Coordination complexes of aryl- and alkylphosphonium cyclopentadienylides (cyclopentadienylidene ylides), C5R4PR′R′′R′′′ (R=H, alkyl, aryl; R′, R′′, R′′′=alkyl, aryl)

Electron‐Deficient Imidazolium Substituted Cp Ligands and their Ru Complexes

“…we observe three lithium signals that can be assigned to aL i + cation at À0.80 ppm, and in a1 :5 ratio to the half-sandwichl ithium complex 3 at À6.0 ppm and to the lithiocene 4 at À11.7 ppm. The broad signals indicate af ast equilibrium betweent hese species that is confirmed by a 7 Li EXSY NMR experiment. To comparei td irectly with C,w ep erformedt he experiment with LiNTf 2 in toluene, but even at À80 8Co nly the half-sandwich complex can be observed.…”

“….5Et 2 Oa sw ell as LiNTf 2 as lithium salt and deuterated dichloromethane as ap olar,w eakly coordinating solvent( Scheme2). In the case of LiNTf 2 we observe one broad signal in the 7 Li NMR at À7.0 ppm (LiNTf 2 )t hat is diagnostic for ah alf-sandwichl ithium complex.I nt he case of…”

“…Substituents that weaken the MÀCp bond (e.g. Ar, [4] F, [5] Cl, [5] CN, COOR, NO 2 , CF 3 , [6] phosphonium, [7] pyridinium or ammonium groups)a re much less studied. [8,9] One interesting ligand class in this regard is that of cyclopentadienylides.…”

“…-SR 2 + ,-NR 3 + ,-PR 3 + or carbenium. [7,9] The latter can also be described with the resonance structure of ylenes,f or example, as fulvenes or fulvalenes ( Figure 1). In case of an enhanced stabilisation of the separated chargesb ym esomeric effects or aromaticity,t he ylidic character can become dominant.…”

“…[11] This compound exhibits ah ighly ylidic character and can be best described as an imidazolium substituted Cp withouts ignificant ylenec haracter.S ix years later,w ei ntroducedt he dipyrido-anellated ligand C,w hich provides an even stronger charge separation. [12] An analogous class of compounds are phosphoniumc yclopentadienylides, [7] with the Ramirezy lide D being its most prominent representative. [13] The first examples of di(phosphonium)s ubstituted Cp rings E have been reported recently.…”