COORDINATION CHEMISTRY OF LOW-VALENT RHENIUM POLYPYRIDYL COMPLEXES - SYNTHESIS, REACTIVITY, AND ELECTROCHEMISTRY

The complex Re-III(benzil)(PPh(3))Cl-3 (2) is used to synthesize a var iety of Re-III and Re-II polypyridyl complexes of the type cis-[Re-III (L(2))(2)Cl-2](+), [Re-II(L(2))(3)](2+), Re-III(L(3))Cl-3, [Re-III(L(3 ))(2)Cl](2+), and [Re-III(L(4))Cl-2](+), where L(2) = bpy (3 and 6), t bpy (4 and 7), phen (5 and 8): L(3) = terpy (9 and 10); L(4) = TMPA (1 1). The complex cis-[Re-III(bpy)(2)-Cl-2](+) (3) is a useful synthon i n the formation of complexes of the type [Re(bpy)(2)L(x)](n+) that are six- or seven-coordinate Re-III complexes (13, 16, and 18) or octahed ral Re-II or Re-I complexes (12 and 17). The [Re-III(terpy)(2)Cl](2+) (10) complex can be reduced to form the Re-I complex, [Re-I(terpy)(2)L ](+) (21) and then electrochemically reoxidized to form new complexes of the type [Re-III(terpy)(2)L](n+). Similar behavior is observed for the [Re-II(bpy)(3)](2+) (6) complex where [Re-III(bpy)(3)((t)BuNC)](3) (20) and [Re-I(bpy)(3)](+) (19) may be formed. The electrochemistry of these complexes is discussed in relation to their reactivity and th e observed pi-acidity of the polypyridyl ligands. In addition, X-ray c rystal structures for cis-[Re-III(bpy)(2)Cl-2]PF6 (3) and [Re-I(bpy)(3 )]PF6 (19) are reported. cis-[Re-III(bpy)(2)Cl-2]PF6 (3, ReC20H16N4Cl2 F6P) crystallizes in the monoclinic space group C2/c with Z = 4 and la ttice parameters a = 15.043(5) Angstrom, b = 13.261(4) Angstrom, c = 1 2.440(4) Angstrom, and beta = 108.86(2)degrees at -100 degrees C. [Re- I(bpy)(3)]-PF6 (19, ReC30H24N6F6P) crystallizes in the rhombohedral sp ace group R(3) over barc$ (h) (No. 167) with Z = 12 and lattice parame ters a = 13.793(3) Angstrom and c = 51.44(3) Angstrom at -100 degrees C.