Novel BPPFA Palladium Complexes. P,P to P,N Rearrangements Promoted by Chelating κ³-N,P,P-BPPFA Intermediates

Novel palladium complexes with BPPFA ( N, N -dimethyl-1-[2,1‘-bis(diphenylphosphino)ferrocenyl]ethylamine) and the newly prepared ligand 1,1‘-bis(diphenylphosphino)-2-methylferrocene (BPPFMe, 1 ) have been synthesized. Racemic BPPFA reacts with Pd 2 (dba) 3 ·CHCl 3 in the presence of electron-withdrawing alkenes to give palladium(0) complexes Pd(BPPFA)(alkene), where alkene = dimethyl fumarate ( 2 ), maleic anhydride ( 3 ). Displacement of weak donor ligands from the appropriate palladium(II) precursors leads to the derivatives [Pd(η 3 -2-Me-C 3 H 4 )(BPPFA)]TfO ( 4 ), Pd(C 6 F 5 ) 2 (BPPFA) ( 5 ), Pd(C 6 F 5 ) 2 (BPPFMe) ( 6 ), PdMe 2 (BPPFA) ( 7 ), and PdClMe(BPPFA) ( 8 ). Complexes 2 − 4 and 8 each exist in solution as two diastereomers that do not interconvert at room temperature on the NMR time scale. In all mononuclear complexes BPPFA is P,P-coordinated to palladium. When PdClX(cod) (X = Cl, Me) is reacted with ( R C, S P )-BPPFA in a Pd:L ratio higher than 1:1, polynuclear species are formed. A Pd:L ratio of 2:1 leads to the tetranuclear derivatives { cis -PdClX(μ-κ 3 -BPPFA)} 2 {PdX(μ-Cl) 2 PdX} (X = Me ( 9 ), Cl ( 10 )), while a ratio of 1.5:1 gives the trinuclear complexes { cis -PdClX(μ-κ 3 -BPPFA)} 2 ( trans -PdClX) (X = Me ( 11 ), Cl ( 12 )) along with the corresponding tetra- and mononuclear derivatives. Mechanistic studies concerning the formation of the tetranuclear complexes have shown that a P, P to P,N coordination shift and Pd−P bond rupture are feasible processes. Variable-temperature 1 H NMR studies have provided evidence of Pd−N interactions in complexes 2, 5, 7, and 8 that involve an unprecedented terdentate κ 3 N,P,P chelate coordination of BPPFA to palladium. The pentafluorophenyl complexes 5 and 6 each exist in solution as two conformers that are interconvertible by torsional twisting of the Cp rings. In the case of complex 5 this interconversion process is slowed at low temperature to such an extent that both conformers can be observed separately by NMR spectroscopy. This phenomenon is presumably due to the Pd−N interaction. The molecular structures of 2M and 8M ( M = major isomer) have been determined by X-ray diffraction.