Organometallic Chemistry, Coordination Chemistry and Homogeneous Catalysis
Hybrid Ligands with NHC and Classical Donors
Heteroatoms attached to the (mainly imidazol-2-ylidene) N-heterocyclic carbene via a tether at one of the N atoms flanking the carbene carbon, or on the heterocyclic ring at a remote position to the carbene carbon, are used to manage the coordination sphere of the metal and/or modulate the donor properties of the NHC. Thus hybrid monodentate, chelating bidentate or bridging binding modes can be accessed. The charge, H-atom number, hardness/softness and size of the group associated with the heteroatom lead to subtle coordination chemistry also dependent on tautomeric equilibria, intramolecular C-H activations, metallotropism and intamolecular rearrangements.
Relevant recent papers are for example:
Angew. Chem. Int. Ed. 2018, 57, in press. DOI: 10.1002/anie.201808008, Angew. Chem. Int. Ed. 2015, 54, 13691 - 13695, DOI: 10.1002/anie.201505958, Chem. Commun., 2015, 51, 3049-3052, DOI: 10.1039/c4cc08434a, Chem. Commun., 2014, 50, 3055-3057. DOI: 10.1039/c3cc49517e.
Pincer Complexes
The high potential of the pincer ligands for the tuning of the metal environment is exploited by the inclusion of N-heterocyclic carbene donors in symmetrical and non-symmetrical ligand architectures usually with pyridine bridgehead donor. The proton responsiveness and/or redox noninnocence of the pincer framework is studied in stoichiometric reactions by employing well-defined complexes, in particular with 3d-base metals. The aim is catalyst development in reactions such as hydrosilylations, hydrogenations, cross-couplings, alkene oligomerisations and activation of small molecules.
Relevant recent papers are for example:
Dalton Trans., 2016, 45, 2800-2804, DOI: 10.1039/c6dt00144k, Chem. Commun. 2016, 52, 2717-2720, DOI: 10.1039/c5cc10121b, Organometallics, 2016, 35, 903−912, DOI: 10.1021/acs.organomet.6b00048, Organometallics, 2016, 35, 4044-4049. DOI: 10.1021/acs.organomet.6b00685, Dalton Trans., 2018, 47, 7888. DOI: 10.1039/c8dt01279b, Organometallics, 2016, 35, 198–206. DOI: 10.1021/acs.organomet.5b00926, Chem. Commun. 2015, 51, 10699-10702, DOI: 10.1039/C5CC02920A.
Oligonuclear Organometallics
In collaboration with Prof. Pierre Braunstein (University of Strasbourg, France) we study small oligonuclear complexes using ligand designs that place the metals in close proximity. A variety of donors are integrated in the ligand framework, including phosphines, N-heterocyclic carbenes and silylamides. Having initially targeted homometallic complexes of coinage metals or Pd, the project has recently expanded to heterometallics of Pd-Cu Pd-Ag and Au-Ag. The inclusion of other 3d metals is also in progress.
The oligonuclear organometallics are used as probes of the intermetallic interactions and bonding which are rationalised by computational techniques (in collaboration). Together with their derivatives obtained by redox transformations or by substitution of easily displaceable ligands, they are being studied in the framework of catalytic, magnetochemical or photophysical applications. In addition to a palette of spectroscopic techniques employed for the characterisation of the new structures, solution EXAFS/XANES aiming at elucidating the electronic structure of the metal centres are carried out in collaboration with Prof. Moniek Tromp (University of Groningen).
Relevant recent papers are for example:
Chem. Eur. J. 2018, 24, 8787 – 8796. DOI: 10.1002/chem.201801170, Chem. Eur. J. 2017, 23, 6504–6508. DOI: 10.1002/chem.201700496, Inorg. Chem. 2016, 55, 1219-1229, DOI:10.1021/acs.inorgchem.5b02382, Angew. Chem. Int. Ed. 2016, 55, 3338–3341, DOI: 10.1002/anie.201510150, Inorg. Chem. 2016, 55, 8527–8542, DOI: 10.1021/acs.inorgchem.6b01095, Chem. Eur. J. 2017, 23, 6504–6508. DOI: 10.1002/chem.201700496, Inorg. Chem. 2015, 54, 3722–3724, DOI: 10.1021/acs.inorgchem.5b00276, Chem. Commun., 2014, 50, 103-105. 10.1039/C3CC47370H.
Low Coordination Number Reactive Organometallics
The combination of bulky N-heterocyclic carbenes and the bis-(trimethylsilyl)amido ligands led to three- or two-coordinate complexes of Fe, Co and Cr in oxidation states II and I (the latter for Fe and Co). The complexes show interesting magnetic properties: The two-coordinate species show unusually high high magnetic susceptibilities that have been reasonably modelled with the involvement of redox non-innocent N-heterocyclic carbene ligands. In addition, in certain cases unusually distorted molecular geometries are observed due to the increased spatial availability around the metal and the increasingly dominant role of non-covalent interaction exerted by atoms within the molecular space.
Relevant recent papers are for example:
Dalton Trans., 2017, 46, 1163-1171. DOI: 10.1039/C6DT03565E, Chem. Eur. J. 2017, 23, 6504–6508. DOI: 10.1002/chem.201700496, Oil & Gas Science and Technology-Revue d'IFP Energies nouvelles 2016, 71 Issue 2 DOI: 10.2516/ogst/2015047, Organometallics, 2015, 34, 2429–2438, DOI: 10.1021/om501178p. Organometallics, 2013, 32, 1842, DOI: /10.1021/om3012568 | Organometallics 2013, 32, 1842 1850.