Cu(I) Dinuclear Complexes with Tripodal Ligands vs Monodentate Donors:  Triphenylphosphine, Thiourea, and Pyridine. A 1H NMR Titration Study

Complexes [PPh3Cu(TrMes,Me)] (1), [PPh3Cu(TrMe, o -Py)] (2), and [PPh3Cu(BrMespz o -Py)] (3) (TrMes,Me = hydrotris[1,4-dihydro-3-methyl-4-mesityl-5-thioxo-1,2,4-triazolyl]borate; TrMe, o -Py = hydrotris[1,4-dihydro-4-methyl-3-(2-pyridyl)-5-thioxo-1,2,4-triazolyl]borate; BrMespz o -Py = hydro[bis(thioxotriazolyl)-3-(2-pyridyl)pyrazolyl]borate; PPh3 = triphenylphosphine) were synthesized by the reaction of dinuclear complexes [Cu(TrMes,Me)]2, [Cu(TrMe, o -Py)]2, [Cu(BrMespz o -Py)]2, and PPh3. 1−3 were characterized by 1H, 13C, and 31P NMR spectroscopy and ESI-mass spectrometry. Crystal structure analyses were performed for 1 and 2. Both complexes crystallize in the triclinic P1̄ space group with the metal in a slightly distorted tetrahedral geometry (S3P coordination) bound by a κ3-S3 ligand and a PPh3 molecule. The solution molecular structures were investigated by means of variable-temperature (210−310 K, CDCl3, 1−2; 200−310 K, CD2Cl2, 3) and NOESY NMR spectroscopy. The solution structures of 1−2 are in accordance with the X-ray structures, and the complexes do not exhibit fluxional behavior. On the other hand, 3 is subject to an equilibrium between two species with a coalescing temperature of ∼260 K. DFT geometry optimizations suggest that the major species of 3 consists of the BrMespz o -Py ligand bound to Cu(I) in the κ3-S2H fashion with two CS groups and a [Cu···H−B] interaction. A PPh3 completes the copper coordination (S2HP coordination). The complex [TuCu(TrMes,Me)] (4) (Tu = thiourea) was crystallized using an excess of Tu with respect to [Cu(TrMe, 2 -Py)]2 (approximately a 6:1 ratio). The metal adopts a distorted tetrahedral geometry with an overall S3H coordination determined by the bound κ3-S2H ligand (two CS groups and a [B−H···Cu] interaction) and by a Tu. The reactivity of dinuclear complexes [Cu(TrMes,Me)]2, [Cu(TrMe, o -Py)]2, and [Cu(BrMespz o -Py)]2 with monodentate ligands was investigated by means of NMR titrations with PPh3, Tu. and pyridine (Py), and formation constants for the adducts [DCu(L)] (D = monodentate donor, L = tripodal ligand) were determined.