Preparations and structural diversity of copper(I) ethylene adducts with related 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine ligands

The reaction of [Cu(C2H4)n]NO3, Cu turnings, 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz), and ferrocene in Me2CO under C2H4 afforded black crystals of [Cu4(4,5-H2bptz)4][Cu(C2H4)(NO3)2]2(NO3)2·2Me2CO (7). In the [Cu4(4,5-H2bptz)4]4+ cation moiety, four Cu(I) atoms are bridged by four 4,5-H2bptz ligands to form a [4 × 4] grid-like tetranuclear structure. In the [Cu(C2H4)(NO3)2]− anion moiety, the Cu atom is coordinated by two NO3− anions in the unidentate coordination mode and by the CC bond of C2H4 to form a mononuclear Cu(I)–C2H4 adduct in the trigonal-planar geometry. It should be noted that two anionic Cu(I)–C2H4 adducts [Cu(C2H4)(NO3)2]− are present as a co-crystal. The similar reaction of Cu(BF4)2·H2O, Cu turnings, bptz, and ferrocene in MeEtCO under C2H4 afforded colorless crystals of [Cu2(bpdpyz)(C2H4)2](BF4)2 (9). In the [Cu2(bpdpyz)(C2H4)2]2+ cation moiety, each Cu(I) atom is coordinated by two chelate N atoms of bpdpyz and the CC bond of C2H4 to afford an unusual cisoid dinuclear structure. This result shows that 3,6-bis(2-pyridyl)-4,5-dihydropyridazine (bpdpyz) can be produced by the cycloaddition of bptz with C2H4 via a Diels–Alder addition and retro-Diels–Alder elimination of dinitrogen to form complex 9. In contrast, the reaction of Cu(BF4)2·H2O, Cu turnings, and bptz in Me2CO in the absence of ferrocene afforded black crystals of [Cu4(4,5-H2bptz)4](BF4)4·Me2CO (12). Although the apparent structure of the [Cu4(4,5-H2bptz)4]4+ cation moiety is similar to that of the [Cu4(4,5-H2bptz)4]4+ cation moiety in complex 7, the shape of the Cu4 framework is closer to a square structure, resulting in the adjacency of the two opposite tetrazine rings. The preparations and structural diversity of Cu(I)–C2H4 adducts with the related bptz ligands are described in addition to related previous results.