Non-cyclopentadienyl ancillary ligands

The most convenient method for the synthesis of lanthanide dialkyl complexes is the alkane elimination reaction of lanthanide trialkyl complexes with a monoanionic preligand (L H) (Equation 8.15). The monoanionic preligands, which have tunable steric and electronic features, are favored for modifying the stability and reactivity of the complexes. Various bulky substituted cyclopentadienyl [4] and non-cyclopentadienyl derivatives have been used as the spectator ligands. The most common types of monoanionic non-cyclopentadienyl ancillary ligands are summarized in Figure 8.10 [36 8]. 

This chapter summarizes recent advances in rare earth arene chemistry with an emphasis on complexes obtained by reduction and supported by non-cyclopentadienyl ancillary ligands. In order to discuss this area in context, a brief historical view of rare earth organometallic chemistry, in general, is included in the first section, and a brief historical view of bridging arene complexes, in particular, is included in the second section. The other sections describe chemistry from our group and include previously reported examples that are relevant to a paiticular section. 

Piers, W.E. and Emslie, D.J.H. (2002) Non-cyclopentadienyl ancillaries in organogroup 3 metal chemistry a fine balance in ligand design. Coordination Chemistry Reviews, 233—234, 131. 

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. 

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