Crystal and molecular structure of dicarbonyl(hexaethylbenzene)(triethylphosphine)chromium(0). A novel example of conformational variability in hexaethylbenzene .pi. complexes

Synthesis, structures and dynamic NMR spectra of η6-hexaethylbenzene complexes of ruthenium(0) and ruthenium(ii)

“…31 whereas the all-distal conformation is favoured in derivatives containing fairly bulky tertiary phosphines, e.g. [Cr(CO) 2 (L)(η 6 -C 6 Et 6 )] (L = PPh 3 , 2,4 PEt 3 32 ).…”

“…42 Moreover, in solution these conformers co-exist with the 1,3,5-proximal-2,4,6-distal and all-distal compounds. Since the M-P and M-C (arene) distances in 4 and in [Cr(CO) 2 (L)(η 6 -C 6 Et 6 )] (L = PMe 3 , 42 PEt 3 32 ) are very similar, there is no obvious reason based on steric effects for these differences.…”

Hexaethylbenzene: A Sterically Crowded Arene and Conformationally Versatile Ligand

“…Further studies on [(HEB)Cr(CO) 2 PMe 3 ] ( 6 ) and [(HEB)Cr(CO) 2 PEt 3 ] ( 7 ) clarified the situation, in that they revealed the formation of two further conformers (Figure ). In the solid state, the trimethylphosphine complex exists as an 80:20 mixture of the 1,3‐ proximal ‐2,4,5,6‐ distal ( c ) and 1‐ proximal ‐2,3,4,5,6‐ distal ( e ) isomers; in contrast, the triethylphosphine complex exists as a 50:50 mixture of the e and h isomers . Moreover, a subsequent careful scrutiny of the triphenylphosphine compound 3 also revealed the presence of the 1‐ proximal ‐2,3,4,5,6‐ distal conformer e .…”

“…In the solid state, the trimethylphosphine complex exists as an 80:20 mixture of the 1,3-proximal-2,4,5,6-distal (c)a nd 1-proximal-2,3,4,5,6-distal (e)i somers; [14] in contrast, the triethylphosphine complex exists as a5 0:50 mixture of the e and h isomers. [15] Moreover,asubsequent careful scrutinyo ft he triphenylphosphine compound 3 also revealed the presence of the 1-proximal-2,3,4,5,6-distal conformer e.T he existence of multiple con- formers in solution is also clearly evident from variable-temperature 31 PNMR data;t ypically,[ (HEB)Cr(CO) 2 {P(OPh) 3 }] exhibits resonances for at least three conformers, suggested to be c, e and h. [16] It is apparent from theser esults that the favoured conformer,orc onformers, in each case is markedly dependent on the cone angle of the ligand such that bulkier phosphines lead to structures with increasing numberso fdistal ethyl substituents. Moreover,w ith respect to the orientation of the tripod, for obvious steric reasons, eclipsing does not occur beneath a proximal methyl group.…”

Dynamic NMR studies of restricted arene rotation in the chromiu tricarbonyl thiophene and selenophene complexes

“…-109.05 76.24 17131.45 1241.18 9-82.25 10-123.42 ( 16) 123.42 ( 16) 90.17 12- 33.25( 11) 120.39 17-3.0(2) -143.68 ( 11) 92.90 11-56.29 13-179.71 ( 12) 82. 46( 10) - 41.42( 10) .…”