Organoplatinum‐Bridged Cyclotribenzylene Dimers

Abstract

AbstractCyclotribenzylenes (CTBs) combining carbonitrile (−CN) and alkyne (−C2H) substituents were synthesized as racemic mixtures and resolved by HPLC on chiral stationary phases. Two of these compounds were used to prepare platinum‐bridged CTB dimers, in which PtII is bound to the CTBs via Pt−alkynyl bonds in cis configuration. The organometallic complexes were examined by mass spectrometry and NMR spectroscopy, which indicated that they were obtained as mixtures of diastereoisomers (a meso or syn form and a pair of chiral or anti forms) when racemic CTBs were used. Enantiomerically pure complexes were prepared from resolved CTBs, which allowed us to distinguish the NMR signals of the chiral and meso forms in the diastereoisomeric mixtures. In certain conditions, the platinum complexes played the role of a pincer π‐alkynyl ligand for Cu(I) coming from the copper iodide used as a synthetic auxiliary. The Cu+ cations could be easily removed by treatment with NaCN, affording the mononuclear bis‐cyclotribenzylene complexes. These compounds failed to lead to metallo‐cryptophanes by coordination of two [M(dppp)]2+ complex subunits (M=Pd, Pt; dppp=1,3‐bis(diphenylphosphino)propane), each to two carbonitrile substituents belonging to different CTBs, pointing to the superiority of the one pot self‐assembly processes for the preparation of metallo‐cryptophanes.