Conformational variability in π-complexes of hexaethylbenzene. Crystal and molecular structure of [(C6Et6)(C5H5)Fe]BPh4

[η6-1-Chloro-2-(pyrrolidin-1-yl)benzene](η5-cyclopentadienyl)iron(II) hexafluoridophosphate and (η5-cyclopentadienyl){2-[η6-2-(pyrrolidin-1-yl)phenyl]phenol}iron(II) hexafluoridophosphate

“…This second value is among the largest reported from our work, along with the metal-organic compounds value of 5.34 (13) given previously by Jenkins et al (2009). This is also similar to the value of 5.4 reported for the hexaethylbenzene-CpFe complex (Dubois et al, 1989), although lower than the value of 7 reported for the 1,1 0trimethylenebenzene-CpFe cation (Nesmeyanov et al, 1977). No standard uncertainties were provided by these authors in their reports.…”

Hexaethylbenzene: A Sterically Crowded Arene and Conformationally Versatile Ligand

“…[31] Unexpectedly,i n1 989, Zaworotko et al reported that merely replacing the hexafluorophosphate counterion in 20 by tetra-phenylborate, asi n[ (HEB)Fe(C 5 H 5 )][BPh 4 ]( 21), yieldedt he 1proximal-2,3,4,5,6-distal conformer e ( Figure 8). [32] Clearly,t he balance between thesec onformers is delicate, and supports the observation by Hunter,M islow et al that multiple conformers of 20 co-exist in solution. [16] Notably,t he attempted preparation of the [(HEB)Fe(C 5 H 5 )] + cation directly from HEB and [(C 5 H 5 )Fe(CO) 2 Br] in the presence of AlCl 3 resulted insteadi nt he loss of an ethyl substituent and formation of [(C 6 Et 5 H)Fe(C 5 H 5 )] + (22); the X-ray crystal structure of the PF 6 À salt revealed that all five ethyl substituents were oriented distal.…”

“…[63] They raised the possibility that in solutiont he arene itself in 8 could adopt am irror-symmetrical conformer, such as c,t hereby renderings lowed tripodal rotation unnecessary.T hey noted that numerous HEB-metal complexes existed as mixtures of conformers in solution,a nd that the energy differences between such speciesw ere rather small;i np articular, the sandwich cation [(HEB)Fe(C 5 H 5 )] + was found to crystallise as conformers c and e,r espectively,m erely by changing the counterion from hexafluorophosphate to tetraphenylborate. [30,32] In response to this comment, McGlinchey et al then reported the syntheses, variable-temperature 13 The NMR spectrum of 9 was agains plit into the 2:1/2:1 pattern fore ach of the methyl, methylene and ring carbon environments, paralleling the behaviour of the thiocarbonyl complex 8.M ore dramatically,i n10,e ach of the six initially developing resonances( two each for the methyl, methylene and ring carbon atoms) was split into three equally intense peaks ( Figure 18). As before,t he barriers towards ethyl and arene rotation were found to be 11.5 and9 .5 kcal mol À1 ,r espectively.I f the rotationo fe thyl anda rene groups both becames lowo n the NMR time-scale, the chiral nature of the tripod rendered all 18 carbonatoms of the HEB ligand non-equivalent.…”

(η5-Cyclopentadienyl)(η6-1,2-dipyrrolidin-1-ylbenzene)iron(II) hexafluoridophosphate

“…The two aromatic rings are not planar, with an angle of 5.34 (13)° between the planes formed by C1•••C6 and C21•••C25. This is the largest value among those reported previously by our group, although lower than the values 7° reported for 1,1′-trimethylenebenzene-CpFe cation (Nesmeyanov et al, 1977), and 5.4° reported for hexaethylbenzene-CpFe complex (Dubois et al, 1989). No standard uncertainties were given by these authors.…”

“…For the synthesis of the title compound and related structures, see: Lee et al (1989). For the crystal structures of {( 5 -Cp)( 6arene) Fe(II)} + salts, see: Nesmeyanov et al (1977); Dubois et al (1989); Pió rko et al (1995); Manzur et al (2000); Fuentealba et al (2007); Manzur et al (2009) and literature cited therein.…”