Synthesis and Complexation Study of New Aminoalkynyl−amidinate Ligands

Abstract

The current library of amidinate ligands has been extended by the synthesis of two novel dimethylamino‐substituted alkynylamidinate anions of the composition [Me2N−CH2−C≡C−C(NR)2]− (R = iPr, cyclohexyl (Cy)). The unsolvated lithium derivatives Li[Me2N−CH2−C≡C−C(NR)2] (1: R = iPr, 2: R = Cy) were obtained in good yields by treatment of in situ‐prepared Me2N−CH2−C≡C−Li with the respective carbodiimides, R−N=C=N−R. Recrystallization of 1 and 2 from THF afforded the crystalline THF adducts Li[Me2N−CH2−C≡C−C(NR)2] ⋅ nTHF (1 a: R = iPr, n=1; 2 a: R = Cy, n=1.5). Precursor 2 was subsequently used to study initial complexation reactions with selected di‐ and trivalent transition metals. The dark red homoleptic vanadium(III) tris(alkynylamidinate) complex V[Me2N−CH2−C≡C−C(NCy)2]3 (3) was prepared by reaction of VCl3(THF)3 with 3 equiv. of 2 (75 % yield). A salt‐metathesis reaction of 2 with anhydrous FeCl2 in a molar ratio of 2 : 1 afforded the dinuclear homoleptic iron(II) alkynylamidinate complex Fe2[Me2N−CH2−C≡C−C(NCy)2]4 (4) in 69 % isolated yield. Similarly, treatment of Mo2(OAc)4 with 3 or 4 equiv. of 2 provided the dinuclear, heteroleptic molybdenum(II) amidinate complex Mo2(OAc)[Me2N−CH2−C≡C−C(NCy)2]3 (5; yellow crystals, 50 % isolated yield). The cyclohexyl‐substituted title compounds 2 a, 4, and 5 were structurally characterized through single‐crystal X‐ray diffraction studies.

Synthesis and Structural Characterization of Divalent Transition Metal Alkynylamidinate Complexes

“…In the first step the easily accessible lithium cyclopropylethynylamidinate precursors Li[ c ‐C 3 H 5 −C≡C−C(NR) 2 ] ⋅ THF (R= i Pr, Cy) [36] were prepared and structurally characterized. Further in the course of this study, a surprising variety of transition metal and lanthanide alkynylamidinate complexes terminated by cyclopropyl groups could by synthesized and fully characterized [37–44] . In this contribution we now report the synthesis and characterization of several new first and second row transition metal complexes comprising the cyclopropylethynylamidinate ligands.…”

“…Further in the course of this study, a surprising variety of transition metal and lanthanide alkynylamidinate complexes terminated by cyclopropyl groups could by synthesized and fully characterized. [37][38][39][40][41][42][43][44] In this contribution we now report the synthesis and characterization of several new first and second row transition metal complexes comprising the cyclopropylethynylamidinate ligands.…”