Phenazine-substituted polynuclear osmium clusters: Synthesis and DFT evaluation of the C-metalated derivatives Os 3 (CO) 9 (m 3 ,h 2 -C 12 H 7 N 2 )(m-H) and Os 3 (CO) 9 (m 3 ,h 2 -C 12 H 6 N 2 )(m-H) 2 Md. Arshad H. Chowdhury a , Subas Rajbangshi a , Ahibur Rahaman a , Li Yang b , Vladimir N. Nesterov b , Michael G. Richmond b , Shaikh M. Mobin c , Shariff E. Kabir a, * a Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh b Department of Chemistry, University of North Texas, Denton, TX 76209, USA c Discipline of Chemistry, School of Basic Science, Indian Institute of Technology Indore, Khandwa Road, Indore 452 017, India article info Article history: Received 19 October 2014 Received in revised form 5 December 2014 Accepted 6 December 2014 Available online 13 December 2014 Keywords: Triosmium clusters Phenazine ligand Oxidative addition X-ray structures DFT calculations abstract Os 3 (CO) 12 reacts with phenazine in refluxing xylene to yield the monohydride cluster Os 3 (CO) 9 (m 3 ,h 2 - C 12 H 7 N 2 )(m-H) (1) in 18% yield and the dihydride cluster Os 3 (CO) 9 (m 3 ,h 2 -C 12 H 6 N 2 )(m-H) 2 (2) in 21% yield. Compound 1 reacts reversibly with CO to give the decacarbonyl compound Os 3 (CO) 10 (m,h 2 -C 12 H 7 N 2 )(m-H) (3) and with PPh 3 to afford the addition product Os 3 (CO) 9 (m,h 2 -C 12 H 7 N 2 )(PPh 3 )(m-H) (4). Compounds 1, 2, and 4 have been structurally characterized. 1 contains a C-metalated phenazine ligand that is coordinated to the cluster by a dative nitrogen bond and a benzylidene-type bond, the latter which bridges the same cluster edge as the bridging hydride. The activated phenazine ligand in 2 derives from a double CeH bond metalation sequence, affording a face-capping heterocyclic ligand that binds adjacent osmium centers through two seOseC bonds and the third osmium atom via an aryl p bond in an h 2 fashion. Compound 4 exhibits a closed trimetallic Os 3 (CO) 9 core that contains edge-bridging phenazine (C,N coordination) and hydride moieties, and a triphenylphosphine ligand that is coordinated at the non- phenazine-ligated osmium center. These compounds represent rare examples of polynuclear osmium clusters containing C-metalated phenazine ligands. The potential energy surfaces that afford clusters 1 and 2 from Os 3 (CO) 12 and phenazine have been modeled by DFT calculations, and these data indicate that both product clusters originate from the unsaturated cluster Os 3 (CO) 11 . © 2014 Elsevier B.V. All rights reserved. Introduction The diverse reactions of trinuclear metal clusters with aromatic nitrogen heterocycles have been extensively studied over the past few years [1e16]. This research field was initiated in 1975 with Deeming's synthesis and characterization of the metalated pyridyl cluster Os 3 (CO) 10 (m,h 2 -NC 5 H 4 )(m-H), which was isolated from the reaction of Os 3 (CO) 12 with pyridine at elevated temperature [3]. Since then numerous research groups have investigated the reac- tivity of the trimetal clusters M 3 (CO) 12 (where M ¼ Ru, Os) and their labile derivatives M 3 (CO) 10 (NCMe) 2 (M ¼ Ru, Os) with nitro- gen heterocycles such as pyridines [6,8,9,16], pyrazoles [6], py- rimidine [7,13], pyrazine [7,14], quinoxaline [14], quinolines [3,5,7,16], isoquinoline [5], phenanthridine [5], and dihy- drophenanthridine [5]. The resulting substituted clusters were formulated as M 3 (CO) 10 [m,h 2 -(L-H)](m-H), with the hydride derived from the C(2)eH bond of the heterocyclic ring that had undergone an oxidative addition at the cluster. Subsequent investigation of these compounds revealed them to be unreactive towards hydride donors and in hydrogenation catalysis [5,17,18]. Following these reports, the Kabir and Rosenberg groups extended their work to the exploration of cluster activation of saturated nitrogen heterocyclic compounds and secondary aliphatic amines. There they confirmed that the reaction of Os 3 (CO) 10 (NCMe) 2 with pyrrolidine, piperidine, and R 2 NH (where R ¼ isopropyl, Et) afforded a range of products from transalkylation and/or carbonehydrogen bond activation, where the product distribution was shown to be sensitive to the structure and steric bulk of the nitrogen substrate [19e21]. A few years later we reported a new class of triosmium decacarbonyl compounds with the composition [Os 3 (CO) 10 {m,h 2 -(L-H)}(m-H)], * Corresponding author. Tel.: þ880 27791099; fax: þ880 27791052. E-mail address: skabir_ju@yahoo.com (S.E. Kabir). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.12.002 0022-328X/© 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 779 (2015) 21e29