Intermolecular hydrogen bonding in isostructural pincer complexes [OH-(t-BuPOCOPt-Bu)MCl] (M = Pd and Pt)

In the crystal structure of the isostructural title compounds [OH-(t-BuPOCOPt-Bu)PdCl] and [OH-(t-BuPOCOPt-Bu)PtCl] the M II centres are coordinated in a distorted square-planar fashion by the pincer and the chloride ligand.


Chemical context
Since their discovery by Shaw and van Koten in the 1970s (Moulton & Shaw, 1976;van Koten et al., 1978), pincer complexes have received considerable attention in organometallic chemistry and homogeneous catalysis because of their wide applicability for a broad range of stoichiometric and catalytic bond-activation reactions (e.g. Szabo & Wendt, 2014;Valdé s et al., 2018). Modification of the pincer scaffold allows for fine-tuning of the steric and electronic properties that directly influence the reactivity (Peris & Crabtree, 2018). As a consequence, a plethora of transition metal complexes that possess neutral and anionic tridentate pincer ligands with many different combinations of donor atoms have been described. Substitution of the pincer backbone with suitable polar groups provides an excellent opportunity for the introduction of anchoring sites that can be attached covalently to a heterogeneous support (Rimoldi et al., 2016). In this context, hydroxylation of the aromatic ring of a POCOP ligand is a straightforward approach and the ligand precursor phloroglucinol is a readily available compound that can be converted into the corresponding ligand using standard methodologies (Gö ttker-Schnetmann et al., 2004;Garcia-Eleno et al., 2015). This polar functionality can engage in non-covalent interactions with ubiquitous metal-halide fragments. An example for this phenomenon that includes halide-halide interactions was reported recently by Whitwood, Brammer and Perutz, who studied intermolecular halogen bonding of a series of nickel(II) fluoride complexes (Thangavadivale et al., 2018).   Table 1 Hydrogen-bond geometry (Å , ) for 1. Symmetry code: (i) x þ 1 2 ; Ày þ 1 2 ; z À 1 2 . Table 2 Hydrogen-bond geometry (Å , ) for 2. (3) 3.1874 (16) 170 (3) Symmetry code: (i) x þ 1 2 ; Ày þ 1 2 ; z À 1 2 .

Figure 2
Intermolecular hydrogen bonds (depicted as dashed lines) in complex 1. Displacement ellipsoids are drawn at the 30% probability level.

Figure 3
Perspective packing diagram of complex 1 viewed down the b axis showing the hydrogen bonds as dashed lines. Hydrogen atoms (except of OH groups) are omitted for clarity.

Figure 1
Molecular structure of complexes 1 (left) and 2 (right), with displacement ellipsoids drawn at the 30% probability level. Hydrogen atoms (except of the OH group) are omitted for clarity.
the mixture was heated at 388 K for two days, resulting in a yellow solution. Upon slow cooling, complex 1 precipitated as a pale-yellow solid, which was isolated by filtration and washed with cold toluene. Colourless crystals suitable for X-ray analysis were obtained from a saturated toluene solution at 195 K, yield: 216 mg (39%

{2,6-Bis[(di-tert-butylphosphanyl)oxy]-4-hydroxyphenyl}chloridopalladium(II) (1)
Crystal data  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

{2,6-Bis[(di-tert-butylphosphanyl)oxy]-4-hydroxyphenyl}chloridoplatinum(II) (2)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.