Substituent Effects of β-Diketiminate Ligands on the Structure and Physicochemical Properties of Copper(II) Complexes

Abstract

Substituent effects of beta-diketiminate ligands on the structure and physicochemical properties of the copper(II) complexes have been systematically investigated by using 3-iminopropenylamine derivatives R1LR3H, R3-N=CH-C(R1)=CH-NH-R3, where R1 is Me, H, CN, or NO2, and R3 is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp (2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R3=Ph or Dtbp were treated with CuII(OAc)2, bis(beta-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the crystal structures of which were nearly the same as each other regardless of the alpha-substituent (R1); dihedral angles between the two beta-diketiminate coordination planes are 62.5 +/- 1.2 degrees, and the Cu-N bond lengths are 1.959 +/- 0.008 A. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially gII values of the ESR spectra and the d-d bands of the absorption spectra, as well as the electrochemical behaviors of the complexes, are significantly affected by the electronic nature of R1. The ligands with R3=Mes and Dep, on the other hand, gave di(mu-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported by one beta-diketiminate ligand and one didentate acetate ion. Thus, the beta-diketiminate ligands with a variety of substituents (R1 and R3) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear and dinuclear copper(II) complexes with significantly different coordination geometry and properties.

Tuning steric and electronic effects in transition-metal β-diketiminate complexes

“…Steric conflict between N -aryl substituents and metal can also push the metal center out of the β-diketiminate ligand plane in some metal complexes, especially for early transition metals (Table 3.1.2). However, exceptions can be found in L R,Mes TiCl 2 , 52 L Me,R Cr(η 5 -Cp), 62, 63 L R,iPr FeNNFeL, 6, 41 [L Me,R Ni(μ-Cl)] 2 , 24, 25 L Me,R Cu(OAc), 64, 65 [LCu(μ-OH)] 2 , 44-46 [LCu(μ-S)] 2 , 66, 67 and L R,iPr Cu(CO). 68 …”

“…In contrast, with LCu(NCCH 3 ) complexes, the Cu(II) state was less stable with a more electron withdrawing group. 46 Ruthenium(II) complexes of L CF3, m -CF3 Ru(Cl)(Ar) (Ar = arene ligand) were studied to determine the electronic effects of the supporting ligand on the metal and the other coordinating ligands in comparison to analogous complexes with the L Me, m -Me supporting ligand. 85 Interestingly, there was no clear trend between the Ru II /Ru III redox potentials from the cyclic voltammograms through the series L Me,Me , L Me, m -Me , L CF3, m -Me , and L CF3, m -CF3 , indicating that other factors also play a role.…”

A functional model for pMMO (particulate methane monooxygenase): Hydroxylation of alkanes with H2O2 catalyzed by β-diketiminatocopper(II) complexes

“…The former two ligands are those involving a strong electron withdrawing substituent at the center carbon of the ligand framework (a-carbon) but without the b-methyl substituent (R 1 = CN or NO 2 ; R 2 = H), whereas the third one involves an electron-donating substituent such as methyl on the a-carbon (R 1 = Me; R 2 = H). We have also employed a ligand with R 1 = CN and R 2 = Me (the fourth one) in order to get more insights into the steric and/or electronic effects of the substituents [19][20][21].…”

“…Thus, the selected bond lengths and angles of the reported complex 2 CN,H AE OAc are also involved in Table 2 (the data are taken form Ref. [20]). Apparently, the bond angles of C aryl -N-C b of 2 CN,Me AE OAc ($120°) are larger than those of 2 NO 2 ,H AE OAc AE CH 3 OH (115-116°) and of 2 CN,H AE OAc ($117°), which may be due to the steric repulsion between the b-methyl substituent (R 2 = Me) and the isopropyl groups of Dipp (2,6-diisopropylphenyl) in 2 CN,Me AE OAc as previously suggested in the b-diketiminatocopper(I) complex system [13].…”

Practically Usable C3 Building Blocks for the Syntheses of Nitro Heterocycles

“…46 In the present reaction, less nucleophilic aromatic amines are applicable to afford ANADs (R = aromatic ring), which is used as unique "-diketiminate ligands. 47,48 In the …”