Cuprous complexes and dioxygen, VII. Competition between one‐ and two‐electron reduction of O2 in the autoxidation of Cu(1‐methyl‐2‐hydroxymethyl‐imidazole)2+

The complexation of 1‐methyl‐2‐hydroxymethyl‐imidazole (L) with Cu(I) and Cu(II) has been studied in aqueous acetonitrile (AN). Cu(I) forms three complexes, Cu(AN)L+, CuL2+, and Cu(AN)H−1L, with stability constants logK(Cu(AN)+ + L ⇌ Cu(AN)L+) = 4.60 ± 0.02, logβ2 = 11.31 ± 0.04, and logK(Cu(AN)H−1L+H+ ⇌ Cu(AN)L+) = 10.43 ± 0.08 in 0.15M AN. The main species for Cu(II) are CuL2+, CuH−1L+, CuH−1L2+, and CuH−2L2. The autoxidation of CuL2+ was followed with an oxygen sensor and spectrophotometrically. Competition between the formation of superoxide in a one‐electron reduction of O2 and a path leading to H2O2 via binuclear (CuL2)2O was inferred from the rate law with ka = (2.31 ± 0.12) · 104M−2S−1, kb = (1.0 ± 0.2) · 103M−1, kc = (2.85 ± 0.07) · 102M−2S−1, kd = 3.89 ± 0.14M−1S−1, ke = 0.112 ± 0.004, kf = (2.06 ± 0.24) · 10−10M S−1, kg = (1.35 ± 0.07) · 10−7 S−1, and kh = (6.8 ± 1.4) · 10−7M−1 S−1.