Syntheses, homeomorphic and configurational isomerizations, and structures of macrocyclic aliphatic dibridgehead diphosphines; molecules that turn themselves inside out

The diphosphine complexes cis- or trans-PtCl2(P((CH2)(n))(3)P) (n = b/12, c/14, d/16, e/18) are demetalated by MC equivalent to X nucleophiles to give the title compounds (P((CH2)(n))(3))P (3b-e, 91-71%). These empty cages react with PdCl2 or PtCl2 sources to afford trans-MCl2(P((CH2)(n))(3)P). Low temperature P-31 NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in,in (major) and out,out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: Delta H-double dagger; 7.3/8.2 kcal mol(-1), Delta S-double dagger -19.4/-11.8 eu, minor to major). At 150 degrees C, 3b, c, e epimerize to (60-51) : (40-49) mixtures of (in,in/out,out) : in,out isomers, which are separated via the bis(borane) adducts 3b, c, emiddot2BH(3). The configurational stabilities of in,out-3b, c, e preclude phosphorus inversion in the interconversion of in,in and out,out isomers. Low temperature P-31 NMR spectra of in,out-3b, c reveal degenerate in,out/out,in homeomorphic isomerizations (Delta G(Tc)(double dagger) 12.1, 8.5 kcal mol(-1)). When (in,in/out,out)-3b, c, e are crystallized, out,out isomers are obtained, despite the preference for in,in isomers in solution. The lattice structures are analyzed, and the D-3 symmetry of out,out-3c enables a particularly favorable packing motif. Similarly, (in,in/out,out)-3c, emiddot2BH(3) crystallize in out,out conformations, the former with a cycloalkane solvent guest inside.

Automated summary

This article investigates the reaction between diphosphine ligands and transition metal complexes, and characterizes the formation and interconversion of different isomers through NMR and crystal structure analysis.