Synthesis and Coordination of Isomeric Phosphinoferrocene Sulfonates

Two isomeric phosphinoferrocene sulfonates are prepared as homologs of 1′-(diphenylphosphino)ferrocene-1-sulfonic acid and are isolated as stable crystalline ammonium salts. The reactions of these proligands with Pd(II) precursors containing an auxiliary C,N-chelate ligand indicate the hemilabile nature of the phosphinosulfonates and lead to P-monodentate and P,O-bridged species, with the latter crystallizing as higher-molecular assemblies.

Two isomeric phosphinoferrocene sulfonic acids representing methylene congeners of 1′-(diphenylphosphino)ferrocene-1-sulfonic acid, viz. Ph₂PCH₂fcSO₃H (HL¹) and Ph₂PfcCH₂SO₃H (HL², fc = ferrocene-1,1′-diyl) are synthesized and isolated as the stable crystalline ammonium salts (Et₃NH)L¹ and (Et₂NH₂)L². Additional salts with 1,4-diazabicyclo[2.2.2]octane (dabco), namely, (dabcoH₂)(L¹)₂ and (dabcoH)L², are prepared for structural characterization by single-crystal X-ray diffraction analysis. Salts (Et₃NH)L¹ and (Et₂NH₂)L² are further studied as ligands in palladium(II) complexes containing the [2-(dimethylamino-κN)methyl]phenyl-κC ¹ (L^NC) auxiliary ligand. With [(L^NC)Pd(μ-Cl)]₂, the salts reacted under cleavage of the dimeric precursor to produce anionic phosphine complexes (Et₃NH)[(L^NC)PdCl(L¹-κP)] and (Et₂NH₂)[(L^NC)PdCl(L²-κP)]. Subsequent chloride removal with AgNO₃ or, alternatively, the direct reaction of (Et₃NH)L¹ and (Et₂NH₂)L² with the acetate-bridged dimer [(L^NC)Pd(μ-OAc)]₂ afforded the corresponding neutral phosphinosulfonate complexes that crystallized as the cyclic O,P-bridged trimer [(L^NC)PdCl(μ(P,O)-L¹)]₃ and hexamer [(L^NC)PdCl(μ(P,O)-L²)]₆, respectively. This behavior highlights the hybrid and hemilabile nature of the heteroditopic phosphinosulfonate donors in reactions with the soft Pd(II) ions.