Synthesis and structural characterisation of 1'-(diphenylphosphino)ferrocene-1-phosphonic acid, its ammonium salts and Pd(II) complexes.

A new polar phosphinoferrocene ligand, viz. 1'-(diphenylphosphino)ferrocene-1-phosphonic acid (H 2 L), was prepared by hydrolysis of the corresponding phosphonate ethyl ester. However, the compound is relatively unstable, gradually decomposing upon prolonged storage, ultimately affording phosphine oxide H 2 L O. When the phosphine moiety was protected (e.g., in phosphine oxide H 2 L O and adduct H 2 L ·BH 3), no decomposition was observed. An alternative approach to prepare more stable H 2 L surrogates by converting the phosphonic acid into ammonium salts (dabcoH)(H L) and [(OHCH 2 CH 2) 2 NH 2 ](H L) (dabco = 1,4-diazabicyclo[2.2.2]octane) resulted in no significant stabilisation. H 2 L reacted with [PdCl 2 (cod)] (cod = cycloocta-1,5-diene), producing the bis(phosphine) complex, trans -[PdCl 2 (H 2 L -κ P) 2 ]. When mixed with Pd(II)-acetylacetonate (acac) complexes with ortho -metallated auxiliary ligands, [(LCY)Pd(acac)] (LCY = 2-[(dimethylamino-κ N)methyl]phenyl-κ C 1 and 2-[(methylthio-κ S)methyl]phenyl-κ C 1), H 2 L gave rise to bis-chelate complexes of the [(LCY)Pd(H L -κ2 O , P)] type. H 2 L , the ammonium salts featuring the H L − anion, and all Pd(II) complexes were structurally characterised by single-crystal X-ray diffraction analysis. Variations in phosphonate P-O bond lengths observed in the crystal structures were rationalised by DFT computations. Image 1 • A new polar phosphinoferrocene phosphonate ligand was prepared. • The compound was converted to its ammonium salts. • Pd(II) complexes with native and deprotonated ligand were synthesised. • Crystal structures of the salts and Pd(II) complexes were determined. [ABSTRACT FROM AUTHOR]