Kinetics of Environmental Averaging, and the Stereochemistry of (CH3)ClGe(C5H7O2)2. A Case of a Second Order Kinetic Process

Abstract

Dynamic n.m.r. studies on the stereochemistry of (CH3)ClGe(C5H7O2)2 (acac = C5H7O2−), indicate that the complex adopts the cis configuration in CDCl3–CCl4 solutions. Kinetics of environmental averaging of the acac ring proton (—CH=) and acac methyl groups between the respective nonequivalent sites in the C1 isomer have been investigated in the temperature range −31.0 to 23.1° by line-broadening techniques. Kinetics of the averaging process are second order in complex concentration. Activation parameters are: Ea = 6.0 ± 0.3 kcal/mol, ΔS≠ = −30 ± 1 e.u., and k25 = 1.6 × 102 M−1 S−1. Rearrangements are viewed as occurring via a germanium–oxygen bond rupture as a first step to yield a five-coordinate intermediate. The rate-determining sequence is thought to involve proper orientation of two five-coordinate species prior to formation of a bis-acac bridged dimer.