Structures and reactivities of copper(I) and silver(I) complexes of potentially quadridentate N 4 and N 2S 2 donor ligands.

Abstract

In designing model complexes for the activities sites in copper proteins it is important to know the influence of the different hetero-atoms and conformational changes of the carbon skeleton on the chemical and physical properties of the metal centre. We have investigated the structure properties of copper(I) and silver(I) complexes with potentially quadridentate N 4 and N 2S 2 donor ligand system, schematically represented in Fig. 1, which have the connecting ( R)( S)−1,2-diiminocyclohexane group in common From the reaction of the N 4 donor ligand with M(O 3SCF 3) (M = Cu I or Ag I) we obtained dimeric ▪ ▪ [M 2(N 4) 2] 2+ 2O 3SCF − 3 complexes. The X-ray structure of the silver(I) complex showed that each ligand acts in a di-bidentate manner bridging the two metal centre (see Fig. 2). The silver ions have distorted tetrahedral geometries with each Ag I centre taking part in two short AgN (2.25 Å) and two long AgN (2.43 Å) interactions. The NAgN bond angle between the two short AgN bonds is circa 150°[1]. The copper(I) and silver(I) complexes are very stable and do not react further either with excess N 4 ligand or with H 2O, O 2 and CO. However, detailed 1H studies have shown that inter- and intramolecular exchange ( e.g. metal-ion or ligand exchange) occurs. These will be discussed. In contrast to these result reactions of the N 2S 2 ligand system with M(O 3SCF 3) (M = Cu I or Ag I) give rise to two different types of complexes, i.e. a dimeric [M 2(N 2S 2) 2] 2+ 2O 3SCF − 3 and a monomeric [M(N 2S 2) 2] + O 3SCF − 3 complex. According to IH and 109Ag NMR data the dimeric complex has a structure similar to that found for the [M 2(N 4) 2] 2+ 2O 3SCF 3− complex. However, in the [M 2(N 2S 2) 2] 2+ dication the imine-N atoms of the N 2S 2 ligands have strong intersections with the metal centres, while the thiophene-S atoms coordinate only weakly with the metal-IB centre. This coordination behaviour is reflected by the reactivity of the copper(I) complex, which reacts rapidly with CO(ν CO = 2092cm −1. An X-ray study is underway. The X-ray structures of the mononuclear [M(N 2S 2) 2] + O 3SCF − 3 complexes have been resolved for M = Cu I ▪ and M = Ag I to establish the exact molecular conformations and to test the validity of the assumption that copper(I) can be replaced by silver(I) with retention of the structural features [2]. As a result of the constraint of the N 2S 2 system, each ligand is primarily bonded to the metal centre (M = Cu or Ag) by one imine-N atom [N(1) and N(3)] with the remaining three hetero-atoms being held in close proximity to the metal centre (see Fig. 3: M = Cu). These complexes do not react with H 2O, O 2 and CO.