Synthesis of New Late Transition Metal P,P‑, P,N‑, and P,O- Complexes Using Phosphonium Dimers as Convenient Ligand Precursors

The phosphonium dimer [-Cy₂PCH­(OH)­CH₂-]₂(X)₂, X = Cl^–, Br^– was used to synthesize and characterize a variety of late transition metal complexes containing chelating phosphino-enolate (PCy₂CHCHO^–), imine (PCy₂CH₂CHNR, R = Ph, (<i>S</i>)-CHMePh), and oxime (PCy₂CH₂CHNOH) ligands. The phosphonium dimer, when deprotected with base, generates the phosphine aldehyde PCy₂CH₂CHO in situ, which, in the presence of [M­(COD)­Cl]₂, M = Rh, Ir, and a PF₆^– salt, or [Ni­(H₂O)₆]­[BF₄]₂, facilitates a condensation reaction with an amine or hydroxylamine to form phosphino-imine or phosphino-oxime metal complexes [M­(COD)­(P–N)]­[PF₆] or [Ni­(P–N)₂]­[X]₂, X = ClO₄^–, BF₄^–, respectively. In the absence of an amine, phosphino-enolate containing complexes are formed. A neutral Ni­(II) complex Ni­(PCy₂CHCHO)₂ with <i>trans-</i>bis­(phosphino-enolate) ligands which resemble ligands used on nickel for olefin oligomerization, as well as neutral Rh­(I) and Ir­(I) 1,5-cyclooctadiene complexes M­(COD)­(PCy₂CHCHO) are characterized. Both the rhodium and iridium complexes are active olefin hydrogenation catalysts. Reaction of the phosphino-aldehyde with Pt­(COD)­Cl₂ results in the formation of <i>trans</i>-PtCl₂(PCy₂CH₂CHO)₂ with pendant aldehyde groups, and under certain conditions, they undergo an intraligand aldol condensation to form a disphosphine ligand