New j 3 -PNN 0 - and j 4 -PNN 0 O-polydentate ligands: Synthesis, coordination and structural studies Mark R.J. Elsegood, Noelia M. Sanchez-Ballester, Martin B. Smith ⇑ Department of Chemistry, Loughborough University, Loughborough, Leics LE11 3TU, UK article info Article history: Received 22 July 2011 Received in revised form 20 September 2011 Accepted 21 September 2011 Available online 1 October 2011 Keywords: Coordination modes Metallocycles P ligands Late-transition metals X-ray crystallography abstract The three-step synthesis of new mixed P/N/N 0 /O-donor ligands C 6 H 3 (OH){2-NHC(O)CH 2 N@CHC 6 H 4 PPh 2 }(4-CH 3 ) 3aHH and C 6 H 4 (OH){3-NHC(O)CH 2 N@CHC 6 H 4 PPh 2 } 3bHH, by Schiff base condensation of the 1° amines C 6 H 3 (OH){2-NHC(O)CH 2 NH 2 }(4-CH 3 ) 2a or C 6 H 4 (OH){3-NHC(O)CH 2 NH 2 } 2b with C 6 H 4 (CHO)(2-PPh 2 ) in refluxing EtOH, is described. Reaction of 1 equiv. of 3aHH or 3bHH with MCl 2 (cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) affords the j 2 -PN-chelate complexes MCl 2 (3aHH) (M = Pd 4a; M = Pt 4b) and MCl 2 (3bHH) (M = Pt 4c). The dichlorometal(II) complexes 4d and 4e, bearing instead a pen- dant 4-phenolic group, were similarly prepared (in >90% yield). Chloro-bridge cleavage of [Pd(l-Cl) (g 3 -C 3 H 5 )] 2 with 3aHH or 3bHH gave the monocationic j 2 -PN-chelate complexes [Pd(g 3 - C 3 H 5 )(3aHH)]Cl 5a or [Pd(g 3 -C 3 H 5 )(3bHH)]Cl 5b, respectively. Elimination of cod, and single CH 3 proton- ation, from Pt(CH 3 ) 2 (cod) upon reaction with 1 equiv. of 3aHH or 3bHH in C 7 H 8 at room temperature afforded the neutral complexes C 6 H 3 (OH){2-NC(O)CH 2 N@CHC 6 H 4 PPh 2 Pt(CH 3 )}(4-CH 3 ) 6a and C 6 H 4 (OH){3-NC(O)CH 2 N@CHC 6 H 4 PPh 2 Pt(CH 3 )} 6b, respectively bearing a monoanionic (3aH  or 3bH  ) j 3 -PNN 0 -tridentate ligand. Amide and phenol deprotonation were readily achieved, using KO t Bu as base, to give high yields of the j 4 -PNN 0 O-tetradentate complexes C 6 H 3 (O){2-NC(O)CH 2 N@CHC 6 H 4 PPh 2 Pd}(4- CH 3 ) 7a and C 6 H 3 (O){2-NC(O)CH 2 N@CHC 6 H 4 PPh 2 Pt}(4-CH 3 ) 7b bearing the dianionic ligand 3a 2 . All new compounds have been characterised by multinuclear NMR, FTIR, mass spectroscopy and microanaly- sis. Single crystal X-ray studies have been performed on compounds 1b1.5CH 2 Cl 2 , 3bHH0.5Et 2 O, 6bCHCl 3 and 7b0.5Et 2 O. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Organometallic and coordination complexes of tridentate and tetradentate ligands continue to attract wide interest for the diverse ligating capabilities, sensing, magnetic and luminescent properties and catalytic applications. Various donor atom combi- nations have been documented in the literature and, in many cases, contain at least one phosphorus donor centre. A range of different donor atom combinations have been reported for tridentate ligands including amongst others: P 2 B [1],P 2 C [2],P 2 Si [3],P 2 N [4],P 2 O [5], PC 2 [6], PN 2 [7], PNO [8], PNS [8c] and PS 2 [9]. Further- more, while examples of symmetric tetradentate systems are rela- tively common and include, for example, P 2 N 2 [10],O 2 N 2 [11] or S 2 N 2 [12], nonsymmetric tetradentate ligands are considerably more unusual and include P 3 C [13],P 3 Si [14],P 3 N [15], PN 3 [16], PN 2 O [17] and As 2 PN [18]. Herein we describe the synthesis of two new potentially tetradentate ligands bearing a PNN 0 O donor set combination. We demonstrate, given the correct spatial donor atom orientation, that all four donor centres can readily coordinate to a square-planar metal(II) centre. All new compounds are struc- turally supported by a combination of spectroscopic and crystallo- graphic techniques. 2. Experimental 2.1. Materials Standard Schlenk techniques were used for the synthesis of C 6 H 3 (OH){2-NHC(O)CH 2 N@CHC 6 H 4 PPh 2 }(4-CH 3 ) 3aHH and C 6 H 4 (OH){3-NHC(O)CH 2 N@CHC 6 H 4 PPh 2 } 3bHH whilst all other reac- tions were carried out in air using previously distilled solvents un- less otherwise stated. The compounds C 6 H 4 (CHO)(2-PPh 2 ) [19], MCl 2 (cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) [20] and Pt(CH 3 ) 2 (cod) [21] were all prepared according to known procedures. All other chemicals were obtained from commercial sources and used directly without further purification. 2.2. Instrumentation Infrared spectra were recorded as KBr pellets on either a Perkin– Elmer System 2000 (4000–400 cm 1 range) or a Spectrum 100S 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.09.045 ⇑ Corresponding author. Tel.: +44 0 1509 222553; fax: +44 0 1509 223925. E-mail address: m.b.smith@lboro.ac.uk (M.B. Smith). Inorganica Chimica Acta 379 (2011) 115–121 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica