Structural diversity of copper(I) cyclodiene complexes bridged by 3,6-bis (2-pyridyl)-1,2,4,5-tetrazine

The reactions of CuX2 center dot nH(2)O (X = ClO4, BF4), Cu turnings and 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) with excess 1,5-cyclooctadiene (cod) in Me2CO under C2H4 afforded dinuclear Cu(I)-bptz/eta(2), eta(2)-cod-X complexes {(1) and (4)} and dinuclear Cu(I)-2,5-H(2)bptz/eta(2), eta(2)-cod-X complexes {(2) and (5)}. In complexes 1 and 4, each Cu(I) atom is coordinated by two chelate N atoms of bptz and two C=C bonds of eta(2), eta(2)-cod in the distorted tetrahedral geometry to produce a transoid dinuclear structure. It should be noted that the redox state of the central tetrazine ring is electrochemically neutral. In complexes 2 and 5, each Cu(I) atom is coordinated by two chelate N atoms of 2,5-H(2)bptz and two C=C bonds of eta(2), eta(2)-cod in the distorted tetrahedral geometry to afford a transoid dinuclear structure in the 2,5-dihydro form. In contrast, the reactions of Cu(BF4)(2)center dot nH(2)O, Cu turnings and bptz with excess 2,5-norbornadiene (nbd) in MeEtCO under C2H4 afforded Cu(I)-2,5-H(2)bptz/eta(2)-nbd-BF4 complex (6). Each Cu(I) atom is coordinated by two chelate N atoms in bptz and one C=C bond in eta(2)-nbd to form a transoid dinuclear structure in the 2,5-dihydro form. These facts show that the flexible cod can preferentially produce a Cu(I)cyclodiene complex in the eta(2), eta(2)-mode (complexes 1, 2, 4 and 5) while the rigid nbd can produce a Cu (I)-cyclodiene complex in the eta(2)-mode (complex 6). Furthermore, the reaction of Cu(NO3) center dot 3H(2)O, Cu turnings and bptz with excess nbd in Me2CO under C2H4 afforded tetranuclear Cu(I)-4,5-H(2)bptz-NO3 complex (7) containing a unique anionic [Cu-2(nbd)(NO3)(4)](2) moiety. In the cationic [Cu-4(4,5H(2)bptz) 4] 4+ moiety, four Cu(I) atoms are bridged by four 4,5-H(2)bptz ligands to form a [4 x 4] grid-like tetranuclear structure with two 4,5-H(2)bptz ligands lying above the Cu4 mean plane and two lying below. In the anionic [Cu-2(nbd)(NO3)(4)](2) moiety, the two Cu atoms are bridged by one nbd ligand in the mu(2)-eta(2), eta(2)-mode. (C) 2017 Elsevier B. V. All rights reserved.