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.