Iridium–Gold Cluster Compounds: Syntheses, Structures, and an Unusual Ligand-Induced Skeletal Rearrangement

Abstract

The new iridium−gold complex Ir 4 (CO) 11 (Ph)(μ-AuPPh 3 ), 1 was obtained from the reaction of the tetrairidium anion [Ir 4 (CO) 11 (Ph)] − with [Au(PPh 3 )] [NO 3 ]. Two new iridium−gold complexes Ir 4 (CO) 10 (AuPPh 3 ) 2 , 2, and Ir 4 (CO) 11 (AuPPh 3 ) 2 , 3, were obtained from the reaction of [HIr 4 (CO) 11 ] − with [Au(PPh 3 )][NO 3 ]. Compounds 1−3 were structurally characterized by single crystal X-ray diffraction analyses. Compound 2 adds CO reversibly to form compound 3. In this process, the octahedral Ir 4 Au 2 cluster of 2 is converted into the Au(PPh 3 )-capped Ir 4 Au trigonal bipyramidal cluster found in 3. Compounds 2 and 3 have been investigated by DFT computational analyses in order to understand the metal−metal bonding and the mechanism of their interconversion by CO addition and elimination. Compound 2 adds PPh 3 to form the compound Ir 4 (CO) 10 (PPh 3 )-(AuPPh 3 ) 2 , 4, which is structurally similar to 3. Compound 4 loses CO and benzene when heated to form the compound Ir 4 (CO) 9 (μ 3 -PPhC 6 H 4 )(AuPPh 3 ) 2 , 5, which contains a triply bridging PPhC 6 H 4 ligand. ■ INTRODUCTIONApplications for iridium in catalysis continue to grow. 1 Although most catalytic applications are of a homogeneous type, 2 it has been shown that iridium clusters can serve as precursors to heterogeneous nanoscale catalysts that exhibit good activity for the hydrogenation of aromatics and olefins. 3 Years ago, Sinfelt showed that the addition of iridium to platinum greatly improved its activity for the catalytic reforming of petroleum. 4 Heterogeneous iridium−iron catalysts derived from bimetallic cluster complexes have been shown to exhibit exceptional catalytic activity for the formation of methanol from synthesis gas. 5 Recently, gold nanoparticles have been shown to exhibit significant catalytic activity for the oxidation of CO and certain olefins. 6 Combining transition metals with gold has led to interesting new bimetallic catalysts for the oxidation of hydrocarbons. 7 There have been very few reports of iridium−gold carbonyl cluster complexes, 8,9 and their catalytic activity has not yet been investigated.We have recently reported the synthesis and structural characterization of the tetrairidium anion, [Ir 4 (CO) 11 (Ph)] − . 10 [Ir 4 (CO) 11 (Ph)] − has been shown to react with Ir(CO)-(PPh 3 ) 2 Cl to form the pentairidium complex Ir 5 (CO) 12 Ph-(PPh 3 ) by halide displacement combined with the elimination of one PPh 3 ligand, Scheme 1. 10 It also reacts with [(COD)-Ir(Cl)] 2 to form a series of higher nuclearity iridium carbonyl cluster complexes containing COD and COD transformed ligands, Scheme 2. 11 We have now investigated the reaction of [Ir 4 (CO) 11 (Ph)] − with [Au(PPh 3 )][NO 3 ] and have obtained the gold− tetrairidium cluster complex Ir 4 (CO) 11 (Ph)(μ-AuPPh 3 ), 1. For comparisons, we have investigated the reaction of [HIr 4 -(CO) 11 ] − with [Au(PPh 3 )][NO 3 ] and have obtained two new iridium−gold carbonyl cluster complexes Ir 4 (CO) 10 (AuPPh 3 ) 2 , 2, and Ir 4 (CO) 11 (AuPPh 3 ) 2 ...

The Addition of Gold and Tin to Bismuth–Triiridium Carbonyl Complexes

“…In addition, compound 3 contains two SnPh 3 ligands that occupy equatorial coordination sites, one on each of the two Ir(CO) 2 groups. The Ir−Sn bond distances are similar in length, Ir3−Sn1 = 2.6415(18) Å, Ir2−Sn2 = 2.6413 (19) Å, and are similar to those found in the compounds Ir 3 (CO) 6 (SnPh 3 ) 3 -(μ-H) 3 (μ 3 -Bi) 5 and Ir 3 (CO) 6 (SnPh 3 ) 3 (μ-SnPh 2 ) 3 . 27 There is a hydride ligand bridging the Ir−Ir bond between the two tinsubstituted iridium atoms.…”

A Carbene‐Rich but Carbonyl‐Poor [Ir6(IMe)8(CO)2H14]2+ Polyhydride Cluster as a Deactivation Product from Catalytic Glycerol Dehydrogenation

“…These CO ligands must come from the decarbonylation of glyceraldehyde. The geometry of 2 is a “bow tie” or edge‐sharing bitetrahedron,6 previously unreported for Ir complexes, other than in a Au–Ir cluster 7. In spite of its high‐temperature formation,8 it retains 14 H ligands (according to 1 H NMR spectroscopic data and DFT calculations).…”

Semibridging Phenyl Ligands in Iridium–Copper and Iridium–Silver Cluster Compounds: Synthesis, Structures, and Bonding

“…9,10 Iridium is well-known for its ability to produce highly active homogeneous 11 and heterogeneous 12 catalysts. Recently, gold nanoparticles have been shown to exhibit significant activity for the catalytic oxidation of CO and for the oxidation and transformations of unsaturated hydrocarbons.…”