High-resolution solid-state 13C NMR studies of chemisorbed organometallics.: Chemisorptive formation of cation-like and alkylidene organotantalum complexes on high surface area inorganic oxides

C-13 CPMAS NMR spectroscopy has been employed to investigate the surface chemistry of the organotantalum hydrocarbyl/alkylidene complexes, Cp'Ta((CH3)-C-13)(4) (1*), Cp2Ta ((CH3)-C-13)(3) (2*), CP2Ta((CH2)-C-13) ((CH3)-C-13) (3*), and Ta((CHBu)-C-13-Bu-t)((CH2Bu)-C-13-Bu-t)(3) (4*) [Cp' = eta(5)-(CH3)(5)C-5, Cp = eta(5)-C5H5] supported on partially dehydroxylated silica (PDS), dehydroxylated silica (DS), or dehydroxylated gamma-alumina (DA). Mono-Cp tantalum hydrocarbyl 1* undergoes chemisorption to form Cp'Ta((CH3)-C-13)(3)O-Si mu-oxo species on silica, and "cation-like" Cp'Ta((CH3)-C-13)(3)(+) and Cp'Ta((CH3)-C-13)(3)O-Al mu-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((CH3)-C-13)(2)(+) species is the major adsorbate product. On PDS, bis-Cp tantalum alkylidene complex 3* is converted predominantly to a stable "cation-like" Cp2Ta((CH3)-C-13)(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((CHBu)-C-13-Bu-t)((CH2BU)-C-13-B-t)(2)O-Si, mu-oxo-alkylidene species on PDS.