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Platinum(IV)‐Mediated Nitrile–Amidoxime Coupling Reactions: Insights into the Mechanism for the Generation of 1,2,4‐Oxadiazoles
Author(s) -
Bolotin Dmitrii S.,
Bokach Nadezhda A.,
Haukka Matti,
Kukushkin Vadim Yu.
Publication year - 2012
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201100047
Subject(s) - chemistry , nucleophile , medicinal chemistry , nitrile , platinum , ligand (biochemistry) , molar ratio , stereochemistry , organic chemistry , catalysis , biochemistry , receptor
The nucleophilic addition of amidoximes R′C(NH 2 )NOH ( 4 : R′=Me, 5 : CH 2 Ph, 6 : Ph) to coordinated nitriles in the platinum(IV) complexes trans ‐[PtCl 4 (RCN) 2 ] ( 1 : R=Et, 2 : Ph, 3 : NMe 2 ) proceeds in a 1:1 molar ratio and leads to the monoaddition products [PtCl 4 (RCN){H N C(R)ONC(R′)NH 2 }] ( 7 : R/R′: Et/CH 2 Ph, 8 : Et/Ph, 9 : NMe 2 /CH 2 Ph, 10 : NMe 2 /Ph). Meanwhile, if the nucleophilic addition proceeds in a 2:1 molar ratio the reaction gives the bisaddition species [PtCl 4 {H N C(R)ONC(R′)NH 2 } 2 ] ( 11 : R/R′=Et/Me, 12 : Et/CH 2 Ph, 13 : Et/Ph, 14 : Ph/Ph, 15 : NMe 2 /Me, 16 : NMe 2 /CH 2 Ph, 17 : NMe 2 /Ph). All complexes 7 – 17 bear nitrogen‐bound O‐iminoacylated amidoxime groups. The addition of one equivalent of the corresponding amidoxime to each of 7 – 10 leads to 12 , 13 , 16 , and 17 , respectively. Complex [PtCl 4 (NCNMe 2 ){H N C(NMe 2 )ONC(Ph)NH 2 }] ( 10 ), when dissolved in MeNO 2 , gave mer‐ [PtCl 3 {H N C(NMe 2 )O N C(Ph)NHC(NMe 2 ) N H}] ( 18 ) with the newly formed tridentate ligand derived from an unexpected coupling between two Me 2 NCN ligands and the N and the O centers of the amidoxime. The O‐imidoylamidoxime compounds R′C(NH 2 )NOCR(NH) ( 19 – 25 ) were liberated from the corresponding complexes 11 – 17 by treatment with excess NaCN and these metal‐free species were characterized by 1 H and 13 C{ 1 H} NMR spectroscopy. The conversion of 19 – 25 into the 3,5‐substituted 1,2,4‐oxadiazole compounds O a NC(R′)NC b (R) ( a–b ) ( 26 : R/R′=Me/Et, 27 : PhCH 2 /Et, 28 : Ph/Et, 29 : Ph/Ph, 30 : Me/NMe 2 , 31 : PhCH 2 /NMe 2 , 32 : Ph/NMe 2 ) occurs at room temperature and the cyclization is promoted by strong acceptor substituents R′.