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

Two new heterobimetallic complexes, (7- exo -triphenylstannyl)-η 4 -cycloheptatrienylirontricarbonyl ( 3 ) and (7- exo -triphenylstannyl)-η 4 -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 ( 1 H and 13 C). The mode of intramolecular oscillations was switched in solution by reacting 3 with bromodimethylborane, which yielded cleanly (7- exo -phenyl(methyl)boryl)-η 4 -cycloheptatrienylirontricarbonyl ( 14 ), which exhibited a single type of intramolecular dynamics, viz., [1,7]-B + [1,2]-Fe diatropic rearrangement.