Variable-temperature and -pressure proton nuclear magnetic resonance studies of the rates and mechanisms of N,N-dimethylformamide and acetonitrile exchange with the square-pyramidal complexes mono(solvento){3,7,11-tribenzyl-3,7,11,17-tetra-azabicyclo [11.3.1]heptadeca-1(17),13,15-triene}nickel(II)

Abstract

Rates and activation parameters have been determined for solvent (solv) exchange with square-pyramidal complexes [Ni(L¹)(solv)]²⁺[L¹ is the pyridine-containing tetra-aza macrocycle, 3,7,11-tribenzyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1 (17),13,15-triene; solv =N,N-dimethylformamide or acetonitrile] using variable-temperature and -pressure ¹H n.m.r. spectroscopy. At 298.2 K 10^–2k_ex/s^–1= 32.7 ± 1.9 and 3.82 ± 0.29, ΔH^‡sol;kJ mol^–1= 36.3 ± 1.1 and 68.9 ± 3.8, ΔS^‡/J K^–1 mol^–1=–55.8 ± 3.3 and +35.6 ± l2.3, and at 323 K, ΔV^‡/cm³mol^–1=+10.6 ± 0.8 and –3.5 ± 0.9 for solv =N,N-dimethylformamide and acetonitrile respectively. The mechanistic significance of these data is discussed.