A Tantalum Methylidene Complex Supported by a Robust and Sterically Encumbering Aryloxide Ligand

Treatment of [TaCl2(CH3)3] with
2 equiv of NaOAr′ (OAr′ = 2,6-bis­(diphenylmethyl)-4-tert-butylphenoxide) yields cleanly the bis-aryloxide trimethyl
complex [(Ar′O)2Ta­(CH3)3]
(1), which is isolated in 92% yield and is spectroscopically
and structurally characterized. Addition of 2 equiv of HOAr′
to [TaCl2(CH3)3] results in clean
protonation concurrent with formation of the bis-aryloxide methyl
derivative [(Ar′O)2Ta­(CH3)­Cl2] (2), which was also fully characterized, including
an X-ray structure. Despite being close derivatives, complex 1 (trigonal bipyramidal) and 2 (square pyramidal)
possess very different structures, with the e set
in a square-pyramidal molecular orbital diagram being key to their
preferred geometry. Addition of excess ylide, H2CPPh3, to 2 results in formation of the terminal tantalum
methylidene chloride complex [(Ar′O)2TaCH2(Cl)­(H2CPPh3)] (3) in 64%
yield, which is characterized by multinuclear NMR spectroscopy and
a solid-state structure determination.