A Generic One‐Pot Route to Acyclic Two‐Coordinate Silylenes from Silicon(IV) Precursors: Synthesis and Structural Characterization of a Silylsilylene

Abstract

We thank the Leverhulme Trust (F/08699/E), the Australian Research Council and the EPSRC (EP/F019181/1, EP/F055412/1, and computational resources through its National Service for Computational Chemistry Software). We also thank UCL for computing resources through the Research Computing "Legion" cluster and associated services.Supporting information for this article, including synthetic, spectroscopic, and crystallographic data for compounds 2, 4, 5, 6, and {CpFe(CO)} 2 (m-CO)(m-SiBr{N(SiMe 3 )Dipp}, as well as details of the DFT calculations on 3 b, and CIFs for 2, 3 b, 4, 5, 6, and {CpFe(CO)} 2 (m-CO)(m-SiBr{N(SiMe 3 )Dipp}, is available on the WWW under http://dx.Scheme 3. Proposed mechanism for the one-pot formation of acyclic silylenes 3 a and 3 b from 1 through silylenoid intermediates (M = Li or K), and the structure of the digallylsilylenoid 6. Key bond lengths [] and angles [8]: Si

Cyclic Amino(Ylide) Silylene: A Stable Heterocyclic Silylene with Strongly Electron‐Donating Character

“…[4] However,c ompared to the very large family of stable carbenes,t he structural diversity of stable silylenes is still limited, [5] and most of known stable cyclic and acyclicsilylenes are only symmetrically substituted (A-F). [6][7][8][9][10] Only af ew exceptions with an unsymmetrical pattern have recently been reported, namely the acyclica mino(silyl) and amino(boryl) silylenes (G [11] and H [12] ), which are stabilized by p-a nd s-donating substituents.B oth compounds clearly show an ambiphilic reactivity that allows the activation of small molecules such as H 2 .T ot he best of our knowledge, as table silylene featuring two different p-donating groups remains elusive.Out of all the possibilities,wewere interested in an amino/ylide substitution pattern for the stabilization of heterocyclic silylenes (I). In contrast to amino substituents, which behave not only as excellent p donors but also as strong s acceptors toward the silylene center, an effect that is directly related to the electronegativity difference between nitrogen and silicon (3.0 vs.1.9), less-electronegative carbonbased p-donating substituents such as ap hosphonium ylides are strong p donors and poorer s acceptors.T herefore,w e assumed that the combination of these two types of substituents should enhance the nucleophilic character of the corresponding silylenes.Indeed, Driess et al reported that the symmetrical bis-ylide-stabilized silylene D shows an extraordinarily basic character and reacts even with ethereal solvents such as THF or DME.…”

A Stable N‐Hetero‐Rh‐Metallacyclic Silylene

“…Of particular interest, such ag eometric deviation has not been observed for the related complexes featuring rhodium-carbon double [33] or triple bonds. [7,8] In marked contrast, in the case of tetrahedral isomer 6 tet ,these orbitals p* Si-Rh (LUMO + 2) and n Si (HOMOÀ1) are much further apart in energy (DE = 4.037 eV). [30] NBO analysis also shows that, despite the large N1ÀSiÀRh angle (122.58 8), the silylene lone pair orbital of 6 tet (n s )m aintains ap articularly high scharacter (s:7 9.8 %, p: 20.2 %), which is even slightly higher than that calculated for the previously reported donor-stabilized three-membered cyclic silylene (s:7 5.4 %, p: 24.6 %).…”

“…[34] Therefore, such ap articular tetrahedral geometry around the Rh atom observed in the case of 5 could be related to the electropositive character of the Si atom (Si:1 .8, Rh:2 .2) strongly polarizing the SiÀRh s bond (5-D in Figure 2), similar to the previously reported silyl-substituted Rh I complex with an unusual trigonal pyramidal geometry. [7,8] Silylene 5 readily reacts with one equivalent of H 2 at room temperature to afford the corresponding cyclic dihydrosilane 8,w hich was isolated in 61 %y ield (Scheme 2) and characterized by X-diffraction analysis ( Figure 5). [35] Thef rontier molecular orbitals of square-planar isomer 6 sp are classical for as ilylene species with the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) corresponding to the Si lone pair of electrons (n Si )a nd the vacant (p* Si-Rh )o rbital mainly localized at the Si atom, respectively ( Figure 4).…”

“…[5] Indeed, most of the stable silylenes described to date are incorporated in ac yclic structure and afew known stable acyclic (amino)silylenes show an enhanced reactivity and ad ecreased stability. [6][7][8][9][10] In addition to the classical NHSi compounds II [11][12][13] and III, [14] other stable cyclic silylenes IV-VIII,w ith various substitution patterns,h ave been synthesized. [15][16][17][18][19] Furthermore,i th as been clearly established that the nature of the substituents (electronegativity, s-donating ability, bulkiness etc.)…”

“…[26] Caused by an acute Si1ÀRhÀP1 angle [88.1(1) 8 8], the N1ÀSi1ÀRh bond angle is exceptionally large [126.2(1) 8 8]f or six-membered cyclic silylenes (99.3-106.68 8). [7,8] TheS i1 À Rh bond length [2.138 (1) ]issignificantly shorter than Si(sp 2 ) À Rh I (2.299-2.352 ) [17,27] or Si(sp 3 )ÀRh I single bonds (2.236-2.394 ), [28][29][30] thus suggesting an enhanced RhÀSi multiple bond character as ar esult of significant Rh!Si p-back-donation. [7,8] TheS i1 À Rh bond length [2.138 (1) ]issignificantly shorter than Si(sp 2 ) À Rh I (2.299-2.352 ) [17,27] or Si(sp 3 )ÀRh I single bonds (2.236-2.394 ), [28][29][30] thus suggesting an enhanced RhÀSi multiple bond character as ar esult of significant Rh!Si p-back-donation.…”