Linkage isomerism in palladium(II)-chloranilate complexes. Synthesis and mechanistic studies of bis(acetonitrile)(chloranilato)palladium(II) and bis(triphenylphosphine)(chloranilato)palladium(II)
Structural and mechanistic studies are reported of a linkage isomerization process in which the bidentate ligand 2,5-dioxo-3,6-dichloro-1,4-benzoquinone (chloranilate dianion, CA/sup 2/minus//) rearranges to a /pi/-complexed diene (/pi/-CA/sup 2/minus//) from an unusual bis(carbanion) resonance form (C-CA/sup 2/minus//) upon the substitution of acetonitrile by triphenylphosphine in the first coordination sphere of palladium(II). Yellow (Pd(C-CA)(CH/sub 3/CN)/sub 2/) may be prepared in excellent yield from the reaction of K/sub 2/Pd(C-CA)Cl/sub 2/ with AgNO/sub 3/ in acetonitrile solution and combines readily with triphenylphosphine to give purpose (Pd(/pi/-CA)(PPh/sub 3/)/sub 2/). Pd(II)-chloranilate complexes were structurally characterized through NMR (/sup 13/C and /sup 31/P), uv-visible, and infrared spectra. Stopped-flow kinetic studies of the (Pd(C-CA)(CH/sub 3/CN)/sub 2/) transformation to (Pd(/pi/-CA)(PPh/sub 3/)/sub 2/) in acetonitrile solution demonstrate that rate-limiting linkage isomerization (rate constant k/sub i/) follows rapid, preequilibrium formation of (Pd(C-CA)(PPh/sub 3/)/sub 2/) (stepwise formation constants K/sub 1/ and K/sub 2/). At 25.0/degree/C, K/sub 2/ = 2.47 /times/ 10/sub 2/ M/sup /minus/1/ and k/sub i/ = 8.44 /times/ 10/sup /minus/2/ s/sup /minus/1/. Kinetic temperature dependence results gave the activation parameters that govern k/sub i/ (/Delta/H/double dagger/ = 17.1 kcal/mol; /Delta/S/double dagger/ = /minus/6 eu) and standard enthalpy/entropy changes corresponding to K/sub 2/ (/Delta/H/degree/ = /minus/14.0 kcal/mol; /Delta/S/degree/ = /minus/36 eu). The exceptionally high enthalpic activation barrier to linkage isomerization reflects the considerable stability of the five-membered, bis(carbanion) chelate ring in (Pd(C-CA)(CH/sub 3/CN)/sub 2/). 30 references, 4 figures, 2 tables.
- Research Organization:
- Texas Tech Univ., Lubbock (USA)
- OSTI ID:
- 5826309
- Journal Information:
- Inorg. Chem.; (United States), Vol. 27:15
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACETONITRILE
ISOMERIZATION
AROMATICS
CHLORINE COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PALLADIUM COMPLEXES
CARBON 13
CHEMICAL PREPARATION
EXPERIMENTAL DATA
MOLECULAR STRUCTURE
NMR SPECTRA
PHOSPHORUS 31
ULTRAVIOLET SPECTRA
VISIBLE SPECTRA
CARBON ISOTOPES
CHEMICAL REACTIONS
COMPLEXES
DATA
EVEN-ODD NUCLEI
HALOGEN COMPOUNDS
INFORMATION
ISOTOPES
LIGHT NUCLEI
NITRILES
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHORUS ISOTOPES
SPECTRA
STABLE ISOTOPES
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation