Reactivity of the Donor‐Stabilized Guanidinatosilylene [ArNC(NMe₂)­NAr]Si[N(SiMe₃)₂] (Ar = 2,6‐Diiso­propylphenyl)

Abstract

To get more information about the reactivity profile of the donor-stabilized guanidinatosilylene [ArNC(NMe 2 )NAr]Si-[N(SiMe 3 ) 2 ] (1; Ar = 2,6-diisopropylphenyl), a series of test reactions was studied. Thus, treatment of 1 with Me 3 SiN 3 , (PhO) 2 P(O)N 3 , PhC(O)Ph, Me-C≡C-C≡C-Me, Ph-C≡C-C≡C-Ph, CO 2 , CS 2 , ZnCl 2 , or ZnEt 2 yielded the respective products 9-17, all of which were characterized by elemental analyses, NMR spectroscopic investigations in the solid state and in solution, and single-crystal X-ray diffraction studies. The formation of Scheme 1. Chemical structures of compounds 1-8.[a] Te). Thus, the two nitrogen-bound SiMe 3 groups add an additional reactivity facet to the typical silylene reactivity of 1. To gain further information about the synthetic potential of 1, we studied a series of further reactions [reactions with Me 3 SiN 3 , (PhO) 2 P(O)N 3 , PhC(O)Ph, R-C≡C-C≡C-R (R = Me, Ph), CO 2 , CS 2 , ZnCl 2 , or ZnEt 2 ], which led to the formation of compounds 9-17 (Scheme 2). These investigations were performed as part of our ongoing systematic studies on donor-stabilized silylenes. [1][2][3][4] Results and Discussion SynthesesTo gain more information about the reactivity of silylene 1, a series of test reactions was studied. The reactions investigated are summarized in Schemes 3-7 and Scheme 9.Scheme 3 shows the reaction of 1 with the silyl azide Me 3 SiN 3 and the phosphoryl azide (PhO) 2 P(O)N 3 , respectively, to give the four-coordinate silicon(IV) complexes 9 and 10. The syntheses were performed in toluene at 20°C (formation of N 2 ), and compounds 9 and 10 were isolated after crystallization from n-hexane and toluene, respectively, as colorless crystalline solids (yield: 9, 85 %; 10, 80 %). Analogous reactions of other silylenes with alkyl or silyl azides have already been described in the literature. [5] Compounds 9 and 10 contain an Si=N double bond and can be formally regarded as intramolecularly donor-stabilized silaimines. [6] Scheme 3. Syntheses of compounds 9 and 10.Scheme 4 shows the reaction of 1 with benzophenone to give the four-coordinate silicon(IV) compound 11. The synthesis was performed in toluene at 20°C, and 11 was isolated after crystallization from n-hexane as a colorless crystalline solid (yield 87 %). According to the literature, silylenes can react with ketones to form isolable siloxiranes ("genuine" siloxiranes with four-coordinate silicon atoms [7] or donor-stabilized siloxiranes with five-coordinate silicon atoms [8] ). However, we did not isolate the expected [1+2] cycloaddition product 11′; instead, the isomeric 1-sila-2-oxaindane 11 was obtained. As shown in Scheme 4, we propose 11′ (or the corresponding isomer with a four-coordinate silicon atom and a monodentate guanidinato ligand) to be an intermediate in the formation of 11, which then undergoes a rearrangement to afford the intermediate 11′′, followed by a re-aromatization (1,3-H-shift) to give the final product 11. The proposed reaction mechanism is based on a Eur.

Iron(II), Cobalt(II), Nickel(II), and Zinc(II) Silylene Complexes: Reaction of the Silylene [iPrNC(NiPr2)NiPr]2Si with FeBr2, CoBr2, NiBr2⋅MeOCH2CH2OMe, ZnCl2, and ZnBr2

“…Generally, carbonyl‐free silylene complexes of 3d transition metals in the formal oxidation state +2 are very rare and represent (except for the zinc(II) complex 13 ) bis(silylene) or mixed silylene–carbene complexes, most of them being pincer‐type complexes . To the best of our knowledge, four‐coordinate silicon(II) compounds with an SiN 3 M skeleton (M=Fe, Co, Ni) and M in the formal oxidation state +2 (like the spirocyclic compounds 4 – 6 ) have not yet been described in the literature.…”

First Insertions of Carbene Ligands into Ge−N and Si−N Bonds

“…In fact, the last decade has witnessed the blooming of their transition‐metal chemistry, their main‐group derivative chemistry, and their use as ligands in homogeneous catalysts –. However, despite being strong electron‐donating reagents, comparable to or even stronger than very basic phosphanes and N‐heterocyclic carbenes (NHCs), their reactivity as nucleophiles for the formation of E−C bonds (E=Si, Ge, Sn) is as yet underdeveloped …”

“…Some amidinatogermylenes–– and ‐silylenes react with transition metals to give products that result from the insertion of the metal atom into an E−N bond of the corresponding amidinatotetrylene reagent. However, the ring expansion of an amidinatotetrylene by insertion of an organic fragment has only been reported as the result of two very specific reactions that do not involve carbene reagents: a thiocarbonyl group (that arises from CS 2 ) has been inserted into a Si−N bond of a bis(guanidinato)silylene and a 4‐MeOC 6 H 4 CMe fragment (that arises from the ketone 4‐MeOC 6 H 4 C(O)Me) has been inserted into a Ge−N bond of an amidinatogermylene‐borane Lewis pair …”

A cyclopentadienyl functionalized silylene – a flexible ligand for Si- and C-coordination

“…26,27,41 Additionally this is one of very few examples of a [ZnR] + -fragment bound directly to a silicon atom. 42,43 Due to the rearrangement and deprotonation the coordination of the silyl anion is different from that of typical silylene zinc species, which feature a dative bond between zinc complexes ZnR 2 and silylene. The difference in coordination can be attributed to the Cp 4 -ring, which due to its labile proton acts as non-innocent substituent on the silylene.…”