The recursive partitioning technique can be employed to refine the stratification and design of malignant glioma trials.

The complexes [Ln(AlMe4)3] (Ln=Y, La, Ce, Pr, Nd, Sm, Ho, Lu) have been synthesized by an amide elimination route and the structures of [Lu{(micro-Me)2AlMe2}3], [Sm{(micro-Me)2AlMe2}3], [Pr{(micro-Me)2AlMe2}3], and [La{(micro-Me)2AlMe2}2{(micro-Me)3AlMe}] determined by X-ray crystallography. These structures reveal a distinct Ln3+ cation size-dependency. A comprehensive insight into the intrinsic properties and solution coordination phenomena of [Ln(AlMe4)3] complexes has been gained from extended dynamic 1H and 13C NMR spectroscopic studies, as well as 1D 89Y, 2D 1H/89Y, and 27Al NMR spectroscopic investigations. [Ce(AlMe4)3] and [Pr(AlMe4)3] have been used as alkyl precursors for the synthesis of heterobimetallic alkylated rare-earth metal complexes. Both carboxylate and siloxide ligands can be introduced by methane elimination reactions that give the heterobimetallic complexes [Ln{(O2CAriPr)2(micro-AlMe2)}2(AlMe4)(C6H14)n] and [Ln{OSi(OtBu)3}(AlMe3)(AlMe4)2], respectively. [Pr{OSi(OtBu)3}(AlMe3)(AlMe4)2] has been characterized by X-ray structure analysis. All of the cerium and praseodymium complexes are used as precatalysts in the stereospecific polymerization of isoprene (1-3 equivalents of Et2AlCl as co-catalyst) and compared to the corresponding neodymium-based initiators reported previously. The superior catalytic performance of the homoleptic complexes leads to quantitative yields of high-cis-1,4-polyisoprene (>98%) in almost all of the polymerization experiments. In the case of the binary catalyst mixtures derived from carboxylate or siloxide precatalysts quantitative formation of polyisoprene is only observed for nLn:nCl=1:2. The influence of the metal size is illustrated for the heterobimetallic lanthanum, cerium, praseodymium, neodymium, and gadolinium carboxylate complexes, and the highest activities are observed for praseodymium as a metal center in the presence of one equivalent of Et2AlCl.

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Organolanthanide compounds are not only unique model systems for studying the elementary processes of a-olefin polymerization but they can also act as competitive precatalyst systems, [1] however, to date their implementation in this area has been very limited. In contrast, the interaction of lowagglomerated rare-earth metal ("neodymium") complexes, such as alkoxide or carboxylate derivatives, with various organoaluminum reagents is successfully exploited to generate high-performance catalysts for industrial 1,3-diene polymerization.[2] Solubility in aliphatic solvents, low Al:lanthanide(Ln) ratios, cis-stereospecificity, and medium polydispersity are the criteria to be met by such ternary "Ziegler Mischkatalysatoren" (Mischkatalysatoren = mixed catalysts), the mechanisms of which are still not completely understood.[3] Although the homoleptic tetraalkylaluminate complexes Ln(AlR 4 ) 3 have a unique preorganized set of bridged, heterobimetallic moieties, their application in olefin transformations has not been reported so far.[4] Moreover, the compounds Ln(AlR 4 ) 3 are exceptional for they are obtained as alkyl-only ligated monomeric systems, without the formation of ate complexes for the entire lanthanide series. Herein we describe the use of a Ln(AlR 4 ) 3 /Et 2 AlCl binary precatalyst system in highly (cis)stereoregular isoprene polymerization. Additionally, the use of grafted variants as storable singlecomponent heterogeneous catalysts is investigated by employing periodic mesoporous silica MCM-48 as a structured support material.Homoleptic tetramethylaluminate complexes of the trivalent lanthanide metals [Ln{(m-Me)

The organoaluminum-mediated alkylation of tailor-made rare-earth metal carboxylate complexes was studied, and implications of the degree of Ln alkylation and organoaluminum-chloride-mediated cation formation for 1,3-diene polymerization were investigated. Highly substituted rare-earth metal benzoate complexes {Ln(O 2 CC 6 H 2 Me 3 -2,4,6) 3 } n (Ln ) Y, La, Nd), {Ln(O 2 CC 6 H 2 iPr 3 -2,4,6) 3 } n (Ln ) Y, La, Nd, Gd, Lu), {Ln(O 2 CC 6 H 2 tBu 3 -2,4,6) 3 (THF)} n (Ln ) Y, La), {Ln(O 2 CC 6 H 3 Ph 2 -2,6) 3 (THF)} n (Ln ) Y, La), and {Ln(O 2 CC 6 H 3 Mes 2 -2,6) 3 (THF)} n (Ln ) Y, La) were obtained quantitatively according to the silylamide route from Ln[N(SiMe 3 ) 2 ] 3 and alkyl(aryl)-substituted benzoic acids. Such oligomeric carboxylate complexes are insoluble in aliphatic and aromatic solvents, but could be crystallized from donor solvents such as THF, DMSO, and pyridine. X-ray crystallographic analyses indicated the formation of monomeric [Nd(O 2 CC 6 H 2 Me 3 -2,4,6) 3 (DMSO) 3 ] and dimeric [La(O 2 CC 6 H 2 Me 3 -2,4,6) 2 (µ-O 2 CC 6 H 2 Me 3 -2,4,6)-(DMSO) 2 ] 2 depending on the metal ion size. Depending on the steric demand of the benzoate ligands, mono-and bis(tetraalkylaluminate) complexes [Me 2 Al(O 2 CC 6 H 2 iPr 3 -2,4,6) 2 ] 2 Ln[(µ-Me) 2 AlMe 2 ] and {Ln(O 2 CC 6 H 2 tBu 3 -2,4,6)[(µ-Me) 2 AlMe 2 ] 2 } 2 , respectively, could be identified as major product components from the reaction with excess AlR 3 (R ) Me, Et), by means of 1 H NMR spectroscopy and X-ray structure analysis. When activated with Et 2 AlCl, the resulting binary Ziegler-type catalysts efficiently polymerized isoprene (>99% cis-1,4), the polymerization performance depending on the metal center (Nd > Gd > La) and the degree of alkylation ("Ln(AlMe 4 ) 2 " > "Ln(AlMe 4 )"). Equimolar reaction of [Me 2 Al(O 2 -CC 6 H 2 iPr 3 -2,4,6) 2 ] 2 Ln[(µ-Me) 2 AlMe 2 ] with R 2 AlCl (R ) Me, Et) quantitatively produced [Me 2 Al(O 2 -CC 6 H 2 iPr 3 -2,4,6)] 2 , proposing "Me 2 LnCl" as the polymerization-initiating species. Homoleptic Ln(AlMe 4 ) 3 was spotted as a crucial reaction intermediate and was used for the high-yield synthesis of the various alkylated carboxylate complexes according to a novel "tetraalkylaluminate" route.

The structure−reactivity relationship of the rare-earth metal aryl(alk)oxide-promoted coordination polymerization of isoprene was investigated using binary initiating systems Ln(OR)3(AlMe3) x /Et2AlCl (Ln = La, Nd, Y). Depending on the degree of the rare-earth metal aryl(alk)oxide prealkylation (x = 1, 2, 3), such discrete trimethylaluminum (TMA) adduct complexes of rare-earth metal alkoxide and aryloxide components displayed a distinct initiating capability. The heterobimetallic bis-TMA adducts Ln(OAr i Pr)3(AlMe3)2 and tris-TMA adducts Ln(OCH2 tBu)3(AlMe3)3 (Ln = La, Nd) produced highly reactive initiators, whereas the mono-TMA adducts Ln(OAr t Bu)3(AlMe3) were catalytically inactive. The highest reactivities and stereoselectivities (>99% cis) were obtained for a n Ln:n Cl ratio of 1:2. The alkoxide-based tris-TMA adducts gave narrower molecular weight distributions than the aryloxide-based bis-TMA adduct complexes (M w/M n = 1.74−2.37 vs 2.03−4.26). A plausible mechanistic activation/deactivation scenario of the formation of the catalytically active/inactive species is presented.

The reaction of various highly substituted lanthanide(III) and -(II) aryloxide complexes with trimethylaluminum (TMA) was investigated. The solvent-free, π-arene-bridged dimers [Ln(OAr i Pr,H)3]2, derived from the ortho-iPr2-substituted aryloxide ligand OC6H3 i Pr2-2,6, form bis-TMA adduct complexes, Ln(OAr i Pr,H)3(AlMe3)2, for the metal centers yttrium, samarium, and lanthanum. Homoleptic monomeric Ln(OAr)3, featuring a large La center and sterically bulkier ortho-tBu2-substituted aryloxide ligands, afford the mono-TMA adducts La(OAr t Bu,R)3(AlMe3) (R = H, Me). The hetero-bridged moieties “Ln(μ-OAr)(μ-Me)Al” of these adduct complexes are rigid in solution, while at ambient temperature the exchange of bridging and terminal aluminum methyl groups is fast on the NMR time scale. Monomeric Ln(OAr t Bu,R)3 (R = H, Me, tBu) of the smaller rare-earth-metal centers yttrium and lutetium react with TMA to give mono(tetramethylaluminate) complexes of the type (Ar t Bu,RO)2Ln[(μ-Me)2AlMe2]. The heteroleptic Cp*-supported complex (C5Me5)Y(OAr t Bu,H)2 also produced a tetramethylaluminate complex, namely (C5Me5)Y(OAr t Bu,H)[(μ-Me)2AlMe2], in the TMA reaction. The solvated aryloxide complexes Ln(OAr)2(THF) x (x = 1, 2), featuring the divalent rare-earth-metal centers ytterbium and samarium, yield the bis-TMA adduct complexes Ln[(μ-OAr t Bu,R)(μ-Me)AlMe2]2. However, it was found that the generation of homoleptic hexane-insoluble [Ln(AlMe4)2] n is an important reaction pathway governed by the size (oxophilicity) of the metal center (Yb ≫ Sm), the amount of TMA, the reaction period, and the substituents of the aryloxide ligand (OAr i Pr,H ≫ OAr t Bu,H > OAr t Bu,Me ≫ OAr t Bu, t Bu). For the Ln(III) aryloxide complexes, peralkylated complexes Ln(AlMe4)3 were detected only in the presence of the least bulky ligand, OAr i Pr,H. Various mechanistic scenarios are depicted on the basis of the rare-earth-metal species identified, including byproducts such as [Me2Al(μ-OAr)]2, and of the interactivity of rare-earth alkoxide complexes with trialkylaluminum compounds known from the literature. The complexes Y(OC6H3 i Pr2-2,6)[(μ-OC6H3 i Pr2-2,6)(μ-Me)AlMe2]2 and Ln(OC6H3 t Bu2-2,6)2[(μ-Me)2AlMe2] (Ln = Y, Lu) have been characterized by X-ray diffraction structure determinations.

The ambiphilic -phosphinoethylboranes Ph 2 PCH 2 CH 2 BR 2 (BR 2 ) BCy 2 (1a), BBN (1b)), which feature the ethano spacer CH 2 CH 2 between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a,b were fully characterized by elemental analysis and by NMR and IR spectroscopy. X-ray crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through P · · · B donor-acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe 2 . The zwitterionic complexes (dmpe)NiMe(Ph 2 PCH 2 CH 2 BCy 2 Me) (2a) and (dmpe)NiMe(Ph 2 PCH 2 CH 2 [BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C 6 F 5 ) 3 abstracts the methyl group of a coordinated borate ligand to generate a free, three-coordinate borane center in [(dmpe)NiMe(1a)] + [MeB(C 6 F 5 ) 3 ] -(3).