A rare example of a di-cationic hydrido carbonyl tetra-nuclear cluster, [H 2 Rh 2 Pt 2 (CO) 7 (PPh 3 ) 3 ] 2+ q Brian T. Heaton a, * , Jonathan A. Iggo a , Ivan S. Podkorytov b , Vadim I. Ponomarenko c , Stanislav I. Selivanov c , Sergey P. Tunik c, * a Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool L69 7ZD, UK b S.V. Lebedev Central Synthetic Rubber Research Institute, Gapalskaya 1, St. Petersburg 198035, Russia c Department of Chemistry, St. Petersburg University, Universitetskii pr. 26, St. Petersburg 198504, Russia article info Article history: Received 28 November 2008 Received in revised form 21 March 2009 Accepted 26 March 2009 Available online 5 April 2009 This paper is dedicated to Professor Paul Pregosin, in celebration of his 65th birthday Keywords: Carbonyl clusters Hydride ligands Phosphane ligand site occupancy Structure elucidation NMR spectroscopy abstract Addition of excess CF 3 CO 2 H (HTFA) to [Rh 2 Pt 2 (CO) 7 (PPh 3 ) 3 ], I, under nitrogen results in the formation of a salt (X 2+ Y 2À ), which contains only the second example of a di-cationic carbonyl hydride tetra-nuclear cluster, [H 2 Rh 2 Pt 2 (CO) 7 (PPh 3 ) 3 ] 2+ , X 2+ , and a presently partially characterized polymetallic anion Y 2À . The di-cation X 2+ has been characterized by mass spectrometry and a variety of multinuclear NMR methods. Since there is no difference in the electron count for I and X 2+ , it is probable that both I and X 2+ adopt similar butterfly metallic frameworks with a Rh–Rh hinge; in X 2+ , there are two bridging hydrides to the same wing-tip Pt but the phosphine site occupancies on the Rh 2 Pt 2 -framework in I and X 2+ are different. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Cationic carbonyl clusters containing hydride ligands directly attached to metals become less well known as either/both: the po- sitive charge on the cluster increases, or/and the size of the cluster increases. The H-site occupancy in transition metal carbonyl clus- ters is extremely difficult to predict and, although H is often extre- mely fluxional in solution, it is often possible to obtain VT NMR data, especially for clusters which contain a NMR active nucleus (e.g. 31 P, 103 Rh), which elucidates both the H-site occupancy in the static structure and the exact pathway(s) of H-migration. For tri-nuclear carbonyl clusters, there are a number of mono- cationic homo- [1] and hetero-metallic [2] clusters containing hy- dride ligands and fewer examples of di-cationic clusters [1a,3]. They have usually been prepared by protonation of the neutral complex with acids containing a weakly coordinating anion (e.g. [CF 3 CO 2 ] À , [SO 4 ] 2À ). Early attempts [4] to protonate [M 4 (CO) 12 ] (M = Rh, Ir) with H 2 SO 4 (98%) resulted in decomposition when M = Rh but, when M = Ir, 1 H NMR suggested the formation of [H 2 Ir 4 (CO) 12 ] 2+ . This is the only example, to our knowledge, of a tetra-nuclear di-cationic carbonyl cluster containing H-bonded to the metal, although there are examples of mono-cationic ana- logues [5]. For higher nuclearity clusters, it is possible to form hydrido homo-metallic, rhodium carbonyl clusters by protonation of the corresponding anionic cluster with an acid containing weakly coor- dinating anions, but there are no reported examples of cationic high nuclearity hydride containing clusters [6]. Progressive addi- tion of acid to multi-anionic clusters allows the formation of clus- ters with an increasing number of hydrides but, even with excess acid, protonation usually stops before the formation of the neutral hydrido carbonyl cluster e.g. [H x Rh 13 (CO) 24 ] (5Àx)À (x = 1, 2, 3, 4, x – 5) [7]. However, some multi-anionic clusters, e.g. [NiRh 14 - (CO) 28 ] 4À and [NiRh 13 (CO) 25 ] 5À , cannot be protonated in this way [8]. H-site occupancies in carbonyl clusters are difficult to predict, e.g. in the closely related homo-metallic clusters, [HM 6 (CO) 15 ] À (M = Co, Rh), the H-site occupancy is very different; an interstitial hydride is found when M = Co [9] but when M = Rh the hydride occupies a terminal site on the Rh 6 -octahedron [10]. Predicting the site occupancy on protonation of hetero-metallic clusters is even more complicated because of the possibility of rearrangement 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.03.045 q This paper celebrates the 65th birthday of Paul Pregosin and the enormous contributions he has made in using/developing 1 and 2D multinuclear NMR methods in Inorganic Chemistry. * Corresponding authors. Tel.: +44 151 794 3524; fax: +44 151 794 3540 (B.T. Heaton), tel.: +7 812 4284028; fax: +7 812 4286939 (S.P. Tunik). E-mail addresses: bth@liv.ac.uk (B.T. Heaton), stunik@inbox.ru (S.P. Tunik). Inorganica Chimica Acta 363 (2010) 549–554 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica