3,7-Diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) and derivatives: Coordination chemistry and applications

Spontaneous Water-Promoted Self-Aggregation of a Hydrophilic Gold(I) Complex Due to Ligand Sphere Rearrangement

Aggregating gold(I) complexes in solution through short aurophilic contacts promotes new photoluminescent deactivation pathways (aggregation-induced emission, AIE). The time dependence of spontaneous AIE is seldom studied. We examine the behavior of complex [Au(N9-hypoxanthinate)(PTA)] (1) in an aqueous solution with the aid of variable-temperature NMR, time-resolved UV-Vis and photoluminescence spectroscopy, and PGSE NMR. The studies suggest that partial ligand scrambling in favor of the ionic [Au(PTA)2][Au(N9-hypoxanthinate)2] pair followed by anion oligomerization takes place. The results are rationalized with the aid of computational calculations at the TD-DFT level of theory and IRI analysis of the electron density.

Water-Soluble Pd-Imidate Complexes as Versatile Catalysts for the Modification of Unprotected Halonucleosides

Modification of unprotected nucleosides has been attracting continuous interest, since these building blocks themselves and their phosphate-upgraded corresponding nucleotides have shown a plethora of uses in fields like biochemistry or pharmacy. Pd-catalyzed cross-coupling reactions, conducted in water or its mixtures with polar organic solvents, have frequently been the researchers' choice for the functionalization of the purine/pyrimidine base of the unprotected nucleosides. In this scenario, the availability of hydrophilic ligands and its water-soluble palladium complexes has markedly set the pace of the advances. The approach of our group to the synthesis of such complexes, Pd-imidates specifically, has faced critical stages, namely the jump to synthesize water soluble complexes from our experience working in conventional solvents, the preparation of phosphine free complexes and the overall goal of getting catalytic systems able to work close to room temperature. The continuous feedback with Kapdi's group, experienced in the chemistry of nucleosides, has produced over the last decade the interesting results in both fields presented here.

Synthesis of a Novel Series of Cu(I) Complexes Bearing Alkylated 1,3,5-Triaza-7-phosphaadamantane as Homogeneous and Carbon-Supported Catalysts for the Synthesis of 1- and 2-Substituted-1,2,3-triazoles

The N-alkylation of 1,3,5-triaza-7-phosphaadamantane (PTA) with ortho-, meta- and para-substituted nitrobenzyl bromide under mild conditions afforded three hydrophilic PTA ammonium salts, which were used to obtain a new set of seven water-soluble copper(I) complexes. The new compounds were fully characterized and their catalytic activity was investigated for the low power microwave assisted one-pot azide-alkyne cycloaddition reaction in homogeneous aqueous medium to obtain disubstituted 1,2,3-triazoles. The most active catalysts were immobilized on activated carbon (AC), multi-walled carbon nanotubes (CNT), as well as surface functionalized AC and CNT, with the most efficient support being the CNT treated with nitric acid and NaOH. In the presence of the immobilized catalyst, several 1,4-disubstituted-1,2,3-triazoles were obtained from the reaction of terminal alkynes, organic halides and sodium azide in moderate yields up to 80%. Furthermore, the catalyzed reaction of terminal alkynes, formaldehyde and sodium azide afforded 2-hydroxymethyl-2H-1,2,3-triazoles in high yields up to 99%. The immobilized catalyst can be recovered and recycled through simple workup steps and reused up to five consecutive cycles without a marked loss in activity. The described catalytic systems proceed with a broad substrate scope, under microwave irradiation in aqueous medium and according to "click rules".

A new amido-phosphane as ligand for copper and silver complexes. Synthesis, characterization and catalytic application for azide-alkyne cycloaddition in glycerol

The new sterically hindered amido-phosphane 1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-3,7-diylbis(phenylmethanone), DBPTA (1), has been obtained via an open-cage double N-acylation of 1,3,5-triaza-7-phosphadamantane (PTA) using benzoic anhydride. DBPTA is the only acyl derivative of PTA that contains an aromatic appendage. Due to the bulky nature of the benzoyl C(O)Ph groups, they exhibit mutual anti configuration as confirmed by solution NMR and single crystal X-ray diffraction. Compound 1 is readily soluble in common polar organic and green solvents, making it a very versatile ligand that could be used in a variety of reaction systems. To assess the coordination characteristics of the new phosphane, seven copper complexes of formulas [Cu(DBPTA)4]BF4 (2), [CuX(DBPTA)3] {X = Br (3) and I (4)}, [Cu(μ-X)(DBPTA)2]2 {X = Br (5) and I (6)}, [Cu(bpy)(DBPTA)2]Y {Y = BF4 (7) and BPh4 (8)} {bpy = 2,2'-bipyridine}, and three silver complexes with formulas [Ag(DBPTA)4]NO3 (9), [Ag(Tpm*)(DBPTA)]NO3 (10) and [Ag(Tpms)(DBPTA)] (11) {Tpm* = tris(3,5-dimethyl-1-pyrazolyl)methane, Tpms = tris(pyrazol-1-yl)methanesulfonate} have been synthesised. Compounds 1-11 were characterized by elemental analyses and electrospray ionization mass spectrometry (ESI-MS), as well as by FT-IR and NMR (1H, 13C, 31P, COSY and HSQC) spectroscopic techniques. The catalytic activity of the complexes has been investigated for 1,3-dipolar azide-alkyne cycloaddition reaction using glycerol as a reaction medium to afford 1,4-disubstituted-1,2,3-triazoles. Complex 7 was found to be the most efficient catalyst, affording triazoles in yields up to 97% after 18 h under standard bench experimental conditions (at 23 °C, aerobic conditions and in the absence of any additional bases) and up to 98% after 15 minutes under microwave irradiation (125 °C, 30 W). The catalysis proceeds with a broad substrate scope according to "Click" rules providing a significant contribution to "Green Chemistry".

The Catalytic Activity of Carbon-Supported Cu(I)-Phosphine Complexes for the Microwave-Assisted Synthesis of 1,2,3-Triazoles

A set of Cu(I) complexes with 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo-[3.3.1]nonane (DAPTA) phosphine ligands viz. [CuX(κP-DAPTA)3] (1: X = Br; 2: X = I) and [Cu(μ-X)(κP-DAPTA)2]2 (3: X = Br; 4: X = I) were immobilized on activated carbon (AC) and multi-walled carbon nanotubes (CNT), as well as on these materials after surface functionalization. The immobilized copper(I) complexes have shown favorable catalytic activity for the one-pot, microwave-assisted synthesis of 1,2,3-triazoles via the azide-alkyne cycloaddition reaction (CuAAC). The heterogenized systems with a copper loading of only 1.5–1.6% (w/w relative to carbon), established quantitative conversions after 15 min, at 80 °C, using 0.5 mol% of catalyst loading (relative to benzyl bromide). The most efficient supports concerning heterogenization were CNT treated with nitric acid and NaOH, and involving complexes 2 and 4 (in the same order, 2_CNT-ox-Na and 4_CNT-ox-Na). The immobilized catalysts can be recovered and recycled by simple workup and reused up to four consecutive cycles although with loss of activity.

Water-Soluble O-, S- and Se-Functionalized Cyclic Acetyl-triaza-phosphines. Synthesis, Characterization and Application in Catalytic Azide-alkyne Cycloaddition

The 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) derivatives, viz. the already reported 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane 5-oxide (DAPTA=O, 1), the novel 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-5-sulfide (DAPTA=S, 2), and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-5-selenide (DAPTA=Se, 3), have been synthesized under mild conditions. They are soluble in water and most common organic solvents and have been characterized using ¹H and ³¹P NMR spectroscopy and, for 2 and 3, also by single crystal X-ray diffraction. The effect of O, S, or Se at the phosphorus atom on the structural features of the compounds has been investigated, also through the analyses of Hirshfeld surfaces. The presence of 1–3 enhances the activity of copper for the catalytic azide-alkyne cycloaddition reaction in an aqueous medium. The combination of cheaply available copper (II) acetate and compound 1 has been used as a catalyst for the one-pot and 1,4-regioselective procedure to obtain 1,2,3-triazoles with high yields and according to ‘click rules’.