C2-Symmetric ytterbium(II) complexes with a novel, chiral P,N-donor ligand

The diastereomeric secondary phosphanes {(Me3Si)2CH}{C6H4-2-(R or S)-CH(Me)NMe2}PH (3) may readily be isolated as a 50/50 mixture of epimers at phosphorus via the reaction of enantiomerically pure Li{C6H4-2-(R or S)-CH(Me)NMe2} with {(Me3Si)2CH}PCl2, followed by reduction with LiAlH4. Treatment of either C-stereoisomer of 3 with nBuLi(tmeda) gives the lithium phosphanides [{(Me3Si)2CH}{C6H4-2-(R/S)-CH(Me)NMe2}P]Li(tmeda) [(R)-4, (S)-4], which may be isolated as orange, crystalline solids (tmeda=N,N,N′,N′-tetramethylethylenediamine). Treatment of 3 with nBuLi, followed by metathesis with KOtBu yields the corresponding potassium salts [{(Me3Si)2CH}{C6H4-2-(R/S)-CH(Me)NMe2}P]K [(R)-6, (S)-6] as pyrophoric orange solids. A simple metathesis reaction between YbI2 and two equivalents of (R)-6 or (S)-6 gives the C2-symmetric Yb(II) complexes [{(Me3Si)2CH}{C6H4-2-(R/S)-CH(Me)NMe2}P]2Yb·(C6H11Me) [(R)-7, (S)-7], after recrystallization from methylcyclohexane. Compounds 3, 4, 6 and 7 have been characterized by multi-element NMR spectroscopy and (R)-4, (R)-7 and (S)-7 have additionally been characterized by X-ray crystallography.