STEPWISE AQUATION OF 1,2,3- AND 1,2,6-TRIAQUODIETHYLENETRIAMINECHROMIUM(III) CATIONS TO HEXAAQUOCHROMIUM(III) CATION . REACTION KINETICS AND ISOLATION OF BIDENTATE AND UNIDENTATE DIETHYLENETRIAMINE INTERMEDIATES

Aquation of l,2,3-Cr(dien)(OH2)33+ was studied spectrophotometrically in 1-2 F HC104 (μ = 1-2 M, NaClO4) at 50-70°. At μ = 2 M, the first-order rate constant, k1c, is the same in 1 and 2 F HCIO4. At 59.80°, k1c = (5.89 %plusmn; 0.09) × 10−5=sec−1 in 1 FHCIO4 (μ = 1 M); Ea = 24.3 ± 0.7 kcal mol−1, log PZ(sec−1) = 11.72 ± 0.51. By extrapolation, k1c = (8.1 ± 0.8) × 10−7 sec−1 at 25 °. The product is the new complex Cr(dienH)(OH2)44+, with a singly protonated bidentate dien ligand. Aquation of this isolated pink intermediate was investigated in 0.1-2 F HCIO4, (μ = 1-2 M) at 60-80°. At 59.80°, the first-order rate constant is k2 = (2.16 ± 0.03) × 10−5 sec−1 in 1 F HCIO4 (μ = 1 M); Ea = 24.0 ± 0.6 kcal mol−1, log PZ (sec−1) = 11.09 ± 0.40, and k2 = (3.1 ± 0.3) × 10−7 sec−1 at 25° by extrapolation. At 70 and 80°, f2 is the same in 0.1 and 1 F HCIO4 (μ = 1 M). The product is purple Cr(dienH2)(OH2)55+, a new complex with a doubly protonated unidentate dien ligand. Hydrolysis of this isolated second intermediate was studied in 0.1-2 F HCIO4 (μ = 1-2 M) at 60-80°. In 0.1-1 F HCIO4 (μ = 1 M), k3obad = k3 + (k3′/[H+]), where k3 is the first-order rate constant for aquation of Cr(dienH2)(OH2)55+toCr(OH2)63+ and k3 has been interpreted as k3hKa,k3h. being the first-order aquation rate constant of Cr(dienH2)(OH2)4OH4+ and Ka being the first acid dissociation constant of Cr(dienH2)(OH2)55+. At 59.80°, k3 = (2.59 ± 0.13) × l0−6 sec−1 and k3h ∼ 2 × 10−3sec−1; for the k3 path, Ea = 26.5 ± 0.8 kcal mol−1, log PZ (sec−1) = 11.81 ± 0.52, and by extrapolation k3 = (2 ± 1) × 10−8 sec−1 at 25°. Aquation of l,2,6-Cr(dien((OH2)33+ was studied in 0.01-1 F HCIO4 (μ = 0.15-1.1 M) at 15-30°. At 25.00°, the first-order rate constant is k1t = (5.34 ± 0.05) × 10−4 sec−1 in 0.1-1 F HCIO4 (μ = 1.1 M); Ea = 19.2 ± 0.6 kcal mol−1, log PZ (sec−1) = 10.80 ± 0.20. Ionic strength dependences of k1c, k1t, k2, and k3 are small over the ranges involved. The same intermediates appear to be produced in aquation of 1,2,3- and l,2,6-Cr(dien((OH2)33+. Visible absorption spectra of the complexes are presented. © 1969, American Chemical Society. All rights reserved.