A Specific π-Ligand Transfer Reaction via Triple-Decker Sandwich Complex Intermediates

Abstract

Photochemically generated cationic cyclopentadienyl iron fragments [FeCp]+ allow a specific stacking reaction of [(t-Bu3C3P2)Fe(t-Bu2C2P3)]. This results in the transient formation of an unstable cationic Fe-Fe triple-decker sandwich complex which decomposes by deliberating the neutral sandwich complex [CpFe(t-Bu2C2P3)], and is stacked again by a second [FeCp]+-unit, yielding the moderately stable cationic triple-decker sandwich complex [CpFe(t-Bu2C2P3)FeCp]+ with a central mi-eta5:eta5-triphospholyl ligand. Air exposure or storage of solutions at room temperature leads to a destacking and the neutral triphosphaferrocene derivative [CpFe(t-Bu2C2P3)] is formed again almost quantitatively in respect to the pentaphospha-ferrocene educt.

1-Triorganylstannyl-1,2,4-triphosphole: A Versatile Starting Material for Phosphorus-Rich Cage Compounds and π-Complexes

“…The sandwich complex units serve as four-electron donor ligands thorugh one phosphorus lone pair and the electrons of a P 2 unit of the bridging heterocycle. In two of the three cases a comparable elongation of the PÀP bond is observed, [33,35] whereas the addition of a Ru 3 (CO) 9 unit to a 1,2,4-triphosphaferrocene derivative has no significant influence on the PÀP bond length. [34] Spectroscopic investigations: Co NMR spectrum consists of two typically [36] extremely broad resonances at d À 1845 and À 2325.…”

“…Therefore we concentrated our efforts on potential specific routes for the preparation of p complexes that contain the 1,2,4-triphospholyl ligands. Our first attempt at specific ligand transfer with this particular ligand was successful with cyclopentadienyl iron cations, [9] but the observed stacking ± destacking reaction sequence was limited to only a few suitable examples. [10] Hence, the preparation of P-stannyl-substituted 1,2,4-triphosphole derivatives was tried, as these triphospholes might behave as a P-rich cyclopentadienyl analogue of stannylcyclopentadienes, which are excellent and widely applicable reagents for Cp ligand transfer reactions.…”

“…If we compare the extremely slipped 34 VE triple-decker sandwich complex 11 with other triple-deckers with the same total VE count, those with carbacycles or boron heterocycles as middle decks form nonslipped, linear structures. [30] On the other hand, in the case of cyclo-P n (n 5, 6) [43] or phosphorusrich P heterocycles as middle decks, [9,10] 34 VE are avoided and 26 to 30 VE are found; these compounds are also nonslipped. The only exceptions to these findings are the aforementioned compounds [(Cp*Fe(m,h 5 :h 2 -C 2 tBu 2 P 3 )RhCp*(CO)], [31] [(Cp*Fe(m,h 5 :h 2 -cyclo-P 5 )IrCp*(CO)], [32] and 11.…”

“…Compound 11 exhibits extraordinary structural features. It can be viewed as an extremely slipped 34 VE triple-decker sandwich complex, [30] as it contains a bridging 1,2,4-triphospholyl ring, h [9] where the h 5 -bonded metal atom is less perturbed, the MÀP1, MÀC10 and MÀC20 distances are reduced for 11 and the MÀP2 and MÀP3 bonds are elongated.…”

Ligand Exchange Reactions of Triphospholyl Metal Carbonyl Complexes

“…This strong consequence of the phosphorus atoms on symmetry and energy of the frontier orbitals of the complexes implies a comparable significant influence on the reactivity of the compounds. However, in the literature there are only few reports on that point . Best candidates for this approach seemed to be half-sandwich compounds such as triphospholylmetal carbonyl complexes.…”