13C CPMAS NMR spectroscopy has been employed to investigate the surface chemistry of the organotantalum hydrocarbyl/alkylidene complexes, Cp′Ta(13CH3)4 (1*), Cp2Ta(13CH3)3 (2*), Cp2Ta(13CH2)-(13CH3) (3*), and Ta(13CHtBu)(13CH2t Bu)3 (4*) [Cp′ = η5-(CH3)5C5, Cp = η5-C5H5] supported on partially dehydroxylated silica (PDS), dehydroxylated silica (DS), or dehydroxylated γ-alumina (DA). Mono-Cp tantalum hydrocarbyl 1* undergoes chemisorption to form Cp′Ta(13CH3)3O-Si μ-oxo species on silica, and "cation-like" Cp′Ta(13CH3)3+ and Cp′Ta(13CH3)3O-Al μ-oxo species on DA, via pathways analogous to those established for organo-group 4 and actinide complexes. When supported on DA, bis-Cp tantalum hydrocarbyl 2* follows the same chemisorption mode as 1*. However, when 2* is chemisorbed on PDS and DS, a "cation-like" Cp2Ta(13CH3)2+ species is the major adsorbate product. On PDS, bis-Cp tantalum alkylidene complex 3* is converted predominantly to a stable "cation-like" Cp2Ta(13CH3)2+ species, presumably via electrophilic addition of a proton from the PDS surface. In contrast to 3*, Ta alkylidene complex 4* forms predominantly a Ta(13CHtBu)(13CH2t Bu)2O-Si, μ-oxo-alkylidene species on PDS.
ASJC Scopus subject areas