Windle Christopher D, George Michael W, Perutz Robin N, Summers Peter A, Sun Xue Zhong, Whitwood Adrian C
Department of Chemistry , University of York , Heslington , York , YO10 5DD , UK . Email:
School of Chemistry , University of Nottingham , Nottingham , NG7 2RD , UK . Email:
Chem Sci. 2015 Dec 1;6(12):6847-6864. doi: 10.1039/c5sc02099a. Epub 2015 Aug 20.
We report a study of the photocatalytic reduction of CO to CO by zinc porphyrins covalently linked to [Re(2,2'-bipyridine)(CO)L] moieties with visible light of wavelength >520 nm. contains an amide CHNHC(O) link from porphyrin to bipyridine (Bpy), contains an additional methoxybenzamide within the bridge CHNHC(O)CH(OMe)NHC(O), while has a saturated bridge CHNHC(O)CH; each dyad is studied with either L = Br or 3-picoline. The syntheses, spectroscopic characterisation and cyclic voltammetry of and are described. The photocatalytic performance of in DMF/triethanolamine (5 : 1) is approximately an order of magnitude better than or in turnover frequency and turnover number, reaching a turnover number of 360. The performance of the dyads with Re-Br units is very similar to that of the dyads with [Re-pic] units in spite of the adverse free energy of electron transfer. The dyads undergo reactions during photocatalysis: hydrogenation of the porphyrin to form chlorin and isobacteriochlorin units is detected by visible absorption spectroscopy, while IR spectroscopy reveals replacement of the axial ligand by a triethanolaminato group and insertion of CO into the latter to form a carbonate. Time-resolved IR spectra of and (560 nm excitation in CHCl) demonstrated electron transfer from porphyrin to Re(Bpy) units resulting in a shift of (CO) bands to low wavenumbers. The rise time of the charge-separated species for is longest at 8 (±1) ps and its lifetime is also the longest at 320 (±15) ps. The TRIR spectra of and are quite different showing a mixture of MLCT, IL and charge-separated excited states. In the case of , the charge-separated state is absent altogether. The TRIR spectra emphasize the very different excited states of the bromide complexes and the picoline complexes. Thus, the similarity of the photocatalytic data for bromide and picoline dyads suggests that they share common intermediates. Most likely, these involve hydrogenation of the porphyrin and substitution of the axial ligand at rhenium.
我们报道了一项关于通过与[Re(2,2'-联吡啶)(CO)L]部分共价连接的锌卟啉，利用波长>520 nm的可见光将CO光催化还原为CO的研究。 包含一个从卟啉到联吡啶（Bpy）的酰胺CHNHC(O)连接， 在桥CHNHC(O)CH(OMe)NHC(O)内还含有一个甲氧基苯甲酰胺，而 具有一个饱和桥CHNHC(O)CH；每个二元体系均以L = Br或3-甲基吡啶进行研究。描述了 和 的合成、光谱表征及循环伏安法。在DMF/三乙醇胺（5∶1）中， 的光催化性能在周转频率和周转数方面比 或 大约好一个数量级，周转数达到360。尽管电子转移的自由能不利，但含Re-Br单元的二元体系的性能与含[Re-甲基吡啶]单元的二元体系非常相似。二元体系在光催化过程中会发生反应：通过可见吸收光谱检测到卟啉氢化形成二氢卟吩和异菌绿素单元，而红外光谱显示轴向配体被三乙醇胺基团取代，并且CO插入后者形成碳酸盐。 和 （在CHCl中560 nm激发）的时间分辨红外光谱表明电子从卟啉转移到Re(Bpy)单元，导致(CO)带向低波数移动。 的电荷分离物种的上升时间最长，为8（±1）ps，其寿命也最长，为320（±15）ps。 和 的时间分辨红外光谱有很大不同，显示出MLCT、IL和电荷分离激发态的混合。在 的情况下，完全不存在电荷分离态。时间分辨红外光谱强调了溴化物配合物和甲基吡啶配合物非常不同的激发态。因此，溴化物和甲基吡啶二元体系的光催化数据的相似性表明它们共享共同的中间体。最有可能的是，这些涉及卟啉的氢化和铼轴向配体的取代。
