85883-32-5Relevant academic research and scientific papers
Kinetics of hindered rotation about carbon-nitrogen single bonds in some N,N-diisopropyldithiocarbamates
Lindmark, Alan F.,Fay, Robert C.
, p. 2000 - 2006 (2008/10/08)
The metal N,N-diisopropyldithiocarbamate complexes NaL, NiL2, CoL3, AlL3, InL3, and ZrL4 (L = S2CN(i-Pr)2) have been prepared and characterized by IR and 1H NMR spectroscopy. Low-temperature 1H NMR spectra of these compounds exhibit two equally intense isopropyl methyl doublets and two equally intense methine septets, attributed to a ligand conformation in which the methine protons of the inequivalent isopropyl groups are located in the plane of the ligand in environments that may be labeled inner or outer with respect to the quasi-twofold axis of the ligand. Between -50 and +15°C the methyl doublets and methine septets coalesce to a single doublet and a single septet, respectively, owing to hindered rotation about the C-N single bonds. Rate constants (s-1) at -10°C in CH2Cl2 solution vary from 1400 for CoL3 to 8.3 for NaL; Ea = 10-12 kcal/mol and ΔS≠ = -7 to -13 eu. The rates increase with decreasing size, increasing charge, and increasing class b character of the metal ion and with decreasing SCS angle and increasing CNC angle in the analogous N,N-diethyldithiocarbamates. These trends can be understood in terms of a metal-induced variation in the amount of steric congestion in the N(i-Pr)2 group. The methyl ester MeSC(S)N(i-Pr)2 exists in CH2Cl2 solution as a 0.58:0.42 equilibrium mixture of two conformers that have the outer methine proton cis and trans, respectively, to the SMe group. Exchange of isopropyl methyl groups among the four inequivalent sites of the two conformers has been analyzed in terms of hindered rotation about (i) the C-N single bonds and (ii) the C..-N partial double bond. Kinetic data are also reported for rotation about the C..-N bond in the diisobutyl derivative MeSC(S)N(i-Bu)2.
