Computational Study of Tungsten(II)-Catalyzed Rearrangements of Norbornadiene

Rearrangements of norbornadiene (NBD, C7H8) to various alkylidenes, via a hypothetical 7-coordinate tungsten(II) complex W(CO)3I2(NBD), were studied using density-functional theory computations. An extensive search for intermediates and transition states of rearrangement was made. The theoretical method (basis sets and level of DFT) used was justified by new benchmark studies which compare optimized structural parameters to those from crystal structures of several different tungsten complexes. Transition-metal-catalyzed rearrangements of NBD are not as well-known as those of norbornene and are considerably more complicated than had been thought. This work predicts a large variety of intermediates which may be feasible targets for experimental synthesis. All the rearrangement paths to alkylidenes found here feature high activation energies of over 45 kcal mol(-1), implying that self-initiation for the ring-opening metathesis polymerization of NBD via tungsten(II) complexes must occur via an alternative mechanism.