Abstract
This contribution reports the synthesis and structural characterization of several new lithium and lanthanide alkynylamidinate complexes. Treatment of PhC≡CLi with N,N′-diorganocarbodiimides, R–N=C=N–R (R = iPr, Cy (cyclohexyl)), in THF or diethyl ether solution afforded the lithium-propiolamidinates Li[Ph–C≡C–C(NCy)2] S (1: R = iPr, S = THF; 2: R = Cy, S = THF; 3: R = Cy, S = Et2O). Single-crystal X-ray diffraction studies of 1 and 2 showed the presence of typical ladder-type dimeric structures in the solid state. Reactions of anhydrous LnCl3 (Ln = Ce, Nd, Sm or Ho) with 2 in a 1:3 molar ratio in THF afforded a series of new homoleptic lanthanide tris(propiolamidinate) complexes, [Ph–C≡C–C(NCy)2]3Ln (4: Ln = Ce; 5: Ln = Nd; 6: Ln = Sm; 7: Ln = Ho). The products were isolated in moderate to high yields (61%–89%) as brightly colored, crystalline solids. The chloro-functional neodymium(III) bis(cyclopropylethynylamidinate) complex [{c-C3H5–C≡C–C(NiPr)2}2Ln(µ-Cl)(THF)]2 (8) was prepared from NdCl3 and two equiv. of Li[c-C3H5–C≡C–C(NiPr)2] in THF and structurally characterized. A new monomeric Ce(III)-diiminophosphinate complex, [Ph2P(NSiMe3)2]2Ce(µ-Cl)2Li(THF)2 (9), has also been synthesized in a similar manner from CeCl3 and two equiv. of Li[Ph2P(NSiMe3)2]. Structurally, this complex resembles the well-known “ate” complexes (C5Me5)2Ln(µ-Cl)2Li(THF)2. Attempts to oxidize compound 9 using trityl chloride or phenyliodine(III) dichloride did not lead to an isolable cerium(IV) species.
Highlights
Monoanionic N,N′-chelating ligands like amidinates, [RC(NR′)2]−, guanidinates, [R2NC(NR′)2]−, and diiminophosphinates, [R2P(NR′)2]−, are commonly regarded as steric equivalents of the omnipresent cyclopentadienyl ligands [1,2,3,4,5,6,7]
We report the synthesis and structural characterization of two lithium-propiolamidinates and their use as precursors for new homoleptic lanthanide(III)-tris(propiolamidinate) complexes
BuLi at −20 °C in THF or Et2O followed by addition of N,N′-dicyclohexylcarbodiimide
Summary
Monoanionic N,N′-chelating ligands like amidinates, [RC(NR′)2]−, guanidinates, [R2NC(NR′)2]−, and diiminophosphinates, [R2P(NR′)2]−, are commonly regarded as steric equivalents of the omnipresent cyclopentadienyl ligands [1,2,3,4,5,6,7]. The cyclopropyl group was chosen because of the well-known electron-donating ability of this substituent to an adjacent electron-deficient center [37,38,39,40,41,42,43] This would provide a rare chance to electronically influence the amidinate ligand system rather than altering only its steric demand. In the course of this study, we first reported the synthesis and full characterization of a series of lithium-cyclopropylethinylamidinates [44] These precursors are readily available on a large scale using commercially available starting materials (cyclopropylacetylene, N,N′-diorganocarbodiimides). We report the synthesis and structural characterization of two lithium-propiolamidinates and their use as precursors for new homoleptic lanthanide(III)-tris(propiolamidinate) complexes. N,N′-chelating ligands employed in this study: N,N′-Dicyclohexylpropiolamidinate (A); N,N′-diisopropyl-cyclopropylethynylamidinate (B); and N,N′-bis(trimethylsilyl)-P,P-diphenyldiiminophosphinate (C)
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