The strikingly different behavior of the ylide-like, N-heterocyclic silylene LSi: (5: L = CH[(C horizontal lineCH(2))CMe(NAr)(2)]; Ar = 2,6-(i)PrC(6)H(3)) versus its LSi-->Ni(CO)(3) complex 13 to activate E-H bonds (E = S, N) of small molecules is reported. Remarkably, conversion of 5 with hydrogen sulfide leads exclusively to the first isolable silathioformamide, L'Si( horizontal lineS)H (16: L' = CH[C(Me)NAr](2); Ar = 2,6-(i)PrC(6)H(3)) with a donor-supported Si horizontal lineS double bond and four-coordinate silicon. The latter result demonstrates the unusual ambivalent reactivity of 5 by combining two modes of reactivity involving S-H bond activation and subsequent 1,4- and 1,1-addition, respectively. In addition, 5 can serve as a ligand with well-balanced sigma-donor and pi-acceptor capabilities toward transition metals. This has been demonstrated by the isolable [Ni(0)(arene)] complexes 12a-e (arene = Me(n)C(6)H(6-n), n = 0-3), which are ideal precursors for the formation of the corresponding Ni(CO)(3) complex 13. The latter activates a S-H bond in hydrogen sulfide, too, but the presence of the Ni(CO)(3) moiety governs the formation of the complex 17, bearing an unprecedented beta-diketiminate silicon(II) thiol ligand: L'Si(SH): (L' = CH[C(Me)NAr](2); Ar = 2,6-(i)PrC(6)H(3)). Likewise, the Si(II)-->Ni(CO)(3) coordination in 13 steers exclusively 1,4-addition of ammonia, isopropylamine, and phenylhydrazine onto the silylene ligand 5, leading to the corresponding beta-diketiminate silicon(II) amide or hydrazide complexes L'Si(NHR)-->Ni(CO)(3) (23a-c: R = H, (i)Pr, N(H)Ph). IR measurements reveal that the carbonyl stretching frequencies of the Ni(CO)(3) moiety in 23a-c are shifted to even lower wavenumbers in comparison to those of NHCs or phosphines. In other words, the beta-diketiminate silicon(II) amide ligands in 23a-c represent the strongest donors in the series of N-heterocyclic silylenes reported as yet.

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The first silicon(II) hydroxide and related electronically tunable NHSi ligands have been synthesized in the coordination sphere of a [Ni(CO)(3)] moiety through facile addition of water and other electrophiles to the corresponding NHSi-tricarbonylnickel complex. The latter modified silicon (II) ligands are unique and exhibit striking donor/acceptor capabilities depending on their substitution pattern. While strong Lewis acids [H(+) or B(C(6)F(5))(3)] lead to modified silicon(II) ligands in the coordination sphere of nickel with an increased pi-acceptor and decreased sigma-donor character (PF(3)-like), by contrast, addition of water or trifluoromethanesulfonic acid furnishes the corresponding donor-stabilized silicon(II)-nickel complexes with a inverse donor/acceptor strength similar to those of triorganophosphines and NHCs.

Twice, and faster: Reaction of the zwitterionic silylene 1 with AsH3 occurs stepwise at ambient temperature to give the first crystalline, donor‐stabilized arsasilene 3 via its 1,1‐addition product (silylarsane 2). In contrast, the activation of PH3 by 1 merely leads to the phosphorus analogue of 2. The strikingly different metal‐free activation of the series of Group 15 hydrides EH3 (E=N, P, As) by 1 was rationalized with DFT calculations.

The right mix does the trick: Elusive {Ni(0)(eta(6)-arene)} moieties can be dramatically stabilized by the N-heterocyclic silylene ligand 1, which has a zwitterionic mesomeric structure. The sigma, pi-acid-base synergism between nickel and 1 explains the unexpectedly high stability of the new silylene complexes 2, which enables arene exchange studies at a Ni(0) center. Addition of B(C(6)F(5))(3) to 2 affords the zwitterionic silylene complex 3 (see scheme, R=2,6-iPr(2)C(6)H(3)).

There and back: An isocyanide‐centered silene–disilene reversibility was observed for the insertion of isocyanides into unsymmetrically substituted disilenes. This reaction leads to the formation of silenes at room temperature; the disilene is regenerated in the presence of a Lewis acid.

Doppelt und schneller: Die Reaktion des zwitterionischen Silylens 1 mit AsH3 verläuft bei Raumtemperatur schrittweise und ergibt das erste kristalline, donorstabilisierte Arsasilen 3 über sein 1,1‐Additionsprodukt (Silylarsan 2). Dagegen führt die Aktivierung von PH3 durch 1 lediglich zum Phosphoranalogon von 2. Die auffallend unterschiedliche metallfreie Aktivierung der Hydride EH3 (E=N, P, As) der 15. Gruppe durch 1 kann mithilfe von Dichtefunktionalrechnungen erklärt werden.

Proof of concept for the protection of the nucleophilic functionality of disilenidesdisila analogues of vinyllithiumwith preservation of the SiSi bond is reported. 1-Iodo-2,4,6-trimethoxybenzene (TMOP-I) reacts with lithium tris(2,4,6-triisopropylphenyl)disilenide (1), affording the disilene Tip 2 SiSi(Tip)TMOP ( 2) in high yield. The presence of the TMOP group in disilene 2 enables the regioselective addition of polar substrates to the SiSi double bond, including water, ammonia, acetylenes, and isocyanides. NMR spectroscopic analysis of the reductive cleavage of the TMOP group and subsequent trapping of the corresponding disilenides with Me 3 SiCl reveals KC 8 as a highly appropriate reducing agent for the selective deprotection.