One-O donor

A wide variety of complexes are formed by both metals in the +2 oxidation state indeed, it is the most important one for palladium. The complexes can be cationic, neutral or anionic. Both Pd2+ and Pt2+ are soft acids so that many stable complexes are formed with S or P as donor atoms but few with O-donors, though there are important ammines. There are pronounced similarities between corresponding palladium and platinum complexes the latter are more studied (and less labile). 

Figure 5.41 The optimized structure and one of three equivalent leading n-+o donor-acceptor interactions oftheCgHg- -B charge-transfer complex. (The scale in (b) is 9 A along each edge, 50% larger than in other such plots in this book.)...

Carbon monoxide is often both reactant and ligand. As a ligand it is a strong Jt-acceptor and a moderate o-donor. By comparison of IR data one might say that its %-value is around 55, i.e. similar to hexafluoroisopropyl phosphite. 

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