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, (S)-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 trans-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 trans-PtCl2(PCy2CH2CHO)2 with pendant aldehyde groups, and under certain
conditions, they undergo an intraligand aldol condensation to form
a disphosphine ligand.