Functionalised dien ligands of the type (ArNHCH 2 CH 2 ) 2 NR [R = Me, (2-C 5 H 4 N)CH 2 ] and their complexes with iron and cobalt halides Christopher J. Davies, Stephen J. Hilton, Gregory A. Solan * , Wesley Stannard, John Fawcett Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK Received 24 April 2005; accepted 3 June 2005 Available online 19 July 2005 Abstract The alkylation of (ArHNCH 2 CH 2 ) 2 NH with RX [RX = MeI, (2-C 5 H 4 N)CH 2 Cl] under basic conditions gives (ArHNCH 2 CH 2 ) 2 - NMe (Ar = 2,6-Me 2 C 6 H 3 L1a, 2,4-Me 2 C 6 H 3 L1b) and (ArHNCH 2 CH 2 ) 2 {(2-C 5 H 4 N)CH 2 }N (Ar = 2,4,6-Me 3 C 6 H 2 L2a, 2,4- Me 2 C 6 H 3 L2b) in moderate yield, respectively. Alternatively, L1a and L1b can be accessed by the arylation (with Ar–Br) of (H 2 NCH 2 CH 2 ) 2 NMe in the presence of a catalytic quantity of Pd 2 (dba) 3 . Treatment of L1 with CoCl 2 in n-BuOH gave high-spin [{(ArHNCH 2 CH 2 ) 2 NMe}CoCl 2 ] (Ar = 2,6-Me 2 C 6 H 3 1a, 2,4-Me 2 C 6 H 3 1b) in good yield; no reaction occurred with FeCl 2 . The molecular structure of 1a reveals a distorted trigonal bipyramidal geometry with the L1a adopting a mer-configuration. Reaction of L2 with MCl 2 affords the cobalt and iron complexes, [{ArNHCH 2 CH 2 } 2 {(2-C 5 H 4 N)CH 2 }NMCl 2 ] (M = Co, Ar = 2,4,6- Me 3 C 6 H 2 2a, 2,4-Me 2 C 6 H 3 2b; M = Fe, Ar = 2,4,6-Me 3 C 6 H 2 3a, 2,4-Me 2 C 6 H 3 3b); the octahedral frameworks in 2a and 3a are found to be considerably distorted with one of the two M-N(mesityl-substituted) distances noticeably elongated [M-N 2.597(4)– 2.795(2) A ˚ ]; no such inequivalence is observed in solution at room temperature. On activation with methylaluminoxane, complexes 1a and 1b display some activity for the oligomerisation of ethylene. Ó 2005 Published by Elsevier Ltd. Keywords: Iron; Cobalt; Tridentate; Tetradentate; Nitrogen donor; Aryl-substituted 1. Introduction Dianionic ligands derived from functionalised diethy- lenetriamines (dien) have been the subject of consider- able interest in recent years due, in part, to the ability of the tridentate diamido unit to act as an inert spectator ligand for main group [1] and transition metals [2–8] during a variety of chemical transformations. The ame- nability of the dien manifold towards structural varia- tion and, in particular, towards the incorporation of steric bulk has allowed access to a wide range of substi- tuted dien compounds of the type, R 2 -dien (R = silyl [2], aryl [3]) and R 0 R 2 -dien (R 0 = R = silyl [2,4];R 0 = alkyl, R = silyl [5]; R 0 = vinyl, R = alkyl [6]; R 0 = alkyl, R = aryl [7];R 0 = picolyl, R = silyl [8])(Fig. 1). In many cases, ligand synthesis necessitates firstly the introduc- tion of two R groups to the terminal nitrogen atoms in dien to give R 2 -dien and then, in a second step, addi- tion of R 0 group at the central secondary amine to afford R 0 R 2 -dien. Recently, we have been interested in employing the functionalised dien ligands as neutral supports for late transition metals and have prepared a series of 0277-5387/$ - see front matter Ó 2005 Published by Elsevier Ltd. doi:10.1016/j.poly.2005.06.005 * Corresponding author. Tel.: +44 116 252 2096; fax: +44 116 252 3789. E-mail addresses: gas8@leicester.ac.uk, gas8@le.ac.uk (G.A. So- lan). www.elsevier.com/locate/poly Polyhedron 24 (2005) 2017–2026