Bimetallic, Silylene‐Mediated Multielectron Reductions of Carbon Dioxide and Ethylene

Abstract

A metal/ligand cooperative approach to the reduction of small molecules by metal silylene complexes (R 2 Si=M) is demonstrated, whereby silicon activates the incoming substrate and mediates net two-electron transformations by oneelectron redox processes at two metal centers. An appropriately tuned cationic pincer cobalt(I) complex, featuring a central silylene donor, reacts with CO 2 to afford a bimetallic siloxane, featuring two Co II centers, with liberation of CO; reaction of the silylene complex with ethylene yields a similar bimetallic product with an ethylene bridge. Experimental and computational studies suggest a plausible mechanism proceeding by [2+2] cycloaddition to the silylene complex, which is quite sensitive to the steric environment. The Co II /Co II products are reactive to oxidation and reduction. Taken together, these findings demonstrate a strategy for metal/ligand cooperative small-molecule activation that is well-suited to 3d metals.

Tetrelanes versus Tetrylenes as Precursors to Transition Metal Complexes Featuring Tridentate PEP Tetryl Ligands (E=Si, Ge, Sn)

“…This simple synthetic procedure and the easy availability of the starting materials have allowed a wide development of the transition metal chemistry of silanes of type C (Table 2). [9–53] The formation of the metal complex involves the coordination of both P atoms and the oxidative addition of the Si−H bond to a low valent transition metal complex, the most common metal precursors being [Fe(PMe 3 ) 4 ], [RuCl 2 (PPh 3 ) 3 ], [Co 2 (CO) 8 ], [M 2 Cl 2 (cod) 2 ] (M=Rh, Ir), [Ni(cod) 2 ], [NiCl 2 (dme)] (dme=1,2‐dimethoxyethane), [PdCl 2 (MeCN) 2 ] and [PtCl 2 (cod)]. A Si−F bond cleavage was observed in the reaction of Si{( o ‐C 6 H 4 )PPh 2 } 2 F 2 with [IrH(CO)(PPh 3 ) 3 ], which led to [Ir{Si{( o ‐C 6 H 4 )PPh 2 } 2 F}(CO)(PPh 3 )] [39b] .…”

“…The oxidative addition of an Si−Cl bond of Si{( o ‐C 6 H 4 )PPh 2 } 2 Cl 2 to iridium has also been achieved [51] . When the complexes contain an Si−H fragment (R=H), a subsequent derivatization at the Si atom, via silylene (Si=M) intermediates, to PSiP silyl derivatives is possible [40a,42,43–45,47] . Curiously, the dihydridosilane Si{( o ‐C 6 H 4 )PPh 2 } 2 H 2 reacted with [Rh 2 Cl 2 (cod) 2 ] to give the chloridosilyl complex [Rh{SiCl{( o ‐C 6 H 4 )PPh 2 } 2 }(cod)] [44b] .…”