Top Organomet Chem (2020) 67: 227–270
https://doi.org/10.1007/3418_2020_48
# Springer Nature Switzerland AG 2020
Published online: 25 July 2020
Characterizing the Metal–Ligand Bond
Strength via Vibrational Spectroscopy: The
Metal–Ligand Electronic Parameter
(MLEP)
Elfi Kraka and Marek Freindorf
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
2 The Tolman Electronic Parameter (TEP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
3 Local Vibrational Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
3.1 Theory of Local Vibrational Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
3.2 Application of the Local Vibrational Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
4 Assessment of the TEP with the Local Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
4.1 TEP and Mode–Mode Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
4.2 Correlation Between CO and ML Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
5 The Metal–Ligand Electronic Parameter (MLEP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
5.1 Relative Bond Strength Order (BSO) . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . 249
5.2 Intrinsic Strength of Nickel–Phosphine Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
5.3 Special Role of Carbene Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
5.4 Ionic Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
5.5 Generalization of the MLEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
6 Conclusion and Outlook . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
Abstract The field of organometallic chemistry has tremendously grown over the
past decades and become an integral part of many areas of chemistry and beyond.
Organometallic compounds find a wide use in synthesis, where organometallic
compounds are utilized as homogeneous/heterogeneous catalysts or as stoichiometric reagents. In particular, modifying and fine-tuning organometallic catalysts has
been at the focus. This requires an in-depth understanding of the complex metal–
In memoriam of Dieter Cremer.
E. Kraka (*) and M. Freindorf
Computational and Theoretical Chemistry Group (CATCO), Department of Chemistry,
Southern Methodist University, Dallas, TX, USA
e-mail: ekraka@smu.edu
https://doi.org/10.1007/3418_2020_48
# Springer Nature Switzerland AG 2020
Published online: 25 July 2020
Characterizing the Metal–Ligand Bond
Strength via Vibrational Spectroscopy: The
Metal–Ligand Electronic Parameter
(MLEP)
Elfi Kraka and Marek Freindorf
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
2 The Tolman Electronic Parameter (TEP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
3 Local Vibrational Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
3.1 Theory of Local Vibrational Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
3.2 Application of the Local Vibrational Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
4 Assessment of the TEP with the Local Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
4.1 TEP and Mode–Mode Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
4.2 Correlation Between CO and ML Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
5 The Metal–Ligand Electronic Parameter (MLEP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
5.1 Relative Bond Strength Order (BSO) . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . 249
5.2 Intrinsic Strength of Nickel–Phosphine Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
5.3 Special Role of Carbene Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
5.4 Ionic Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
5.5 Generalization of the MLEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
6 Conclusion and Outlook . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
Abstract The field of organometallic chemistry has tremendously grown over the
past decades and become an integral part of many areas of chemistry and beyond.
Organometallic compounds find a wide use in synthesis, where organometallic
compounds are utilized as homogeneous/heterogeneous catalysts or as stoichiometric reagents. In particular, modifying and fine-tuning organometallic catalysts has
been at the focus. This requires an in-depth understanding of the complex metal–
In memoriam of Dieter Cremer.
E. Kraka (*) and M. Freindorf
Computational and Theoretical Chemistry Group (CATCO), Department of Chemistry,
Southern Methodist University, Dallas, TX, USA
e-mail: ekraka@smu.edu