Stabilization of Heteroleptic Heavier Alkaline Earth Metal Complexes with an Encapsulating Dipyrromethene Ligand

Abstract

A new dipyrromethene ligand with 9‐anthracenyl substituents for steric shielding of the metal has been introduced. The ligand, AnthDPM‐H (3), was directly deprotonated with MN′′2 {M = Mg, Ca, Sr, Ba, Zn; N′′ = N(SiMe3)2} to give (AnthDPM)MN′′ (4–8) in the form of highly fluorescent substances that are intensively colored from deep‐red to purple. Crystal structures reveal in all cases monomeric complexes with tricoordinate metals. Also the crystal structure of (AnthDPM)K, prepared by reaction of 3 with KN′′, is presented. The metal's coordination sphere in complexes 4–8 is further saturated by anagostic M···MeSi interactions which are most important for the smaller metals Mg and Zn. For the larger metals, Ca–Ba, the anthracenyl‐substituents assist in metal coordination. These secondary metal π‐interactions result in very high thermal stabilities. The least stable complex (AnthDPM)BaN′′ decomposes at circa 100 °C. The dipyrromethene complexes are clearly more stable than the corresponding β‐diketiminate complexes (DIPPBDI)MN′′ {DIPPBDI = CH[C(Me)N‐DIPP]2, DIPP =2,6‐diisopropylphenyl} which partially decompose at room temperature. These heteroleptic complexes of similar constitution, with metals ranging from Mg to Ba, form a new series that is potentially useful for investigations towards metal effects in early main group metal catalysis.

Magnesium Cyanide or Isocyanide?

“…Mg À N2 bite angle of 92.88(8)8 8 deviates from the ideal equatorial angle of 1208 8 but is in the range of values found in other DPM magnesium complexes. [29,30] Single-crystal Xray diffraction also shows significant signals at high 2q angles. An isocyanide arrangement, MgÀNC, was clearly confirmed by refinement of the alternative cyanide connectivity,Mg À C N. Thel atter did not only give much higher wR2 and R1 values but also showed an unrealistically high displacement parameter for the terminal Natom whereas those for the Mgbound Cw ere too low (Figure 1b).…”

Magnesium Cyanide or Isocyanide?

“…[29,30] Single-crystal Xray diffraction also shows significant signals at high 2q angles. [29,30] Single-crystal Xray diffraction also shows significant signals at high 2q angles.…”

Low‐Coordinate Monomeric Zinc Hydride Complexes with Encapsulating Dipyrromethene Ligands and Reactivity with B(C6F5)3

“…Starting materials and research chemicals were obtained from commercial suppliers, where appropriate and used without further purification. Diethylzinc, [25] K[(iPr)NHBH 3 ], [26] t Bu DPM-H, [17] Ad DPM-H, [17] Mes DPM-H, [18] DIPP DPM-H, [15] Mes *DPM-H, [17] Anth DPM-H [16] and ( DIPP DPM)ZnH [15] were synthesized following literature known procedures. NMR spectra were measured on Bruker Avance III HD 400 MHz and Bruker Avance III HD 600 MHz spectrometers.…”

“…[17] The mesityl (Mes) [18] and 2,4,6-triphenyl-phenyl (Mes*) [17] substituted ligands are bright yellow and red, respectively. Dipyrromethene ligands with DIPP [15] and 9-anthracenyl [16] substituents have been introduced by us and are orange and red, respectively.…”