The activation of carbodicarbene (CDC)-Rh(I) pincer complexes by secondary binding of metal salts is reported for the catalytic site-selective hydro-heteroarylation of dienes (up to 98% yield and >98:2 γ:α). Reactions are promoted by 5 mol % of a readily available tridentate (CDC)-Rh complex in the presence of an inexpensive lithium salt. The reaction is compatible with a variety of terminal and internal dienes and tolerant of ester, alkyl halide, and boronate ester functional groups. X-ray data and mechanistic experiments provide support for the role of the metal salts on catalyst activation and shed light on the reaction mechanism. The increased efficiency (120 to 22 °C) made available by catalytic amounts of metal salts to catalysts containing C(0) donors is a significant aspect of the disclosed studies.
A carbodicarbene (CDC)-based pincer ligand scaffold is reported, along with its application to site-selective Rh(I)-catalyzed intermolecular hydroamination of 1,3-dienes with aryl and alkyl amines. To the best of our knowledge, this is the first example of the use of a well-defined CDC complex as an efficient catalyst. Transformations proceed in the presence of 1.0-5.0 mol % Rh complex at 35-120 °C; allylic amines are obtained in up to 97% yield and with >98:2 site selectivity.
Catalytic enantioselective addition of N-heteroarenes to terminal and internal 1,3-dienes is reported. Reactions are promoted by 5 mol % of Rh catalyst supported by a new chiral pincer carbodicarbene ligand that delivers allylic substituted arenes in up to 95% yield and up to 98:2 er. Mechanistic and X-ray evidence is presented that supports that the reaction proceeds via a Rh(III)-η-allyl.
A series of NNO tridentate Schiff base ligands were used
to prepare
zinc amide and zinc phenoxide complexes that were shown to be efficient l-lactide ring-opening polymerization (ROP) catalysts. The complexes
were prepared from ketoimines bearing a pendant quinoline donor, zinc
bis(trimethylsilyl)amide, and 2,6-di-tert-butylphenol.
They were characterized with 1H and 13C NMR,
absorbance spectroscopy, microanalysis, and X-ray crystallography.
The zinc amide and zinc phenoxide structures showed mononuclear complexes
with tridentate coordination by the ketoiminate ligands. ROP of l-lactide with the zinc amides and phenoxide complexes gave
isotactic poly-l-lactide with generally low molecular weight
distributions. As compared to their amide counterparts, the zinc phenoxide
complexes showed superior lactide ROP behavior in terms of percent
conversion as a function of time, measured molecular weights closer
to the predicted values, and lower polydispersity index values. Increasing
size of the substituent at the 2-position on quinoline (H, Me, Ph)
improved the synthesis of the complexes but adversely affected the
ROP.
Alkyl-alkyl cross-coupling is a powerful C-C bond forming transformation typically catalyzed by late transition metals. Herein we report a mechanistic investigation into an early transition metal-catalyzed variant of this reaction. Through this mechanistic understanding, an ideal Y catalyst was determined through tuning of the metal in order to optimize for oxidation potential, the rate limiting step in this reaction. A wide substrate scope is revealed that includes a variety of functional groups as well as unactivated substrates.
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