Competitive Reaction Pathways in the Addition of Phenylacetylene to Diamidonaphthalene-Bridged Diiridium Complexes

The oxidative addition of phenylacetylene to the monohydrido diiridium complex [Ir 2 (μ-1,8-(NH) 2 naphth)H(CO) 2 (PiPr 3 ) 2 ](CF 3 SO 3 ) ( 2 ) and the diiridium(II) species [Ir 2 (μ-1,8-(NH) 2 naphth)(CF 3 SO 3 ) 2 (CO) 2 (PiPr 3 ) 2 ] ( 3 ) has been studied. The kinetic product of the addition to 2 is the dihydridoalkynyl complex [Ir 2 (μ-1,8-(NH) 2 naphth)(μ-C⋮CPh)H 2 (CO) 2 (PiPr 3 ) 2 ](CF 3 SO 3 ) ( 4 ), in which the alkynyl ligand bridges the iridium atoms in a μ,η 1:η 2 -coordination mode. Compound 4 isomerizes in acetone solution to give the hydride-bridged complex [Ir 2 (μ-1,8-(NH) 2 naphth)(μ-H)H(C⋮CPh)(CO) 2 (PiPr 3 ) 2 ](CF 3 SO 3 ) ( 5 ), in which both the alkynyl and the terminal hydride ligands are in a trans position with respect to the bridging hydride. The reaction of phenylacetylene with 3 gives different kinetic products depending on the solvent used. In CH 2 Cl 2, the diiridium(III) derivative [Ir 2 (μ-1,8-(NH) 2 naphth)H(C⋮CPh)(CO) 2 (PiPr 3 ) 2 ](CF 3 SO 3 ) 2 ( 6 ) is obtained. On heating these CH 2 Cl 2 solutions, 6 isomerizes into the vinylidene-bridged complex [Ir 2 (μ-1,8-(NH) 2 naphth)(μ-C CHPh)(CF 3 SO 3 ) 2 (CO) 2 (PiPr 3 ) 2 ]( 7 ), which has been characterized by X-ray diffraction. The triflate ligands of 7 can be substituted by acetonitrile ligands to give the dicationic compound [Ir 2 (μ-1,8-(NH) 2 naphth)(μ-C CHPh)(NCCH 3 ) 2 (CO) 2 (PiPr 3 ) 2 ](CF 3 SO 3 ) 2 ( 8 ). With acetone as the reaction solvent, the addition of phenylacetylene to 3 affords deprotonated compounds of formula [Ir 2 (μ-1,8-(NH) 2 naphth)(C⋮CPh)(CO) 2 (PiPr 3 ) 2 ](CF 3 SO 3 ) ( 9 and 10 ). The thermally stable isomer 10 can be protonated to give 7 but can also react with an excess of phenylacetylene to give the neutral diiridium(II) species [Ir 2 (μ-1,8-(NH) 2 naphth)(C⋮CPh) 2 (CO) 2 (PiPr 3 ) 2 ] ( 11 ), which is the isolable product of the reaction of 3 with an excess of phenylacetylene in acetone. When this latter reaction is carried out in acetone/H 2 O as solvent, the acylalkynyl diiridium(II) complex [Ir 2 (μ-1,8-(NH) 2 naphth)(C⋮CPh)(C(O)CH 2 Ph)(CO) 2 (PiPr 3 ) 2 ] ( 12 ) is the major reaction product. The molecular structure of 12 was determined by X-ray diffraction.