Fluxionality in the Tropolone Hinokitiol Chelate

Abstract

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 RuCl2(PPh3)3 and MHCl­(CO)­(PR3)3 (M = Ru, R = Ph; M = Os, R = Ph and p-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) d6 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 31P NMR. Chlorination with N-chlorosuccinimide results in MCl­(CO)­(hino)­(PPh3)2 (M = Ru and Os). Together these results quantify the fluxionality of this important chelate which in turn has consequences for its biochemistry.

Organometallic Chemistry of the Difluorodithiophosphate Anion

“…The crystal structure of 4 revealed the formation of the cis ‐triphenylphosphine isomer. While less common than complexes with trans ‐triphenylphosphines, complexes with cis ‐triphenylphosphines have been observed: we have for example observed this with a tropolonate derivative, hinokitiol and it has been reported by others previously [30,44–46] …”

“…This can be attributed to less electron density being donated to the metal by the S 2 PF 2 − ligand resulting in weaker π‐backbonding to the carbonyl compared to the S 2 CNH 2 − complexes. Finally, the strong carbonyl stretching band at 1937.0 cm −1 in 2 is at the high end of the range [42] for isostructural RuH(CO)(chelateanion)(PPh 3 ) 2 and also suggests weak σ‐donation by the S 2 PF 2 − anion, or perhaps a degree of π‐backbonding. Structurally, Table 3, significantly larger ligand bite angles and longer Ru−S bond lengths are observed in the S 2 PF 2 complexes.…”

“…While less common than complexes with trans-triphenylphosphines, complexes with cis-triphenylphosphines have been observed: we have for example observed this with a tropolonate derivative, hinokitiol and it has been reported by others previously. [30,[44][45][46] A comparison with complexes of a different small sulfurcontaining ligand, the primary dithiocarbamate analogues RuH(CO)(S 2 CNH 2 )(PPh 3 ) 2 and RuCl(CO)(S 2 CNH 2 )(PPh 3 ) 2 reveals several interesting features. [42] Chlorination of the hydrido complexes with N-chlorosuccinimide results in a change in the geometry of the triphenylphosphines from trans to cis in both cases.…”

Separation of Isomers and Mechanisms of Inversion of Stereochemistry of Group 9 d6 Tris-Chelate Complexes of Hinokitiol

“…Hinokitiol, or 4-isopropyltropolone, is a well-known natural product extracted from the heartwood of the red cedar tree. Although it is readily available, its biological and liganding properties have been surveyed but much of its fundamental chemistry needs further attention. − Recently we have synthesized several osmium and ruthenium complexes of hinokitiol and have studied the unusual fluxional behavior of some of these complexes . Tris-chelate complexes of hinokitiol are less common: only the iron complex has been synthesized previously .…”

“…12−14 Recently we have synthesized several osmium and ruthenium complexes of hinokitiol and have studied the unusual fluxional behavior of some of these complexes. 15 Tris-chelate complexes of hinokitiol are less common: only the iron complex has been synthesized previously. 16 Because of the availability of hinokitiol, tris-chelate complexes of d 6 group 9 complexes of hinokitiol may be a good choice for PVED measurements.…”