Structure and reactivity of aquacarbonylruthenium(II) complexes. An x-ray and oxygen-17 NMR study

The water exchange on [Ru(CO)(H2O-eq)(4)(H2O-ax)](tos)(2) (1), [Ru(CO)(2)(H 2O-eq)(2)(H2O-ax)(2)] (tos)2 (2), and [Ru(CO)(3)(H2O)(3)](ClO4)(2) (3), the O-17 exchange between the bulk water and the carbonyl oxygens have been st udied by O-17 NMR spectroscopy, and the X-ray crystallographic structures o f 1 and 2 have been determined. The water exchange of equatorially and axia lly coordinated water molecules on 1 and 2 follow an id mechanism and an ch aracterized by k(eq)(298) (s(-1)), Delta H-double dagger (kJ/mol), and Delt a S-double dagger (J/(mol K)) of (2.54 +/- 0.05) x 10(-6), 111.6 +/- 0.4, a nd 22.4 +/- 1 (1-eq); (3.54 +/- 0.02) x 10(-2) and 81 (1-ax); (1.58 +/- 0.1 4) x 10(-7), 120.3 +/- 2, and 28.4 +/- 4 (2-eq); and (4.53 +/- 0.05) x 10(- 4), 97.9 +/- 1, and 19.3 +/- 3 (2-ax). The observed reactivities correlate with the strength of the Ru-OH2 bonds, as expressed by their length obtaine d by X-ray studies: 2.079 (1-eq), 2.140 (1-ax), 2.073 (2-eq), and 2.110 (2- ax) Angstrom. 3 is strongly acidic with a pK(a) of -0.14 at 262 K. Therefor e, the acid-dependent water exchange can take place through 3 or Ru(CO)(3)( H2O)(3)OH+ with an estimated k(eq)(298) of 10(-4)/10(-5) s(-1) and k(OH)(26 2) of 0.053 +/- 0.006 s(-1). The O-17 exchange rate between the bulk water and the carbonyl oxygens increases from 1 to 2 to 3. For 1 an upper limit o f 10(-8) s(-1) was estimated. For 2, no acid dependence of k(Ru)(CO) betwee n 0.1 and 1 m Htos was observed. At 312.6 K, in 0.1 and 1 m Htos, k(Ru)(CO) = (1.18 +/- 0.03) x 10(-4). For the tricarbonyl complex, the exchange can proceed through 3 or Ru(CO)(3)(H2O)(2)OH+ with k(Ru)(CO) and k(RuOH)(CO) of respectively, 0.003 +/- 0.002 and 0.024 +/- 0.003 s(-1), with a ruthenacar boxylic acid intermediate.