$C_{60}$ -metal cluster complexes: synthesis, characterization and theoretical studies

Abstract

The studies involve the synthesis, characterization, and theoretical studies of metallofullerene compounds. Heating a mixture of $Ir_4(CO)_9(PPh_3)_3$ (II-1) and 2 equiv of $C_{60}$ in refluxing chlorobenzene (CB) affords a “butterfly” $tetrairidium-C_{60}$ complex $Ir_4(CO)_6{μ_3-κ^3-PPh_2(ο-C_6H_4)P(ο-C_6H_4)PPh(η^1-ο-C_6H_4)}(μ_3-η^2:η^2:η^2-C_{60})$ (II-3, 36%). Brief thermolysis of II-1 in refluxing CB gives a “butterfly” complex $Ir_4(CO)_8{μ-κ^2-PPh_2(ο-C_6H_4)PPh}{μ_3-PPh_2(η^1:η^2-ο-C_6H_4)}$ (II-2, 64%) that is both ortho-phosphorylated and ortho-metalated. Interestingly, reaction of II-2 with 2 equiv of $C_{60}$ in refluxing CB produces II-3 (41%) by $C_{60}$ -assisted ortho-phosphorylation, indicating that II-2 is the reaction intermediate for the final product II-3. Compounds II-2 and II-3 have been characterized by spectroscopic and microanalytical methods as well as by single crystal X-ray diffraction studies. Cyclic voltammetry (CV) has been used to examine the electrochemical properties of II-2, II-3, and a related known “butterfly” complex $Ir_4(CO)_6(μ-CO){μ_3-κ^2-PPh_2(o-C_6H_4)P(η^1-o-C_6H_4)}(μ_3-η^2:η^2:η^2-C_{60})$ (II-4). These CV data suggest that a C60-mediated electron transfer to the iridium cluster center takes place for the species $II-3^{3-}$ and $II-4^{2-}$ in compounds II-3 and II-4. The electrochemical properties of II-3 and II-4 have been rationalized by molecular orbital calculations using the density functional theory (DFT) and by charge distribution studies employing the Mulliken and Hirshfeld population analyses. On the other hand, reaction of $Ir_4(CO)_8(PMe_3)_4$ (III-1) with excess (4 equiv) $C_{60}$ in refluxing 1,2-dichlorobenzene, followed by treatment with $CNCH_2Ph$ at $70^\circ C$, affords a square-planar complex with two $C_{60}$ ligands and a face-capping methylidyne ligand, $Ir_4(CO)_3(μ_4-CH)(PMe_3)_2(μ-PMe_2)(CNCH_2Ph)(μ-η^2:η^2-C_{60})(μ_4-η^1:η^1:η^2:η^2-C_{60})$ (III-2, 13%) as the major product. Compo...