A ‘2+2’ complex of trans-[ReO 2 ] + with isocyanide and triphenylphosphine Xandri Schoultz, Thomas I.A. Gerber ⁎, Richard Betz, Eric C. Hosten Department of Chemistry, Nelson Mandela Metropolitan University, 6031 Port Elizabeth, South Africa abstract article info Article history: Received 11 June 2014 Received in revised form 24 July 2014 Accepted 31 July 2014 Available online 1 August 2014 Keywords: Rhenium(V) Trans-dioxo Isocyanide Crystal structure The reaction of cis-[ReO 2 I(PPh 3 ) 2 ] with a twofold molar excess of cyclohexyl isocyanide in ethanol led to the iso- lation of the complex salt [ReO 2 (CNCy) 2 (PPh 3 ) 2 ](ReO 4 )(1). The cation contains the trans-[ReO 2 ] + core with a trans disposition of the isocyanides and the bulky triphenylphosphine ligands. Compound 1 was characterized by FTIR and UV–Vis spectroscopy, elemental analysis and single crystal X-ray diffraction. © 2014 Elsevier B.V. All rights reserved. Rhenium complexes with isocyanide as a ligand have received con- siderable attention in the literature [1–6]. This is mainly due to the ap- plication of [ 99m Tc(MIBI) 6 ] + (MIBI = 2-methoxyisobutyl isocyanide) as a cardiac imaging agent in nuclear medicine [7]. Isocyanides are π-acceptor ligands that stabilize low and medium oxidation states, and examples of high-valent complexes are rare. Although rhenium(I) and (III) complexes of isonitriles have been well studied, not many research efforts have focussed on the electron-poor + V oxidation state [1–6]. The only well characterized oxorhenium(V) isocyanide complexes are [ReOCl 3 (L) 2 ] (L = isocyanide), synthesized from [ReOCl 3 (SMe 2 )(OPPh 3 )], and its further reaction in wet acetone to form the oxo-bridged dimer (μ-O)[ReOCl 2 (L) 2 ] 2 [8,9]. We have isolated the trans-dioxo rhenium(V) complex salt trans- [ReO 2 (CNCy) 2 (PPh 3 ) 2 ](ReO 4 )(1; Cy = cyclohexyl) from the reaction of a twofold molar excess of cyclohexyl isocyanide (CNCy) with cis- [Re V O 2 I(PPh 3 ) 2 ] in ethanol [10]. This is the first reported dioxo isocyanide complex of rhenium(V), and it is unusual since it contains the good π- acceptor ligands PPh 3 and CNCy coordinated to the electron-deficient and hard ReO 2 + core. The trans-[ReO 2 ] + core is common for rhenium(V), and it is normally formed when ligands which are only σ-donors or poor π-donors are coordinated to the metal [11–14]. It would seem that the small cone angle of the isocyanide is essential for the stabilization of [ReO 2 (CNCy) 2 (PPh 3 ) 2 ] + if used in conjunction with triphenylphosphine, with a large cone angle. This is supported by the fact the tert-butyl equiv- alent, i.e. [ReO 2 (CN-t-Bu) 2 (PPh 3 ) 2 ](ReO 4 ), could not be synthesized by us. In the IR spectrum of 1 the ν(Re_O) of the trans-[ReO 2 ] + moiety ap- pears as a strong band at 793 cm -1 , with ν(Re_O) of the [ReO 4 ] - counter-ion at 904 cm -1 . A sharp peak of medium intensity at 2080 cm -1 is assigned to ν(C`N) of the isocyanide ligands. The electronic absorption spectrum in DMF solution exhibits a band a 438 nm (ε = 550 M -1 cm -1 ), which is assigned to the (d xy ) 2 → (d xy ) 1 (d xz ,d yz ) 1 transition, as was reported earlier for trans-dioxorhenium(V) compounds [15,16]. Fig. 1 shows an ORTEP illustration of 1, which is an octahedral trans- dioxorhenium(V) complex containing two triphenylphosphine and two cyclohexyl isocyanide ligands [17]. The crystal structure consists of two in- dependent cations per unit cell with the associated perrhenate anions. Each [ReO 2 (CNCy) 2 (PPh 3 ) 2 ] + cation has a crystallographic center of sym- metry, and there are no bonding interactions between the cation and anion. The two isonitrile ligands are coordinated trans to each other and cis to the oxo groups, and lie almost perpendicular to the rhenium-oxo bonds [O(1)\Re\C(1) = 89.2(3)°; O(1)\Re\C(2) = 89.5(4)°]. The trans angles around the metal are linear [O(1)\Re\O(2) = 178.7(3)°; P(1)\Re\P(2) = 179.04(7)°; C(1)\Re\C(2) = 178.6(5)°]. The average Re_O distance is 1.771(6) Å, which falls in the range observed for trans- [ReO 2 ] + complexes [11–14]. The Re\C bond distances [average of 2.10(2) Å] correspond well with those in other isocyanide monooxorhenium(V) complexes [average of 2.08(2) Å], and suggest that π-back bonding from rhenium(V) to the isonitriles is not extensive [8,9]. The average of the C(1)\N(1) and C(2)\N(2) bond lengths is 1.14(2) Å, and the average C\N\C bond angle of 171(2)° indicates insignificant interligand repulsion between the cyclohexyl and phenyl rings of PPh 3 . Appendix A. Supplementary material Supplementary data for 1 (CCDC 1007690) are available from CCDC, 12 Union Road, Cambridge CB2 IEZ, UK on request. These data can be Inorganic Chemistry Communications 47 (2014) 162–163 ⁎ Corresponding author. E-mail address: Thomas.gerber@nmmu.ac.za (T.I.A. Gerber). http://dx.doi.org/10.1016/j.inoche.2014.07.040 1387-7003/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche