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-exophenyl(methyl)boryl)- η⁴-cycloheptatrienylirontricarbonyl (14), which exhibited a single type of intramolecular dynamics, viz., [1,7]-B + [1,2]-Fe diatropic rearrangement.