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 ...