Yttrium complexes cyclopentadienyl

Sun, J.L., Berg, D.J., and Twamley, B. (2008) Yttrium complexes of a phenanthrene-fused cyclopentadienyl synthetic, structural, and reactivity studies. Organometallics, 27, 683. 

These dimers are less reactive or unreactive in catalytic reactions of interest, and thus some substitution on the cyclopentadienyl ligands is necessary to prevent dimer formation through steric hindrance to association. Pentamethylcy-clopentadienyl (Cp ) ligands are useful for this, and lead to catalytic systems that are highly reactive and yet exquisitely selective in the insertion of mono-substituted alkenes. One such precatalyst system is the yttrium complex Cp 2YMe THF. Although Lewis bases normally depress catalytic activity because they compete for empty coordination sites on the catalyst, in this precatalyst the single THF of solvation appears to catalyze the hydrometallation process [Eq. (5)] [15] in the same manner that Lewis bases catalyze the hydroboration of olefins with 9-BBN [16] ... 

Solvent-free cyclopentadienyl rare earth dichlorides have not been prepared. Only the cyclopentadienyl lanthanide dichlorides coordinated by three tetrahydrofuran molecules of the heavier lanthanides could be isolated and some of their properties were investigated (Manastyrskyj et al., 1963 Ely and Tsutsui, 1975). The corresponding yttrium complex was mentioned in a paper by Jamerson et al. (1974), but no characterization of the compound was given. The preparation of the cyclopentadienyl rare earth dichloride complexes with 2 coordinated tetrahydrofuran Ugands of Eu, with 3 THE ligands of La and TM and with 4 THE ligands of La, Sm, Eu, Tm, and Yb was also described in the meantime (Suleimanov et al., 1982c, d). 

These intramolecular hydroaminations lead to the formation of chiral products. Thus, several studies have been devoted to developing ligands for enantioselective, intramolecular hydroaminations of olefins catalyzed by lanthanide complexes. ° Selectivities of these reactions with chiral cyclopentadienyl derivatives have been modest. Selectivities have been higher with catalysts containing non-cyclopentadienyl ligands. Some of tlie most selective catalysts are the yttrium complexes of the bis(thiolate) ligands reported by Livinghouse, the scandium and lutetium complexes of 33 -disubstituted binaphtholates reported by Hultzsch, and the BINAM-based bisamidates of Schafer.- A representative cyclization catalyzed by a member of each of these classes of catalyst are shown in Equation 16.64. 

Ihara, E. Yoshioko, S. Furo, M. Katsura, K. Yasuda, H. Mohri, S. Kanehisa, N. Kai, Y. Synthesis and olefin polymerization catalysts of new trivalent samarium and yttrium complexes with bridging bis(cyclopentadienyl) ligands. Organometallics 2001, 20, 1752-1761. 

Scheme 12 (A) Yttrium complexes with hybrid scorpionate/cyclopentadienyl ligands and (B) examples of double activation of Si-H and Si-N bonds.

Non-cyclopentadienyl single-site lanthanide alkoxides mostly feature N-donor-based ancillary ligands. Examples include bulky bis(arylamidinate)-yttrium(III) alkoxides, phenoxides and amides such as complexes (307)-(309), which initiate the ROP of LA.892 However, control over molecular weight is poor and polydispersities are broad (typically >1.5), with the exception of (309) in the presence of exogenous benzyl alcohol. 

A recent development in this field involves the combination of benzamidi-nate ligands with cyclopentadienyl or cyclooctatetraenyl ligands in the coordination sphere of lanthanide ions. The first lanthanide complexes containing both benzamidinate and pentamethylcyclopentadienyl bonded to yttrium was reported by Teuben et al. Yttrium aryloxides as well as anhydrous yttrium trichloride can be used as starting materials in these preparations (Eq. 19, Scheme 5) [27] ... 

Roesky introduced bis(iminophosphorano)methanides to rare earth chemistry with a comprehensive study of trivalent rare earth bis(imino-phosphorano)methanide dichlorides by the synthesis of samarium (51), dysprosium (52), erbium (53), ytterbium (54), lutetium (55), and yttrium (56) derivatives.37 Complexes 51-56 were prepared from the corresponding anhydrous rare earth trichlorides and 7 in THF and 51 and 56 were further derivatised with two equivalents of potassium diphenylamide to produce 57 and 58, respectively.37 Additionally, treatment of 51, 53, and 56 with two equivalents of sodium cyclopentadienyl resulted in the formation of the bis(cyclopentadienly) derivatives 59-61.38 In 51-61 a metal-methanide bond was observed in the solid state, and for 56 this was shown to persist in solution by 13C NMR spectroscopy (8Ch 17.6 ppm, JYc = 3.6 2/py = 89.1 Hz). However, for 61 the NMR data suggested the yttrium-carbon bond was lost in solution. DFT calculations supported the presence of an yttrium-methanide contact in 56 with a calculated shared electron number (SEN) of 0.40 for the yttrium-carbon bond in a monomeric gas phase model of 56 for comparison, the yttrium-nitrogen bond SEN was calculated to be 0.41. 

Phosphorus, arsenic, antimony, and bismuth ligands have been discussed in CCC (1987).153 Complexes containing bonds between scandium, yttrium, and phosphorus or arsenic have been reviewed,154 as have complexes with neutral phosphorus ligands.155 Many of the complexes described in these reviews contain organic substituents such as cyclopentadienyl or alkyl groups. 

More recently the chemistry has been extended to yttrium alkyl and hydrido complexes stabilized by tridentate-linked amido-cyclopentadienyl ligands. A typical synthetic route is illustrated in Scheme 68.293... 

Few examples of asymmetric hydrosilylations of styrene derivatives with chiral lan-thanocene catalysts have been reported (13) [29], The cyclopentadienyl-free chiral yttrium diamidobiphenyl complex 8 was used for asymmetric hydrosilylation of norbornene with high enantioselectivity (14) [53],... 

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