Reactions between isocyanides and a binuclear nickel(II) phosphine complex linked by a bridged bis(cyclopentadienyl) ligand. X-ray molecular structure of [(CN t Bu)(PPh 3 )Ni {l-(g-C 5 H 4 )CMe 2 (g-C 5 H 4 )}Ni(PPh 3 )(CN t Bu)][PF 6 ] 2 Alejandro F.G. Ribeiro a , Pedro T. Gomes a, * , Alberto R. Dias a , Joa ˜o L. Ferreira da Silva a , M. Teresa Duarte a , Rui T. Henriques b , Cristina Freire c a Centro de Quı ´mica Estrutural, Departamento de Engenharia Quı ´mica, Instituto Superior Te ´cnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b Instituto de Telecomunicac ¸o ˜ es – Polo de Lisboa and Departamento de Engenharia Quı ´mica, Instituto Superior Te ´cnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal c REQUIMTE/Departamento de Quı ´mica, Faculdade de Cie ˆncias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal Received 20 April 2004; accepted 28 June 2004 Available online 11 September 2004 Dedicated to Professor Malcolm L.H. Green Abstract The reaction between the binuclear dicationic compound [(PPh 3 ) 2 Ni{l-(g-C 5 H 4 )CMe 2 (g-C 5 H 4 )}Ni(PPh 3 ) 2 ][PF 6 ] 2 (1) and either 2 or 4 equivalents of isocyanides leads to the substitution of a single PPh 3 ligand per nickel atom. The new binuclear compounds [(CNR)(PPh 3 )Ni{l-(g-C 5 H 4 )CMe 2 (g-C 5 H 4 )}Ni(PPh 3 )(CNR)][PF 6 ] 2 (R = S-()-CH(Ph)Me (2), cyclohexyl (3), tert-butyl (4) and mesityl (5)) were prepared in almost quantitative yields and were fully characterised by elemental analysis, FT-IR and NMR spec- troscopies. In the X-ray crystal structure of 4 two crystallographically inequivalent CpNi(PPh 3 )(CN t Bu) moieties are observed, where the Ni(PPh 3 )(CN t Bu) fragments are positioned on the C 5 H 4 faces of the bridging ligand to minimise inter-ring repulsions. Addition of an excess of S-()-CNCH(Ph)Me to 1 results in the catalytic polymerisation of the isocyanide, yielding polymers of increasing molecular weights when the ratio [CNR] o /[Ni] o is increased, consistent with non-living polymerisation. The molecular weights of the poly(S-()-1-phenylethyl isocyanide) (6) obtained with complex 1 are higher than those obtained with the related mononuclear complex [Ni(g-C 5 H 5 )(PPh 3 ) 2 ]PF 6 (8), which suggests an initiation step involving migratory insertion of isocyanide into the Ni–cyclopentadienyl bonds. An EPR spectrum of the reaction mixture acquired at 77 K, after 10 min of polymerisation at 20 °C, reveals the existence of two pentacoordinated Ni(I) 3d 9 chain propagating species with trigonal bipyramidal geometry (d z 2 ground state). One of the Ni species contains two PPh 3 ligands occupying both axial positions of an axially distorted trigonal bipyramid, whereas the other species contains an axially coordinated PPh 3 and either a PPh 3 coordinated in the equatorial plane or dissociated from the nickel atom. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Binuclear compounds; Isocyanides; Nickel; Polymerisation; Ring-coupled bis-cyclopentadienyl ligand; X-ray molecular structure 1. Introduction Despite the great number of NiCp (Cp = g-C 5 H 5 ) compounds reported in the literature, those containing isocyanide ligands (C„NR) are scarce. In the 1960s, 0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2004.06.030 * Corresponding author. Tel.: +351 218419612; fax: +351 218464455/7. E-mail address: pedro.t.gomes@ist.utl.pt (P.T. Gomes). www.elsevier.com/locate/poly Polyhedron 23 (2004) 2715–2724