Use of alkane elimination in the one-step synthesis of organoscandium complexes containing a new multidentate cyclopentadienyl ligand

A new multidentate ligand, CpH^NMeSiN(H)R (SiNR = -SiMe₂N-tert-butyl; NMe = 3-CH₂-CH₂NMe₂; 1) was prepared in 71% yield as a mixture of 1,3 and 1,2 isomers (≈7:3) in one step from CpH^NMe, Me₂SiCl₂, and tert-butylamine. The ligand was attached to scandium in an efficient alkane elimination reaction by treatment of in situ generated Sc(CH₂SiMe₃)₃·-2THF with diproteo 1, yielding the alkylscandium species [(Cp^NMeSiNR)Sc(CH₂SiMe₃)], 2, directly in 52% yield. The reaction was 100% diastereoselective for the (1S)-(R_Sc)/(1R)-(S_Sc) pair of enantiomers. Treatment of 2 with dihydrogen gave two of four possible diastereomeric μ-dihydrides. The C_i symmetric R1-trans-1′S diasteriomer 3a was characterized crystallographically. Thermolysis of 2 at 70 °C for 3 days resulted in metalation of an N-methyl group and loss of Me₄Si. A mixture of two dimeric compounds with bridging methylene units was formed, one of which was identified as the C_i symmetric 1R-trans-1′S diasteriomer 4a by X-ray crystallography.