Bis-Silylene-Supported Aluminium Atoms with Aluminylene and Alane Character.

The suitability of electron-rich bis-silylenes, specifically the neutral chelating [SiII(Xant)SiII] ligand (SiII=PhC(NtBu)2Si, Xant=9,9-dimethylxanthene) and the anionic [SiII(NAcrid)SiII)]- pincer ligand (NAcrid=2,7,9,9-tetramethylacridane), has been successfully probed to stabilize monovalent bis-silylene-supported aluminium complexes (aluminylenes). At first, the unprecedented aluminium(III) iodide precursors [SiII(Xant)SiII]AlI2 + I- 1 and [SiII(NAcrid)SiII)]AlI2 2 were synthesized using AlI3 and [SiII(Xant)SiII] or [SiII(NAcrid)SiII)]Li(OEt2)], respectively, and structurally characterized. While reduction of 1 with KC8 led merely to unidentified products, the dehalogenation of 2 afforded the dimer of the desired {[SiII(NAcrid)SiII)]Al:} aluminylene with a four-membered SiIV 2AlIII 2 ring. Remarkably, the proposed aluminylene intermediates [SiII(Xant)SiII]AlII and {[SiII(NAcrid)SiII)]Al:} could be produced through reaction of 1 and 2 with Collman's reagent, K2Fe(CO)4, and trapped as AlI:→Fe(CO)4 complexes 5 and 6, respectively. While 6 is stable in solution, 5 loses one CO ligand in solution to afford the silylene- and aluminylene-coordinated iron(0) complex 7 from an intramolecular substitution reaction. The electronic structures of the novel compounds were investigated by Density Functional Theory calculations.

Room-Temperature-Observable Interconversion Between Si(IV) and Si(II) via Reversible Intramolecular Insertion Into an Aromatic C-C Bond.

An easily isolable silacycloheptatriene (silepin) 1 b was synthesized from the reaction of a N-heterocyclic imino (IPrN) substituted tribromosilane IPrNSiBr3 with the sterically congested bis(trimethylsilyl)triisopropylsilyl silanide KSi(TMS)2 Si(i Pr)3 (BTTPS). In solution, the Si(IV) silepin 1 b is in a thermodynamic equilibrium with the acyclic Si(II) silylene 1 a. The relative concentration of the Si(II) or Si(IV) isomers can be controlled by temperature variation and observed by variable temperature NMR and UV/Vis spectroscopy. DFT calculations show a small reaction barrier for the Si(II)⇌Si(IV) interconversion and a small energy gap between the Si(II) and Si(IV) species. The reactivity of 1 a/b is demonstrated on a variety of small molecules.

Modification of Yttrium Silyl-Bridged Amide Alkyl Complexes through Si-H/C-H Cross-Dehydrocoupling of Silanes with a Silylamino Ligand: Synthesis, Reactivity, and Mechanism.

A new method for the modification of a silylamino ligand has been developed through mono and dual C(sp3 )-H/Si-H cross-dehydrocoupling with silanes. The reaction of [LY{η2 -(C,N)-CH2 Si(Me2 )NSiMe3 }] (L=bis(2,6-diisopropylphenyl)-ß-diketiminato, L' (1L '); L=tris(3,5-dimethylpyrazolyl)borate, TpMe2 (1TpMe2 )) with 2 equivalents of PhSiH3 in toluene gave the complexes [LY{η2 -(C,N)-C(SiH2 Ph)2 Si(Me2 )NSiMe3 }] (L=L' (2L' ); L=TpMe2 (2TpMe2 )). Moreover, 1TpMe2 reacted with the secondary silanes Ph2 SiH2 and Et2 SiH2 to afford the corresponding mono C-H activation products [TpMe2 Y{η2 -(C,N)-CH(SiHR2 )Si(Me2 )NSiMe3 }] (R=Ph (4 b); R=Et (4 c)). The equimolar reaction of 1TpMe2 with PhSiH3 also produced the mono C-H activation product 4 a ([TpMe2 Y{η2 -(C,N)-CH(SiH2 Ph)Si(Me2 )NSiMe3 }(thf)]). A study of their reactivity showed that4 a facilely reacted with 2 equivalents of benzothiazole by an unusual 1,1-addition of the C=N bond of the benzothiazolyl unit to the Si-H bond to give the C-H/Si-H cross-dehydrocoupling product [(TpMe2 )Y{η3 -(N,N,N)-N(SiMe3 )SiMe2 CH2 Si(Ph)(CSC6 H4 N)(CHSC6 H4 N)}] (5). These results indicate that this modification endows the silylamino ligand with novel reactivity.

σ-Silane Platinum(II) Complexes as Intermediates in C-Si Bond-Coupling Processes.

Platinum complexes [Pt(NHC')(NHC)][BArF ] (in which NHC' denotes a cyclometalated N-heterocyclic carbene ligand, NHC) react with primary silanes RSiH3 to afford the cyclometalated platinum(II) silyl complexes [Pt(NHC-SiHR')(NHC)][BArF ] through a process that involves the formation of C-Si and Pt-Si bonds with concomitant extrusion of H2 . Low-temperature NMR studies indicate that the process proceeds through initial formation of the σ-SiH complexes [Pt(NHC')(NHC)(HSiH2 R)][BArF ], which are stable at temperatures below -10 °C. At higher temperatures, activation of one Si-H bond followed by a C-Si coupling reaction generates an agostic SiH platinum hydride derivative [Pt(H)(NHC'-SiH2 R)(NHC)][BArF ], which undergoes a second Si-H bond activation to afford the final products. Computational modeling of the reaction mechanism indicates that the stereochemistry of the silyl/hydride ligands after the first Si-H bond cleavage dictates the nature of the products, favoring the formation of a C-Si bond over a C-H bond, in contrast to previous results obtained for tertiary silanes. Furthermore, the process involves a trans-to-cis isomerization of the NHC ligand before the second Si-H bond cleavage.

Is the R3 Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy.

The computation of metal-silyl interaction energies indicates the existence of situations in which the silyl group behaves as a Z-type ligand according to the Green method of covalent-bond classification. There is a scale of relative intrinsic silylicity Π, defined as the ratio of the intrinsic silyl-to-triflate interaction energy of a silyltriflate as a reference compound relative to the silyl-to-metal interaction of given complex, that can reveal in a straightforward manner the propensity of SiR3 groups to behave chemically as metal-bound "silylium" ions, namely, [SiR3 ]+ . Emblematic cases, either taken from the Cambridge Structural Database (CSD) or constructed for the purpose of this study, were also investigated from the viewpoints of extended transition-state natural orbitals for chemical valence (ETS-NOCV) and quantum theory of atoms in molecules (QTAIM) analyses. It is shown in the case of POBMUP-which is the iridium 1,3-bis[(di-tert-butylphosphino)oxy]benzene (POCOP) complex isolated by Brookhart et al.-how slight variations of molecular charge and structure can drastically affect the relative intrinsic silylicity of the SiEt3 group that is weakly bonded to the hydrido-iridium motif.

An NHC-Silyl-NHC Pincer Ligand for the Oxidative Addition of C-H, N-H, and O-H Bonds to Cobalt(I) Complexes.

N-Heterocyclic carbene based pincer ligands bearing a central silyl donor, [CSiC]- , have been envisioned as a class of strongly σ-donating ligands that can be used for synthesizing electron-rich transition-metal complexes for the activation of inert bonds. However, this type of pincer ligand and complexes thereof have remained elusive owing to their challenging synthesis. We herein describe the first synthesis of a CSiC pincer ligand scaffold through the coupling of a silyl-NHC chelate with a benzyl-NHC chelate induced by one-electron oxidation in the coordination sphere of a cobalt complex. The monoanionic CSiC ligand stabilizes the CoI dinitrogen complex [(CSiC)Co(N2 )] with an unusual coordination geometry and enables the challenging oxidative addition of E-H bonds (E=C, N, O) to CoI to form CoIII complexes. The structure and reactivity of the cobalt(I) complex are ascribed to the unique electronic properties of the CSiC pincer ligand, which provides a strong trans effect and pronounced σ-donation.

Molecular Calcium Hydride: Dicalcium Trihydride Cation Stabilized by a Neutral NNNN-Type Macrocyclic Ligand.

Hydrogenolysis of bis(triphenylsilyl)calcium containing the neutral NNNN-type macrocyclic amine ligand Me4TACD [Ca(Me4TACD)(SiPh3)2] (2), gave the cationic dinuclear calcium hydride [Ca2H3(Me4TACD)2](SiPh3) (3), characterized by NMR spectroscopy, single-crystal X-ray analysis, and DFT calculations. Compound 3 reacted with deuterium to give the deuteride [D3]-3.

µ3-η(2):η(2):η(2)-Coordination of Primary Silane on a Triruthenium Plane.

A µ3-η(2):η(2):η(2)-silane complex, [(Cp*Ru)3(µ3-η(2):η(2):η(2)-H3SitBu)(µ-H)3] (2 a; Cp* = η(5)-C5Me5), was synthesized from the reaction of [{Cp*Ru(µ-H)}3(µ3-H)2] (1) with tBuSiH3. Complex 2 a is the first example of a silane ligand adopting a µ3-η(2):η(2):η(2) coordination mode. This unprecedented coordination mode was established by NMR and IR spectroscopy as well as X-ray diffraction analysis and supported by a density functional study. Variable-temperature NMR analysis implied that 2 a equilibrates with a tautomeric µ3-silyl complex (3 a). Although 3 a was not isolated, the corresponding µ3-silyl complex, [(Cp*Ru)3(µ3-η(2):η(2)-H2SiPh)(H)(µ-H)3] (3 b), was obtained from the reaction of 1 with PhSiH3. Treatment of 2 a with PhSiH3 resulted in a silane exchange reaction, leading to the formation of 3 b accompanied by the elimination of tBuSiH3. This result indicates that the µ3-silane complex can be regarded as an "arrested" intermediate for the oxidative addition/reductive elimination of a primary silane to a trinuclear site.

Novel Distorted Pentagonal-Pyramidal Coordination of Anionic Oxodiperoxo Molybdenum and Tungsten Complexes.

Model compounds for silica surfaces modified with metal complexes are provided by the mononuclear anionic diperoxo species 1 and the dinuclear complex anions 2 (M = Mo, W). They were obtained in fair to nearly quantitative yields by the reactions of Ph3 SiOH and [Ph2 Si(OH)]2 O, respectively, with an aqueous solution of [MO(O2 )2 (H2 O)2 ].

A Symmetrically Bridging Triarylsilyl Ligand in a Dinuclear Rhodium Complex: Synthesis and Structure of [LRh(H)(µ-Cl)(µ-SiAr2 )(µ-SiAr3 )Rh(H)L] (Ar=Ph, p-FC6 H4 ; L=PiPr3 ).

Simply warming solutions of the dinuclear complexes 1 provides novel complexes 2 [Eq. (a); Ar = Ph, p-FC6 H4 ; L = PiPr3 ], which contain a bridging triarylsilyl ligand and show unusual thermal stability. Compounds with this type of symmetric structure are of interest as models of the transition state for the migration of tertiary silyl groups in a bimetallic framework.