Molecules that Turn Themselves Inside-Out: Tuning in/out Equilibria and Homeomorphic Isomerization in Macrobicyclic Dibridgehead Diphosphines P((CH2)n)3P Newly Accessible by Earth-Abundant-Metal Templates

Photolyses of trans-<(K<(Fe(CO)(3)(P((CH2)(n))(3)P)over bar>)over bar>) (n= 10 (a), 12 (b), 14 (c), 16 (d), 18 (e)) in the presence of PMe3 provide the first economical and scalable route to macrobicyclic dibridgehead diphosphines P((CH2)(n))(3)P (1). These are isolated as mixtures of in,in/out,out isomers that equilibrate with degenerate in, out/out, in isomers at 150 degrees C via pyramidal inversion at phosphorus. For the entire series, VT P-31 NMR data establish or bound K-eq, rates, and activation parameters for a variety of phenomena, many of which involve homeomorphic isomerizations, topological processes by which certain molecules can turn themselves inside out (e. g., in, in (sic) out, out). This provides the first detailed mapping of such trends in homologous series of aliphatic bicyclic compounds XE((CH2)(n))(3)EX with any type of bridgehead. Isomeric diborane adducts 1a,d center dot 2BH(3) are also characterized. Crystal structures of out, out-1a and in, in-1a center dot 2BH(3) aid isomer assignments and reveal unusual cage conformations.

Automated summary

Photolysis can provide an economical and scalable route to synthesize macrobicyclic dibridgehead diphosphines. The isomers of these compounds can equilibrate via pyramidal inversion at high temperature. The study of these compounds using P-31 NMR data reveals various phenomena including homeomorphic isomerizations. The properties of isomeric diborane adducts were also investigated.