Molecular rectangles from platinum(II) and bridging dicarbene, diisocyanide and 4,4'-bipyridine ligands

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.