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Samarocene sandwich complexes with superbulky penta-arylcyclopentadienyl ligands have been prepared and were structurally characterized: [(4-EtC6H4)(5)C-5](2)Sm (1) and [(4-iPrC(6)H(4))(5)C-5](2)Sm (2). Analogous to the previously reported synthesis of [(4-nBuC(6)H(4))(5)C-5](2)Sm, reaction of (DMAT)(2)center dot Sm(THF)(2) (DMAT = 2-Me2N-alpha-Me3Si-benzyl) and the appropriate Ar5C5H ligand gave 1 (66% yield) and 2 (59% yield). In contrast to the high reactivity of Cp*Sm-2, complex 1 has been shown to be surprisingly stable toward reaction with a large variety of reagents. Even under forcing conditions, no reaction with N-2, CO, CO2, pyrazine, trans-stilbene, pyridine, P-4, and benzophenone was observed. Complex 1 reacts with cuminil ArC(O)C(O)Ar (Ar = 4-iPrC(6)H(4)) to yield the Sm(III) sandwich complex [(4-EtC6H4)(5)C-5](2)Sm[ArC(O)C(O)Ar] (3), which could be isolated in 83% yield as a dark-red crystalline material. Complex 2 reacts with oxygen in the presence of phenazine to yield the bimetallic Sm(III) complex [(4-iPrC(6)H(4))(5)C5Sm(eta(1)-phenazine)]2(mu:eta(2)-eta(2)-O-2)(2) (4) in 25% yield as dark-red crystals. The unusually high redox-stability of deca-arylsamarocenes originates from steric hindrance of the Sm metal center.

The new complexes [MoBr(eta(3)-C3H5)(CO)(2)(L)(2)] (C1) and [MX2(CO)(3)(L)(2)] (M = Mo(II), X = I (C-2); M = Mo(II), X = Br (C-3); M = W(II), X = I (C-4); M = W(II), X = Br (C5)) were synthesized by reaction of 2-amino-1,3,4-thiadiazole (L) with [MoBr(eta(3)-C3H5)(CO)(2)(NCCH3)(2)] (1), [MoI2(CO)(3)(CH3CN)(2)](M = Mo (2); M = W (4)), or [MoBr2(CO)(3)(CH3CN)(2)](M = Mo (3); M = W (5)) in 2:1 ratio. The five complexes were immobilized in MCM-41, yielding the materials MCM-Cn (n = 1-5), and C1 was also immobilized in silica gel (Silica-C1) and in a polyhedral oligomeric silsesquioxane (Cube-C1). Complexes and materials were fully characterized by spectroscopic techniques and elemental analysis. DFT calculations showed that several C1 isomers should coexist. The as synthesized and supported complexes were tested as catalysts on the oxidation of geraniol, cis-hex-3-en-1-ol, trans-hex-3-en-1-ol, (S)-limonene, and 1-octene. The conversions and TOF significantly depend on the complex and the nature of the substrate. The general conclusions are (i) complex C1 has the highest activity; (ii) tungsten complexes C4 and C5 are more active than the molybdenum analogues; (iii) the immobilization of the catalysts improves the performance; and (iv) silica gel and the polyhedral oligomeric silsesquioxane supports modify the selectivity, leading to products different from the one obtained with MCM for specific substrates.

Decamethylzirconocene cation [Cp*2ZrMe](+) (2) decomposes in bromobenzene-d(5) solution to generate sigma-aryl species [Cp*Zr-2(2-C6H4Br-kappa Br,C)][B(C6F5)(4)] (3). This a-bond metathesis reaction is catalyzed by tertiary amines via a two-step mechanism, in which the amine acts as a proton relay. In benzene-d(6) compound 2 decomposes via C H bond activation of one of the Cp* ligands to generate tucked-in compound [Cp*{eta(5):eta(1)-C5Me4(CH2)}Zr](+) (4). In the presence of Et3N, no formation of tucked-in compound 4 is observed, but instead an overall double C-H bond activation and C-N bond cleavage of the tertiary amine is observed, resulting in [Cp*Zr-2{C(Me)NEt-kappa C,N}](+) (6). A mechanism is proposed that nominates [Cp*2ZrNEt2](+) as an intermediate, the result of a C-H bond activation of Et3N, followed by beta-amide elimination. Attempted synthesis of this species by treatment of Cp*Zr-2(NEt2)Me with [Ph3C][B(C6F5)(4)] results, again, in formation of compound [6](+). The presence of Et3N also has an effect on the stability of THF adduct [Cp*2ZrMe(THF)](+) as the amine performs a nucleophilic THF ring-opening to generate [Cp*2ZrMe{O(CH2)(4)NEt3}](+) (7). The results show that amine coproducts, often generated in the synthesis of cationic transition-metal complexes, are not necessarily innocent.

Two new monoanionic tetradentate triamino-amide ligands, [(Me2NCH2CH2)(2)N-B-N(t-Bu)](-) (B = (CH2)(2), L-1; SiMe2, L-2) were prepared. Reaction of LIH with Y(CH2SiMe3)(3)(THF)(2) yielded (LY)-Y-1(CH2SiMe3)(2) (1), which was structurally characterized. Compound 1 decomposes at ambient temperature via metalation of one of the NMe2 methyl groups to give {[(CH2)MeN(CH2)(2)] [Me2N(CH2)(2)]N(CH2)(2)N(t-Bu)}Y(CH2SiMe3) (2). Attempts to prepare (LY)-Y-1(CH2SiMe3)(2) resulted in very rapid ligand metalation. Both 1 and 2 react with [PhNMe2H][B(C6F5)(4)] to generate the cation [(L-1)YCH2SiMe3](+). The combination of 1 and [Ph3C] [B(C6F5)(4)] is active in catalytic ethene polymerization, but with a short catalyst lifetime. The metalated complex 2 reacts with ethene and with pyridine by stoichiometric insertion into the Y-CH2N bond, and the latter product was structurally characterized. In (LY)-Y-1(X)(CH2SiMe3) complexes, the Y-amine distance trans to X is very sensitive to the nature of X, suggesting the presence of a trans influence.

The incompletely condensed silsesquioxane disilanol (c-C5H9)(7)Si7O9(OH)(2)OSiMePh2 has been used as a backbone for the synthesis of the diphosphinite ligand (C-C5H9)(7)Si7O9(OPPh2)(2)-OSiMePh2 (1), based on a silsesquioxane framework. By reaction with black selenium, the corresponding selenide (2) was obtained, showing a J(Se-P) value of 815 Hz in the P-31 NMR spectrum. DFT calculations established a good insight into the electron density of the P atoms present in the two model compounds CH3OPPh2 (3) and Ph2P(HSiOH)(2)OPH2 (4). The Mulliken charge distributions show a clear electron-withdrawing effect of the siloxy group, which is also present in diphosphinite ligand 1. By reaction of compound 1 with PdCl2-(C6H5CN)(2), the palladium complex [PdCl2R(OPPh2)(2)] (5) was obtained (R = (C-C5H9)(7)Si7O9-OSiMePh2). From a similar reaction of 1 with PtCl2(cod), the platinum analogue [PtCl2R(OPPh2)(2)] (6) could be isolated. The equimolar reaction Of Mo(CO)(4)(pip)(2) (pip = piperidine) with 1 yielded the molybdenum complex [Mo(CO)(4)R(OPPh2)(2)] (7). Ligand 1 showed a clear tendency to coordinate in a cis fashion for all complexes 5-7, as was determined by NMR spectroscopy and X-ray crystallography. However, the analogous reaction of 1 with RhCl(CO)(2) dimer yielded the mononuclear trans-[RhCl(CO)(1)] (8). Complexes 5-8 have been structurally characterized as the first examples of transition-metal complexes with a silsesquioxane-based bidentate phosphinite ligand.