367276-96-8Relevant academic research and scientific papers
N/O- and C-bound (enolato)palladium complexes with hydrotris(pyrazoly)borato ligands (TpR: R = iPr2, Me2) obtained via dehydrative condensation between the hydroxo complexes TpRPd(Py)OH and active methylene compounds: Factors determining the isomer distribution and dimerization of cyano compounds
Kujime, Masato,Hikichi, Shiro,Akita, Munetaka
, p. 4049 - 4060 (2001)
Reaction of a hydroxopalladium complex bearing the TpiPr2 ligand, (TpiPri2)(py)Pd-OH (1iPr2), with active methylene compounds, X-CH2-Y 2 [dicyanomethane (2a), methyl cyanoacetate (2b), benzoylacetonitrile (2c)], resulted in dehydrative condensation to afford the N/O-bound enolates, (TpiPr2)(py)Pd-X-CH-Y 3iPr2a-c. When the hydroxo complex 1Mei2 with the less bulky TpMe2 ligand was allowed to react with 2 at 0°C, similar N/O-bound enolato complexes, (TpMe2)(py)Pd-X-CH-Y (3Mei2a-c), were obtained as kinetic products, which were gradually converted to the more stable C-bound enolato complexes (TpMe2)(py)Pd-CHXY (4Me2a-c) upon warming to 50°C. X-ray crystallography of the N/O- and C-bound enolates reveals that (1) the Pd center adopts the square-planar or square-pyramidal geometry, (2) the structure of the C-bound isomer is consistent with the canonical structure with the localized bonding scheme, and (3) in the N/O-bound isomers the negative charge is delocalized over the X-CH-Y linkage to form the zwitterionic structure. The N-bound enolato complexes 3a,b obtained from cyano compounds further reacted with the cyano compounds to give the 1:2 condensates: i.e., the 2-cyanoethenylamido complexes (TpR)(py)Pd-NH-C(CH2Y)=CCN-(Y) (6), whereas the C-bound enolates 4Me2a,b showed no indication of the dimerization. Thus, the present study reveals that the reactivity of transition-metal enolates is dependent on their structures.
