Lanthanide allyl complexes

Table 15 Anionic, cationic, and neutral lanthanide allyl complexes reported in diene polymerization ...

Reaction of tetranuclear lanthanide octahydrides with styrene provides lanthanide benzylic allyl heptahydride complexes through the insertion of a styrene molecule into one Ln-H bond. The lanthanide benzylic allyl complexes can be considered as the intermediates of styrene hydrogenation. Indeed, both the lanthanide octahydrides and the lanthanide benzylic allyl complexes can catalyze styrene hydrogenation efficiently in the presence of H2 [89]. Lanthanide hydrides react with 1,3-cyclohexadiene to form lanthanide allylic complexes via 1,4-addition [90]. However, these lanthanide hydride clusters can not catalyze the polymerization of styrene and 1,4-cyclohexadiene. 

The allyl group is able to form both a- and jr-bonded complexes with the actinides. The 71 complexes will be considered here because of the similarities of the homoal-lyls with the lanthanide and actinide homoalkyls. The limiting modes of bonding in metal allyl complexes and the ratio of PMR intensities from magnetically equi valent protons are illustrated in Fig. 14. 

Molander has developed effective protocols for the cyclization/hydrosilylation of 1,6-enynes catalyzed by lanthanide metallocene complexes/ For example, reaction of cyclohexyl-substituted 1,6-enyne 15a with phenylsilane catalyzed by Cp 2YMe(THF) in cyclohexane at room temperature for 2h gave silylated alkylidene cyclopentane 16a as a 6.5 1 mixture of trans. cis isomers (Table 5, entry 1). The diastereoselectivity of the reaction depended strongly on the nature of the allylic substituent. For example, yttrium-catalyzed cyclization/ hydrosilylation of the ethyl-substituted enyne 15b gave silylated cyclopentane 16b in 88% yield as a single diastereomer (Table 5, entry 2). 

Although heterobimetallic complexes with alkylated rare-earth metal centers were proposed to promote 1,3-diene polymerization via an allyl insertion mechanism, details of the polymerization mechanism and of the structure of the catalytically active center(s) are rare [58,83,118-125]. Moreover, until now, the interaction of the cationizing chloride-donating reagent with alkylated rare-earth metal centers is not well-understood. Lanthanide carboxylate complexes, which are used in the industrial-scale polymerization of butadiene and isoprene, are generally derived from octanoic, versatic, and... 

Lithium lanthanum jr-allyl complexes, LiLn(All)4 dioxane, where Ln = Ce, Nd, Sm, Gd, Dy have been synthesized and used as catalysts in the polymerization of butadiene. The data show the predominance of 1,4-trans product. The catalytic activity of the lanthanides was nearly the same as evidenced by the percent yield in the range 78-90. 

The compound can be isolated in pentane, recrystallized, and characterized by IR, H NMR and x-ray diffraction. The bis(cyclopentadienyl)lanthanide(f -allyl) complexes are also stable decomposition occurs at greater than 200°C... 

As the first catalytically active allyl-lanthanide compounds, the tetrakis(allyl) complexes Li[Ln(C3H5)4] dioxane, with Ln = Ce, Nd, Sm, Gd, and Dy, have been described [47]. More recently the field of allyl-lanthanide chemistry was extended considerably by the synthesis of the neutral tris(allyl) compounds of lanthanum and neodymium, LnlCsHj), n dioxane (Ln = La, n = 1.5 Ln = Nd, n = 1) from the tetrakis(allyl) complexes by abstraction of allyllithium with tri(ethyl)boron according to eqs. (1) and (2) [48]. For the catalytic properties of the allylneodymium(III) complexes, see [106],... 

The synthesis and characterization of the first bis- and tris[ 1 -(tu-alken-l-yl)indenyl] lanthanide complexes (Ln = Gd, Er, Y, Lu) have been reported. l-Allyl-2,4,7-trimethyl-lFI-indene and l-(3-buten-l-yl)-4,7-dimethyl-lH-indene were prepared from (2,4,7-trimethylindenyl)lithium and allyl chloride or from (4,7-dimethylindenyl)lithium and 4-bromo-l -butene.677 The reactions of the trichlorides of gadolinium, erbium, yttrium, lutetium, and ytterbium in molar ratios in TFIF produce the bis(l-allyl-2,4,7-trimethylindenyl)lanthanide chloride complexes L2LnCl(THF) (Ln = Gd, Er), bis( 1 -buten-1-yM,7-dimcthyIindcnyI)lanthanide complexes (Ln = Y, Lu) or the heterometallic complexes bis(l-buten-l-yl-4,7-dimethylindenyl)Yb(/r-Cl)2Li(THF)2 (Scheme 180).677... 

We can visualise the capability of suitable lanthanide (Ln) compounds (J, 6), e.g. as homogeneous catalysts with respect to olefins, by invoking similar intermediates. Although the series of reportedly catalytically active Ln-complexes spans from the pure trihalide via tris(B-diketonato)complexes to the organo-metallic tris(cyclopentadienyl) and tetra(allyl)complexes (8), respectively, no really optimal combination of ligands on a Ln-element has been found so far. Promising aspects are, however, based on some evidence for "reaction steering" in that either cis- or trans-polybutadienes can be obtained from 1,3-dienes, and either polymers or metathesis products from monoolefins, respectively (Table I). 

Various lanthanide halides (ScCR, YCI3, LaCl3,Ndl3) react with K2[3-(C3H3SiMe3-l)2SiMe2] to form a/ 5a-bis(allyl) complexes. The lanthanum derivative has been structurally authenticated as a coordination polymer (14), in which allyl anions interleave alternating lanthanum and potassium ions the latter display K- -MeSi contacts of 2.79(3) and 2.96(4) kd... 

Scandium group elements as well as the lanthanides form allyl complexes in which the central atom has H- 3 oxidation state, while the actinides give compounds possessing + 4 oxidation states (Table 7.14). These complexes are formed by reactions of metal halides with allyl compounds of magnesium, lithium, tin, etc. " " ... 

Complexes Containing Three-Electron n-Ligands Table 7.14. Allyl Complexes of the Group 3 Metals, the Lanthanides, and the Actinides ... 

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