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Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents
Published on: May 28, 2014
Computational and Spectroscopic Studies of Re(I) Bipyridyl Complexes Containing 2,6-Dimethylphenylisocyanide (CNx)
Stanislav R Stoyanov1, John M Villegas1, Arvin J Cruz1
1Department of Chemistry, Wichita State University, 1845 N. Fairmount Street, Wichita, Kansas 67260-0051, Department of Chemistry, Bethany College, 421 N. First Street, Lindsborg, Kansas 67456-1897, and Department of Chemistry, Texas A & M University, P.O. Box 30012, College Station, Texas 77842-3012.
Abstract:
Density Functional Theory (DFT) calculations produce optimized geometries of the complexes [Re(CO)3(bpy)Cl] (1), [Re(CO)3(bpy)(py)](CF3SO3) (2), [Re(CO)3(bpy)(CNx)](CF3SO3) (3), and [Re(CO)(bpy)(CNx)3](CF3SO3) (4), where bpy = 2,2'-bipyridine, py = pyridine, and CNx = 2,6-dimethylphenylisocyanide in their ground and lowest-lying triplet states. The ground-state optimized geometry for the cation of [Re(CO)3(bpy)(CNx)](CF3SO3) (3) results in a Re-C (CNx) bond length of 2.10 Å, a Re-C (CO) bond length trans to CNx of 2.01 Å, and a Re-C (CO) bond length cis to CNx of 1.96 Å which compares favorably to the single-crystal analysis of a Re-C (CNx) bond length of 2.074(4) Å, a Re-C (CO) bond length trans to CNx of 1.971(4) Å, and Re-C (CO) bond length cis to CNx of 1.932(4) Å. The majority of the singlet excited-state energies calculated using Time-dependent Density Functional Theory (TDDFT) and Conductor-like Polarizable Continuum Model (CPCM) are metal-ligand-to-ligand charge transfer (MLLCT) states and are in good agreement with the UV-vis spectral energies for the complexes in ethanol. The complexes exhibit emission both at room temperature and at 77 K except 4 which is only emissive at 77 K. The 77 K emission lifetimes range from 3.9 μs for 1 to 8.8 μs for 3. The emissive lowest-lying triplet state is a (3)MLLCT state for complexes 1-3 but a triplet ligand-to-metal charge transfer ((3)LMCT) state for complex 4. The electronic, electrochemical, thermodynamic, HOMO-LUMO, and emitting-state energy gaps as well as the emission lifetimes increase in the order 1 < 2 < 3. A (3)d-d excited- state, which is located above the (3)LMCT state, accounts for the loss of room-temperature emission for complex 4.
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