Rare-Earth-Metal Methyl and Methylidene Complexes Stabilized by Tp R,R' -Scorpionato Ligands─Size Matters.

Homoleptic tetramethylaluminates Ln(AlMe 4 ) 3 react with KTp t Bu,Me (Tp t Bu,Me = tris(3- t Bu-5-Me-pyrazolyl)borato) to yield rare-earth-metal methylidene complexes (Tp t Bu,Me )Ln(μ 3 -CH 2 )[(μ-Me)AlMe 2 ] 2 (Ln = La, Ce, Nd). The lanthanum reaction is prone to additional C-H- and B-N-bond activation, affording coproducts La[HB(pz Me, t Bu )(pz CMe2,Me ) 2 ][(μ-CH 2 )(μ-Me)AlMe 2 ] 2 and [La(μ-pz t Bu,Me )(AlMe 4 ) 2 ] 2 (pz t Bu,Me = 3- t Bu-5-Me-pyrazolato). The protonolysis reaction of Ln(AlMe 4 ) 3 and Hpz t Bu,Me provides more efficient access to [Ln(μ-pz t Bu,Me )(AlMe 4 ) 2 ] 2 (Ln = La, Nd). Treatment of Ln(AlMe 4 ) 3 with KTp Me,Me led to methylidene complexes (Tp Me,Me )Ln(μ 3 -CH 2 )[(μ-Me)AlMe 2 ] 2 (Ln = Nd, Sm) or bis(tetramethylaluminate) complexes (Tp Me,Me )Ln(AlMe 4 ) 2 (Ln = Y, Lu). The neodymium reaction generated methine derivative (Tp Me,Me )Nd[(μ 4 -CH)(AlMe 2 ) 2 (μ-pz ,Me,Me )][(μ-Me)AlMe 2 ] as a minor coproduct. The reaction of Ln(GaMe 4 ) 3 (Ln = Y, La, Ce, Nd, Sm, Ho) with HTp t Bu,Me gave methylidene complexes (Tp t Bu,Me )Ln(μ 3 -CH 2 )[(μ-Me)GaMe 2 ] 2 (Ln = La, Ce, Nd, Sm) and alkyl complexes (Tp t Bu,Me )LnMe[(μ-Me)GaMe 3 ] (Ln = Y, Ho), while competing B-N bond activation reactions produced GaMe 2 [BH(Me)(μ-pz t Bu,Me ) 2 ] and (Tp t Bu,Me )Ln(η 2 -pz t Bu,Me )[(μ-Me)GaMe 3 ] (Ln = Y, Ho). The steric impact of the Tp R,Me ligands was examined by cone angle calculations. Rare-earth-metal methylidene complexes (Tp t Bu,Me )Ln(μ 3 -CH 2 )[(μ-Me)EMe 2 ] 2 (E = Al, Ga) successfully promote carbonyl methylenation reactions upon addition of ketone.