Complexes of N‐Confused Porphyrin Derivatives as Ortho‐Metallating Ligands. Synthesis, Structure, Redox Properties, and Chirality

Abstract A family of transition metal complexes of meso‐aryl‐2‐aza‐21‐carbaporphyrin (N‐confused porphyrin, NCP) derivatives acting as ortho‐metallating ligands for ruthenium(II), rhodium(III), and iridium(III) is synthesized and characterized by XRD, spectroscopic, and electrochemical methods. The chirality of these systems is shown by the separation of the enantiomers and analyzed by circular dichroism and DFT. A preliminary catalytic study indicates the activity of the iridium(III) ortho‐metallated complexes in the N‐heterocyclization of primary amines with diols.


Introduction
The coordination chemistry of 2-aza-21-carbaporphyrin, a.k.a.Nconfused porphyrin (NCP, Figure 1) started simultaneously with the discovery of this porphyrinoid. [1,2]5][6][7][8][9][10][11][12][13][14][15][16][17][18] The unique feature of NCP is the presence of a built-in extra-annular nitrogen donor that can be treated as an additional ligation site, naturally enriching the coordination chemistry of this macrocycle when compared with its isomer, i.e., regular porphyrin or various core-modified analogues, including carbaporphyrins. [19,20]][23] In a quite complicated structure of mixed-valence tetrarhodium bis(NCP) DOI: 10.1002/advs.202306696tetracarbonyl complex, two external nitrogens are coordinated to a bridging dicarbonylrhodium(0) unit. [13]Meanwhile, in a monomeric dirhodium(I) system, one dicarbonylrhodium(I) center occupies two internal nitrogen sites and the external nitrogen is coordinated to the chlorodicarbonylrhodium(I) unit. [7]Upon coordination of two dicarbonyliridium(I) moieties, the NCP ligand undergoes inversion which results in the ligation of all four nitrogens inside the distorted macrocycle. [12]Owing to the close location of the meso-aryl at C20, the metal binding N2 can be a part of a six-membered metallacycle involving C1, C20, C ipso , and C ortho (Figure 1).Such an ortho-metallation has been relatively rarely observed and structurally characterized for NCP derivatives.In palladium(II) and platinum(II) dimers, the NCP subunits are bridged by the metal ions, [24][25][26] while doubly-ortho-metallation of Pt II or Pt IV has been found to occur in [Pt(3,3′-(NCP) 2 )] or [Pt{3,3′-(NCP)}L 1 L 2 ] comprising two directly linked NCP subunits. [27,28]In some of these complexes, the macrocyclic core is not involved in coordination, and in all of them, the confused pyrrole is tipped from the mean plane of the regular pyrroles which may be a prerequisite for the ortho-metallation.
In this paper, we report the synthesis and characterization of several late transition metal complexes comprising NCP or its derivatives with the ortho-C20-N2 chelating motif.We focus on the structural features of the NCP complexes that can be useful for transferring chirality onto the exposed "external" metal center M 1 or potential catalytic activity.

Syntheses and Characterizations
As starting materials for our syntheses of bis-metallic systems, we chose two previously reported compounds bearing a substituent at the C21 position coordinated to either nickel(II) [29][30][31][32][33] or ruthenium(II). [34,35]The common features of these, otherwise different complexes are chirality, significant deviation from planarity of the porphyrin ring in the region of confused pyrrole, and unoccupied/non-protonated N2.These systems were subjected to reaction with organometallic dimeric complexes of ruthenium(II), rhodium(III), or iridium(III) with two chlorides and either neutral  6 -para-cymene (Cym) or  5 -pentamethylcyclopentadienyl anion (Cp*).Under mild conditions (reflux of DCM solution in the presence of sodium acetate as a proton scavenger) the reaction resulted in the substitution of one chloride by carbanionic ortho-C20 and coordination of N2 atoms (Scheme 1).The ortho-metallation efficacy varied depending on the metal ion from 35-40% reaction yield for Rh III , 54-60% for Ru II , and up to 85-93% for Ir III .Slightly better results were obtained for NiMeP compared with those for RuSPy.We showed also that under the analogous condition, the reaction of [IrCl 2 Cp*] 2 with ClNCP free base yielded ortho-metallated derivative ClNCPIrCp* (Scheme 1) with a good outcome (83% yield).
The new complexes were characterized by high-resolution mass spectrometry, 1 H and 13 2).For the ortho-metallated rhodium(III) complexes, NiMePRhCp* and RuSPyRhCp*, a close resemblance of 1 H NMR spectral patterns to those of the respective Ir III systems were observed.The major difference is an additional splitting of all multiplets of the 20-phenyl protons due to 1 H-103 Rh spin-spin coupling (J RhH = 1.3-1.5 Hz).Significantly, the orthocarbon of the C20 phenyl substituent, identified on the basis of 1 H, 13 C HSQC and 1 H, 13 C HMBC experiments (Figure S7B and S13B, Supporting Information), gives rise to a doublet at  C 169.8 ppm with 1 J RhC = 31.1 Hz for NiMePRhCp* and at  C 169.9 ppm with 1 J RhC = 30.9Hz for RuSPyRhCp* unequivocally proving coordination of the carbanion.The 13 C-103 Rh coupling could be observed also for cyclopentadiene carbon atoms in 13 C NMR of both complexes giving rise to doublets at about  C 96 ppm with 1 J RhC = 6.1 Hz.The 1 H NMR characteristics of ClNCPIrCp* differ from the nickel(II) and ruthenium(II) complexes with 21-CH and 22,24-NH resonances arising in the upfield region of the spectrum ( −4.69 and broad signals at  −1.05, −1.10 ppm, respectively) reflecting a free-base character of the macrocyclic core.Interestingly, for all pentamethylcyclopentadienyl-comprising systems, correlations of the coordinated ortho-C with methyl protons of the  5 -Cp* ligand were observed in the 1 H, 13 C HMBC maps (Figures S3B, S7B, S9B, S13B, and S15B, Supporting Information), regardless of the metal ion.Such correlations appeared despite the fact that the coupled nuclei were separated by four bonds.The correlations may be accounted for by the anionic character of the Cp* ligand resulting in a relatively high electron density available that enhanced 1 H-13 C coupling.Significantly, for the neutral  6 -Cym ligand in NiMePRuCym or RuSPyRuCym, there was no such a correlation observed, in spite of only three bonds separating aryl protons of this ligand and the Ru II -coordinating ortho-C at 20-Ph.
The electronic spectrum of ClNCPIrCp* resembles that of the starting porphyrin ClNCP with ≈65 nm and 15 nm bathochromic shifts of the lowest-energy Q band and the Soret band, respectively observed for the complex (Figure S1, Supporting Information).For the NiMeP and RuSPy, the spectral changes due to external coordination are much more profound, though similar to each other, regardless of the ortho-metallated cation (Figure 3).These alterations involve a decrease in the relative intensity of the spectra in the Soret region near 430 nm and an increase of the absorbance in the Q band region, i.e., above 500 nm.

Crystal Structures
Solid state structures of the selected ortho-metallated systems were elucidated using the single crystal X-ray diffraction analyses (Figure 4 Figures S39-S44, Supporting Information).The structures determined based on diffraction data clearly showed the coordination mode of iridium(III), ruthenium(II), and rhodium(III) ions to ClNCP or metalloligands NiMeP and RuSPy.Metalloligands bind iridium(III), ruthenium(II), and rhodium(III) ions through the N2 donor atom and the ortho-carbon of the aryl ring from the C20 meso-position.The coordination sphere of metal ions located at the periphery of the macrocycle is supplemented by chloride and pentamethylcyclopentadienyl ligands (in ClNCPIrCp*, NiMePIrCp * , RuSPyIrCp*, and RuSPyRhCp*) or chloride and p-cymene ligands (in NiMePRuCym).Coordinating metal ions at the edges of metalloligands retain a structural motif referred to as a "piano stool" or a half-sandwich complex. [36]Data on bond lengths around iridium(III), ruthenium(II), and rhodium(III) ions are summarized in Table 1 along with selected bond lengths for the dimeric metal sources.[39] Interestingly, RuSPyIrCp* and RuSPyRhCp* are isostructural when  crystallized from benzene/hexane, both forming tris(benzene) solvates.
The steric hindrance introduced by Cp* or Cym ligands forces them to be specifically positioned relative to methyl or mercaptopyridyl substituents at the C21 atom of metalloligand.As a consequence, they are located on opposite sides of the macro-cyclic plane, and, in the case of compounds RuSPyIrCp* and RuSPyRhCp*, on the same side as the CO ligand.The specific setting of the p-cymene relative to the macrocyclic system was established for NiMePRuCym with the isopropyl group above the metalloligand plane.Such an orientation of the Cym ligand is somewhat unexpected considering solution 1 H NMR results suggesting methyl rather than the isopropyl group directed toward the macrocycle interior (vide supra).It may be accounted for by packing forces for which the ligand orientation in the crystal with a smaller substituent situated beyond the perimeter of the macrocycle is more favorable.The deviation of the porphyrin ring from planarity due to sp 3 hybridization of C21, characteristic for the starting metalloligand NiMeP and RuSPy, is retained upon coordinating the metal ion to the periphery of the macrocycle.However, the external ortho-metallation does not significantly change the bond distance between the metal ion [nickel(II) or ruthenium(II)] located in the cavity of the macrocycle and the C21 carbon atom.The Ni─C21 bond length is 2.004(4) Å [29] in NiMeP, while in NiMePIrCp* and NiMePRuCym it is 2.022(1) Å and 2.015(2) Å, respectively.For RuSPy-containing systems, this bond length alteration is even less pronounced: from 2.118(3) Å in the metalloligand to 2.110(2) and 2.116(1) Å in RuSPyIrCp* and RuSPyRhCp*, respectively.Analyses of the out-of-plane porphyrin ring distortions were carried out using the PorphStruct tool [40] which was based on the normal-coordinate structure decomposition (NSD) approach [41,42] (Table 2 and Figure 5).The comparative NSD analyses applied for starting systems, i.e., ClNCP, NiMeP, and RuSPy, indicated a moderate effect of the ortho-metallation on the total out-of-plane distortion of the porphyrin (D oop ).In fact, in some instances (ClNCPIrCp*, RuSPyIrCp*, RuSPyRhCp*, Table 2, entries 2, 7, and 8, respectively) the chelation at the NCP perimeter led to a less pronounced displacement than that observed in the starting ligand (NCP, entry 1; RuSPy, entry 6).The most significant deviation   increase due to ortho-metallation was observed for the NiMeP metalloligand (Table 2, entry 3) upon chelation of RuCymCl moiety (entry 5).All systems indicated a significant saddling distortion which, again, increased only in NiMePRuCym.The increasing doming, ruffling, and waving distortions were observed for almost all systems upon external chelation, although these components gave rather minor contributions to D oop which is dominated by the saddling.Displacement of metal ions from the mean plane of the porphyrin in a metalloligand (d M-mpln ) slightly increased after an external metal ion was introduced, though an opposite effect was observed for the displacement from an MCNNN mean plane (d M-ccpln ).A common structural feature for the complexes under study as well as for NCP free base, is a pronounced deviation of the confused pyrrole plane from that of the porphyrin ring.Such a deviation can be parametrized by a dihedral angle (DH, Table 2) between the confused pyrrole mean plane and the mean plane defined by all non-hydrogen atoms of the macrocycle, except N2, C3, and C21.Apparently, a significant increase of this angle upon external chelation was observed only for the NiMeP-containing complexes (Table 2, entries 4 and 5).
The individual atom displacements from the mean plane are typical for the saddle-distorted porphyrins with alternate directions of the pyrrole deviation (Figure 5).Significantly, in the bimetallic Table 2. Analyses of the out-of-plane displacements for the macrocyclic ring of NCP calculated by means of PorphyStruct. [40]on the basis of SCXRD structures.d) dihedral angle between the mean plane defined by all non-hydrogen atoms of the macrocyclic ring except C21, N2, and C3 but including core-coordinated metal, and the mean plane of the confused pyrrole; e) X-ray data taken from ref. [2]; f) X-ray data taken from ref. [29]; g) X-ray data taken from ref.
[34]; h) X-ray data taken from ref. [25]; systems NiMePIrCp* and NiMePRuCym, the displacement of the meso-carbons is significantly more pronounced than in the starting NiMeP, where those atoms are located almost in the mean plane.It is particularly evident for C20 and is related to the coordination of N2 and the aryl at C20.The external chelation slightly increases the displacement of N2 and C3 in these two systems with respect to the metalloligand, in line with the increasing DH.Generally, the atoms are more displaced in NiMeP and its ortho-metallated derivatives than in RuSPy and its complexes.
All ortho-metallated complexes are chiral, as are their precursors in the solid state.However, these systems crystallized in centrosymmetric space groups as racemates and in Figure 4 only one enantiomer for each of the complexes has been shown.

Chirality
Our attempt to separate enantiomers of the externally metallated NCP derivatives involved HPLC methods with a chiral stationary phase.The enantiomers of several of these systems are presented in Figure 6 as they appear in the solid-state structures, along with definitions of their absolute configurations.For these definitions, we took an external metallacycle which is common to all these ortho-metallated systems, i.e., M─N2─C1─C20─C ipso ─C ortho as a chirality plane.
Although metalloligands NiMeP and RuSPy are intrinsically chiral due to the presence of a chirality center at the coordinated C21, [43] the ortho-metallation introduces its own chirality related to a differentiation of the porphyrin faces.Apparently, these two chirality sources are not independent, that is, upon external chelation of the racemic mixture of NiMeP or RuSPy only a pair of enantiomers is formed and no other NMRdistinguishable stereoisomers can be observed.Hence, the external metallation is stereoselective although two diastereomers can be potentially formed, differing in orientation of chloride and the organometallic ligands (Cp* or Cym) at the externally chelated metal with respect to the macrocycle.The crystal structures reveal roughly the same orientation of the chloride ligand at the external metal center and the substituent at C21.Thus, the chirality of the bimetallic monomers in the solid state and solution is predefined by the starting metalloligands [43,44] with absolute configurations S or R at C21 in the metalloligands invariantly giving rise to the configurations P or M, respectively in the ortho-metallated complexes.The separation of the bimetallic enantiomers by the HPLC method was expected to be effective through two approaches (Scheme 2).The first method involved a separation of enantiomers prior to the external chelation (Figure 7A,B,C,E), while in the second approach, separation proceeded ortho-metallation (Figure 7D,F; Figures S29 and S30, Supporting Information).The first method allows high enantiopurity of the bimetallic systems and, in principle, can be applied for many other metal ions resulting in chirality transfer from the metalloligand toward the external metal center which may be a site of catalytic reaction.Importantly, the absolute configurations of such complexes can be deduced directly from the absolute configuration of the metalloligand.The second method is more useful for the systems for which the external chelation is less effective, such as NiMePRhCp* or RuSPyRhCp*.
The asymmetry of these configurationally stable systems arises from the presence of the chiral center at the C21 atom.Conversely, the NCP free base is chiral in the solid state owing to its non-planarity but in solution, the molecule is configurationally unstable and no enantiomer separation is possible.This is due to a flipping of the confused pyrrole allowing fast interconversion of the enantiomers, unlike in several 21-substituted NCP derivatives. [45,46]Thus, chelation of metal ion by N2 and the ortho carbon atom of the adjacent meso-aryl such as in ClNCPIrCp* or NCPPtPPh 3 [25] as well as double chelation in directly bound 3,3′-(NCP) 2 Pt [28] is sufficient to stabilize the configuration.The external ortho-metallation provides a lock preventing fast interconversion of enantiomers and participates in the differentiation of the macrocycle faces.Thus, for ClNCPIrCp*, we were able to separate enantiomers and record their circular dichroic spectra (Figures S27 and S28, Supporting Information) indicating the chirality of this system and its configurational stability.The absolute configurations of the separated enantiomers were assigned based on TD-DFT simulations of the CD spectra (Figures S23-S27, Tables S7-S12, Supporting Information).

Redox Properties
The electrochemical properties of the ortho-metallated complexes were studied by means of cyclic and differential pulse voltammetry (Figure 8; Figure S35, Supporting Information).The electrode potentials were collected in Table 3.For all but one complex system the first oxidations were reversible, and for a majority, the second oxidations appeared to be reversible as well.Conversely, for almost all complexes there was no reversible reduction.Oxidation potentials were relatively low and the external coordination did not significantly affect the first oxidation potentials compared to the metalloligands NiMeP and RuSPy (Table 3, entries 8, 9) or ligand ClNCP (Table 3, entry 10).It was not the case for RuSPyIrCp* and RuSPyRuCym (Table 3, entries 5 and 7) for which 90 and 190 mV cathodic shifts were observed, respectively.
The redox properties of the ortho-metallated species and their precursors can be analyzed theoretically through comparison of the frontier orbitals energies (Figure 9).Apparently, the Scheme 2. Two approaches applicable for the separation of enantiomers of the ortho-metallated complexes.

Table 3. Electrode potentials of the orthometallated complexes and metalloligands.
Entry  3).On the other hand, the optical HOMO-LUMO energy gaps (oHLG in Table 3.), obtained from the experimental UV-vis spectra are even lower (by 0.1-0.2eV) than the values derived from the electrochemical potentials.Spectrophotometric titration of both NiMeP and RuSPy orthometallated derivatives with tris(4-bromophenyl)ammoniumyl hexachloroantimonate (BAHA, Magic blue), a one-electron oxidant of reduction potential 0.70 V [47] allowed monitoring of the spectral changes upon oxidation (Figure 10).According to our electrochemical data, this oxidant was sufficiently strong for the first and the second oxidation to be achieved for all systems, except RuSPy for which E Ox2 is too high (Table 3, entry 9).The ob-served changes in the spectral region between 400 and 800 nm upon the addition of one equivalent of BAHA, suggested metalcentered oxidation in all the bimetallic systems (Figure 10A,D; Figure S31-S34, Supporting Information).For the RuSPyMCp* complexes (M = Ir III , Rh III ), the first oxidation resulted in an increase of the Soret-like band intensity with a small (Δ = 15 nm) bathochromic shift and a decrease of the Q-type band (Figure 10A; Figure S34, Supporting Information).Such changes suggest that the conjugation of the -electrons of the aromatic macrocycle remains intact after one electron is removed.Further addition of BAHA resulted in a gradual increase of the absorbance in the NIR region at ≈1500 nm which is indicative of a radical species, thus suggesting a ligand-centered second oxidation process.These spectral changes are in sharp contrast to those observed for the RuSPy metalloligand for which a pronounced decrease of the Soret-like and an increase of the Q-like bands were observed and no further spectral alteration occurred after passing 1 equiv of BAHA (Figure 10B).Such a pattern of spectral changes may suggest a porphyrin-centered oxidation to the cation metalloradical rather than Ru-centered oxidation.On the other hand, titration of ClNCPIrCp* with BAHA indicated an initial decrease of the Soret-like band at 448 nm and its bathochromic shift up to 463 nm upon the addition of 1 equiv of the oxidant.The changes were followed by an increase in intensity of this band with a further redshift to 469 nm which was accompanied by the absorbance increase at 816 nm and the formation of the broadband at 1500 nm when approaching 2 equiv of BAHA (Figure S31, Supporting Information).Thus, apparently despite oxidation of the "empty" macrocycle in ClNCPIrCp* the aromaticity of the system is retained and typical spectral features of the porphyrinoids, i.e., the strong Soretlike band and weaker Q-type bands are observed even for the two-electron oxidized species.The first oxidations of the systems comprising NiMeP are nickel-centered.The highly anisotropic orthorhombic frozen dichloromethane ESR spectra obtained by the BAHA addition (Figure 9C) closely resemble those of various 21-alkylated nickel(III) NCP species. [32,33,48,49]For NiMePIrCp*, the addition of more than 1.5 equiv of BAHA resulted in a gradual decrease of the nickel(III) signal intensity, moderate changes of the Zeeman tensor components, and in the appearance of a radical signal at g = 2.0029.Also, spectrophotometric titration with BAHA revealed fine changes in the Soret and Q regions up to 1.2 equiv, followed by a gradual increase of the band at 435 nm and the final appearance of the NIR band upon the addition of more than 2 equiv of the oxidant (Figure 9D). [50]Interestingly, for the very similar complex, i.e., NiMePRhCp*, the changes of the ESR spectra upon the addition of 1.5 or more equivalents of BAHA are different, involving slight alteration of g 2 and g 3 components, not the appearance of the radical signal (Figure S35, Supporting Information).Similarly, the addition of BAHA to the solution of NiMePRuCym gave rise to an orthorhombic spectrum in frozen DCM (Figure S36, Supporting Information) but no strong radical signal was observed upon the addition of more than 2 equiv of BAHA.For reference purposes, we performed also the ESR-monitored oxidation for the starting metalloligand NiMeP indicating a decrease of the Zeeman tensor anisotropy upon the addition of an excess of BAHA with changes of g 1 from 2.382 to 2.285, g 2 from 2.168 to 2.2019, and g 3 from 2.086 to 2.111 for the spectra recorded in the presence of 1.2 and 3 equiv, respectively (Figure S37, Supporting Information).Again, no accompanying radical formation was observed.The differences among the systems comprising NiMeP in the second oxidation potentials and ESR behavior are surely related to the external coordination, although no clear tendencies can be derived from such a limited data set.It can be also rationally expected that for both groups of the ortho-metallated complexes, oxidation of the metalloligand strongly affects elec-tron density in the environment of the externally coordinated metal ion.

Catalysis
For preliminary studies of the catalytic function of the externally ortho-metallated systems, we chose N-heterocyclization reaction of benzylamine with 1,6-hexanediol which has been shown to be effectively catalyzed by iridium(III) complex [IrCl 2 Cp*] 2 in toluene under basic conditions (Table 4). [51]Small-scale reactions (0.5 mmol) were carried out in the presence of all orthometallated iridium(III) complexes described in this paper as well as for the original catalyst [IrCl 2 Cp*] 2 , ClNCP ligand, and both metalloligands, for the reference.The samples were prepared in the inert and dry atmosphere of a glove box to avoid any interference of oxygen and moisture with the reagents, and the reactions were carried out in sealed vials.The reaction results were analyzed qualitatively using GC/MS and quantitatively using the GC/FID technique, and for the selected systems, 1 H NMR quantitative analysis was applied with 2,4,6-collidine as the internal standard.As expected, only iridium(III)-comprising systems appeared to be catalytically active in the heterocyclizaction reaction, while neither of the ligands supported the 7-membered ring formation.The best catalyst, i.e., ClNCPIrCp* (Table 4, entry 6) gave rise to the yield exceeding that of the original catalyst [IrCl 2 Cp*] 2 with higher glycol conversion and better chemoselectivity.Also NiMePIrCp* seemed to be a more selective catalyst than [IrCl 2 Cp*] 2 with a similar yield of the main reaction product (Table 4, entries 2 and 1).Surprisingly, no heterocyclization was observed for RuSPyIrCp* used as a catalyst, despite several attempts.It may be due to a less labile character of the Ir─Cl bond in this complex than in other systems.According to the proposed reaction mechanism, [51] in the early stage of the catalytic process, coordination of the glycolic anion to the iridium center is required which implies chloride substitution (originally present in the ortho-metallated systems).A significantly longer C─Ir bond in RuSPyIrCp* (2.083(5) Å) than those in NiMePIrCp* (2.041(3) Å) or ClNCPIrCp* (2.051(6) Å) may be responsible for a weaker trans effect of the meso-aryl carbanion coordinated to the iridium(III) center on the opposite side to the chloride, making its exchange less effective.Of course, some other structural features, such as the presence and type of the metal ion within the macrocyclic cavity, flexibility of the molecular skeleton and its deformations, etc., may be decisive for the catalytic activity of the iridium complexes.Although at the present stage, we cannot offer any more conclusive accounting for the observed differences, it is clear that distinctions in the reaction yields among the systems used in this study indicate an influence of the porphyrinchelating ligand on the catalytic activity of the externally coordinated metal center.

Conclusion
We have shown here that the ortho-metallation of the NCP by representative late metals of the second and third rows of transition metals appears to be facilitated by a deviation of the confused pyrrole from the macrocycle mean plane.Such a deviation can be  b) With respect to 1,6-hexanediol; c) The reported yield was 74% [51] ; d) Results from GC-MS/FID analysis only.
easily achieved when the macrocyclic crevice is empty, and thus, when the ligand is sufficiently flexible to conform the external donor set, i.e., the external N2 atom and a C ortho atom of the aryl at the meso-C20 position to afford chelation.This strong out-ofplane deflection also allows the coordination of other ligands supplementing the coordination sphere of the metal.Importantly, in the already known ortho-metallated NCP complexes, the metals (Pd 2+ , Pt 2+ ) coordinated to the ligand exterior adopt invariantly a square-planar geometry.In the present report, we show that a piano-stool environment is also a suitable geometry for this type of complex, despite the presence of relatively voluminous ligands (Cym or Cp*).Although not as flexible as a free base, the C21substituted NCP derivatives coordinating in the macrocyclic interior to Ni 2+ in the square planar or Ru 2+ in the octahedral environments, comprise the confused pyrrole unit that is permanently deviated from the mean plane of the porphyrinoid.This arrangement makes complexes such as NiMeP or RuSPy effective metalloligands suitable for ortho-metallation.The ortho-metallated systems are chiral and can be obtained in a non-racemic form by either separation of the final bimetallic complexes or by the external metalation of the separated enantiomers of metalloligands, as no racemization is possible upon N2-C ortho chelation.Favorably, the external chelation occurs stereoselectively with only one arrangement of the metal environment and the macrocycle.Thus, the chiral information can be transferred from the metalloligand to the externally situated metal center of the asymmetric environment.The redox properties of the bimetallic complexes are not profoundly altered in comparison to those of the appropriate metalloligands as has been shown here by electrochemical studies as well as by spectrophotometric and ESR-monitored oxidation.Preliminary recognition of an influence of the ortho-metallated ligand on the catalytic activity of the externally coordinated iridium(III) centers indicated that the heterocyclization reaction is totally absent for the system comprising RuSPy metalloligand (i.e., RuSPyIrCp*), despite the same donor set as in NiMePIrCp* or ClNCPIrCp* that effectively catalyzed this reaction.The study on these and other analogous systems directed toward recognition of their catalytic potential and redox properties will be continued in our laboratory.

Experimental Section
General Methods and Instrumentation: Commercial reagents were used without further purification.Solvents were freshly distilled from the appropriate drying agents or purified under nitrogen with the mBraun MBSPS-800 before use.Column chromatography was performed by using silica gel 60 (200-300 mesh ASTM).The NMR spectra were recorded on a Bruker Avance III spectrometer, operating at 500 MHz for 1 H and 125 MHz for 13 C, or a Bruker Avance III spectrometer operating at 600 MHz for 1 H and 150 MHz for 13 C. TMS was used as an internal reference for 1 H and 13 C chemical shifts and CDCl 3 was used as solvent.Standard pulse programs from the Bruker library were used for homo-and heteronuclear 2D experiments.ESR spectra (X-band) were recorded on a Bruker ELEXSYS E500 spectrometer.Mass spectrometry measurements were conducted by using the electrospray ionization technique on a Bruker Daltonics microTOF-Q or using the MALDI method on a Bruker ultrafleXtreme spectrometer.Absorption UV/Vis/NIR spectra were recorded by using a Varian Cary 60 and Jasco V-770 spectrophotometers.Circular dichroic spectra were recorded by means of Jasco 1500 spectropolarimeter equipped with a flow cell attached to the Hitachi-Merck LaChrom HPLC system allowing detection of the chiral fraction and CD spectra measurement in a stopped-flow technique.Enantiomer resolutions were performed using either Chirex 3010 or Chirex 3014 column (25 × 0.46 cm).The product of the catalytic reactions was analyzed utilizing an Agilent 8890 gas chromatograph equipped with an Agilent 122-5532 column (30 m × 250 μm × 0.25 μm with DB-5 ms stationary phase) and with mass spectrometer detector Agilent 5977B.Quantitative analyses were performed on the same chromatograph with Agilent 19091S-433UI column and FID detector.Electrochemical measurements were performed by means of Autolab (Metrohm) potentiostat/galvanostat system for dichloromethane solutions with a glassy carbon, a platinum wire, and Ag/Ag + as the working, auxiliary, and pseudoreference electrodes, respectively.Tetrabutylammonium hexafluorophosphate was used as a supporting electrolyte.The potentials were referenced with the ferrocene/ferrocenium couple used as an internal standard.
The X-ray diffraction was measured using either XtaLAB Synergy R or Xcalibur, Onyx diffractometers using a copper source of radiation ( = 1.54184Å), and collected with CCD camera.The standard temperature of the measurement was 100 K.The structures were solved using direct methods with SHELXT [52] and refined by the full-matrix least-squares method on all F 2 data by using the SHELXL [53] incorporated in the OLEX2 program. [54]All hydrogen atoms, including those located in the difference density map, were placed in calculated positions and refined as the riding model.Crystallographic details are collected in Tables S2-S6 (Supporting Information).CCDC 2 284 427, 2 284 430, 2 284 431, 2 284 433, and 2 284 434 contain supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif .
Synthesis of ClNCPIrCp*: A sample of 0.040 g (0.054 mmol) ClNCP, 0.044 g (0.054 mmol) dichloro(pentamethylcyclopentadienyl)iridium(III) dimer, 0.044 g (0.540 mmol) anhydrous sodium acetate and 20 mL dichloromethane were placed in a two-necked flask.The reaction mixture was purged for 20 min with N 2 and then refluxed for 12 h.After this time, the reaction mixture was filtered, and the solution was concentrated and separated on a silica-gel column.The compound was eluted using 0.5% MeOH in dichloromethane.The collected fraction was evaporated to dryness and recrystallized from the dichloromethane/n-hexane system.Yield 0.049 g (83%).
Selected Data for ClNCPIrCp*: 1  Synthesis of NiMePIrCp*: A sample of 0.025 g (0.036 mmol) of NiMeP, along with 0.016 g (0.020 mmol) of dichloro(pentamethylcyclopentadienyl)iridium(III) dimer, 0.016 g (0.2 mmol) anhydrous sodium acetate and 10 mL of dichloromethane were placed in a two-neck round bottom flask.The mixture was purged for 20 min with N 2 and then refluxed for 18 h.In the next stage, The reaction mixture was then filtered, concentrated, and passed down a silica gel column.The compound was eluted with 30% ethyl acetate in n-hexane.The collected fraction was evaporated to dryness and recrystallized from the dichloromethane/n-hexane.Yield 0.035 g (93%).
Selected Data for RuSPyRuCym: Synthesis of RuSPyRhCp*: A sample of 0.020 g (0.024 mmol) of compound RuSPy, 0.007 g (0.012 mmol) dichloro(pentamethylcyclopentadienyl)rhodium(III) dimer, 0.010 g (0.120 mmol) of anhydrous sodium acetate and 10 mL of chloroform was placed in a two-neck round-bottom flask.The mixture was purged with N 2 gas for 20 min and then refluxed for 24 h.After this time, another portion of 0.007 g (0.012 mmol) of dichloro(cyclopentadienyl) rhodium(III) dimer and 0.010 g (0.120 mmol) of anhydrous sodium acetate was added and heated for another 24 h under reflux.In the next stage, the mixture was filtered, concentrated and separated by a silica gel chromatographic column.The compound was eluted with 30-35% ethyl acetate in n-hexane.The collected fraction was evaporated to dryness and recrystallized from the dichloromethane/n-hexane.Yield 0.009 g (35%).
C NMR, including homo-and heteronuclear 2D correlation experiments, UV-vis-NIR spectroscopy, and single crystal XRD analyses.The ESI+ HRMS indicated the presence of the incoming metal ion as well as Cym or Cp* moieties in each case, though all cations were stripped of chloride.The 1 H NMR spectra revealed the preservation of most of the spectral features typical of NiMeP, RuSPy, or ClNCP in the complexes formed and the appearance of new signals related to the presence of Cp* or Cym (Figure 2).Thus, the spectra of the systems with Cp* comprise a very strong (15H) signal at about  0.8 ppm due to methyl protons, indicating fast rotation around the M-Cp* direction.On the other hand, the differentiation of aryl and isopropyl resonances of the RuCym moiety is in line with the slow motions of the Cym ligand at the 1 H NMR time scale.Moreover, an upfield shift of all the Cym protons with respect to those observed for starting [RuCl 2 Cym] 2 , indicates the position of this moiety over the aromatic frame of the macrocyclic ligands.Significantly, this aromatic ring shielding effect is strongest for the cymene methyl Me c (Δ 0.7-1.4ppm) suggesting the orientation of the ligand with the isopropyl group situated rather outside, while Me c is above the macrocycle.The number of meso-aryl distinct signals in the spectra of RuSPyIrCp* and RuSPyRuCym recorded at room temperature, reflects diastereotopic inequivalence of the macrocyclic faces and slow, at the NMR timescale, rotation of these substituents around C ipso ─C meso bonds, resulting in differentiation of ortho-and meta-H resonances of phenyls at C5, C10, and C15.Conversely, these meso-phenyl protons in NiMePIrCp* and NiMePRuCym give rise to severely broadened signals indicating intermediate rotation rate of the substituents and diastereotopicity of the complex faces.The only sharp mesoaryl signals are those of phenyl at the C20 position due to the complete freezing of its rotation by ortho-metallation.The chemical shifts and coupling patterns are similar in all these orthometallated complexes comprising a doublet for 20-m at about 8.3 ppm, a doublet for 20-o′ at about 7.7 ppm, and two triplets for 20-m′ and 20-p at ≈7.3 and 7.2 ppm, respectively (Figure

Figure 4 .
Figure 4. Perspective views (50% displacement ellipsoid plots and stick diagrams) of molecular structures of A) ClNCPIrCp*, B) NiMePRuCym, C) NiMePIrCp*, and D) RuSPyIrCp*.All solvent molecules are omitted.In the stick representations of the side views, all hydrogens and all but orthometallated aryl substituents are removed for clarity.

Figure 6 .
Figure 6.Definition of absolute configuration at metalacyclic part of the systems A) and enantiomers along with chirality definitions for the selected ortho-metallated NCP complexes, B) ClNCPIrCp*, C) NiMePRuCym, and D) RuSPyRhCp*.

Figure 7 .
Figure 7. A) HPLC profiles for RuSPy on chiral stationary phase column (Chirex 3010, 1% MeOH in CH 2 Cl 2 , 2 mL min −1 ); top, CD and bottom, absorbance detection at 363 nm.B) CD (top) and absorbance (bottom) spectra of the HPLC-separated fractions of RuSPy.C) superimposed CD spectra (CH 2 Cl 2 , 298 K) of S-NiMeP (orange trace) and P-NiMePIrCP* (purple trace) obtained by metalation of the former with [IrCl 2 Cp*] 2 .D) CD spectra of enantiomers of NiMePRuCym separated by the chiral stationary phase HPLC.E) superimposed CD spectra (CH 2 Cl 2 , 298 K) of S-RuSPy (blue trace) and P-RuSPyIrCP* (red trace) obtained by metallation of the former with [IrCl 2 Cp*] 2 .F) CD spectra of enantiomers of RuSPyRuCym separated by the chiral stationary phase HPLC.The absolute configurations were assigned to the enantiomers on the basis of TD-DFT simulations of the CD spectra (Figures S23-S26, Supporting Information).

Figure 8 .
Figure 8. Cyclic (CV, black traces) and differential pulse (DP, purple traces) voltammograms of A) NiMePIrCp*, B) RuSPyIrCp*, C) ClNCPIrCp*, D) NiMeRuCym, E) RuSPyRuCym, and F) RuSPyRhCp*.The experiments were carried out in a dichloromethane solution of [Bu 4 N]PF 6 (0.1 m) using a glassy carbon working electrode, a platinum wire as an auxiliary electrode, and Ag/AgCl as a pseudoreference electrode.The green numbers associated with DP peaks are electrode potentials in volts.The partial CV scans are given to indicate the reversibility of some of the processes.

Figure 9 .
Figure 9. DFT-calculated frontier orbitals energies of specified systems with the experimentally estimated energies of the HOMO and LUMO derived from the electrochemical data (green sticks).

Figure 10 .
Figure 10.Spectrophotometric titration of dichloromethane solutions of A) RuSPyIrCp*, B) RuSPy, and D) NiMePIrCp* with tris(4bromophenyl)ammoniumyl hexachloroantimonate (BAHA) and selected ESR spectra recorded in frozen dichloromethane solutions (120 K) upon addition of specified amounts of BAHA (C).The black arrows in (A) and (B) indicate the direction of the absorbance changes before, while the red arrows-after the addition of 1 equiv of BAHA.

Table 1 .
Bond lengths d for the externally chelated metal ions.