Alkaline Earth Metal Imido Complexes with Doubly Deprotonated Amidine and β‐Diketimine Ligands. Issue 37 (24th September 2020)

• Record Type: Journal Article
• Authors: Martin, Johannes; Langer, Jens; Elsen, Holger; Harder, Sjoerd
• Is Part Of: European journal of inorganic chemistry. Issue 37(2020)
• Page Start: 3573
• Page End: 3579
• Publication Date: 2020-09-24
• Subjects: Alkaline earth metals -- Imido ligands -- β‐Diketiminates -- Amidinates -- Density functional calculations; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.202000783
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : Double deprotonation of the amidine DIPP‐N=C( t Bu)‐NH2 or β‐diketimine DIPP‐N=C(Me)‐C(H)=C(Me)‐NH2 (DIPP = 2, 6‐diisopropylphenyl) with strong benzylcalcium or strontium bases gave metal imido complexes with the anions DIPP‐N=C( t Bu)‐N 2– (Am 2– ) and DIPP‐N=C(Me)‐C(H)=C(Me)‐N 2– (BDI 2– ) which crystallized as tetrameric complexes with typical Ca4 N4 or Sr4 N4 cubane frameworks. Crystal structures of [(Am)Ca· THF]4, [(BDI)Ca· THF]4 and the first Sr imido complex [(Am)Sr· THF]4 are presented. Calculated geometries of [(Am)Ca· THF]4 and [(BDI)Ca· THF]4 (B3PW91/6‐311++G**) are in good agreement with the crystal structures. Also complexes with monoanionic ligands (Am‐H) – and (BDI‐H) – are reported. Charge delocalization in the ligand backbone is discussed. Ligand–metal bonds are calculated to be circa 90 % ionic; the NPA charges on Ca is circa +1.8. The negative charge on the ligand is delocalized over the ligand backbone but there is still considerable electron density on the terminal N (–1.4). Despite this high negative charge, the reactivity of these complexes is generally low due to the strongly bound cubane core. Reaction of [(Am)Ca· THF]4 with phenyl cyanide gave the [(Am)Ca· PhCN]4, clearly demonstrating its low reactivity. Attempts to break the tetrameric cluster in smaller aggregates by addition of 18‐crown‐6 led to protonation and isolation of (Am‐H)2 Ca· (18‐crown‐6). Reaction of [(Am)Ca· THF]4 with i PrN=C=N i Pr gave after addition a complex with a unique amido‐guanidinate ligand. Abstract : Calcium and strontium complexes with doubly N‐deprotonated amidinate and β‐diketiminate ligands are introduced. There is charge delocalization over the ligand backbone but still a considerable negative charge at the terminal N. Tetrameric aggregates, typical for group 2 metal imido complexes, are formed.