SYNTHESIS AND REACTIVITY OF (ETA(3)-PENTADIENYL)IR(PET(3))(2) AND (ETA(3)-2,4-DIMETHYLPENTADIENYL)IR(PET(3))(2)

Treatment of[ClIr(PEt(3))(2)](2) with potassium pentadienide or potass ium 2,4-dimethylpentadienide produces (eta(3)-pentadienyl)Ir(PEt(3))(2 ) (1) or (eta(3)-2,4-dimethylpentadienyl)Ir(PEt(3))(2) (2) in high yie ld, In solution, compound 1 exists as a 70:30 equilibrium mixture of a ntipentadienyl (1a) and syn-pentadienyl (1s) isomers, while compound 2 exists exclusively in the anti form. Both 1a and 2 undergo a low-ener gy fluxional process that exchanges the ends of the anti-eta(3)-pentad ienyl ligand via an 18e(-) eta(5)-pentadienyl intermediate. Treatment of 1 and 2 with Lewis bases, L, leads to the formation of known (penta dienyl)Ir(PEt(3))(2)L complexes. In particular, addition of 1 equiv of PEt(3) to 1 and 2 produces ((1,4,5-eta)pentadienyl)Ir(PEt(3))(3) and mer-CH=C(Me)CH=C(Me)CH2Ir(PEt(3))(3)(H), respectively, while addition of CO produces )(2)(CO)/((1-3-eta)-pentadienyl)Ir(PEt(3))(2)-(CO) and ,5-eta)-2,4-dimethylpentadienyl)Ir(PEt(3))(2)(CO), respectively. Compo unds 1 and 2 also react with Lewis acids, Hence, treatment with trifli c acid produces (eta(5)-pentadienyl)Ir(PEt(3))(2)(H)(O3SCF3-)-O-+ (3) and )-2,4-dimethylpentadienyl)Ir(PEt(3))(2)(H)+O3SCF3- (4), respective ly, while treatment with methyl triflate generates (eta(5)-pentadienyl )Ir(PEt(3))(2)(CH3)(+). O3SCF3- (5) and 2,4-dimethylpentadienyl)Ir(PEt (3))(2)(CH3)+O3SCF3- (6), respectively. Compounds 3-6 adopt unsymmetri cal structures in which. one phosphine resides under a pentadienyl edg e while the other phosphine is situated under the pentadienyl mouth, C ompound 3 undergoes a fluxional process in solution that involves rota tion of the eta(5)-pentadienyl ligand with respect to the Ir(PEt(3))(2 )(H) fragment, Under this process, the two phosphines exchange positio ns and the two ends of the pentadienyl ligand become equivalent. Compo unds 3-6 react with bis(triphenylphosphine)nitrogen(1+) chloride (PPNCl-), a source of Cl-, to produce (syn-eta(3)-pentadienyl)Ir(PEt(3))(2 )(H)(Cl) (7), ta(3)-2,4-dimethylpentadienyl)Ir(PEt(3))(2)(H)(Cl) (8), (syn-eta 3-pentadienyl)Ir(PEt(3))(2)(CH3)(Cl) (9), and (3)-2,4-dimethy lpentadienyl)Ir(PEt(3))(2)(CH3)(Cl) (10), respectively. In these compo unds, the phosphine ligands are situated trans to the pentadienyl liga nds.