A New Concept for Chelate Ligands with Planar Chirality

The chiral donor substituted phosphaferrocene derivatives CpFe(3,4-Me2-2-R-C4HP) 6 (R = CH2CH2NMe2), 7 (R = CH2NMe2), and 8 (R = CH2OPPh2) were synthesized as racemates starting from 2-formyl-3,4-dimethylphosphaferrocene. The P,N-ligand 6 reacted with [Cp*RuCl]4 in THF to give the six-ring chelate complex Cp*RuCl(6) (⋮10) which was characterized by single-crystal X-ray diffraction analysis. The complexation reaction was found to proceed diastereoselectively with respect to the newly created stereogenic center on the ruthenium atom. Under similar conditions, the reaction of ligand 7 with [Cp*RuCl]4 did not lead to chelate formation. Instead, two isomers of the bis-P-coordinated complex Cp*RuCl(7)2 (⋮11) were observed by NMR spectroscopy. Reaction of the phosphinite ligand 8 with (PhCN)2PdCl2 in toluene produced the six-ring chelate complex cis-PdCl2(8) (⋮12). The crystal structure of 12 has been determined.