Reactions of Ir(acac)(cyclooctene)(PCy(3)) with H-2, HC CR, HSiR(3), and HSnPh(3): The acetylacetonato ligand as a stabilizer for iridium(I), iridium(III), and iridium(V) derivatives

The acetylacetonato complex Ir(acac)(cyclooctene)(PCy(3)) (1) reacts with molecular hydrogen in the presence of 1 equiv of PCy(3) to give Ir(acac)H-2(PCy(3))(2) (2). The addition of 1 equiv of PhC=CH to a benzene-d(6) solution of 1 causes the displacement of the coordinated olefin and the formation of Ir(acac)(eta(2)-PhC=CH)(PCy(3)) (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{kappa(3)-CH=C(Ph)CH[C(O)CH3](2)}(C(2)Ph)(CPh=CH2)(PCy(3)) (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-C-3(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(C(2)Ph)(PCy(3))(2) (5). Under the same conditions, CyC=CH and Me(3)SiC=CH afford the corresponding hydrido-alkynyl derivatives Ir(acac)H(C(2)R)(PCy(3))2 (R=Cy (6), Me(3)Si (7)), The addition of silanes HSiR(3) to 1 gives Ir(acac)H(SiR(3))(PCy(3)) (SiR(3) = SiEts (8), SiPh(3) (9), SiHPh(2) (10)). The structure of 8 was also determined by an X-ray analysis. The coordination geometry around the metallic center of 8 can be 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 PCy(3), the reactions of 1 with silanes lead to Ir(acac)H(SiR(3))(PCy(3))(2) (SiR(3) = SiEt(3) (11), SiHPh(2) (12), SiH(2)Ph (13)), Complex 1 also reacts with HSnPh(3). In the absence of PCy(3) the reaction product is Ir(acac)H(SnPh(3))(PCy(3)) (14), while in the presence of PCy(3) the six-coordinate derivative Ir(acac)H(SnPh(3))(PCys)(2) (18) is obtained, Under atmospheric pressure of hydrogen, complex 8 is converted into the trihydrido-silyl-iridium(v) derivative Ir(acac)H-3(SiEt(3))(PCy(3)) (32). In solution, this complex is fluxional with values of Delta H-double dagger and Delta S-double dagger 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 HSiEt(3) to PhC=CH. In all experiments, PhCH=CH2, PhC=CSiEt(3), cis-PhCH=CH(SiEt(3)), trans-PhCH=CH(SiEt(3)), and Ph(SiEt(3))C=CH2 were obtained, The major product in all cases is the thermodynamically less stable cis-PhCH=CH(SiEt(3)), resulting from the anti-addition of the silane to the alkyne, This product is selectively formed in approximately 70% yield.