2117-28-4Relevant academic research and scientific papers
Reactivity of a P–H Functionalized Al/P-Based Frustrated Lewis Pair – Hydrophosphination versus Classic Adduct Formation
Uhl, Werner,Keweloh, Lukas,Hepp, Alexander,Stegemann, Frank,Layh, Marcus,Bergander, Klaus
, p. 1978 - 1990 (2017)
The P–H functionalized Al/P-based frustrated Lewis pair (FLP) Mes(H)P–C[Al{CH(SiMe3)2}2]=C(H)–tBu (3) has the typical functionality of FLPs with Lewis acidic and basic centers in a single molecule and is able to transfer the P bound H atom to activated substrates. Nevertheless, 3 reacted with NH3 only by adduct formation with the N atom coordinated to Al (5). The relatively low basicity of the P atom prevented the formation of a hydrogen bridge between P and Al. Similarly, benzil and 3 afforded a simple adduct (6) with only one C=O group bonded to P and Al. The second C=O group and the P–H moiety were unaffected. 6 has two stereogenic centers, and the resulting diastereomers were identified by crystal structure determinations. Migration of the P bound H atom was only observed for substrates containing basic N atoms. Nitriles gave heterocyclic iminophosphine adducts (7) in which the N–H groups were coordinated to the Al atoms. An isocyanate and two isothiocyanates afforded adducts via Al–X and P–C bond formation (X = O, S), and phosphaurea derivatives (8a to 8c) resulted from H shift to the exocyclic N atoms. A carbodiimide reacted with 3 by the formation of a phosphaguanidine (8d) with the imine N atom coordinated to Al. The latter reactions proceed under mild conditions and represent formally the hydrophosphination of unsaturated substrates.
Synthesis of and the Crystalline Monomeric Bulky Alkyl-lithium Complexes and ; X-Ray Crystal Structure of (pmdeta)> 2N(Me)2NMe2>
Lappert, Michael F.,Engelhardt, Lutz M.,Raston, Colin L.,White, Allan H.
, p. 1323 - 1324 (1982)
Reaction of SiMe4 or CH2(SiMe3)2 in n-C6H14 with LiBun(pmdeta) affords in high yield Li(CH2SiMe3)(pmdeta) or Li(pmdeta), (2) respectively, the latter also being available from Li(tmeda), (1), and pmdeta; crystalline compounds (1) and (2) are monomers (ebullioscopy, C6H12), and for (2) this is also shown by X-ray crystallography, with the short Li-C distance indicative of a covalent bond.
Bridging coordination of gallium-gallium bonds by chelating ligands - Limitations of the stability of digallium derivatives
Uhl, Werner,Cuypers, Lars,Schüler, Kristiane,Spies, Thomas,Strohmann, Carsten,Lehmen, Klaus
, p. 1526 - 1534 (2000)
The reactions of bis[bis(trimethylsilyl)methyl]-di(μ-acetato)digallium(Ga-Ga) (2) with lithium-2-amido-1-methylbenzimidazole in the molar ratios of 1 to 1 or 1 to 2 yielded by the precipitation of lithium aceatate new digallium compounds, in which the intact Ga-Ga bonds were bridged by two chelating ligands. The replacement of only one acetato group gave compound 5, that possesses two different bridging ligands with the benzimidazole group coordinated by its terminal amido function and that nitrogen atom of the heterocycle which is not attached to a methyl group. If both acetato groups were replaced by imdazole ligands, two products were obtained, in which the chelates are transferred in each other either by a mirror plane parallel to the Ga-Ga bond (cis, 6) or by a twofold rotational axis perpendicular to the element-element bond (trans, 7). 7 is thermodynamically favored and was irreversibly formed by heating of the mixture. 5 and 7 were characterized by crystal structure determinations and have Ga atoms in a chiral environment. Weaker donor ligands such as diphenyl(lithiomethyl)-(piperidinomethyl)silane, which in principal is able to coordinate via its carbanionic carbon atom and more weakly via its sterically shielded piperidino nitrogen atom, led to the cleavage of the Ga-Ga bond. The mononuclear compound 8 was isolated, in which the Ga atom is attached to one bis(trimethylsilyl)methyl group and two (piperidinomethyl)silyl substituents. Furthermore, the synthesis of a dialkyl-bis(1,3-dionato)digallium derivative (9) is reported, in which the chelating 1,3-dionato groups are terminally coordinated to the Ga atoms of the unsupported Ga-Ga bond.
Samarium-mediated redistribution of silanes and formation of trinuclear samarium-silicon clusters
Radu, Nora S.,Hollander, Frederick J.,Tilley, T. Don,Rheingold, Arnold L.
, p. 2459 - 2460 (1996)
The samarium complex Cp*2SmCH(SiMe3)2 (Cp* = C5Me5), unlike the related alkyls Cp*2LnCH(SiMe3)2 (Ln = Y, Nd), mediates the redistribution of hydrosilanes while being converted to trisamarium clusters, including Cp*6Sm3(μ-SiH3)(μ 3-η1,η1,η2-SiH 2-SiH2).
α-Stabilization by Silyl and Phosphino Substitution
Roemer, Bettina,Gatev, Geo G.,Zhong, Meili,Brauman, John I.
, p. 2919 - 2924 (2007/10/03)
The electron affinity of the bis(dimethylphosphino)methyl radical was measured to be 35.3+/-0.2 kcal/mol, using electron photodetachment spectroscopy in an ion cyclotron resonance spectrometer.Using equilibrium measurements, ΔHacido of bis(dimethylphosphino)methane and bis(trimethylsilyl)methane was determined to be 370+/-3 and 373+/-3 kcal/mol, respectively.From measured and known electron electron affinities and gas-phase acidities, we derive C-H bond dissociation energies: bis(dimethylphosphino)methane, 92+/-3 kcal/mol, and bis(trimethylsilyl)methane, 95+/-3 kcal/mol. ΔHacido of trimethylphosphine was bracketed at 383-387 kcal/mol.The α-stabilization effect of silyl and phosphino substitution is large and comparable in size to stabilization by thio and chloro substitution.Possible mechanisms of stabilization are discussed.
Synthesis of disilylmethanes and polysilacarbosilanes, precursors of silicon carbide-based materials
Bacque, Eric,Birot, Marc,Pillot, Jean-Paul,Lapouyade, Paulette,Gerval, Pierre,Biran, Claude,Dunogues, Jacques
, p. 99 - 107 (2007/10/03)
Using a new procedure, substituted disilylmethanes have been prepared from chlorosilanes, dichloromethane, and magnesium in tetrahydrofuran. Bis(chlorosilyl)methanes can be used as comonomers for the synthesis of polysilacarbosilanes, which are transformed into polycarbosilanes, precursors of silicon carbide.
Polychlorinated materials as a source of polyanionic synthons
Guijarro, Albert,Yus, Miguel
, p. 1797 - 1810 (2007/10/03)
The reaction of dichloromethane (1a) or dichlorodideuteriomethane (1b) with an excess of lithium powder (1:7 molar ratio) and a catalytic amount of DTBB (5 mol%) in the presence of a carbonyl compound 2 (1:2 molar ratio) in THF at -40°C yields, after hydrolysis, the corresponding 1,3-diols 3 in moderate yields. The process is applied to other gem-dichlorinated materials such as 7,7-dichloro [4.1.0]heptane (4), 1,1-dichlorotetramethylcyclopropane (7) and dichloromethyl methyl ether (10), using pivalaldehyde as electrophile. Starting from 1,1,1-trichlorinated compounds or tetrachloromethane (14) and using chlorotrimethylsilane as electrophile at temperatures ranging between -80 and -90°C, the corresponding polysilylated compounds 15-17 are prepared applying the mentioned methodology.
The synthesis of -substituted dialkyldichlorosilanes and their conversion into polysiloxanes
Ducker, Graham E.,Tipping, Anthony E.
, p. 253 - 262 (2007/10/02)
Attack of the oxyl (CF3)2NO. (1) on an ethyl group of the silane Et2SiCl2 occurs at both the α- and β-positions relative to silicon (ratio 31:45), whereas with the silane PrnSiMeCl2 attack takes place at the β-position of the propyl group.With the disilane Me3SiCH2SiMe3, the mojor silicon-containing products formed from treatment with oxyl 1 are Me3SiF, (CF3)2NOSiMe3 and Me3SiSiMe3.Speier-catalysed (H2PtCl6) addition of the silane HSiCl2X (X = Me and Cl) to the alkene (CF3)2NOCH2CH=CH2 gives the adducts (CF3)2NOCH2CH2CH2SiCl2X (29, X = Me) and (28, X = Cl)in high yield.The substituted dichlorosilanes (CF3)2NOCH2CH2SiEtCl2 (9), (CF3)2NOCHMeCH2SiMeCl2 (14) and (CF3)2NOCH2CH2CH2SiMeCl2 (29) are converted into corresponding polysiloxanes ("prepolymers" of low molecular weight) by reaction with reagents including water, acid, base and metal oxides; equilibration of the polysiloxane "prepolymer" 38, derived from dichlorosilane 29 by heating with powdered KOH, affords a solid rubbery polysiloxane.
Preparation of Cross-Linked Polycarbosilane and its Conversion to Silicon Carbide Ceramics
Michalczyk, M. J.,Davidson, F.
, p. 895 - 900 (2007/10/02)
Cross-linked polycarbosilanes are obtained from the reaction of Cl2MeSiCHCl2 and Mg in tetrahydrofuran, folowed by reduction with LiAlH4.Analysis by NMR spectroscopy shows that most polycarbosilane is of the formula n. - Keywords.Pre-ceramic polymer; Cross-linked, Polycarbosilane, Silicon carbide.
Manipulation of organolanthanide coordinative unsaturation. Synthesis, structures, structural dynamics, comparative reactivity, and comparative thermochemistry of dinuclear μ-hydrides and μ-alkyls with [μ-R2Si(Me4C5)(C5H 4)]2 supporting ligation
Stern, David,Sabat, Michal,Marks, Tobin J.
, p. 9558 - 9575 (2007/10/02)
This contribution describes lutetium and yttrium hydrocarbyl and hydride chemistry based upon the chelating R2Si(η5-C5H4)(η 5-Me4C5)2- ligand (R = Me, Et; abbreviated R2SiCpCp″). The ligand is prepared by reaction of the corresponding R2Si(Cp″)Cl derivative with NaC5H5. Subsequent metalation and reaction with MCl3·3THF (M = Y, Lu) yields R2SiCpCp″MCl2-Li(OEt2)2 + complexes, which in turn can be alkylated to yield R2SiCpCp″MCHTMS2 derivatives (TMS = SiMe3). Pertinent crystallographic data for Me2SiCpCp″LuCHTMS2 at -120 °C: P1 (no. 2), z = 4, a = 16.049 (3) A?, b = 17.945 (4) A?, c = 8.993 (3) A?, α = 93.36 (2)°, β= 90.92 (2)°, and γ = 82.54 (2)°; A(F) = 0.030 for 6085 independent reflections with I > 3σ(I). The structure is of a "bent-sandwich" Cp′2MX-type (Cp′ = η5-Me5C5) with relaxed interligand nonbonded interactions vis-a?-vis the Cp′2M and Me2SiCp″2M analogues (Lu-CHTMS2 = 2.365 (7) A?) and having one close Lu?MeSi (Lu-C = 2.820 (8) A?) secondary interaction. These alkyls initiate the polymerization of ethylene and undergo relatively slow hydrogenolysis to yield dihydrides of stoichiometry (R2SiCpCp″MH)2 via detectable intermediates of stoichiometry (R2SiCpCp″)2M2(H)(CHTMS2). Pertinent crystallographic data for (Et2SiCpCp″LuH)2 at -120 °C: p21/n (no. 14), z = 2, a = 11.558 (3) A?, b = 8.590 (2) A?, c = 18.029 (3) A?, β= 100.10 (2) A?, R(F) = 0.022 for 2656 independent reflections with I > 3σ(I). The structure has an idealized C2h,Lu(μ-Et2SiCpCp″)2(μ-H) 2Lu geometry with both bridging Et2SiCpCp″ and hydride ligands (Lu-H = 2.16 (4), 2.13 (4) A?). These complexes react slowly (compared to monomeric Cp′2MH and Me2SiCp″2MH), reversibly, and regiospecifically with α-olefins to form bridging alkyls of structure M(μ-R2SiCpCp″)2(μ-H)(μ-R′)M, R′ = ethyl, n-propyl, n-hexyl. Pertinent crystallographic data for Lu(μ-Et2SiCpCp″)2(μ-H)(μ-CH 2CH3)Lu at -120 °C: P21/c (no. 14), z = 6, a= 11.679 (4) A?, b = 25.755 (5) A?, c = 18.074 (2) A?, β= 99.41 (2)°; A(F) = 0.058 for 4643 independent reflections with I > 3σ(I). The Lu(μ-Et2SiCpCp″)2(μ-H)Lu framework is nearly identical to that in the dihydride above. The μ-ethyl fragment is bound very unsymmetrically with Lu-C(α) = 2.46 (2) and 2.58 (2) A?, 〈 Lu-C(α)-C(β) = 148 (1)° and 84.7 (5)°. In addition, Lu-C(β) = 2.78 (2) A? suggests a strong secondary bonding interaction. Hydrogenolysis of the μ-alkyl linkages is considerably slower than for terminal alkyl bonds in Cp′2M(alkyl) and Me2SiCp″2M(alkyl) complexes. NMR studies of the μ-alkyls reveal rapid rotation of the μ-alkyl ligands about the μ-H-μ-C(α) vectors down to -85 °C and rapid inversion at C(α) occurring with ΔG? = 12.5-13.5 kcal/mol (Tc = +11- +39 °C). Kinetic (rate law: ν = k[dihydride][olefin]) and equilibration measurements reveal that the hydride addition process to 1-hexene (Et2SiCpCp″LuH)2 + 1-hexene ? Lu(μEt2SiCpCp)2(μ-H)(μ-n-hexyl)Lu is described by ΔH = -10.7 (6) kcal/mol, ΔS = -25 (2) eu, ΔH? = 12.0 (4) kcal/mol, and ΔS? = -38.6 (7) eu. These results indicate that, in comparison to terminal bonding modes with similar metal ancillary ligation, lanthanide μ-H ligands are kinetically deactivated with respect to olefin insertion (a rate depression of ～ 108-1010), and μ-alkyl ligands are kinetically deactivated with respect to hydrogenolysis (a rate depression of ～108-109). Moreover, relative to a bridging hydride ligand, lanthanide μ-alkyl coordination is found to be no more and probably less thermodynamically stable than terminal alkyl coordination.
