New hydrosoluble and air-stable Cu(I) halide compounds, viz. [CuX(DAPTA)₃] (1) and (2), and [Cu(μ-X)(DAPTA)₂]₂ (3) and (4) (X = Br or I, in this order), have been prepared by reacting Cu(I) halide (i.e., bromide or iodide) with 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) under mild conditions. They represent the first examples of Cu(I) halide complexes bearing the DAPTA ligand, which have been fully characterized by elemental analysis, IR, ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopies, ESI-MS⁺ and, for 4, also by single-crystal X-ray diffraction (SCXRD) analyses. Complexes 1–4 are efficient catalysts for the one-pot microwave assisted three-component (terminal alkyne, organic halide and NaN₃) Huisgen cycloaddition reaction in aqueous media to afford the corresponding disubstituted triazoles. The catalysis proceeds with a broad alkyne substrate scope and according to “click rules”. Photophysical studies of compound 4 showed an unusual reversible thermochromic behaviour exhibiting a blue emission at 298 K due to the halide-to-ligand charge transfer (³XLCT) and a red emission at 77 K because of the {Cu₂I₂} unit.

By reacting copper(II) or nickel(II) salts with sodium 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl) benzenesulfonate (NaHL) in an EtOH/H₂O solvent mixture and in the presence of ethylenediamine (en), [Cu(HL)₂(en)₂] (1) or {[Ni(en)₃](HL)₂}·C₂H₅OH·6H₂O (2) were synthesized, respectively. In MeOH, the coordination polymer [Cu(μ-L¹-1κO,NN′N′′:2κO′)]_n (3) was obtained, where L¹ refers to a dianionic ligand species attained via Schiff-base condensation of NaHL with en on the Cu(II) metal centre, whereas no reaction was obtained in the case of Ni(II). All the compounds were characterised by IR spectroscopy, ESI-MS, elemental and single-crystal diffraction. The Cu(II) compounds 1 and 3 act as effective homogenous catalysts for the cyanosilylation reaction of a variety of aldehydes with trimethylsilyl cyanide affording the corresponding cyanohydrin trimethylsilyl ethers in high yields (up to 93%) and at room temperature.

A series of water soluble copper(II) complexes, [Cu(κO¹O²N-H₂L¹)(H₂O)₂]·2H₂O (2), [Cu(κO-H₃L¹)₂(H₂O)₄] (3), [Cu(κO-H₄L²)₂(H₂O)₄] (5) and [Cu(H₂O)₆]·2H₂L³·2(CH₃)₂NCHO (7), were prepared by the reaction of Cu(NO₃)₂·3H₂O with sodium (Z)-2-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)benzenesulfonate, [Na(μ₄-1:2κO¹,2κO²,3κO³,4κO⁴-H₃L¹)]_n (1; for 2 and 3), sodium (Z)-3-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)-4-hydroxybenzene-sulfonate, [Na(μ-1κO¹,2κO²-H₄L²)]₂ (4; for 5) or sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazineyl)naphthalene-1-sulfonate, [Na(μ-1κO¹O²,2κO³-H₂L³)(CH₃OH)₂]₂ (6; for 7). Compounds 1–7 were fully characterized, also by single-crystal X-ray diffraction analysis, and applied as homogeneous catalysts for the azide–alkyne cycloaddition (AAC) reaction to afford 1,4-disubstituted 1,2,3-triazoles. A structure–catalytic activity relationship has been recognized for the first time on the basis of the occurrence of resonance- and charge-assisted hydrogen bond interactions (RAHB and CAHB), in charge and ligand binding modes, enabling the catalytic activity of the compounds to be ordered as follows: Cu(NO₃)₂ ≪ 7 (complex salt with RAHB and CAHB) < 3 (with RAHB and CAHB) < 5 (with RAHB) < 2 (neither RAHB nor CAHB). Complex 2, without such non-covalent interactions, was found to be the most efficient catalyst for the AAC reaction, affording up to 98% product yield after being placed for 15 min, at 125 °C, in a water/acetonitrile mixture under low power (10 W) MW irradiation.

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.