Fluxionality of [(Ph3P)3M(X)] (M = Rh, Ir). the red and orange forms of [(Ph3P)3Ir(Cl)]. Which phosphine dissociates faster from wilkinson's catalyst?

Jenni Goodman, Vladimir V. Grushin, Roman B. Larichev, Stuart A. MacGregor, William J. Marshall, D. Christopher Roe

Research output: Contribution to journalArticlepeer-review


NMR studies of intramolecular exchange in [(Ph3P) 3Rh(X)] (X = CF3, CH3, H, Ph, Cl) have produced full sets of activation parameters for X = CH3 (Ea = 16.4 ± 0.6 kcal mol-1, ΔH = 16.0 ± 0.6 kcal mol-1, and ΔS = 12.7 ± 2.5 eu), H (Ea = 10.7 ± 0.2 kcal mol-1, ΔH = 10.3 ± 0.2 kcal mol-1, and ΔS = -7.2 ± 0.8 eu), and Cl (Ea = 16.3 ± 0.2 kcal mol-1, ΔH = 15.7 ± 0.2 kcal mol-1, and ΔS = -0.8 ± 0.8 eu). Computational studies have shown that for strong trans influence ligands (X = H, Me, Ph, CF3), the rearrangement occurs via a near-trigonal transition state that is made more accessible by bulkier ligands and strongly donating X. The exceedingly fast exchange in novel [(Ph3P) 3Rh(CF3)] (12.1 s-1 at -100 °C) is due to strong electron donation from the CF3 ligand to Rh, as demonstrated by computed charge distributions. For weaker donors X, this transition state is insufficiently stabilized, and hence intramolecular exchange in [(Ph 3P)3Rh(Cl)] proceeds via a different, spin-crossover mechanism involving triplet, distorted-tetrahedral [(Ph3P) 3Rh(Cl)] as an intermediate. Simultaneous intermolecular exchange of [(Ph3P)3Rh(Cl)] with free PPh3 (THF) via a dissociative mechanism occurs exclusively from the sites cis to Cl (E a = 19.0 ± 0.3 kcal mol-1, ΔH = 18.5 ± 0.3 kcal mol-1, and ΔS = 4.4 ± 0.9 eu). Similar exchange processes are much slower for [(Ph3P)3Ir(Cl)] which has been found to exist in orange and red crystallographic forms isostructural with those of [(Ph 3P)3Rh(Cl)].

Original languageEnglish
Pages (from-to)12013-12026
Number of pages14
JournalJournal of the American Chemical Society
Issue number34
Publication statusPublished - 1 Sept 2010


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