202479-93-4Relevant academic research and scientific papers
Alkyne ligand enhancement of the substitution lability of mononuclear osmium, ruthenium, and iron carbonyls
Pearson, Jean,Cooke, Jason,Takats, Josef,Jordan
, p. 1434 - 1440 (1998)
The kinetic influence of an alkyne ligand, hexafluorobut-2-yne (HFB), as been investigated by studying the reactions of phosphines (PR3) with the complexes M(CO)4(η2-HFB) (M = Fe, Ru, Os). The rate of production of M(CO)3(PR3)(η2-HFB) is independent of the nature and concentration of the phosphine in all cases, indicating that the rate-controlling step is CO dissociation. The kinetic parameters, k1 (s-1, 25 °C). ΔH* (kJ mol- 1), and ΔS* (cal mol-1 K-1) are: 9.5, 88.2 ± 2.3, 70 ± 10 (Fe), 1.25 x 10-2, 103.6 ± 2.4, 66 ± 8.6 (Ru); 3.5 x 10-3, 99.5 ± 0.8, 21 + 2.7 (Os). When the rate constants at 25 °C for M(CO)4(η2-HFB) are compared to those of the parent M(CO)5, the ratios are ~3 x 1013, 1.8 x 102 and 1 x 107 for M = Fe, Ru, an Os, respectively. Clearly the alkyne increases the substitution lability, and the effect is spectacular with Fe, very large with Os, and substantial but relatively more modest with Ru. The increased lability results mainly from a reduced ΔH* of ~80, 10, and 33 kJ mol-1 for Fe, Ru, and Os, respectively, and this is attributed largely to stabilization of the transition state by 4-electron donation from the alkyne ligand. Also reported are kinetics of formation of some trans M(CO)2(PR3)2(η2-HFB) complexes and an extension of earlier work on the Os(CO)5/PPh3 system.
