454485-22-4Relevant academic research and scientific papers
Reactions of Cp*(PMe3)Ir(Me)OTf with silanes: Role of base-free silylene complexes in rearrangements of the resulting silicon-based ligands
Klei, Steven R.,Don Tilley,Bergman, Robert G.
, p. 3376 - 3387 (2008/10/08)
The mechanisms of silicon-hydrogen activation by Cp*(PMe3)Ir(Me)OTf (Cp* = η5-C5-Me5, OTf = OSO2CF3; 1) and rearrangements of the resulting silyliridium complexes were investigated. The scope of this reaction has been studied for silanes with a variety of substituents. Silylene complexes of the type [Cp*(PMe3)Ir(SiR2)(H)] [X] (X = OTf, R = Mes, 6; X = B(C6F5)4, R = Ph, 16) have been isolated, and the likelihood of their involvement in the rearrangements is discussed. The kinetics of the isomerization reaction of the cyclometalated iridium(V) complex {Cp*(PMe3)Ir(H)[κ2-SiH(Mes)(2-CH2-4 ,6-Me2C6H2)]}[OTf] (5) to the iridium silylene [Cp*(PMe3)Ir(SiMes2)(H)] [OTf] (6) were examined using NMR spectroscopic techniques. The primary kinetic isotope effect (Si-H vs Si-D bond) for this process was determined to be 1.4 ± 0.1, implying a rate-limiting hydride migration from silicon to iridium. The activation parameters for this isomerization have also been measured: ΔH? = 23 ± 2 kcal/mol and ΔS? = 0.1 ± 0.01 eu. Slow hydride migration to produce a silylene complex from either Cp*(PMe3)Ir(Me)OTf (1) or [Cp*(PMe3Ir(Me)(CH2Cl2)][BC6F 5)4] (17) is observed for large substituents on silicon. However, production of the sterically less crowded complex [Cp*(PMe3)Ir(SiPh2)(H)] [B(C6F5)4] (16) is extremely rapid upon reaction of 17 with H2SiPh2. This argues for the intermediacy of a three-coordinate silicon species.
