Silicagel support mediated nonphotolytic cleavage of the rhenium–rhenium bond of [{NC 5H 4NNC 6H 4(R)}(CO) 3Re 0] 2. Synthesis of the monomeric species Re I{NC 5H 4NNC 6H 4(R)}(CO) 3Cl, crystal structure, spectroscopic and electron-transfer properties

Abstract

The reaction of Re 2(CO) 10 with the 2-arylazopyridine ligand, L [LNC 5H 4–NN–C 6H 4(R), RH, o-Me/Cl, m-Me/Cl] in dry THF under a dinitrogen atmosphere afforded a metal–metal bonded product of the type (L)(CO) 3Re 0–Re 0 (CO) 3(L) 1. On a silica gel column and in the presence of chlorinated solvents (CHCl 3 or CH 2Cl 2) the complex 1 transformed into a mononuclear complex of composition Re I(L)(CO) 3Cl 2, where the cleavage of Re–Re bond of 1 and the oxidative addition of chlorine to the rhenium center have taken place consecutively. The molecular structure of the complex 2a (RH) has been determined by single crystal X-ray diffraction. The crystal lattice consists of two crystallographically independent Re(L 1)(CO) 3Cl molecules which are non-superimposable mirror images; d and l enantiomers, exist in a 1:1 ratio. The complexes 2 display irreversible Re I→Re II oxidation processes near 1.5 V versus SCE and two quasi-reversible azo (NN) reductions in the ranges −0.28 to −0.48 V and −0.83 to −1.06 V versus SCE. The complexes of the type 1 exhibit only four successive azo reductions in the range 0 to −2 V versus SCE. Both the complexes ( 1 and 2) display dπ(Re)→π*L metal-to-ligand charge-transfer transitions near 500 nm and intraligand n–π* and π–π* transitions near 400 and 300 nm, respectively. The complexes 2 are susceptible to a spontaneous chloride exchange reaction.