Gas‐Phase Transformation of Fluorinated Benzoporphyrins to Porphyrin‐Embedded Conical Nanocarbons

Abstract Geodesic nitrogen‐containing graphene fragments are interesting candidates for various material applications, but the available synthetic protocols, which need to overcome intrinsic strain energy during the formation of the bowl‐shaped skeletons, are often incompatible with heteroatom‐embedded structures. Through this mass spectrometry‐based gas‐phase study, we show by means of collision‐induced dissociation experiments and supported by density functional theory calculations, the first evidence for the formation of a porphyrin‐embedded conical nanocarbon. The influences of metalation and functionalization of the used tetrabenzoporphyrins have been investigated, which revealed different cyclization efficiencies, different ionization possibilities, and a variation of the dissociation pathway. Our results suggest a stepwise process for HF elimination from the fjord region, which supports a selective pathway towards bent nitrogen‐containing graphene fragments.

and are referenced to residual protic impurities in the solvent ( 1 H NMR), or to the deuterated solvent itself ( 13 C NMR). The resonance multiplicities are indicated as "s" (singlet), "d" (doublet), "t" (triplet), "q" (quartet) and "m" (multiplet). Signals referred to as "bs" (broad singlet) are not clearly resolved or significantly broadened. LDI/MALDI-ToF (nitrogen UV-laser, 337 nm) mass spectra were obtained by using a Bruker ultrafleXreme spectrometer with 2,5-dihydroxybenzoic acid (DHB) or (E)-2-(3-(4-(tert-butyl)phenyl)-2methylallylidene)malononitrile (dctb) as matrices. ESI/APPI-ToF mass spectrometry was carried out on a Bruker maXis 4G UHR TOF MS/MS-spectromter or a Bruker micrOTOF II focus TOF MS-spectrometer. IR spectroscopy was performed on a Bruker FT-IR Tensor 27 and Pike MIRacle ATR unit. The ATR unit was equipped with a diamond crystal plate and high-pressure clamp. Spectra were recorded as solid samples directly from the diamond crystal. All absorptions ṽ are given in wave numbers [cm -1 ]. UV/vis spectroscopy was carried out on a Varian Cary 5000 UV-Vis-NIR spectrometer. Spectra were recorded at room temperature using quartz cuvettes with a path length of 1 cm. Fluorescence spectra were recorded on a Shimadzu RF-5301PC spectrofluorophotometer.

Synthesis of molecules
General Procedure to free-base derivatives Herein  values. [1] General information on metalated derivatives Metalated derivatives were used for MS analysis without further spectroscopic characterization. Fluorinated benzoporphyrins show very poor solubility in common organic solvents, in particular if they are present as metalated species. However, whereas free-base species can be easily solubilized by addition of trifluoroacetic acid, this strategy does not apply for metalated derivatives. [1] meso-Tetrakis (

Wet-chemical palladium-catalyzed C-H activation
As a starting point for the conditions of the Pd-catalyzed CH-activation we were inspired by the work of L. T. Scott on indeno-fused corannulenes, who utilized Pd(PCy3)2Cl2 as catalyst, DBU as base and DMAc as solvent. [2] We applied this conditions to 8 and analyzed the reaction outcome by mass spectrometry as well as absorption spectroscopy. It is important to mention, that much higher concentration of the catalyst as well as longer reaction times were necessary to initiate the cyclization (see Table S1).
A significant broadening of all absorption features is observed for the reaction outcome in comparison with the reactant as depicted in Figure S30a. Furthermore, a red-shit of the Soret band and the Q-bands is found, which can be interpreted as an indicator for the π-extension of the TATBP macrocycle. According to mass spectrometry, three reaction events could be recognized: 1. C-C bond formation via HCl elimination, 2. Pdinsertion and 3. exchange of residual Cl substituents by hydrogens (hydrodehalogenation). Based on the isotopic pattern, it is assumed that the observed ion peak consists of several species, which differ in the number of formed C-C bonds.
If the different constitutional isomers are also considered, it is not surprising that all attempts to separate the mixture by means of column chromatography or HPLC were unsuccessful. Even if the exact product distribution cannot be determined, since all derived ions might differ in their ionization ability, a rough estimation is achieved by simulation of the ion peak. As shown in Figure S30b, the measured spectrum is well represented by the simulated mixture of 8Pd-5HCl, 8Pd-4HCl, 8Pd-3HCl, 8Pd-2HCl and 8Pd-1HCl with a distribution of 1 : 7 : 5 : 4 : 4. Furthermore, the same product distribution was found when 8Pd instead of 8 was used as starting material, which led to the conclusion that palladium insertion occurs early during the reaction.
Moreover, we found an interesting trend of the reaction outcome screening the reaction of 8 in a temperature range from 150 to 300 °C. For temperatures below 180 °C, neither HCl elimination, Pd-insertion nor hydrodehalogenation took place, while a shift of signals to higher m/z values is found with increasing temperature. This observation suggests that higher temperatures favor the undesired hydrodehalogenation reaction, which is demonstrated in Figure S31 by simulating the mass spectra of the reaction outcome at 180, 240 and 300 °C, respectively.

S40
Since aryl bromides usually show a better reactivity in Pd-catalyzed reactions, we exchanged 8 for its brominated derivate S1, but no significant difference was observed as summarized in Table S2. Table S2. Experimental conditions for Pd-catalyzed C-H activation: A 5 mL MW vial equipped with a magnetic stir bar was charged with S1 (10 mg), Pd(PCy3)2Cl2, and dissolved in DMAc/DBU (2.5 mL, 4:1, v:v). The mixture was deoxygenated and reacted in the microwave reactor: elevated temperatures, 4 h, high absorption level). CH2Cl2 (50 mL) was added and the organic layer was washed with 10% aqueous HCl (2x 20 mL), 10% aqueous Na2CO3 (2x 20 mL) and brine (20 mL). After drying over MgSO4, the solvent was removed, and the residue was filtered over silica gel (THF). After evaporation of the solvent a dark green solid was obtained.

Wet-chemical intramolecular oxidative cyclodehydrogenation
In addition to the Pd-catalyzed cyclization attempts, the intramolecular oxidative cyclodehydrogenation pathway was tested (see examples in Table S3). It has been demonstrated that this approach is a powerful tool for fusing aromatic units at the meso-b-position of the porphyrin macrocycle via 5-or 6-membered ring formation. [3,4] Therefore, S2 as well as S2Ni or S3 were tested under standard conditions using FeCl3 in MeNO2, but no reaction was observed and only starting material was recovered.
Even harsher reaction conditions, like e.g. DDQ and Trifluoromethanesulfonic acid did not lead to any C-C bond formation, however partial hydrolysis of the methyl ether was detected by mass spectrometry.

General information
ESI experiments were conducted in positive ion-mode and with two different ESI mass spectrometers.
The first instrument was an ultra-high resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer (solariX, Bruker, Bremen, Germany). The

General information
For comparison of our mass spectra with DFT data we performed geometry optimizations for the detected cations. Starting with the intact benzoporphyrin cation we stepwise eliminated HF under consideration of all possible pathways, following the path of the most stable intermediate.
For the quantum chemical calculations in the manuscript, we employed the rangeseparated hybrid functional wB97X-D, [5] which employs the Grimme D2 correction, in combination with the 6-311G(d,p) Pople basis set, using the Spartan '16 work package. [6] Comparable results were obtained from the exchange-correlation functional of Perdew, Burke, and Ernzerhof (PBE) [7] in combination with the def2-TZVP basis set of Weigend and Ahlrichs [8] using the RI-J [9] and MARI-J [10] approximation. Additionally the Grimme D3 dispersion correction [11] was employed. All quantum chemical calculations were performed using the Turbomole suite. [12] The following numbering for cyclized bonds is used in the tables below.    rel. E / eV

Normal-coordinate structural decomposition analysis
For Normal-coordinate Structural Decomposition (NSD) analyses, we used the NSD engine program as provided by J. A. Shelnutt, [13] which was kindly handed to us by the Senge group from Dublin. The theory and development of this method have been described by Shelnutt and co-workers. [14][15][16] NSD employs the decomposition of the conformation of the porphyrin macrocycle by a basis set composed of its various normal modes of vibration. The result affords the quantitative separation of the contributing distortions to the macrocycle conformation.
The summaries of the NSD are given in Å: The