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Issue 27, 2019
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Ambient and high-pressure kinetic investigation of methanol substitution in fac-[Re(Trop)(CO)3(MeOH)] by different monodentate nucleophiles

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Abstract

Methanol substitution in the fac-[Re(CO)3(Trop)(MeOH)] complex (Trop = tropolonate) was studied with a range of seven nucleophiles, namely pyridine (Py), 4-dimethylaminopyridine (DMAP), imidazole (Im), thiourea (TU), 1-methyl-2-thiourea (MeTU), bromide (Br) and iodide (I) at variable temperature, and at ambient and high pressure. The substitution products were characterized by NMR, IR and UV/vis spectroscopy, and by chemical analysis, and the crystal structures of two of these, namely fac-[Re(Trop)(CO)3(Im)] and fac-[Re(Trop)(CO)3(DMAP)], are reported. High-pressure kinetic studies with four of these entering nucleophiles in methanol at 25 °C on fac-[Re(Trop)(CO)3(MeOH)] yielded the following activation volumes, ΔV(kL), for the ligation by four nucleophiles as defined by kL (cm3 mol−1): Im: 9.0 ± 0.2; Py: 10.1 ± 0.2; TU: 10.0 ± 0.3 and MeTU: 14.5 ± 0.3. Since these experimental ΔV(kL) values were positive but smaller than expected, it was interpreted that these indicated a dissociative/dissociative interchange pathway for these substitution reactions. Kinetic studies at ambient pressure and variable temperature in methanol on fac-[Re(Trop)(CO)3(MeOH)] with a range of eight entering nucleophiles pointed more clearly to a dissociative pathway and yielded the following results, wherein a clear linear free-energy relationship (LFER) was established for the entering nucleophiles Py, DMAP, Im, TU, MeTU, NCS, Br and I, within the following ranges: kL (ligation; M−1 s−1), 0.263 ± 0.001 to 0.765 ± 0.002; k−L (solvolysis; s−1), (0.07 ± 0.01) × 10−3 to 0.674 ± 0.001; KL (equilibrium; M−1); 1.06 ± 0.01 to 2000 ± 500; ΔH(kL) (kJ mol−1), 58.0 ± 0.7 to 76.1 ± 0.6, and ΔS(kL) (J K−1 mol−1); −55 ± 2 to 6 ± 3.

Graphical abstract: Ambient and high-pressure kinetic investigation of methanol substitution in fac-[Re(Trop)(CO)3(MeOH)] by different monodentate nucleophiles

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Article information


Submitted
10 Apr 2019
Accepted
01 May 2019
First published
01 May 2019

Dalton Trans., 2019,48, 9984-9997
Article type
Paper

Ambient and high-pressure kinetic investigation of methanol substitution in fac-[Re(Trop)(CO)3(MeOH)] by different monodentate nucleophiles

M. Schutte-Smith, A. Roodt and H. G. Visser, Dalton Trans., 2019, 48, 9984
DOI: 10.1039/C9DT01528K

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