Bulky guanidinate stabilized homoleptic magnesium, calcium and zinc complexes and their catalytic activity in the Tishchenko reaction

• Bis(guanidinate) stabilized Mg(II), Ca(II) and Zn(II) complexes.
• Homoleptic complexes of magnesium, calcium and zinc.
• Dimerization of aldehydes i.e., Tishchenko reaction.
• X-ray crystal structures of bis(guanidinate) magnesium, calcium and zinc complexes.

Bulky guanidinate stabilized homoleptic complexes of [LM(thf)nL] [L = {ArNC (NiPr2)NAr} (Ar = 2,6- Me2–C6H3)]; M = Mg, Ca, and Zn; n = 0–1) have been synthesized with three different synthetic routes. First, treatment of bis{bis(trimethylsilyl)amide}s of Mg, Ca, and Zn i.e. [M{(N(SiMe3)2}2] (M = Mg, Ca(thf)2, and Zn) with free guanidine ligand (LH) at 80 °C, elimination of NH(SiMe3)2 and formation of [LM(thf)nL] (M = Mg, Ca and Zn; n = 0–1) (3–5) complexes were occurred. Second, the reaction of two equivalents of potassium salt of LH with metal dihalides via salt metathesis led to the formation of homoleptic complexes. Third, the reaction between MR2 (M = Mg, Ca, Zn; R = alkyl or OTf) and LH at reflux temperature, formation of bis(guanidinate) magnesium, calcium, and zinc complexes have been observed. The solid state structures of LH(1), LK(2) and all three bis(guanidinate) magnesium, calcium and zinc complexes (3–5) were confirmed by X-ray structural analysis. Furthermore, dimerization of a range of aromatic, heteroaromatic and aliphatic aldehydes (Tishchenko reaction) has been demonstrated by using catalysts 3–5.

Bulky bis(guanidinate) supported Mg(II), Ca(II) and Zn(II) complexes have been synthesized and characterized. Furthermore, bis(guanidinate) magnesium, calcium, and magnesium bis(hexamethyldisilazide) compounds show excellent catalytic activity for the dimerization of various aldehydes i.e. Tishchenko reaction.Figure optionsDownload as PowerPoint slide