Table 1.

Overpotential (η) for proton reduction by various homogeneous catalysts

Catalyst	Ecat/V	Acid	$E_{\mathrm{HA}}^0$/Va	−η/V	Ref.
Fe2(bdt)(CO)6	−1.31	HOTs	−0.65	0.66	47
Fe2(bdt)(CO)6	−2.10	HOAc	−1.46	0.64	46
Fe2(pdt)(CO)6 (process I)	−1.59	HOTs	−0.65	0.94	54
Fe2(pdt)(CO)6 (process II)	−1.81	HOTs	−0.65	1.16	48
[Fe2(pdt)(μ-H)(CO)4(PMe3)(CNH)]+	−1.43	HOTs	−0.65	0.78	50
Fe2(bdt)(CO)5P(OMe)3	−1.18	HOTs	−0.65	0.53	52
Co(dmgBF2)2(MeCN)2	−0.93	CF3CO2H	−0.89	0.04	4

^a$E_{\mathrm{HA}}^0=E_{{\mathrm{H}}^{+}}^0-0.059$ pK_a,HA, with $E_{{\mathrm{H}}^{+}}^0=-0.14$ and −0.77 V in MeCN and DMF, respectively.