Titanium-Catalyzed Hydrohydrazination of Carbodiimides
摘要:
Hydrazinediido complexes of the type [Cp*Ti-(NxylN)(NNR2)(L)] (R = Ph, Me; Ar, fluorene, L = (BuNH2)-Bu-t, Py; 3a-e) have been synthesized and used as catalysts for the hydrohydrazination of a series of carbodiimides, yielding aminoguanidines or fluoreneiminoguanidines. The highest yields were obtained for diarylhydrazines and fluorenone 5 hydrazone at temperatures between 80 and 105 degrees C. Stoichiometric reactions of hydraz inediido complexes with (PrNCNPr)-Pr-i-Pr-i led to an equilibrium with the resulting [2 + 2] cydoadducts 4a-f, which were characterized by H-1, C-13, and N-15 NMR spectroscopy as well as X-ray diffraction. The proposed mechanism, which is closely related to that previously established for the hydrohydrazination of alkynes and allenes, was found to be consistent with the results of a kinetic study. The dynamic structures of aminoguanidines and fluoreneiminoguanidines were characterized by NMR spectroscopy, and the minimum configurations were foud to be stabilized by intramolecular hydrogen bonding.
Titanium Hydrazinediido Half-Sandwich Complexes: Highly Active Catalysts for the Hydrohydrazination of Terminal Alkynes at Ambient Temperature
作者:Katharina Weitershaus、Hubert Wadepohl、Lutz H. Gade
DOI:10.1021/om900155t
日期:2009.6.22
characterization in solution. All three hydrazinediido compounds 1a, 2a, and 3 were found to display remarkable activities in catalytic hydrohydrazinations at ambienttemperatures. For catalyst loadings of 5 mol % complete conversions of the terminal alkynes and diynes with Markovnikov regioselectivities of over 99% selectivity were observed within 1 h.