Proton sponge, in the presence of mer-RhCl3(dmso)3 or [RuCl(dppb)12(p-CI), (dmso = dimethyl sulphoxide, dppb = Ph2P[CH2I4PPh2), generates (via a net hydride loss from one methyl group) the 1 ,I ,3-trimethyl-2,3-dihydroperimidinium cation, which is isolated as the counter-ion in complexes containing the anions tran~-[RhCt~(dmso)~]and { [ Ru CI (d p p b) 12( p-C I )3} -.We reported recently1 on the facile dehydrogenation of triethylamine in the presence of rner-RhC13(dmso)3 (dmso = dimethyl sulphoxide) , with resulting formation of the ylidic enamine complex RhC13(dmso)2(a-CH2CH=NEt2). We now

. Can. J. Chem. 64, 2440 (1 986).The rhodium(II1) octaethylporphyrin complex Rh(OEP)(PPh3)C1 (I) has been synthesized via Rh(II1) or Rh(1) precursors, and fully characterized both by spectroscopy and single~rystal data. The crystals, available as a bis(ch1oroform) solvate are triclinic, P1, a = 13.478(5), b = 14.300(5), c = 15.346(4)A, a = 102.33(2), P = 102.89(2), y = 90.56(3)", Z = 2, D, = 1.384gcm-'.The structure was determined from Mo diffractometer data and refined by least-squa;es methods to R = 0.095, R,. = 0.068 for 5189 reflections. The octahedrally coordinated rhodium atom is displaced by 0.077 A from the mean plane of thq four N atoms, towards the triphenylphosphine group. The average Rh -ring nitrogen distance is 2.024 A, Rh-P is 2.306 (3) [Traduit par la revue]

The kinetics of bromination of the 1,2-dihydro-1,3-dimethyl-2-oxopyrimidinium cation (Q+) in aqueous media (pH 0–5) have been studied using the stopped-flow method. At the higher acidities (pH < 2) the results are consistent with rate determining attack by bromine upon the pseudobase (QOH), whereas at low acidities (pH > 4) it appears that pseudobase formation is rate determining. The change occurs because at high acidity the reversal of the pseudobase QOH to the cation is fast relative to bromine attack, whereas at low acidity the converse is true. Results obtained at intermediate acidities (pH 2–4) are consistent with this interpretation.A separate kinetic study of pseudobase formation (and decomposition) yielded rate constants in good agreement with those derived from the bromination study.

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