Synthesis and characterisation of palladium() complexes with hybrid phosphinoferrocene ligands bearing additional O-donor substituents

While 1,1′-bis(diphenylphosphino)ferrocene (dppf) is widely used as a ligand in coordination chemistry and catalysis, its congeners with oxygen-containing functional groups have long been overlooked. Accordingly, we studied the coordination behaviour in Pd( ii ) complexes of three phosphinoferrocene ligands bearing secondary O-donor groups, Ph 2 PfcR, wherein R = CHO ( 1 ), Ac ( 2 ) and CMe 2 (OH) ( 3 ), and fc = ferrocene-1,1′-diyl. Depending on the stoichiometry, reactions of 1-3 (L) with [PdCl 2 (cod)] (cod = η 2 :η 2 -cycloocta-1,5-diene) produced the respective mono- and dipalladium complexes, trans -[PdCl 2 (L-κ P ) 2 ] and trans -[PdCl(μ-Cl)(L-κ P )] 2 . Compound [PdCl(μ-Cl)( 3 -κ P )] 2 was found to dehydrate readily, giving rise to [PdCl(μ-Cl)(Ph 2 PfcC(Me)&z.dbd;CH 2 -κ P )] 2 . Furthermore, ligands 1-3 cleaved [(L NC )Pd(μ-Cl)] 2 (L NC = 2-((dimethylamino-κ N )methyl)phenyl-κ C 1 ), yielding [(L NC )PdCl(L-κ P )], which were converted into the cationic complexes [(L NC )PdCl(L)]X (L/X = 1 /PF 6 , 2 /SbF 6 , 3 /PF 6 ). Compounds with ligands 1 and 2 were structurally authenticated as stable bis-chelate complexes. In contrast, the product featuring ligand 3 was rather unstable and converted into [(L NC )Pd(AcOEt-κ O )( 3 -κ P )][PF 6 ] upon recrystallisation. Weak oxygen coordination was confirmed via reactions of [(L NC )PdCl(L)]X with (PhCH 2 NEt 3 )Cl in which the parent chloride complexes were regenerated, and this was further corroborated by DFT computations. Our findings, pointing to hemilabile coordination of 1-3 , are relevant for catalysis because de-coordination of the weaker binding O-donor moiety may open a vacant site for a substrate, thereby enhancing the catalytic properties of metal complexes with ligands of this type. Coordination of phosphinoferrocene ligands with O-donor substituents to Pd( ii ) is affected by the nature of the oxygen functions and may results in hemilabile species.