Chemistry of Bridging Phosphanes: A Comparative Study within CuI-AgI-AuI Triad-Based Homonuclear Dimers

Abstract

Bridging ligands in AgI and AuI bimetallic complexes: The P moiety of bis(2-pyridyl)phosphole acts as a symmetrically, semi-, or non-bridging donor in AgI dimers (see figure). In related AuI complexes, only the non-bridging mode is observed. An unsaturated AgI dimer is used as an adaptive molecular clip for the synthesis of -stacked metallocyclophanes. Bis(2-pyridyl)phosphole C reacted with AgPF6 and dppm giving rise to dicationic dimer 1 in which C acts as a 1N:1,2P:2N-donor with a symmetrically bridging P-centre. This complex gives the first example of dimers based on trigonal planar metal centres bearing a bridging 3,3-phosphane ligand. The reaction of two equivalents of C with AgPF6 and Ag afforded dicationic dimers 2 and 3 of general formula Ag2(C)22+, respectively. X-ray diffraction studies showed that one ligand C acts as a 1N:1,2P:2N-donor with a symmetrically bridging P-centre and one behaves as a 1N:2P-chelate. In complex 3, one toluene molecule interacts with an Ag centre, giving the first example of a mixed coordination dimer featuring a bridging P-donor. AgI-dimers 4 a-c of the general formula Ag2(C)32+, 2 X- (X=PF6, BF4, Al[OC(CF3)3]4) have been prepared according to different routes and characterised by X-ray diffraction study. In these derivatives, C exhibits a variety of coordination modes depending on the nature of the counteranion and of the solvent molecules included in the asymmetric units. These complexes can feature 0, 1, or 2 bridging P-donors. These results definitively demonstrate that the P-centre of phosphane ligands can easily switch from a bridging to a semi-bridging and a non-bridging coordination mode. Dimer 2 is used as an adaptive molecular clip for the synthesis of -stacked metallocyclophanes 7 a, b and 8 upon reaction with ditopic linkers. X-ray diffraction studies revealed that these supramolecular species behave as receptors for the counteranions (PF6, BF4) and that the nature of the anion impacts the stereochemistry of the supramolecular metallocyclophanes. AuI-Dimers 10 a, b bearing two ligands C acting as 1N:2P-chelates are prepared and characterised in the solid-state.