Zwitterionic and Cationic Titanium and Vanadium Complexes Having Terminal M-C Multiple Bonds. The Role of the β-Diketiminate Ligand in Formation of Charge-Separated Species

Treatment of the neopentylidene complex ([ArNC(Me)](2)CH)Ti=(CRBu)-Bu-t(OTf) (1) with a strong base such as an alkyl reagent (lithium or potassium salt) results in deprotonation of the beta-diketiminate beta-methyl group to form complex (ArN(Me)CCHC(CH2)NAr)Ti=(CHBu)-Bu-t(THF) (2) along with liberation of the alkane. Likewise, ligand deprotonation of ([ArNC(Me)](2)CH)V equivalent to(CBu)-Bu-t-(OTf) (3), in THF or Et2O, results in formation of the alkylidyne-solvent adduct (ArNC(Me)CHC(CH2)NAr)V equivalent to(CBu)-Bu-t(L) (L = THF, 4-THF; L = Et2O, 4-OEt2), concomitant with alkane formation. The connectivity in compound 4-Et2O has been established by single-crystal X-ray diffraction studies. Compounds 2 and 4-THF react with B(C6F5)(3) to produce the first examples of terminal titanium alkylidene and vanadium alkylidyne zwitterions, namely, the borane adducts (ArNC(Me)CHC(CH2B(C6F5)(3))NAr)Ti=(CHBu)-Bu-t(THF) (5) and (ArNC(Me)CHC(CH2B(C6F5)(3))NAr)V (CBu)-Bu-t-(THF) (6), respectively. The solid state structure for each zwitterion was also obtained. Compounds 2 and 4-THF react readily with [HNMe2Ph][B(C6F5)(4)] to produce the discrete salts [([ArNC(Me)CH)Ti=(CHBu)-Bu-t(THF)][B(C6F5)(4)] (7) and [([ArNC(Me)](2)CH)V (CBu)-Bu-t(THF)][B(C6F5)(4)] (8), respectively, via protonation of the methylene group in the N,N'-chelating ligand ArNC(Me)CHC(CH2)NAr2- to re-form the beta-diketiminate scaffold. The reactivity of 7 allows for spectroscopic elucidation only at low temperatures., while complex 8 has been fully characterized including a single-crystal X-ray structure.