Binding Properties of Two Novel Phosphane-Modified Tetrapodants and Their Bimetallic Transition Metal Complexes

Abstract

Two novel phosphane ligands 3 and 4 based on the rigid diphenylglycoluril molecule have been synthesized and characterised. Binding studies with 3 and 4, using 1,3‐dihydroxybenzene derivatives reveal that ligands 3 and 4 behave similarly to clip molecule 5, which has the same binding site as ligands 3 and 4. The size of the flexible spacers in the ligands has been varied and the effect of this variation on the association constant of resorcinol derivatives has been determined. These cavity‐containing ligands are able to coordinate two transition metal centres, leading to bimetallic macrocycles. The metallamacrocycles formed from 4 containing platinum or rhodium bind the guest, olivetol (5‐pentylbenzene‐1,3‐diol), almost four times as strongly as the free tetrapodant 4. Complexes of 4 having palladium centres display similar or reduced binding affinities for resorcinol derivatives, when compared to free 4. Metal complexes of ligand 3 do not form host‐guest complexes, probably because of a too small a ring‐size of the metallamacrocycle.

Neutral Macrocycles via Halide-Induced Ring Opening of Binuclear Condensed Intermediates

“…Successful clean displacement of the Rh I −S bonds in 2 was achieved via the addition of [Me 4 N]Cl in the presence of CO (1 atm), which resulted in the quantitative formation of the neutral macrocycle ( 5 ) (Scheme ). Compound 5 has been characterized by 1 H NMR spectroscopy (see Supporting Information), 31 P{ 1 H} NMR spectroscopy, which shows a characteristic doublet at 24 ppm ( J Rh - P = 124 Hz) for the two magnetically equivalent phosphine ligands, and FTIR spectroscopy, which exhibits a characteristic ν co band at 1976 cm -1 . While 5 is stable in solution, upon exposure to vacuum or nitrogen purge, 5 is converted back to 2 , which precludes characterization of it by mass spectrometry or combustion analysis.…”