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Controlled polymerization for the synthesis of structurally precise conjugated polymers remains a challenging problem in polymer chemistry. Catalyst-transfer polymerization (CTP) based on Pd-catalyzed Suzuki–Miyaura cross-coupling is one of the promising approaches toward solving this challenge. Recent introduction of N-methyliminodiacetic acid (MIDA) boronates as monomers for Suzuki–Miyaura CTP has extended this approach toward a broader variety of monomer structures and led to improved control over the polymerization, particularly for heteroaromatic systems (such as thiophenes). Previously, we found that MIDA boronate monomer polymerization could be facilitated by Ag+-mediated reaction conditions due to shifting the Pd catalytic cycle toward a more efficient oxo-Pd transmetalation pathway where MIDA boronates could participate in transmetalation directly without prior hydrolysis to boronic acid. In this work, we continued studying this novel process and investigated the dual role of the MIDA boronate functional group in the case of less reactive fluorenyl (and potentially other all-carbon aromatic systems) monomers. With such monomers, the MIDA boronate group enables the controlled polymerization but also produces a hydrolysis byproduct, hindering the polymerization. We also investigated the role of Ag+in counteracting this hindering effect. Steric bulkiness of the MIDA boronate functional group may also slow down the Suzuki–Miyaura CTP process. These complications could reduce the synthetic value of MIDA boronate monomers in Suzuki–Miyaura CTP, although better understanding of these implications and a proper choice of polymerization conditions and catalytic initiators could to some extent mitigate such problems. As part of this work, we also uncovered a “critical length” phenomenon, which results in a dual molecular weight distribution of the resulting conjugated polymer, both with MIDA boronate and boronic acid monomers. This phenomenon could account for the experimentally observed loss of polymerization control beyond formation of the polymer chains of a certain “critical length”, even despite the formally “living” nature of the polymer chains. The generality of this phenomenon and whether it is restricted to using Pd catalytic systems based on Buchwald-type phosphine ligands remain to be studied. Overall, these new findings paint a sophisticated picture of the Suzuki–Miyaura CTP process with MIDA boronate monomers where the mere presence of a Pd center on the polymer chain is not sufficient to sustain the polymerization (even if a chain could be considered “living” in the sense of possessing a Pd center), and the choice of the phosphine ligand on the Pd center is an effective tool to overcome the “critical length” restriction.

A new synthetic method to build aryl-fused 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) is reported. The intramolecular cyclization step was completed in a short time (1–2 h) and in high yields (>90%), due to the intrinsic rigid structural conformation of the precursor BODIPY and the high reactivity of its 1,7-bromo groups. The [a]phenanthrene-fused BODIPYs 4a–cwere characterized by NMR spectroscopy, HRMS, DFT calculations, and, in the case of 4a, by X-ray crystallography. Spectroscopic studies show that 4a–cstrongly absorb and emit in the NIR spectral region, in the range 642–701 nm. In addition, BODIPYs 4band 4cexhibit no toxicity in the light or dark in HEp2 cells and accumulate intracellularly in a time-dependent manner, mainly in the cell endoplasmic reticulum. These results suggest the potential use of [a]phenanthrene-fused BODIPYs as NIR bioimaging probes.

A series of trivalent lanthanide hydroxysulfates, Ln(OH)SO4, (Ln = Pr through Yb, except radioactive Pm) has been synthesized via hydrothermal methods from Ln2(SO4)3·8H2O by reaction with aqueous NaOH at 170 °C in Teflon lined Parr steel autoclaves, and were characterized by single crystal X-ray diffraction and FT-IR spectroscopy. Two types of arrangements were found in the solid state. The lighter (Ln = Pr−Nd, Sm−Gd) and heavier lanthanide(III) hydroxysulfates (Tb−Yb) are each isostructural. Both structure types exhibit the monoclinic space group P21/n, but the unit cell content is doubled with two crystallographically distinct LnO8polyhedra for the heavier lanthanide compounds. The lighter complexes maintain the coordination number 9, forming a three-dimensional extended lattice. The heavier counterparts exhibit the coordination number 8, and arrange as infinite columns of two crystallographically different LnO8polyhedra, while extending along the “c” axis. These columns of LnO8polyhedra are surrounded and separated by six columns of sulfate ions, also elongating in the “c” direction. The rigid sulfate entities seem to obstruct the closing in of the lighter LnO9polyhedra, and show an inclining degree of torsion into the “ac” layers. The crystal lattice of the lighter 4f complexes can sufficiently withstand the tension buildup, caused by the decreasing Ln3+radius, up to Gd(OH)SO4. The energy profile of this structural arrangement then seems to exceed levels at which this structure type is favorable. The lattice arrangement of the heavier Ln-analogues seems to offer a lower energy profile. This appears to be the preferred arrangement for the heavier lanthanide hydroxysulfates, whose crystal lattice exhibits more flexibility, as the coordination sphere of these analogues is less crowded. The IR absorbance frequencies of the hydroxide ligands correlate as a function of the Ln3+ionic radius. This corresponds well with the X-ray single crystal analysis data.