Frustrated Lewis Pair Behavior of [Cp2ZrOCR2CH2PPh2]+ Cations

Reactions of Cp2ZrMe2 with 1 equiv of 2-diphenylphosphino-substituted alcohols Ph2PCH2CR2OH = H, CH3) gave the neutral monomethyl zirconocene alkoxy complexes Cp2Zr(Me)OCR2CH2PPh2 (7) by means of methane elimination. Treatment of the complexes 7 with the alkyl abstraction reagent [Ph3C](+)[B(C6F5)(4)](-) resulted in the formation of the cationic complexes 8. X-ray crystal structure analysis shows that 8a (R = H) is a doubly oxygen bridged dimer and 8b (R = CH3) is a monomer with P-Zr coordination. Complexes 8 show some typical Zr+/P FLP reactivity. For example, complex 8a undergoes selective 1,4-addition to chalcone to produce the nine-membered metallacyclic product 13. Complex 8b reacts with benzaldehyde and an ynone reagent to form the respective Zr+/P addition products 14 and 15. Complex 8b also adds to the N=O functionality of nitrosobenzene with formation of 20. Treatment of 8b with NO gave the six-membered metallaheterocycle 21 by oxidation of the phosphane. The reaction of compound 8b with 0.5 mol equiv of nitrobenzene afforded a mixture of complexes 20 and 21 in a 1:1 molar ratio.