Synthesis and reactivity of the first isolated hydrogen-bridged silanol-silanolate anions.

Weitkamp R, Neumann B, Stammler H-G, Hoge B. Synthesis and reactivity of the first isolated hydrogen-bridged silanol-silanolate anions. Angewandte Chemie International Edition. 2020;59(14):5494-5499.We report on the first examples of isolated silanol-silanolate anions, utilizing weakly coordinating phosphazenium counterions. The silanolate anions are synthesized by the reaction of the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol-silanolate anions are postulated intermediates in the hydroxide mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles due to the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Direct functionalization of white phosphorus with anionic dicarbenes and mesoionic carbenes: facile access to 1,2,3-triphosphol-2-ides

Rottschäfer D, Blomeyer S, Neumann B, Stammler H-G, Ghadwal R. Direct functionalization of white phosphorus with anionic dicarbenes and mesoionic carbenes: facile access to 1,2,3-triphosphol-2-ides. CHEMICAL SCIENCE. 2019;10(48):11078-11085.A series of unique C2P3-ring compounds [(ADC(Ar))P-3] (ADC(Ar) = ArC{(DippN)C}(2); Dipp = 2,6-iPr(2)C(6)H(3); Ar = Ph 4a, 3-MeC(6)H(4)4b, 4-MeC(6)H(4)4c, and 4-Me(2)NC(6)H(4)4d) are readily accessible in an almost quantitative yield by the direct functionalization of white phosphorus (P-4) with appropriate anionic dicarbenes [Li(ADC(Ar))]. The formation of 1,2,3-triphosphol-2-ides (4a-4d) suggests unprecedented [3 + 1] fragmentation of P-4 into P-3(+) and P-. The P-3(+) cation is trapped by the (ADC(Ar))(-) to give 4, while the putative P- anion reacts with additional P-4 to yield the Li3P7 species, a useful reagent in the synthesis of organophosphorus compounds. Remarkably, the P-4 fragmentation is also viable with the related mesoionic carbenes (iMICs(Ar)) (iMIC(Ar) = ArC{(DippN)(2)CCH}, i stands for imidazole-based) giving rise to 4. DFT calculations reveal that both the C3N2 and C2P3-rings of 4 are 6 pi-electron aromatic systems. The natural bonding orbital (NBO) analyses indicate that compounds 4 are mesoionic species featuring a negatively polarized C2P3-ring. The HOMO-3 of 4 is mainly the lone-pair at the central phosphorus atom that undergoes sigma-bond formation with a variety of metal-electrophiles to yield complexes [{(ADC(Ar))P-3}M(CO)(n)] (M = Fe, n = 4, Ar = Ph 5a or 4-Me-C(6)H(4)5b; M = Mo, n = 5, Ar = Ph 6; M = W, n = 5, Ar = 4-Me(2)NC(6)H(4)7)

Cycloaddition Reactions of the Diphosphenyl Complex (η5-C5Me5)(CO)2Fe-P=P-Mes* (Mes* = 2,4,6-tBu3C6H2) with Hexafluoroacetone. X-Ray Structure Analyses of (η5-C5Me5)(CO) Fe P(=PMes*)OC(CF3)2CO and (η5-C5Me5)(CO)2FePP(Mes*)OC(CF3)2

Weber L, Buchwald S, Lentz D, Preugschat D, Stammler H-G, Neumann B. Cycloaddition Reactions of the Diphosphenyl Complex (η5-C5Me5)(CO)2Fe-P=P-Mes* (Mes* = 2,4,6-tBu3C6H2) with Hexafluoroacetone. X-Ray Structure Analyses of (η5-C5Me5)(CO) Fe P(=PMes*)OC(CF3)2CO and (η5-C5Me5)(CO)2FePP(Mes*)OC(CF3)2. Organometallics. 1992;11(7):2351-2353.The diphosphenyl complex (eta-5-C5Me5)-(CO)2Fe-P=P-Mes* (Mes* = 2,4,6-tBu3C6H2) undergoes a [3 + 2] dipolar cycloaddition with hexafluoroacetone to give the metalla heterocycle (eta-5-C5Me5)(CO)-Fe-P(=PMes*)OC(CF3)2C(O) with a remarkably short Fe-P bond (2.084 (4) angstrom) and an exocyclic P=P bond. When stored in solution at -40-degrees-C, this complex partly rearranges to the metalated 1-oxa-2,3-diphosphetane (eta-5-C5Me5)(CO)2Fe-P-P(Mes*)OC(CF3)2. The molecular structures of both isomers were elucidated by single-crystal X-ray analyses

Aryl-Aryl Interactions in (aryl-perhalogenated) 1,2-Diaryldisilanes.

Mitzel NW, Linnemannstöns M, Schwabedissen J, Neumann B, Stammler H-G, Berger R. Aryl-Aryl Interactions in (aryl-perhalogenated) 1,2-Diaryldisilanes. Chemistry. 2020;26(10):2169-2173.Three 1,2-diaryltetramethyldisilanes X5C6-(SiMe2)2-C6X5 with two C6H5, C6F5 or C6Cl5 groups were studied concerning the im-por-tan-ce of London dispersion driven interactions between their aryl groups. They were prepared from 1,2-di-chlo-rotetra-methyl-disi-la-ne by salt elimination. Their structures were determi-ned in the solid state by X-ray diffraction and for free molecules by gas elec-tron-diffraction. The solid-state struc-tures of the fluori-nated and chlo-rinated derivatives are domi-na-ted by aryl-aryl inter-actions. Unex-pectedly, Cl5C6-(SiMe2)2-C6Cl5 exists exclusive-ly as eclipsed syn-conformer in the gas phase with strongly distor-ted Si-C6Cl5 units due to strong intramo-le-cular interactions. In contrast, F5C6-(SiMe2)2-C6F5 reveals wea-ker inter-actions. The contributions to the total interaction energy was analyzed by SAPT calculations. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

FUNCTIONALIZED SILICON-COMPOUNDS WITH OMEGA-TETRAMETHYL AND OMEGA-PENTAMETHYLCYCLOPENTADIENYLALKYL LIGANDS - MOLECULAR-COMPONENTS FOR THE PREPARATION OF METALLIC POLYMERS

Jutzi P, Heidemann T, Neumann B, Stammler H-G. Funktionalisierte Siliciumverbindungen mit [omega]-Tetramethyl- und [omega]-Pentamethylcyclopentadienylalkyl-Liganden: Molekulare Bausteine zur Darstellung von Metall-haltigen Polymeren. Journal of Organometallic Chemistry. 1994;472(1-2):27-38.Peralkylierte Cyclopentadien-Systeme des Typs Me5C5(CH2)3Si(Me)mY3-m, die über eine Alkyliden-Spacergruppe mit einer funktionalisierten Silan-Einheit verknüpft sind, sind auf zwei verschiedenen Wegen synthetisiert worden. Als Beispiel für den ersten Weg wird die Synthese des Disiloxans [Me5C5CH2)3Si(Me)2]2O (2) beschrieben, welches ausgehend von der Iodverbindung [I(CH2)3Si(Me)2]2O (1) durch Umsetzung mit Me5C5K dargestellt werden kann. Das Trichlorsilan Me5C5(CH2)3SiCl3 (4), als Synthesebeispiel für den zweiten Weg, ist über Hydrosilylierung von 1-Prop-2-enyl-1,2,3,4,5-pentamethylcyclopenta-2,4-dien (3) zugänglich. Beide Synthesewege sind auch zur Darstellung der teilweise alkylierten Cyclopentadiensysteme des Typs Me4HC5(CH2)3Si(Me)mY3-m geeignet. So führen die Umsetzungen der [omega]-Iodalkyl-triethoxysilane I(CH2)nSi(OEt)3 (n = 1, 2, 3) mit Me4HC5K zu den entsprechenden [omega]-(Tetramethylcyclopentadienyl)alkyl-triethoxysilanen 5–7. Verbindungen 5–7 liegen als Isomerengemische vor; das Verhältnis zwischen den Isomeren, die ein allylständiges oder ein vinylständiges Wasserstoffatom am Cyclopentadienring aufweisen, ist abhängig von der Spacerlänge. Isomerengemische der 4-(Tetramethylcyclopentadienyl)butyl-silane des Typs Me4HC5(CH2)4Si(Me)mCl3-m (m = 1, 2, 3) (8–10) mit ausschließlich allyiständigem Wasserstoffatom am Cyclopentadienring können durch Hydrositylierung von 1-But-3-enyl-2,3,4,5-tetramethyleyclopentadien dargestellt werden. Die am Siliciumatom funktionalisierten Verbindungen 2 und 4–10 können weiter derivatisiert werden. An ausgewählten Beispielen wird die Hydrolyse, die Alkoholyse, die reduktive Kupplung, die Heterogenisierung und die Polykondensationsreaktion näher untersucht. So erhält man das Silanol 12 und das Disiloxan 13, die Alkoxysilane 14–17, das Disilan 18 und die funktionalisierten Kieselgele 19–20. Verbindungen 2, 4–10 und 12–20 dienen als “Pool” zur Darstellung von Übergangsmetall-Derivaten. Beispielsweise wird die Dicarbonyl—Cobalt-Verbindung 21 durch Umsetzung von 8 mit Co2(CO)8 gebildet. Reaktion von 16 mit K und FeCl2 liefert das Ferrocen-Derivat 22. Die [eta]4-gebundenen Pt(II)- und Pd(II)-Komplexe 23–27 können durch Umsetzung der funktionalisierten Si---O-Verbindungen 2, 13, und 19–20 mit [PtCl2(Ethylen)]2 oder PdCl2(PhCN)2 erhalten werden.Peralkylated cyclopentadiene systems of the type Me5C5(CH2)3Si(Me)mY3-m, which possess cyclopentadiene units connected with a functionalized silane fragment by an alkylidene spacer group, are prepared via two routes. As an example of the first route, the disiloxane [Me5C5(CH2)3Si(Me)2]2O (2) has been synthesized from the corresponding iodo compound [I(CH2)3Si(Me)2]2O (1) by reaction with Me5C5K. The trichlorosilane Me5C5(CH2)3SiCl3 (4), as an example of a compound prepared via the second route, has been isolated after hydrosilylation of 1-prop-2-enyl-1,2,3,4,5-pentamethylcyclopenta-2,4-diene (3) with HSiCl3. Both synthetic methods are also suitable for the preparation of partly alkylated cyclopentadiene systems of the type Me4HC5(CH2)nSi(Me)mY3-m. Thus the omega-iodoalkyltriethoxysilanes I(CH2)nSi(OEt)3 (n = 1, 2, 3) react with Me4HC5K to give the corresponding omega-(tetramethyl-cyclopentadienyl)alkyl-triethoxysilanes 5-7. Compounds 5-7 consist of a mixture of isomers; the ratio between isomers having an allylic or vinylic hydrogen atom at the cyclopentadiene ring depends on the spacer length. Isomeric mixtures of the 4-(tetramethyl-cyclopentadienyl)butyl-silanes of the type Me4HC5(CH2)4Si(Me)mCl3-m (M = 1, 2, 3) (8-10) with an allylic hydrogen atom at the cyclopentadiene ring have been prepared by hydrosilylation of 1-but-3-enyl-2,3,4,5-tetramethylcyclopentadiene. The silane fragment in the alkylated cyclopentadiene systems 2 and 4-10 can be modified further. As examples hydrolysis, alcoholysis, reductive coupling, heterogenisation and polycondensation reactions are described. Following theses procedures the corresponding silanol 12 and disiloxane 13 have been prepared as well as the alkoxysilanes 14-17, the disilane 18 and the functionalized silicagels 19 and 20. Compounds 2, 4-10 and 12-20 serve as a ''pool'' for the preparation of transition metal complexes. The dicarbonyl cobalt compound 21 has been synthesized by reaction of 8 with CO2(CO)8. Reaction of 16 with K and FeCl2 gives the corresponding ferrocene derivative 22. The eta4-bound Pt(II) and Pd(II)-complexes 23-27 have been prepared by reaction of the functionalized Si-O-compounds 2, 13, and 19-20 with [PtCl2(Ethylen)]2 and PdCl2(PhCN)2, respectively

BIS(PENTAMETHYLCYCLOPENTADIENYL)KETONE AND THIOKETONE - CARBON-COMPOUNDS WITH PREFORMED DIELS-ALDER GEOMETRY

Jutzi P, SCHWARTZEN KH, Mix A, Stammler H-G, Neumann B. Bis(pentamethylcyclopentadienyl)keton und -thioketon: Kohlenstoff-Verbindungen mit präformierter Diels-Alder-Geometrie. CHEMISCHE BERICHTE-RECUEIL. 1993;126(2):415-420.1,2,3,4,5-Pentamethyl-1,3-cyclopentadien-5-carbonyl chloride (2) is formed in good yields by the reaction of pentamethylcyclopentadienyllithium (1) with phosgene. The corresponding carbothioyl chloride 3 is synthesized by treatment of 1 with thiophosgene. Both acyl chlorides are stable against air and moisture and difficult to attack in S(N)2-type reactions. Treatment of 2 and 3 with trimethyl(pentamethylcyclopentadienyl)stannane in the presence of boron trifluoride - ether leads to bis(1,2,3,4,5-pentamethyl-1,3-cyclopentadien-5-yl) ketone (S) and thioketone (6), respectively. Even at room temperature, S and 6 tend to intramolecular [4 + 2] cycloaddition reactions. X-ray crystal structure investigations of 2, 5, and 6 show the steric demand of the pentamethylcyclopentadienyl ligand and explain the untypical chemical behavior of 2 and the easy [2 + 4] cycloaddition reactions of 5 and 6

PENTAMETHYLDISILANYL-SUBSTITUTED CYCLOPENTADIENES - SYNTHESIS, STRUCTURE AND DYNAMIC BEHAVIOR

Jutzi P, Kleimeier J, Krallmann R, Stammler H-G, Neumann B. Pentamethyldisilanyl-substituierte Cyclopentadiene: Synthese, Struktur und dynamisches Verhalten. Journal of Organometallic Chemistry. 1993;462(1-2):57-67.The pentamethyldisilanyl-substituted cyclopentadienes Me(n)C(5)H(6-n-m)(Si(2)Me(5))(m) (for n = 0: 1 (m = 1), 2 (m = 2), 3 (m = 3), 4 (m = 4); for n = 1: 5 (m = 1), 7 (m = 2), 9 (m = 3); for n = 3: 13 (m = 1), 14 (m = 2); for n = 4: 15 (m = I)) are accessible in good yields by treatment of the corresponding cyclopentadienyllithium compounds with Me(5)Si(2)Cl. The mono-Me(5)Si(2)-substituted species 1 and 5 are present only to a small extend in form of vinylic isomers and to a greater extend as isomers with the Me(5)Si(2)-group in allylic position; the latter possess a dynamic structure due to sigmatropic rearrangements. In the twice-Me(5)Si(2)-substituted cyclopentadienes 2 and 7, the 5,5 and 2,5 isomers are observed, which can be interconverted by silatropic shifts; in addition, the presence of two vinylic isomers can be proved in the case of 2. In the cyclopentadiene species 3 and 9 with three Me(5)Si(2) groups, only the 2,5,5 isomers can be detected by NMR spectroscopy. Compound 3 possesses a fluxional structure and can thus be deprotonated. On the other hand, 9 does not show a fluxional behaviour and thus cannot be deprotonated. The cyclopentadiene 4 with four Me(5)Si(2) substituents possesses a static structure and cannot be deprotonated. The 2,3,5,5 position of the substituents is proved by an X-ray crystal structure analysis. Only two Me(5)Si(2) groups can be incorporated in the carbon skeleton of 1,2,4-trimethylcyclopentadiene, whereby compounds of the type 1,2,4-Me(3)C(5)H(3-n)(Si(2)Me(5))(n) (13: n = 1; 14: n = 2) are formed. Surprisingly, 14 cannot be deprotonated with (n)BuLi and KH, respectively. The reaction of Me(4)C(5)HLi with Me(5)Si(2)Cl leads to the cyclopentadiene Me(4)C(5)HSi(2)Me(5) (15). Though compound 15 can be deprotonated, further reaction of the resulting anion with Me(5)Si(2)Cl does not lead to the expected cyclopentadiene Me(4)C(5)(Si(2)Me(5))(2) (16). On the other hand, 16 can be prepared by metallation of 14 with C8K and further reaction with CH3I. In contrast to 14, compound 4 cannot be deprotonated with C8K; the reaction of 4 with C8K and CH3I leads to 9 via Si-C bond splitting. The pentamethyldisilanyl-substituted pentamethylcyclopentadiene Me(5)C(5)Si(2)Me(5) (17) is obtained by reaction of Me(5)C(5)K with Me(5)Si(2)Cl; compound 17 shows dynamic behaviour; the migration of the Me(5)Si(2) group is slower than that of the Me(3)Si group in Me(5)C(5)SiMe(3). Three ElMe(3) groups can be introduced stepwise into the 1,2,4-Me(3)C(5)H(3) molecule, as demonstrated by the exemplary synthesis of the cyclopentadienes 1,2,4-Me(3)C(5)H(3-n)(SiMe(3))(n) (10: n = 1; 11: n = 2) and 1,2,4-Me(3)C(5)(SiMe(3))(2)SnMe(3) (12).Die Si2Me5-substituierten Cyclopentadiene MenC5H6-n-m(Si2Me5)m (für n = 0: 1 (m = 1), 2 (m = 2), 3 (m = 3), 4 (m = 4); für n = 1: 5 (m = 1), 7 (m = 2), 9 (m = 3); für n = 3: 13 (m = 1), 14 (m = 2); für n = 4: 15 (m = 1)) sind durch Umsetzung der entsprechenden Cyclopentadienyl-Lithium-Verbindung mit Me5Si2Cl in guten Ausbeuten zugänglich. In den einfach Si2Me5-substituierten Systemen 1 und 5 findet man zu einem geringen Anteil Isomere mit vinylständiger Si2Me5-Gruppe und zu einem überwiegenden Anteil das Isomer mit allylständiger Si2Me5-Gruppe, welches aufgrund von sigmatropen Umlagerungen eine dynamische Struktur besitzt. In den zweifach Si2Me5- substituierten Cyclopentadienen 2 und 7 beobachtet man die jeweiligen 5,5- und 2,5-Isomere, welche durch Silatropie miteinander im Gleichgewicht stehen; zusätzlich lassen sich in 2 noch zwei Isomere mit ausschließlich vinylständigen Substituenten nachweisen. In den dreifach Si2Me5-substituierten Systemen 3 und 9 ist nur das 2,5,5-Isomere nachweisbar. 3 besitzt eine dynamische Struktur und ist deshalb deprotonierbar. 9 hingegen ist nicht dynamisch und aufgrund des Fehlens einer Allyl-H-Funktion nicht deprotonierbar. Auch das vierfach Si2Me5-substituierte Cyclopentadien 4 zeigt keine Moleküldynamik und kann nicht deprotoniert werden; die 2,3,5,5-Anordnung der Substituenten in 4 wird anhand einer Röntgenstrukturanalyse belegt. Im 1,2,4-Trimethylcyclopentadien gelingt jedoch nur die Einführung von zwei Si2Me5-Gruppen, wobei die Verbindungen des Typs 1,2,4-Me3C5H3-n(Si2Me5)n (13: n = 1; 14: n = 2) entstehen. Überraschenderweise ist 14 mit nBuLi oder KH nicht deprotonierbar. Die Umsetzung von Me4C5HLi mit Me5Si2Cl führtzum Cyclopentadien Me4C5HSi2Me5 (15). Obwohl 15 deprotonierbar ist, gelingt durch Umsetzung des Anions mit Me5Si2Cl die Synthese von Me4C5(Si2Me5)2 (16) nicht. Verbindung 16 läßt sich allerdings durch Metallierung von 14 mit C8K und anschließende Umsetzung mit CH3I darstellen. Im Gegensatz dazu kann 4 mit C8K nicht deprotoniert werden; die Umsetzung mit C8K und CH3I läuft über Si-C-Bindungsspaltung zu 9. Das Cyclopentadienyldisilan Me5C5Si2Me5 (17) erhält man durch Umsetzung von Me5C5K mit Me5Si2Cl; 17 zeigt dynamisches Verhalten, die Wanderungsgeschwindigkeit der Si2Me5-Gruppe ist geringer als die der SiMe3-Gruppe im Cyclopentadienylsilan Me5C5SiMe3. Im Cyclopentadien 1,2,4-Me3C5H3 lassen sich sukzessiv drei ElMe3-Gruppen (El = Si, Sn) einführen, wie durch die beispielhafte Synthese von 1,2,4-Me3C5H3-n(SiMe3)n (10: n = 1, 11: n = 2) und 1,2,4-Me3 C5(SiMe3)2SnMe3 (12) gezeigt wird