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), Journal Name: Inorg. Chem.; (United States) Vol. 25:23; 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
CHEMICAL REACTIONS
COMPLEXES
DATA
DECOMPOSITION
DEUTERIUM
EXPERIMENTAL DATA
HYDROGEN ISOTOPES
HYDROLYSIS
INFORMATION
ISOTOPE APPLICATIONS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
LYSIS
NICKEL COMPLEXES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
SOLVOLYSIS
STABLE ISOTOPES
TRACER TECHNIQUES
TRANSITION ELEMENT COMPLEXES