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

A novel series of pi-complexes of phosphino ligands, [Cp*Ru(eta(6)-arene-PAr2)][OTf], has been prepared in which the diarylphosphine unit is attached to a metalated pi-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(eta(6)-p-CH3C6H4-P(p-tol)(2)-Au-Cl)][OTf] and [Cp*Ru(eta(6)-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(eta(6)-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.