Ytterbium complexes Yttrium

Ytterbium complexes dipositive oxidation state hydrated ions, 1109 Yttrium complexes, 1059... 

Seheme 6.3 Synthesis of yttrium and ytterbium complexes with mono-aryloxo-functlonallzed NHCs. 

Recently, rare-earth metal complexes have attracted considerable attention as initiators for the preparation of PLA via ROP of lactides, and promising results were reported in most cases [94—100]. Group 3 members (e.g. scandium, yttrium) and lanthanides such as lutetium, ytterbium, and samarium have been frequently used to develop catalysts for the ROP of lactide. The principal objectives of applying rare-earth complexes as initiators for the preparation of PLAs were to investigate (1) how the spectator ligands would affect the polymerization dynamics (i.e., reaction kinetics, polymer composition, etc.), and (2) the relative catalytic efficiency of lanthanide(II) and (III) towards ROPs. 

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. 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

Attempts to synthesize the clathrochelate complexes of lanthanide ions via template condensation of the tripodal amine tren with formaldehyde bis-(dimethylamino)methane derivative on the rare-earth metal ion were successful only for ytterbium. The [Yb(metr)](CF3S03)3 AN clathrochelate was obtained in 3-5% yield [165]. With ytterbium cation, as well as with cerium, praseodymium, europium, yttrium, and lanthanum ions, the major reaction products proved to be mono- and dibridged semiclathrochelate complexes with ligands 1 and 2 (Scheme 71). 

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... 

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