Yttrium amidate complexes

Figure 16 Yttrium amidate complexes for ring-opening polymerization give polylactide. Reproduced from [52b, 52c] with permission of Elsevier...

Yttrium amidate complexes have been reported as efficient catalysts for amide bond formation. These complexes do not require the presence of additional oxidants, bases or heating to react efficiendy. Only 5 mol% of this complex at room temperature in toluene is able to efficiently catalyse the oxidative amidation of aldehydes. 

In 2003, Livinghouse et al. also reported that chelating bis(thiophosphonic amidates) complexes of lanthanide metals, such as yttrium or neodymium, were able to catalyse intramolecular alkene hydroaminations. These complexes were prepared by attachment of the appropriate ligands to the metals by direct metalation with Ln[N(TMS)2]3- When applied to the cyclisation of 2-amino-5-hexene, these catalysts led to the formation of the corresponding pyrrolidine as a mixture of two diastereomers in almost quantitative yields and diastereos-electivities of up to 88% de (Scheme 10.81). 

Bambirra, S., van Leusen, D., Meetsma, A., Hessen, B., and Teuben, J.H. Neutral and cationic yttrium alkyl complexes with linked 1,4,7-triazacyclononane-amide monoanionic ancillary ligands synthesis and catalytic ethene polymerisation, Chem. Comm. (2001), 637-638. 

The amide complex of Cp Ln such as Cp2LnN(SiMe3)2, where Ln = Nd, Yb has been characterized [181] and the Y complex was found to be roughly of trigonal planar geometry and coordinately unsaturated which favours the formation of weak Y-methyl contacts and a short Y-N distance due to the donation of lone-pair of electrons by nitrogen to yttrium. 

Bambirra, S., Boot, S.J., Tazelaar, C.GJ. etal. (2004) Yttrium alkyl complexes with triamino-amide ligands. Organometallics, 23, 1891. 

In a follow up report from Zi s group [52c], a very related set of two more yttrium mono- and bis(amidate) complexes were reported for their ROP reactivity. Not surprisingly their reactivities as initiators led to very similar polylactide formation, however with slightly less control over the stereoregularity of the polymer. 

Mikami, K., Kotera, O., Motoyama, Y, and Tanaka, M. 1998. Synthesis, structure and high catalytic activity in the Diels-Alder reaction of ytterbium(lll) and yttrium(lll) bis(trifluoromethanesulfonyl)amide complexes. Inorg. Chem. Commun. 1 10-11. 

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. 

The supported silylamide complexes display lower activities than the homogeneous counterparts Ln[N(SiMe3)2]3, with the yttrium (12c) and samarium surface complexes (12d) revealing the worst performance. Conversely, the yttrium sUyl-amide-based material 12c gave complete conversion of hept-l-yne after 15 h at 100 °C. It was speculated that the relatively high tail-to-head selectivity of 82% Pj, obtained for both fresh and recovered catalyst 12c, could be due to the bulky siloxo surface ligand [117]. 

R CN (Table 2) [86]. The molecular structure of the 2,2-dimethylpropanonitrile derivative contains unsymmetrically bridging alkylidene amide ligands. Reaction of the yttrium and erbium hydride species with isonitrile results in the formation of a formidoyl moiety (Table 2) [87], Surprisingly the Ln-N interaction is in the range of the nitrile product A similar molecular structure was found in the oximato complex [Cp2Gd(/i-t/2-ONCMe2)]2 (Gd-Nav 2.42(1) A) [88]. 

Finally, a samarium aluminate tetramer featuring /J-dikeliminalo ligands was obtained in low yield (20%) by J. Arnold et al. (Scheme 54) [224], Once again this example corroborates the feasibility of selective [amide] [alkyl] transformations in N-ligand-based postlanthanidocene chemistry, previously observed for octaethylporphyrin yttrium complexes by C.J. Schaverien [225, 226],... 

The first confirmation of cis-binding of cations by the amide functions came from an X-ray crystal structure of the complex between 38 (m, n = 2) and yttrium perchlorate [65]. The stoichiometry was 1 2 1 ligand H2O) and the seven-... 

CCC (1987) contains a section on sulfoxides, amide, amine oxides, and related ligands that have sections on phosphine oxides and arsine oxides.159 Phosphine and arsine oxide complexes of yttrium and the lanthanides were highlighted in CCC (1987).1 Scandium and yttrium phosphine oxide complexes have been reinvestigated and characterized by multinuclear NMR and X-ray... 

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