Phosphorus Ylide as a Precursor for the Formation of New High-Valent Tantalum Phosphonio Methylidyne Complexes

Two new high-valent tantalum(V) phosphonio methylidyne complexes, [CpTa(C−PPh 3 )(CH−PPh 3 )Cl] ( 4 ) and [CpTa(C−PPh 3 )(CH−PPh 3 ) 2 ] ( 5 ), have been obtained respectively via transylidation reactions of CpTaCl 4 with 5 and 7 equiv of the phosphorus ylide Ph 3 P CH 2 . Complex 4 was structurally analyzed with X-ray diffraction. The possible formation mechanism has been discussed. To our knowledge this presentation is the first example of a stable tantalum complex with a terminal [M⋮C−PPh 3 ] function.