Fluxionality in the Tropolone Hinokitiol Chelate.

Tropolonate complexes of Ru(II), Ru(III), and Os(II) with hinokitiol, also termed β-thuljaplicin, or 4-isopropyltropolone, readily formed by chloride and triarylphosphine substitution in RuCl(PPh) and MHCl(CO)(PR) (M = Ru, R = Ph; M = Os, R = Ph and -tolyl). The resulting colorful complexes have variable and strong charge transfer bands and also have a surprising combination of stereochemical selectivity and lability. For the Os(II) d examples, the tropolone chelate has a fluxionality with a barrier of only 90 kJ/mol for the R = aryl examples, as determined by variable-temperature P NMR. Chlorination with -chlorosuccinimide results in MCl(CO)(hino)(PPh) (M = Ru and Os). Together these results quantify the fluxionality of this important chelate which in turn has consequences for its biochemistry.