Synthesis, Structural Characterization, Reactivity, and Catalytic Properties of Copper(I) Complexes with a Series of Tetradentate Tripodal Tris(pyrazolylmethyl)amine Ligands

Novel tris­(pyrazolylmethyl)­amine ligands Tpa^Me3, Tpa*^,Br, and Tpa^Br3 have been synthesized and structurally characterized. The coordination chemistries of these three new tetradentate tripodal ligands and the already known Tpa and Tpa* have been explored using different copper­(I) salts as starting materials. Cationic copper­(I) complexes [Tpa^<i>x</i>Cu]­PF₆ (<b>1</b>–<b>4</b>) have been isolated from the reaction of [Cu­(NCMe)₄]­PF₆ and 1 equiv of the ligand. Complexes <b>2</b> (Tpa^<i>x</i> = Tpa*) and <b>3</b> (Tpa^<i>x</i> = Tpa^Me3) have been characterized by X-ray studies. The former is a 1D helical coordination polymer, and the latter is a tetranuclear helicate. In both structures, the Tpa^<i>x</i> ligand adopts a μ²:κ²:κ¹-coordination mode. However, in solution, all of the four complexes form fluxional species. When CuI is used as the copper­(I) source, neutral compounds <b>5</b>–<b>8</b> have been obtained. Complexes <b>6</b>–<b>8</b> exhibit a 1:1 metal-to-ligand ratio, whereas <b>5</b> presents 2:1 stoichiometry. Its solid-state structure has been determined by X-ray diffraction, revealing its 3D polymeric nature. The polymer is composed by the assembly of [Tpa₂Cu₄I₄] units, in which Cu₄I₄ presents a step-stair structure. The Tpa ligands bridge the Cu₄I₄ clusters, adopting also a μ²:κ²:κ¹-coordination mode. As observed for the cationic derivatives, the NMR spectra of <b>5</b>–<b>8</b> show the equivalence of the three pyrazolyl arms of the ligands in these complexes. The reactivities of cationic copper­(I) derivatives <b>1</b>–<b>4</b> with PPh₃ and CO have been explored. In all cases, 1:1 adducts [Tpa^<i>x</i>CuL]­PF₆ [L = PPh₃ (<b>9</b>–<b>11</b>), CO (<b>12</b>–<b>15</b>)] have been isolated. The crystal structure of [Tpa*Cu­(PPh₃)]­PF₆ (<b>9</b>) has been obtained, showing that the coordination geometry around copper­(I) is trigonal-pyramidal with the apical position occupied by the tertiary amine N atom. The Tpa* ligand binds the Cu center to three of its four N atoms, with one pyrazolyl arm remaining uncoordinated. In solution, the carbonyl adducts <b>13</b>–<b>15</b> exist as a mixture of two isomers; the four- and five-coordinate species can be distinguished by means of their IR ν_CO stretching bands. Finally, the catalytic activities of complexes <b>1</b>–<b>4</b> have been demonstrated in carbene- and nitrene-transfer reactions