Indirect and Direct Grafting of Transition Metals to Siliconoids

Unsaturated charge-neutral silicon clusters (siliconoids) are important as gas-phase intermediates between molecules and the elemental bulk. With stable zirconocene- and hafnocene-substituted derivatives, we here report the first examples containing directly bonded transition-metal fragments that are readily accessible from the ligato-lithiated Si6 siliconoid (1Li) and Cp2 MCl2 (M=Zr, Hf). Charge-neutral siliconoid ligands with pending tetrylene functionality were prepared by the reaction of amidinato chloro tetrylenes [PhC(NtBu)2 ]ECl (E=Si, Ge, Sn) with 1Li, thus confirming the principal compatibility of such low-valent functionalities with the unsaturated Si6 cluster scaffold. The pronounced donor properties of the tetrylene/siliconoid hybrids allow for their coordination to the Fe(CO)4 fragment

Cationic Tetrylene‐Iron(0) Complexes: Access Points for Cooperative, Reversible Bond Activation and Open‐Shell Iron(−I) Ferrato‐Tetrylenes

The open-shell cationic stannylene-iron(0) complex 4 (4=[PhiPDippSn⋅Fe⋅IPr]+; PhiPDipp={[Ph2PCH2Si(iPr)2](Dipp)N}; Dipp=2,6-iPr2C6H3; IPr=[(Dipp)NC(H)]2C:) cooperatively and reversibly cleaves dihydrogen at the Sn−Fe interface under mild conditions (1.5 bar, 298 K), in forming bridging hydrido-complex 6. The One-electron oreduction of the related GeII−Fe0 complex 3 leads to oxidative addition of one C−P linkage of the PhiPDipp ligand in an intermediary Fe−I complex, leading to FeI phosphide species 7. One-electron reduction reaction of 4 gives access to the iron(−I) ferrato-stannylene, 8, giving evidence for the transient formation of such a species in the reduction of 3. The covalently bound tin(II)-iron(−I) compound 8 has been characterised through EPR spectroscopy, SQUID magnetometry, and supporting computational analysis, which strongly indicate a high localization of electron spin density at Fe−I in this unique d9-iron complex.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Verband der Chemischen Industrie http://dx.doi.org/10.13039/100007215Peer Reviewe

Exohedral functionalization vs. core expansion of siliconoids with Group 9 metals: catalytic activity in alkene isomerization

Taking advantage of pendant tetrylene side-arms, stable unsaturated Si6 silicon clusters (siliconoids) with the benzpolarene motif (the energetic counterpart of benzene in silicon chemistry) are successfully employed as ligands towards Group 9 metals. The pronounced σ-donating properties of the tetrylene moieties allow for sequential oxidative addition and reductive elimination events without complete dissociation of the ligand at any stage. In this manner, either covalently linked or core-expanded metallasiliconoids are obtained. [Rh(CO)2Cl]2 inserts into an endohedral Si–Si bond of the silylene-functionalized hexasilabenzpolarene leading to an unprecedented coordination sphere of the Rh centre with five silicon atoms in the initial product, which is subsequentially converted to a simpler derivative under reconstruction of the Si6 benzpolarene motif. In the case of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) a similar Si–Si insertion leads to the contraction of the Si6 cluster core with concomitant transfer of a chlorine atom to a silicon vertex generating an exohedral chlorosilyl group. Metallasiliconoids are employed in the isomerization of terminal alkenes to 2-alkenes as a catalytic benchmark reaction, which proceeds with competitive selectivities and reaction rates in the case of iridium complexes

A comparison for donor-acceptor interactions between E(PH3)2 and NHEMe ligands (E = C to Pb) of W(CO)5 complexes using energy decomposition analysis method with natural orbitals for chemical valence theory

Quantum chemical calculations at the BP86/TZ2P+ level of theory are performed for a comparison of density functional theory (DFT) between tetrylones [(CO)5W-{E(PH3)2}] (W5-EP2) and tetrylenes [(CO)5W-{NHEMe}] (W5-NHEMe) when E = C to Pb. The EDA-NOCV results suggest that the W-E bond dissociation energies (BDEs) in tetrylone complexes increase from the lighter to the heavier homologues. The W-E bond dissociation energies (BDEs) trend in W5-EP2 comes from the increase in (CO)5W←E(PH3)2 donation and strong electrostatic attraction, and that the ligands E(PH3)2 (EP2) are strong s-donors and very weak π-donors. The W-E BDEs trend in tetrylene complexes W5-NHEMe is opposite to that of the W5-EP2 complexes which decrease from the lighter to the heavier homologues. The NHEMe ligands are strong s-donors and weak π-acceptors. NOCV pairs were used in a description of the chemical bond between the W(CO)5 fragment and the ligands in the transition-metal complexes and the results indicated that the NOCV pairs lead to very valuable description of the bonding situation of the fragment-ligand bond in complexes. Keywords. Density functional theory; Bond dissociation energies (BDEs); Energy decomposition analysis (EDA); Natural Orbitals for Chemical Valence (NOCV)

Frustrated Lewis Pairs from Al–E{14} Bonds (E{14} = Ge, Sn, Pb)

The potassium aluminyl K[Al(NON)] ([NON] 2−=[O(SiMe 2NDipp) 2] 2−, Dipp=2,6-iPr 2C 6H 3) reacts with group 14 chloroamidinates E {14}(Am)Cl (E {14}=Ge, Sn, Pb. [Am] −=[tBuC(NDipp) 2] −) to form (NON)Al−E {14}(Am) Lewis pairs with unsupported Al−E {14} bonds, including the first structurally authenticated Al−Pb bond. Analysis using spectroscopic (NMR, UV-vis and Mössbauer for E {14}=Sn), X-ray diffraction and computational (DFT, QTAIM, TD-DFT) methods conclude an Al−E {14} σ-bond derived from a Lewis basic Al and a Lewis acidic tetrylene, with back-donation from the E {14} s-orbital lone pair donor NBO to acceptor NBOs on Al that are derived from s/p-orbitals. The reaction of the Al−Ge compound with CO 2 forms the dioxocarbene (NON)Al(μ-O 2C)Ge(Am), whilst under the same conditions the Al−Sn compound reacts with additional CO 2 to form the carbonate, (NON)Al(μ-CO 3)Sn(Am). Addition of ethene to the Al−E {14} (E {14}=Ge, Sn) compounds introduces an ethylene bridge between the aluminium and group 14 atoms forming a frustrated Lewis pair (FLP). Reaction of the (Al/Ge) FLP with CO 2 forms an activation product with new Al−O and Ge−C bonds, whilst reaction with iPrN=C=NiPr proceeds with insertion into the Al−C bond to form an aluminium amidinate.</p

Stable functionalized unsaturated siliconoids : from a Tetrylene / Siliconoid hybrid to application in homogeneous catalysis

Siliconoids have received tremendous attention due to the prominent role of silicon in technologies of the modern society. The presence of the partially unsubstituted cluster scaffold resembles silicon surface materials at molecular regimes. While siliconoids play important roles as presumed intermediates during chemical vapor deposition processes or in heterogeneous catalysis, the possibility to graft functional groups to the Si6 benzpolarene scaffold is a prerequisite for their incorporation as building blocks into extended systems. Main attention of this thesis is the introduction and transformation of functionalities in the periphery of Si6 siliconoids. Dichlorinated metallocenes of Group 4 are shown to be suitable reagents for the transfer of metals to the Si6 siliconoid. The electrophilic transfer of a chlorinated amidinato tetrylene to the Si6 siliconoid facilitates the coordination to transition metal fragments. As will be shown, depending on the nature of the substituents of the transition metal fragments, different and unprecedented structural motifs can be obtained. In context of the application of siliconoids in homogeneous catalysis, the reactivity of a silylene/siliconoid hybrid towards chalcogens and carbon monoxide was investigated resulting in unprecedented and unsaturated chalcogen-expanded heterosiliconoids as well as in the full cleavage of the C≡O triple bond under formation of an Si=C Enol ether bridge in the peripherie of the cluster scaffold.Silicoide erregten aufgrund der herausragenden Rolle von Silicium in den Technologien der modernen Gesellschaft eine enorme Aufmerksamkeit. Das Vorhandensein des teilweise unsubstituierten Clustergerüsts ähnelt Siliciumoberflächenmaterialien im molekularen Bereich. Während Silicoide als vermutete Zwischenprodukte bei chemischen Gasphasenabscheidungsprozessen oder bei der heterogenen Katalyse eine wichtige Rolle spielen, ist die Möglichkeit, funktionelle Gruppen auf das Si6 Benzpolarengerüst zu übertragen eine Voraussetzung für deren Einbau als Bausteine in erweiterte Systeme. Das Hauptaugenmerk dieser Arbeit liegt auf der Einführung und Transformation von Funktionalitäten in der Peripherie von Si6 Silicoiden. Es wurde gezeigt, dass dichlorierte Metallocene der Gruppe 4 geeignete Reagenzien für die Übertragung von Metallen auf das Si6 Siliciumgerüst sind. Der elektrophile Transfer eines chlorierten Amidinatotetrylens auf ein Si6 Silicoid erleichtert die Koordination an Übergangsmetallfragmente. Wie gezeigt werden wird, können unabhängig von der Art der Substituenten der Übergangsmetallfragmente unterschiedliche und beispiellose Strukturmotive erhalten werden. Im Zusammenhang mit der Anwendung von Silicoiden in der homogenen Katalyse wurde die Reaktivität eines Silylen/Silicoid Hybrids gegenüber Chalkogenen und Kohlenmonoxid untersucht, was zu beispiellosen, ungesättigten Chalkogenexpandierten Heterosilicoiden, sowie zur vollständigen Spaltung der C≡O Dreifachbindung unter Bildung einer Si=C Enoletherbrücke in der Peripherie des Clustergerüsts führte

Experimentelle und theoretische Studien zu amino- und silylsubstituierten cyclischen Tetrylenen

Verbindungen, in denen Gruppe 14 Elemente zweifach koordiniert sind (Tetrylene), eignen sich gut als Ausgangsstoffe zur Synthese von Mehrfachbindungssystemen, Metallkomplexen und kationischen Verbindungen. Im Rahmen dieser Arbeit wurde speziell der Einsatz amino- sowie silylsubstituierter cyclischer Tetrylene (Silylene, Germylene, Stannylene und Plumbylene) zur Darstellung entsprechender niederkoordinierter Verbindungen der Gruppe 14 Elemente untersucht. In diesem Zusammenhang wurde die Synthese eines bislang unbekannten N-heterocyclischen Stannylens und die Darstellung eines Wolframpentacarbonylsilylenkomplexes vorgestellt. Auf Grundlage experimenteller Ergebnisse konnten die Bindungseigenschaften von N-heterocyclischen Silylenen in Komplexen erklärt werden. Zusätzlich wurde mit Hilfe quantenchemische Rechnungen herausgestellt, dass nicht kovalente Wechselwirkungen einen großen Beitrag zur Bindungssituation in Tetrylendimeren und Tetrylenmetallkomplexen leisten

Dehydrogenative Double C−H Bond Activation in a Germylene-Rhodium Complex

Transition metal tetrylene complexes offer great opportunities for molecular cooperation due to the ambiphilic character of the group 14 element. Here we focus on the coordination of germylene [(ArMes2)2Ge :] (ArMes=C6H3-2,6-(C6H2-2,4,6-Me3)2) to [RhCl(COD)]2 (COD=1,5-cyclooctadiene), which yields a neutral germyl complex in which the rhodium center exhibits both η6- and η2-coordination to two mesityl rings in an unusual pincer-type structure. Chloride abstraction from this species triggers a singular dehydrogenative double C−H bond activation across the Ge/Rh motif. We have isolated and fully characterized three rhodium-germyl species associated to three C−H cleavage events along this process. The reaction mechanism has been further investigated by computational means, supporting the key cooperative action of rhodium and germanium centers.European Research Council 756575Junta de Andalucia P18-FR-468

Tetrelanes versus tetrylenes as precursors to transition metal complexes featuring tridentate PEP tetryl ligands (E=Si, Ge, Sn)

Research grants obtained from Ministerio de Economía y Competitividad (RED2018-102387-T) and Agencia Estatal de Investigación (PID2019-104652GB-I00/AEI/10.13039/ 501100011033) are gratefully acknowledged