An Unusual Organoyttrium Alkyl Complex Containing a [C 5 HMe 3 (η 3 ‐CH 2 )‐C 5 H 4 N‐κ] − Ligand and an Elusive Cyclopentadienide‐Based Scandium Tuck‐Over Zwitterion Obtained by CH Bond Activation

The acid–base reaction between Y(CH 2 SiMe 3 ) 3 (thf) 2 and the pyridyl‐functionalized cyclopentadienyl (Cp) ligand C 5 Me 4 HC 5 H 4 N (1 equiv) at 0 °C afforded a mixture of two products: (η 5 :κ‐C 5 Me 4 C 5 H 4 N)Y(CH 2 SiMe 3 ) 2 (thf) ( 1 a ) and (η 5 :κ‐C 5 Me 4 C 5 H 4 N) 2 YCH 2 SiMe 3 ( 1 b ), in a 5:2 ratio. Addition of the same ligand (2 equiv) to Y(CH 2 SiMe 3 ) 3 (thf) 2 , however, generated 1 b together with the novel complex 1 c , the first well defined yttrium mono(alkyl) complex (η 5 :κ‐C 5 Me 4 C 5 H 4 N)[C 5 HMe 3 (η 3 ‐CH 2 )‐C 5 H 4 N‐κ]Y(CH 2 SiMe 3 ) containing a rare κ/η 3 ‐allylic coordination mode in which the CH bond activation occurs unexpectedly with the allylic methyl group rather than conventionally on Cp ring. If the central metal was changed to lutetium, the equimolar reaction between Lu(CH 2 SiMe 3 ) 3 (thf) 2 and C 5 Me 4 HC 5 H 4 N exclusively afforded the bis(alkyl) product (η 5 :κ‐C 5 Me 4 C 5 H 4 N)Lu(CH 2 SiMe 3 ) 2 (thf) ( 2 a ). Similarly, the reaction between the ligand (2 equiv) and Lu(CH 2 SiMe 3 ) 3 (thf) 2 gave the mono(alkyl) complex (η 5 :κ‐C 5 Me 4 C 5 H 4 N) 2 LuCH 2 SiMe 3 ( 2 b ), in which no ligand redistribution was observed. Strikingly, treatment of Sc(CH 2 SiMe 3 ) 3 (thf) 2 with C 5 Me 4 HC 5 H 4 N in either 1:1 or 1:2 ratio at 0 °C generated the first cyclopentadienide‐based scandium zwitterionic “tuck‐over” complex 3 , (η 5 :κ‐C 5 Me 4 C 5 H 4 N)Sc(thf)[μ‐η 5 :η 1 :κ‐C 5 Me 3 (CH 2 )‐C 5 H 4 N]Sc(CH 2 SiMe 3 ) 3 . In the zwitterion, the dianionic ligand [C 5 Me 3 (CH 2 )‐C 5 H 4 N] 2− binds both to Sc1 3+ and to Sc2 3+ , in η 5 and η 1 /κ modes. In addition, the reaction chemistry, the molecular structures, and the mechanism are also discussed in detail.