Kinetic and mechanistic investigation of the substitution reactions of four and five co-ordinated rhodium stibine complexes with a bulky phosphite

Summary, in English

The substitution reaction of trans-[Rh(Cl)(CO)(SbPh3)(2)] (1) with tris(2,4-di-tert-butylphenyl)phosphite (2,4-TBPP) to form trans-[Rh(Cl)(CO)(2,4-TBPP)(2)] (4) in two consecutive steps has been investigated by UV-vis stopped-flow spectrophotometry. The experiments were performed in dichloromethane and in ethyl acetate, at 298 K and 268 K respectively for the first reaction step, and for the second reaction step over a temperature range from 278 to 313 K in both solvents. The first step is very fast (up to 1630 s(-1)) and on the limit of what is observable with the stopped-flow technique. Introduction of the five-coordinate complex trans-[Rh(Cl)(CO)(SbPh3)(3)] (2) in equilibrium with (1), by adding an excess SbPh3, led to a significant decrease in overall reaction rate for the formation of the intermediate trans-[Rh(Cl)-(CO)(SbPh3)(2)(2,4-TBPP)] (3). Activation parameters for the second substitution reaction, in which 3 is converted to 4, has been determined as Delta H double dagger = 22.85 +/- 0.17 and 28.38 +/- 0.10 kJ mol(-1) and Delta S double dagger = - 144.7 +/- 0.6 and -100.9 +/- 0.4 J mol(-1) K-1 for CH2Cl2 and EtOAc respectively, supporting an associative pathway. A strongly coordinating solvent promotes both reactions. In all reaction steps a strong tendency for stibines to promote 5-coordinated, fairly stable intermediates is manifested.

• Author: Clare Hennion; Klara Jonasson; Ola Wendt; Andreas Roodt
• Department/s: Centre for Analysis and Synthesis
• Publishing year: 2013
• Language: English
• Pages: 14134-14139
• Publication/Series: Dalton Transactions
• Volume: 42
• Issue: 39
• Links: http://dx.doi.org/10.1039/c3dt51757h
• Document type: Journal article
• Publisher: Royal Society of Chemistry
• Topic: Chemical Sciences
• Status: Published
• ISBN/ISSN/Other: ISSN: 1477-9234