A Highly Stable Rhenium-Cobalt System for Photocatalytic H2 Production: Unraveling the Performance-Limiting Steps

Increased long-term performance was found for photocatalytic H-2 production in a homogeneous combination of [Re(NCS)(CO)(3)bipy] (1; bipy = 2,2'-bipyridine), [Co(dmgH)(2)] (dmgH(2) = dimethylglyoxime), triethanolamine (TEOA), and [HTEOA][BF4] in N,N-dimethylformamide, achieving TONRe up to 6000 (H/Re). The system proceeded by reductive quenching of (star)1 by TEOA, followed by fast (k(1) = 1.3 x 10(8) M-1 s(-1)) electron transfer to [Co-II(dmgH)(2)] and subsequent protonation (K-2) and elimination (k(3), second-order process in cobalt) of H-2. Observed quantum yields were up to similar to 90% (H produced per absorbed photon). The type of acid had a substantial effect on the long-term stability. A decomposition pathway involving cobalt is limiting the long-term performance. Time-resolved infrared (IR) spectroscopy confirmed that photooxidized TEOA generates a second reducing equivalent, which can be transferred to 1 (70%, k(2e)(-) = 3.3 x 10(8) M-1 s(-1)) if no [Co-II(dmgH)(2)] is present.