Palladium pincer complexes composed of six-membered fused metallacycles have been synthesized directly from 1,3-bis(2-pyridyloxy)benzene. The pincer complexes show remarkably high turnover numbers and frequencies in the Heck reaction.

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[structure: see text] The recognition of dopamine in water has been achieved with tripodal oxazoline-based artificial receptors, capable of providing a preorganized hydrophobic environment by rational design, which mimics a hydrophobic pocket predicted for a human D2 receptor. The receptors show an amphiphilic nature owing to the presence of hydrophilic sulfonate groups at the periphery of the tripodal oxazoline ligands, which seems to contribute in forming the preorganized hydrophobic environment. The artificial receptors recognized dopamine hydrochloride in water with reasonable selectivity among various organoammonium guests examined. The observed binding behavior of the receptors was explained by evoking guest inclusion in the preorganized hydrophobic pocket-like environment and not by simple ion-pairing interactions. The rationally predicted 1:1 inclusion binding mode was supported by binding studies such as with a reference receptor that cannot provide a similar binding pocket, Job and VT-NMR experiments, electrospray ionization mass analysis, and guest selectivity data. This study implies that an effective hydrophobic environment can be generated even from an acyclic, small molecular artificial receptor. Such a preorganized hydrophobic environment, as being utilized in biological systems, can be effectively used as a complementary binding force for the recognition of organoammonium guests such as dopamine hydrochloride in water.

[structure: see text] A phenylglycinol-derived tripodal oxazoline with C1-symmetry (C1-PhBTO) was synthesized, and its enantioselective recognition behavior toward alpha-chiral primary organoammonium ions was studied. The C1-PhBTO receptor showed higher selectivity with an opposite sense of enantio-discrimination compared to other C1-symmetric analogues examined but lower selectivity with the same sense of enantioselection compared to its C3-symmetric analogue. Binding studies indicated that the C1-symmetric receptors, particularly C1-PhBTO, interact with the guests in a 2:1 host-guest complex mode in stark contrast to its C3-symmetric analogues.

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