Reversible Insertion of Unactivated Alkenes into Silicon(II)–Tin Bonds

Abstract

The migratory insertion of alkenes is one of the most fundamental processes in organometallic chemistry and thus plays a crucial role in many catalytic processes, such as polymerization, [1] 1,2-addition reactions, [2,3] and Heck-type reactions. [4] In many cases, the insertion reaction is reversible, and a key step in catalysis is the formation of alkenes through a b-hydride elimination from alkyl transition-metal complexes.In the case of nonmetallic systems, the olefin-insertion reaction is long-known in the chemistry of Group 13 elements, as in the case of alkene hydroboration. [5,6] Olefin polymerization promoted by aluminum-based catalysts is believed to proceed through olefin insertion into an Al À C bond, [7] although the mechanism and active catalytic species are still controversial. [8] The thermal decomposition of trisopropylaluminum through b elimination is a well-known synthetic method involving diisobutylaluminum hydride (DIBAL). [9] In marked contrast, similar chemistry of Group 14 elements is underdeveloped. Only a few hydrostannylation [10] and hydrogermylation [11] reactions of unsaturated compounds with tin(II) or germanium(II) hydrides [12] have recently been reported. It was also reported that the hydrogermylation reaction of a phosphaalkyne is reversible. [13] We recently developed stable silylene-phosphine complexes, which showed high reactivity as silylenes [14] and as phosphonium silaylides. [15] In particular, we reported that they react reversibly with unactivated alkenes, such as ethylene, in a [2+1] cycloaddition process. [16] Furthermore, in the case of the silicon(II) hydride derivative 1 a-H (named in analogy with 1 a-Sn in Scheme 1), the oxidative addition was followed by a migratory insertion of the alkene into the Si À H bond to regenerate a reactive Si II species. [17] This reaction can be regarded as a transition-metal-catalyst-free hydrosilylation process.Many other alkene-insertion reactions into a siliconheteroatom bond, such as silylstannylation, [3b] have also been described as synthetically useful transformations, although such reactions generally require transition-metal catalysts. Thus, we were interested in extrapolating our system to other silylene-phosphine complexes featuring a silicon(II)-heteroatom bond, such as a Si II ÀSn bond. Herein, we report that alkene insertion into the Si II ÀSn bond of trimethylstannylsubstituted silylene-phosphine complexes 1-Sn takes place without any catalyst and under very mild conditions. Of particular interest is the reversibility of the insertion reaction even at room temperature.The trimethylstannyl-substituted silylene complexes 1-Sn can be prepared readily from the corresponding chlorosilylene [18] derivatives by treatment with one equivalent of trimethylstannyllithium. Products 1 a-Sn (81 % yield) and 1 b-Sn (85 % yield) could both be isolated in the solid state and were characterized in solution as well as by X-ray diffraction analysis (Figure 1, top). [19] Complex 1 a-Sn slowly reacted with ethylene gas (10 bar) at room ...

1,2- and 1,1-Migratory Insertion Reactions of Silylated Germylene Adducts

“…Similar alkyne insertion reactivity was later observed for a diborylstannylene [15]. A related ethylene insertion was observed previously in the Si-Sn bond of a stannylated silylene adduct [16], and later in the Si-Si bond of the stable acyclic silylene dipp(Me 3 Si)N-Si-Si(SiMe 3 ) 3 (dipp = 2,6-iPr 2 C 6 H 3 ) [17]. More recently, Sasamori, Tokitoh and co-workers reported the spectacular example of a digermyne acting as a main group catalyst for the cyclotrimerization of arylacetylenes.…”

“…All hydrogen atoms omitted for clarity (bond lengths in Ả, angles in deg). Ge(1)-P(1) 2.3900 (16), Ge(1)-Ge(2) 2.4980(9), Ge(1)-Ge(3) 2.5114(9), Ge(2)-Cl(1) 2.2177 (15), Ge(2)-Cl(2) 2.2228 (15), Ge(2)-Si(1) 2.3966 (15), Ge(3)-Cl(3) 2.2149 (15), Ge(3)-Cl(4) 2.2397 (16), Ge(3)-Si(5) 2.4101 (18)…”

Donor‐Stabilized 1,3‐Disila‐2,4‐diazacyclobutadiene with a Nonbonded Si⋅⋅⋅Si Distance Compressed to a Si=Si Double Bond Length

“…This low value may be due to local diamagnetic phenomena and 2 can actually be considered to be slightly antiaromatic . The Si1−P bond distances are only slightly longer than those observed for phosphine‐stabilized silylenes (2.31–2.35 Å), thus suggesting a strong coordination of the phosphine ligands on the Si IV atoms. Of particular interest, both isomers of 2 present exceptionally short Si1⋅⋅⋅Si1′ diagonal distances [ 2 a : 2.23502(17) Å, 2 b : 2.2303(10) Å], which are significantly shorter than those observed for tetramesityl‐1,3‐disiloxanes (2.31–2.39 Å), and are within the range expected for Si=Si bonds (2.15–2.23 Å) …”

Temperature‐Dependent Electron Shuffle in Molecular Group 13/15 Intermetallic Complexes

“…[14] Nikonov et al reported on the reversible reaction of RAl and RAlH 2 , yielding the dialane R(H)AlÀAl(H)R. [15] Furthermore, alkynes reversibly react with Lapperts stannylene [(Me 3 Si) 2 CH] 2 Sn and with a digallane, [16,17] whereas the reversible, temperature-controlled binding and release of C 2 H 4 was observed in reactions with a distannyne and with Si II complexes. [18,19] Ragogna et al reported the reversible, photoinduced activation of P 4 by reaction with a Ge II compound. [20] In contrast, the formation of a fully reversible equilibrium between a low-valent main-group metal complex and the corresponding intermetallic complex is without precedent.…”