Crystal structure of the new palladium complexes tetrakis(1,3-dimethylimidazolium-2-ylidene)palladium(II) hexadecacarbonyltetrarhenium diethyl ether disolvate and octa-μ-carbonyl-dicarbonyltetrakis(triphenylphosphane)palladiumdirhenium (unknown solvate)

The investigation of the coordination chemistry of heterometallic transition-metal complexes of palladium (Pd) and rhenium (Re) led to the isolation and crystallographic characterization of tetrakis(1,3-dimethylimidazolium-2-ylidene)palladium(II) hexadecacarbonyltetrarhenium diethyl ether disolvate, [Pd(C5H8N2)4][Re4(CO)16]·2C4H10O or [Pd(IMe)4][Re4(CO)16]·2C4H10O, (1), and dicarbonylocta-μ-carbonyl-tetrakis(triphenylphosphane)palladiumdirhenium, [Pd4Re2(C18H15P)4(CO)10] or Pd4Re2(PPh3)4(μ-CO)8(CO)2, (2), from the reaction of Pd(PPh3)4 with 1,3-dimethylimidazolium-2-carboxylate and Re2(CO)10 in a toluene–acetonitrile mixture.


Figure 3
A view of the packing of compound 1.

Figure 1
Displacement ellipsoid plot of Pd(IMe) 4 Re 4 (CO) 16 Á2C 4 H 10 O (1), drawn at the 30% probability level. All hydrogen atoms and solvent molecules are omitted for clarity. many carbonyl-OÁ Á ÁH 3 C and carbonyl-OÁ Á ÁHC intermolecular contacts (Table 1) are present. The diethyl ether molecule resides in voids between four adjacent cations and anions featuring an OÁ Á ÁHC contact (2.32 Å ) with one of the carbenes at the palladium atom. Nostacking is observed in structure 2, but several weak C-HÁ Á Á and C-HÁ Á ÁOC contacts ( Fig. 4 and Table 2) are present. The axial CO groups of the Re(CO) 5 fragments point towards voids filled with an unidentified solvent (Fig. 5).

Database survey
A search for related structures of palladium cations in the Cambridge Structural Database (CSD Version 5.42, update of November 2020; Groom et al., 2016) resulted in 27 hits. Of the structures found, the closest structures considering the connectivity of the atoms are tetrakis(N-methylimidazolin-2ylidene)palladium(II) diiodide (JOKCIV; Fehlhammer et al., 1992) and bis[methylenebis(3-methylimidazol-2-ylidene)]palladium(II) diiodide dimethylsulfoxide solvate (REFQID; Heckenroth et al., 2006). The cation in 1 is the first structurally characterized palladium complex ion containing four NHC ligands with substituents at the 1,3 positions of the imidazole ring. There are a number of compounds containing the tetranuclear [Re 4 (CO) 16 ] 2À anion, which is also found in the compound reported here. A search of the CSD found two closely related cluster compounds, viz. bis(tetraethylammonium) hexadecacarbonyl-tetrarhenium (EAMCRE; Ciani et al., 1978) and bis(tetra-n-butylammonium)hexadecacarbonyltetrarhenium (BATCRE10; Churchill & Bau, 1968). The palladium-rhenium carbonyl cluster in 2 has not been structurally characterized previously.

Figure 4
A view of the packing of compound 2. Table 2 Hydrogen-bond geometry (Å , ) for 2.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.95 Å (sp 2 ), 0.98 Å (methyl) and 0.99 Å (methylene), with common isotropic temperature factors for all hydrogen atoms of the aromatic rings and methyl groups. SADI restraints on bond lengths and DELU restraints on anisotropic thermal parameters were used to model the disordered carbene ligand and diethyl ether molecule over two positions. For the refinement of 2, four reflections (100, 010, 200, 021) were omitted because they showed a significantly lower intensity than calculated, most probably caused by obstruction from the beam stop. The residual electron density in 2 was difficult to model and therefore, the SQUEEZE routine (Spek, 2015) in PLATON (Spek, 2020) was used to remove the contribution of the electron density in the solvent region from the intensity data and the solvent-free model was employed for the final refinement. The cavity with a volume of ca 311 Å 3 contains approximately 98 electrons. For both structures, data collection: APEX2 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Octa-µ-carbonyl-dicarbonyltetrakis(triphenylphosphane)palladiumdirhenium (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.