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), Journal Name: Inorg. Chem.; (United States) Vol. 27:15; ISSN INOCA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ACETONITRILE
AROMATICS
CARBON 13
CARBON ISOTOPES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
CHLORINE COMPOUNDS
COMPLEXES
DATA
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HALOGEN COMPOUNDS
INFORMATION
ISOMERIZATION
ISOTOPES
LIGHT NUCLEI
MOLECULAR STRUCTURE
NITRILES
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PALLADIUM COMPLEXES
PHOSPHORUS 31
PHOSPHORUS ISOTOPES
SPECTRA
STABLE ISOTOPES
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
ULTRAVIOLET SPECTRA
VISIBLE SPECTRA