N/O- and C-Bound (Enolato)palladium Complexes with Hydrotris(pyrazolyl)borato Ligands (TpR: R = iPr2, Me2) Obtained via Dehydrative Condensation between the Hydroxo Co
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- 作者：Masato Kujime ; Shiro Hikichi ; and Munetaka Akita
- 刊名：Organometallics
- 出版年：2001
- 出版时间：September 17, 2001
- 年：2001
- 卷：20
- 期：19
- 页码：4049 - 4060
- 全文大小：197K
- 年卷期：v.20,no.19(September 17, 2001)
- ISSN：1520-6041
文摘
Reaction of a hydroxopalladium complex bearing the TpiPr2 ligand, (TpiPr2)(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-boundenolates, (TpiPr2)(py)Pd-X-CH-Y 3iPr2a-c. When the hydroxo complex 1Me2 with the lessbulky TpMe2 ligand was allowed to react with 2 at 0 
C, similar N/O-bound enolato complexes,(TpMe2)(py)Pd-X-CH-Y (3Me2a-c), were obtained as kinetic products, which were graduallyconverted 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 revealsthat (1) the Pd center adopts the square-planar or square-pyramidal geometry, (2) thestructure of the C-bound isomer is consistent with the canonical structure with the localizedbonding scheme, and (3) in the N/O-bound isomers the negative charge is delocalized overthe X-CH-Y linkage to form the zwitterionic structure. The N-bound enolato complexes3a,b obtained from cyano compounds further reacted with the cyano compounds to give the1:2 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 dependenton their structures.
C, similar N/O-bound enolato complexes,(TpMe2)(py)Pd-X-CH-Y (3Me2a-c), were obtained as kinetic products, which were graduallyconverted 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 revealsthat (1) the Pd center adopts the square-planar or square-pyramidal geometry, (2) thestructure of the C-bound isomer is consistent with the canonical structure with the localizedbonding scheme, and (3) in the N/O-bound isomers the negative charge is delocalized overthe X-CH-Y linkage to form the zwitterionic structure. The N-bound enolato complexes3a,b obtained from cyano compounds further reacted with the cyano compounds to give the1:2 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 dependenton their structures.