TY - JOUR
T1 - Proton NMR Kinetic Study of Ligand Exchange on Bis(1,4-dithiane)platinum(II), Bis(1,4-dithiane)palladium(II) and Tetrakis(dimethylsulfide)platinum(II)
T2 - High Presssure NMR Kinetics 51
AU - Frey, Urban
AU - Elmroth, Sofi K.C.
AU - Moullet, B.
AU - Elding, Lars Ivar
AU - Merbach, Andre E.
PY - 1991/12/25
Y1 - 1991/12/25
N2 - Ligand exchange on square-planar Pt(1,4-dithiane)2(2+), Pd(1,4-dithiane)2(2+), and Pt(Me2S)4(2+) has been studied as a function of temperature and pressure by H-1 NMR line-broadening, isotopic labeling, and magnetization transfer experiments with deuteriated nitromethane as solvent. Second-order rate constants and activation parameters are as follows: for 1,4-dithiane exchange on Pt(1,4-dithiane)2(2+), k2(298) = 28.8 +/- 4.8 m-1 s-1, DELTA-H double-ended dagger = 32.9 +/- 3.6 kJ mol-1, DELTA-S double-ended dagger = -106 +/- 11 J K-1 mol-1, and DELTA-V double-ended dagger = -12.6 +/- 1.1 cm3 mol-1; for 1,4-dithiane exchange on Pd(1,4-dithiane)2(2+), k2(298) = 9780 +/- 300 m-1 s-1, DELTA-H double-ended dagger = 22.9 +/- 0.6 kJ mol-1, DELTA-S double-ended dagger = -91.6 +/- 2.1 J K-1 mol-1, and DELTA-V double-ended dagger = -9.8 +/- 0.4 cm3 mol-1; for Me2S exchange on Pt(Me2S)4(2+), k2(298) = 1.54 +/- 0.07 m-1 s-1, DELTA-H double-ended dagger = 42.1 +/- 0.7 kJ mol-1, DELTA-S double-ended dagger = -100.2 +/- 2.2 J K-1 mol-1, and DELTA-V double-ended dagger = -22.0 +/- 1.3 cm3 mol-1. Second-order kinetics and negative entropies and volumes of activation indicate associative, I(a) or A, exchange mechanisms. For both metal centers, exchange of the chelated and strongly bound 1,4-dithiane, corrected for statistics, is faster than that of Me2S, probably due to steric factors. The ratio in reactivity for Pd/Pt is only ca. 1300 for Me2S and 340 for 1,4-dithiane, indicating a more pronounced sensitivity of Pt(II) to the electronic properties of the coordinated and entering ligands. Accordingly, activation volumes are more negative in the case of platinum. DELTA-V double-ended dagger for the Me2S exchange on Pt(II) is the most negative one reported so far for a square-planar solvent exchange.
AB - Ligand exchange on square-planar Pt(1,4-dithiane)2(2+), Pd(1,4-dithiane)2(2+), and Pt(Me2S)4(2+) has been studied as a function of temperature and pressure by H-1 NMR line-broadening, isotopic labeling, and magnetization transfer experiments with deuteriated nitromethane as solvent. Second-order rate constants and activation parameters are as follows: for 1,4-dithiane exchange on Pt(1,4-dithiane)2(2+), k2(298) = 28.8 +/- 4.8 m-1 s-1, DELTA-H double-ended dagger = 32.9 +/- 3.6 kJ mol-1, DELTA-S double-ended dagger = -106 +/- 11 J K-1 mol-1, and DELTA-V double-ended dagger = -12.6 +/- 1.1 cm3 mol-1; for 1,4-dithiane exchange on Pd(1,4-dithiane)2(2+), k2(298) = 9780 +/- 300 m-1 s-1, DELTA-H double-ended dagger = 22.9 +/- 0.6 kJ mol-1, DELTA-S double-ended dagger = -91.6 +/- 2.1 J K-1 mol-1, and DELTA-V double-ended dagger = -9.8 +/- 0.4 cm3 mol-1; for Me2S exchange on Pt(Me2S)4(2+), k2(298) = 1.54 +/- 0.07 m-1 s-1, DELTA-H double-ended dagger = 42.1 +/- 0.7 kJ mol-1, DELTA-S double-ended dagger = -100.2 +/- 2.2 J K-1 mol-1, and DELTA-V double-ended dagger = -22.0 +/- 1.3 cm3 mol-1. Second-order kinetics and negative entropies and volumes of activation indicate associative, I(a) or A, exchange mechanisms. For both metal centers, exchange of the chelated and strongly bound 1,4-dithiane, corrected for statistics, is faster than that of Me2S, probably due to steric factors. The ratio in reactivity for Pd/Pt is only ca. 1300 for Me2S and 340 for 1,4-dithiane, indicating a more pronounced sensitivity of Pt(II) to the electronic properties of the coordinated and entering ligands. Accordingly, activation volumes are more negative in the case of platinum. DELTA-V double-ended dagger for the Me2S exchange on Pt(II) is the most negative one reported so far for a square-planar solvent exchange.
KW - Platinum(II)
KW - Palladium(II)
KW - 1,4-dithiane
KW - Tetrakis(dimethylsulfide
KW - Ligand exchange
KW - Proton NMR
KW - Kinetics
KW - Reaction mechanism
U2 - 10.1021/ic00026a034
DO - 10.1021/ic00026a034
M3 - Article
SN - 1520-510X
VL - 30
SP - 5033
EP - 5037
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 26
ER -