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

Abstract

Reactions of cis- or trans-PtCl2(P((CH2)n)3P) (n = b/12, c/14, d/16, e/18) and MC≡CR or KC≡N give the dibridgehead diphosphines P((CH2)n)3)P (3b-e, 91-71%). These react with MCl2 sources (M = Pd, Pt)...

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

“…The chemical shifts varied moderately (−29.1 to −26.9 ppm and −35.2 to −33.4), consistent with temperature‐dependent equilibria involving the dozens of conformations of comparable energy as found by simulated thermal annealing computations [8] . In line with chemical shift trends established for 1 b , c , [4b] the minor downfield signal was assigned to in,in ‐ 1 a , and the major upfield signal to out,out ‐ 1 a . This is confirmed crystallographically below.…”

“…The preceding ( in,in / out,out ): in,out mixtures cannot be chromatographically or otherwise separated. Nonetheless, as demonstrated for 1 b , c , e earlier, [4b] they can be converted to bis (BH 3 ) adducts that give distinct R f values on silica gel. As a preliminary step, shown in Scheme 5 (top), the samples of ( in,in / out , out )‐ 1 a , d produced in Scheme 4 were treated with excess Me 2 S⋅BH 3 .…”

“…We have suggested that the crossover to more stable in,in isomers in larger macrobicycles is due to dispersion forces, [4b] a factor also invoked with certain salts of in,in ‐ 6 ⋅ 2H + (Scheme 6) some time ago [28] . For all limiting isomers of 1 a – e , thermal annealing simulations reveal an abundance of closely spaced low energy conformers, [8] consistent with the highly temperature dependent 31 P{ 1 H} NMR chemical shifts.…”

“…( in,in / out , out )‐P((CH 2 ) 14 ) 3 P (( in,in / out , out )‐1 c) [4b] . Complex 5 c (0.259 g, 0.327 mmol), [18a] PMe 3 (0.34 mL, 3.27 mmol), and hexanes (6 mL) were irradiated as described for ( in,in / out , out )‐ 1 a .…”

Synthesis of Dimethyldisilabicycloalkanes: Cage-Size Effects on the Relative Stabilities between In,Out and Twist-Out,Out Forms

“…Specifically, selective synthesis and characterization were conducted on out,out isomers of bicycloalkane 1 . Homeomorphic conversions between in,out forms of diphosphabicycloalkane were observed using nuclear magnetic resonance (NMR) spectroscopy, leading to the isolation and characterization of twist-out,out-bicyclo[14.14.14]­alkane 2 , by Gladysz and co-workers . von Delius and co-workers reported the NMR spectroscopic observation of an equilibrium between out,out and in,in forms in bicycloalkanes containing poly­(ethylene oxide) chains 3 …”