[(dpp-bian)ZnZn(dpp-bian)]: A Zinc-Zinc-Bonded Compound Supported by Radical-Anionic Ligands

摘要

In 2004, Carmona and co-workers reported the isolation of the first molecular zinc compound having a direct metal-metal bond, [Cp~*ZnZnCp~*] (1 a; Cp~*=C5Me5).[1] Following this pioneering work, Robinson and co-workers synthesized the three-coordinate zinc ketiminate derivative [{HC(CMeNAr)_2}ZnZn{HC(CMeNAr)_2}] (2) (Ar=2,6-iPr_2C_6H_3).[2] A further breakthrough in this field was the synthesis by Power and co-workers of the two-coordinate compound, [ArZnZnAr] (3) (Ar=2,6-(2,6-iPr_2C_6H_3)_2C_6H_3), in which stabilization of ZnZn bonding was achieved using a bulky aryl ligand.[3] While our paper was being submitted, another dizincocene, [(C_5Me_4Et)ZnZn(C_5Me_4Et)] (1 b), was prepared and investigated by X-ray crystallography as well as computationally.[1d] So far, compounds 1-3 are the only examples of zinc organic derivatives which have a direct ZnZn bond. The metal-metal bonds in these compounds (1 a: 2.305(3); 1 b: 2.295(3); 2: 2.3586(7); 3: 2.3591(9) a) are significantly shorter than the sum of zinc covalent radii (2.5 a).[4] Density functional theory (DFT) calculations (B3 LYP) for 1-3 showed that in 1 a[1b] and 2[2] the metal 4 s orbitals mainly contribute to the ZnZn bond, whereas in 3 this bond is formed from the overlap of 4 pz orbitals.