Figure 5. Spectroscopic evidence confirming the reactions of [1]²⁺ with known hydrogenase substrates H₂ and CO.

a, IR spectra of dichloromethane solutions of [1]²⁺ before and after treatment with CO (1 atm) and H₂ (1 atm) at 25 °C. In each case, the formation of a new carbonyl-containing species is indicated by the appearance of new ν_CO bands on the addition of the indicated substrate. b, ³¹P NMR spectrum (202 MHz, CD₂Cl₂) of [1(CO)]²⁺ at −60 °C showing the conversion of the ³¹P NMR-silent paramagnetic [1]²⁺ to the ³¹P NMR-active diamagnetic adduct [1(CO)]²⁺. c, ¹H NMR (500 MHz, CD₂Cl₂) hydride resonance of [1H]⁺ obtained from treatment of [1]²⁺ with H₂ and P(o-tol)₃.