Triaryl Phosphite Complexes of Cobalt, Nickel, Platinum, and Rhodium

TRIARYL PHOSPHITE COMPLEXES OF COBALT, NICKEL, PLATINUM, AND RHODIUM 

The preparations described here are developed from published work by Malatesta et al.5 and from more recent studies in the contributors own laboratory.2 The cobalt and nickel complexes are prepared by reduction of the corresponding metal nitrates with sodium tetrahydroborate in the presence of excess ligand, whereas the syntheses of the rhodium and platinum complexes involve simple ligand exchange processes. The preparative routes are suitable for use with triphenyl- or p-substituted triphenyl phosphites reactions involving o- or m-substituted triphenyl phosphites give much reduced yields of products which are difficult to crystallize and are very air-sensitive. These features probably reflect the unfavorable stereochemistry of the o- and m-substituted ligands. 

The cobalt complexes described here, together with the triethyl phosphite analog,6-8 are the only examples of simple cobalt phosphite hydride complexes reported to date and were the first examples of metal hydrides stabilized by phosphite ligands. 

Tris- and tetrakis(triaryl phosphite)platinum(O) complexes have been prepared by reduction of platinum(II) phosphite derivatives with hydrazine.5 The tetrakis complexes have also been prepared by ligand exchange processes, and the synthesis described here is based on this latter procedure. The chemistry of platinum phosphite complexes has not been extensively studied. 

The hydridotetrakis(triphenyl phosphite)rhodium complex described below is the first example of a rhodium hydride complex stabilized by phosphite ligands.2 

---