Synthesis of group 4 metallocene-substituted ylides and their reactions with ketones

Article abstract of DOI:10.1016/0022-328X(87)80041-4

A new method has been developed to synthezise group 4 metallocene ylides.Ph3P=CH2 reacts with in situ generated (η²-ethene)MCp2 (M = Zr, Hf), (η²-aryne)MCp2 (M = Ti, Zr), or with (η⁴-conjugated diene)MCp2 (M = Zr, Hf) via intramolecular hydrogen transfer to form metallocene ylides Cp2M(R)CH=PPh3.In some cases competitive methylene transfer occurs leading to four-membered metallacycles.The metallocene ylides all exhibit a substantial metal to carbon ?-interaction, increasing in strength on going from hafnium to titanium as the central metal atom.Ylide reactivity is greatly reduced.With a non-enolizable ketone, Cp2Zr(CH2CH=CHCH3)CH=PPh3 reacts via the reverse of metallocene ylide forming reaction.With enolizable ketones, zirconocene or hafnocene ylides serve as bases and form metal enolates.The resulting enolate (E)/(Z) ratio strongly depends on the group R of the metallocene ylide base Cp2Zr(R)CH=PPh3.