Table 1. Selected results for the chemical optimization of the performance of [η⁶-(arene)Ru(Biot-q-L)CI]⊂(strept)avidin as an artificial metalloenzyme for the transfer hydrogenation of acetophenone 2a.

Entry	Ligand	η6-arene	Protein	Conversion, %	ee, %
1*	Biot-p-L	p-cymene	WT-Sav	51	28 (R)
2†	Biot-p-L	p-cymene	WT-Sav	55	57 (R)
3†	Biot-p-L	p-cymene	WT-Avi	24	22 (R)
4†	Biot-m-L	p-cymene	WT-Sav	20	6 (S)
5†	Biot-o-L	p-cymene	WT-Sav	18	3 (S)
6†	Biot-p-L	Benzene	WT-Sav	29	56 (S)
7†	Biot-p-L	Benzene	WT-Avi	17	17 (R)

All catalytic runs were carried out at 45°C for 40 h at pH_initial = 6.25, using a Ru/acetophenone 2a/formate ratio of 1:100:4,200. Conversions and enantioselectivities were determined by HPLC on Chiralcel OB-H.

^*Nonbuffered 0.5 M formate solution.

^†Mixed buffer HCO₂Na (0.5 M) + B(OH)₃ (0.47 M).