Synthesis and Study of Heterobimetallic Complexes Supported by a Ferrocene-Based Bisphosphine−Diamine Ligand

The difunctional bisphosphine−diamine ligand 1, the racemate of (S)-N-[2-(dimethylamino)ethyl]-N-methyl-1-[(R)-1',2-bis(diphenylphosphino)ferrocenyl]ethylamine, has been used to prepare several novel heterobimetallic complexes for potential catalysis applications based on cooperative interactions between two reactive metal centers. The complexes were characterized by electron ionization mass spectrometry (ESI-MS) and multinuclear NMR spectroscopy. Specifically, 31P NMR spectroscopy was used to characterize the binding modes of the ligand. The X-ray crystal structure of 10 (containing Pt and Cu) confirms a (P,P)-binding mode for Pd and an (N,N)-binding mode for Cu. The distance between Pt and Cu metal centers was 4.528(3) Å. Palladium complexes of 1 exist as an equilibrium mixture of isomers involving (P,P)- and (P,N)-coordination modes for palladium (Keq = 1.90 at 22 °C; ΔH = −4.3(4) kcal/mol and ΔS = −13(1) eu). This isomerization process can be suppressed by the addition of (Et2O)MgBr2 to 1, which forms the (N,N)-bound Mg complex 4. This complex reacted with trans-(PPh3)2PdBr2 to form the bimetallic complex 5, in which Pd is (P,P)-bound.