Variable-Valent Re&tbd1;NAr Species. A Family of Re(VI)NAr Amide Complexes and Their Re(V)NAr Imine Precursors Related by Oxygen Atom Transfer.

Abstract

Imide complexes of type Re(V)Cl(3)(X-SB)(NC(6)H(4)Y(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-XC(6)H(4)NH(2). Treatment of 4 or 5 (but not 6) with aqueous nitric acid in acetonitrile afforded Re(VI)Cl(3)(X-PA)(NC(6)H(4)Y(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 ReCl(3)N(3) coordination sphere. The trans influence of the imide nitrogen considerably lengthens the Re-N(pyridine) bond. The ReNC(6)H(4)Y(p) group has the triple-bonded linear moiety, Re&tbd1;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) approximately 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) approximately 1.91; A(av) approximately 490 G). Crystal data for the complexes are as follows: 5(Cl,Cl), empirical formula C(19)H(15)Cl(5)N(3)Re, crystal system monoclinic, space group P2(1)/c, a = 13.360(6) Å, b = 12.110(3) Å, c = 14.954(9) Å, beta = 111.41(4) degrees, V = 2252.4(1.7) Å(3), Z = 4; 6(OMe,OMe), empirical formula C(26)H(23)Cl(3)N(3)O(2)Re, 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) Å(3), Z = 8; 7(Me,Me), empirical formula C(20)H(18)Cl(3)N(3)ORe, crystal system monoclinic, space group P2(1)/c, a = 7.071(2) Å, b = 17.541(6) Å, c = 16.857(8) Å, beta = 100.59(3) degrees, V = 2055.3(1.3) Å(3), Z = 4.