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Carbocations as Secondary Coordination Sphere Z-Type Ligands – Anion-Induced Au(I)/Au(III) Oxidation and Impact on Reactivity
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submitted on 08.08.2019 and posted on 09.08.2019by Lewis Wilkins, Francois Gabbai
describe our efforts towards the design of phosphine-based ligands featuring an
electrophilic carbocationic moiety positioned to enter the secondary
coordination sphere of the phosphine-bound metal atom. Using simple synthetic protocols, we have
been able to obtain and fully characterize the complexes [(o-Ph2P(C6H4)Acr)AuCl]+
(+, Acr = 9-N-methylacridinium) and [(o-Ph2P(C6H4)Xan)AuCl]+
(+, Xan =
9-xanthylium). While only weak
interactions occur between the gold atom and the methylium centers of these
complexes, the more Lewis acidic +
readily reacts with chloride to afford a trivalent phosphine gold dichloride
derivative (7) in which the metal
atom is covalently bound to the former methylium center. This anion-induced Au(I)/Au(III) oxidation is
accompanied by a conversion of the Lewis acidic methylium center in + into an X-type ligand in
This transformation leads us to conclude that the methylium center acts
as a latent Z-type ligand poised to increase the Lewis acidity of the gold
center, a notion supported by the carbophilic reactivity of these complexes.