The First Crystal and Molecular Structure of asyn-Acetato-Bridged Dinuclear Cyclometallated Complex [Pd{2,3,4-(MeO)3C6HC(H)=NCH2CH2OH}(μ-OAc)]2

Abstract

Treatment of the Schiff base ligands 2,3,4-(MeO) 3 C 6 H 2 C(H)= NR (R = CH 2 CH 2 OH, 1; R = Me, 17; R = Et, 18; R = Pr, 19; R = tBu, 20) with palladium(II) acetate in toluene gave the dinuclear cyclometallated complexes [Pd{2,3,4-(Me-O) 3 C 6 HC(H)=NR}(µ-O 2 CMe)] 2 (R = CH 2 CH 2 OH, 2; R = Me, 21; R = Et, 22; R = Pr, 23; R = tBu, 24), with the ligand bonded to the palladium atom through the imine nitrogen and the C6 carbon atoms. The 1 H and 13 C{ 1 H} NMR spectra of the complexes showed the presence of the anti and syn isomers in solution. The anti/syn ratio varies with the solvent and the nature of the imine nitrogen substituent R. Complex 24 with the bulky tBu group showed a 28:1 ratio in chloroform whilst the less bulky substituted complexes showed lower ratios. The X-ray crystal structure of the syn isomer of complex 2 is described. Reaction of the acetato-bridged complex 2 with PPh 3 gave the mononuclear complex 4, in a bridge-splitting reaction. Reaction of 2 with the diphosphanes dppm, dppp and dppb in a 1:1 molar ratio gave the dinuclear cyclometallated complexes 5, 6 and 7, respectively. Treatment of 2 with an aqueous solution of sodium chloride gave the chlorobridged complex 3. Treatment of the cyclometallated chloro-

Activation of C–H and C–Br bonds in cyclopalladation reactions of Schiff base ligands: Influence of the benzylidene ring substituents

“…The Pd-C bond lengths of 2.047(6) and 2.034(5) Å for 3a and 3b, respectively, are similar to those found in related cyclometallated complexes [30,33] with C trans to phosphorus but longer than Pd-C distances found in cyclometalated complexes with carbon trans to nitrogen or chlorine, supporting a phosphine ligand in the trans position.…”

Cyclometallated imine complexes with oxygen-functionalised side-chains: Effect of the nature of the functional group, chain length and charge on coordination of the oxygen

“…The equivalence of the acetate groups means either that the complex is an anti-isomer rather than syn or that the isomers are exchanging fast on the NMR timescale. Fast exchange, at room temperature, of syn and anti isomers of a cyclometallated oxazoline has been reported by Balavoine et al [20] though for other cyclometallated complexes exchange was slow on the NMR timescale and both isomers were observed [13,21].…”

“…In addition, the majority of tridentate cyclometallated complexes are symmetrical pincer ligands with the carbon as the central atom, PCP and NCN ligands being particularly common [2,4]. Unsymmetrical C,N-bidentate cyclometallated ligands with pendant donor atoms can in principle act as tridentate ligands, examples with C,N,N [5][6][7], C,N,S [8,9], and C,N,O [10][11][12][13][14][15] ligands have all been reported, some specific examples are shown in Fig. 1 [6,8,10].…”

“…As regards C,N cyclopalladated complexes with pendant O-donor ligands there are examples of alcohol [10,13,14], ether [12], amide [15] and hydrazone and related groups [16] but so far there has been little systematic attempt to evaluate the effect of length of the tether and nature of the functional group on coordination of the oxygen functionality. The aim of this work is to assess what factors control coordination of an ether or alcohol ligand tethered to a C,N-chelate and to establish whether this interaction can be hemilabile [17].…”

Cyclopalladation of 2-tert-butyl-4,4-dimethyl-2-oxazoline in solution and on silica gel

“…We suggest that complex 4 exists in CDCl 3 and C 6 D 6 solution as two geometrical isomers, syn and anti (Scheme 3). The existence of two geometrical isomers has been reported for a number of cyclopalladated complexes [19,[23][24][25], including complexes 2 and 3 [11].…”