10.1021/ic060837g.s009 Jacqueline R. Houston Jacqueline R. Houston Marilyn M. Olmstead Marilyn M. Olmstead William H. Casey William H. Casey Substituent Effects in Five Oxo-Centered Trinuclear Rhodium(III) Clusters American Chemical Society 2006 R group alkyl chain 298K 103 Rh NMR spectra chemical shift data water exchange rates CH 2Cl CH 3 CHCl 2. Activation parameters CH 2CH water substitution rates CH 2CH CH 2CH CH 2Cl 103 Rh NMR chemical shifts span 2006-09-18 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Substituent_Effects_in_Five_Oxo_Centered_Trinuclear_Rhodium_III_Clusters/3058891 We here report the rates of water substitution by methanol-<i>d</i><sub>4</sub> for four new oxo-centered trinuclear rhodium(III) clusters with different carboxylate-bridging ligands, [Rh<sub>3</sub>(μ<sub>3</sub>-O)(μ-O<sub>2</sub>CR)<sub>6</sub>(OH<sub>2</sub>)<sub>3</sub>]<sup>+</sup> (R = CH<sub>2</sub>CH<sub>3</sub>, CH<sub>2</sub>CH<sub>2</sub>Cl, CH<sub>2</sub>Cl, and CHCl<sub>2</sub>), and [Rh<sub>3</sub>(μ<sub>3</sub>-O)(μ-O<sub>2</sub>CCH<sub>3</sub>)<sub>6</sub>(OH<sub>2</sub>)<sub>3</sub>]<sup>+</sup>. By varying the R group alkyl chain, water substitution rates were found to span almost 3 orders of magnitude (<i>k</i><sup>298K</sup> = 1.2 × 10<sup>-2</sup>−2.3 × 10<sup>-5</sup> s<sup>-1</sup>) and reflect the following trend R = CH<sub>2</sub>CH<sub>3</sub> > CH<sub>3</sub> > CH<sub>2</sub>CH<sub>2</sub>Cl > CH<sub>2</sub>Cl > CHCl<sub>2</sub>. Activation parameters for substitution point toward a dissociative activation pathway (Δ<i>H</i><sup>⧧</sup> = 99−115 kJ mol<sup>-1</sup>; Δ<i>S</i><sup>⧧</sup> = 48−52 J mol<sup>-1</sup> K<sup>-1</sup>), indicating that there is little association with the incoming methanol molecule during the formation of the transition-state complex. Because the mechanism for substitution in all five trimers has a considerable dissociative character, substitution rates are likely very similar to water exchange rates. These data suggest that the kinetic reactivity of the ligated waters is heavily influenced by the inductive ability of the aliphatic substituents, but yet the mechanism of substitution remains virtually unchanged. Structural data are also reported for the four new rhodium(III) trimer salts as well as <sup>103</sup>Rh NMR spectra. We find that <sup>103</sup>Rh NMR chemical shifts span more than 200 ppm and mirror the same reactivity trend found for the rates of water substitution (<sup>103</sup>Rh δ (9406−9620 ppm):  R = CH<sub>2</sub>CH<sub>3</sub> < CH<sub>3</sub> < CH<sub>2</sub>CH<sub>2</sub>Cl < CH<sub>2</sub>Cl < CHCl<sub>2</sub>). Taken together, these data suggest a means for estimating water exchange rates for other oxo-centered rhodium(III) trimers from chemical shift data alone.