Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Richard D Adams

Abstract

Platinum group metal derived bimetallic clusters have been used as precursors to nanoscale catalysts which have been proven to be more effective than their monometallic counterparts. Iridium is a platinum group metal and its applications in catalysis continue to grow. To take advantages of synergies between mixed-metals, we modified iridium clusters with other metal ligands like tin, germanium, and group IB (gold, silver, copper) etc. and obtained a fairly large amount of new iridium derived bimetallic clusters which could be precursors to catalysts with superior properties than that available nowadays. The reaction of Ir4(CO)12 with Ph3SnOH in the presence of [Bu4N]OH gave two products: [Bu4N]][Ir4(CO)11(SnPh3)] (2.1; 45% yield) and [Bu4N][Ir4(μ-H)(CO)10(SnPh3)2] (2.2; 5.5% yield). Compound 2.2 can be obtained from 2.1 in better yield by treatment with an excess of Ph3SnOH in the presence of [Bu4N]OH at 25℃ over 15h. The reaction of Ir4(CO)11(PPh3) with Ph3SnOH in the presence of [Bu4N]OH gave the complex Ir4(µ-H)(CO)10(SnPh3)(PPh3) (2.3, 44% yield). It is proposed that these reactions occur by the addition of the anion[OSnPh3]- generated in situ to a CO ligand of the Ir4(CO)12 to form a stanyl-substituted metallocarboxylate ligand that subsequently loses CO2 and transferred the SnPh3 group to a metal atom. Similar reactions of Os3(CO)12 with the compounds Ph3MOH, M = Sn, Ge under basic conditions yielded the first examples of metal carbonyl cluster complexes containing bridging stannyl- and germyl- substituted metallocarboxylate ligands in the complexes Os3(CO)10(μ-O=COMPh3)(μ-OH), M = Sn, Ge, 2.4, 2.5 which further validated the above proposal.

The reaction of Ir4(CO)11(PPh3) with GePh3H and Me3NO at room temperature has yielded a new complex Ir4(CO)10(PPh3)(GePh3)(µ-H), 3.1 in 54% yield by decarbonylation and oxidative addition of the GeH bond of the GePh3H to the cluster. Compound 3.1 was converted to the GePh2-bridged complex Ir4(CO)10(PPh3)(μ-GePh2), 3.2 in 95% yield when heated to 40 ℃, by the cleavage of a phenyl ring from the GePh3 ligand and the elimination of a molecule of benzene. The reaction of 3.2 with GePh3H at 65 ℃ yielded the new tetrahedral Ir4 complex Ir4(CO)7(PPh3)(GePh2)(GePh3)(µ3-η2-GePhC6H4)(µ-H)2, 3.3. Compound 3.3 was converted to the complex Ir4(CO)7(PPh3)(GePh2)2(µ3-η2-GePhC6H4)(µ-H), 3.5 by cleavage of a phenyl ring from the GePh3 ligand and the elimination of a molecule of benzene. The structure of 3.3 and 3.5 both consist of a tetrahedral Ir4 cluster with an rare ortho-metallated bridging µ3-η2-GePh(C6H4) ligand. The reaction of 3.2 with GePh2H2 at 40 ℃ yielded the tetrairidium complex Ir4(CO)6(PPh3)(GePh2)3(GePh2H)(µ-H)3, 3.6.

A new air-stable σ-phenyl tetrairidium carbonyl salt [Et4N][Ir4(CO)11Ph], 4.1, has been obtained by transmetalation reactions between [Et4N][Ir4(CO)11Br] and SnPh3OH in 45% yield or SnPh4 in 36% yield. Compound 4.1 reacts with PPh3 to yield the complex [Et4N][Ir4(CO)10(μ-2-PPh2C6H4)], 4.2 which contains an ortho-metalated bridging μ-2-PPh2C6H4 ligand. Compound 4.1 reacts with Ir(CO)(PPh3)2Cl by halide displacement to yield two new uncharged pentairidium complexes Ir5(CO)12(Ph)(PPh3), 4.3, and Ir5(CO)11(PPh3)( μ-2-PPh2C6H4), 4.4. Compound 4.3 and 4.4 both contain trigonal-bipyramidal clusters of iridium atoms. Compound 4.4 was also obtained from 4.3 by reaction with PPh3.

The reaction of compound 4.1 with [Ir(COD)Cl] (COD=1,5-cyclooctadiene) yielded the two known tetrairidium compounds Ir4(CO)10(COD) and Ir4(CO)7(COD)(µ4-C8H10), 4.5 and the three new higher nuclearity complexes Ir5(CO)11(Ph)(COD), 4.6, Ir5(CO)9(Ph)(COD)2, 4.7 and Ir9(CO)15(Ph)(µ3-C8H10)(COD), 4.8, containing σ-coordinated phenyl ligands. Compound 4.6 and 4.7 contain trigonal-bypyramidal Ir5 clusters. Compound 4.8 was shown to be formed by the condensation of 4.5 and 4.6 with nine iridium atoms in the form of a tricapped octahedron. Compound 4.7 reacts with COD to yield the compound Ir5(CO)7(COD)2(µ4-ŋ2:ŋ1-C8H11) 4.9 in a cluster-opening process that cleaves two hydrogen atoms form one of the COD C-C double bonds, eliminates the σ-phenyl ligand, and transfers one of the hydrogen atoms the other C-C double bond to form a metalated µ4-ŋ2:ŋ1-C8H11 cyclooctyne ligand.

The reaction of compound 4.1 with [Au(PPh3)][NO3] yield a new iridium-gold complex Ir4(CO)11(Ph)(µ-AuPPh3), 5.1. Two new iridium-gold complexes Ir4(CO)10(AuPPh3)2, 5.2, and Ir4(CO)11(AuPPh3)2, 5.3, were obtained from the reaction of [HIr4(CO)11]- with [Au(PPh3)][NO3]. The octahedral Ir4Au2 cluster of 5.2 is reversibly converted into the Au(PPh3)-capped Ir4Au trigonal bipyramidal cluster of 5.3 by adding CO. Compound 5.2 adds PPh3 to form the compound Ir4(CO)10(PPh3)(AuPPh3)2, 5.4, which is structurally similar to 5.3. Compound 5.4 loses CO and benzene when heated to form the compound Ir4(CO)9(µ3-PPhC6H4)(AuPPh3)2, 5.5, which contains a triply bridging PPhC6H4 ligand.

The compounds Ir4(CO)11(R)(σ-AuPPh3), (5.1, R = C6H5, 5.6, R = CH3, and 5.7, R = 2-C16H10) were obtained from the reactions of [NEt4][Ir4(CO)11Br¬] with (R)Au(PPh3), R = C6H5, CH3, and 1-C16H10 at 25 oC by the loss of Br- and the oxidative addition of the Au-C bond of the (R)Au(PPh3) to the Ir4 cluster. The reaction of (CH3)Au(PPh3) with [PPN][HIr4(CO)11] yielded compound 5.6 and the higher nuclearity compound Ir4(CO)9(CH3)2(AuPPh3)4, 5.8. The reaction of PhAu(PPh3) with [PPN][HIr4(CO)11] yielded compound 5.1 and the higher nuclearity compounds Ir4(CO)9(PPh3)(Ph)(AuPPh3)3, 5.9 and Ir4(CO)9(Ph)2(AuPPh3)4, 5.10. Compounds 5.8 and 5.10 were obtained in better yields from the reactions of Ir4(CO)11(AuPPh3)2, 5.3 with (CH3)Au(PPh3) and PhAu(PPh3), respectively. Compound 5.9 was obtained independently in a high yield by the reaction of Ir4(CO)10(PPh3)(AuPPh3)2, 5.4 with PhAu(PPh3). The reaction of 5.7 with (CH3)Au(PPh3) was found to yield the digold compound Ir4(CO)9(µ-ŋ3-O=CC16H8)(µ-AuPPh3)(µ3-AuPPh3),5.11 in 25% yield.

Reactions of the tetrairidium anion [Ir4(CO)11(Ph)]-, 4.1 with [Cu(NCMe)4][BF4] and Ag[NO3] have yielded the new iridium-copper and iridium-silver complexes Ir4(CO)11(μ-ŋ1-Ph)[μ3-Cu(NCMe)], 6.2 and the [Et4N][{Ir4(CO)11Ph}2(μ4-Ag)], 6.3, respectively. Compound 6.3 reacts with a second equivalent of Ag[NO3] to yield the uncharged complex [Ir4(CO)11]2(μ4-Ag)(μ-Ag)(μ3-Ph)(μ-Ph), 6.4 that contains two Ir4(CO)11 clusters linked by a quadruply-bridging silver atom and one triply bridging Ph ligand. When dissolved in NCMe, compound 6.4 is split in two and adds one equivalent of NCMe to the Ag atom in each half to form the compound Ir4(CO)11(ŋ1-Ph)[μ3-Ag(NCMe)], 6.5 (73% yield). Unlike 6.2, the phenyl ligand in 6.5 is terminally coordinated. When 6.4 was treated with PPh3, the complex Ir4(CO)11(μ-ŋ1-Ph)[μ3-Ag(PPh3)], 6.6 was obtained in 87% yield. The cluster of 6.6 is structurally similar to that of 6.5 except that the phenyl ligand has adopted a semi-bridging coordination to the silver atom similar to that found for the phenyl ligand and the copper atom in 6.2.

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© 2013, Mingwei Chen

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