Reactions of Diamidonaphthalene-Bridged Diiridium Tetrahydrides with Alkynes: Hydrogenation, Vinylidene Formation, and Catalytic C−C Coupling

The diamidonaphthalene-bridged diiridium tetrahydride [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }(μ-H)H 3 (NCMe)(P i Pr 3 ) 2 ] ( 1 ) reacts with an excess of internal alkynes such as diphenylacetylene, 2-butyne, or 1-phenyl-1-propyne to give the diiridium(I) alkene compounds [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }{η 2 - Z -CH(R) CHR‘} 2 (P i Pr 3 ) 2 ] (R, R‘ = Ph, 4; R, R‘ = Me, 5; and R = Ph, R‘ = Me, 6 ), respectively. The bis- Z -alkenyl reaction intermediate [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }(μ-H)H{ Z -C(Ph) CHPh} 2 (NCMe)(P i Pr 3 ) 2 ] ( 3 ) has been isolated and characterized in the case of diphenylacetylene as substrate. The reactions of diphenylacetylene and 2-butyne with the carbonyl analogue of 1, [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }(μ-H)H 3 (CO)(P i Pr 3 ) 2 ] ( 2 ), afford the alkene-carbonyl compounds [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }{η 2 - Z -CH(R) CHR}(CO)(P i Pr 3 ) 2 ] (R = Ph, 7; R = Me, 8 ). Similar reactions using silyl-substituted alkyne substrates seem to involve alkyne to vinylidene rearrangements. Thus, reaction of 1 with excess trimethylsilyl-1-propyne affords the product [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 ){η 2 -CH 2 C(Me)SiMe 3 } 2 (P i Pr 3 ) 2 ] ( 10 ) through the bis-gem-alkenyl intermediate [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }(μ-H)H{CH C(Me)SiMe 3 } 2 (NCMe)(P i Pr 3 ) 2 ] ( 9 ). A similar reaction with bis(trimethylsilyl)acetylene forms the bis-vinylidene complex [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 ){C C(SiMe 3 ) 2 } 2 (P i Pr 3 ) 2 ] ( 11 ) together with 2 equiv of H 2 C C(SiMe 3 ) 2 . The corresponding reactions of these silyl-substituted alkynes with complex 2 give the mixed-valence compound [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 }H{CH C(Me)SiMe 3 }(CO)(P i Pr 3 ) 2 ] ( 12 ) and the vinylidene-carbonyl derivative [Ir 2 {μ-1,8-(NH) 2 C 10 H 6 ){C C(SiMe 3 ) 2 }(CO)(P i Pr 3 ) 2 ] ( 13 ) as final products, respectively. The complexes 4 − 6 and 11 are effective catalysts for 1-alkyne couplings to give mixtures of Z -butenyne dimers and hexadienyne trimers.