Erwan Le Roux

Intramolecular Hydroamination/Cyclization of Aminoalkenes Catalyzed by Ln(N(SiMe3)2)3 Grafted onto Periodic Mesoporous Silicas

Homoleptic rare-earth metal silylamide complexes Ln[N(SiMe(3))(2)](3) (Ln = Y, La, Nd) were grafted onto a series of partially dehydroxylated periodic mesoporous silica (PMS) supports, SBA-15(-500) (d(p) = 7.9 nm), SBA-15LP(-500) (d(p) = 16.6 nm), and MCM-41(-500) (d(p) = 4.1 nm). The hybrid materials Ln[N(SiMe(3))(2)](3)@PMS efficiently catalyze the intramolecular hydroamination/cyclization reaction of 2,2-dimethyl-4-penten-1-amine. Under the prevailing slurry conditions the metal size (Y > La > Nd), the pore size, and the particle morphology affect the catalytic performance. Material Y[N(SiMe(3))(2)](3)@SBA-15LP(-500) displayed the highest activity (TOF = up to 420 h(-1) at 60 °C), with the extralarge pores minimizing restrictive product inhibition and substrate diffusion effects. The catalytic activity of Y[N(SiMe(3))(2)](3)@SBA-15LP(-500) is found to be much higher than that of the molecular counterpart (TOF = up to 54 h(-1)), and its recyclability is demonstrated.

Elusive Trimethyllanthanum: Snapshots of Extensive Methyl Group Degradation in LaAl Heterobimetallic Complexes

Reactions of [La(AlMe4)3] and [Y(AlMe4)3] with PMe3 show that the phosphine can cleave Ln--CH3--Al linkages, separating Me3Al(PMe3). PMe3 (3 mol equiv) reacts with [Y(AlMe4)3] to give [(YMe3)n] contaminated with by-products containing phosphorus and aluminum. The La-based analog, [(LaMe3)n], is not formed selectively from the reaction of [La(AlMe4)3] with PMe3 or Et2O, which rather yields insoluble La/Al heterobimetallic products. Three multi-nuclear La-based clusters were obtained from a reaction of [La(AlMe4)3] with PMe3 (1 equiv) and identified by X-ray structure analyses. Each cluster exhibits extensive methyl group degradation and contains methylene, methine, or carbide moieties. [La4Al8(CH)4(CH2)2(CH3)20(PMe3)] has a [La4(CH)4] cuboid core supported by AlMe3, Me2AlCH2AlMe2, and PMe3 ligands. [La4Al8(C)(CH)2(CH2)2(CH3)22(toluene)] also contains a cuboid core, [La3Al(C)(CH)2(CH2)], which includes one exo cubic lanthanum atom, and is supported by AlMe3, Me3AlCH2AlMe2, (AlMe4)-, and toluene ligands. The lanthanum atoms in [La5Al9(CH)6(CH3)30] are arranged in a trigonal bipyramidal fashion with (CH) functionalities capping each face. The [La5(CH)6]3- core is formally balanced by three AlMe2 + moieties and is additionally supported by six AlMe3 ligands. The unit cell contains two independent La5 clusters, one with pseudo-C3h and the other with pseudo-D3 symmetry, as well as two molecules of the separation co-product Me3Al(PMe3).

[(SiO)TaVCl2Me2]: A Well‐Defined Silica‐Supported Tantalum(V) Surface Complex as Catalyst Precursor for the Selective Cocatalyst‐Free Trimerization of Ethylene

Over the last 50 years, the production of linear a-olefins by ethylene oligomerization has gained increasing interest in industrial and academic research. Currently, numerous studies in this field have been reported and developed into industrial processes: titanium-based catalysts for the dimerization of ethylene (Alpha-butol, IFP); chromium-based catalysts for the trimerization of ethylene (Phillips Petroleum), and more recently chromium-bearing PNP ligand for ethylene tetramerization (SASOL). Along with these nowclassical systems, which require co-catalysts such as MAO, Sen also reported the use of tantalum pentachloride in combination with an alkylating agent, such as SnMe4, ZnMe2, AlMe3, or MeLi. In this case, the catalysts is assumed to be Ta species formed in situ by the reduction of TaMe2Cl3 in the presence of ethylene. In this context, Mashima and coworkers have shown that Ta active species can be alternatively formed by reduction of TaCl5 by 3,6-bis(trimethylsilyl)-1,4-cyclohexadiene derivatives. However the catalytic performances of these systems require the addition of cocatalysts. In several instances, site isolation on the oxide surface has been highly beneficial to the design of efficient catalysts, compared to inactive or rapidly deactivating molecular analogues, which is in particular due to the absence of bimolecular reactions between supported metal complexes. When considering the reaction intermediates, and in the view of developing well-defined silica supported species, we targeted the immobilization of Me3TaCl2 [9] onto an inorganic carrier, silica, by surface organometallic chemistry (SOMC) as a catalyst precursor. Herein, we report the synthesis and the surface characterization of the grafted organometallic species ( SiO)TaCl2Me2 2 in view of its application in ethylene oligomerization. Furthermore, mechanistic studies on this selective catalytic process have been successfully achieved thanks to the dynamic reactor used. They indicate three different pathways for the initiation process. SBA-15 was selected because of its ordered mesoporous network with large surface area (Supporting Information, Figures S1, S2). This porous silica was subjected to partial dehydroxylation under vacuum at 700 8C to afford SBA15(700), which features mostly isolated silanols, as indicated on the IR spectrum by the characteristic sharp peak at 3747 cm 1 (Supporting Information, Figure S3). SBA-15(700) was reacted with TaCl2Me3 1 (Supporting Information, Figure S4), and the resulting powder was characterized to determine the organometallic species on the surface prior to its catalytic application. Elemental analysis gave 14.8% Ta, 1.65% C, and 0.39 % H, with a ratio of Ta/C/Cl = 1:1.97:1.88 (theoretical: Ta/C/Cl = 1:2:2). H-MAS NMR spectrum of 2 unexpectedly displays two major signals at 1.27 ppm and 0.85 ppm with a broad peak at 1.90 ppm and a very weak signal at 0.03 ppm, which is probably due to methane or a trace amount of SiMe (see below for further comments, and the Supporting Information, Figure S5). The NMR signal at 1.9 ppm most likely corresponds to the small amount of unreacted silanols, in agreement with IR spectroscopy results. Two peaks appear at 1.27 and 0.85 ppm that would be consistent with two inequivalent methyl groups coming from one species or indicating the presence of two distinct species. Proton double (DQ)and triple (TQ)-quantum correlation spectra under 22 kHz MAS (Supporting Information, Figure S6) confirm that these two signals correspond to methyl groups, most likely from two different species in view of the absence of correlation of diagonal peak. Autocorrelation peaks are observed on the diagonal of the 2D DQ spectrum for all the protons (notably, this shows that unreacted silanols are in close proximity to each other and most likely located in micropores). A strong autocorrelation [*] Y. Chen, E. Callens, E. Abou-Hamad, J.-M. Basset KAUST Catalysis Center King Abdullah University of Science and Technology Thuwal 23955-6900 (Kingdom of Saudi Arabia) E-mail: jeanmarie.basset@kaust.edu.sa

Silica‐Grafted Neodymium Catalysts for the Production of Ultrahigh‐Molecular‐Weight cis‐1,4‐Polyisoprene

Supported neodymium‐based Ziegler‐type catalysts are obtained by grafting homoleptic methylaluminate Nd(AlMe4)3 onto high‐surface silica materials including periodic mesoporous silicas MCM‐41, SBA‐15, and KIT‐6. Low [Et2AlCl]‐cocatalyst contents allow for the fabrication of polyisoprenes with ultrahigh molecular weight (UHMWPI). The synthetic rubbers display molecular weights as high as 3×106 g mol−1, polydispersity indices as low as 1.2, and microstructures with 99 % cis‐stereospecificity. Combined analysis of the organolanthanide/silica hybrid materials by nitrogen physisorption, FTIR and magic angle spinning NMR spectroscopies, and elemental (metal) analysis assist in elucidating the intrapore surface organometallic chemistry and suggest the formation of unprecedented organolanthanide species.