Yttrium Complexes Featuring Different Y–C Bonds. Comparative Reactivity Studies: Toward Terminal Imido Complexes

The reactions of 2,6-diisopropylaniline with equimolar amounts of alkyl–heteroaryl yttrium complexes containing Y–C­(sp3, alkyl) along with Y–C­(sp2, heteroaryl) bonds resulting from intramolecular C–H bond activation of the amido–pyridinate ligands [NNOBzFur]­YCH2SiMe3(THF)2, [NNSBzTh]­YCH2SiMe3(THF)2, and [NNSEtTh]­YCH2SiMe3(THF)2 have been scrutinized with the aim of synthesizing yttrium terminal imido species. These reactions occur at ambient temperature with the protonolysis of the Y–C­(sp3, alkyl) bond, thus affording anilido–heteroaryl species and maintaining the residual Y–C­(sp2, heteroaryl) bond untouched. However, the subsequent transformation of the as-synthesized anilido–heteroaryl complexes depends on the nature of the substituent on the 6-position of the pyridyl ring. In the case of the benzofuryl yttrium derivative [NNOBzFur]­YNH-2,6-iPr2C6H3(THF)2 (4), heating to 50 °C results in benzofuran ring opening with the formation of an anilido species supported by a dianionic amido–yne–phenolate ligand framework, [NNCCO]­YNH-2,6-iPr2C6H3(THF) (6). In contrast, a complex containing a benzothiophenyl moiety, [NNSBzTh]­YNH-2,6-iPr2C6H3(THF)2 (7), slowly undergoes protonation of the Y–C­(sp2, heteroaryl) bond and a ligand redistribution reaction takes place, affording an yttrium bis­(anilido) species supported by a monoanionic amido–pyridinate ligand featuring intramolecular Y–S heteroaryl coordination, [NNSBzTh]­Y­[NH-2,6-iPr2C6H3]2 (9). It is worth noting that an yttrium complex containing α-thiophenyl fragment, [NNSEtTh]­YNH-2,6-iPr2C6H3(THF)2 (10), turned out to be extraordinarily robust and no transformation was ever detected even upon heating the complex at 100 °C for prolonged times.