Variable-valent ReNAr species. A family of ReVINAr amide complexes and their ReVNAr imine precursors related by oxygen atom transfer

Abstract

Imide complexes of type ReVCl₃(X-SB)(NC₆H⁴Y(p)), with X, Y= H, Me, OMe, Cl have been synthesized where X-SB is the Schiff base of pyridine-2-carboxaldehyde (the corresponding complex is 4), 2-acetylpyridine (5), 2-benzoylpyridine (6), and anilines, p-XC₆H₄NH₂. Treatment of 4 or 5 (but not 6) with aqueous nitric acid in acetonitrile afforded Re^VICl₃(X-PA)(NC₆H₄Y(p)), 7, via oxygen atom transfer (X-PA = monoanionic picolinamide). In the structures of 5(X=Cl,Y=Cl), 6(OMe,OMe), and 7(Me,Me), the chlorine atoms are meridionally disposed in a ReCl₃N₃ coordination sphere. The trans influence of the imide nitrogen considerably lengthens the Re-N(pyridine) bond. The ReNC₆H₄Y(p) group has the triple-bonded linear moiety, ReN-C. The amide group in 7(Me,Me) is planar. In 6(OMe,OMe) the two aryl rings on the imine function block water attack and hence amide formation. The rhenium(VI)-rhenium(V) E_1/2 values for 4-6 (0.7-1.0 V vs SCE) are much higher than that for 7 (E_1/2~0.15 V), which displays the rhenium(VII)-rhenium(VI) couple near 1.6 V. Six EPR hyperfine lines are observed for solutions of 7 at room temperature (g_iso ~1.91; A_av ~490 G). Crystal data for the complexes are as follows: 5(Cl,Cl), empirical formula C₁₉H₁₅C_l5N₃Re, crystal system monoclinic, space group P2₁/c, a = 13.360(6) Å, b = 12.110(3) Å, c = 14.954(9) Å, β = 111.41(4)°, V = 2252.4(1.7) ų, Z = 4; 6(OMe,OMe), empirical formula C₂₆H₂₃C_l3N₃O₂Re, crystal system orthorhombic, space group Pbca, a = 12.079(5) Å, b = 17.083(9) Å, c = 26.049(9) Å, V = 5375.4(4.0) ų, Z = 8; 7(Me,Me), empirical formula C₂₀H₁₈Cl₃N₃ORe, crystal system monoclinic, space group P2₁/c, a = 7.071(2) Å, b = 17.541(6) Å, c = 16.857(8) Å, β = 100.59(3)°, V = 2055.3(1.3) ų, Z = 4.