Oligo- and polymerization of phospha [2]ferrocenophanes to one dimensional phosphorus chains with ferrocenylene handles

A lithium halide exchange reaction at low-temperature, via the treatment of 2,6-di(isopropyl)phenyllithium on 1,1′-bis-(dichlorophosphino)ferrocene, resulted in the first isolated example of an aryl-substituted diphospha [2]ferrocenophane (diphospha [2]FCP) 2. Although compound 2 did not show any recognizable thermal reaction at higher temperature (up to 350 °C), its tert-butyl-substituted counterpart 1 underwent a clean selective heat-mediated P–C cleavage reaction, followed by an inter-molecular rearrangement, to produce a P–P fused bis [3]ferrocenophane 3 with all-trans oriented P-chain, which upon further heating gave a polyferrocenylphosphane tBu-[Fc'P2]n-tBu (4). Since polymer 4 is insoluble in common organic solvents, it has been characterized with solid-state techniques, including solid-state NMR. Density functional theory (DFT) has further been employed to identify possible pathways for P–C bond cleavage on 1 and 2, as well as to evaluate accessible pathways for further polymerization toward 4.