Aromaticity of benzene in the facial coordination mode: A structural and theoretical study

作者：Wadepohl H^*; Castano ME

来源：Chemistry - A European Journal, 2003, 9(21): 5266-5273.

DOI：10.1002/chem.200304875

• arene ligands
• aromaticity
• cluster compounds
• density functional calculations
• structure correlation

The effects of facial coordination of benzene to a trinuclear transition-metal cluster have been studied by structure correlation and DFT calculational methods. Data taken from the X-ray crystal structures of twelve complexes [{(eta-C5H4R") Co}(3)(mu(3)-eta(2):eta(2):eta(2)- C(6)A(4)RR')] 1b-1m were analyzed by using standard statistical methods. The prototypal facial arene ligand is considerably expanded with respect to free benzene and shows a small but highly significant Kekule distortion (d(CC) = 1.42, 1.45 Angstrom). DFT MO calculations were carried out on the model complexes [{(eta-C5H5)M)(3)(mu-eta(2):eta(2):eta(2)-C6H6)] 1a (M = Co), 2 (M = Rh), and 3 (M = Ir). Ring currents in the facial benzene and apical cyclopentadienyl ligands have been assessed by nucleus independent chemical shift (NICS) calculations. Compared to the free ligand (with the optimized D-6h structure as well as with D-3h and a C-3v geometries similar to that in the prototypal facial arene), facial benzene exhibits somewhat reduced but still substantial cyclic electron delocalization (CED). The calculated order of CED is benzene similar to[(CO)(3)Cr(eta-C6H6)] 4 > 1 > 2 > 3.

• 出版日期2003-11-7