Scandium, metathesis reaction

In this equilibrium (a a bond metathesis reaction ), the scandium-hydrogen bond in to(pentamethylcyclopentadienyl)scandium hydride is replaced by a scandium-carbon bond in phenylto(pentamethylcyclopendienyl) scandium... 

The preparation of a tribenzyl scandium complex has been known for a long time [21], Recently, the neutral salt-free tribenzyl lanthanide complexes Ln(CH2Ph)3(THF)3 (Ln = La, Lu, Sc) and La(CH2Ph-4-Me)3(THF)3 have been successfully synthesized by the straightforward metathesis reaction of LnX3 with three equivalents of KCH2Ph-4-R (R = H, Me) [22,23], The neutral triaminosubstituted benzyl lanthanide complexes can be conveniently prepared by... 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

In this section we reviewed the latest theoretical studies on the metathesis reaction. In general, it has been shown that the metathesis reaction at first yields adduct complex then activation of the H-R bond takes place with a four-center transition state, which leads to the second adduct. It occurs more easily for scandium complexes than for lutetium analogues. The a-metathesis reactivity between R-H and M-R bonds decreases in the order of R C2H... 

Equation 21. Metathesis reaction of a scandium methyl complex to an oligosilanyl complex. 

Sadow AD, Tilley TD (2005) Synthesis and charactraizahon of scandium silyl complexes of the type Cp 2ScSiHRR. o-hond metathesis reactions and catalytic dehydrogenative silation of hydrocarbons. J Am Chtan Soc 127 643... 

In this reaction, a C—H bond in methane is made, and a C—H bond of benzene is cleaved, but the oxidation state of the scandium center remains +3. This class of reaction, which is not hmited to early transition metals, is called sigma-bond metathesis. In this mechanism, the metal is first postulated to coordinate the bond to be activated in an rf- fashion, followed by formation of a four-centered transition state that leads to an exchange of ligands at the metal (Figure 14.8). 

Some of the first reactions of soluble metal complexes with methane occurred by a-bond metathesis. Like the first examples of oxidative addition of alkyl C-H bonds, the first examples of a-bond metathesis with alkyl C-H bonds were intramolecular. Yet, the lute-tium- and yttrium-methyl complexes, Cp MMe (M = Lu and Y) were shown by Watson to react intermolecularly with C-labeled methane to form the labeled methyl complexes and unlabeled methane at 70 °C (Equation 6.51). Related scandium compounds have now been shown to undergo similar reactions with alkanes, and a thoracyclobutane... 

Recently, scandium-catalyzed hydromethylation of propene to iso-butane was achieved, but the reaction was very slow. The large isotope effect (CH4 vs CD4) is consistent with a n-bond metathesis mechanism (Scheme 4) (74). 

The exploration of the chemistry of terphenyl derivatives of the group 3 metals is due mainly to Rabe and coworkers [13-18]. The ligands used were of the formula C6H3-2,6-Ar2 (Ar = CeHs, C6H2-2,4,6-Mc3, 1-naphthyl, or 3-MeO-C6H4). The halide complexes 1-3 could readily be obtained by simple salt metathesis from the reaction of the terphenyl lithium with anhydrous metal trichlorides MCI3 (M = Sc or Y) in THF at room temperature [13,14], The yttilum complexes 2 and 3 were isolated in moderate yield (ca. 50%) however, only a low yield of the scandium complex 1 could be obtained, most likely because of C-H bond activation as indicated by NMR spectroscopy. These metatheses reactions did not proceed in aromatic solvents or hexanes probably as a result of the low solubility of the reactants in these media. Complex 1 decomposes slowly in THF solution, while 2 and 3 are considerably more stable. 

Metal vinyl and aryl complexes are two typical classes of products resulting from sp C—H bond activation from alkene and arene substrates, respectively. Bercaw and coworkers conducted a systematic study of the reactions between Cp 2ScR (R = alkyl or hydride) and various hydrocarbons and found that while ethylene underwent rapid polymerization with Cp 2ScMe, substituted alkenes, such as styrene and isobutene, were readily activated through cr-bond metathesis to result in scandium vinyl compounds (Scheme 8A). One... 

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