zwei verschiedene kinetische Analysemethoden auf Basis der zeitvarianten Normierungsanalyse (VTNA) werden für die Untersuchung von Reaktionen mit Katalysator‐Desaktivierungsprozessen und ‐Aktivierungsprozessen beschrieben. Die studierten Fälle sind eine von einem supramolekularen Rh‐Komplex katalysierte Hydroformylierung und eine aminokatalytische Michael‐Reaktion.
Herein is reported the efficient preparation of a set of enantiopure bisphosphine ligands, whose backbone incorporates an array of diverse crown ethers as distal regulation sites via well-defined ...supramolecular interactions to tune the catalytic properties of the bisphosphine groups. These new ligands enabled very good catalytic activity in rhodium-mediated asymmetric hydrogenations at low catalyst loadings, while the enantioselectivity remained moderate. Slightly positive regulation effects for the enantioselectivity of the hydrogenation reactions were obtained as a result of the combination of the appropriate bisphosphine ligand and different regulation agents.
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