Hydrolysis of the nickel-carbon bond of organonickel tetramethylcyclam complexes
The cationic organometallic complexes (1R,4S,8R,11S)-RNi(tmc)/sup +/ (where tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) hydrolyze in alkaline, aqueous solutions to yield the alkane RH and HONi(tmc)/sup +/, the hydroxonickel(II) macrocycle. The rates of reaction are independent of pH (for 9 < pH < 13). Aside from a few special cases, the hydrolysis rate constants are rather insensitive to the variation of R in a series of 20 compounds that includes alkyls (R = CH/sub 3/, C/sub 2/H/sub 5/, n-C/sub 3/H/sub 7/, i-C/sub 3/H/sub 7/, sec-C/sub 4/H/sub 9/, CH/sub 2/C/sub 6/H/sub 5/), cyclopropyl, and substituted alkyls (e.g., (CH/sub 2/)/sub n/X, with X = Br, Cl, OH, and OTs; n = 3-6). These complexes, and also such bimetallic analogues as (Ni(tmc)(CH/sub 2/)/sub 5/Cr((15)aneN/sub 4/)/sup 3 +/), have k/sub hyd/ in the range (0.8-2.7) x 10/sup -2/ s/sup -1/ at 25.0/sup 0/C. The activation parameters also span a narrow range, with ..delta..H double dagger approx. 16 kcal mol/sup -1/ and ..delta..S double dagger approx. -14 cal mol/sup -1/ K/sup -1/. The solvent deuterium kinetic isotope effect determined for several of these complexes is appreciable, k/sub H//k/sub D/ = 2.2-3.5, suggesting appreciable proton transfer from water to the incipient hydrocarbon in the transition state. Nucleophilic assistance by OH/sup -/, OAc/sup -/, and NH/sub 3/ was not observed. Exceptions to the general pattern were noted. The most striking cases are R = (CH/sub 2/)/sub 3/OH, where the enhanced rate of hydrolysis (k/sub hyd/ = 0.23 s/sup -1/) suggests assistance from the pendant OH group in a cyclic transition state and cycloalkyls (other than cyclopropyl), where the enhanced rates (e.g., cyclobutyl approx. 0.2 s/sup -1/ and cyclopentyl > 2 s/sup -1/) suggest an acceleration by the strain of the nickel-carbon bond. In acidic solutions, the hydrolysis rate is enhanced because of direct protonolysis. The bimolecular reaction between C/sub 2/H/sub 5/Ni(tmc)/sup +/ and H/sub 3/O/sup +/ has k = 5 x 10/sup 5/ M/sup -1/ s/sup -1/. 26 references, 3 figures, 3 tables.
- Research Organization:
- Iowa State Univ., Ames
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 7138484
- Journal Information:
- Inorg. Chem.; (United States), Vol. 25:23
- Country of Publication:
- United States
- Language:
- English
Similar Records
Reduction-induced cleavage of the cobalt-carbon bond in macrocyclic organocobalt complexes
Organochromium(III) macrocyclic complexes. Factors controlling homolytic vs heterolytic cleavage of the chromium-carbon bond
Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DEUTERIUM
ISOTOPE EFFECTS
NICKEL COMPLEXES
HYDROLYSIS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
EXPERIMENTAL DATA
TRACER TECHNIQUES
CHEMICAL REACTIONS
COMPLEXES
DATA
DECOMPOSITION
HYDROGEN ISOTOPES
INFORMATION
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
LYSIS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
SOLVOLYSIS
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation