Stereochemistry of chiral ruthenium- and iron-cyclopentadienyl alkylidenecarbene-diphosphine complexes

摘要: Abstract The non-rigid behaviour of complexes the type [η-C 5 H )M(Ph 2 PCHRCHR′PPh2)(CCHR″)] PF 6 (M Ru or Fe; R,R′H, CH 3 (CH ) ; R″ , C tC 4 9 ; not all combinations) has been investigated through 31 P NMR spectroscopy at variable temperature. preferred geometry in solution is one which plane alkylidenecarbene moiety perpendicular to containing carbene carbon atom, metal atom and centroid cyclopentadienyl ligand, barrier rotation being 9–10 kcal/mol. When R ≠ R′, least case ruthenium complexes, stereogenic sterically stable. For chiral diphosphine ligands, two rotamers are a diastereomeric relationship. differences population diastereomers (asymmetric induction) seem be mostly determined by steric reasons. They increase on going from iron, increasing size alkylidene group using diphosphines cause larger crowding around metal. Furthermore for having asymmetric induction also depends absolute configuration (the ligand same).