Iridium-Ruthenium/Osmium-Gold Cluster Complexes: Unique Structures and Properties

Chapter Two The first Ir-Ru cluster complex was synthesized was the electron-rich, anionic, planar cluster complex [PPN][IrRu6(CO)23], 2.5, (PPN=Bis(triphenylphophoranylidene)-ammonium) which obtained from the reaction of [PPN][IrRu3(CO)13] with one equivalent ruthenium carbonyl (Ru3(CO)12) at 66 oC (THF reflux) for 12h. Compound 2.5 could also be synthesized by using the mono-Iridium compound [PPN][Ir(CO)4] reacts with two equivalent of ruthenium carbonyl. In compound 2.5, all seven metal atoms lie in a plane (max deviation = 0.043(1) Å) with the iridium atom in the center circumscribed by a hexagonal ring of six ruthenium atoms. The anion 2.5 contains 104 valence electrons while both the EAN rule and the PSEP theory predict a total of 102 electrons for this structure. Complex 2.5 is highly colored and exhibits two broad absorptions in the visible region of the spectrum. Even more interestingly, anion 2.5 exhibits a rare luminescence in the 350 nm region when excited with 235 or 275 nm radiations. Computational analyses have been performed to explain its metal-metal bonding and electronic properties. Anion 2.5 reacts with [Ph3PAu][NO3] to yield the uncharged planar complex Ru5Ir(CO)20AuPPh3, 2.6 in low yield (3%) by metal atom substitution. The structure of 2.6 is same to that of 2.5 except one of the Ru atoms replaced by a gold atom. All of the metal atoms in 2.6 lie virtually in the same plane. The Au atom exhibits the greatest deviation from the best least-squares plane, 0.140Å. The Ir-Ru and Ru-Ru distances are similar to those in 2.5. Complex 2.6 contains only 102 valence electrons, which agreed with the EAN rule and the PSEP theory. Interestingly, compound 2.6 also exhibits a significant absorption in the visible region of the spectrum: two overlapping absorptions at 494 nm (ε = 14082 cm-1∙M-1), 520 nm (ε =16858 cm-1∙M-1) and one broad absorption at 649 nm (ε =3198 cm-1∙M-1). DFT calculations have also been performed to explain its metal-metal bonding and electronic properties. Chapter Three Four new compounds were obtained from the reaction of HIrRu3(CO)13 with PBut3 (tri-tert-butylphosphine) in CH2Cl2 at reflux temperature. They have been identified as IrRu3(CO)12P(t-Bu)3(μ-H), 3.1, (15%), Ir2Ru3(CO)15P(t-Bu)3, 3.2, (2.6% based on Ruthenium), IrRu2(CO)9[P(t-Bu)3](μ-H), 3.3, (29%) and IrRu3(CO)10[P(t-Bu)3]2(μ3-η2-CO)(μ-H), 3.4, (19%). When compound 3.1 was treated with excess of PBut3, compounds 3.3 and 3.4 were obtained in 18.3% and 36.8% yields respectively. When compound 3.4 was allowed to react with excess Ru(CO)5, which was generated by irradiation of Ru3(CO)12 in a hexane solvent, a new compound IrRu4(CO)12(μ4-CO)[P(t-Bu)3]2(μ3-H), 3.5, was obtained in 66% yield. When compound 3.5 was treated with CO in a refluxed hexane solution, a new compound IrRu4(CO)14P(t-Bu)3(μ4-η2-CO)(μ-H), 3.6, was obtained in 18% yield. Compound 3.6 can further react with CO at 10 atm 70 ºC to produce compound 3.3 in 36% yield. Compound 3.1 is brown in color and simply a P(t-Bu)3 substitution derivative of its parent IrRu3(CO)13(μ3-H). Compound 3.1 contains a closed tetrahedral cluster of four metal atoms, one of Ir and three of Ru. There is one hydrido ligand in 3.1 that bridges the Ir(1) - Ru(1) bond. The phosphine ligand is coordinated to the iridium atom, Ir(1) - P(1) = 2.4825(15) Å. The cluster contains a total of 60 valence electrons and is thus, electronically saturated, i.e. all metal atoms formally have 18 electron configurations. Compound 3.2 contains five metal atoms, two of Ir and three of Ru. The metal atoms are arranged in the form of a spiked-tetrahedron. The tetrahedral group contains the two iridium atoms and two of the ruthenium atoms. The fourth Ru atom, Ru(1), is the spike that is bonded only to the iridium atom. There is one P(t-Bu)3 ligand in 3.2, and it is coordinated to Ru(1). There is an η2-quadruply bridging carbonyl ligand which is coordinated to three metal atoms Ir(1), Ru(2) and Ru(3) by its carbon atom. The oxygen atom is coordinated only to Ru(1). Compound 3.2 contains a total of 76 valence electrons which is precisely the number expected for a spiked-tetrahedral cluster of five metal atoms. Compound 3.3 contains only three metal atoms, one of Ir and two Ru. They are arranged in a triangle. There is one hydrido ligand that bridges the Ir(1) - Ru(1) bond. The phosphine ligand is coordinated to the iridium atom. There are eight terminally coordinated carbonyl ligands and there is one CO, C(1) - O(1), ligand that bridges the Ir(1) - Ru(1) bond. Overall, compound 3.3 contains a total of 46 valence electrons and it is thus electron deficient by the amount of two electrons. DFT molecular orbital calculations were performed by using the PBEsol functional in the ADF program library. Compound 3.4 contains four metal atoms, one of Ir and three of Ru. They are arranged in the form of a butterfly tetrahedron. There are two P(t-Bu)3 ligands, one on Ir(1) and the other on Ru(1) and these two metal atoms occupy the less crowded wing-tip positions of the butterfly tetrahedron. The metal - metal bond distances are fairly normal. The long length of Ru(1) - Ru(3) can be attributed to the presence of a hydrido ligand that bridges that bond. The most interesting ligand in 3.4 is a η2-triply-bridging CO ligand, C(2) - O(2). The carbon atom is bonded to three of the metal atoms. The oxygen atom is bonded to Ru(1) and as a result, the CO bond distance is long compared that of the terminally coordinated CO ligands. In order to understand the nature of the coordination of the triply-bridging CO ligand better, a geometry-optimized DFT molecular orbital analysis of compound 3.4 was performed. Compound 3.5 contains five metal atoms, one of Ir and four of Ru. The metal atoms are arranged in the form of an iridium-capped butterfly tetrahedron of four ruthenium atoms. There are two P(t-Bu)3 ligands, one on the iridium atom Ir(1) and the other on Ru(2). The hydrido ligand was found to be a triply-bridging ligand across the Ir(1) - Ru(1) - Ru(3) triangle. Compound 3.5 contains a η2-quadruply-bridging CO ligand, C(1) - O(1). The carbon atom is bonded to all four ruthenium atoms. The oxygen atom is bonded only to Ru(2). As found in 3.4, the CO bond distance is also long. In order to understand the nature of the coordination of the interesting CO ligand, a geometry-optimized DFT molecular orbital analysis of compound 3.5 was also performed. Compound 3.6 also contains five metal atoms, one of Ir and four of Ru. The cluster is very similar to that of 3.2 having the metal atoms are arranged in the form of a spiked-tetrahedron. The iridium atom is contained in the tetrahedral portion of the cluster. Ru(1) is the spike that is bonded only to the iridium atom. There is only one P(t-Bu)3 ligand in 3.6, and it is coordinated to the ruthenium atom labeled Ru(1). There is one hydrido ligand H(1) that bridges the Ru(2) - Ru(3) bond. An η2-quadruply bridging carbonyl ligand, C(1) - O(1) is coordinated to three metal atoms Ir(1), Ru(2) and Ru(4) by its carbon atom. The oxygen atom is coordinated only to Ru(1), which is very similar to that found in 3.2. Like 3.2, compound 3.6 contains a total of 76 valence electrons which is precisely the number expected for a spiked-tetrahedral cluster of five metal atoms. DFT molecular orbital analysis of compound 3.6 was also performed. Chapter Four Three new Ir-Ru-Au trimetallic cluster complexes: IrRu3(CO)13AuPPh3, 4.1, HIrRu3(CO)12(AuPPh3)2, 4.2, and IrRu3(CO)12(AuPPh3)3, 4.3 were obtained in low yields from the reaction of HIrRu3(CO)13 with [(AuPPh3)3O][BF4]. Compounds 4.1 and 4.3 were subsequently obtained in much better yields (82%) and (84%) from the reactions of [AuPPh3][NO3] and [(AuPPh3)3O][BF4] with [PPN][IrRu3(CO)13] respectively. The Compounds 4.1 contains an Au(PPh3) group that bridging a Ru3 triangular face of the tetrahedral IrRu3 cluster. Compound 4.1 could be viewed as an Au(PPh3) capped tetrahedral IrRu3 structure which has 60 valence electrons. The metal cluster in 4.2 can be described as an Au(PPh3) capped trigonal-bipyramidal AuIrRu3 cluster, but this AuIrRu3 cluster is not the same as that in 4.1. The Au atom in AuIrRu3 cluster in 4.2 caps an IrRu2 triangle not the Ru3 triangle as in 4.1 and the Au(PPh3) cap on that bridges one of the Au-Ir-Ru triangles. There is a hydride that bridges one of the Ru-Ru bonds. If we see the Au(PPh3) group as a ligand which donates one electron to the cluster, compound 4.2 will have 60 valence electrons which obey both the EAN rule and the PSEP theory. Compound 4.2 exhibits only one phosphorus resonance in its 31P NMR spectrum at room temperature, but it shows two resonances as expected at -80 oC. This temperature dependence can be explained by a dynamical exchange process that leads to an interchange of the environments of the two inequivalent Au(PPh3) groups in 4.2 on the NMR timescale at room temperature. A possible mechanism was proposed to explain this dynamical exchange process. Compound 4.3 contains three Au(PPh3) groups combined with the IrRu3 cluster of the original reagents HIrRu3(CO)13 or anion [IrRu3(CO)13]-. The metal cluster in 4.3 can be described in different ways. It could be described as an IrRu3 tetrahedron with three bridging Au(PPh3) groups. Alternatively, the cluster could be described as a seven atom pentagonal bipyramidal Au3IrRu3 cluster with an additional bond between the apical atoms. If one considers compound 4.3 as a IrRu3 tetrahedron with three one electron Au(PPh3) donors, then the cluster contains a total of 60 electrons and the Ir and each of the Ru atoms will formally have 18 electron configurations. The 31P NMR spectrum of 4.3 exhibits only one phosphorus resonance at room temperature, but shows two resonances in a 2/1 ratio resonances as expected at -80 oC. As the temperature is raised, the two resonances broaden and coalesce in a process indicative of a dynamical averaging. The broadened spectra were simulated in order to obtain exchange rates and activation parameters for the exchange process. A dynamical exchange process that leads to an interchange of the two types Au(PPh3) groups on the NMR timescale at room temperature seems to be the most likely. A variety of mechanisms can be envisioned, but all must involve the cleavage of at least one of the Au-Au bonds. Chapter Five The reaction of Os3(CO)10(NCMe)2, 5.1 with C6H5Au(PPh3) has yielded the complex Os3(CO)10(μ,η1-C6H5)(μ-AuPPh3), 5.2, which contains an bridging η1-phenyl ligand and an Au(PPh3) group that bridges the same unsaturated Os−Os bond in the 46-electron cluster complex. When it was heated to reflux in an octane solution (125 °C), compound 5.2 was decarbonylated and converted to the complex Os3(CO)9(μ3-C6H4)(μ-AuPPh3)(μ-H), 5.3, which contains a triply bridging benzyne ligand by a CH cleavage on the bridging phenyl ring. The reaction of 5.1 with (1-C10H7)Au(PPh3) (1-C10H7 = 1-naphthyl) or (2-C10H7)Au(PPh3) (2-C10H7 = 2-naphthyl) yielded the complex Os3(CO)10(μ-2-C10H7)(μ-AuPPh3), 5.4, which exists as two isomeric forms in the solid state. A 1,2-hydrogen shift in the naphthyl ligand occurred in the formation of 5.4. The green isomer 5.4a is structurally similar to 5.2 and contains a bridging η1-2-naphthyl ligand and a bridging Au(PPh3) group and is electronically unsaturated overall. The pink isomer 5.4b contains a bridging η2-2- naphthyl ligand and a bridging Au(PPh3) group and is electronically saturated. The pink isomer is found in hexane solution and was converted to the complex Os3(CO)9(μ3-C10H6)(μ-AuPPh3)(μ-H), 5.5 when heated to reflux in octane (125 °C) for 30 min. Compound 5.5 is the first naphthyne compound that has ever been made which contains a triply bridging 1,2-naphthyne ligand. The reaction of 5.1 with (1-C16H9)Au(PPh3) (1-C16H9 = 1-pyrenyl) yielded the complex Os3(CO)10(μ-2-C16H9)(μ-AuPPh3), 5.6, which also exists as two isomeric forms. A 1,2-hydrogen shift and 2,4-hydrogen shift in the pyrenyl ligand occurred in the formation of 5.6. The green isomer 5.6 is structurally similar to 5.2 and contains a bridging η1-2-pyrenyl ligand and a bridging Au(PPh3) group and is electronically unsaturated overall. The brown isomer 5.7 contains a bridging η1-4-pyrenyl ligand and a bridging Au(PPh3) group and is also electronically unsaturated. When heated to reflux in an octane solution (125 °C), both compound 5.6 and 5.7 were decarbonylated and converted to the corresponding pyryne complex Os3(CO)9(μ3-1,2-C16H8)(μ-AuPPh3)(μ-H), 5.8 and Os3(CO)9(μ3-4,5-C16H8)(μ-AuPPh3)(μ-H), 5.9 which contain triply bridging pyryne ligands by a CH cleavage on the bridging pyrenyl ring. To further understand the bonding between the phenyl group and the metal cluster, DFT (Density Functional Theory) calculation on compound 5.2 was conducted, the fragment analysis revealed the bonding of the phenyl to the unsaturated Os-Os bond not only consist with σ-bond, but π donation from the phenyl ligand to the cluster was involved as well. Chapter Six Variable temperature NMR studies of the compound Os3(CO)10(µ-η1-C6H5)(µ-AuPPh3), 6.1 (5.2) have revealed the first example of hindered rotation of the bridging phenyl ligand about the metal-metal bond. The activation parameters for the process:Hǂ = 72.34 KJ/mol, Sǂ= -2.65 J/K*mol were determined. A density functional theory analysis has provided a mechanism that involves a partial shift of the ligand out of the bridging position with the formation of an agostic interaction of one of the ortho-positioned CH bonds of the phenyl ring at the neighboring metal atom. Compound 6.2 (5.6) was also found to behave similarly. Surprisingly, the calculated activation parameters for compound 6.2: Hǂ = 70.93(61) kJ/mol and Sǂ= = −6.98(1.83) J/(K*mol) which are very similar to those for compound 6.1