Formation of the paramagletic Ni(I) p-allyl complex in the Ni(allyl) 2 e (2,6-diisopropylphenyl)diazabutadiene system Peter B. Kraikivskii a, * , Vitaly V. Saraev a , Victoria V. Bocharova a , Galina V. Romanenko b , Stanislav K. Petrovskii a , Dmitrii A. Matveev a a Irkutsk State University, 664003, Irkutsk, K. Marx str. 1, Russia b The Institute International Tomography Center of the Siberian Branch of the Russian Academy of Sciences, 630090, Novosibirsk, Institutskaya str., 3A, Russia article info Article history: Received 24 April 2011 Received in revised form 5 July 2011 Accepted 18 July 2011 Keywords: Monovalent nickel Diimine ligands Chelates Structure elucidation abstract It has been shown that the reaction of Ni(allyl) 2 with (2,6-diisopropylphenyl)diazabutadiene gives the imino-amide Ni complex (1). The imino-amide moiety of this complex undergoes some complicated rearrangements resulting in spontaneous formation of a paramagnetic p-allyl Ni(I) complex. Nickel complexes formed in the system have been studied with ESR, FTIR, 2D NMR, and mass spectrometry. The structure of complex 1 was studied with X-ray diffraction. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The analysis of the literature on transition metal allyl complexes, from the first obtained compounds [1,2] to the present day [3e6], demonstrates that p-allyl structures of transition metals play considerable role in catalytic reactions. A p-allyl fragment can be a part of the starting transition metal complex or formed straightly in the coordination sphere of a transition metal when complexes treated with olefins in the course of the catalysis. As a rule, in cata- lytic systems p-allyl complex is stabilized by different organo- elemental ligands. In 1995 Brookhart with coworkers proposed a catalytic system based on nickel and palladium diimine complexes. [7] This system had a definite advantage of converting lower olefins into linear polymers enriched with a-isomers. One of the perspec- tive ways for the evolution of this type of catalytic systems is the incorporation of diazabutadiene diimine ligands in starting cationic or neutral allyl complexes of nickel and palladium [8]. Despite the intensive investigation of these catalytic systems, the question if N- bearing ligands can undergo conversions within organometallic complexes remains open. In the literature almost all proposed mechanisms for the catalytic cycle do not consider the possibility of changing the nature of the metaleligand bond as well as the struc- ture of the diimine ligand itself [9e14]. Up to this moment the ligand is commonly considered as an inalterable unit acting as a “guest” in the catalytic cycle, that is, it can coordinate to the metal center or leave its coordination sphere in the unchanged form. Thus, the possibility of any metamorphosis of the ligand is usually not considered. In addition, most of works grounds mechanisms of the catalytic cycle on nickel(0) and nickel(II) complexes, with the Ni þ2 form regarded as more stable one, second only to the stability of colloidal nickel [9,12e14]. Nevertheless, certain papers do state that Ni(I) species are formed both in the systems based on Ni(II) allyl complexes [6] and in the systems with diimine ligands [10]. To the above we can add that there are very few papers on nickel allyl systems in spite of the intensive studies of transition metal allyl complexes by and large. Most researchers deal with allyl complexes of palladium [15]. This obviously results from the low stability of nickel allyl complexes as well as the inefficiency of the wide used NMR specroscopy for their study [16]. This work reports a detailed spectroscopic (NMR, ESR and IR) examination of the complexation between Ni(allyl) 2 and bis(2,6- diisopropylphenyl)diazabutadiene, one of the most effective, widespread and synthetically available ligands. 2. Results and discussion When a yellow solution of Ni(allyl) 2 in diethyl ether was mixed with the equimolar amount bis(2,6-diisopropylphenyl)diazabutadiene (DAB) at 5  C, the solution color turned bright red. Addition of some pentane to the reaction mixture and subsequent cooling to 30  C * Corresponding author. Tel.: þ7 3952 425935. E-mail address: peter10@list.ru (P.B. Kraikivskii). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem 0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2011.07.023 Journal of Organometallic Chemistry 696 (2011) 3483e3490