Syntheses and properties of NCN-bridged tri- and tetranuclear complexes of cobalt and rhodium Keiichi Takahata a , Noriyuki Iwadate a , Hidenobu Kajitani b , Yoshiaki Tanabe a , Youichi Ishii a, * a Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan b Institute of Industrial Science, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8505, Japan Received 28 February 2006; accepted 7 April 2006 Available online 30 August 2006 Abstract The reaction of [Cp * CoI 2 ] 2 (1b) with 2 equiv of NaNCNH affords the 16-membered macrocyclic NCNH-bridged tetracobalt(III) com- plex [Cp * CoI(l 2 -NCNH-N,N 0 )] 4 (2b), while that with 2 equiv of Na 2 NCN yields the C 3 -elongated cubane-like NCN-bridged tetraco- balt(III) complex [Cp * Co(l 3 -NCN-N,N,N 0 ) 3 (CoCp * ) 3 (l 3 -NCN-N,N,N)] (4b). Treatment of [Cp * RhCl 2 ] 2 (1c) with 2 equiv of NaNCNH gives the C 3 -elongated cubane-like tetrarhodium(III) complex [Cp * Rh(l 3 -NCN-N,N,N 0 ) 3 (RhCp * ) 3 (l 3 -NCN-N,N,N)] (4c) via the macrocyclic complex [Cp * RhCl(l 2 -NCNH-N,N 0 )] 4 (2c). On the other hand, the reaction of [Cp * CoCl] 2 (7) with Na 2 NCN affords the anionic bis(NCN)-capped tricobalt(II) complex Na[(Cp * Co) 3 (l 3 -NCN-N,N,N) 2 ](6). The molecular structures of complexes 2b Æ CH 2 Cl 2 and 4c Æ 2C 6 H 6 have been confirmed by X-ray analyses. The electrochemical properties of these types of NCN-bridged group 9 metal complexes have also been examined. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Cyanamide; Cobalt; Rhodium; Iridium; Cluster; Redox 1. Introduction Recent studies on the polynuclear transition metal com- plexes with nitrogen-based bridging ligands such as cyano or azido have revealed that these ligands can act as effective glue to construct nano-scaled polymetallic molecular cages which sometimes serve as host molecules, molecular semi- conductors, and molecular magnets [1]. Although cyana- mide anions (NCN 2 and NCNH  ) are among such molecules to be expected to work as unique bridging ligands for the construction of polynuclear systems owing to their soft, sterically small, and potentially polydentate nature, transition metal complexes with NCN- [2] or NCNH- bridges [3] have poorly been explored. Recently we have shown that the diiridium(III) complex [Cp * IrCl 2 ] 2 (1a, Cp * = g 5 -C 5 Me 5 ) reacts with NaNCNH or Na 2 NCN to afford the 16-membered macrocyclic NCNH-bridged tetr- airidium complex [Cp * IrCl(l 2 -NCNH-N,N 0 )] 4 (2a) or the NCN-bridged diiridium complex [Cp * Ir(l 2 -NCN-N,N)] 2 (3), respectively, which can further be converted into the C 3 -elongated cubane-like NCN-bridged tetrairidium complex [Cp * Ir(l 3 -NCN-N,N,N 0 ) 3 (IrCp * ) 3 (l 3 -NCN-N,N,N)] (4a), the regular cubane-type NCN-bridged tetrairidium complex [Cp * Ir(l 3 -NCN-N,N,N)] 4 (5) and the heterotrinu- clear complexes [(Cp * Ir) 2 (ML)(l 3 -NCN-N,N,N) 2 ] + (ML = RuCp, Rh(cod), Pd(g 3 -C 3 H 5 ); Cp = g 5 -C 5 H 5 ; cod = cyclo- octa-1,5-diene) (Scheme 1) [4]. In this study, we have synthe- sized cobalt and rhodium analogues of the 16-membered macrocyclic and C 3 -elongated cubane-like complexes, [Cp * CoI(l 2 -NCNH-N,N 0 )] 4 (2b) and [Cp * M(l 3 -NCN- N,N,N 0 ) 3 (MCp * ) 3 (l 3 -NCN-N,N,N)] (M = Co (4b), Rh (4c)), as well as the anionic bis(NCN)-capped tricobalt(II) complex Na[(Cp * Co) 3 (l 3 -NCN-N,N,N) 2 ] (6), and have compared their chemical properties. 0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2006.08.054 * Corresponding author. Tel.: +81 3 3817 1901; fax: +81 3 3817 1895. E-mail addresses: ytanabe@chem.chuo-u.ac.jp (Y. Tanabe), ishii@ chem.chuo-u.ac.jp (Y. Ishii). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 692 (2007) 208–216