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The kinetics of metal-centered rearrangement and rotation about the C-N bonds in N,N-dimethylmonothioarbamate ligands of the eight-coordinate dodecahedral complexes [M(Me,mtc),] (M = Ti, Zr) have been studied by total line-shape analysis of variable-temperature 'H NMR spectra. The barriers AG* to metal-centered rearrangement are 9-1 2 kcal/mol; AG' values for C=N rotation are -17-20 kcal/mol. The [M(Me,mtc),] complexes rearrange much more slowly than analogous dithiocarbamates [M(R,dtc),] (M = Ti, Zr; R = Et, n-Pr), which are still nonrigid on the NMR time scale at -140 OC. This difference in the behavior of the mtc and dtc complexes points to a polytopal rearrangement mechanism. Also reported are kinetic data for exchange of inequivalent isopropyl methyl groups in [Ti(i-Pr,mtc),]: AG'(25 "C) = 18.4 i 0.1 kcal/mol; AH* = 16.4 f 0.3 kcal/mol; AS* = -6.7 * 0.7 eu. The latter process involves rotation about the isopropyl-nitrogen (C-N) single bonds and rotation about the C-N partial double bond.