Platinum ω‑Alkenyl Compounds as Chemical Vapor Deposition Precursors. Mechanistic Studies of the Thermolysis of Pt[CH2CMe2CH2CHCH2]2 in Solution and the Origin of Rapid Nucleation

The compound cis-bis­(η1,η2-2,2-dimethylpent-4-en-1-yl)­platinum, Pt­[CH2CMe2CH2CHCH2]2 (3), is a recently discovered chemical vapor deposition (CVD) precursor for the deposition of highly smooth platinum thin films without nucleation delays on a variety of substrates. This paper describes detailed mechanistic studies of the pathway by which 3 reacts upon being heated in solution. In various solvents between 90 and 130 °C, 3 decomposes to generate ∼1 equiv of 4,4-dimethylpentenes by addition of a hydrogen atom to the pentenyl ligands in 3. The “extra” hydrogen atoms arise by dehydrogenation of other pentenyl ligands; some of these dehydrogenated ligands are released as methyl-substituted methylenecyclobutanes and cyclobutenes. A combination of isotope labeling and kinetic studies suggests that 3 decomposes by C–H activation of both allylic and olefinic C–H bonds to give transient platinum hydride intermediates, followed by reductive elimination steps to form the pentene products, but that the exact mechanism is solvent-dependent. In C6F6, solvent association occurs before C–H bond activation, and the rate-determining step for thermolysis is most likely the formation of a Pt σ complex. In hydrocarbon solvents, the solvent is little involved before C–H bond activation, and the rate-determining step is most likely the formation of a Pt σ complex only for γ-C–H and ε-C–H bond activation, but cleavage or formation of a C–H bond for δ-C–H bond activation. A comparison of the thermolysis reactions under CVD conditions and in solution suggests that the high smoothness of the CVD-grown films is due in part to rapid nucleation (which is a consequence of the availability of low-barrier CC bond dissociation pathways) and in part to the formation of carbon-containing species that passivate the Pt surface.