Synthesis and structure of novel strontium complexes of unsymmetrically functionalized b-diketimine ligands Sheby M. George a , Gyu Hwan Yon b , Bo Keun Park a , Kang Mun Lee c , Youngkyu Do c , Chang Gyoun Kim a,⇑ , Taek-Mo Chung a,⇑ a Advanced Materials Division, Korea Research Institute of Chemical Technology, Yuseong P.O. Box 107, Daejeon 305-600, Republic of Korea b Bio-Organic Science Division, Korea Research Institute of Chemical Technology, Yuseong P.O. Box 107, Daejeon 305-600, Republic of Korea c Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea article info Article history: Received 26 March 2011 Received in revised form 5 August 2011 Accepted 12 October 2011 Available online 20 October 2011 Keywords: Strontium complexes b-Diketiminate ligands Tridentate ligands Crystal structure Thermal properties abstract A series of tridentate b-diketiminate ligands, (2Z,4E)-4-{[2-(dimethylamino)ethyl]imino}-N-(propan- 2-yl)pent-2-en-2-amine (L 1 H), (2Z,4E)-4-{[3-(dimethylamino)propyl]imino}-N-(tert-butyl)pent-2-en- 2-amine (L 2 H), and (2Z,4E)-4-{[3-(dimethyl-amino)propyl]imino}-N-(propan-2-yl)pent-2-en-2-amine (L 3 H), and their strontium complexes, SrL 1 2 (1), SrL 2 2 (2), and SrL 3 2 (3) were synthesized as potential stron- tium precursors, by the reaction of Sr[N(SiMe 3 ) 2 ] 2 and two equivalents of L 1 H, L 2 H, and L 3 H, respectively. Compounds 1–3 were characterized by spectroscopic (IR, MS, 1 H and 13 C NMR), microanalytical methods, and single crystal X-ray diffractometry. The X-ray crystal structure reveals that complex 1 has a mono- clinic space group, C2/c. The structure shows the bonding of two b-diketiminate ligands to the strontium metal through six nitrogen atoms. Additionally, the isopropyl groups on the ligands force 1 to attain a highly distorted octahedron. Thermogravimetric analyses of the compounds 1–3 exhibit a primary mass loss on 130–300 °C region. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The interest in the organometallic chemistry of heavier alkaline earth elements such as, barium, strontium, and calcium is driven by their potential application in organic synthesis [1], lactide poly- merization [2], and as precursors for the growth of thin films [3]. The synthesis of new compounds of strontium and other alkaline earth metals are often challenged by poor compound stability due to the small charge to size ratio and the formation of oligo- meric compounds with low solubility and poor volatility as a result of the large size of heavier group 2 ions. These challenges were solved up to a large extend by employing sterically demanding li- gands [4] such as b-diketiminate [5], indene [6], cyclopentadienyl [7], and guanidinate [4c] which provided grater encapsulation of the metal resulting in stable and soluble monomeric compounds. Complexes containing b-diketiminate ligands were first reported in 1968 [8]. But these ligands were rarely explored in organometallic and inorganic chemistry before 1990. Since 1990, b-diketiminate ligands [HC(C(R)N(R 0 )) 2 )] À have been widely investigated in transition, lanthanide, and main group metal chemistry [9]. b-Diketiminate ligands commonly act as bidentate four-electron donors through formation of two metal-nitrogen r- bonds. Aside from their interesting structural features, b-diketimi- nate ligands have been employed as important spectator ligands in catalytic processes and are often used as cyclopentadienyl or b- diketonato ligand replacements. The versatility of b-diketiminate ligands is due to the fact that they can be modified at the nitrogen and the carbon atoms of the ligand core to suit different steric and electronic demands of organometallic complexes. In pursuit of no- vel, structurally interesting alkaline earth metal complexes, we exploited the structural tunability of the b-diketiminate ligands to design new diketiminate derivatives and their strontium com- plexes. Herein, we present synthesis and structural characteriza- tion of new strontium complexes using newly synthesized unsymmetrically functionalized b-diketiminate ligands. 2. Experimental 2.1. Materials Sr[N(SiMe 2 ) 2 ] 2 Á2DME was prepared using the literature method [10]. All reactions were carried out in inert dry condition using standard Schlenk techniques or in argon filled glove box. Hexane and toluene were purified by Innovative Technology PS-MD-4 sol- vent purification system. All other chemicals were purchased from Aldrich and used as received. 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.10.044 ⇑ Corresponding authors. Fax: +82 42 861 4151. E-mail addresses: cgkim@krict.re.kr (C.G. Kim), tmchung@krict.re.kr (T.-M. Chung). Inorganica Chimica Acta 383 (2012) 67–71 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica