Preparation of Novel Rhodonocenium Complexes via [2 + 2 + 1] Cyclotrimerization of Terminal Aryl Alkynes

Reactions of [Cp*Rh(η 2 -NO 3 )(OTf)] ( 1 ), which bears two labile ligands (NO 3 - and OTf - ), with a terminal aryl alkyne (phenylacetylene (HC⋮CPh) or 4-ethynyltoluene (HC⋮CC 6 H 4 CH 3 )) in alcohol (EtOH or n -BuOH) gave the substituted-rhodocenium cation [Cp*Rh(η 5 -C 5 H 2 Ar 2 −CH(Ar)OR)] + (OTf) - ( 2a − d: Ar = Ph, p -tolyl; R = Et, n -Bu). Treatment of 1 with 4-ethynyltoluene in ethanol followed by the addition of a pseudo-halide (HSPh, Me 3 SiN 3, or Me 3 SiNCS) in dichloromethane also produced the substituted-rhodocenium cation [Cp*Rh(η 5 -C 5 H 2 ( p -tolyl) 2 −CH( p -tolyl)Nu)] + (OTf) - (Nu - = SPh ( 3a ), N 3 ( 3b ), NCS ( 3c )). All products appeared to have been formed by the formal [2 + 2 + 1] cyclotrimerization of the terminal aryl alkynes and the subsequent nucleophilic addition of the alcohol or pseudo-halide at the exocyclic double bond of a fulvene intermediate. Molecular structures of 2b, c and 3a, c were determined by X-ray diffraction. All complexes are isostructural and show sandwich-type structures composed of one Cp* ligand and one substituted-Cp ligand.