Self-assembly of isomeric clamshell dimers of platinum(ii)

Abstract

The controlled synthesis of isomeric organoplatinum clamshell dimers [Pt₂Me₂(μ₂-κ³-6-dppd)₂]²⁺, 6-dppd = 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine, is reported. The new complexes are formed selectively by self-assembly from mononuclear precursors, taking advantage of the slow cis–trans isomerization at platinum(II). Thus reaction of endo-[PtClMe(κ²-6-dppd)] with AgOTf gave endo,endo-[Pt₂Me₂(μ₂-κ³-6-dppd)₂]²⁺, while the reaction of [PtMe₂(κ²-6-dppd)] with HOTf in solvent S = Me₂CO or MeCN gave first a mixture of exo- and endo-[PtMe(S)(κ²-6-dppd)]⁺ and then, by loss of solvent, a mixture of exo,exo- and endo,endo-[Pt₂Me₂(μ₂-κ³-6-dppd)₂]²⁺. The endo,endo isomer slowly isomerized to the more stable exo,exo isomer in solution. Reaction of PPh₃ with endo-[PtClMe(κ²-6-dppd)] gave a mixture of endo- and exo-[PtMe(PPh₃)(κ²-6-dppd)]⁺ but reaction with exo,exo-[Pt₂Me₂(μ₂-κ³-6-dppd)₂]²⁺ gave exo-[PtMe(PPh₃)(κ²-6-dppd)]⁺ selectively, with retention of stereochemistry. The structures of the clamshell dimers and of key precursors are reported and equilibria are studied both experimentally and by DFT calculations.