title: Large improvement in the catalytic activity due to small changes in the diimine ligands: new mechanistic insight into the dirhodium(II,II) complex-based photocatalytic H2 production.
abstract: Two dirhodium(II) complexes, [Rh(II)(2)(μ-O(2)CCH(3))(2)(bpy)(2)](O(2)CCH(3))(2) (Rh(2)bpy(2); bpy = 2,2'-bipyridine) and [Rh(II)(2)(μ-O(2)CCH(3))(2)(phen)(2)](O(2)CCH(3))(2) (Rh(2)phen(2); phen = 1,10-phenanthroline) were synthesized, and their photocatalytic H(2) production activities were studied in multicomponent systems, containing [Ir(III)(ppy)(2)(dtbbpy)](+) (ppy = 2-phenylpyridine, dtbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) as the photosensitizer (PS) and triethylamine as the sacrificial reductant (SR). There is a more than 6-fold increase in the photocatalytic activity from Rh(2)bpy(2) to Rh(2)phen(2) just using phen in place of bpy. A turnover number as high as 2622 was obtained after 50 h of irradiation of a system containing 16.7 μM Rh(2)phen(2), 50 μM PS, and 0.6 M SR. The electrochemical, luminescence quenching, and transient absorption experiments demonstrate that Rh(I)Rh(I) is the true catalyst for the proton reduction. The real-time absorption spectra confirm that a new Rh-based species formed upon irradiation of the Rh(2)phen(2)-based multicomponent system, which exhibits an absorption centered at ∼575 nm. This 575-nm intermediate may account for the much higher H(2) evolution efficiency of Rh(2)phen(2). Our work highlights the importance of N-based chelate ligands and opens a new avenue for pursuing more efficient Rh(II)(2)-based complexes in photocatalytic H(2) production application.
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Jingfan
authors.initials: J
authors.lastname: Xie
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.forename: Qianxiong
authors.initials: Q
authors.lastname: Zhou
authors.forename: Weibo
authors.initials: W
authors.lastname: Wang
authors.forename: Yuanjun
authors.initials: Y
authors.lastname: Hou
authors.forename: Baowen
authors.initials: B
authors.lastname: Zhang
authors.forename: Xuesong
authors.initials: X
authors.lastname: Wang