Synthesis and reactivity of trans-N,N′-dimethyl-meso-octaalkylporphyrinogen Sm(II), Eu(II) and Yb(II) complexes: Metal-based influences on the reduction of t-butyl-1,4-diazabuta-1,3-diene

Developments in the Coordination Chemistry of Europium(II)

“…[60] The formation of the bimetallic Sm 3+ complex bridged by the reduced [ t Bu-DAB] 2− is driven by the reducing power of Sm 2+ towards t Bu-DAB, but the steric constraints due to the bulky tert -butyl moieties makes this reaction reversible. [60] Because Eu 2+ has a more positive Ln 2+ /Ln 3+ oxidation potential (−0.35 V vs. NHE) than Sm 2+ (−1.55 V vs. NHE), the driving force to form an analogous bimetallic Eu 3+ complex is hindered, presumably because the reducing strength of Eu 2+ is not sufficient to reduce t Bu-DAB. These examples of controlled redox potential could be useful in selective reductions during multistep syntheses and for developing the first Eu 2+ -containing complex that could act as multielectron reductant.…”

“…While the other synthetic methods involve redox reactions to obtain Eu 2+ , the metathesis approach makes use of Eu 2+ halides and alkali‐metal‐containing ligands as precursors to generate the desired Eu 2+ ‐containing complex. The metathesis reaction has been successful in preparing several Eu 2+ ‐containing complexes including the bimetallic [Eu 2 (Ap*py) 3 I(THF)] ( 48 ), where Ap*py is deprotonated 6‐methylpyridin‐2‐yl‐[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl]amine,59 a monometallic Eu 2+ ‐containing trans ‐ N , N′ ‐dimethyl‐ meso ‐octaethylporphyrinogen complex ( 49 ),60 a Eu 2+ ‐containing benzamidinate complex [Eu{PhC{NSi(CH 3 ) 3 }{2,6‐(iPr) 2 NC 6 H 3 }} 2 (THF) 2 ] ( 50 ),61 a Eu 2+ complex with olefin‐substituted cyclopentadienyl ligands [{C 5 (CH 3 ) 4 Si(CH 3 ) 2 CH 2 CH=CH 2 } 2 Eu] ( 51 ),62 bis(diphosphanylamido) complex [{(Ph 2 P) 2 N} 2 Eu(THF) 3 ] ( 52 ),63 a Eu 2+ complex containing bis(phosphinimino)methanide ligands [{{(CH 3 ) 3 SiNPPh 2 } 2 CH}EuI(THF)] 2 ( 53 ),64 an aminotroponiminate complex of composition [{( i Pr) 2 ATI}Eu{N{Si(CH 3 ) 2 }}(THF) 2 ] ( 54 ), where ( i Pr) 2 ATI is N ‐isopropyl‐2‐(isopropylamino)troponiminate,65 and a monometallic, heteroleptic complex [(DIP 2 pyr)Eu(THF) 3 ] ( 55 ), where DIP 2 pyr is 2,5‐bis[( N ‐2,6‐diisopropylphenyl)iminomethyl]pyrrolyl (Figure 6). 66 Complexes 48 – 55 were prepared by the metathesis reaction of [EuI 2 (THF) x ], where labile THF, iodine, or both are displaced by the desired ligand.…”

“…However, when the same Eu 2+ ‐containing bisamidinate complex was allowed to react with diphenyl ditellurides and iodine, both reactions were unsuccessful, indicating that the reducing strength of Eu 2+ was not sufficient to reduce diphenylditellurides and iodine 61. Also, in the case of the macrocyclic ligand system trans ‐ N , N′ ‐dimethyl‐ meso ‐octaethylporphyrinogen, the Eu 2+ ‐containing complex cannot reduce tert ‐butyl‐1,4‐diazabuta‐1,3‐diene ( t Bu‐DAB) 60. However, the analogous Sm 2+ complex forms a bimetallic complex when reacted with t Bu‐DAB 60.…”

“…Also, in the case of the macrocyclic ligand system trans ‐ N , N′ ‐dimethyl‐ meso ‐octaethylporphyrinogen, the Eu 2+ ‐containing complex cannot reduce tert ‐butyl‐1,4‐diazabuta‐1,3‐diene ( t Bu‐DAB) 60. However, the analogous Sm 2+ complex forms a bimetallic complex when reacted with t Bu‐DAB 60. The formation of the bimetallic Sm 3+ complex bridged by the reduced [ t Bu‐DAB] 2– is driven by the reducing power of Sm 2+ towards t Bu‐DAB, but the steric constraints due to the bulky tert ‐butyl moieties makes this reaction reversible 60.…”

“…However, the analogous Sm 2+ complex forms a bimetallic complex when reacted with t Bu‐DAB 60. The formation of the bimetallic Sm 3+ complex bridged by the reduced [ t Bu‐DAB] 2– is driven by the reducing power of Sm 2+ towards t Bu‐DAB, but the steric constraints due to the bulky tert ‐butyl moieties makes this reaction reversible 60. Because Eu 2+ has a more positive Ln 2+ /Ln 3+ oxidation potential(–0.35 V vs. NHE) than Sm 2+ (–1.55 V vs. NHE), the driving force to form an analogous bimetallic Eu 3+ complex is hindered, presumably because the reducing strength of Eu 2+ is not sufficient to reduce t Bu‐DAB.…”