www.elsevier.nl/locate/jorganchem Journal of Organometallic Chemistry 588 (1999) 200 – 204 Reduction of rhenium decacarbonyl by samarium(II): synthesis and structure of the spiked triangular anion [HRe 4 (CO) 17 ] - Anna C. Hillier a , Andrea Sella a, *, Mark R.J. Elsegood b a Christopher Ingold Laboratories, Department of Chemistry, UCL, 20 Gordon Street, London, WC1H 0AJ, UK b Department of Chemistry, Bedson Building, Uniersity of Newcastle upon Tyne, Newcastle upon Tyne, NE17RU, UK Received 8 April 1999; received in revised form 23 June 1999 Abstract The reaction of [Sm(Tp Me,Me 2 )] with [Re 2 (CO) 10 ] gives [Sm(Tp Me,Me 2 )]Re(CO) 5 , which on further heating gives moderate yields of [Sm(Tp Me,Me ) 2 ] 2 [Re 4 (CO) 17 ]. Crystallization from toluene yields [Sm(Tp Me,Me ) 2 ][HRe 4 (CO) 17 ], which has been crystallographically characterized. It consists of a 64-electron cluster that adopts a spiked triangular structure with the hydride bridging two metal atoms in the equatorial plane of the cluster. A mechanism for the formation of these tetranuclear clusters is proposed. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Rhenium; Carbonyl; Samarium; Cluster; Hydride 1. Introduction The synthesis of transition metal cluster compounds is an area of wide interest to inorganic and materials chemists. A number of methods have been developed for the synthesis of large clusters. These include ligand dissociation via photolysis, thermolysis, or chemically induced ligand elimination using reagents such as trimethylamine-N -oxide, or by displacement of anionic and weakly coordinated ligands. Oligomerization of unsaturated/multiply bonded systems provides another approach to the creation of larger clusters. In some cases the use of potentially bridging ligands encourages the formation of MM bonds [1]. Redox condensation reactions initiated by electron transfer have been used to synthesize clusters either by conproportionation or through carbonyl labilization. Sodium benzophenone ketyl has been widely used for such reactions. The reaction of sodium with M 3 (CO) 12 (M =Ru, Os) at reflux in THF gives good yields of [M 6 (CO) 18 ] 2 - [2]. The reduction of Re 2 (CO) 10 with sodium in glyme-like solvents results in the efficient formation of [Re 4 (CO) 16 ] 2 - [3] and, at higher temperatures, of the carbido clusters [HRe 6 C(CO) 18 ] 3 - and [HRe 5 C- (CO) 16 ] 2 - [4]. The wide use of samarium(II) as a mild one-electron reducing agent in organic chemistry suggests that it might have a useful role as an alternative reductant in cluster synthesis. We have recently become interested in the reactivity of pyrazolylborate complexes of samar- ium and ytterbium(II) with transition metal carbonyls because of the range of reactivity observed with the carbonyl groups themselves. This ranges from the for- mation of isocarbonyls [5], the conversion of CO to formate by adventitious water [6] and the formation of salts. In this paper we report the reaction of [Sm(Tp Me,Me ) 2 ] with Re 2 (CO) 10 , in which the samariu- m(II) reagent acts as a mild redox agent capable of producing a previously unknown tetranuclear cluster. 2. Results and discussion In contrast to the reactions of Sm(Tp Me,Me ) 2 , 1, with other transition metal carbonyl such as Co 2 (CO) 8 and [CpM(CO) 3 ] 2 (M =Cr, Mo, W), which occur at room temperature, no change was observed after 2 days when a 2:1 ratio of 1 was stirred with Re 2 (CO) 10 . When heated to 80°C a slow reaction ensued, in which ap- * Corresponding author. Fax: +44-71-380-7463. E-mail address: a.sella@ucl.ac.uk (A. Sella) 0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0022-328X(99)00375-7