Reversible Dimerization of Phosphine‐Stabilized Silylenes by Silylene Insertion into Si^II–H and Si^II–Cl σ‐Bonds at Room Temperature

Abstract

Contrary to the classical silylene dimerization leading to ad isilene structure,p hosphine stabilized hydroand chloro-silylenes (2a,b)u ndergo an unique dimerization via silylene insertion into SiÀX s-bonds (X = H, Cl), whichi s reversible at room temperature.DFT calculations indicate that the insertion reaction proceeds in one step in ac oncerted manner.The dimerization of silylenes to the corresponding disilene is one of the most common reactions of these low-coordinate silicon species (type A). Since the synthesis of the first stable silylene by West et al., [1] as ignificant number of disilenes were synthesized by this method. [2] It has been experimentally and theoretically shown that the bonding situation in disilenes and their stability strongly depend on the nature of the substituents. [3] Indeed, ar eversible disilene-silylene equilibrium has been observed for some sterically overcrowded silylenes I [4] and II, [5] and p-donor (Br,a mino) substituted species III, [6] IV, [7] and V. [8] Particularly,i nt he case of V,i ts dimer is stable only in the solid state.Theoretical calculations predicted that silylenes with al arge singlet-triplet energy gap (DE ST )a nd featuring an electronegative group with al one pair dimerize by the interaction between the substituent lone pair and the silylene empty orbital, leading to af our-membered ring structures (type B). [9, 7b] It is interesting to note that in the case of bisdiisopropylamino silylene IV,b oth types of dimerization processes (Si=Si bonded A,and N-bridged B)were observed, spectroscopically in solution, depending on the temperature. [7,10] In contrast, the stable cyclic diaminosilylene VI does not dimerize to the corresponding tetraaminodisilene,o rNbridged dimer,but instead undergoes the insertion reaction of another silylene into aS i ÀNb ond to generate the transient amino-silyl silylene VII (inserted dimer,t ype C), which readily dimerizes to the diaminodisilyl disilene VIII. [11] Interestingly,b oth steps are reversible at room temperature, and such ad imerization process (type C), involving ar eversible silylene insertion into a s-bond, in mild conditions,i s extremely rare,a lthough non-reversible insertion reactions are typical for transient silylenes.H erein we report the reversible dimerization of phosphine-stabilized silylenes 2, leading to inserted dimers 3 (type C), which can be isolated and fully characterized in the solid state.Recently,wehave reported the synthesis of the first stable phosphine-supported Si II hydride 2c-H and chloride 2c-Cl (Scheme 1) [12,15] by reduction of the corresponding chlorosilane derivatives 1c-X (X = H, Cl), and the unique reactivity of 2c-H with olefins as well as with diphenylacetylene. [13] In the present study,wehave investigated the relationship between Scheme 1. Synthesis of hydro-and chlorosilylenes (2a,b,c-X)and their reversible dimerization by silylene insertion into a s-SiÀXb ond (X = H, Cl).

Oxidative Addition and Reductive Elimination at Main-Group Element Centers

“…Baceiredo and Kato reported the reversible dimerization of phosphine-stabilized silylenes as a consequence of oxidative addition and reductive elimination of Si−H bonds. 408 The reduction of dichlorosilane 545 at room temperature yielded a mixture of hydrosilylene 546 and the dimer 547 as a result of Si− H bond activation (Scheme 172). Initially, the ratio of 546 and 547 was 70:30.…”

Thermal rearrangement of a 1,2-bis(silylene): Synthesis and crystal structure of a silyl-silylene

“…The Si−Si distance in 3, 2.394(1) Å, lies in the known range for such interactions, and is comparable to Si−Si distances in related silyl-silylenes, e.g. 2.386(1) Å in 1b, and 2.377(5) Å in {PhC(NBu t ) 2 }Si-Si(H){(Bu t N) 2 C(H)Ph} (Protchenko et al, 2013;Rodriguez et al, 2015;Yamaguchi and Sekiguchi, 2011;Zhang et al 2010).…”