The synthesis, aromaticity, and NMR properties of [14]annulene fused organometallics. Determination of the effective bond localizing ability ("relative aromaticity") and diamagnetic anisotropy of several organometallic moieties

The aromatic ring current probe, the bridged [14]annulene dimethyldihydropyrene, 1, is used to investigate the bond localization effects of the organometallic species tricarbonylchromiumbenzene, 37, hexamethylbenzenerutheniumbenzene, 38, tricarbonylmanganesecyclopentadienyl, 40, and pentamethylcyclopentadienylrutheniumcyclopentadienyl, 39, when fused to the annulene. Benzo[a]dimethyldihydropyrene 2 was converted to the two isomers of its tricarbonylchromium complex, 9 and 10, in 60% yield using ligand exchange with naphthalene and to its hexamethylbenzene-ruthenium complexes 11 and 12 with [RuCl2(HMB)](2) and AgBF4. The cyclopentadienide fused dihydropyrene 5 was synthesized from dimethyldihydropyrene 1 in eight steps, and then on reaction with pentacarbonyl manganese bromide gave the tricarbonylmanganese complex of 5, as two isomers 28 and 29 in 61% yield, and with (Cp*RuCl2)(n) gave 70% yield of the dihydropyrene annelated ruthenocene isomers 26 and 27. Bis(tricarbonylchromium) complexes 32-34 were obtained in 50% yield from the dibenzannulene 30. The H-1 NMR spectra for each complex were analyzed in detail with regard to ring current shielding of the internal methyl protons and ring current deshielding of the external protons. The McGlinchey equation was used to remove diamagnetic anisotropy effects, and the resultant chemical shift values were consistent with coupling constant results, which together yielded bond fixation data of the annulene, caused by the organometallic. The relative bond fixing ability of the organometallics was found to be in the order: Cp-Ru-Cp* > benzene-Ru2+-(HMB) > Cp-Mn(CO)(3) > benzene-Cr(CO)(3) > benzene. Alternance parameter evidence is presented that the complexes are aromatic, and the authors discuss the relative aromaticity of the complexes to benzene.