Understanding the coordination chemistry of a σ interaction to a single metal center is of particular interest in our group. For instance, the binding of a Si–H bond to a single metal center is an important step in metal catalyzed hydrosilylation, which is an important chemical technology in both commercial and academic synthesis. Thus, determining binding modes of a Si-H-M moiety is crucial in metal-catalyzed transformations involved in various hydrosilylation. Along with a well-known oxidative addition process of a Si-H bond, a silyl coordination to a metal center can also be achieved via a nonclassical σ-SiH interaction. To explore the details of a hydrosilylation mechanism, a Si-H bond was introduced to a series of divalent metal ions by preparing nickel and cobalt complexes supported by an anionic diphosphinosilyl RSiP2 ligand (RSiP2 = RSiH[2-PiPr2-C6H4]2; R = Me or Ph). While a clean conversion occurs in the reaction of a silane ligand with nickel(II) bromide, the corresponding cobalt reaction to prepare a cobalt congener (MeSiP2)CoBr reveals the formation of a low-temperature stable cobalt-SiH intermediate species (MeSiHP2)CoBr2. The green intermediate was carefully investigated by employing low-temperature UV-Vis and ENDOR spectroscopies. The exact position of the H atom in the paramagnetic cobalt intermediate was detected and revealed a Co–H bond distance of ~1.53 Å. Surprisingly, we found evidence that the Si–H bond activation proceeds via deprotonation followed by Co–silyl coordination. As an another interest of a σ interaction to a single metal center, the same moiety was also introduced to a copper(I) ion to minimize geometry relaxation in metal-to-ligand charge transfer (MLCT) excited states by lifting the degeneracy of relevant Cu d-based orbitals. Such effect can be evaluated by studying the emission property of copper complexes and ultimately lead to further development of efficient copper emitters. A series of corresponding cuprous complexes (RSiHP2)Cu(CbzR) were prepared and their emission properties studied. A blue/green emission band at λmax = 474–513 nm was established with a high quantum efficiency and a long lifetime. This emissive behavior contrasts with tetrahedral copper analogues, which do not display the blue emission due to a significant Jahn-Teller distortion after the MLCT transition from nearly degenerate Cu d-based orbitals. Details of the syntheses and photophysical properties of copper complexes will be discussed.

Cobalt and copper σ-complexes with a diphosphine-hydrosilane ligand

253rd National Meeting (2017)

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