The first four-membered ring cyclic triphosphenium ions with carbon substituents (methyl or cyclohexyl) on the outer phosphorus atoms have been identified in solution by31 P NMR spectroscopy. The cyclohexyl derivative in the presence of [SnCl 6 ] 2− as counterion was stable enough for methylation by methyl triflate to be carried out.
The first transition metal complexes of cyclic triphosphenium ions have been unequivocally identified in solution by (31)P NMR spectroscopy. The ligands coordinate to platinum(II) via the central phosphorus atom, but only when at least one of the outer phosphorus atoms has non-aromatic substituents. Depending on the system, either trans- (the kinetic reaction product) and/or cis- (the thermodynamic reaction product) complexes are formed. The (1)J coupling constants between (195)Pt and the central phosphorus atom of the CTI (P(A)) are small for both cis- and trans-isomers, between 900 and 1300 Hz, whereas other phosphanes in these complexes derived from the platinum(II) starting material show normal (1)J(PtP) values. These results suggest a possible long P-Pt bond between the overall positively charged ligand and the platinum(II) cation. Calculations including predicted (31)P NMR shifts for the CTIs and their Pt(II) complexes largely support our experimental findings.
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