Reactivity of a Neutral Yttrium(III) Trimethyl Complex toward Brønsted and Lewis Acids.

The present study corroborates that the neutral tridentate N-ligand trimethyl-triazacyclononane (Me3TACN) qualifies as a versatile platform to study selective ligand exchange with rare-earth-metal alkyl complexes, herein [(Me3TACN)YMe3]. Treatment with Brønsted-acidic bis(dimethylsilyl)amine, HN(SiHMe2)2, gave selectively the mono-exchanged heteroleptic complex [(Me3TACN)YMe2{N(SiHMe2)2}]. Depending on the molecular ratio employed, the reaction of [(Me3TACN)YMe3] with AlMe3 resulted in the isolation/crystallization of [(Me3TACN)YMe2(AlMe4)] [1:1] or ion-separated [(Me3TACN)YMe(AlMe4)][AlMe4] [1:2] and [(Me3TACN)YMe(AlMe4)][Al2Me7] [1:3]. Analogous reactions with the heavier group 13 methyls GaMe3 and InMe3 generated mixed methyl/tetramethylgallato complex [(Me3TACN)YMe2(GaMe4)] and ion-separated [{(Me3TACN)YMe2}2{µ-Me}][InMe4]. Finally, dimethylalane, HAlMe2, converted [(Me3TACN)YMe3] into heteroaluminate [(Me3TACN)Y(HAlMe3)3], representing an AlMe3-supported, molecular yttrium trihydride complex. All compounds were investigated by single crystal X-ray diffraction (SC-XRD), homo- and heteronuclear (13C, 27Al, 89Y, 115In) NMR as well as IR spectroscopies and elemental analyses.

Facile Energy Release from Substituted Dewar Isomers of 1,2­Dihydro-1,2­azaborinines Catalyzed by Coinage Metal Lewis Acids.

Molecular solar thermal systems (MOST) represent an auspicious solution for the storage of solar energy. We report silver salts as a unique class of catalysts, capable of releasing the stored energy from the promising 1,2-dihydro-1,2-azaborinine based MOST system. Mechanistic investigations provided insights into the silver catalyzed thermal backreaction, concurrently unveiling the first crystal structure of a 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar isomer of 1,2-dihydro-1,2-azaborinine. Quantification of activation energies by kinetic experiments has elucidated the advantageous energy outcomes associated with Lewis acid catalysts, a phenomenon corroborated through computational analysis. By means of low temperature NMR spectroscopy, mechanistic insights into the coordination of Ag+ to the 1,2-dihydro-1,2-azaborinine were gained.

Terminal dysprosium and holmium organoimides.

Terminal rare-earth-metal imide complexes TptBu,MeLn(NC6H3iPr2-2,6)(dmap) of the mid-late rare-earth elements dysprosium and holmium were synthesized via double methane elimination of Lewis acid stabilized dialkyl precursors TptBu,MeLnMe(GaMe4) with primary aniline derivative H2NC6H3iPr2-2,6 (H2NAriPr). Exploiting the weaker Ln-CH3⋯[GaMe3] interaction compared to the aluminium congener, addition of the aniline derivative leads to the mixed methyl/anilido species TptBu,MeLnMe(HNAriPr) which readily eliminate methane after being exposed to the Lewis base DMAP ([double bond, length as m-dash]N,N-dimethyl-4-aminopyridine). Under the same conditions, [AlMe3]-stabilized dimethyl rare-earth-metal complexes transform immediately to Lewis acid bridged imides TptBu,MeLn(µ2-NC6H3Me2-2,6)(µ2-Me)AlMe2 (Ln = Dy, Ho). DMAP/THF donor exchange is accomplished by treatment of TptBu,MeLn(NC6H3iPr2-2,6)(dmap) with 9-BBN in THF while the terminal imides readily insert carbon dioxide to afford carbamate complexes.

Rare-Earth-Metal Methyl and Methylidene Complexes Stabilized by TpR,R'-Scorpionato Ligands─Size Matters.

Homoleptic tetramethylaluminates Ln(AlMe4)3 react with KTptBu,Me (TptBu,Me = tris(3-tBu-5-Me-pyrazolyl)borato) to yield rare-earth-metal methylidene complexes (TptBu,Me)Ln(µ3-CH2)[(µ-Me)AlMe2]2 (Ln = La, Ce, Nd). The lanthanum reaction is prone to additional C-H- and B-N-bond activation, affording coproducts La[HB(pzMe,tBu)(pzCMe2,Me)2][(µ-CH2)(µ-Me)AlMe2]2 and [La(µ-pztBu,Me)(AlMe4)2]2 (pztBu,Me = 3-tBu-5-Me-pyrazolato). The protonolysis reaction of Ln(AlMe4)3 and HpztBu,Me provides more efficient access to [Ln(µ-pztBu,Me)(AlMe4)2]2 (Ln = La, Nd). Treatment of Ln(AlMe4)3 with KTpMe,Me led to methylidene complexes (TpMe,Me)Ln(µ3-CH2)[(µ-Me)AlMe2]2 (Ln = Nd, Sm) or bis(tetramethylaluminate) complexes (TpMe,Me)Ln(AlMe4)2 (Ln = Y, Lu). The neodymium reaction generated methine derivative (TpMe,Me)Nd[(µ4-CH)(AlMe2)2(µ-pz,Me,Me)][(µ-Me)AlMe2] as a minor coproduct. The reaction of Ln(GaMe4)3 (Ln = Y, La, Ce, Nd, Sm, Ho) with HTptBu,Me gave methylidene complexes (TptBu,Me)Ln(µ3-CH2)[(µ-Me)GaMe2]2 (Ln = La, Ce, Nd, Sm) and alkyl complexes (TptBu,Me)LnMe[(µ-Me)GaMe3] (Ln = Y, Ho), while competing B-N bond activation reactions produced GaMe2[BH(Me)(µ-pztBu,Me)2] and (TptBu,Me)Ln(η2-pztBu,Me)[(µ-Me)GaMe3] (Ln = Y, Ho). The steric impact of the TpR,Me ligands was examined by cone angle calculations. Rare-earth-metal methylidene complexes (TptBu,Me)Ln(µ3-CH2)[(µ-Me)EMe2]2 (E = Al, Ga) successfully promote carbonyl methylenation reactions upon addition of ketone.

Yttrium Complexes with Group 13 Heterobenzene-Type Ligands.

The yttrium gallabenzene complex [(1-Me-3,5-tBu2 -C5 H3 Ga)(µ-Me)Y(2,4-dtbp)] is accessible from Y(GaMe4 )3 and K(2,4-dtbp) via a tandem salt metathesis/methane elimination (2,4-dtbp=2,4-di-tert-butyl-pentadienyl). The pentadienyl ligand in [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(2,4-dtbp)] (E=Al, Ga) is easily displaced by salt metathesis with KC5 Me5 and KTpMe,Me (TpMe,Me =tris(pyrazolyl-Me2 -3,5)borato) affording [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(TpMe,Me )] and [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(C5 Me5 )]. The yttrium center in [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(2,4-dtbp)] readily forms adducts with neutral Lewis bases like 4-DMAP (4-dimethylaminopyridine), PMe3 , DMPE (1,2-bis(dimethylphosphino)ethane), and DME (1,2-dimethoxyethane). In stark contrast, addition of TMEDA (N,N,N',N'-tetramethylethylenediamine) results in methyl/pentadienyl exchange between aluminum and yttrium resulting in [(1-(2,4-dtbp)-1-Me-3,5-tBu2 -C5 H3 Al)Y(Me)(tmeda)]. The bonding features of the newly synthesized complexes are analyzed by single-crystal X-ray diffraction (SCXRD) and heteronuclear (89 Y, 31 P) NMR spectroscopy.

A Terminal Yttrium Phosphinidene.

Terminal, nondirectional ionic "multiple" bond interactions between group 15 elements and rare-earth metals (Ln) have remained a challenging target until present. Although reports on terminal imide species have accumulated in the meantime, examples of terminal congeners with the higher homologue phosphorus are yet elusive. Herein, we present the synthesis of the first terminal yttrium organophosphinidene complex, TptBu,MeY(═PC6H3iPr2-2,6)(DMAP)2, according to a double-deprotonation sequence previously established for organoimides of the smaller rare-earth metals. Subsequent deprotonation of the primary phosphane H2PC6H3iPr2-2,6 (H2PAriPr) with discrete dimethyl compound TptBu,MeYMe2 in the presence of DMAP under simultaneous methane elimination generated a terminal multiply bonded phosphorus. The primary phosphide intermediates TptBu,MeYMe(HPAriPr) and TptBu,MeYMe(HNPAriPr)(DMAP) are isolable species and were also obtained and fully characterized for holmium and dysprosium. The Lewis acid-stabilized yttrium phosphinidene TptBu,MeY[(µ2-PAriPr)(µ2-Me)AlMe2] was obtained by treatment of H2PAriPr with TptBu,MeYMe(AlMe4) but could not be converted into a terminal phosphinidene via cleavage of trimethylaluminum. The corresponding reaction of H2PAriPr with TptBu,MeYMe(GaMe4) led to adduct [GaMe3(PH2AriPr)] rather than to the formation of a yttrium phosphinidene. The yttrium-phosphorus interaction in the obtained organophosphide and phosphinidene complexes was scrutinized by 31P/89Y NMR spectroscopy and DFT calculations, unambiguously supporting the existence of multiple bonding.

Potential precursors for terminal ytterbium(II) imide complexes bearing the hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand.

Monomeric, divalent ytterbium primary amides TptBu,MeYb(NHR)(thf)x (R = C6H3iPr2-2,6 = AriPr = Dipp, C6H3(CF3)2-3,5 = ArCF3, SiPh3) supported by the bulky hydrotris(3-tBu-5-Me-pyrazolyl)borato scorpionate ligand are synthesized acccording to salt metathesis and protonolysis protocols, respectively. Yb(II) precursors comprise YbI2(thf)2, Yb[N(SiMe3)2]2(thf)2 and TptBu,MeYb[N(SiMe3)2]. Complexes TptBu,MeYb(NHR)(thf)x readily engage in donor (thf) exchange with nitrogen donors like DMAP (4-dimethylaminopyridine) and pyridine. Treatment of TptBu,MeYb(NHArCF3)(thf)2 with the Lewis acids AlMe3 and GaMe3 results in the heterobimetallic complexes TptBu,MeYb(NHArCF3)(MMe3) (M = Al, Ga). Reactions of TptBu,MeYb(NHR)(thf)x (R = AriPr, ArCF3) with the halogenating agents C2Cl6 and TeBr4 give access to trivalent complexes [TptBu,MeYb(NHR)(X)] (X = Cl, Br). The ytterbium(II) complexes under study display 171Yb NMR chemical shifts in the range 582 ppm for TptBu,MeYb(NHArCF3)(GaMe3) to 954 ppm for TptBu,MeYb(NHSiPh3)(dmap). The salt-metathesis route is also applicable for the synthesis of complexes TptBu,MeLn(NHAriPr)(thf) (Ln = Sm, Eu) and TptBu,MeYb(NHArMe) (ArMe = C6H3Me2-2,6).

Triisobutylaluminium-promoted formation of lanthanide hydrides.

Discrete lanthanide(III) isobutylaluminates Ln[N(SiMe3)2](HAliBu3)(AliBu4) (Ln = La, Pr, Nd) are obtained from Ln[N(SiMe3)2]3 and triisobutylaluminium (TIBA). Nd[N(SiMe3)2](HAliBu3)(AliBu4) reacts with crown ether to give the ion pair [Nd(18-c-6){N(SiMe3)2}(HAliBu3)][AliBu4], featuring a strong Nd-H interaction in the solid state. The equimolar reaction of La[N(SiMe3)2](HAliBu3)(AliBu4) with fluorene resulted in the concomitant formation of [(µ-fluorenyl)3La2(µ-H)(HAliBu3)2] and (fluorenyl)2La[N(SiMe3)2]. [(µ-Fluorenyl)3La2(µ-H)(HAliBu3)2] features fluorenyl ligands with a µ-η6:η6 coordination around the hydrido-bridged dilanthanum core motif. The reported complexes are the first crystallographically characterized, ancillary ligand-free lanthanide(III) tetraisobutylaluminates, and display potential model systems for Ziegler-type polymerization catalysis.

Divalent Lanthanide Tetraisobutylaluminates: Reactivity and Living Isoprene Polymerization.

Lanthanide (Ln) tetraisobutylaluminates constitute key components in commercial 1,3-diene polymerization catalysts, and likewise are the homogeneous rare-earth-metal catalysts of prime industrial importance. Discrete divalent rare-earth-metal complexes [Ln(AliBu4 )2 ] (Ln=Sm, Eu, Yb) reported here display the first structurally characterized homoleptic metal tetraisobutylaluminates. Treatment of [Ln(AliBu4 )2 ] with C2 Cl6 gives access to SmII /SmIII mixed-valence cluster [Sm6 Cl8 (AliBu4 )6 ] and the YbII cluster [Yb4 Cl4 (AliBu4 )4 ], respectively. Reaction with B(C6 F5 )3 leads to hydride abstraction and formation of arene-coordinated hydroborates such as [Sm{HB(C6 F5 )3 }2 (toluene)2 ]. Complexes [Ln(AliBu4 )2 ] engage in single-component isoprene polymerization, affording high cis-1,4 polyisoprenes with narrow molecular weight distributions. Binary [Yb(AliBu4 )2 ]/[HNPhMe2 ][B(C6 F5 )4 ] fabricates polyisoprene in a perfectly living manner. The catalytically active species are scrutinized by NMR spectroscopy.

Titanium(IV) Surface Complexes Bearing Chelating Catecholato Ligands for Enhanced Band-Gap Reduction.

Protonolysis reactions between dimethylamido titanium(IV) catecholate [Ti(CAT)(NMe2)2]2 and neopentanol or tris(tert-butoxy)silanol gave catecholato-bridged dimers [(Ti(CAT)(OCH2tBu)2)(HNMe2)]2 and [Ti(CAT){OSi(OtBu)3}2(HNMe2)2]2, respectively. Analogous reactions using the dimeric dimethylamido titanium(IV) (3,6-di-tert-butyl)catecholate [Ti(CATtBu2-3,6)(NMe2)2]2 yielded the monomeric Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2 and Ti(CATtBu2-3,6)[OSi(OtBu)3]2(HNMe2)2. The neopentoxide complex Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2 engaged in further protonolysis reactions with Si-OH groups and was consequentially used for grafting onto mesoporous silica KIT-6. Upon immobilization, the surface complex [Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2]@[KIT-6] retained the bidentate chelating geometry of the catecholato ligand. This convergent grafting strategy was compared with a sequential and an aqueous approach, which gave either a mixture of bidentate chelating species with a bipodally anchored Ti(IV) center along with other physisorbed surface species or not clearly identifiable surface species. Extension of the convergent and aqueous approaches to anatase mesoporous titania (m-TiO2) enabled optical and electronic investigations of the corresponding surface species, revealing that the band-gap reduction is more pronounced for the bidentate chelating species (convergent approach) than for that obtained via the aqueous approach. The applied methods include X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and solid-state UV/vis spectroscopy. The energy-level alignment for the surface species from the aqueous approach, calculated from experimental data, accounts for the well-known type II excitation mechanism, whereas the findings indicate a distinct excitation mechanism for the bidentate chelating surface species of the material [Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2]@[m-TiO2].

Distinct Reactivity of Trimethylytterbium toward AlMe3 and GaMe3 : Synthesis of Donor-Stabilized Dimethylytterbium.

Me3 TACN (1,4,7-trimethyl-1,4,7-triazacyclononane)-stabilized trimethylytterbium was obtained via a salt-metathesis protocol employing [(Me3 TACN)YbCl3 ] and methyllithium. Complex [(Me3 TACN)YbMe3 ] seems not to engage in redox chemistry with potassium graphite and is thermally quite stable in the solid state. Treatment of trivalent [(Me3 TACN)YbMe3 ] with 3 equiv. of AlMe3 afforded divalent tetramethylaluminate complex [(Me3 TACN)Yb(AlMe4 )2 ]. The reaction of [(Me3 TACN)YbMe3 ] with GaMe3 in THF gave trivalent ion pair [(Me3 TACN)YbMe2 (thf)][GaMe4 ], which is susceptible to reduction with KC8 . The thermally very labile divalent [(Me3 TACN)YbMe(µ-Me)]2 is the first discrete donor adduct of a divalent dimethyl rare-earth-metal complex.

Schlenk's Legacy-Methyllithium Put under Close Scrutiny.

Commercially available stock solutions of organolithium reagents are well-implemented tools in organic and organometallic chemistry. However, such solutions are inherently contaminated with lithium halide salts, which can complicate certain synthesis protocols and purification processes. Here, we report the isolation of chloride-free methyllithium employing K[N(SiMe3 )2 ] as a halide-trapping reagent. The influence of distinct LiCl contaminations on the 7 Li-NMR chemical shift is examined and their quantification demonstrated. The structural parameters of new chloride-free monomeric methyllithium complex [(Me3 TACN)LiCH3 ], ligated by an azacrown ether, are assessed by comparison with a halide-contaminated variant and monomeric lithium chloride [(Me3 TACN)LiCl], further emphasizing the effect of halide impurities.

Rare-earth-metal trimethylsilylmethyl ate complexes.

En route to putative rare-earth-metal alkylidene complex Li[Lu(CH2SiMe3)2(CHSiMe3)], according to Schumann's original protocol, the reaction of YCl3 with LiCH2SiMe3 in a mixture of diethyl ether and n-pentane afforded a neosilyl ate complex of composition Li3Y(CH2SiMe3)6. Tetrametallic complex Li3Y(CH2SiMe3)6 shows an unprecedented structural motif in the solid state and was further characterized by heteronuclear 1H/13C/7Li/29Si/89Y, as well as VT NMR and DRIFT spectroscopies. Analysis of the thermolysis product via heteronuclear NMR spectroscopy and its reactivity towards benzophenone gave strong evidence for an alkylidene formation upon decomposition. Application of a similar protocol for the smallest rare-earth-metal scandium led to the isolation of ate complex [Li(thf)4][LiSc2(CH2SiMe3)8] as the preferred crystallized product. Here, the reaction of adduct ScCl3(thf)3 and LiCH2SiMe3 was performed in Et2O/n-hexane, in the absence of additional THF. The reaction of LaCl3(thf) with 3 equiv. of LiCH2SiMe3 in THF/Et2O at -40 °C yielded the ate complex [Li(thf)4][La(CH2SiMe3)4(thf)], which is the first of its kind.

Molecular Ln(III)-H-E(II) Linkages (Ln=Y, Lu; E=Ge, Sn, Pb).

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH3 and trivalent rare-earth-metallocene alkyls [Cp*2 Ln(CH{SiMe3 }2 )] gave complexes [Cp*2 Ln(µ-H)2 SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*2 Ln(µ-H)2 EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)2 ] to the rare-earth-metal hydrides [(Cp*2 LnH)2 ]. The lead compounds [Cp*2 Ln(µ-H)2 PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.

[(CH3 )Al(CH2 )]12 : Methylaluminomethylene (MAM-12).

The molecular structure of enigmatic "poly(aluminium-methyl-methylene)" (first reported in 1968) has been unraveled in a transmetalation reaction with gallium methylene [Ga8 (CH2 )12 ] and AlMe3 . The existence of cage-like methylaluminomethylene moieties was initially suggested by the reaction of rare-earth-metallocene complex [Cp*2 Lu{(µ-Me)2 AlMe2 }] with excess AlMe3 affording the deca-aluminium cluster [Cp*4 Lu2 (µ3 -CH2 )12 Al10 (CH3 )8 ] in low yield (Cp*=C5 Me5 ). Treatment of [Ga8 (CH2 )12 ] with excess AlMe3 reproducibly gave the crystalline dodeca-aluminium complex [(CH3 )12 Al12 (µ3 -CH2 )12 ] (MAM-12). Revisiting a previous approach to "poly(aluminium-methyl-methylene" by using a (C5 H5 )2 TiCl2 /AlMe3 (1 : 100) mixture led to amorphous solids displaying solubility behavior and spectroscopic features similar to those of crystalline MAM-12. The gallium methylene-derived MAM-12 was used as an efficient methylene transfer reagent for ketones.

Chromous siloxides of variable nuclearity and magnetism.

Treatment of Cr[N(SiMe3)2]2(thf)2 with HOSiR3 (R = Et, iPr) in THF afforded the bridged CrII siloxide complexes Cr3(OSiEt3)2(µ-OSiEt3)4(thf)2 and Cr2(OSiiPr3)2(µ-OSiiPr3)2(thf)2 in high yield. Exposure of these compounds to vacuum in aliphatic solvents led to the loss of coordinated THF and to the formation of the homoleptic chromous siloxides Cr4(µ-OSiEt3)8 and Cr3(OSiiPr3)2(µ-OSiiPr3)4, respectively, in moderate to high yield. Use of TMEDA as a potentially bidentate donor molecule gave the monomeric cis-coordinated siloxide Cr(OSiiPr3)2(tmeda) (tmeda = N,N,N',N'-tetramethylethane-1,2-diamine). Oxidation of Cr2(OSiiPr3)2(µ-OSiiPr3)2(thf)2 with CHI3 and C2Cl6 produced the trigonal bipyramidal chromic compound CrIII(OSiiPr)3(thf)2 and asymmetrically coordinated Cr2Cl3(OSiiPr3)3(thf)3, respectively. Magnetic measurements (Evans and SQUID) hinted at (a) antiferromagnetic interactions between the CrII centres, (b) revealed higher effective magnetic moments (µeff) for cis-coordinated monomeric heteroleptic complexes compared to trans-coordinated ones, and (c) pointed out the highest (µeff) for the tetranuclear complex Cr4(µ-OSiEt3)8 (6.26µB, SQUID, 300 K; Cr⋯Cradjacent avg. 2.535 A).

Open-Shell Early Lanthanide Terminal Imides.

Group 3- and 4f-element organometallic chemistry and reactivity are decisively driven by the rare-earth-metal/lanthanide (Ln) ion size and associated electronegativity/ionicity/Lewis acidity criteria. For these reasons, the synthesis of terminal "unsupported" imides [Ln═NR] of the smaller, closed-shell Sc(III), Lu(III), Y(III), and increasingly covalent Ce(IV) has involved distinct reaction protocols while derivatives of the "early" large Ln(III) have remained elusive. Herein, we report such terminal imides of open-shell lanthanide cations Ce(III), Nd(III), and Sm(III) according to a new reaction protocol. Lewis-acid-stabilized methylidene complexes [TptBu,MeLn(µ3-CH2){(µ2-Me)MMe2}2] (Ln = Ce, Nd, Sm; M = Al, Ga) react with 2,6-diisopropylaniline (H2NAriPr) via methane elimination. The formation of arylimide complexes is governed by the Ln(III) size, the Lewis acidity of the group 13 metal alkyl, steric factors, the presence of a donor solvent, and the sterics and acidity (pKa) of the aromatic amine. Crucially, terminal arylimides [TptBu,MeLn(═NAriPr)(THF)2] (Ln = Ce, Nd, Sm) are formed only for M = Ga, and for M = Al, the Lewis-acid-stabilized imides [TptBu,MeLn(NAriPr)(AlMe3)] (Ln = Ce, Nd, Sm) are persistent. In stark contrast, the [GaMe3]-stabilized imide [TptBu,MeLn(NAriPr)(GaMe3)] (Ln = Nd, Sm) is reversibly formed in noncoordinating solvents.

Kinetic stabilization allows structural analysis of a benzoborirene.

Formal reduction of (2-bromophenyl)chloro(2,2'',4,4'',6,6''-hexaisopropyl-[1,1':3',1''-terphenyl]-2'-yl)borane with tert-butyl lithium at low temperatures yields a highly strained benzoborirene that is kinetically stabilized by the bulky terphenyl substituent. The target compound withstands heating to 80 °C, and represents the first benzoborirene fully characterized by single-crystal X-ray crystallography. The bond length pattern of the six-membered ring of the parent benzoborirene follows an anti-Mills-Nixon distortion.

Yttrium tris(trimethylsilylmethyl) complexes grafted onto MCM-48 mesoporous silica nanoparticles.

A series of tris(trimethylsilylmethyl) yttrium donor adduct complexes was synthesized and fully characterized by X-ray diffraction, 1H/13C/29Si/31P/89Y heteronuclear NMR and FTIR spectroscopies as well as elemental analyses. Treatment of Y(CH2SiMe3)3(thf)x with various donors Do led to complete (Do = TMEDA, DMAP) and partial displacement of THF (Do = NHCiPr, DMPE). Exceptionally large 89Y NMR shifts to low field were observed for the new complexes. Complexes Y(CH2SiMe3)3(tmeda) and Y(CH2SiMe3)3(dmpe)(thf) were chosen to perform surface organometallic chemistry, due to a comparatively higher thermal stability and the availability of the 31P nucleus as a spectroscopic probe, respectively. Mesoporous nanoparticles of the MCM-48-type were synthesized and used as a 3rd generation silica support. The parent and hybrid materials were characterized using X-ray powder diffraction, solid-state-NMR spectroscopy, DRIFTS, elemental analyses, N2-physisorption, and scanning electron microscopy (SEM). The presence of surface-bound yttrium alkyl moieties was further proven by the reaction with carbon dioxide. Quantification of the surface silanol population by means of HN(SiHMe2)2-promoted surface silylation is shown to be superior to titration with lithium alkyl LiCH2SiMe3.

Pentamethylcyclopentadienyl Complexes of Cerium(IV): Synthesis, Reactivity, and Electrochemistry.

Treatment of Cp*2CeCl2K(THF) with alkali-metal alkoxides and siloxides in the presence of hexachloroethane generates the monomeric bis(pentamethylcyclopentadienyl) cerium(IV) complexes Cp*2Ce(OR)2 (Cp* = C5Me5; R = Et, iPr, CH2tBu, tBu, SiMe3, or SiPh3). Large substituents R trigger ligand scrambling to half-sandwich complexes Cp*Ce(OR)3, which could be isolated for R = tBu and SiPh3. Similar reactions with sodium aryloxide NaOAr (OAr = OC6H3iPr2-2,6) led to Cp*2Ce(OAr)Cl. Treatment of tris(cyclopentadienyl) complexes CpR3CeCl (CpH = Cp = C5H5; CpMe = C5H4Me) with NaOAr afforded CpMe2Ce(OAr)2 and Cp3Ce(OAr). The cerium(IV) complexes display a pseudotetrahedral geometry in the solid state. Cyclic voltammetry revealed mostly chemically reversible as well as electrochemically quasi-reversible redox processes with potentials ranging from -0.84 to -1.61 V versus Fc/Fc+. Switching from sandwich to half-sandwich complexes decreased the electrochemical potentials drastically, showing better stabilization of the cerium(IV) center in the case of Cp*Ce(OR)3 than in the case of Cp*2Ce(OR)2. Enhanced stabilization of the cerium +IV oxidation state could be further demonstrated in the series alkoxy > siloxy > aryloxy as well as C5Me5 > C5HMe4.