Reactions of Ir(acac)(cyclooctene)(PCy3) with H2, HC≡CR, HSiR3, and HSnPh3: The acetylacetonato ligand as a stabilizer for iridium(I), iridium(III), and iridium(V) derivatives

摘要

The acetylacetonato complex Ir(acac)(cyclooctene)(PCy3) (1) reacts with molecular hydrogen in the presence of 1 equiv of PCy3 to give Ir(acac)H2(PCy3)2 (2). The addition of 1 equiv of PhC≡CH to a benzene-d6 solution of 1 causes the displacement of the coordinated olefin and the formation of Ir(acac)(η2-PhC≡CH)(PCy3) (3). The addition of hexane to this solution reverses the reaction and precipitates 1. The treatment of 1 with 3 equiv of PhC≡CH affords Ir{κ3-CH=C(Ph)CH[C(O)CH3]2}(C 2Ph)(CPh=CH2)(PCy3) (4), which is a result of the oxidative addition of the HC≡ bond of an alkyne, the insertion of a second alkyne into an Ir-C3(acac) bond, and the subsequent insertion of a third alkyne into the Ir-H bond, previously formed. The structure of 4 was determined by an X-ray investigation. The coordination geometry around the iridium atom can be rationalized as a distorted octahedron with the bicyclic ligand occupying three coordination sites of a octahedral face. In the presence of PCy3 the reaction of 1 and PhC≡CH leads to Ir(acac)H(C2Ph)(PCy3)2 (5). Under the same conditions, CyC=CH and Me3SiC≡CH afford the corresponding hydrido-alkynyl derivatives Ir(acac)H-(C2R)(PCy3)2 (R = Cy (6), Me3Si (7)). The addition of silanes HSiR3 to 1 gives Ir(acac)H-(SiR3)(PCy3) (SiR3 = SiEt3 (8), SiPh3 (9), SiHPh2 (10)). The structure of 8 was also determined by an X-ray analysis. The coordination geometry around the metallic center of 8 can be rationalized as a square pyramid with the triethylsilyl group located at the apex. In the presence of PCy3, the reactions of 1 with silanes lead to Ir(acac)H(SiR3)(PCy3)2 (SiR3 = SiEt3 (11), SiHPh2 (12), SiH2Ph (13)). Complex 1 also reacts with HSnPh3. In the absence of PCy3 the reaction product is Ir(acac)H(SnPh3)(PCy3) (14), while in the presence of PCy3 the six-coordinate derivative Ir(acac)H(SnPh3)(PCy3)2 (15) is obtained. Under atmospheric pressure of hydrogen, complex 8 is converted into the trihydrido-silyl-iridium(V) derivative Ir(acac)H3(SiEt3)(PCy3) (32). In solution, this complex is fluxional with values of ΔH# and ΔS# of 12.23 (± 0.76) kcal mol-1 and 1.45 (± 1.84) cal K-1 mol-1, respectively. Complex 8 has also been found to be an active catalyst for the addition of HSiEt3 to PhC≡CH. In all experiments, PhCH=CH2, PhC≡CSiEt3, cis-PhCH=CH(SiEt3), trans-PhCH=CH(SiEt3), and Ph(SiEt3)C=CH2 were obtained. The major product in all cases is the thermodynamically less stable cis-PhCH=CH(SiEt3), resulting from the anti-addition of the silane to the alkyne. This product is selectively formed in approximately 70% yield.