Co(II)-Mediated and microwave assisted coupling between 2,6-diaminopyridine and nitriles. A new synthetic route to N-(6-aminopyridin-2-yl)carboximidamides

Abstract

The Chinese lantern type Co 2 (O 2 CBu t ) 4 {2,6 (NH 2 ) 2 C 5 H 3 N} 2 complex reacts with RCN (R = Me or Pr n ) under microwave irradiation (MWI) to give the mononuclear amidine complexes Co(O 2 CBu t ) 2 {H 2 N(C 5 H 3 N)NHC(R)=NH} (R = Me (4a) or Pr n (4c)). Under microwave irradiation, the addition of 2,6 diaminopyridine to acetonitrile in the presence of the pivalate complexes Co 2 (µ 2 OH 2 )(O 2 CBu t ) 4 (HO 2 CBu t ) 4 (1) or [Co(OH) n (O 2 CBu t ) 2-n ] x (2) afforded complex 4a in higher yield compared to the corresponding reaction performed earlier without MWI. The use of MWI makes it possible to perform analogous reactions with nitriles RCN (R = Et, Pr n , or Ph) giving rise to complexes 4b-d, respectively. Compounds 4a-d were characterized by elemental analysis and IR spectroscopy. The structure of complex 4c was established by X ray diffraction. Amidines H 2 N(C 5 H 3 N)NHC(R)=NH, which formed in the coordination sphere of cobalt(II), were isolated in the free state from methanolic solu tions of complexes 4a-d under the action of Na 2 S and were characterized by electrospray mass spectrometry and 1 H and 13 C{ 1 H} NMR spectroscopy. The reactions of 2 aminopyridine with both complexes 1 and 2 in acetonitrile under microwave irradiation produced the Co(O 2 CBu t ) 2 (H 2 NC 5 H 4 N) 2 complex.In recent years, microwave irradiation (MWI) has found increasing use in various areas of preparative chem istry. 1-12 The main advantages of the use of MWI are a substantial shortening (by an order of magnitude) of the duration of the chemical process, an increase in selectiv ity of the major reaction, and an increase in the purity of the reaction product. 2,4,6-8,10-12 Most examples of the successful use of microwave activation, where the advan tages of the use of MWI are obvious, refer to organic synthesis. 1,6-10,12 Nevertheless, the microwave promoted synthesis of coordination compounds has been docu mented in numerous publications. 13-25 In particular, MWI is used for the preparation of nanophases and nanocrystalline compounds starting from metal com plexes, 16,19,20 the substitution of ligands, 17,18,21 and the synthesis of phthalocyanines. 13-15,22,23 In two recent pub lications, 24,25 it has been demonstrated that MWI can be used for a substantial acceleration of reactions of coordi nated ligands, such as [2+3] cycloaddition reactions 25 and the nucleophilic addition 24 to inner sphere ni triles RCN.It is known 26-29 that coordination to a metal center already leads to electrophilic activation of nitriles, which depends substantially on the nature and oxidation state of the central atom. The aim of the present study was to examine the possibility of combining two methods of ac tivation of the RCN ligand, viz., MWI and coordination, for the preparation of amidine complexes of cobalt start ing from heterocyclic amines (aminopyridines) and Co II pivalate complexes in nitrile media. Another purpose was to develop an alternative two step synthesis of free amidines, including the preparation of inner spher...

Hetarylamidines derived from PtIV-mediated coupling of nitriles with aminoheterocycles

“…Even additional activation of the system with microwave irradiation did not lead to the formation of coupling products starting from mono amino derivatives of pyridines. 29 In the present study, we demonstrated that propiononitrile, which is electro philically activated through coordination to Pt IV in the trans [PtCl 4 (EtCN) 2 ] complex under mild conditions (30-35 °C) in anhydrous (to prevent hydrolysis of the starting platinum complex) dichloromethane, is involved in nucleophilic addition reactions with a number of 2 aminoheterocyclic derivatives, including monoamino pyridines. These reactions produced the hetarylamidine complexes trans [PtCl 4 {NH=C(Et)NHHet} 2 ] (1-5) (Scheme 1).…”

Influence of the nature of organic ligands on the character of thermal decomposition products of CoII and NiII pivalate complexes with amino derivatives of pyridine

“…According to the X ray diffraction data, the complexes [(2,6 NH 2 ) 2 C 5 H 3 N] 2 Ni(η 2 OOCBu t ) 2 (3), [(2 NH 2 ) (6 Me)C 5 H 3 N] 2 Co(η 2 OOCBu t ) 2 (4), which was isolat ed with two benzene molecules of solvation (4•2C 6 H 6 ), [(2 NH 2 )(6 Me)C 5 H 3 N] 2 Ni(η 2 OOCBu t ) 2 (5), and [(2 NH 2 )C 5 H 4 N] 2 Co(η 2 OOCBu t ) 2 (6), which is isos tructural with the known cobalt derivative, 28 have similar molecular structures (Fig. 1, Table 1).…”

“…28- 30 The spectroscopic characteristics of the nickel containing complex [(2 NH 2 )C 5 H 4 N] 2 Ni(η 2 OOCBu t ) 2 (7) are similar to those of cobalt analog 6 characterized by X ray dif fraction. 28 In the crystal structures of 3-5, there are intermolec ular hydrogen bonding between the hydrogen atoms of the amino groups of the pyridine ligands and the oxygen at oms of the carboxylate groups. In the crystal structures of (8) or Ni (9), respectively.…”

Microwave-Assisted Synthesis of Coordination and Organometallic Compounds

“…The antibacterial activity of the ligands and complexes was studied. Additionally, the Chinese-lantern-type Co 2 (O 2 CBut) 4 {2,6-(NH 2 ) 2 C 5 H 3 N} 2 complex reacted with RCN (R = Me or Pr) under microwave irradiation to give the mononuclear amidine complexes Co(O 2 CBut) 2 {H 2 N(C 5 H 3 N)NHC(R):NH} (R = Me or Pr) (Bokach et al, 2006). Al-containing mesoporous silicates (Al-MCM-41 and Al-HMS) supported Mn(salen) catalysts were prepared by three different methods: impregnation of salen ligand and support with dichloromethane and then irradiated by microwave (method A), direct solidstate interaction between salen complex and support under microwave irradiation (method B), as well as the conventional ion exchange (method C) (Yin et al, 2005;Zhang et al, 2003).…”