Synthesis, characterization and crystal structures of mono-, di- and trinuclear rhenium(I) tricarbonyl complexes with 2,3,5,6-tetra(2-pyridyl)pyrazine

Abstract

A series of rhenium(I) tricarbonyl complexes with the ligand 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) were synthesized and characterized crystallographically. Two different coordination modes were found when tppz functions as a monobidentate ligand. Rhenium(I) may be bound to tppz through pyrazine and pyridyl nitrogens completing a 5-membered coordination ring when the reaction was carried out in toluene. However, the same reaction in methanol produced a yellow complex in which rhenium(I) was bound to tppz through two adjacent pyridyl nitrogens with a 7-membered coordination ring. In the presence of an excess amount of [ReBr(CO) 5], the dinuclear complex [{ReBr(CO) 3} 2(μ-tppz)] ( 3) was isolated, while the trinuclear complex [{ReCl(CO) 3} 3(μ-tppz)] ( 4) was obtained in the case of [ReCl(CO) 5]. Crystal data for 1, C 27H 16ClN 6O 3Re·MeOH: monoclinic, P2 1/ n, a=9.2217(7), b=10.7628(8), c=26.932(2) Å, β=94.130(1)°, V=2666.1(3) Å 3, Z=4. 2, C 27H 16BrN 6O 3Re: monoclinic, P2 1/ n, a=9.2931(6), b=10.2387(7), c=27.993(2) Å, β=94.615(1)°, V=2654.8(3) Å 3, Z=4. 1′, C 27H 16ClN 6O 3Re·2H 2O: monoclinic, C 2/ c, a=18.584(4), b=21.693(5), c=15.392(4) Å, β=122.328(3)°, V=5243(2) Å 3, Z=8. 3, C 30H 16Br 2N 6O 6Re 2: triclinic, P 1 ̄ , a=7.4668(6), b=11.4902(10), c=19.3736(16) Å, α=73.659(2), β=85.183(2), γ=77.097(1)°, V=1554.3(2) Å 3, Z=2. 4, C 33H 16Cl 3N 6O 9Re 3·1/2C 6H 6: orthorhombic, Pbca, a=18.828(1), b=16.715(1), c=25.366(2) Å, V=7983.2(10) Å 3, Z=8.