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)}(2) (1) as a minor product and brown plate crystals of Cu(2)(2,5-H(2)bptz)(C(2)H(4))(2)(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) 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)(2)·Me(2)CO (3) and Cu(2)(bpdpyz)(C(2)H(4))(2)(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)(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)(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) 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) cation moieties are different: one has a nearly planar structure and the other possesses a boat conformation owing to the bent central dihydrotetrazine ring.