PAPER www.rsc.org/dalton | Dalton Transactions Sodium complexes containing 2-iminopyrrolyl ligands: the influence of steric hindrance in the formation of coordination polymers† Clara S. B. Gomes, D. Suresh, Pedro T. Gomes,* Luis F. Veiros, M. Teresa Duarte, Teresa G. Nunes and M. Conceic ¸˜ ao Oliveira Received 7th April 2009, Accepted 28th September 2009 First published as an Advance Article on the web 10th November 2009 DOI: 10.1039/b905948b Iminopyrrolyl complexes of sodium were prepared from the reaction of 2-arylformiminopyrrole ligand precursors (aryl = C 6 H 5 (I); 2,6-Me 2 C 6 H 3 (II); 2,4,6-Me 3 C 6 H 2 (III); 2,6- i Pr 2 C 6 H 3 (IV)) with one equivalent of sodium hydride. The resulting corresponding compounds 1–4,[{Na(m 2 :k 2 N,N¢- iminopyrrolyl)} 2n (OEt 2 ) 2x ](n ≥ 1; x = 0 or 1), were obtained in moderate to high yields and were characterised by NMR spectroscopy, high resolution mass spectrometry and X-ray diffraction, when suitable crystals were obtained. The X-ray structure of compound 1 (n ≫ 1; x = 0) reveals the formation of a coordination polymer with repeating units consisting of dimers that contain two iminopyrrolyl ligands chelating two sodium atoms, where both pyrrolyl rings exhibit bridging s + s coordination to the Na atoms within the dimer; the self-assembling of the polymer is established by additional p-bonds (h 5 -coordination) of each of the pyrrolyl rings to the sodium atoms of the adjacent dimer units. Conversely, the structure of complex D IV (n = x = 1) shows it as one of such dimers capped by two diethyl ether molecules, each coordinated to the sodium atoms (n = 2; x = 1). DFT calculations indicate that the differences between the structures of 1–4 arise from the increasing bulkiness imposed by the corresponding substituents of the iminic aryl groups. Introduction Bidentate 2-iminopyrrole ligand precursors (Chart 1, A) are easily prepared by the condensation of 2-formylpyrrole with a variety of aliphatic or aromatic amines. In recent years, these compounds have attracted considerable attention in the areas of organometallic and coordination chemistry, and several classes of transition metal complexes containing bidentate iminopyrrolyl ligands (Chart 1, B) have been synthesised, being mainly used as polymerisation catalysts. 1,2 This interest has arisen from the high flexibility of their design, making possible the introduction Chart 1 2-Iminopyrrole (A) and 2-iminopyrrolyl (B) derivatives. Centro de Qu´ ımica Estrutural, Departamento de Engenharia Qu´ ımica e Biol´ ogica, Instituto Superior T´ ecnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. E-mail: pedro.t.gomes@ist.utl.pt; Fax: +351 218419612; Tel: +351 218419612 † Electronic supplementary information (ESI) available: Figures with rep- resentations of the asymmetric unit of ligand precursor I in polymorphic form I_A, NMR and high resolution mass spectra of compounds 1–4 and 4*, optimised DFT structures, and the corresponding tables of selected bond distances and angles, and atomic coordinates. CCDC reference numbers 727070–727074. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b905948b of several kinds of steric and electronic features on the ligand, as required in polymerisation catalysis. Despite this current interest in the research and synthetic applications of iminopyrrolyl ligands, the first examples of homoleptic metal complexes of Co(II), Ni(II), Pd(II), Cu(II) and Zn(II) containing these kind of ligands, although only with alkylimino groups, were described in the 1960s. 3 Our group and other authors have been interested in the chemistry of arylamino derivatives of these ligands, having recently reported the synthesis and characterisation of several homoleptic complexes of Cr(II) and Cr(III), 4,5 Co(II), 6,7 Ni(II) 7,8,9 and Zn(II). 10,11 Group 4 7,12-18 and rare-earth 19,20 metal complexes containing iminopyrrolyl ligands have been particularly studied, in part due to their interest as olefin polymerisation catalysts. The syntheses of these complexes are based on the depro- tonation of iminopyrrole ligand precursors with a strong base, most usually Li n Bu or NaH, and further reaction with the corresponding transition- or rare-earth metal salts. The interme- diate alkali-metal iminopyrrolyl complexes are generally prepared and employed in situ and, for this reason, these species have rarely been isolated from solution 8,9 and poorly characterised in the solid state, particularly in what concerns their molecular structure. Conversely, despite the coordination of the simple pyrrolyl ligand to metals which has been extensively studied and its typical coordination modes characterised (Chart 2), 21 only a few examples involving this ligand and sodium are reported. Of particular significance to this work, and among other cases of pyrrolyl mixed p- and s-coordination to sodium, 22,23 is the solid state structure of sodium 2,3,4,5-tetramethylpyrrolyl that was reported as polymeric, [Na(NC 4 Me 4 )] n , the catena-(m 3 -h 5 ,s 2 - 2,3,4,5-tetramethyl-1-sodiopyrrole-N,N), consisting of a double chain with alternating sodium and nitrogen atoms, in which each 736 | Dalton Trans., 2010, 39, 736–748 This journal is © The Royal Society of Chemistry 2010