Dynamic Behavior of Heterobimetallic Derivatives of Cycloheptatriene. Chemically Induced Switch of the Vibration Mode in Molecular Oscillators

Two new heterobimetallic complexes, (7-exo-triphenylstannyl)-η4-cycloheptatrienylirontricarbonyl (3) and (7-exo-triphenylstannyl)-η4-cycloheptatrienylrutheniumtricarbonyl (5),
have been synthesized via the ligand exchange reactions from triphenyl(cycloheptatrienyl)tin (1). Both 3 and 5 are fluxional. Facile [1,3]-Fe and [1,3]-Ru haptotropic shifts are the
fastest dynamic processes observed in 3 and 5, respectively. Slower diatropic rearrangements
involving simultaneous [1,7]-Sn and [1,2]-M (or [1,4]-M) migrations (M = Fe, Ru) were
observed in each case. Activation parameters of the fast rearrangements in 3 and 5 were
determined via 2D EXSY NMR (1H and 13C). The mode of intramolecular oscillations was
switched in solution by reacting 3 with bromodimethylborane, which yielded cleanly (7-exo-phenyl(methyl)boryl)-η4-cycloheptatrienylirontricarbonyl (14), which exhibited a single type
of intramolecular dynamics, viz., [1,7]-B + [1,2]-Fe diatropic rearrangement.