Figure 1.

¹H NMR spectra showing the formation of complex 2 [(η⁵-C₅Me₅)Ir(phen)(H)]⁺ and its reaction with menadione in [D₄]MeOD/H₂O (1:9) at 298 K. a) Menadione alone. b) Formation of hydrido complex 2 from reaction of [(η⁵-C₅Me₅)Ir(phen)(H₂O)]²⁺ (1; 1 mm) with NADH (2 mm). c) Disappearance of signals of hydride 2 and broadening of signals of menadione 10 min after addition of menadione (1 mm) to mixture in (b).