Synthesis, Characterization, and Reactivity of Tris(imido)chromium(VI) Complexes.

Multiple tris(imido)chromium(VI) complexes, including neutral and ionic compounds, have been synthesized and characterized. ( t BuN) 2 Cr(NH t Bu)Cl can be deprotonated by KN(SiMe 3 ) 2 , yielding K[( t BuN) 3 CrCl]. This tris(imido) anion undergoes nucleophilic substitution by PPh 3 and t BuNH 2 to form ( t BuN) 3 Cr(PPh 3 ) and ( t BuN) 2 Cr(NH t Bu) 2 , respectively. ( t BuN) 2 Cr(NH t Bu) 2 loses one amido proton to form K[( t BuN) 3 Cr(NH t Bu)] upon reaction with KN(SiMe 3 ) 2 . The imido ligands of K[( t BuN) 3 CrCl] and ( t BuN) 3 Cr(PPh 3 ) are attacked by the electrophile MeI to produce ( t BuN) 2 Cr(NMe t Bu)Cl and ( t BuN) 2 Cr(NMe t Bu)I, respectively. An alternate way to make tris(imido) anions is deprotonation of ( t BuN) 2 Cr(NH t Bu)Cl by an alkyl lithium reagent, e.g., Me 3 SiCH 2 Li. The resulting Li[( t BuN) 3 CrCl] was alkylated by a second equivalent of Me 3 SiCH 2 Li to form Li[( t BuN) 3 Cr(CH 2 SiMe 3 )]. Reactivity studies of tris(imido) complexes show cycloaddition with PhNCO or CO 2 to form metallacycles.