Di- and tetranuclear palladium complexes incorporating phospha- and diphosphaferrocenes as ligands

Monophosphaferrocenes 1 and 4 react with [Pd(COD)Cl-2] (COD =cyclooctadiene ) to afford cis-[Pd(1 or 4)(2)Cl-2] complexes that slowly decompose in solu tion to give dimeric complexes 3 and 6 of general formula [{Pd(1 or 4)Cl}(2 )], In these dimers, which incorporate a Pd-Pd bend, phosphaferrocenes act as four electron donors through the phosphorus-atom lone pair (mu (2)-bonde d) and through one orbital of appropriate symmetry at iron, These dimers ca n also be more conventionally prepared from the reaction of cis[Pd(1 or 4) Cl-2] complexes with [Pd(dba)(2)] (dba=dibenzylidene acetone). The reaction of octaethyldiphosphaferrocene (7) with [Pd(COD)Cl-2] yields a dinuclear c omplex [Pd-2(7)(2)Cl-4] (8) in which the two ligands 7 are coordinated in a trans fashion through the phosphorus-atom lone pairs. Decomposition of 8 i n solution yields a dimeric dicationic complex of general formula [{Pd-2(7) (2)Cl}(2)](2+)[FeCl4](2)(-) (9a) incorporating four palladium atoms. In eac h ligand, one phospholyl ring behaves as a two-electron donor through the p hosphorus-atom lone pair whereas the second binds two palladium centers in a mu (2)-fashion. A plausible mechanism that explains the formation of dime rs 3, 6, and 9a involves the preliminary oxidation of the mono- or diphosph aferrocene ligand, Parallel experiments aimed at confirming this hypothesis have shown that complex 9a can be synthesized from the reaction of FeCl2 w ith complex 8. Also presented is another synthetic approach to the synthesi s of the tetranuclear complex 9b (counterion is GaCl4-) from the reaction o f the palladium(0) complex [Pd(7)(2)] (10) with [Pd(COD)Cl-2] in the presen ce of GaCl3 as chloride abstractor.