Synthesis and characterization of a dipyridocatecholate silicon complex David A. Lee, Sang K. Moon, Adrian N. Sizeland, Nicholas W. Gould, Eshere M. Gbarbea, Deborah Owusu, Daniel S. Jones, Thomas A. Schmedake ⁎ Department of Chemistry, University of North Carolina-Charlotte, Charlotte, NC 28223, USA abstract article info Article history: Received 14 January 2013 Accepted 23 March 2013 Available online 10 April 2013 Keywords: Hexacoordinate silicon Polypyridine 29 Si NMR 1,10-Phenanthroline-5,6-dione Dipyridocatecholate The reaction of [Si(bpy) 2 I 2 ]I 2 with 1,10-phenanthroline-5,6-dione followed by metathesis provides various salts of [Si(bpy) 2 (dpcat)] +2 (1, bpy = 2,2′-bipyridine and dpcat = dipyridocatecholate). Recrystallization of [Si(bpy) 2 (dpcat)](ClO 4 ) 2 from an aqueous solution of NaClO 4 afforded orange crystals of Na[Si(bpy) 2 (dpcatH)](ClO 4 ) 4 ·3H 2 O (2), in which silicon possesses a distorted octahedral geometry. The dipyridocatecholate ligand is coordinated to the silicon through the oxygen atoms, and one of the nitrogen atoms is protonated. 29 Si NMR and ESI-mass spectroscopy indicate [Si(bpy) 2 (dpcat)] +2 maintains its hexacoordinate structure in solution. The complex is stable with respect to hydrolysis, and degassed aqueous solutions luminesce at 410 nm. © 2013 Elsevier B.V. All rights reserved. The ligand 1,10-phenanthroline-5,6-dione is a versatile ligand in transition metal coordination chemistry since it possesses both quinone and diimine functionality. The ambidentate bonding ability was demon- strated by Balch in synthesizing an O,O′-dipyridocatecholate complex of platinum and an N,N′-phendione complex of palladium (Scheme 1) [1]. Transition metal complexes of phendione have since been explored in applications such as catalysis [2–4], sensing [5], and non-linear optics [6]. Its role as a bridging ligand between metal centers has been demon- strated and explored [7–10]. Furthermore, N,N′-phendione complexes can act as precursors for DNA-active dipyridophenazine complexes [11] and tetrapyridophenazine (tpphz) bridged polynuclear complexes [12]. Our group is interested in robust, redox active hexacoordinate silicon analogs of transition metal complexes, and reviews of the hexacoordinate silicon chemistry literature point to diimine and catecholate ligands as particularly good ligands for targeting such novel hydrolytically stable complexes [13,14]. We recently showed that Si(bpy) 3 +4 and Si(terpyridine) 2 +4 complexes can be reduced with up to six elec- trons, and that both species exhibit counter-ion dependent outer sphere charge transfer bands spanning the entire visible spectrum [15]. Xiang recently demonstrated Si(1,10-phenanthroline) 2 (arenediolate) +2 complexes have biological activity, with a high binding constant 1.7(± 0.6) × 10 6 M -1 for calf thymus DNA [16]. Silicon complexes of 1,10-phenanthroline-5,6-dione would be particularly interesting due to the ligands previously mentioned electronic, chemical, and bridging properties. Consequently, we initiated the following study to explore the binding mode of phendione in hexacoordinate silicon complexes. Phendione [17] was combined with [Si(bpy) 2 I 2 ]I 2 [18] in pyridine and heated inside a sealed ampoule to generate a dark red precipitate in a 70% yield, determined to be [Si(bpy) 2 (dpcat)](I - )(I 3 - ) based on elemental analysis, ESI-mass spectroscopy, and NMR spectroscopy (Scheme 2) [19]. The product was consistent with a mechanism in which phendione displaced iodides to generate an intermediate [Si(bpy) 2 (O, O-phendione)] +4 , which could then be reduced by two iodide ions to form [Si(bpy) 2 (dpcat)](I - )(I 3 - ). Alternatively, [Si(bpy) 2 (dpcat)]I 2 can be synthesized by refluxing dipyridocatechol with [Si(bpy) 2 I 2 ]I 2 in acetonitrile. After many unsuccessful attempts to grow X-ray quality crystals of 1 with a variety of counter-ions and solvents, we were able to obtain suitable orange rectangular crystals (monoclinic, P2 1 /c space group) from an aqueous solution of [Si(bpy) 2 (dpcat)](ClO 4 ) 2 and excess NaClO 4 [20]. The crystal structure contains one protonated 1, Inorganic Chemistry Communications 33 (2013) 125–128 ⁎ Corresponding author at: UNC Charlotte, Department of Chemistry, 9201 University City Blvd. Charlotte, NC 28223. Tel.: +1 704 687 4011; fax: +1 704 687 3151. E-mail address: tschmeda@uncc.edu (T.A. Schmedake). URL: http://www.chemistry.uncc.edu (T.A. Schmedake). Scheme 1. Ambidentate bonding modes demonstrated by Balch. 1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2013.03.031 Contents lists available at SciVerse ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche