Molecular rectangles from platinum(ii) and bridging dicarbene, diisocyanide and 4,4′-bipyridine ligands

Abstract

A series of benzobisimidazolium salts have been prepared and treated with [PtCl₂(dppe)] or [PtCl₂(dmpe)] in the presence of sodium acetate to yield dinuclear dicarbene-bridged complexes of the type [(P^P)(X)Pt(benzodicarbene)Pt(X)(P^P)](X)₂ [5]Br₂–[11]I₂. The reaction of compounds [7]Br₂ and [11]I₂ with AgPF₆ in acetonitrile led to the exchange of the metal-bound bromo or iodo ligands for acetonitrile and the formation of complexes [(dmpe)(MeCN)Pt(benzodicarbene)Pt(MeCN)(dmpe)](PF₆)₄ [12](PF₆)₄ and [13](PF₆)₄. The dinuclear complex [13](PF₆)₄ reacts with 4,4′-bipyridine (4,4′-bipy) to give the molecular rectangle [15](PF₆)₈ featuring two bridging dicarbene and two bridging 4,4′-bipy ligands. Complex [13](PF₆)₄ also reacts with β,β′-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 16 followed by hydrolysis of the Si–O bonds and intramolecular carbene formation to yield the molecular square [18](BF₄)₈ featuring bridging NR,NR- and NH,O-substituted dicarbene ligands. Reaction of the dinuclear complex [12](PF₆)₄ containing a sterically demanding N,N′,N′′,N′′′-substituted dicarbene ligand under otherwise identical reaction conditions did not lead to any molecular rectangles. The molecular square [19](BF₄)₈ was synthesized from β,β′-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 16 and [PtCl₂(dmpe)] in the presence of AgBF₄. It reacts to yield the molecular square [20](BF₄)₈ with four NH,O-substituted dicarbene ligands by Si–O bond cleavage and subsequent intramolecular cyclization.