Our aim was to develop the synthetic potential and reaction chemistry of Ir3+ and Ru2+ electrophiles by preparing well-characterized complexes whose properties are controllable by modification of the ancillary ligand environment Specifically, we prepared a series of ruthenium complexes to serve as selective hydrogenation and hydrogenolysis catalysts of furan derivatives. We also expanded the synthesis of electrophilic Ir3+ di-thiolate complexes. These types of compounds could eventually serve as catalysts precursors for the addition of weak nucleophiles to alkynes and nitriles.

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The binding of molecular hydrogen to a metal center leads to the elongation of the H−H bond and subsequently to its cleavage along the reaction coordinate for the oxidative addition of H2. There has been considerable interest in the study of the activation of dihydrogen and map out the reaction coordinate for the homolysis of H2 on a metal center. A large number of H2 complexes reported to date possess H−H distances ranging from 0.8 to 1.0 Å. A relatively fewer examples of elongated dihydrogen complexes wherein the H−H distances fall in the range of 1.0 to 1.5 Å, are known. Study of the elongated dihydrogen complexes is of great significance because of its relevance in important catalytic processes such as hydrogenation, hydrogenolysis, and hydroformylation. Objectives The objectives of this work are as follows: (a) Synthesis and characterization of elongated dihydrogen complexes with chelating phosphine coligands by varying the electron donor ability. (b) Trap the various intermediate states in the process of oxidative addition of H2 to a metal center. (c) Map the reaction coordinate for the oxidative addition for the oxidative addition of H2 to a metal center. Results We have synthesized and characterized two new elongated dihydrogen complexes cis-[Ir(H)(η2-S2CH)(η2-H2)(PR3)2][BF4] (PR3 = PCy3, PPh3) wherein hydrogen atom undergoes site exchange between the H2 and the hydride sites. The dynamics of the exchange was studied using NMR spectroscopy. In addition, a series of ruthenium dihydrogen complexes of the type trans-[Ru(Cl)(η2-H2)(PP)][BF4] (PP = 1,2- Synopsis bis(diarylphosphino)ethane) has been synthesized and characterized wherein the aryl group is a benzyl moiety with a substituent (p-fluoro, H, m-methyl, p-methyl, p-isopropyl); in this series of complexes, a small increment in the electron donor ability (decrease in Hammett substituent constants) of the chelating phosphine ligand resulted in an elongation of the H−H bond by a small, yet significant amount. We also synthesized a series of 16-electron dicationic dihydrogen complexes bearing elongated dihydrogen ligand. In addition, we prepared a series of dihydrogen complexes of the type [RuCp/Cp*(PP)(η2-H2)][OTf] (PP = 1,2-bis(diarylphosphino)ethane, 1,2-bis(diarylphosphino)methane, 1,2-bis(dialkylphosphino)methane) bearing elongated H2 ligand (dHH = 1.0 to 1.17 Å); in this series of complexes as well, we found that the H−H bond distances increased as the donor ability of the chelating phosphines increased in small increments, along the reaction coordinate for the oxidative addition of H2 to a metal center. This investigation therefore, has established a very nice correlation between the H−H bond lengths and the Hammett substitutent constants (donor properties) resulting in the construction of dihydrogen complexes along the reaction coordinate for the oxidative addition of H2 to a metal center.