Ru-η6-Arene Cations [{( Ph2PC6H4) 2B( η6-Ph)}RuX]+ ( X=Cl, H) as Lewis Acids

The reactivity of [{(Ph2PC6H4)(2)B((6)-Ph)}RuCl][B(C6F5)(4)] (1) as a Lewis acid was investigated. Treatment of 1 with mono and multidentate phosphorus Lewis bases afforded the Lewis acid-base adducts with the ortho-carbon atom of the coordinated arene ring. Similar reactivity was observed upon treatment with N-heterocyclic carbenes; however, adduct formation occurred at both ortho- and para-carbon atoms of the bound arene with the para-position being favoured by increased steric demands. Interestingly treatment with isocyanides resulted in adduct formation with the B-centre of the ligand framework. The hydride-cation [{(Ph2PC6H4)(2)B((6)-Ph)}RuH] [B(C6F5)(4)] was prepared via reaction of 1 with silane. This species in the presence of a bulky phosphine behaves as a frustrated Lewis pair (FLP) to activate H-2 between the phosphorus centre and the ortho-carbon atom of the (6)-arene ring.