Date of Award
Open Access Dissertation
Chemistry and Biochemistry
Richard D. Adams
CHAPTER 2 The reaction of Ir3(CO)9(μ3-Bi), 2.1, with BiPh3 has yielded a iridium−bismuth cluster complex Ir5(CO)10(μ3-Bi)2(μ4-Bi), 2.2. The first examples of bimetallic iridium−bismuth nanoparticles have been subsequently synthesized from 2.1 and 2.2, and these have been securely anchored onto the inner walls of mesoporous silica. These isolated, bimetallic iridium−bismuth nanoparticles display a superior catalytic performance, when compared to their analogous monometallic counterparts and equivalent physical mixtures, in the C−H activation of 3-picoline to yield niacin.
CHAPTER 3 The reaction of Ir3(CO)9(μ3-Bi) with Ph3GeH yielded the compound Ir3(CO)6(GePh3)3(μ3-Bi)(μ-H)3 3.1 When 3.1 was heated to reflux in hexane, it was transformed into the compound Ir3(CO)6(μ-GePh2)3(μ3-Bi) 3.2, which contains three bridging GePh2 ligands by loss of 3 equiv of benzene. The reaction of Ir3(CO)9(μ3-Bi) with Ph3SnH yielded the compounds Ir3(CO)6(SnPh3)3(μ3-Bi)(μ-H)3 3.3 and Ir3(CO)6-(μ-SnPh2)3(μ3-Bi) 3.4, respectively. Compounds 3.1−3.4 were characterized crystallographically. Compounds 3.1 and 3.3 each have three terminally coordinated EPh3 (E = Ge, Sn) ligands in equatorial coordination sites, one on each of the iridium atoms. In solution compounds 3.1 and 3.3 exist as two isomers. The major isomer has the structure found in the solid state. The two isomers interconvert rapidly on the NMR time scale by tripodal, trigonal-twist rearrangement mechanisms: for 3.1, ΔH⧧ = 66.6 kJ/mol and ΔS⧧ = 1.58 J/(K mol), and for 3.3, ΔH⧧ = 65.6 kJ/mol and ΔS⧧ = −1.4 J/(K mol). The molecular orbitals and UV−vis spectra of 3.2 were calculated and analyzed by ADF DFT computational treatments. The visible spectrum is dominated by transitions from the Ir−Bi bonding orbitals HOMO-3 and HOMO-4 to an Ir−Ir antibonding orbital, the LUMO, in the Ir3 core of the complex.
CHAPTER 4 Ir3(CO)9(μ3-Bi) was found to react with PhAu(NHC) by losing one CO ligand and then oxidatively adding the Au – C bond to the phenyl ligand of the PhAu(NHC) to one of the iridium atoms to yield the compound 4.2 that contains a σ-phenyl coordinated ligand and an Au(NHC) group bridging one of the Ir – Bi bonds of the cluster. Based on the structural analysis and the MO and QTAIM calculations, the Au – Bi interaction is substantial and is comparable in character to the Ir – Bi and Ir – Ir bonds in this cluster. We have shown previously that Ir3(CO)9(μ3-Bi) reacts with HSnPh3 by adding three equivalents of HSnPh3 to yield the compound Ir3(CO)6(SnPh3)3(μ3-Bi)(μ-H)3, (Figure 4.2).5 Compound 4.2 will add only two equivalents of HSnPh3 to yield 4.3. It is possible that the bridging Au(NHC) group with the bulky NHC ligand inhibits a third addition of HSnPh3 by producing a blocking effect proximate to the third Ir atom. Finally, we observed that water can facilitate the cleavage of phenyl groups from the SnPh3 ligands in 4.3 presumably with the formation of some benzene and the formation of an OH grouping bridging the two tin atoms to yield the compound 4.4. The O-bridged linking of tin and germanium ligands could lead to design and synthesis of interesting new chelating ligands in polynuclear metal complexes in the future.
CHAPTER 5 Compound 5.1 readily loses CO upon heating and condenses to form the hexairidium product 5.2. Years ago, Adams et al. showed that bridging sulfido ligands could facilitate condensation and self-condensation reactions of osmium and ruthenium carbonyl cluster complexes to produce higher nuclearity complexes 16 – 19. The lone pair of electrons on the sulfido ligands clearly played a key role in the formation of new bonds between the condensing species 17-19. The bridging bismuth ligand in 5.1 formally contains a lone pair of electrons and these electrons may also serve to facilitate the self-condensation of 5.1 to form the hexairidium complex 5.2 even though no intermediates were isolated that would confirm that such interactions did in fact occur in the course of the formation of 5.2. Because of its facile elimination of CO, it was easy to prepare the PPh3 derivatives 5.3 - 5.5 of 5.1 by reactions between 5.1 and PPh3. Compound 5.3 eliminated CO and PPh3 to yield 5.6 , the PPh3 derivative of 5.2 by a condensation reaction, but 5.6 could be obtained in an even better yield by treatment of 5.2 with PPh3. Pyrolysis of 5.3 also yielded a pentairidum complex 5.8 having a square pyramidal cluster of metal atoms in a very low yield by a combination of cluster and ligand degradation and reassembly. Compound 5.8 has an interesting structure and ligands. Unfortunately, we have not yet been able to synthesize compound 5.8 in a systematic way. Pyrolysis of 5.4 did not yield any higher nuclearity metal compounds, but did yield the complex 5.7, an o-metallated PPh3 derivative of 5.4 in a high yield. Complex 5.7 was also obtained in a low yield from the pyrolysis of 5.3. The condensation of 5.1 with Ru3(CO)10(NCMe)2 yielded compounds 5.9 and 5.10, ( Scheme 5.2) , the first examples of iridium-ruthenium carbonyl complexes containing bismuth ligands. We have not been able to establish the mechanisms of the formation of 5.9 and 5.10 in this work, but we suspect that the Bi ligand in 5.1 probably played a role in the condensation processes leading to these products.
CHAPTER 6 The synthesis and chemistry of heavy atom metallaheterocycles remained largely unexplored until Adams et al1,2,3. and Leong et al.4,5 started synthesizing unusual new metallaheterocycles by linking heavy transition metal groupings with heavy atom bridging ligands, such as diphenylbismuth and diphenylantimony. A novel Iridium - Bismuth metallaheterocycle, 6.1 has been synthesized by the reaction of [HIr4(CO)11]- and Ph2BiCl in methylene chloride solvent at 0ºC for 10 mintues. The compound, 6.1 is formed by a simple salt elimination and a self dimerzation process while eliminating CO from the electron rich monomeric Ir4(CO)11(μ-BiPh2)(μ-H) (62 valence electrons) to form [Ir4(CO)10(μ-BiPh2)(μ-H)]2 dimer.
Elpitiya, G. R.(2015). Iridium – Bismuth Carbonyl Cluster Complexes: New Directions for Chemistry and Selective Oxidation Catalysis. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/3645