The synthesis of (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr from [(C 5 Me 5 ) 2 Ln][(µ-Ph) 2 BPh 2 ] and KC 5 Me 5 completes the series of sterically crowded (C 5 Me 5 ) 3 Ln complexes for the larger lanthanides, La-Nd and Sm, and allows a comparison of structure and reactivity as a function of metal size. Synthesis of these new (C 5 Me 5 ) 3 Ln complexes required silylated glassware, which surprisingly was not necessary for the more sterically crowded analogues. (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr display longer Ln-C(C 5 Me 5 ) distances than any previously described Ce or Pr complexes containing the (C 5 Me 5 )ligand. The η 1 -C 5 Me 5 alkyl-like reactivity of the (C 5 Me 5 ) 3 Ln complexes was investigated with CO, ethylene, THF, and H 2 . The sterically induced reduction (SIR) reactivity of the (C 5 Me 5 ) 3 Ln complexes was examined with SedPPh 3 , AgBPh 4 , C 8 H 8 , and phenazine. All of these data indicate that (C 5 Me 5 ) 3 Ln reactivity increases with decreasing size of the metal and hence increased steric crowding. The reactivity of (C 5 Me 5 ) 3 Ln with CO 2 and with Et 3 NHBPh 4 was examined since each substrate could react by either η 1 -C 5 Me 5 alkyl or SIR pathways. In both cases, alkyl-like reactivity is observed: CO 2 forms the insertion product (C 5 Me 5 ) 2 Ln(O 2 CC 5 Me 5 ), containing a carboxylate with a pentamethylcyclopentadiene substituent, and Et 3 NHBPh 4 forms [(C 5 Me 5 ) 2 Ln][(µ-Ph) 2 BPh 2 ] and C 5 Me 5 H. The reactions of (C 5 Me 5 ) 3 Sm with aryl halides and primary alkyl halide radical clocks (RX) yield C 5 Me 5 R, C 5 Me 5 X, (C 5 Me 5 ) 2 , R-R, and [(C 5 Me 5 ) x SmX y ] z as products, which indicate that SIR is not the only reaction pathway with these substrates. The X-ray crystal structures of the (C 5 Me 5 ) 3 Ln reaction products [(C 5 Me 5 ) 2 La] 2 (µ-η 2 :η 2 -Se 2 ), [(C 5 Me 5 ) 2 (THF)La] 2 (µ-η 2 :η 2 -Se 2 ), [(C 5 Me 5 ) 2 La] 2 (µ-η 3 :η 3 -C 12 N 2 H 8 ), [(C 5 Me 5 ) 2 Sm(µ-I)] 3 , and (C 5 Me 5 ) 2 Sm(O 2 CC 5 Me 5 ) are described as well as a new synthesis of (C 5 Me 5 ) 3 Sm from (C 5 Me 5 ) 2 Sm and (C 5 Me 5 ) 2 .

Synthesis of the sterically crowded Tris(pentamethylcyclopentadienyl) lanthanide complexes, (C 5Me5)3Ln, has demonstrated that organometallic complexes with unconventionally long metal ligand bond lengths can be isolated that provide options to develop new types of ligand reactivity based on steric crowding. Previously, the (C 5Me5)3M complexes were known only with the larger lanthanides, La-Sm. The synthesis of even more crowded complexes of the smaller metals Gd and Y is reported here. These complexes allow an evaluation of the size͞reactivity correlations previously limited to the larger metals and demonstrate a previously undescribed type of C 5Me5-based reaction, namely C-H bond activation. (C 5Me5)3Gd, was prepared from GdCl3 through (C 5Me5)2GdCl2K(THF)2, (C5Me5)2Gd(C3H5), and [(C5Me5)2Gd][BPh4] and structurally characterized by x-ray crystallography. Although Gd 3؉ is redox-inactive, (C5Me5)3Gd functions as a reducing agent in reactions with 1,3,5,7-cyclooctatetraene (COT) and triphenylphosphine selenide to make (C 5Me5)Gd(C8H8), [(C5Me5)2Gd]2Se2, and [(C 5Me5)2Gd]2Se depending on the stoichiometry used. When the analogous synthetic method was attempted with yttrium in arene solvents, the previously characterized (C 5Me5)2YR complexes (R‫؍‬C 6H5, CH2C6H5) were isolated instead, i.e., C-H bond activation of solvent occurred. To avoid this problem, (C 5Me5)3Y was synthesized in high yield from [(C 5Me5)2YH]2 and tetramethylfulvene in aliphatic solvents. Isolated (C 5Me5)3Y was found to metalate benzene and toluene with concomitant formation of C 5Me5H, a reaction contrary to the normal pK a values of these hydrocarbons. In this case, the normally inert (C 5Me5) 1؊ ligand engages in C-H bond activation due to the extreme steric crowding.sterically induced reduction ͉ lanthanide ͉ pentamethylcyclopentadienyl ͉ arene activation ͉ long-bond organometallics

Communication Ruthenium Olefin Metathesis Catalysts for the Ethenolysis of Renewable FeedstocksRuthenium olefin metathesis catalysts have been evaluated for the ethenolysis of methyl oleate, a natural seed oil derivative, to produce useful terminal olefins. Several N-heterocyclic carbene-based ruthenium catalysts demonstrate good activity and selectivity for the formation of terminal olefins. In particular, catalysts (10) and (21) achieved higher TONs (A20 000).

N-aryl, N-alkyl N-heterocyclic carbene (NHC) ruthenium metathesis catalysts are highly selective toward the ethenolysis of methyl oleate, giving selectivity as high as 95% for the kinetic, ethenolysis products over the thermodynamic, self-metathesis products. The examples described herein represent some of the most selective NHC-based ruthenium catalysts for ethenolysis reactions to date. Furthermore, many of these catalysts show unusual preference and stability toward propagating as a methylidene species, and provide good yields and turnover numbers (TONs) at relatively low catalyst loading (<500 ppm). A catalyst comparison showed that ruthenium complexes bearing sterically hindered NHC substituents afforded greater selectivity and stability, and exhibited longer catalyst lifetime during reactions. Comparative analysis of the catalyst preference for kinetic versus thermodynamic product formation was achieved via evaluation of their steady-state conversion in the cross-metathesis reaction of terminal olefins. These results coincided with the observed ethenolysis selectivities, in which the more selective catalysts reach a steady-state characterized by lower conversion to cross-metathesis products compared to less selective catalysts, which show higher conversion to cross-metathesis products.

The vinyl C-H bond of tetramethylfulvene is activated in the presence of [(C5Me5)2LuH]x, 1, to form a vinyl organolutetium complex, (C5Me5)2Lu(CH=C5Me4), 2. Also formed in the reaction is the "tuck-over" complex, (C5Me5)2Lu(mu-H)(mu-eta1:eta5-CH2C5Me4)Lu(C5Me5), 3, containing a (CH2C5Me4)2- moiety long postulated to exist in organolutetium chemistry but never crystallographically characterized. Evidence for these C-H bond activations by a "(C5Me5)3Lu" intermediate, 4, is presented. Complex 3 can also be made in high yield by thermolysis of 1. Under H2, 1 catalytically hydrogenates TMF to C5Me5H.

The well-defined coordination environment of trivalent [(C5Me5)2Ln]+ complexes has been used to examine the reaction chemistry of the lanthanide carboxylate and R2AlCl (R = Me, Et, iBu) components used in the preparation of lanthanide-based diene polymerization catalysts. Each of the R2AlCl reagents can replace a carboxylate ligand with chloride in reactions with [(C5Me5)2Sm(O2CC6H5)]2, but instead of forming a simple chloride complex like [(C5Me5)2SmCl]3, bimetallic lanthanide aluminum dichloro complexes (C5Me5)2Sm(μ-Cl)2AlR2 are generated by ligand redistribution. These bis(chloride)-bridged complexes are also readily formed from the divalent precursor (C5Me5)2Sm(THF)2 and R2AlCl. However, the analogous reaction between (C5Me5)2Sm(THF)2 and Et3Al gives (C5Me5)2Sm(THF)(μ-η2-Et)AlEt3, which contains the first Ln(III)−(η2-Et) linkage, a coordination mode that differentiates Et from Me. To determine if mixed mono-chloride/alkyl-bridged (C5Me5)2Ln(μ-Cl)(μ-R)AlR2 complexes can be isolated, (C5Me5)2Y(μ-Cl)YCl(C5Me5)2 was reacted with R3Al. These reactions form [(C5Me5)2Y(μ-Cl)(μ-R)AlR2] x complexes, but again there is a differentiation on the basis of R:  the Me complex is a dimer and the others are monomers. (C5Me5)2Y(μ-Cl)2AlR2 complexes were similarly prepared for comparison with the mixed ligand species and for additional Me, Et, and iBu comparisons.

A series of ruthenium catalysts have been screened under ring closing metathesis (RCM) conditions to produce five-, six-, and seven-membered carbamate-protected cyclic amines. Many of these catalysts demonstrated excellent RCM activity and yields with as low as 500 ppm catalyst loadings. RCM of the five-membered carbamate-series could be run neat, the six-membered carbamate-series could be run at 1.0 M concentrations and the seven-membered carbamate-series worked best at 0.2 M to 0.05 M concentrations.

The reductive reactivity of lanthanide hydride ligands in the [(C5Me5)2LnH]x complexes (Ln = Sm, La, Y) was examined to see if these hydride ligands would react like the actinide hydrides in [(C5Me5)2AnH2]2 (An = U, Th) and [(C5Me5)2UH]2. Each lanthanide hydride complex reduces PhSSPh to make [(C5Me5)2Ln(mu-SPh)]2 in approximately 90% yield. [(C5Me5)2SmH]2 reduces phenazine and anthracene to make [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C12H8N2) and [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C10H14), respectively, but the analogous [(C5Me5)2LaH]x and [(C5Me5)2YH]2 reactions are more complicated. All three lanthanide hydrides reduce C8H8 to make (C5Me5)Ln(C8H8) and (C5Me5)3Ln, a reaction that constitutes another synthetic route to (C5Me5)3Ln complexes. In the reaction of [(C5Me5)2YH]2 with C8H8, two unusual byproducts are obtained. In benzene, a (C5Me5)Y[(eta(5)-C5Me4CH2-C5Me4CH2-eta(3))] complex forms in which two (C5Me5)(1-) rings are linked to make a new type of ansa-allyl-cyclopentadienyl dianion that binds as a pentahapto-trihapto chelate. In cyclohexane, a (C5Me5)2Y(mu-eta(8):eta(1)-C8H7)Y(C5Me5) complex forms in which a (C8H8)(2-) ring is metalated to form a bridging (C8H7)(3-) trianion.