Note Transformations of the Vaska-type complex trans-[RhCl(CO)(PTA) 2 ] (PTA = 1,3,5- triaza-7-phosphaadamantane) during stepwise addition of HCl: Synthesis, characterization and crystal structure of trans-[RhCl 2 (PTA)(PTAH)] Piotr Smolen ´ ski a,b,⇑ , Alexander M. Kirillov b , M. Fátima C. Guedes da Silva b,c , Armando J.L. Pombeiro b,⇑ a Faculty of Chemistry, University of Wrocław, 50-383, ul. F. Joliot-Curie14, Wroclaw, Poland b Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal c Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Av. do Campo Grande, 376, 1749-024 Lisbon, Portugal article info Article history: Received 13 August 2011 Accepted 2 September 2011 Available online 16 September 2011 Keywords: Rhodium(I) 1,3,5-Triaza-7-phosphaadamantane Water-soluble complexes Phosphine ligands Crystal structure NMR spectroscopy abstract The new aqua-soluble rhodium(I) complex trans-[RhCl 2 (PTA)(PTAH)] (1) {PTAH = N-protonated form of 1,3,5-triaza-7-phosphaadamantane (PTA)} has been synthesized via the reaction of trans- [RhCl(CO)(PTA) 2 ] with aqueous HCl or N-chlorosuccinimide, or by the treatment of RhCl 3 with PTA. Com- pound 1 has been characterized by IR, 1 H and 31 P{H} NMR spectroscopies, ESI–MS(+), elemental and sin- gle crystal X-ray diffraction analyses, the latter showing a square planar {RhCl 2 P 2 } geometry. Besides, the stepwise addition of diluted HCl to an aqueous solution of trans-[RhCl(CO)(PTA) 2 ] has been monitored by 31 P{ 1 H} NMR and ESI–MS(+) techniques, allowing to detect a number of intermediate Rh(I) species. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction In recent years, the application of the aminophosphine 1,3,5-tri- aza-7-phosphaadamantane (PTA) and its derivatives [1] as water- soluble ligands for the synthesis of different metal complexes be- came a rapidly growing area of research, since many coordination compounds of PTA show interesting catalytic [1,2], biological [1,3] or photoluminescent properties [1,4]. In particular, Rh and Ru com- plexes with PTA and its N-protonated or N-alkylated derivatives are known as efficient and versatile catalysts for the hydrogena- tion, hydroformylation and isomerization of unsaturated sub- strates in aqueous systems [5]. A noteworthy feature of PTA consists in the selective proton- ation of one of its nitrogen atoms, rather than the phosphorus cen- tre, giving a cationic [PTAH] + ligand (Scheme 1) in acidic aqueous solutions (pH < 6.5) [1]. The protonation of PTA moieties coordi- nated to a metal centre can also affect the electronic properties of other ligands [5a,6], thus often improving e.g. catalytic [5a] or bio- logical [3c] activities of metal complexes. However, in contrast to the rich family of compounds bearing neutral PTA ligands, com- plexes with [PTAH] + are less common [7,8], whereas the derivatives containing both PTA/PTAH moieties are limited to single examples [5a,6a,8a,e]. In pursuit of our general project focused on the synthesis of new coordination compounds bearing PTA and derived ligands [6a,c,9], we have directed our attention to the Vaska-type complex trans- [RhCl(CO)(PTA) 2 ](A) that was previously reported and applied in catalysis by one of us [10]. Aiming at the synthesis of a related compound with a protonated PTAH moiety, we have now studied the reactivity of A towards the stepwise addition of hydrochloric acid. Hence, we report herein (i) the synthesis, characterization and X-ray crystal structure of the new rhodium(I) complex trans- [RhCl 2 (PTA)(PTAH)] (1), and (ii) the ESI–MS(+) and 31 P{ 1 H} NMR monitoring of the interconversion of A into 1, which allowed to de- tect a few intermediate Rh(I) species. 2. Experimental 2.1. General All syntheses were performed at room temperature (r.t., ca. 20 °C) under an inert atmosphere of dry oxygen-free dinitrogen, using standard Schlenk techniques. Solvents were dried and distilled prior to use. RhCl 3 Á3H 2 O, N-chlorosuccinimide (1-chloropyrroli- dine-2,5-dione) were used as received (Aldrich), while 1,3,5-tri- aza-7-phosphaadamantane (PTA) [11] and trans-[RhCl(CO)(PTA) 2 ] 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.09.002 ⇑ Corresponding authors at: Faculty of Chemistry, University of Wrocław, 50-383, ul. F. Joliot-Curie14, Wroclaw, Poland (P. Smolen ´ ski). E-mail addresses: piotr.smolenski@chem.uni.wroc.pl (P. Smolen ´ ski), pombeiro@ist.utl.pt (A.J.L. Pombeiro). Inorganica Chimica Acta 378 (2011) 342–346 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica