Two Series of New Volatile Rare‐Earth Metal Tris(guanidinates) and Tris(amidinates)

Abstract

Two series of new volatile, homoleptic lanthanide(III) tris(guanidinate) and tris(amidinate) complexes were synthesized and fully characterized. Treatment of anhydrous rare‐earth metal(III) chlorides, LnCl3, with three equiv. of the aziridine‐derived lithium guanidinate Li[c‐C2H4NC(NiPr)2] (3) afforded the new homoleptic tris(guanidinate) complexes [c‐C2H4NC(NiPr)2]3Ln (4) (Ln = Sc, Pr, Nd, Sm, Eu, Ho, Tm) in good yields (68–80 %). In a similar manner, the homoleptic tris(amidinate) complexes [iPrC(NiPr)2]3Ln (6) Ln = Sc, Ce, Pr, Nd, Tb, Dy, Er, Yb) were prepared from LnCl3 and the all‐isopropyl‐substituted lithium amidinate Li[iPrC(NiPr)2] (5) in a molar ratio of 1:3. Variable‐temperature 1H NMR studies of the paramagnetic derivatives 4Pr–4Tm revealed Curie‐type behavior. 1H NMR spectroscopic data of complexes 6 indicated severe steric crowding due to the presence of nine isopropyl groups in these molecules. The molecular and crystal structures of eight title compounds (4Sc, 4Pr, 4Nd, 4Sm, 4Eu, 4Ho, 4Tm, and 6Er) were determined through single‐crystal X‐ray diffraction studies. All complexes 4 exhibit similar molecular structures, comprising distorted octahedral molecular structures with small bite angles. Sublimation temperatures of 4 at 0.05 mbar were determined to be in the range between 151 °C (4Eu) and 194 °C (4Tm), whereas the complexes 6 sublime in the temperature range between 140 °C (6Sc) and 180 °C (6Ce), so that the use of these precursors in future ALD or CVD studies appears feasible.

New Homoleptic Rare‐Earth Metal Complexes Comprising the Unsymmetrically Substituted Amidinate Ligand [MeC(NEt)(NtBu)]–

“…The formation of a pure scandium species was corroborated by the presence of a single resonance at δ = 208 ppm in the 45 Sc NMR spectrum of 4 . This is in good agreement with the 45 Sc NMR resonance of the closely related homoleptic scandium guanidinate complex Sc[ c ‐C 2 H 4 N–C(N i Pr) 2 ] 3 ( c ‐C 2 H 4 N = aziridyl), which was found at δ = 203 ppm …”

“…Different from the high‐coordinate complexes 2 and 3 , the Ln –N bond lengths in 5 are in a much narrower range of 233.4(4)–236.8(5) pm. These values are relatively small as compared to those observed in the related binary holmium amidinate Ho[ c Pr–C≡C–C(N i Pr) 2 ] 3 [Ho–N 234.2(2)–238.3(3) pm] and in the guanidinate Ho[ c –C 2 H 4 N–C(N i Pr) 2 ] 3 [Ho–N 234.8(3)–239.6(3) pm] . The range of Ho–N distances usually observed in hexa‐coordinate complexes is 230–260 pm .…”

“…This is in good agreement with the 45 Sc NMR resonance of the closely related homoleptic scandium guanidinate complex Sc[c-C 2 H 4 N-C(NiPr) 2 ] 3 (c-C 2 H 4 N = aziridyl), which was found at δ = 203 ppm. [30]…”

“…[28] The central holmium atom [32] and in the guanidinate (3)-239.6(3) pm]. [30] The range of Ho-N distances usually observed in hexa-coordinate complexes is 230-260 pm. [31] Worth mentioning, 5 is isotypic with the earlier reported gadolinium analog Gd(L) 3 .…”

Rare-earth metal complexes with redox-active formazanate ligands

“…The values of the bite angle of N-Sm-N in complex 2 (65.12(6)°to 69.59(6)°) are more obtuse than these in other homoleptic tris (guanidinates) samarium complexes (54.6(2)°to 55.62(7)°). 25,26 The Sm-N bond lengths (2.373(2) Å to 2.497(2) Å) lie between representative covalent and donor-acceptor bonds. 27,28 They are also comparable to those in other homoleptic Sm complexes with related bidentate N-ligands.…”