Structure and dynamics of P,N-containing heterocycles and their metal complexes in solution

Conformations and dynamics of 1,5-diaza-3,7-diphosphacyclooctane (1) with chiral l-menthyl substituents on the phosphorus atoms and several metal complexes thereof were investigated by a variety of DNMR methods. In solution 1 adopts a C(2) symmetrical "crown"-like conformation (CW) and the conformational preference and dynamics of the complexes depend on the type of metal: for the Cu complex the CW form is preferred, whereas the Pd, Pt, or Mo complexes exist in an equilibrium of two "chair-boat"-like conformations (CB/CB*). The barriers of interconversion between these two conformations for the Pd and Pt complexes are about 2 times higher than for the Mo complex. Quantum chemical calculations (B3LYP/6-31G(d)) are in agreement with experimental findings.