|Ph.D Student||Kratish Yosi|
|Subject||Activation of E-H bonds (E= Pt, Si, Ge, Sn) Using RnM|
Reagents (M= Li, Mg, Zn, Hg)
|Department||Department of Chemistry||Supervisors||? 18? Yitzhak Apeloig|
|Dr. Dmitry Bravo-Zhivotovs|
The hydrogen-metal exchange reaction is a very powerful method for introducing a metal function into a molecule. This step is actively employed in organic chemistry for conversion of C-H bonds to C-M bonds. In this thesis we studied similar hydrogen-metal exchange reactions for heavy carbon analogs; silicon, germanium and tin in hope that we could metalated their E-H bonds (E = Si, Ge, Sn) generating new group 14 anions. In addition, we studied similar metalation reactions for Pt-H bonds in platinum hydride complexes. In this case metallation of the Pt-H bond will lead to multi-metallic complexes having Pt-M bonds. These kind of heterometallic complexes could be good candidates for performing catalysis. Most of this Ph.D. thesis is dedicated to the synthesis, isolation, characterization and study of reactions of new metal containing reagents.
We present the first examples of direct metalation of Si-H bonds in hydridosilanes by R`MgX (R`= tBu, tBuMe2Si, X= Cl, Br) and R``2Mg (R`` = nBu, tBu) in a solvent free, salt free, one pot synthesis of novel sila-Grignard reagents. For example: the Grignard reagent, tBuMgCl react with (Me3Si)3SiH to give the corresponding sila-Grignard (Me3Si)3SiMgCl compound in quantitative yields. By using a silane which has two Si-H bonds we were able to replace each hydrogen with a magnesium substituent. Thus, the reaction of dihydrido silane (tBuMe2Si)2SiH2 with tBuMgCl yielded a geminal magnesium substituted silane (tBuMe2Si)2Si(MgCl)2, in a one pot reaction.
We found a new convenient method for generation of reactive bis(silyl)stannylenes from tris(silyl)tin hydrides. Thus, when the bulky tin hydride (tBu2MeSi)3SnH is heated at 70°C an intermediate bis(silyl)stannylene ,(tBu2MeSi)2Sn꞉, is generated which then dimerizes to the known distannene ,(tBu2MeSi)2Sn=Sn(SiMetBu2)2.
We found that Pt-H bonds can also participate in hydrogen-metal exchange reaction leading to new complexes having Pt-M (M= Hg, Zn) bonds. For example, the known platinum dihydride (dtbpe)PtH2 react with (tBu2MeSi)2Hg yielding novel multi-metallic (dtbpe)Pt(HgSiMetBu2)2 (1) complex and tBu2MeSiH.
The first persistent platinum(I) centered radical, (dtbpe)(tBu2MeSiHg)Pt•, was generated by homolytic cleavage of one of the Pt-HgSiR3 bonds of the bis(silylmercury)platinum(II) complex 1. The Pt(I) radical was characterized by EPR spectroscopy and density functional theory (DFT) calculations.
We found that simple phosphine substituted platinum(0) complexes Pt(PEt3)3, (dmpe)Pt(PEt3)2, (dtbpe)Pt(PEt3) (all are easily prepared) and Pt(PPh3)4 (commercially available) effectively catalyze the direct deuteration of silanes with D2 at 1 atm pressure under mild conditions in excellent to good yields. The catalysis is mediated by platinum deuteride/hydride intermediates which are in equilibrium with the phosphino Pt(0) catalyst. The mechanism for the catalysis is also supported by DFT calculations.