Molecular Orbital (MO) Theory
Source: Tamara M. Powers, Department of Chemistry, Texas A&M University
This protocol serves as a guide in the synthesis of two metal complexes featuring the ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf): M(dppf)Cl2, where M = Ni or Pd. While both of these transition metal complexes are 4-coordinate, they exhibit different geometries at the metal center. Using molecular orbital (MO) theory in conjunction with 1H NMR and Evans method, we will determine the geometry of these two compounds.
NOTE: For safety precautions, the Schlenk line safety should be reviewed prior to conducting the experiments. Glassware should be inspected for star cracks before using. Care should be taken to ensure that O2 is not condensed in the Schlenk line trap if using liquid N2. At liquid N2 temperature, O2 condenses and is explosive in the presence of organic solvents. If it is suspected that O2 has been condensed or a blue liquid is observed in the cold trap, leave the trap
Pd(dppf)Cl2:
1H NMR (chloroform-d, 400 MHz, δ, ppm): 4.22 (alpha-H), 4.42 (beta-H), 7.89, 7.44, 7.54 (aromatic)3.
Ni(dppf)Cl2:
1H NMR (chloroform-d, 300 MHz, δ, ppm): 20.85, 10.04, 4.23, 3.98, 1.52, -3.31, -7.10.
Evans Method, looking at the 19F shift of trifluorotoluene:
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This video demonstrated how MO theory can be used as a model of bonding in transition metal complexes. We synthesized two complexes with the general formula M(dppf)Cl2. When M = Ni, the 4-coordinate complex exhibits a tetrahedral geometry. Replacing the Ni atom with a larger transition metal (Pd), the molecule takes on square planar geometry.
Previously, we learned about the important role ferrocene plays in the field of organometallic chemistry. Substituted ferrocenes, including dp
- Corain, B., Longato, B., Favero, G. Heteropolymetallic Complexes of 1,1’-Bis(diphenylphosphino)ferrocene (dppf). III*. Comparative Physicochemical Properties of (dppf)MCl2 (M = Co, Ni, Pd, Pt, Zn, Cd, Hg). Inorg Chim Acta. 157, 259-266 (1989).
- Cullen, W. R., Einstein, F. W. B., Jones, T., Kim, T.-J. Structures of three hydrogenation catalysts [(P-P)Rh(NBD)]ClO4 and some comparative rate studies where (P-P) = (η5-R1R2PC5H4)(η5-R3R4PC5H4)Fe (R1 = R2 = R3 = R4 = Ph, R1 = R2 = Ph, R3 = R4 = CMe3, R1 = R3 = Ph, R2 = R4 = CMe3). Organometallics. 4(2), 346-351 (1983).
- Colacot, T. J., C.-Olivares, R., H.-Ortega, S. Synthesis, X-ray, spectroscopic and a preliminary Suzuki coupling screening studies of a complete series of dppfMX2 (M = Pt, Pd, X = Cl, Br, I). J Organomet Chem. 637-639, 691-697 (2001).
- Rudie, A. W., Lichtenberg, D. W., Katcher, M. L., Davison, A. Comparative Study of 1,1’-bis(diphenylphosphino)cobaltocinium hexafluorophosphate and 1,1’-bis(dipenylphosphino)ferrocene as Bidentate Ligands. Inorg Chem. 17(10), 2859-2863, 1978.
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