Structural Studies and Reactions of Rhenium and Rhenium-Gold Metal Carbonyl Complexes

The six-membered heavy atom heterocycles [Re2(CO)8(μ-H)(μ-SbPh2)]2, 2.1 and Pd[Re2(CO)8(μ-H)(μ-SbPh2)]2, 2.3, have been prepared by the palladium-catalyzed ring-opening cyclo-dimerization of the three-membered heterocycle Re2(CO)8(μ-H)(μ-SbPh2). The palladium atom that lies in the center of the heterocycle 2.3 was removed to yield 2.1. The palladium removal was found to be partially reversible leading to an unusual example of host-guest behavior. A related dipalladium complex Pd2Re4(μ-Ph)(CO)16(μ4-SbPh)(μ3-SbPh2)(μ-H)2, 2.2, was also formed in these reactions of palladium with Re2(CO)8(μ-H)(μ-SbPh2). Thermolysis of 2.1 at 85 °C yielded Re3(CO)12(μ-SbPh2)(μ-H)2, 2.4 (2.9% yield), Re3(CO)12(μ-SbPh2)2(μ-H), 2.5 (25.1% yield), and Re3(CO)13(μ-SbPh)(μ-H), 2.6 (14.6% yield). The electronic structure of 2.1 and 2.3 were also investigated by DFT computational analyses. CHAPTER 3 The compounds Re2(CO)8(μ-AuPPh3)2, 3.1, a dimer of Re(CO)4(μ-AuPPh3) and Re2(CO)8(PPh3)2 were obtained from UV-Vis induced decarbonylation of the compound Re(CO)5[Au(PPh3)]. Compound 3.1 contains two rhenium atoms bridged by two AuPPh3 groups. It is formally unsaturated, 32 valence electrons, and exhibits a short Re – Re interaction, Re – Re = 2.9070(3) Å, in the solid state. The nature of the metal – metal bonding in 3.1 was established by DFT computational analyses which provided evidence not only for σ-bonding but also for some complementary π-bonding directly between the two rhenium atoms. The electronic structure of Re2(CO)8(μ-H)2, 3.2 was similarly analyzed and is compared with 3.1. Compound 3.1 is intensely colored due to metal-based low energy allowed electronic transitions between the HOMO and HOMO-2 and the LUMO. Compound 3.1 reacts with I2 to yield Re2(CO)8(μ-AuPPh3)(μ-I), 3.3 and the known compound Re2(CO)8(μ-I)2, 3.4 by substitution of the bridging AuPPh3 groups with bridging iodide ligands. Compound 3.3 is electronically saturated, 34 valence electrons, and contains a formal Re – Re single bond, Re – Re = 3.2067(5) Å. The bonding in compounds 3.3, 3.4 and Re2(CO)10 were also analyzed computationally and was compared with 3.1 and 3.2. CHAPTER 4 The electronically unsaturated dirhenium complex Re2(CO)8(μ-AuPPh3)(μ-Ph), 4.1 was obtained from the reaction of Re2(CO)8[μ-η2-C(H)=C(H)Bun](μ-H) with Au(PPh3)Ph. The bridging AuPPh3 group was replaced by a bridging hydrido ligand to yield the unsaturated dirhenium complex Re2(CO)8(μ-H)(μ-Ph), 4.2 by reaction of 4.1 with HSnPh3. Compound 4.2 reductively eliminates benzene upon addition of NCMe at 25 °C. The electronic structure of 4.2 and the mechanism of the reductive elimination of the benzene molecule in its reaction with NCMe were investigated by DFT computational analyses. Reacting compound 4.2 with N,N-Diethylaniline formed another unsaturated dirhenium complex Re2(CO)8(μ-H)[μ- (C2H5)2NC6H4], 4.3. This reaction showed a C-H bond activation at the phenyl ring of 4.3. CHAPTER 5 Compound 5.1 was first isolated from the reaction of 4.1 with Ph3SnH. In this chapter, an improved synthesis of 5.1 was reported. Interestingly enough, compound 5.1 is the first example of an X-ray crystallographic characterization of a gold-tin cluster complex having phenyl substituents. CHAPTER 6 Reaction of HgI2 with 4.1 yielded an interesting product [Re2(CO)8(μ-HgI)(μ-η1-C6H5)]2, 6.1. In the solid state, compound 6.1 consists of a centrosymmetric dimer of empirical formula unit Re2(CO)8(μ-HgI)(μ-η1-C6H5). The dimer is being held together by two bridging iodide ligands between the two mercury atoms. The reaction of Re2(CO)8[μ-η2-C(H)=C(H)Bun](μ-H) with HgPh2 produced another new rhenium mercury complex, {Re2(CO)8[μ-η2-C(H)=C(H)Bun]}2(μ4-Hg), 6.2 which consists of a spiro, μ4 mercury atom bridging two hexenyl-bridged Re2(CO)8[μ-η2-C(H)=C(H)Bun] groupings.