Direct transmetallation between palladacyclic complexes and arylboronic acid occurs to give isolable transmetallation products. In THF, the reaction occurs <0.5 h. Prolonged reaction leads to the generation of a dinuclear Pd complex bearing bridging μ-hydroxo and μ-acetoxy ligands. Insight into precatalyst activation for Suzuki-Miyaura cross-couplings mediated by palladacycles has been gained, where acetate and N-imidate anions activate a neutral arylboronic acid.
Here, we have demonstrated that the presence of a carbonyl group at C7 position prevents the olefin metathesis of endo-norbornene derivatives due to complexation of the metal alkylidene. Time-dependent NMR studies showed the presence of new proton signals in the metal alkylidene region, which indicate the formation of metal complex with the carbonyl group of the substrate. These observations were further proved by ESI-MS analysis. Whereas computational studies showed that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular to that of norbornene olefin. These endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively. Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6], and [5/6/5] carbo-tricyclic cores of natural products in one step. Whereas the RRM of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent yields.
Homocoupling of arylboronic acids can be successfully achieved in commercial grade THF using [Pd(Phbz)(X)(PPh 3 )] palladacycles as catalysts (Phbz ¼ N-phenylbenzaldimine; X ¼ imidate or acetate).Symmetric biaryls were obtained in good yields working under mild conditions in an air atmosphere at room temperature. The reaction occurs without the addition of an exogenous base. The reaction conditions were optimized to provide the homocoupled products in excellent yield. Evidence for the transmetallation step being important for precatalyst activation has been gathered. The influence of electronic properties of the arylboronic acids on the outcome of the homocoupling reaction has been assessed through competition experiments.
The
development of the site-selective Suzuki–Miyaura cross-coupling
of dibromoanthracene as an efficient strategy toward organic light
emitting diodes (OLEDs) is disclosed in this article. An unprecedented
step-economic palladacycle-promoted triple Suzuki coupling protocol
allowed the synthesis of three new OLED emitters and could prove to
be a useful general strategy for researchers working in this field.
Characterization of the synthesized molecules by UV–vis spectroscopy
and thermogravimetric analysis–differential scanning calorimetry
followed by density functional theory studies of the different properties
strongly confirms the derivatives possess more significant hole mobility
character than electron transfer capability.
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