Coordination Flexibility in Homoleptic Divalent Lanthanoid (Sm, Eu, Yb) Formamidinates upon Desolvation
Olga Mironova1, Taisiya S Sukhikh1, Sergey N Konchenko1
1Nikolaev Institute of Inorganic Chemistry SB RAS, 630090 Novosibirsk, Russia.
Abstract:
Complexes of "classical" divalent lanthanoids (Sm, Eu, Yb) with formamidinate ligands bearing dipp substituents (dippForm- = HC(Ndipp)2-, dipp = 2,6-diisopropylphenyl) were obtained in donor-free form, i.e., not containing neutral donor molecules. Two synthetic routes were developed: direct desolvation of complexes with coordinated tetrahydrofuran (thf), [Ln(dippForm)2(thf)2], by heating under vacuum or in toluene solution, and salt metathesis from thf-free precursors. Fully desolvated compounds crystallize as binuclear complexes: centrosymmetric [Ln(dippForm)2]2 for Ln = Sm, Eu, and asymmetric [Yb2(dippForm)4]. The coordination sphere of the Ln ion is complemented by η6-arene coordination of the dipp substituents, and in Sm and Eu complexes, the bridging formamidinate adopts an unknown-to-date μ-κ2N,η6-arene coordination mode. The Yb complex monomerizes in a toluene solution and crystallizes as a rare example of a Ln(II) complex containing a terminal neutral arene ligand, [Yb(dippForm)2(η6-PhMe)]. Partially desolvated species [Ln(dippForm)2(thf)] (Ln = Sm, Eu) are labile and prone to disproportionation in solution, in contrast to the known ytterbium analog. The desolvated Sm complex was shown to reduce pentaphosphaferrocene [Cp*FeP5] to a unique radical-anionic form stabilized by the samarium (bis)formamidinate cation, [Sm(dippForm)2(μ-P5)FeCp*]. The fully desolvated lanthanoid complexes are promising for further reactivity and catalytic studies, where control over the coordination environment is crucial.
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