Precursor Approach to Lanthanide Dioxo Monocarbodiimides Ln₂O₂CN₂ (Ln=Y, Ho, Er, Yb) by Insertion of CO₂ into Organometallic Ln–N Compounds

Abstract

We present two organometallic precursor approaches leading to the hitherto-unknown dioxo monocarbodiimides (Ln(2)O(2)CN(2)) of the late lanthanides Ho, Er, and Yb as well as yttrium. One involves insertion of CO(2), and the other one is a straightforward route using a molecular single-source precursor. To this end the reactivity of the activated amido lanthanide compound [(Cp(2)ErNH(2))(2)] towards carbon dioxide absorption under supercritical conditions was studied. Selective insertion of CO(2) into the amido complex yielded the single-source precursor [Er(2)(O(2)CN(2)H(4))Cp(4)], which was characterized by vibrational spectroscopy and thermal and elemental analyses. Ammonolysis of this amorphous compound at 700 degrees C affords Er(2)O(2)CN(2). To gain deeper insight into the structural characteristics of the amorphous precursor, a similar molecular carbamato complex was synthesized and fully characterized. X-ray structure analysis of the dimeric complex [Cp(4)Ho(2){mu-eta(1):eta(2)-OC(OtBu)NH}] shows an unusual bonding mode of the tert-butylcarbamate ligand, which acts as both a bridging and side-on chelating group. Ammonolysis of this compound also yielded dioxo monocarbodiimides, and therefore the crystalline carbamato complex turned out to be an alternative precursor for the straightforward synthesis of Ln(2)O(2)CN(2). Analogously, the dioxo monocarbodiimides of Y, Ho, Er, and Yb were synthesized by this route. The crystal structures were determined from X-ray powder diffraction data and refined by the Rietveld method (Ln=Ho, Er). Further spectroscopic characterization and elemental analysis evidenced the existence of phase-pure products. The dioxo monocarbodiimides of holmium and erbium crystallize in the trigonal space group P[over]3m1. According to X-ray powder diffraction, they adopt the Ln(2)O(2)CN(2) (Ln=Ce-Gd) structure type.

Synthesis of Rare Earth (Oxo)nitridocarbonates by Employment of Supercritical Carbon Dioxide, Single‐source Precursor, Solid‐State, and Ion Exchange Reactions

“…[35][36][37] whose crystal structure was refined based on XRPD data by the Rietveld method. [16] The overall yield of Ln 2 O 2 CN 2 obtained in four reaction steps based on Cp 3 Ln as starting material (Scheme 1) is > 25 mol %. With this synthetic approach it was possible to synthesize pure lanthanide dioxy mono-carbodiimides starting from NH 3 and CO 2 and the well-known [7] The structures were refined in the space group P3m1 by the Rietveld method.…”

“…The absorption of CO 2 and the resulting amorphous products have been studied by IR spectroscopy, elemental analysis, and temperature programmed in situ mass spectrometry (MS) studies. [16] Two organometallic pathways towards phase-pure synthesis of the heavy lanthanide dioxy mono-carbodiimides have been elaborated. The first involves insertion of CO 2 provide a deeper insight into the structural characteristics of the carbamate precursor, the second approach targeted the synthesis of a crystalline carbamato complex (6) which has been fully characterized.…”

“…After ammonolysis, the precursor approach yielded the hitherto unknown dioxy mono-carbodiimides of Y, Er, Ho and Yb (7; Scheme 1). [16] Supercritical CO 2 (scCO 2 ) allows reactions to be carried out in "liquid" carbon dioxide under mild reaction conditions. The mild temperature conditions (50 °C, 220 bar) are of special interest for these precursor compounds because the latter can be carboxylated before thermal degradation of the Cp ligands occurs.…”

“…[8][9][10][11][12][13][14][15][16] However, the synthesis of the heavy rare earth lanthanide dioxy mono-carbodiimides (Ln = Tb -Lu) has not been reported until recently. [13,15,16] Due to the high thermal stability of binary rare earth oxides, carbides and nitrides specific synthesis routes are inevitable to expand the field of lanthanide (oxo)nitridocarbonates.…”

“…[8][9][10][11][12][13][14][15][16] However, the synthesis of the heavy rare earth lanthanide dioxy mono-carbodiimides (Ln = Tb -Lu) has not been reported until recently. [13,15,16] Due to the high thermal stability of binary rare earth oxides, carbides and nitrides specific synthesis routes are inevitable to expand the field of lanthanide (oxo)nitridocarbonates. Metathesis reactions between lanthanide halides and lithium cyanamide studied by Meyer et al [17] gave access to various rare earth carbodiimide compounds characterized in the last years: La 2 O(CN 2 ) 2 ; [18] Ln 2 (CN 2 ) 3 (Ln = Y, La -Lu); [19] Ce 3 (CN 2 ) 3 N; [20] LiEu 2 (CN 2 )I 3 ; [21] EuCN 2 .…”