Rhenium(VII) and -(V) imido and oxo complexes containing 1,4,7-triazacyclononane: synthesis, electrochemistry and crystal structures

摘要

A new class of cationic rhenium(VII) imido and oxo complexes with the macrocyclic ligand 1,4,7-triazacyclononane (L) was prepared. Depending on the reaction conditions, [(L-H)Re((NBu)-Bu-t)(2)(OSiMe3)](+) (1) [(L-H) denotes deprotonation at N], [LRe((NBu)-Bu-t)(2)O](+) (2) and/or [LRe((NBu)-Bu-t)(2)((NHBu)-Bu-t)](2+) (4) can be obtained by the treatment of Re((NBu)-Bu-t)(3)(OSiMe3) with L. Reaction of 2 . BPh4 with trifluoromethanesulfonic anhydride gives [(L-H)Re((NBu)-Bu-t)(2)(CF3SO3)]BPh4 (3 . BPh4). Interaction of [Re((NBu)-Bu-t)(2)(OSiMe3)(mu-O)](2) with L yields [LRe((NBu)-Bu-t)O-2](+) (5). In contrast to the t-butylimido analogues, only [LRe(NAr)(2)O]Cl (6 . Cl) is isolated from the reaction of Re(NAr)(3)Cl with excess L. Complexes 2, 5 and 6 are stable in 0.1 M CF3CO2H. Electrochemically, they undergo proton-coupled two electron reductions at pH 1 with E-pc (cathodic peak potential) of -0.30, -0.29 and -0.12 V versus SCE respectively. Constant potential electrolysis of 6 at -0.3 V affords a green solution which is rapidly oxidised in air to give [LRe(NAr)O-2](+) (7). The reduction of 5 . ClO4 by zinc in the presence of oxalic acid and CF3CO2H affords the rhenium(V) species [LRe((NBu)-Bu-t)(oxalate)]ClO4 (8 . ClO4) and [LRe((NBu)-Bu-t)(CF3CO2)(2)]ClO4 (9 . ClO4) respectively. The molecular structures of 2 . ClO4, 3 . BPh4, 5 . ClO4, 6 . Cl . 2H(2)O, and 8 . ClO4 have been determined by X-ray crystal analysis. The Re-N(L) bonds which are trans to imido and oxo ligands are comparatively long (2.344-2.243 Angstrom). The range of Re-N(imido) and Re-O(oxo) distances (1.67-1.78 Angstrom and 1.71-1.76 Angstrom respectively) can be rationalised by the oxo/imido ligand ratio in the Re(VII) complexes. (C) 1998 Elsevier Science S.A. All rights reserved. [References: 39]