Six strongly fluorescent four-coordinate organoboron N,Cchelates, containing an arylisoquinoline skeleton, were prepared. Remarkably, the fluorescence quantum yields reach values of up to 0.74 in oxygen-free toluene. The strong B-N interaction was corroborated by the single-crystal X-ray analysis of two dyes. The intramolecular charge-transfer (ICT) character of the fluorophores was evidenced by solvatochromic studies and time-dependent density-functional-theory calculations at the PCM(toluene)/CAM-B3LYP/6-311++G(2d,p)//PCM(toluene)/B3LYP/6-311G(2d,p) level of theory. The compounds combine high chemical stability with high photostability (especially when equipped with electron-donating substituents). The strong fluorescence and the large Stokes shifts predestine these compounds for their use in confocal fluorescence microscopy. This was demonstrated for the imaging of the N13 mouse microgial cell line. As a surplus, significant two-photon absorption cross sections (up to 61 GM) allow the use of excitation wavelengths in the near-infrared region (> 800 nm).

The direct activation of unreactive C À H bonds has emerged as a very active field in organic synthesis.[1] One of the best established reactions in this area is the direct borylation of arenes with bis(pinacolato)diboron (B 2 pin 2 ) or pinacolborane (HBpin). After the seminal work by Smith, Hartwig, Miyaura, and their respective co-workers, this method has reached an impressive level of chemical efficiency, [2] mainly because of the introduction of the [Ir(m-X)(cod)] 2 /di-tert-butylbipyridine (dtbpy; X = Cl, OMe; cod = 1,5-cyclooctadiene) precatalyst system. The regioselectivity of this reaction is typically driven by steric factors, [3] thus making the method complementary to directed ortho-metalation (DoM) reactions.[4] Very recently, however, directed ortho borylations have been accomplished by using directing groups such as siloxide or silylamine [5] and carbonyl functionalities, [6] but the absence of any nitrogendirected borylation is noteworthy. Herein, we present our results on the regioselective ortho CÀH borylation of 2-arylpyridines (isoquinolines) and aromatic hydrazones.The regioselectivity of Ir III /dtbpy-catalyzed reactions can be arguably attributed to the lack of a coordination site in complex B, which results from coordination of the directing atom Y to the established catalytic species A[2c] (Scheme 1). In this scenario, the direct activation of arene CÀH bonds can only proceed through intermediate C and is therefore mainly controlled by steric factors. On the other hand, the ability of transition metals to selectively activate arene C À H bonds in 2-aryl pyridines [1d] made us speculate that such a reaction would only require the generation of an additional coordination site at an appropriate stage. Therefore, we decided to investigate the behavior of potentially hemilabile N,N ligands, [7] in which one of the nitrogen atoms is a weaker donor that is prone to dissociation and therefore able to generate the required coordination site. It was foreseen that an ideal ligand should still be a good donor in order to maintain a high level of reactivity as in the reference dtbpy-based system. Based on our own experience with related ligands, [8] pyridine hydrazones 2-4, which maintain one of the pyridine units in their structures, and bishydrazone 5 were considered as candidates (Scheme 2). Additionally, pyridine imine 6 [9] and pyridine amine 7 were included for comparison in the preliminary screenings. The relative activity of in situ formed [IrCl(cod)] 2 /N,N-ligand catalysts (ligand = 1-7) was investigated by using the borylation of 1-

The use of hemilabile pyridine-hydrazone N,N-ligands allows the highly selective Ir-catalyzed ortho,ortho'-directed diborylation of aromatic N,N-dimethylhydrazones in near-quantitative yields. One-pot sequential Suzuki-Miyaura cross-coupling with different aryl bromides provides a short entry to unsymmetrically substituted 2,6-diarylbenzaldehyde derivatives.