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The cationic zirconocene-phosphinoaryloxide complexes Cp(2)ZrOC(6)H(4)P(t-Bu)(2)B(C(6)F(5))(4) (3) and Cp*(2)ZrOC(6)H(4)P(t-Bu)(2)B(C(6)F(5))(4) (4) were synthesized by the reaction of Cp(2)ZrMe(2) or Cp*(2)ZrMe(2) with 2-(diphenylphosphino)phenol followed by protonation with 2,6-di-tert-butylpyridiniumB(C(6)F(5))(4). Compound 3 exhibits a Zr-P bond, whereas the bulkier Cp* derivative 4 was isolated as a chlorobenzene adduct without this Zr-P interaction. These compounds can be described as transition-metal-containing versions of linked frustrated Lewis pairs (FLPs), and treatment of 4 with H(2) under mild conditions cleaved H(2) in a fashion analogous to that for main-group FLPs. Their reactivity in amine borane dehydrogenation also mimics that of main-group FLPs, and they dehydrogenate a range of amine borane adducts. However, in contrast to main-group FLPs, 3 and 4 achieve this transformation in a catalytic rather than stoichiometric sense, with rates superior to those for previous high-valent catalysts.
Chapman et al. (Fri,) studied this question.