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

Monophosphaferrocenes and 4 react with [Pd(COD)Cl2] (COD = cyclooctadiene) to afford cis- [Pd(1 or 4)2Cl2] complexes that slowly decompose in solution to give dimeric complexes 3 and 6 of general formula [[Pd(1 or 4)Cl]2]. In these dimers, which incorporate a Pd-Pd bond, phosphaferrocenes act as four electron donors through the phosphorus-atom lone pair (mu2-bonded) and through one orbital of appropriate symmetry at iron. These dimers can also be more conventionally prepared from the reaction of cis- [Pd(1 or 4) Cl2] complexes with [Pd(dba)2] (dba = dibenzylidene acetone). The reaction of octaethyldiphosphaferrocene (7) with [Pd(COD)Cl2] yields a dinuclear complex [Pd2(7)2Cl4] (8) in which the two ligands 7 are coordinated in a trans fashion through the phosphorus-atom lone pairs. Decomposition of 8 in solution yields a dimeric dicationic complex of general formula [[Pd2(7)2Cl]2]2+[FeCl4]2- (9a) incorporating four palladium atoms. In each ligand. one phospholyl ring behaves as a two-electron donor through the phosphorus-atom lone pair whereas the second binds two palladium centers in a mu2-fashion. A plausible mechanism that explains the formation of dimers 3, 6, and 9a involves the preliminary oxidation of the mono- or diphosphaferrocene ligand. Parallel experiments aimed at confirming this hypothesis have shown that complex 9a can be synthesized from the reaction of FeCl2 with complex 8. Also presented is another synthetic approach to the synthesis of the tetranuclear complex 9b (counterion is GaCl4-) from the reaction of the palladium(0) complex [Pd(7)2] (10) with [Pd(COD)Cl2] the presence of GaCl3 as chloride abstractor.