Transition-Metal Silyl and Stannyl Complexes

Catalytic or stoichiometric transformations of organosilicon or organotin compounds in the coordination sphere of transition metals still do not have the same importance as that of carbon compounds, although significant progress was made in understanding the making and breaking of silicon(tin)-element (Si-E, Sn-E) bonds in the coordination sphere of transition-metals. In the activation step, a Si-E or Sn-E bond is broken and a metal-silicon (M-Si) or metal-tin (M-Sn) bond is formed. The reverse reaction, formation of a new Si-E' or Sn-E' bond by cleavage of the M-Si (M-Sn) bond, often constitutes the product-forming step.

The goal of our research is to develop stoichiometric or catalytic transformations of organosilicon or organotin compounds in the coordination sphere of transition metals by oxidative addition / reductive elimination reactions.

We investigate the chemical parameters that govern the selective formation and breaking of Si-Si and related bonds by transition-metal compounds. Recent research is focussed on the use of hemilabile ligands for reactivity enhancement of metal complexes towards organosilicon compounds. Contrary to organometallic chemistry, hemilabile auxiliary ligands are hardly used in the chemistry of metal-silicon compounds. We found that Pt(II) complexes with hemilabile P,N-chelating ligands, (P∩N)PtX₂(P∩N = (κ²-P,N)-R′₂PCH₂CH₂NR₂), undergo several remarkable reactions none of which is found when analogous bis(diphenylphosphino)ethane-substituted complexes, (dppe)PtX₂, are employed instead of (P∩N)PtX₂.

In the reaction of (P∩N)PtMe₂with HSiR₃, mono- and bis(silyl) complexes, (P∩N)Pt(SiR₃)Me (Me trans to P) and (P∩N)Pt(SiR₃)₂, are formed. While the first methyl ligand is eliminated as methylsilane MeSiR₃, the second ends up as methane. In addition, catalytic redistribution of HSiR₃ to SiR₄ is observed.
The complexes (P∩N)PtMe₂ catalyze the formation of R₃Si-O-SiR₃ from R₃Si-H and oxygen, as well as the dehydrogenative dimerization of HSnR₃ (R = Bu, Ph) to Sn₂R₆and the formation of cyclo-Sn₅Ph₁₀ from Ph₂SnH₂, respectively.
(P∩N)PtMe₂ (R = Et, ⁱPr) reacts with PhMe₂SiCl in a stoichiometric reaction to give the disilane Si₂Ph₂Me₄, (P∩N)Pt(Cl)Me₃and (P∩N)Pt(Cl)Me.

[(k²-P,N)-Ph₂PCH₂CH₂NR₂]PtMe₂ also activates C-Cl bonds. In the reaction with CCl₄, the complexes (P∩N)Pt(Me)Cl, (P∩N)Pt(Me)₃Cl and (P∩N)Pt(CCl=CH₂)Cl are obtained.
When both chlorinated hydrocarbons and HSiR₃ are present, catalytic Si-H/C-Cl exchange is observed with (P∩N)Pt(Cl)Me as the catalysts. For example, a mixture of Ph₂MeSiH and CCl₄ is catalytically converted into Ph₂MeSiCl and CH_4-xCl_x (x = 0-3).

Selected publications:

U.Schubert, Adv. Organomet. Chem. 1990, 30, 151-187; "λ²-Coordination of Si-H Sigma Bonds to Transition Metals".
U.Schubert, M.Schwarz, F.Möller, Organometallics 1994, 13, 1554-1555; "A Strong W··H··Si-Interaction in the 16-Electron Carbene Complex (CO)₄WC(NMe₂)SiHMes₂".
S.Gilbert, M.Knorr, S.Mock, U.Schubert, J. Organomet. Chem. 1994, 480, 241-254; "Darstellung, Struktur und Reaktivität der Trihydrido-Silyl- und -Stannyl-Komplexe L₃FeH₃(ER₃) (E = Si, Sn)".
U.Schubert in B.Marciniec, J.Chojnowski (Eds.) Progress in Organosilicon Chemistry, Gordon and Breach, Basel, 1995, "Activation of Si-X Bonds by Electron-Deficient Transition Metals", p.287-307.
U.Schubert, H.Gilges, Organometallics 1996, 15, 2373-2375; "Magnitude of the Chelate Effect in the Oxidative Addition of Si-H Bonds".
H.Gilges, G.Kickelbick, U.Schubert, J.Organomet.Chem. 1997, 548, 57-63; "Intramolecular Si-E (E = Si, Sn) Oxidative Addition of Ph₂P(CH₂)_n-SiR′₂ER₃ Ligands (n = 1, 2) to Pt(0)".
H.Gilges, U.Schubert, Eur.J.Inorg.Chem. 1998, 897-903; "Chelate-Assisted Oxidative Addition of Phenyl- and Alkyltin Groups to Nickel and Platinum".
H.Gilges, U.Schubert, Organometallics 1999, 17, 4760-4761; "Oxidative Addition of Nonactivated Si-C Bonds to Platinum(0) Centers".
J.Pfeiffer, U.Schubert, Organometallics 1999, 18, 3245-3248; "Enhanced Reactivity of a Platinum Dimethyl Complex toward Trimethoxysilane due to a P,N-Chelating Co Ligand".
J.Pfeiffer, G.Kickelbick, U.Schubert, Organometallics 2000, 19, 62-71; "Platinum Dimethyl Complexes with Hemilabile P,N-Chelating Ligands: Synthesis, Structure, and Reactions with Iodotrimethylsilane and 1,2-Bis(dimethylsilyl)benzene".
J.Pfeiffer, G.Kickelbick, U.Schubert, Organometallics 2000, 19, 957-959; "Synthesis of a Bis(silanolate) Complex from a Bis(silyl) Complex by Air Oxidation: Evidence for the Participation of Silanolate Complexes in the Transition-Metal-Catalyzed Formation of Disiloxanes from Hydridosilanes".
U.Schubert, J.Pfeiffer, F.Stöhr, D.Sturmayr, S.Thompson, J. Organomet.Chem. 2000, 646, 53-58; "Transformations of Organosilanes by Pt(II) Complexes with Hemilabile P,N-Chelating Ligands".
F.Stöhr, D.Sturmayr, G.Kickelbick, U.Schubert, Eur.J.Inorg.Chem. 2002, 2305-2311; "C-Cl and Si-Cl Activation by P,N-chelated Pt(II)-Complexes".
F.Stöhr, D.Sturmayr, U.Schubert, J.Chem.Soc.Chem.Comm. 2002, 2222-2223; "C-Cl / Si-H Exchange Catalyzed by P,N-chelated Pt(II) Complexes".
S.M.Thompson, U.Schubert, Inorg.Chim.Acta 2003, 350, 329-338; "Dehydrogenative Stannane Coupling by Platinum Complexes".
S.M.Thompson, F.Stöhr, D.Sturmayr, G.Kickelbick, U.Schubert, J. Organomet. Chem. 2003, 686, 183-191; "Reaction of hydrogenosilanes with dimethyl Pt(II) complexes promoted by hemilabile P,N-chelating ligands".
D.Sturmayr, U.Schubert, Eur.J.Inorg.Chem. 2004, 776-782; "A Comparison of the Reactivity of Chloroalkanes and Chlorosilanes towards Activated Pt^II Complexes by DFT Calculations".
D.Sturmayr, U.Schubert, Eur.J.Inorg.Chem. 2004, 2658-2661; "DFT Calculations on the C-Cl/Si-H Exchange Catalyzed by P,N-Chelated Pt^II Complexes".