Cobaltabisdicarbollide based metallodendrimers with cyclotriphosphazene core Chandra S. Mahanta a , Rupesh Bhavsar b , Barada P. Dash c, * , Rashmirekha Satapathy a, ** a Department of Chemistry, Ravenshaw University, Cuttack, Odisha 753 003, India b Organic Materials Innovation Centre, School of Chemistry, University of Manchester, Manchester M13 9PL, United Kingdom c Department of Chemistry, Siksha 'O' Anusandhan (Deemed to be University), Bhubaneswar, Odisha 751 030, India article info Article history: Received 7 January 2018 Received in revised form 13 February 2018 Accepted 15 February 2018 Available online xxx Dedicated to Professor Narayan S. Hosmane on the occasion of his 70 th birthday Keywords: Cobalt bis(dicarbollide) anion Cyclotriphosphazene Metallodendrimer Oxonium ring opening abstract Cyclotriphosphazene core based metallodendrimers containing six and twelve cobalt bis(dicarbollide) moieties on the periphery have been synthesized. The ring opening reaction of the cyclic oxonium de- rivative of the cobalt bis(dicarbollide) anion, [3,3 0 -Co(8-C 4 H 8 O 2 -1,2-C 2 B 9 H 10 )(1 0 ,2 0 -C 2 B 9 H 11 )], has been efficiently used for the synthesis of the dendrimers. The newly synthesized dendrimers have been characterized by 1 H, 13 C, 11 B, 31 P NMR and MALDI-TOF mass spectrometry, and the UV-Vis spectroscopy was used to determine the number of cobalt bis(dicarbollide) units present in the dendrimer molecules. These dendrimers are extremely thermally robust, with 83% and 87% mass retention at 600  C. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Cobalt bis(dicarbollide) anion, [3,3 0 -Co(1,2-C 2 B 9 H 11 ) 2 ] - , is one of the most widely used metallacarboranes in synthetic chemistry [1]. Because of its high chemical and thermal stability, it has been used for various applications such as radionuclide removal from nuclear waste [2], conducting polymers [3], coordination polymers [4], HIV protease inhibitors and other medicinal applications [5]. Several approaches have been developed to synthesize metallodendrimers containing either multiple carborane clusters or cobalt bis(di- carbollide) moieties [6]. Carbosilane and carbosiloxane core-based polyanionic macromolecules containing four and eight cobalt bis(dicarbollide) moieties in the periphery were synthesized via successive alkenylation and hydrosilylation reactions [7]. Fluores- cent phenylene cored Frechet-type poly(aryl ether) dendrimers were synthesized via hydrosilylation reactions on the terminal allyl ether functional groups in the presence of Karstedt catalyst [8]. Ring opening of zwitterionic oxonium derivative of cobalt bis(di- carbollide) anion, [3,3 0 -Co(8-C 4 H 8 O 2 -1,2-C 2 B 9 H 10 )(1 0 ,2 0 -C 2 B 9 H 11 )] has been extensively used for its functionalization [1]. Polyanionic poly-(alkyl aryl-ether) dendrimers containing four and eight cobalt bis(dicarbollide) moieties were synthesized via the ring opening reactions of the oxonium derivative. A correlation between the number of cobalt bis(dicarbollides) and the absorbance was observed for the reported compounds. Therefore, the UV-vis ab- sorption was found to be a good tool for estimating the number of cobalt bis(dicarbollide) moieties attached to the periphery of the dendrimers [9]. Phenylene and triazine core based dendritic mol- ecules containing three to six cobalt bis(dicarbollide) clusters were synthesized via silicon tetrachloride mediated trimerization of ar- omatic ketones and triflic acid mediated trimerization of aromatic nitriles respectively. It was found that compounds containing multiple cobalt bis(dicarbollide) units were highly thermally stable and only 10e30% mass loss was observed up to 700  C. Enhanced the thermal stability was observed for compounds containing higher numbers of cobalt bis(dicarbollide) moieties [10]. In the present work, a facile approach has been developed for the prep- aration of cyclotriphosphazene core-based dendritic molecules containing multiple cobalt bis(dicarbollide) clusters. Cyclotriphosphazenes are a class of thermally and chemically * Corresponding author. ** Corresponding author. E-mail addresses: barada.dash@gmail.com (B.P. Dash), rashmi.satapathy@gmail. com, rashmi@ravenshawuniversity.ac.in (R. Satapathy). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem https://doi.org/10.1016/j.jorganchem.2018.02.022 0022-328X/© 2018 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry xxx (2018) 1e6 Please cite this article in press as: C.S. Mahanta, et al., Journal of Organometallic Chemistry (2018), https://doi.org/10.1016/ j.jorganchem.2018.02.022