Chiral Recognition and Photoreaction β-Amino Acids with Iridium(III) Complexes

beta-Amino acids (AAs), homologs of alpha-AAs, are important building blocks of biological materials. Herein, chiral recognitions of beta-AAs with Ir(III) complexes are reported, in favor of formation of the thermodynamically stable Lambda-[Ir(pq)(2)(D-beta-AAs)] and Delta-[Ir(pq)(2)(L-beta-AAs)] (pq is 2-phenylquinoline) diastereomers. The photoreactions of [Ir(pq)(2)(beta-AA)] complexes are observed in an EtOH solution in the presence of O-2 at room temperature. The primary beta-AAs complexes, such as rac-[Ir(pq)(2)(beta-ala)] (beta-ala is beta-alanine), Delta-[Ir(pq)(2)(D-beta-ma)] and Lambda-[Ir(pq)(2)(D-beta-ma)] (beta-ma is beta-methylalanine), Delta-[Ir(pq)(2)(D-beta-pa)] and Lambda-[Ir(pq)(2)(D-beta-pa)] (beta-pa is beta-phenylalanine), and rac-[Ir(pq)(2)(beta-dma)] (beta-dma is 3,3-dimethyl-beta-alanine), are interligand C-N cross-coupling in situ between pq and beta-AAs ligands. The secondary beta-AA complexes Delta-[Ir(pq)(2)(L-beta-pro)] and Lambda-[Ir(pq)(2)(L-beta-pro)], (beta-pro is beta-proline, 2-(pyrrolidin-2-yl)acetic acid) are dehydrogenatively oxidized into imino acid complexes Delta-[Ir(pq)(2)(L-beta-pro-2H(beta'))] and Lambda-[Ir(pq)(2)(L-beta-pro-2H(beta'))] (L-beta-pro-2H(beta') = 2-(3,4-dihydro-2H-pyrrol-2-yl)acetic acid), respectively. Moreover, the dehydrogenative reaction in Delta-[Ir(pq)(2)(L-beta-pro)] diastereomer is regioselective depending on the reaction temperature, affording Delta-[Ir(pq)(2)(L-beta-pro-2H(beta'))] and Lambda-[Ir(pq)(2)(L-beta-pro-2H(beta'))] (beta-pro-2H(beta') = 2-(3,4-dihydro-2H-pyrrol-5-yl)acetic acid) at low temperature. The chiral recognitions and photoreactions of Ir(III)-beta-AAs complexes are much different from the previous observations in Ir(III)-alpha-AAs complexes.