The complex bis(acetylacetonato)platinum(II) is
inactive in the dark but forms a highly
reactive hydrosilation catalyst upon irradiation with near-UV light.
Vinyldimethylsilane is polymerized
with it. Poly[(dimethyl)vinylsilane] is the major product; minor
components consist of the dimers 1,1,2,3,3-pentamethyl-1,3-disilacyclopentane and
1,1,4,4-tetramethyl-1,4-disilacyclohexane and oligomers.
After
photoactivation the catalyst remains reactive for an indefinite period
of time with hydride and vinyl
polymer end-groups, thus the molecular weight of the major product
increased from 5500 g/mol (M
w)
shortly after irradiation to 12300 g/mol in six months due to
end-linking of polymer chains. Photoactivation
of the catalyst and the subsequent step polymerization reaction are
unaffected by dissolved air.
Three platinum(II) bis(β-diketonate) complexes are highly active for photocatalytic hydrosilation cross-linking of oligo[(methylsilylene)methylene] with tetravinylsilane. Platinum(II) bis(benzoylacetonate), platinum(II) bis(trifluoroacetylacetonate), and platinum(II) bis(benzoyltrifluoroacetonate) are photoactivated by visible light for catalysis, while platinum(II) bis(hexafluoroacetylacetonate) can be used as a thermal catalyst. Kinetic data from FT-IR and UV-visible spectroscopies characterizing Si-H bond conversion and catalyst photolysis are reported.
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