Catalytic CeN bond formation in guanylation reaction by N-heterocyclic carbene supported magnesium(II) and zinc(II) amide complexes Ashim Baishya, Milan Kr. Barman, Thota Peddarao, Sharanappa Nembenna * School of Chemical Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar 751005, India article info Article history: Received 6 June 2014 Received in revised form 19 July 2014 Accepted 25 July 2014 Available online 4 August 2014 Keywords: Catalysis Guanidine Magnesium Neutral ligand Zinc abstract The catalytic activity of N-heterocyclic carbene (NHC) supported magnesium(II) and a zinc(II) amide complex towards the addition of NeH bond of amine to carbodiimide was studied. Treatment of a free carbene i.e., 1,3-di-tert-butylimidazol-2-ylidene (I t Bu) with magnesium and zinc bis(amide) i.e.,M [N(SiMe 3 ) 2 ] 2 ,M ¼ Mg or Zn in toluene led to the formation of I t Bu:M[N(SiMe 3 ) 2 ] 2 ,M ¼ Mg(1) and Zn(2) compounds, respectively. Both 1 and 2 were characterized by multinuclear ( 1 H, 13 C and 29 Si) NMR spectroscopy and single X-ray crystal structure analysis. Solid state structures revealed that both com- plexes are monomeric in nature and their magnesium and zinc atoms are three coordinated and dis- torted trigonal planar in geometries. Furthermore, compounds 1 and 2 were tested as catalysts for the guanylation reaction of addition of amine to carbodiimide and turned to be excellent catalysts. © 2014 Elsevier B.V. All rights reserved. Introduction Metal catalyzed CeN bond formation reactions by the addition of amine to carbodiimide are important in guanidine synthesis [1]. Guanidines are used as bases as well as catalysts in organic syn- thesis [2]. And also, they are used as ancillary ligands [3] in a variety of main group [4], transition [5] and lanthanide [6] metal com- plexes. Moreover, guanidines are the important structural motifs found in many biologically and pharmaceutically active molecules [7]. Thus, synthesis of guanidines has attracted much attention in organic synthesis and coordination/organometallic chemistry. The synthesis of guanidines has been thoroughly examined by a variety of methods [8]. Among all methods, the convenient method is the direct addition of primary aliphatic amine to carbodiimide, but it requires very harsh reaction conditions [9]. In contrast to primary aliphatic amines, primary aromatic and secondary amines do not react with carbodiimide, even at harsh reaction conditions. Therefore, the catalytic hydroamination of carbodiimides is the most attractive method. This is an atom economical and most convenient approach for the synthesis of guanidines. In recent years, the construction of a new CeN bond in guanylation reaction (addition of amine NeH bond to carbodiimide) was achieved by the transition [10] and lanthanide [11] metal complexes. Additionally, there are few reports on the main group metal catalyzed hydro- amination of carbodiimides. In 2006, Richeson's group reported the first example of the commercially available lithium amide catalyzed CeN bond formation in guanylation reaction [12]. Hill and co- workers have shown the heavier group 2 element catalyzed hydroamination of carbodiimides [13]. Alonso-Moreno et al., demonstrated the lithium alkyl and magnesium dialkyls catalyzed reaction of amines with carbodiimides [14]. Moreover, very recently, Bergman's group described the guanidinato stabilized aluminum(III) alkyl complex catalyzed hydroamination of carbo- diimide. [15] And also, Zhang and coworkers have used commer- cially available AlMe 3 as catalyst for the guanylation reaction [16]. To the best of our knowledge there are no reports on N-heterocyclic carbene (NHC) stabilized magnesium and zinc bis(amides) as cat- alysts for guanylation reaction of both primary aromatic and cyclic secondary amines with carbodiimides. In 1991, Arduengo and coworkers reported the synthesis and characterization of the first room temperature stable crystalline N- heterocyclic carbene (NHC) [17]. Since then NHC's have got enor- mous importance in both organometallic synthesis and catalysis [18]. Their strong s donating properties led to the isolation of stable metal complexes that are usually resistant to decomposition. Despite the widely developed coordination chemistry of NHC's * Corresponding author. Tel.: þ91 674 2304126; fax: þ91 674 2302436. E-mail address: snembenna@niser.ac.in (S. Nembenna). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.07.021 0022-328X/© 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 769 (2014) 112e118