The group activities are centred in the areas of Organometallic/Coordination Chemistry and Catalysis, involving: i) the synthesis of new polyfunctional chelating ligands and their coordination to metal centres to produce complexes with specific electronic and stereochemical properties, ii) the study of their molecular structures, using solution NMR, X-ray diffraction and DFT, and iii) experimental reactivity studies, stoichiometric or catalytic, and computational mechanistic calculations, all together providing an integrated vision of the chemical behaviour of the systems. The application of the new metal complexes as catalysts for several organic reactions (e.g. polymerization, hydrogenation, oxidation, sulfoxidation, hydroamination) or as functional materials (e.g luminescent, magnetic, bioactive) is an important objective of the group. Some of the most significant current lines of research are outlined below.

Nickel(II) and palladium(II) complexes as aluminium-free catalysts for olefin polymerisation

Nickel and palladium complexes are important catalyst precursors for the polymerisation of olefins and their copolymerisation with polar monomers. The use of alkylaluminium cocatalysts is in general a requirement for their activation. We have synthesised a family of iminopyrrolyl Ni(II) catalysts containing a metal-carbon bond, which is active per se in the polymerisation of ethylene. Further development of this family and its extension to Pd(II) complexes are expected to give rise to greener aluminium-free catalysts that can operate in aqueous media, namely under emulsion polymerisation conditions.

Nickel catalysts

α-Diimino copper complexes as catalysts for alkyne-azide cycloaddition and mediators of ATRP

Click chemistry and ATRP are important fields of catalytic or metal-mediated chemical processes where copper complexes play a key role. We have been developing a family of α-diimino complexes of Cu(I) and Cu(II) that behave, respectively, as catalysts for the cycloaddition of alkynes and azides, and as mediators of the reverse Atom Transfer Radical Polymerisation (ATRP) of vinyl.[1]

Cover of EJIC 9/2013Cu(I) catalysts

Luminescent boron complexes for optoelectronic applications

Light emitting molecules play important roles as sensors, in solar energy conversion, in optelectronic devices. Several aspects of the synthesis, molecular structure, and photophysical characterization of a new family of highly photoluminescent tetracoordinate boron complexes are being investigated. These organoboron derivatives contain a bidentate 2-iminopyrrolyl ligand that can be fine-tuned either electronically or sterically, leading to different emission colors.[2] Diverse strategies used for the tuning of these compounds are being employed. These complexes are good emitters in electroluminescent layers of Organic Light Emitting Diode (OLED) devices. Extension of these studies to molecules incorporating transition-metal or lanthanide-based fragments is being carried out.

Luminescent Boron

Diazo- and metal-free synthesis of β-lactams

β-lactams are important building blocks in organic synthesis normally obtained by cycloadditions and C–H insertion reactions on carbene species resulting from metal catalysed decomposition of diazo-precursors. A novel process for the synthesis of β-lactams was developed, in which the lactams are formed in a single step from β-ketoamines via iodonium ylides. This is a diazo- metal and metal-free process and occurs under very mild conditions. DFT studies proved that the reaction mechanism involves a free carbene intermediate. This work was classified as a VIP paper and chosen to illustrate the magazine cover.[3]

B-lactams

Diamine bisphenolate complexes of early metals: catalytic applications and cytotoxic properties

Diamine bisphenolate sets combine two hard anionic moieties that suit the electronic requirements of oxophilic early metals (G3-G6) with two neutral donors, which provide additional intramolecular stabilization. By changing the substituents of the phenolate and/or the amine groups it was possible to prepare a collection of ligand architectures that stabilize several metal oxidation states and modulate the structures and properties of metal complexes. The investigation of i) radical reactions of M(III) (M = Ti, V, Y, Sm),[4] ii) M=O (M = Ti, V, Mo, W) complexes as epoxidation and sulfoxidation catalysts,[5] iii) propylene polymerization using Ti and Zr chiral catalysts[6] and iv) cytotoxic properties of Ti complexes against several cancer cell-lines,[7] are examples of the work recently carried out.

AmPh1AmPh2

Metal complexes anchored by dianionic cyclam-based ligands: from fundamental to applied chemistry

It was not until recently that saturated azamacrocyclic ligands have received attention in the context of early-metal chemistry. Aiming to explore novel reactivity patterns, we introduced a new family of dianionic cyclams as ancillary ligands of TM and Ln complexes.[8] The thermodynamic stability provided by the cyclic array, the possibility of introducing several substituent groups at the nitrogen atoms and the flexibility to adopt different coordination modes and conformations are at the origin of unique properties of these systems, which were investigated in different type of catalytic reactions. For instance, phenoxido Zr(IV) complexes polymerize rac-lactide to form PLA displaying cyclam end-groups.[8f] The latter type of compounds, unknown until date, reveals potential biological applications as they combine a macrocyclic host with biodegradable and biocompatible oligomers/polymers. Several Zr and Y complexes are very active catalysts of hydroamination of aminoalkenes. The mechanism of the reactions, studied by NMR and computational methods, revealed that the macrocycle displays a central role that involves reversible C-H activation of the cyclam pending arms.[8e]

Fig2Fig1

 References

1. (a) L. Li, P. S. Lopes, V. Rosa, C. A. Figueira, M. A. N. D. A. Lemos, M. T. Duarte, T. Avilés, P. T. Gomes, Dalton Trans. 2012, 41, 5144–5154 (DOI: 10.1039/C2DT11854H); (b) L. Li, P. S. Lopes, C. A. Figueira, C. S. B. Gomes, M. T. Duarte, V. Rosa, C. Fliedel, T. Avilés, P. T. Gomes, Eur. J. Inorg. Chem. 2013, 1404-1417 (DOI: 10.1002/ejic.201390037); (c) C. Fliedel, V. Rosa, C. I. M. Santos, P. J. Gonzalez, R. M. Almeida, C. S. B. Gomes, P. T. Gomes, M. A. N. D. A. Lemos, G. Aullón, R. Welter, T. Avilés, Dalton Trans. 2014, 43, 13041-13054 (DOI: 10.1039/C4DT01069H).

2. (a) D. Suresh, C. S. B. Gomes, P. T. Gomes, R. E. Di Paolo, A. L. Maçanita, M. J. Calhorda, A. Charas, J. Morgado, M. T. Duarte, Dalton Trans. 2012, 41, 8502–8505 (DOI: 10.1039/C2DT30487B); (b) D. Suresh, P. S. Lopes, B. Ferreira, C. A. Figueira, C. S. B. Gomes, P. T. Gomes, R. E. Di Paolo, A. L. Maçanita, M. T. Duarte, A. Charas, J. Morgado, M. J. Calhorda, Chem. Eur. J. 2014, 20, 4126-4140, 2014 (DOI: 10.1002/chem.201303607).

3. L. F. R. Gomes, L. F. Veiros, N. Maulide, C. A. M. Afonso, Chem. Eur. J. 2014, in press (DOI: 10.1002/chem.201404990).

4. (a) S. Barroso, F. Madeira, M. J. Calhorda, M. J. Ferreira, M. T. Duarte, A. M. Martins, Inorg. Chem. 2013, 52, 9427-9439 (DOI: 10.1021/ic401008y); (b) J. M. Carretas, S. Barroso, J. Cui, A. Cruz, I. C. Santos, A. M. Martins, Inorg. Chim. Acta 2013, 407, 175-180 (DOI: 10.1016/j.ica.2013.07.051); (c) S. Barroso, J. Cui, J. M. Carretas, A. Cruz, I. C. Santos, M. T. Duarte, J. P. Telo, N. Marques, A. M. Martins, Organomet. 2009, 28, 3449-3458 (DOI: 10.1021/om9001389).

5. (a) S. Barroso, P. Adão, F. Madeira, M. T. Duarte, J. C. Pessoa, A. M. Martins, Inorg. Chem. 2010, 49, 7452-7463 (DOI: 10.1021/ic1007704); (b) F. Madeira, S. Barroso, S. Namorado, P. M. Reis, B. Royo, A. M. Martins, Inorg. Chim. Acta 2012, 383, 152-156 (DOI: 10.1016/j.ica.2011.10.071).

6. S. Barroso, P. Adão, M. T. Duarte, A. Meetsma, J. C. Pessoa, M. W. Bouwkamp, A. M. Martins, Eur. J. Inorg. Chem. 2011, 4277-4290 (DOI: 10.1002/ejic.201100470).

7. S. Barroso, A. M. Coelho, S. Gómez-Ruiz, M. J. Calhorda, Ž. Žižak, G. N. Kaluđerović, A. M. Martins, Dalton Trans. 2014, DOI: 10.1039/C4DT00975D.

8. (a) R. F. Munhá, L. G. Alves, N. Maulide, M. T. Duarte, I. E. Markó, M. D. Fryzuk, A. M. Martins, Inorg. Chem. Commun. 2008, 11, 1174-1176 (DOI: 10.1016/j.inoche.2008.07.002); (b) R. F. Munhá, L. F. Veiros, M. T. Duarte, M. D. Fryzuk, A. M. Martins, Dalton Trans. 2009, 7494-7508 (DOI: 10.1039/b907335c); (c) L. G. Alves, M. A. Antunes, I. Matos, R. F. Munhá, M. T. Duarte, A. C. Fernandes, M. M. Marques, A. M. Martins, Inorg. Chim. Acta 2010, 363, 1823-1830 (DOI: 10.1016/j.ica.2010.02.018) ; (d) R. F. Munhá, M. A. Antunes, L. G. Alves, L. F. Veiros, M. D. Fryzuk, A. M. Martins, Organometallics 2010, 29, 3753-3764 (DOI: 10.1021/om100465d); (e) M. A. Antunes, R. F. Munhá, L. G. Alves, L. Schafer, A. M. Martins, J. Organomet. Chem. 2011, 696, 2-6 (DOI: 10.1016/j.jorganchem.2010.08.039); (f) L. G. Alves, F. Hild, R. F. Munhá, L. F. Veiros, S. Dagorne, A. M. Martins, Dalton Trans. 2012, 14288-14298 (DOI: 10.1039/c2dt31133j); (g) L. G. Alves, A. M. Martins, Inorg. Chem. 2012, 51, 11-12 (DOI: 10.1021/ic201750y).