Inorganic Chemistry, Vol.36, No.17, 3595-3601, 1997
Variable-valent Re NAr species. A family of ReVINAr amide complexes and their ReVNAr imine precursors related by oxygen atom transfer
Imide complexes of type (ReCl3)-Cl-V(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 (ReCl3)-Cl-VI(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, Re equivalent to N-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 similar to 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) similar to 1.91; A(av) similar to 490 G). Crystal data for the complexes are as follows: 5(Cl,Cl), empirical formula C19H15Cl5N3Re, crystal system monoclinic, space group P2(1)/c, a = 13.360(6) Angstrom, b = 12.110(3) Angstrom, c = 14.954(9) Angstrom, beta = 111.41(4)degrees, V = 2252.4(1.7) Angstrom(3), Z = 4; 6(OMe,OMe), empirical formula C26H23Cl3N3O2Re, crystal system orthorhombic, space group Pbca, a = 12.079(5) Angstrom, b = 17.083(9) Angstrom, c = 26.049(9) Angstrom, V = 5375.4(4.0) Angstrom(3), Z = 8; 7(Me,Me), empirical formula C20H18Cl3N3ORe, crystal system monoclinic, space group P2(1)/c, a = 7.071(2) Angstrom, b = 17.541(6) Angstrom, c = 16.857(8) Angstrom, beta = 100.59(3)degrees, V = 2055.3(1.3) Angstrom(3), Z = 4.