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Oxidation of CH 3 NH 2 and (CH 3 ) 2 NH by Ni III (cyclam)(H 2 O) 2 3+ in Aqueous Solutions
Author(s) -
Shamir Dror,
Zilbermann Israel,
Maimon Eric,
Meyerstein Dan
Publication year - 2004
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200400033
Subject(s) - chemistry , cyclam , amine gas treating , nickel , ligand (biochemistry) , medicinal chemistry , crystallography , inorganic chemistry , stereochemistry , metal , organic chemistry , biochemistry , receptor
Ni II (1,4,8,11‐tetraazacyclotetradecane) 2+ , Ni II L 2+ , is a good electrocatalyst for the oxidation of CH 3 NH 2 and (CH 3 ) 2 NH but not of (CH 3 ) 3 N. The oxidation kinetics of the amines by Ni III L(H 2 O) 2 3+ indicate that the amines are good axial ligands to the tervalent nickel complex. The complexes Ni III L[N(CH 3 ) i H 3− i ](H 2 O) 3+ are stronger oxidants than the complexes Ni III L[N(CH 3 ) i H 3− i ] 2 3+ . The oxidation is base‐catalyzed and obeys a second‐order rate law in Ni III LX 2 . It is proposed that the key step is Ni III −L(H 2 O)[N(CH 3 ) i H 2− i ] 2+ + Ni III LX 2 → LNi II −N(=CH 2 )(CH 3 ) i −1 H 2− i + Ni II L 2+ + H 3 O + + 2 X. Naturally, N(CH 3 ) 3 is not oxidized by this mechanism. Of special interest is the observation that the axial ligands CH 3 NH 2 and (CH 3 ) 2 NH are oxidized by the central cation, while the cyclam ligand, which has four secondary amine groups bound to the nickel( III ) ion, and axially bound pendant primary amine groups, which are covalently linked to the macrocyclic ligand, are relatively stable. This difference in the behavior of axially bound amine groups is attributed to the free rotation of the axially bound N(CH 3 ) i H 3− i ligands that is required for the oxidation to proceed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)