Organochromium(III) macrocyclic complexes. Factors controlling homolytic vs heterolytic cleavage of the chromium carbon bond

• Published in: Inorganic chemistry Vol. 29; no. 21; pp. 4318 - 4322
• Main Authors: Shi, Shu, Espenson, James H, Bakac, Andreja
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.10.1990
• Subjects: 400201 - Chemical & Physicochemical Properties; 400202 - Isotope Effects, Isotope Exchange, & Isotope Separation; ALKANES; CHEMICAL REACTION KINETICS; CHEMICAL REACTIONS; Chemistry; CHROMIUM COMPLEXES; COMPLEXES; DATA; DECOMPOSITION; DEUTERIUM; Exact sciences and technology; EXPERIMENTAL DATA; HETEROCYCLIC COMPOUNDS; HYDROCARBONS; HYDROGEN ISOTOPES; HYDROLYSIS; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ISOTOPE EFFECTS; ISOTOPES; KINETICS; Kinetics and mechanisms; LIGHT NUCLEI; LYSIS; NUCLEI; NUMERICAL DATA; ODD-ODD NUCLEI; Organic chemistry; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; REACTION KINETICS; Reactivity and mechanisms; SOLVOLYSIS; STABLE ISOTOPES; TRANSITION ELEMENT COMPLEXES; Chromium Organic compounds; Nitrogen heterocycle; Activation parameter; Transition metal Complexes; Trivalent metal Complexes; Macrocycle; Hydrolysis; Hydroxo complex; Organic free radical; Chromium III Complexes; Chemical decomposition; Kinetics; Chemical reactivity; Hydrates
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic00346a030

Kinetics studies were done of the homolytic and heterolytic cleavage reactions of the chromium-carbon bonds in the complexes RCr(L)A{sup n+} (where L = (15)aneN{sub 4} = 1,4,8,12-tetraazacyclopentadecane; A = H{sub 2}O, OH{sup {minus}}). Activation parameters for homolysis of RCrL(H{sub 2}O){sup 2+} are as follows: 111 {plus minus} 2, 54 {plus minus} 6 (R = p-CH{sub 3}C{sub 6}H{sub 4}CH{sub 2}); 103 {plus minus} 2, 28 {plus minus} 5 (C{sub 6}H{sub 5}CH{sub 2}); 101 {plus minus} 3, 22 {plus minus} 9 (p-BrC{sub 6}H{sub 4}CH{sub 2}); 110 {plus minus} 3, 62 {plus minus} 6 (i-C{sub 3}H{sub 7}). The {Delta}H{sup {double dagger}} and {Delta}S{sup {double dagger}} parameters are considerably smaller than those for homolysis of (H{sub 2}O){sub 5}CrR{sup 2+} analogues. Primary alkyl macrocyclic complexes do not undergo homolysis. The complexes RCrL(OH){sup +} slowly hydrolyze for R = n-C{sub 3}H{sub 7} and i-C{sub 3}H{sub 7} whereas those for which R = ArCH{sub 2} do not. The activation parameters for hydrolysis are 78 {plus minus} 1, {minus}53 {plus minus} 2 (R = i-C{sub 3}H{sub 7}) and 83 {plus minus} 3, {minus}46 {plus minus} 9 (n-C{sub 3}H{sub 7}). This pathway shows no solvent deuterium isotope effect. The complexes RCrL(H{sub 2}O){sup 2+} are not subject to acidolysis by H{sub 3}O{sup +} or H{sub 2}O, unlike their (H{sub 2}O){sub 5}CrR{sup 2+} analogues. 23 refs., 3 figs., 2 tabs.