The cobalt-catalyzed alkoxylation of C(sp(2) )H bonds in aromatic and olefinic carboxamides has been developed. The reaction proceeded under mild conditions in the presence of Co(OAc)2 ⋅4H2 O as the catalyst and tolerates a wide range of both alcohols and benzamide substrates, including even olefinic carboxamides. In addition, this reaction is the first example of the direct alkoxylation of alkenes through CH bond activation.

Aryl-based pincer metal complexes with anionic terdentate ligands have been widely applied in organic synthesis, organometallic catalysis and other related areas. Synthetically, the most simple and convenient method for the construction of these complexes is the direct metal-induced C(aryl)-H bond activation, which can be fulfilled by choosing the appropriate functional donor groups in the two side arms of the aryl-based pincer preligands. In this perspective, we wish to summarize some results achieved by our group in this context. Successful examples include symmetrical chiral bis(imidazoline) NCN pincer complexes with Ni(II), Pd(II) and Pt(II), bis(phosphinite) and bis(phosphoramidite) PCP pincer Pd(II) complexes, unsymmetrical (pyrazolyl)phosphinite, (amino)phosphinite and (imino)phosphinite PCN pincer Pd(II) complexes, chiral (imidazolinyl)phosphinite and (imidazolinyl)phosphoramidite PCN pincer complexes with Ni(II) and Pd(II) as well as unsymmetrical (oxazolinyl)amine and (oxazolinyl)pyrazole NCN' pincer Pd(II) complexes. Among them, the P-donor containing complexes are efficiently synthesized by the "one-pot phosphorylation/metalation" method. The obtained symmetrical and unsymmetrical pincer complexes have been used as catalysts in Suzuki-Miyaura reaction (Pd), asymmetric Friedel-Crafts alkylation of indole with trans-β-nitrostyrene (Pt) as well as in asymmetric allylation of aldehyde and sulfonimine (Pd). In the Suzuki couplings conducted at 40-50 °C, some unsymmetrical Pd complexes exhibit much higher activity than the related symmetrical ones which can be attributed to their faster release of active Pd(0) species resulting from the hemilabile coordination of the ligands. Literature results on the synthesis of some related pincer complexes as well as their activities in the above catalytic reactions are also presented.

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Chiral 3-(2 0 -imidazolinyl)anilines 3aÀc were easily synthesized by converting the carboxyl and nitro groups in commercially available 3-nitrobenzoic acid to chiral imidazoline and amine, respectively. The one-pot phosphorylation/metalation reaction of 3-(2 0 -imidazolinyl)anilines 3aÀc, where the amino group in 3aÀc was first phosphorylated by reaction with PPh 2 Cl, followed by metalation with PdCl 2 or anhydrous NiCl 2 in situ, afforded the three unsymmetrical chiral PCN pincer Pd(II) complexes 4aÀc and the Ni(II) complex 5a with aryl-based aminophosphineÀimidazoline ligands via aryl CÀH bond activation of the related ligands. All of the new compounds were characterized by elemental analysis (HRMS for ligand precursors), 1 H and 13 C NMR, 31 P{ 1 H} NMR (for pincer complexes), and IR spectra. The molecular structures of Pd complexes 4a,c and that of Ni complex 5a have been determined by X-ray single-crystal diffraction. Each complex adopts a typical distorted-square-planar geometry. The potential of the obtained chiral pincers in the asymmetric addition of diarylphosphines to β-substituted enones or trans-β-nitrostyrene was investigated. The Pd pincer 4c, the chirality of which originated from L-phenylglycinol, was found to be an effective catalyst for the asymmetric addition of diphenylphosphine to a series of β-aryl enones with high enantioselectivities (12 examples, 51À94% ee's). In particular, excellent yields and enantioselectivities (>90% yields and g90% ee's) were obtained when β-aryl groups in the enones bore an electron-withdrawing group such as p-NO 2 .

A series of new PCN pincer palladium(II) complexes with phosphinito group 2a−d and 3 were conveniently prepared via facile one-pot phosphorylation/palladation reaction of pyrazolyl or amino-containing m-phenol derivatives with chlorophosphines and PdCl2. Two PCP pincer complexes 4a,b were also readily obtained from resorcinol in an analogous yet simplified manner. All of the new complexes have been fully characterized by 1H NMR, 13C{1H} NMR, 31P{1H} NMR, IR, ESI-MS, and elemental analysis. Additionally, the molecular structures of 2a−d have been determined by X-ray single-crystal diffraction.