Gold Compounds Anchored to a Metalated Arene Scaffold: Synthesis, X‑ray Molecular Structures, and Cycloisomerization of Enyne

A novel
series of π-complexes of phosphino ligands, [Cp*Ru­(η6-arene-PAr2)]­[OTf], has been prepared
in which the diarylphosphine unit is attached to a metalated π-arene
scaffold. These organometallic phosphino ligands display either an
electron-donating methyl group (−PAr2 = −P­(p-tol)2) or electron-withdrawing trifluoromethyl
group (−PAr2 = −P­(p-C6H4CF3)2). This unique class
of metallo ligands was converted to heterodinuclear gold complexes
upon treatment with [AuCl­(tht)]. The molecular structures of [Cp*Ru­(η6-p-CH3C6H4-P­(p-tol)2-Au-Cl)]­[OTf] and [Cp*Ru­(η6-C6H5-P­(p-C6H4CF3)2)-Au-Cl]­[OTf]
were ascertained by single-crystal X-ray diffraction. A comparative
study of these structures with that of [Cp*Ru­(η6-C6H5-PPh2-Au-Cl)]­[OTf]
previously reported revealed important information about the electronic
nature of the gold center when it is bonded to a −PPh2, −P­(p-tol)2, or −P­(p-C6H4CF3)2 metallo
ligand. DFT computations also shed light on the effect of [Cp*Ru+] coordination to [AuCl­(PAr3)] precatalysts. Several
complexes of the family with electron-donating and -withdrawing groups
were evaluated toward cycloisomerization reactions of a classical N-tethered 1,6-enyne. These results are presented and discussed.