Structural diversity among copper(I) ethylene adducts of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine

The reaction of Cu(ClO(4))·6H(2)O, Cu turnings, and 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) in Me(2)CO under C(2)H(4) afforded brownish-red needle crystals of {[Cu(2)(bptz˙(-))(C(2)H(4))(2)](ClO(4))}(2) (1) as a minor product and brown plate crystals of [Cu(2)(2,5-H(2)bptz)(C(2)H(4))(2)](ClO(4))(2)·2Me(2)CO (2). The X-ray crystallographic study showed that complex 1 is composed of two independent [Cu(2)(bptz˙(-))(C(2)H(4))(2)](+) cation moieties and two ClO(4)(-) anions. In both of the cation moieties, each Cu(I) atom is coordinated by two chelate N atoms of bptz˙(-) and the C=C bond of C(2)H(4) in the trigonal-planar geometry to form a unique transoid dinuclear Cu(I)-bptz˙(-)/C(2)H(4) adduct bearing a metal-stabilized tetrazine anion radical, bptz˙(-), which was produced by the one-electron reduction of bptz. In contrast, complex 2 consists of one [Cu(2)(2,5-H(2)bptz)(C(2)H(4))(2)](2+) cation moiety, two ClO(4)(-) anions, and two solvated Me(2)CO molecules. Each Cu(I) atom is coordinated by two chelate N atoms of 2,5-H(2)bptz and the C=C bond of C(2)H(4) in the trigonal-planar geometry to afford a transoid dinuclear Cu(I)-C(2)H(4) adduct with 2,5-H(2)bptz, which was produced by the two-electron reduction of bptz. Additionally, the similar reaction of Cu(ClO(4))·6H(2)O, Cu turnings, and bptz in Me(2)CO or MeEtCO under C(2)H(4) in the presence of ferrocene afforded orange brick crystals of [Cu(2)(bpdpyz)(C(2)H(4))(2)](ClO(4))(2)·Me(2)CO (3) and [Cu(2)(bpdpyz)(C(2)H(4))(2)](ClO(4))(2) (4), respectively, together with complex 1 in higher yield. This result shows that 3,6-bis(2-pyridyl)-4,5-dihydropyridazine (bpdpyz) was produced by the cycloaddition of bptz with C(2)H(4)via a Diels-Alder addition and retro-Diels-Alder elimination of dinitrogen. In complexes 3 and 4, each Cu(I) atom is coordinated by two chelate N atoms of bpdpyz and the C=C bond of C(2)H(4) to afford an unusual cisoid dinuclear Cu(I)-C(2)H(4) adduct. Further attempts to react excess [Cu(C(2)H(4))(n)]ClO(4) with bptz in Me(2)CO under C(2)H(4) afforded black brick crystals of [Cu(4)(4,5-H(2)bptz)(4)](ClO(4))(4)·2Me(2)CO (5) together with complex 1. Complex is the first [4 × 4] grid-like tetranuclear Cu(I) complex constructed by the combination of Cu(I) ion and 4,5-H(2)bptz. The four Cu(I) atoms are spanned by four 4,5-H(2)bptz ligands, with two lying above the Cu(4) mean plane and two lying below. In contrast, the similar reaction of excess [Cu(C(2)H(4))(n)]ClO(4) with bptz in Me(2)CO under C(2)H(4) in the presence of ferrocene afforded reddish-brown brick crystals of {[Cu(2)(2,5-H(2)bptz)(C(2)H(4))(2)](ClO(4))(2)}(2)·Me(2)CO (6) together with complexes 1 and 5. Complex 6 is composed of two independent [Cu(2)(2,5-H(2)bptz)(C(2)H(4))(2)](2+) cation moieties, four ClO(4)(-) anions, and a solvated Me(2)CO molecule. It is interesting that the structures of the two [Cu(2)(2,5-H(2)bptz)(C(2)H(4))(2)](2+) cation moieties are different: one has a nearly planar structure and the other possesses a boat conformation owing to the bent central dihydrotetrazine ring.