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 ?-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.