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

Abstract

Chiral 1,8-diaza-3,6,10,13-tetraphosphacyclotetradecanes were obtained by condensation of 1,2-bis(phenylphosphanyl)ethane, paraformaldehyde and optically pure (S)-(+)-sec-butylamine or racemic sec-butylamine. The covalent self-assembly stereoselectively led to only one enantiomer, 14-P 4 SSSS C 2 SS, starting with the optically pure sec-butylamine, and to two enantiomeric pairs, 14-P 4 SSSS 3057Scheme 4. Transformation of mixture of 1a -1c after dissolution in C 6 D 6 .

Dynamic Covalent Chemistry Approach toward 18-Membered P4N2 Macrocycles and Their Nickel(II) Complexes

“…There are processes of isomer interconversion and partial splitting of 16-membered P 4 N 2 macrocycles into two 8-membered P 2 N cycles 23 and practically full splitting of 14-membered P 4 N 2 macrocycles into two 7membered P 2 N cycles. 25,26 According to 31 P{H} NMR spectroscopic studies, in solution, the pure stereoisomers of the 18-membered P 4 N 2 macrocycles 1−5 form a dynamic system of cyclic aminomethylphosphines where the initial isomer (rac-I for compounds 1−3 and meso-I for compounds 4 and 5) prevails (Figures S25−S29). The second main signal in the 31 P{ 1 H} spectra of macrocycles 1−5 in the region from −31 to −37 ppm belongs to another stereoisomer of 18- However, in contrast to the 31 P{ 1 H} spectra of 14-and 16-membered P 4 N 2 macrocycles, the intensity of signals of possible 9-membered cycles in the spectra of 18-membered macrocycles is very low, which indicates the predominant process of stereoisomerization, whereas the splitting into 9-membered cycles is negligible.…”

“…It indicates the reversibility of P–C and C–N bond formation, interconversion of all components of the dynamic system, and self-correction of the reaction, which characterize the covalent self-assembly of macrocycles according to DCvC principles. In the final reaction mixtures, several intensive signals in the range of −30 to −40 ppm were observed, which are typical for macrocyclic aminomethylphosphines. − The intensity of the signals of byproducts (acyclic aminomethylphosphines or possible 9-membered cycles as products of [1 + 1] cyclocondensation reactions in the range of −24 to −28 ppm) was noticeably lower than that of the macrocyclic product, indicating that the formation of 18-membered macrocycles is more favorable in comparison with other possible products of the condensation reaction.…”

“… Formation of a tetra­phosphonium macrocycle was observed in the tetramerization of 3-(diphenylphosphino)­propanal under acidic conditions . Our previous works clearly demonstrate that the Mannich-like condensation reaction of primary phosphines or secondary bis-phosphines, formaldehyde, and primary or secondary amines and bis-amines can be employed for the selective synthesis of a wide range of macrocyclic aminomethylphosphines, namely [P 2 N 2 ] 2 -cyclophanes, [P 2 N 4 ]-cyclophanes, [P 4 N 2 ]-cryptand, and [P 4 N 2 ]-corands. − Their synthesis, which is accompanied by reversible P–C and C–N bond formation, proceeds with a remarkable stereoselectivity. Thus, in accordance with the main principles of DCvC (reversibility, thermodynamic control, interconversion of molecular components of the dynamic system) in the covalent self-assembly of [P 4 N 2 ]-corands, only one isomer with a preferred configuration of the four endocyclic phosphorus atoms is isolated from the dynamic system containing five possible stereoisomers of [P 4 N 2 ]-corands (Figure ) and [P 2 N]-corands as products of [1 + 1] condensations as well as cyclic and acyclic oligomers…”

“…Thus, the 16- and 20-membered macrocycles (where n = 3 and 5, correspondingly) were always isolated as the meso -I ( R P S P S P R P ) isomers, − but their 14-membered and one 18-membered homologues (where n = 2 and 4, correspondingly) were rac -I R P R P R P R P / S P S P S P S P isomers. ,− Based on these observations, an empirical rule for predicting the configuration of the preferred [P 4 N 2 ] macrocycle on the number of methylene fragments (even or odd) in the initial bis-phosphine was deduced . Unexpectedly, the meso -I isomer of 14-membered P 4 N 2 macrocycles was recently obtained from the reaction mixture of 1,2-bis­(phenylphosphino)­ethane, formaldehyde, and primary amine when a different workup procedure of the reaction mixture was employed, namely crystallization from diethyl ether or ethanol instead of crystallization from DMF .…”

“…The behavior of [P 4 N 2 ]-corands in solutions appears to be more complex than expected due to the lability of the P–CH 2 –N fragment. Thus, the interconversion of isomers for 16-membered P 4 N 2 macrocycles and splitting of 14-membered P 4 N 2 macrocycles into two 7-membered P 2 N macrocycles have been found. − It turned out that many external factors, in particular temperature, solvent, presence of protons or metal ions, influence these processes.…”