Synthesis and Stereoselective Interconversion of Chiral 1‐Aza‐3,6‐diphosphacycloheptanes

Abstract

Cyclic seven-membered bisphosphanes, namely 1-aza-3,6diphosphacycloheptanes 3-5 (3: 3,6-diphenyl-1-(1-phenylethyl)-1-aza-3,6-diphosphacycloheptane; 4: 1-[(1R)-1-(4Јmethoxyphenyl)ethyl]-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane; 5: 3,6-diphenyl-1-[(1R)-1-phenylpropyl]-1-aza-3,6-diphosphacycloheptane), with chiral exocyclic substituents at the nitrogen positions have been synthesized, with the prevailing formation of meso stereoisomers (P R P S ) as kinetically controlled products, by stereoselective condensation of 1,2-bis(phenylphosphanyl)ethane, formaldehyde and primary optically pure amines, namely (S)-(-)-1-phenylethylamine, (R)-(+)-1-phenylethylamine, (R)-(+)-1-phenylpropylamine, (R)-(+)-1-(4Ј-methoxyphenyl)ethylamine. The meso stereoisomers of bisphosphanes 3 RSS , 3-5 RSR readily form neutral and cationic P,P-chelate complexes 6-9 with platinum(II) (6:

Self‐Assembly of Chiral 1,8‐Diaza‐3,6,10,13‐tetraphosphacyclotetradecanes via Dynamic Transformation of 7‐ and 14‐Membered Aminomethylphosphines

“…Initially isomers 2a* and 2b* prevail in solution, whereas in the equilibrium mixture, the quantity of isomer 2b* is only ca. 25 %, and equal (37 %) for each 2a* and 2c* ; a similar behaviour was earlier demonstrated for chiral 7‐membered 1‐aza‐3,6‐diphosphacycloheptanes . This can easily be understood, as formation of 2a* and 2b* requires only breaking of the C–N bond of the P–CH 2 –N fragment and one intramolecular nucleophilic attack on the methylenephosphonium fragment, while for isomer 2c* along with these processes, a second series of C–N bond breaking and nucleophilic attack is necessary (Scheme ).…”

“…The 31 P{ 1 H} NMR spectra of both reaction mixtures are practically identical and contain three main groups of signals in the field of –24 to –29 ppm (Figures S1, S2, Supporting Information). Signals in this region usually indicate the formation of 7‐membered 1‐aza‐3,6‐diphosphacycloheptanes . In addition, two (for reaction with optically pure amine) or three (for reaction with racemic amine) minor signals at –31 to –32 ppm indicate the formation of the 14‐membered macrocycles.…”

“…The type of amine used affects the result of the condensation reaction of 1,2‐bis(phenylphosphanyl)ethane, paraformaldehyde and primary amines. In particular, the rac isomer of 7‐membered P 2 N cycles (7‐P 2 RR/SS ) was obtained by condensation with arylamines and the meso isomer (7‐P 2 RS ) isomer with optically pure α‐methylbenzyl‐ or 1‐(4‐methoxyphenyl)ethylamines, instead of 14‐membered tetrakis‐phosphines . Kinetic experiments together with DFT calculations indicated the thermodynamic preference of the isomer 7‐P 2 RR/SS in all cases , .…”

“…In particular, the rac isomer of 7‐membered P 2 N cycles (7‐P 2 RR/SS ) was obtained by condensation with arylamines and the meso isomer (7‐P 2 RS ) isomer with optically pure α‐methylbenzyl‐ or 1‐(4‐methoxyphenyl)ethylamines, instead of 14‐membered tetrakis‐phosphines . Kinetic experiments together with DFT calculations indicated the thermodynamic preference of the isomer 7‐P 2 RR/SS in all cases , . Nevertheless, 14‐membered P 4 N 2 macrocycles were successfully obtained with various alkylamines as kinetically controlled products .…”

Synthesis of platinum, palladium and rhodium complexes of α-aminophosphine ligands

“…Isomers of these heterocycles differ from each other in respect of chelating abilities. 80 Only the meso (RS) form contains the two P atoms in the appropriate position suitable for complexation, while in the optically active derivatives (RR and SS), the lone pairs are present at different sides of the 7-membered ring (Scheme 44).…”