Azadipyrromethene Dye Derivatives in Coordination Chemistry: the Structure–Property Relationship in Homoleptic Metal(II) Complexes

As a chromophore closely related to dipyrromethene (DPM),
the azadipyrromethene
(ADPM) family has attracted much interest in the life sciences and
optoelectronic fields. A high-yielding microwave-assisted synthesis
is reported for new homoleptic complexes of cobalt­(II), nickel­(II),
copper­(II) and zinc­(II) based on the tetrakis­(p-methoxyphenyl)­azadipyrromethene
ligand 1b. These complexes are compared with other homoleptic
complexes of the same metal­(II) series based on the tetraphenylazadipyrromethene 1a and also with related BF2+ chelates
(Aza-BODIPYs 6a and 6b) for a better understanding
of trends arising from substitution of the chelate and/or the electron-donating
effect of the p-methoxy substituents. The electrochemical
behavior of the new compounds 2b, 3b, and 5b in dichloromethane revealed two pseudoreversible reductions
(2b, −1.09 and −1.25 V vs SCE; 3b, −1.05 and −1.29 V; 5b, −1.13
and −1.25 V) followed by a third irreversible process (2b, −1.78 V; 3b, −1.80 V; 5b, −1.77 V) along with two pseudoreversible oxidations
(2b, 0.55 and 0.80 V; 3b, 0.56 and 0.80
V; 5b, 0.55 and 0.80 V) followed by two closely spaced
irreversible processes (2b, 1.21 and 1.27 V; 3b, 1.21 and 1.28 V; 5b, 1.22 and 1.25 V). On its side,
copper­(II) homoleptic complex 4b revealed only one pseudoreversible
reduction at −0.59 V followed by three irreversible processes
at −0.95, −1.54, and −1.74 V, respectively. The
oxidation behavior of this complex exhibited two pseudoreversible
processes (0.55 and 0.82 V) and two irreversible processes (1.19 and
1.25 V). The redox processes are assigned and discussed in relation
to their photophysical properties. X-ray structures for 1b and related copper­(II) complex 2b are also discussed.

作为一种与二吡喃甲烷（DPM）密切相关的色团，氮杂二吡喃甲烷（ADPM）系列在生命科学和光电子领域引起了广泛的关注。本文报道了一种基于四甲基氧基苯基氮杂二吡喃甲烷配体1b的新型同配位钴(II)、镍(II)、铜(II)和锌(II)复杂物的微波辅助高收率合成方法。这些复杂物与同系列的基于四苯基氮杂二吡喃甲烷1a的同配位复杂物以及其他相关BF2+螯合物（Aza-BODIPYs 6a和6b）进行了比较，旨在更好地理解由于螯合剂替换以及p-甲氧基取代基的电子供体效应所引起的变化趋势。新化合物2b、3b和5b在二氯甲烷中的电化学行为表现为两个伪可逆还原过程（2b，−1.09和−1.25 V vs SCE；3b，−1.05和−1.29 V；5b，−1.13和−1.25 V），随后是一个不可逆的第三过程（2b，−1.78 V；3b，−1.80 V；5b，−1.77 V），以及两个伪可逆氧化过程（2b，0.55和0.80 V；3b，0.56和0.80 V；5b，0.55和0.80 V），随后是两个紧密相邻的不可逆过程（2b，1.21和1.27 V；3b，1.21和1.28 V；5b，1.22和1.25 V）。另一方面，铜(II)同配位复杂物4b仅表现出一个伪可逆还原过程（−0.59 V），随后分别在−0.95、−1.54和−1.74 V出现三个不可逆过程。该复杂物的氧化行为表现出两个伪可逆过程（0.55和0.82 V）和两个不可逆过程（1.19和1.25 V）。这些氧化还原过程被归属并与其光物理性质相关联讨论。此外，1b及其相关铜(II)复杂物2b的X射线结构也被讨论。