OBSERVATION OF AN UNUSUAL LIGAND-INDUCED REARRANGEMENT OF A TITANACYCLOPENTADIENE RING

The sodium amalgam reduction of [(ArO)2TiCl2] (1; ArO = 2,6-diisopropylphenoxide) in the presence of the diynes 1,8-bis(trimethylsilyl)-1,7-octadiyne, Me3SiC = C(CH2)4C = CSiMe3, and 1,8-bis(dimethylphenylsilyl)-1,7-octadiyne, PhMe2SiC = C(CH2)4C = CSiMe2Ph yields the titanacyclopentadiene complexes [ArO)2Ti{C2(R)2C6H8}] (R = SiMe3 (1a), R = SiMe2Ph (1b)). Reaction of 1b with PMe3 results in a ligand-induced rearrangement to form [(ArO)2Ti{C(SiMe2Ph)2C6H8C(PMe3)}] (2). An X-ray crystallographic analysis has shown that complex 2 is a phosphorus ylide derivative in which migration of a dimethylphenylsilyl substituent has occurred from one alpha-carbon to the other. The solid-state structure of 2 shows a five-membered titanacycle ring in which the PMe3 group is bound to one alpha-carbon and both SiMe3Ph substituents are bound to the other alpha-carbon on the ring. The three carbon-carbon bonds within the ring (C(11)-C(1) = 1.45(1) angstrom, C(1)-C(2) = 1.39(1) angstrom, C(2)-C(21) = 1.502(9) angstrom) are indicative of a titanacyclopent-3-ene structure. The phosphorus-carbon (alpha) bond distance (1.704(8) angstrom) is shorter than the other three phosphorus-carbond distances (1.771(8), 1.807(8), 1.795(8) angstrom) and is consistent with a phosphorus-carbon (alpha) double bond.