Enantiopure Ruthenocenes Cp*Ru(1,2‐C5H3R1R2) with a Planar Chiral Cyclopentadienyl Ligand and a Pentamethylcyclopentadienyl Spectator Ligand

Abstract

AbstractKreutzberger’s synthesis was used to produce 6‐(morpholino)fulvene (7a) from 1,3,5‐triazine, cyclopentadiene and morpholine (94 %). Likewise with (S)‐2‐(methoxymethyl)pyrrolidine (HSMP) the 6‐[(S)‐2‐(methoxymethyl)pyrrolidino] analogue 7b was obtained (62 %). Hydride addition from NaBHEt3 in toluene afforded the cyclopentadienides Na[C5H4CH2–N(C2H4)2O] (8a) (83 %) and Na(C5H4CH2–SMP) (8b) (90 %). Cp*Ru(C5H4CH2–SMP) (5) was synthesized from [Cp*RuCl]4 and 8b (84 % yield). The related methyleneiminium salt [Cp*Ru(C5H4CH=SMP)]PF6 (9) was made from [Cp*Ru(MeCN)3]PF6 and 7b and could be transformed into 5 by hydride addition from LiAlH4 in THF. Diastereoselective lithiation of 5 with LisBu in Et2O/cyclohexane and subsequent quenching with electrophiles E–X gave enantiomerically pure (de > 98 %), 1,2‐disubstituted complexes Cp*Ru(E–C5H3CH2–SMP) 10a–i with E = F, Cl, Br, I, Me, CD3, SiMe3, PPh2, Au(PPh3) as oils. The chiral auxiliary was removed from 10a, b, and f by quaternization with MeI and subsequent reductive cleavage with LiAlH4 in THF to afford the exclusively planar chiral complexes Cp*Ru(1‐E‐2‐MeC5H3) 14a (E = F), 14b (E = Cl), and 14f (E = CD3). The complexes 14a,b,f no longer possess central chirality. The crystal structure of 12, a LiI adduct of 10f, gave the absolute configuration via internal reference to the (S)‐stereochemistry of the SMP group. The absolute configuration of the planar chiral complex 14b was determined from the anomalous X‐ray dispersion of the crystals of 14b.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)