Copper-dioxygen interactions are of interest due to their importance in biological systems as reversible O-2-carriers, oxygenases, or oxidases and also because of their role in industrial and laboratory oxidation processes. Here we report on the kinetics (stopped-flow, -90 to 10 degreesC of O-2-binding to a series of dicopper(I) complexes, [Cu-2(Nn)(MeCN)(2)](2+) (1(Nn))(-(CH2)(n)- (n = 3-5) linked bis[2-(2-pyridyl)ethyl]amine, PY2) and their close mononuclear analogue, [(MePY2)Cu(MeCN)](+) (3. which form mu-eta (2):eta (2)-peroxodicopper(II) complexes [Cu-2(Nn)-(O-2)](2+) (O-2)](2+) (2(Nn)) and [{(MePY2)Cu}(2)(O-2)](2+) (4), respectively. The overall kinetic mechanism involves initial reversible (k(+,open)/k(-.open)) formation of a nondetectable intermediate O-2-adduct [Cu-2(Nn)(O-2)](2+) (open), suggested to be a Cu-I. . . Cu-II-O-2(-) species, followed by its reversible closure (k(+,closed)/k(-.closed)) to form 2(Nn). At higher temperatures (253 to 283 K), the first equilibrium lies far to the left and the observed rate law involves a simple reversible binding equilibrium process (K-on,K-high = (k(+,open)/k(-,open))(k(+,closed))). From 213 to 233 K the slow step in the oxygenation is the first reaction (k(on,low) = k(+,open)), and first-order behavior (in 1(Nn) and O-2) is observed. For either temperature regime, the DeltaH double dagger for formation of 2(Nn) are low (DeltaH double dagger = -11 to 10 kJ/mol; k(on,low) = 1.1 x 10(3) to 4.1 x 10(3) M-1 s(-1), k(on,high) = 2.2 x 10(3) to 2.8 x 10(4) M-1 s(-1)), reflecting the likely occurrence of preequilibria, The DeltaH degrees ranges between -81 and -84 kJ mol(-1) for the formation of 2(Nn), and the corresponding equilibrium constant (K-1) increases (3 x 10(8) to 5 x 10(10) M-1; 183 K) going from n = 3 to 5, Below 213 K, the half-life for formation of 2(Nn) increases with, rather than being independent of, the concentration of 1(Nn), probably due to the oligomerization of 1(Nn) at these temperatures. The Or reaction chemistry of 3 in CH2Cl3 is complicated, including the presence of induction periods, and could not be fully analyzed. However, qualitative comparisons show the expected slower intermolecular reaction of 3 with Or compared to the intramolecular first-order reactions of 1(Nn), Due to the likelihood of the partial dimerization of 3 in solution, the t(1/2) for the formation of 4 remains constant with increasing complex concentration rather than decreasing. Acetonitrile significantly influences tho kinetics of the O-2 reactions with 1(Nn) and 3. For 1(N4), the presence of MeCN inhibits the formation of a previously (Jung et al, J. Am. Chem. Sec. 1996, 118, 3763-3764) observed intermediate. Small amounts of added MeCN considerably slow the oxygenation rates of 3, inhibit its full formation to J, and increase the length of the induction period. The results for 1(Nn) and their mononuclear analogue 3 are presented, and they are compared with each other as well as with other dinucleating dicopper(I) systems.