Heptadentate, Octadentate, Or Even Nonadentate? Denticity in the Unexpected Formation of an All-Carbon Donor-Atom Ligand in Rh^III(Cp*)(Anthracenyl-NHC) Complexes

Abstract

Investigations on incorporating an N-flanking anthracenyl moiety to [Rh­(Cp*)­(NHC)­Cl2] complexes surprisingly led to the formation of an intramolecular C–C bond between the Cp* and anthracenyl moieties, with additional auxiliary interactions between the metal and the anthracenyl ring system. In silico modeling supports a reaction mechanism whereby Rh­(η4-tetramethylfulvene) intermediates undergo metallocycloaddition and the abstraction of a chlorido ligand, affording unique cationic complexes that feature Rh centers coordinated by a nonadentate ligand with exclusively carbon donor atoms. Some Rh–C interactions were extremely weak but nevertheless exhibited covalent bonding character. These weak Rh–C interactions were readily displaced by stronger electron donors, and the nonadentate ligand reverted to the heptadentate coordination mode observed in the intermediate. As far as we are aware, this study provides the first conclusive evidence of complexes bearing a single nonadentate κ9-coordinating ligand that features only carbon donors bound to a metal center.

Anthracenyl Functionalization of Half-Sandwich Carbene Complexes: In Vitro Anticancer Activity and Reactions with Biomolecules

“…Complex 4a crystallized in the P 2 1 /n monoclinic space group and featured the pseudo-octahedral piano-stool configuration similar to that of the Rh analogue (Supporting Information). The bond lengths for Ir–C carbene (2.040(2) Å) and Ir–Cl (2.4155(6) and 2.4272(6) Å) are similar to those observed for the Rh analog. The Cp* ligand of one molecule of 4a interacted through π-stacking with the anthracene moiety of another molecule, with the shortest distance at 3.394 Å.…”

“…Ruthenium­(III) chloride hydrate (99%), iridium­(III) chloride hydrate (99%), and rhodium­(III) chloride hydrate (99%) were purchased from Precious Metal Online, and Os­(III)­chloride hydrate (55% metal content) was purchased from Heraeus South Africa. [Ru­(cym)­Cl 2 ] 2 , [Os­(cym)­Cl 2 ] 2 , [Ir­(Cp*)­Cl 2 ] 2 , [Rh­(Cp*)­Cl 2 ] 2 , 3-(anthracen-9-yl­methyl)-1-methyl­(benz)­imidazolium chloride, and Rh complexes 3a and 5a were synthesized following literature procedures.…”

“…We have recently expanded to anthracenyl-functionalized NHC–Rh III (Cp*) complexes, which underwent interesting reactions in solution involving intramolecular C–C bond formation and the formation of a complex with a multidentate all-carbon-donor-atom ligand . Here, we report on a series of isostructural Ru, Os, Rh, and Ir complexes featuring an NHC ligand with a pendant anthracenyl substituent.…”

“…41 We have recently expanded to anthracenyl-functionalized NHC−Rh III (Cp*) complexes, which underwent interesting reactions in solution involving intramolecular C−C bond formation and the formation of a complex with a multidentate all-carbon-donor-atom ligand. 44 Here, we report on a series of isostructural Ru, Os, Rh, and Ir complexes featuring an NHC ligand with a pendant anthracenyl substituent. We investigated the anticancer activity of the complexes in different human cancer cell lines in terms of cytotoxicity and cell morphology and studied their interactions with biomolecules, including the characterization of binding to hen egg white lysozyme (HEWL) by protein crystallography.…”

Synthetic Strategy Towards Heterodimetallic Half-Sandwich Complexes Based on a Symmetric Ditopic Ligand

“…In the case of the Os-Ir compound 2f , minor changes were observed, but these were not as pronounced as those observed for 2c ( Supplementary Figure S22 ). Interestingly, for the Cp* signals in the spectra of both compounds, we observed changes in the aliphatic region which require further investigations ( Banerjee et al, 2018 ; Lee B. Y. T. et al, 2021 ; Lee B. et al, 2021 ). In 10% DMSO- d 6 /D 2 O, the spectra of 2f changed over time which was suppressed by the addition of 100 mM NaCl, to approximate the standard chloride concentration in blood.…”