Abstract
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 tetra-kis-(1,3-di-methyl-imidazolium-2-yl-idene)palladium(II) hexa-deca-carbonyl-tetra-rhenium diethyl ether disolvate, [Pd(C5H8N2)4][Re4(CO)16]·2C4H10O or [Pd(IMe)4][Re4(CO)16]·2C4H10O, (1), and octa-μ-carbonyl-di-carbonyl-tetra-kis-(tri-phenyl-phosphane)palladium-dirhenium, [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-di-methyl-imidazolium-2-carboxyl-ate and Re2(CO)10 in a toluene-aceto-nitrile mixture. In complex 1 the Re-Re bond lengths [2.9767 (3)-3.0133 (2) Å] are close to double the covalent Re radii (1.51 Å). The palladium-rhenium carbonyl cluster 2 has not been structurally characterized previously; the Pd-Re bond lengths [2.7582 (2)-2.7796 (2) Å] are about 0.1 Å shorter than the sum of the covalent Pd and Re radii (1.39+1.51 = 2.90 Å). One carbene ligand and a diethyl ether mol-ecule are disordered over two positions with occupancy ratios of 0.5:0.5 and 0.625 (15):0.375 (15) in 1. An unidentified solvent is present in compound 2. The given chemical formula and other crystal data do not take into account the unknown solvent mol-ecule(s). The SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18] in PLATON 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 Å3 contains approximately 98 electrons.
Highlights
The investigation of the coordination chemistry of heterometallic transitionmetal 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
In complex 1 the Re—Re bond lengths [2.9767 (3)–3.0133 (2) A ] are close to double the covalent Re radii (1.51 A )
One carbene ligand and a diethyl ether molecule are disordered over two positions with occupancy ratios of 0.5:0.5 and 0.625 (15):0.375 (15) in 1
Summary
Bimetallic catalysts comprising palladium (Pd) and rhenium (Re) have important applications in alkane reforming, industrial chemical production, hydrodechlorination and biomass conversion (Thompson & Lamb, 2016; Bonarowska et al, 1999; Malinowski et al, 1998; Juszczyk & Karpinski, 2001). Heterometallic Pd–Re clusters are suitable precursors for such a catalytic system. We found that the reaction of Pd(PPh3) with 1,3-dimethylimidazolium-2-carboxylate and Re2(CO) in a toluene–acetonitrile mixture produces a mixture of two compounds: [Pd(IMe)4][Re4(CO)16]Á2C4H10O (1) and Pd4Re2(PPh3)4(-CO)8(CO) (2) where IMe is 1,3-dimethylimidazolium-2-ylidene. Triphenylphosphine oxide and the known complex Re2(CO)8(PPh3) (Adams et al, 2013) were isolated from the reaction mixture
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