Cyanide as a versatile Lewis base ligand at a dinitrogen-binding iron(II) centre: mono- and heteronuclear adducts Sı ´lvia S.P.R. Almeida a , M. Fa ´tima C. Guedes da Silva a,b , Lucjan B. Jerzykiewicz c , Piotr Sobota c , Armando J.L. Pombeiro a, * a Centro de Quı ´mica Estrutural, Complexo I, Instituto Superior Te ´cnico, Av. Rovisco pais, 1049-001 Lisbon, Portugal b Universidade Luso ´fona de Humanidades e Tecnologias, Campo Grande, 376, 1749-024 Lisbon, Portugal c Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland Received 1 April 2003; accepted 5 April 2003 Dedicated to Professor Joa ¯o J.R. Frau ´sto da Silva in recognition of his achievements. Abstract The ligated cyanide in trans -[FeH(CN)(dppe) 2 ] is activated towards aroylation, alkylation and addition of various transition metal Lewis acids, in particular [WCl 4 (PPh 3 ) 2 ], [ReOCl 3 (PPh 3 ) 2 ], [PdCl 2 (PPh 3 ) 2 ] and [PtCl(Ph)(PPh 3 ) 2 ], to give, in the former case, mononuclear isocyanide complexes and, in the latter case, heteronuclear adducts with bridging cyanide. Their syntheses and spectroscopic characterisation are presented, as well as results of the X-ray diffraction analyses of a trinuclear complex with the {Fe  /C  /N /W  /N  /C  /Fe } unit and of the parent cyano trans- [FeH(CN)(dppe) 2 ] complex. The cyanide bridge allows the electronic communication between the metal centres as indicated by a cyclic voltammetric study. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Cyanide; Bridging cyanide; Isocyanide; Transition metal Lewis acid; Heteronuclear complexes 1. Introduction The coordination chemistry of cyanide is a matter of widespread interest in various fields of chemistry and biochemistry, its origins remitting to about three cen- turies ago since the discovery of Prussian Blue, possibly the oldest known coordination compound. A number of binding modes of cyanide are known (the most common being the terminal C-bound and the terminal C,N-bridging ones), conferring a high synthetic versatility to this ligand namely for the preparation of a wide variety of types of complexes [1] with relevance, e.g. in organometallic and inorganic chemistries, mate- rial and medicinal sciences. Cyano-bridged mixed va- lence complexes are within those which are attracting a high current interest in view of their potential use, e.g. in molecular electronics, molecular magnetism and electro- chromism. From a biological point of view, it is noteworthy to mention that aqueous cyanide is a known substrate of nitrogenase [2] and iron-cyanide complexes have been recognised in active sites of iron-only and iron /nickel hydrogenases [3]. Within our continuous interest on the investigation of the activation, by dinitrogen-binding metal sites, of nitrogenase substrates, such as nitriles [4  /8], cyana- mides [9  /12], isocyanides [13 /24], alkynes and alkyne- derived species [21 /32], we have also been studying cyanide in particular at some Re I [16,33  /36] or Fe II [17] phosphinic centres and its activation towards electro- philes. Hence, reaction of [NBu 4 ][trans -Re(CN) 2 (dppe) 2 ] with a protic acid (HBF 4 , [Et 3 NH][BPh 4 ], CH 3 COOH), added in stoichiometric amount, gives, on protonation of one of the cyano-ligands, the hydrogen isocyanide * Corresponding author. Tel.:  /351-2184 19237; fax:  /351-2184 64455/7. E-mail address: pombeiro@ist.utl.pt (A.J.L. Pombeiro). Inorganica Chimica Acta 356 (2003) 259  /266 www.elsevier.com/locate/ica 0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0020-1693(03)00249-4