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

Abstract

The diamidonaphthalene-bridged diiridium tetrahydride [Ir2{μ-1,8-(NH)2C10H6}(μ-H)H3(NCMe)(PiPr3)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 [Ir2{μ-1,8-(NH)2C10H6}{η2-Z-CH(R)CHR‘}2(PiPr3)2] (R, R‘ = Ph, 4; R, R‘ = Me, 5; and R = Ph, R‘ = Me, 6), respectively. The bis-Z-alkenyl reaction intermediate [Ir2{μ-1,8-(NH)2C10H6}(μ-H)H{Z-C(Ph)CHPh}2(NCMe)(PiPr3)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, [Ir2{μ-1,8-(NH)2C10H6}(μ-H)H3(CO)(PiPr3)2] (2), afford the alkene-carbonyl compounds [Ir2{μ-1,8-(NH)2C10H6}{η2-Z-CH(R)CHR}(CO)(PiPr3)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 [Ir2{μ-1,8-(NH)2C10H6){η2-CH2C(Me)SiMe3}2(PiPr3)2] (10) through the bis-gem-alkenyl intermediate [Ir2{μ-1,8-(NH)2C10H6}(μ-H)H{CHC(Me)SiMe3}2(NCMe)(PiPr3)2] (9). A similar reaction with bis(trimethylsilyl)acetylene forms the bis-vinylidene complex [Ir2{μ-1,8-(NH)2C10H6){CC(SiMe3)2}2(PiPr3)2] (11) together with 2 equiv of H2CC(SiMe3)2. The corresponding reactions of these silyl-substituted alkynes with complex 2 give the mixed-valence compound [Ir2{μ-1,8-(NH)2C10H6}H{CHC(Me)SiMe3}(CO)(PiPr3)2] (12) and the vinylidene-carbonyl derivative [Ir2{μ-1,8-(NH)2C10H6){CC(SiMe3)2}(CO)(PiPr3)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.