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Tris-(2-pyridylmethyl)amines (TPA or TPMA) are polipyrydine-based ligands extensively used in catalysis and supramolecular chemistry due their capability to form stable tetradentate complexes with a large variety of metals. The unsubstituted ligand, which is also commercially available, can be synthesised by consecutive alkylation of a picoline or by reductive amination of a pyridine aldehyde. In this article, we report a novel synthetic method which opens to the post-functionalisation of these ligands in the benzylic position. This novel derivatization strategy, beside providing synthetic access to novel structures and functions, has been used to prepare a series of metal complexes which have been tested in photochemical hydrogen evolution.

Three gold(i) tripodal complexes containing the tris(2-pyridylmethyl)amine (TPA) ligand coordinated to Au-PR 3 moieties (PR 3 = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane, PTA (1), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, DAPTA (2) and triphenylphosphane (3)) were prepared together with a cage-like structure containing triphosphane 1,1,1-tris(diphenylphosphinomethyl)ethane (4). The luminescence of these complexes has been studied and they show a red shift upon the formation of heterometallic complexes by reaction with Zn(NO 3 ) 2 , CuCl and [Cu(CH 3 CN) 4 ]BF 4 . The different coordination motifs of the Zn 2+ and Cu + heterometallic species and the resulting changes in the recorded absorption, emission and NMR spectra were analysed and supported by TD-DFT calculations.

The chance to have persistent organic radicals in combination with metals has attracted much interest since it offers the possibility of having new functional molecules with multiple open-shell elements. In this study, we report the synthesis of two tripodal tris(2-pyridyl)methylamine ligands (TPMA) functionalized with nitronyl nitroxide persistent radicals. The newly formed ligands have been used to coordinate zinc(ii), copper(ii), iron(ii) and cobalt(ii). The resulting complexes have been investigated by means of electron paramagnetic resonance (EPR), ESI-MS, FT-IR spectroscopy and X-ray diffraction. An electron reduction of the N-O radical moiety has been observed, depending on the metal used for the formation of the complex and the reaction conditions. We have observed small differences in the EPR spectra depending on the meta or para position of the radical moiety in the complex structure and some antiferromagnetic interactions between the paramagnetic M(ii) ions and the radical species.

Novel cobalt, nickel, and iron complexes based on the pentadentate 8-hydroxyquinoline-di(2-picolyl)amine ligand were synthesized and thoroughly characterized. X-ray structures of both the cobalt and iron complexes were also obtained, showing the tendency to adopt a pseudo-octahedral geometry by coordination of an additional sixth ligand. These metal complexes were then studied as potential hydrogen-evolving catalysts (HECs) under both electrochemical and light-driven conditions. In particular, two different photochemical systems were tested involving either Ru(bpy) 3 2+ /ascorbic acid or Ir(ppy) 2 (bpy) + /TEA sensitizer/sacrificial donor couples. The electrochemical results showed that these metal complexes may behave as competent HECs. However, under photochemical conditions, only the cobalt compound displayed substantial hydrogen-evolving activity in both ruthenium- and iridium-based systems. The nickel and iron complexes, on the other hand, exhibited appreciable photocatalytic activity only in the iridium-based photochemical system, while showing negligible hydrogen evolution ability when employed in the ruthenium-based one.

Amino triphenolate tungsten(vi) complexes have been prepared and they proved to be efficient catalysts in haloperoxidation reactions using hydrogen peroxide as a terminal oxidant and inorganic sources of halides. In particular, interesting results have been obtained in the challenging chloroperoxidation reactivity (catalyst loading down to 0.05% with TONs up to 900). A comparison among three different metal complexes bearing the same ligand (vanadium(v), molybdenum(vi) and tungsten(vi)) showed much better performances of the last complex both on bromo and chloro peroxidations.

C(3)-symmetric Ti(IV) amino triphenolate complexes efficiently catalyze, without previous activation and in excellent yields, the oxidation of sulfides at room temperature, using both CHP and the more environment friendly aqueous hydrogen peroxide as terminal oxidants, with catalyst loadings down to 0.01%. The Ti(IV) catalysts and the intermediate Ti(IV)-peroxo complexes have been characterized in solution by (1)H NMR and ESI-MS techniques and via density functional studies.

Triphenolamines are highly modular tetradentate molecules that effectively coordinate to transition metals and main group elements with podand topology. They form chiral complexes with intrinsically well defined coordination geometries controlled by the ligand, in particular by the nature of the substituents in ortho position to the phenol, which are able to influence their reactivity and stability. The metal complexes, especially Ti(iv) and V(v), have been found to be effective catalyst in polymerization reactions and oxygen transfer processes.

A novel, mononuclear Ti(IV) amine triphenolate complex obtained by reaction of Ti(OiPr)(4) with tris(2-hydroxy-3-phenylbenzyl)amine bearing phenyl ortho-substituents affords quantitatively and spontaneously the corresponding heterochiral micro-oxo dinuclear compound whereas an analogous chiral, enantiopure complex maintains its mononuclear structure even in the presence of an excess of water.