Selective Schiff Base Formation of Group 9 Organometallic Complexes with Functionalized Spirobifluorene Ligands

Organic amines are important compounds present in a wide variety of products, which makes the development of new systems for their detection an interesting field of study. New organometallic complexes of group 9 [MCp*X(2′-R-2-py-SBF)] (M = Ir, Rh; R = H, X = Cl (6), R = H, X = OAc (7), R = CHO, X = Cl (8)), and [IrCp*Cl(2′, 7-diCHO-2-py-SBF)] (9) (Cp* pentamethylcyclopentadienyl, SBF = 9,9’-spirobifluorene) bearing bidentate C–N ligands based on 9,9′-spirobifluorene were obtained and characterized by NMR spectroscopy, mass spectrometry, IR spectroscopy, and X-ray diffraction analysis when possible. The formation of a Schiff base to give complexes with the formula [MCp*Cl(2′-CH=NR-2-py-SBF)] (M = Ir, Rh; R = alkyl or aryl (10–12)), through condensation of an amine, and the aldehyde group present in these new complexes was studied leading to a selective reactivity depending on the nature of the amine and the metal center. While the iridium complexes only react with aromatic amines, the rhodium derivative requires heat for those but can react at room temperature with aliphatic amines.


Introduction
Organometallic complexes as sensors in the detection of amines are of vital importance due to the presence of these organic derivatives in pharmaceutical, organic, and food products, as well as in our organisms, where they fundamentally control many of the physiological functions [1].For example, the coordination of amines to iridium compounds has been previously described for generating luminescence, which makes them good candidates as sensors [2,3].Another way of detecting amines is through the formation of imine derivatives, Schiff bases [4][5][6][7].Thus, chiral aldehydes have been used with chiral amine compounds, giving rise to diastereomeric imines, where the 1 H NMR spectroscopy technique allows the enantiomeric purity of the amines to be determined [5].
Regarding sensors, the development of imidazolium polymer based on 2,2′,7,7′-tetraimidazole spirobifluorene can easily detect iron (III) or dichromate anion [20].In addition, 2,2′ substituted SBF-based dendrimers have been used for the detection of explosives [21].Herein, the synthesis of cyclometallated iridium and rhodium complexes with a bidentate C-N ligand based on 9,9′-spirobifluorene where one of its branches bears an aldehyde substituent is proposed.The group will allow us to analyze the behavior of this type of organometallic complexes towards aliphatic and aromatic amines with a view to their future application as amine detection sensors.

Results and Discussion
The obtaining of the spirobifluorene-functionalized ligands was based on common organic reactions summarized in Scheme 1.Thus, using 2-bromo-9,9′-spirobifluorene as a starting reagent and PdCl2(1,1'-bis(diphenylphosphino)ferrocene) as a catalyst, a pinacolboranyl substituent can be introduced to give 1.This compound reacts through a Suzuki−Miyaura cross-coupling reaction with 2-bromopyridine to provide 2, a spirobifluorene functionalized with a pyridine ligand.Then, compound 2 reacts with TiCl4 and dichloromethyl-methylether as a formyl source by Rieche formylation leading to compound 3. Thus, compound 3 bears an aldehyde group at the second branch of the spirobifluorene moiety as the presence of a pyridine substituent already in the system produces, apart from a -I effect, a +R effect at position 7 of the same branch promoting the electrophilic aromatic substitution only at the second branch even with a little excess of formylation reagents [22].Herein, the synthesis of cyclometallated iridium and rhodium complexes with a bidentate C-N ligand based on 9,9 -spirobifluorene where one of its branches bears an aldehyde substituent is proposed.The group will allow us to analyze the behavior of this type of organometallic complexes towards aliphatic and aromatic amines with a view to their future application as amine detection sensors.

Results and Discussion
The obtaining of the spirobifluorene-functionalized ligands was based on common organic reactions summarized in Scheme 1.Thus, using 2-bromo-9,9 -spirobifluorene as a starting reagent and PdCl 2 (1,1 -bis(diphenylphosphino)ferrocene) as a catalyst, a pinacolboranyl substituent can be introduced to give 1.This compound reacts through a Suzuki−Miyaura cross-coupling reaction with 2-bromopyridine to provide 2, a spirobifluorene functionalized with a pyridine ligand.Then, compound 2 reacts with TiCl 4 and dichloromethyl-methylether as a formyl source by Rieche formylation leading to compound 3. Thus, compound 3 bears an aldehyde group at the second branch of the spirobifluorene moiety as the presence of a pyridine substituent already in the system produces, apart from a -I effect, a +R effect at position 7 of the same branch promoting the electrophilic aromatic substitution only at the second branch even with a little excess of formylation reagents [22].
Molecules 2023, 28, x FOR PEER REVIEW 3 of 20 Scheme 1. Synthetic routes of the organic compounds used in this work.
In addition, a double-formylated compound could be obtained.To avoid deactivating processes, the first step was the diformylation from the bromo-substituted derivative.In this case, the bromine group only presents an inductive effect (-I); therefore, the absence of the +R effect avoids the hampering of the diformylation in a stoichiometric reaction.Note that the introduction of the first CHO substituent has a very strong deactivating effect in its branch, promoting the second formylation at the bromine branch.Afterward, Scheme 1. Synthetic routes of the organic compounds used in this work.
In addition, a double-formylated compound could be obtained.To avoid deactivating processes, the first step was the diformylation from the bromo-substituted derivative.In this case, the bromine group only presents an inductive effect (-I); therefore, the absence of the +R effect avoids the hampering of the diformylation in a stoichiometric reaction.Note that the introduction of the first CHO substituent has a very strong deactivating effect in its branch, promoting the second formylation at the bromine branch.Afterward, the borylation reaction using the same methodology as before was performed.Thus, 4 was obtained bearing an aldehyde group at each spirobifluorene branch, in positions 2 and 7. Again, the C-C coupling reaction finally provided the targeted compound 5 (see experimental section for characterization of all the organic derivatives).
Treatment of compound 2 with the dimeric complex [MCp*(Cl)(µ-Cl)] 2 (M = Ir, Rh) in presence of potassium acetate led to the formation of a mixture of [MCp*Cl(2-py-SBF)] (M = Ir (Ir6), Rh (Rh6)) and [MCp*(OCOCH 3 )(2-py-SBF)] (M = Ir (Ir7), Rh (Rh7)) (Cp* = pentamethylcyclopentadienyl, SBF = 9,9 -spirobifluorene) in an approximate 1:2 ratio for iridium and 1:1.5 ratio for rhodium, respectively (Scheme 2).This ratio was determined by integration at the 1 H NMR spectra using the Cp* signals as well as the resonance of the CH group directly bonded to the nitrogen atom of the pyridine moiety.Complex 7 stems from a competition between the starting dimers [MCp*(Cl)(µ-Cl)] 2 (M = Ir, Rh) and complex 6 toward a reaction with KOAc.However, lower amounts of acetate or shorter reaction times led to lower conversions of the starting material with the same product ratio, and therefore, salt metathesis could not be avoided.Scheme 1. Synthetic routes of the organic compounds used in this work.
In addition, a double-formylated compound could be obtained.To avoid deactivating processes, the first step was the diformylation from the bromo-substituted derivative.In this case, the bromine group only presents an inductive effect (-I); therefore, the absence of the +R effect avoids the hampering of the diformylation in a stoichiometric reaction.Note that the introduction of the first CHO substituent has a very strong deactivating effect in its branch, promoting the second formylation at the bromine branch.Afterward, the borylation reaction using the same methodology as before was performed.Thus, 4 was obtained bearing an aldehyde group at each spirobifluorene branch, in positions 2′ and 7. Again, the C-C coupling reaction finally provided the targeted compound 5 (see experimental section for characterization of all the organic derivatives).
Treatment of compound 2 with the dimeric complex [MCp*(Cl)(µ-Cl)]2 (M = Ir, Rh) in presence of potassium acetate led to the formation of a mixture of [MCp*Cl(2-py-SBF)] (M = Ir (Ir6), Rh (Rh6)) and [MCp*(OCOCH3)(2-py-SBF)] (M = Ir (Ir7), Rh (Rh7)) (Cp* = pentamethylcyclopentadienyl, SBF = 9,9'-spirobifluorene) in an approximate 1:2 ratio for iridium and 1:1.5 ratio for rhodium, respectively(Scheme 2).This ratio was determined by integration at the 1 H NMR spectra using the Cp* signals as well as the resonance of the CH group directly bonded to the nitrogen atom of the pyridine moiety.Complex 7 stems from a competition between the starting dimers [MCp*(Cl)(µ-Cl)]2 (M = Ir, Rh) and complex 6 toward a reaction with KOAc.However, lower amounts of acetate or shorter reaction times led to lower conversions of the starting material with the same product ratio, and therefore, salt metathesis could not be avoided.For characterization, mass spectrometry was attempted.In the case of the rhodium complexes, the ionization provoked their decomposition, while for iridium, the release of the chloride or acetate ligand was observed with the molecular peak at m/z = 720.2218.However, the ligand exchange was suggested by the NMR spectra analysis for both transition metal complexes.Thus, two sets of signals are clearly identified for the iridium complexes in both 1 H and 13 C{ 1 H} NMR spectra in CD 2 Cl 2 .The acetate ligand is confirmed by the presence of resonance in the 1 H NMR spectrum at 1.66 ppm integrating by 3H and the carbon resonances in 13 C{ 1 H} NMR spectrum at 177.2 and 23.1 ppm for the carbonyl and the methyl groups, respectively.However, at rhodium complexes, the signals are overlapped in 1 H NMR where the methyl group of the acetate ligand confirm the presence of complex Rh7, and the integration of the signals together with the 13 C{ 1 H} NMR data allows the identification of both compounds.Apart from the acetate ligand of complex 7, the most characteristic resonances of 6 and 7 are the Cp* signal at around 1.7 ppm and the carbon resonance bonded to the metal (C3).The latter appears at around 164 ppm for iridium as a singlet and 179 ppm as a doublet of 32 Hz for the rhodium complexes due to the one-bond coupling of the carbon atom with the rhodium nucleus.
Finally, crystals adequate for X-ray diffraction analysis were obtained for complex 6 (Figure 2, left and center).In addition, low-quality crystals of Ir7 were also obtained.Although the latter are not suitable for publication, they confirmed the presence of the acetate ligand in the iridium coordination sphere instead of the chloride (Figure 2, right).The asymmetric unit of the metallacycle complexes Ir6 and Rh6 only contains the iridium or rhodium neutral complex.In both cases, it consists of the pentamethylcyclopentadienyl ligand η 5 -coordinated to the iridium atom and a chloride ligand.The metal atom forms part of a five-member ring due to the coordination of a spirobifluorene ortho substituted with a pyridine group in a chelating form to the metal.The five-member ring is almost planar with a deviation of the metal center of 0.099 Å or 0.133 Å for the iridium or the rhodium complex, respectively.Note that the coordination sphere presents a "three-ledge piano stool" structure in an octahedral arrangement.As shown in Table 1, both complexes present very similar bond lengths and angles despite the metal center change.The M-N bond lengths of 2.097(3) Å and 2.094(2) Å are longer than the M-C bond lengths of 2.047(3) Å and 2.027(2) Å with values in the range of those reported in literature for iridium and rhodium mononuclear complexes bearing other bidentate C-N ligands such as 2-phenylpyridinyl (ppy) or 2-(p-tolyl)pyridinyl [23][24][25].Also, the distance between the centroid (CT) of the Cp* ring and the metal center is 1.823 Å and 1.833 Å for iridium and rhodium, respectively.This value is slightly shorter than the 2.104 Å reported for [RhCp*(SPh)(ppy)] [23] but similar to other carbon-based metallacyclic systems [26,27].
Finally, crystals adequate for X-ray diffraction analysis were obtained for complex 6 (Figure 2, left and center).In addition, low-quality crystals of Ir7 were also obtained.Although the latter are not suitable for publication, they confirmed the presence of the acetate ligand in the iridium coordination sphere instead of the chloride (Figure 2, right).The asymmetric unit of the metallacycle complexes Ir6 and Rh6 only contains the iridium or rhodium neutral complex.In both cases, it consists of the pentamethylcyclopentadienyl ligand η 5 -coordinated to the iridium atom and a chloride ligand.The metal atom forms part of a five-member ring due to the coordination of a spirobifluorene ortho substituted with a pyridine group in a chelating form to the metal.The five-member ring is almost planar with a deviation of the metal center of 0.099 Å or 0.133 Å for the iridium or the rhodium complex, respectively.Note that the coordination sphere presents a "three-ledge piano stool" structure in an octahedral arrangement.As shown in Table 1, both complexes present very similar bond lengths and angles despite the metal center change.The M-N bond lengths of 2.097(3) Å and 2.094(2) Å are longer than the M-C bond lengths of 2.047(3) Å and 2.027(2) Å with values in the range of those reported in literature for iridium and rhodium mononuclear complexes bearing other bidentate C-N ligands such as 2-phenylpyridinyl (ppy) or 2-(p-tolyl)pyridinyl [23][24][25].Also, the distance between the centroid (CT) of the Cp* ring and the metal center is 1.823 Å and 1.833 Å for iridium and rhodium, respectively.This value is slightly shorter than the 2.104 Å reported for [RhCp*(SPh)(ppy)] [23] but similar to other carbon-based metallacyclic systems [26,27].In the search for an organometallic complex bearing an aldehyde group, the formylation reaction of complexes 6 and 7 was attempted without success.Therefore, organic compounds bearing an aldehyde substituent at the spirobifluorene moiety were chosen as ligands.Thus, the reaction of [MCp*(Cl)(µ-Cl)] 2 (M = Ir, Rh) with the spirobifluorenefunctionalized compound 3 in the presence of KOAc in CH 2 Cl 2 led to the synthesis of the new metallacyclic complexes (R,M)/(R,P)-[MCp*Cl(2 -CHO-2-py-SBF)] (M = Rh (Rh8), Ir (Ir8)).Similarly, (R,M)/(R,P)-[IrCp*Cl(2 ,7-di(CHO)-2-py-SBF)] (Ir9) was also synthesized from 5 (Scheme 3).Note that in these cases, the excess of potassium acetate in the reaction mixture did not produce the ligand exchange, and therefore, complexes bearing an acetate ligand were not observed.In addition, complexes 8 and Ir9 were obtained as a mixture of diastereomers in around a 60:40 ratio due to the presence of two chiral entities: the iridium atom and the chiral axis at the spirobifluorene moiety as a result of the different substitution at both branches.
compounds bearing an aldehyde substituent at the spirobifluorene moiety were chosen as ligands.Thus, the reaction of [MCp*(Cl)(µ-Cl)]2 (M = Ir, Rh) with the spirobifluorenefunctionalized compound 3 in the presence of KOAc in CH2Cl2 led to the synthesis of the new metallacyclic complexes (R,M)/(R,P)-[MCp*Cl(2′-CHO-2-py-SBF)] (M = Rh (Rh8), Ir (Ir8)).Similarly, (R,M)/(R,P)-[IrCp*Cl(2′,7-di(CHO)-2-py-SBF)] (Ir9) was also synthesized from 5 (Scheme 3).Note that in these cases, the excess of potassium acetate in the reaction mixture did not produce the ligand exchange, and therefore, complexes bearing an acetate ligand were not observed.In addition, complexes 8 and Ir9 were obtained as a mixture of diastereomers in around a 60:40 ratio due to the presence of two chiral entities: the iridium atom and the chiral axis at the spirobifluorene moiety as a result of the different substitution at both branches.Complexes 8 and Ir9 were fully characterized by NMR spectroscopy, mass spectrometry, and IR spectroscopy (see experimental for full details).Although the mass spectra show the corresponding isotopic pattern and molecular peak after losing the chloride ligand, the presence of diastereomers can only be determined by the NMR data.Thus, two sets of signals are observed for all the complexes.Particularly, the 1 H NMR spectra show two signals corresponding to the aldehyde group at 9.75 and 9.88 ppm for Ir8 and 9.77 and 9.86 ppm for Rh8, while complex Ir9 shows two resonances at 9.87 and 9.82 ppm for one diastereomer and two at 9.83 and 9.73 ppm for the other.Similarly, in 13 C{ 1 H} NMR the aldehydes group are also observed with resonances at 192.2 and 191.9 ppm for Ir8, 192.0 and 191.9 ppm for Rh8 and between 192.0 and 191.8 ppm, the four signals corresponding to Ir9.As happened before, the coordination of the spirobifluorene ligand is determined by the disappearance of the C-H resonance at position 3, while quaternary carbon atoms are observed at 166.8 and 166.7 ppm for Ir8 and 166.4 and 166.3 ppm for Ir9, all as singlets.For Rh8, again, two doublets of 30 Hz due to the coupling to the rhodium atom are observed at 180.0 and 179.9 ppm.Finally, the presence of the aldehyde group is Scheme 3. Synthesis of complexes 8 and Ir9.
Complexes 8 and Ir9 were fully characterized by NMR spectroscopy, mass spectrometry, and IR spectroscopy (see experimental for full details).Although the mass spectra show the corresponding isotopic pattern and molecular peak after losing the chloride ligand, the presence of diastereomers can only be determined by the NMR data.Thus, two sets of signals are observed for all the complexes.Particularly, the 1 H NMR spectra show two signals corresponding to the aldehyde group at 9.75 and 9.88 ppm for Ir8 and 9.77 and 9.86 ppm for Rh8, while complex Ir9 shows two resonances at 9.87 and 9.82 ppm for one diastereomer and two at 9.83 and 9.73 ppm for the other.Similarly, in 13 C{ 1 H} NMR the aldehydes group are also observed with resonances at 192.2 and 191.9 ppm for Ir8, 192.0 and 191.9 ppm for Rh8 and between 192.0 and 191.8 ppm, the four signals corresponding to Ir9.As happened before, the coordination of the spirobifluorene ligand is determined by the disappearance of the C-H resonance at position 3, while quaternary carbon atoms are observed at 166.8 and 166.7 ppm for Ir8 and 166.4 and 166.3 ppm for Ir9, all as singlets.For Rh8, again, two doublets of 30 Hz due to the coupling to the rhodium atom are observed at 180.0 and 179.9 ppm.Finally, the presence of the aldehyde group is also confirmed by the IR spectra with bands corresponding to the C=O stretching frequency at 1738 and 1691 cm −1 for Ir8 and Rh8, respectively, and 1690 and 1600 cm −1 for Ir9.
Once these complexes were characterized, their reactivity toward amines was studied.The synthesis of the Schiff bases implies the formation of stoichiometric amounts of water; however, it can be a reversible reaction in the presence of water traces.Therefore, treatment of complex Ir8 with an excess of amines and in the presence of activated molecular sieves can force the reaction leading to the imine complexes ) in the reaction mixture.Thus, aniline, o-phenylenediamine, and ethylenediamine were used as proof of concept performing the reaction in chloroform in one day, which provided different outcomes (Table 2).The reaction with the aromatic amines (entries 1 and 2) provided, at room temperature, quantitative conversion of complex Ir8 towards the formation of an imine substituent at the spirobifluorene moiety.However, the aliphatic amine did not react with complex Ir8 even at high temperatures (entries 3 and 4).Other common reaction conditions for the formation of organic imines, such as heating in ethanol or methanol in the presence of acetic acid as a catalyst (or without it), were also attempted without performing better.day, which provided different outcomes (Table 2).The reaction with the aromatic amines (entries 1 and 2) provided, at room temperature, quantitative conversion of complex Ir8 towards the formation of an imine substituent at the spirobifluorene moiety.However, the aliphatic amine did not react with complex Ir8 even at high temperatures (entries 3 and 4).Other common reaction conditions for the formation of organic imines, such as heating in ethanol or methanol in the presence of acetic acid as a catalyst (or without it), were also attempted without performing better.On the other hand, the rhodium complex Rh8 was not capable of activating aniline at room temperature and required heating to 343 K to form the imine quantitatively (entries 5 and 6).Interestingly, the metal change to rhodium allowed the reaction of ethylenediamine to form the corresponding imine complex at room temperature (entry 7).
In order to provide more anchor points for the amine, the complex bearing two aldehyde groups, Ir9, reacted toward aniline giving, after one day at room temperature, the diimine complex (R,M)/(R,P)-[IrCp*Cl(2',7-di(CH=NPh)-2-py-SBF)] (Ir13) (Scheme 4).As happened with complex Ir8, no reaction was observed for ethylenediamine.On the other hand, the rhodium complex Rh8 was not capable of activating aniline at room temperature and required heating to 343 K to form the imine quantitatively (entries 5 and 6).Interestingly, the metal change to rhodium allowed the reaction of ethylenediamine to form the corresponding imine complex at room temperature (entry 7).
In order to provide more anchor points for the amine, the complex bearing two aldehyde groups, Ir9, reacted toward aniline giving, after one day at room temperature, the diimine complex (R,M)/(R,P)-[IrCp*Cl(2 ,7-di(CH=NPh)-2-py-SBF)] (Ir13) (Scheme 4).As happened with complex Ir8, no reaction was observed for ethylenediamine.As it has been mentioned, the formation of complexes Ir10, Ir11, Ir13, Rh10 and Rh12 can be reversed, leading to instability and difficulties in the full characterization.In some cases, the excess amine was removed successfully, but during characterization, the equilibrium between aldehyde and imine was observed due to possible water traces even on a previously dried solvent.However, in all cases, the 1 H NMR spectra, together with 2D experiments and the IR spectra, allowed the identification of the characteristic resonances and confirmed their structure (Table 3).Note that, again, the complexes appear as diastereomers due to the stereogenic metal center and the axial chirality provided by the substitution pattern at the spirobifluorene moiety.As it has been mentioned, the formation of complexes Ir10, Ir11, Ir13, Rh10 and Rh12 can be reversed, leading to instability and difficulties in the full characterization.In some cases, the excess amine was removed successfully, but during characterization, the equilibrium between aldehyde and imine was observed due to possible water traces even on a previously dried solvent.However, in all cases, the 1 H NMR spectra, together with 2D experiments and the IR spectra, allowed the identification of the characteristic resonances and confirmed their structure (Table 3).Note that, again, the complexes appear as diastereomers due to the stereogenic metal center and the axial chirality provided by the substitution pattern at the spirobifluorene moiety.While the carbon resonances at position 3 in the 13 C{ 1 H} NMR spectrum are similar to the ones described for previous complexes, the CHO resonances at both 1 H and 13 C{ 1 H} NMR spectra disappear.Instead, new singlets in 1 H NMR spectra are observed between 8.00 and 8.40 ppm, which correlate in the HSQC NMR experiment with carbon resonances at around 160 ppm, confirming the presence of an imine substituent at the spirobifluorene moiety.For example, Figure 3 shows the correlation between the imine protons of both diastereomers and their carbon nucleus in complex Rh10.In addition, the C=O stretching band disappears at the IR spectra, and a new absorption band at around 1600 cm −1 is observed corresponding to the C=N stretching mode.

Materials and Methods
All experiments were carried out under an atmosphere of argon by Schlenk techniques.Solvents were dried by the usual procedures [28] and, prior to use, distilled under argon.All reagents were obtained from commercial sources.The starting material [MCp*(µ-Cl)Cl]2 (M = Ir, Rh) was prepared as described in the literature [29].Unless stated, NMR spectra were recorded in CD2Cl2 or CDCl3 at room temperature on a Bruker ARX-400 instrument with resonating frequencies of 400 MHz ( 1 H) and 100 MHz ( 13 C{ 1 H}) using the solvent as the internal lock. 1 H and 13 C{ 1 H} signals are referred to as internal TMS; downfield shifts (expressed in ppm) are considered positive. 1H and 13 C{ 1 H} NMR

Materials and Methods
All experiments were carried out under an atmosphere of argon by Schlenk techniques.Solvents were dried by the usual procedures [28] and, prior to use, distilled under argon.All reagents were obtained from commercial sources.The starting material [MCp*(µ-Cl)Cl] 2 (M = Ir, Rh) was prepared as described in the literature [29].Unless stated, NMR spectra were recorded in CD 2 Cl 2 or CDCl 3 at room temperature on a Bruker ARX-400 instrument with resonating frequencies of 400 MHz ( 1 H) and 100 MHz ( 13 C{ 1 H}) using the solvent as the internal lock. 1 H and 13 C{ 1 H} signals are referred to as internal TMS; downfield shifts (expressed in ppm) are considered positive. 1H and 13 C{ 1 H} NMR (or JMOD, J-modulated spin echo experiment) signal assignments were confirmed by { 1 H, 1 H} COSY, { 1 H, 1 H} NOESY, { 1 H, 13 C} HSQC, { 1 H, 13 C} HMBC, and/or DEPT experiments.Coupling constants are given in hertz.Mass spectra are referred to the most abundant isotopes and they were acquired using an Apex-Qe or a SolariX XR spectrometer by a high or low-resolution electrospray technique.IR spectra were measured on a Jasco FT/IR-6100 instrument.All the 1D NMR spectroscopy experiments and a comparison of some IR spectra can be found at the Supplementary Materials.
mixture was purged with N2 for 30 min.Then, the reaction was heated at 363 K for 24 h, and the formation of two yellow phases was observed.After cooling down the reaction mixture, the aqueous phase was extracted three times with CH2Cl2 and the organic phases were combined and washed twice with H2O and once with saturated NaCl.The resultant solution was dried with Na2SO4, and the volatiles were removed under vacuum.The crude product was purified through a chromatographic column (SiO2, hexane/AcOEt 95/5 to 85/15), affording 2 as a pale yellow solid (1.08 g, 2,74 mmol, 85%).This synthesis is based on the one found in the literature using the SBF-B(OH)2 derivative as a starting compound [31].
A solution of 2 (200 mg, 0.51 mmol) in CH 2 Cl 2 (10 mL) was stirred at 273 K for 5 min.Then, TiCl 4 (289 mg, 1.53 mmol) was added dropwise and stirred for 30 min at 273 K, leading to a purple solution.After that, CH 3 OCHCl 2 (176 mg, 1.53 mmol) was added, and the solution was warmed to 298 K overnight.After the reaction time, water was added at 273 K, the product was extracted three times with CH 2 Cl 2, and the organic phases were combined and washed twice with H 2 O and once with saturated NaCl.The resultant solution was dried with Na 2 SO 4, and the volatiles were removed under vacuum.The crude product was purified through a chromatographic column (SiO 2 , hexane/AcOEt 80/20 to 70/30), leading to a pale yellow solid after removing the volatiles (160 mg, 0.38 mmol, 74%).
Molecules 2023, 28, x FOR PEER REVIEW 10 of 20 A solution of 2 (200 mg, 0.51 mmol) in CH2Cl2 (10 mL) was stirred at 273 K for 5 min.Then, TiCl4 (289 mg, 1.53 mmol) was added dropwise and stirred for 30 min at 273 K, leading to a purple solution.After that, CH3OCHCl2 (176 mg, 1.53 mmol) was added, and the solution was warmed to 298 K overnight.After the reaction time, water was added at 273 K, the product was extracted three times with CH2Cl2, and the organic phases were combined and washed twice with H2O and once with saturated NaCl.The resultant solution was dried with Na2SO4, and the volatiles were removed under vacuum.The crude product was purified through a chromatographic column (SiO2, hexane/AcOEt 80/20 to 70/30), leading to a pale yellow solid after removing the volatiles (160 mg, 0.38 mmol, 74%).
ture was purged with N2 for 30 min.Then, the reaction was heated at 353 K for 48 h, and the formation of two yellow phases was observed.After cooling down the reaction mixture, the aqueous phase was extracted three times with CH2Cl2 and the organic phases were combined and washed twice with H2O and once with saturated NaCl.The resultant solution was dried with Na2SO4, and the volatiles were removed under vacuum.The crude product was purified through a chromatographic column (SiO2, hexane/AcOEt 75/25), affording 5 as a pale yellow solid (105 mg, 0.23 mmol, 73%).[MCp*Cl(µ-Cl)] 2 (M = Ir, Rh) (96 mg for Ir and 74 mg for Rh, 0.12 mmol) were dissolved in CH 2 Cl 2 (15 mL), and 2 (100 mg, 0.25 mmol) was added, followed by KOAc (30 mg, 0.30 mmol).After stirring for 24 h at room temperature, the color changed from orange to yellow (for Ir) or from red to orange (for Rh), and the solution was filtrated through Celite ® .Then, the volatiles were removed by vacuum.Later, pentane (3 × 5 mL) was added.For the rhodium complexes, products were washed with pentane, while for iridium, a partial extraction of them with pentane was achieved.In the latter case, the volatiles of pentane solution were, again, removed by vacuum, leading to a mixture of [IrCp*Cl(2-py-SBF)] (Ir6) and [IrCp*(OCOCH 3 )(2-py-SBF)] (Ir2) in a 1:3 ratio.Meanwhile, the solid that precipitates with pentane was dried in a vacuum, giving a mixture of  [MCp*Cl(µ-Cl)]2 (M = Ir, Rh) (96 mg for Ir and 74 mg for Rh, 0.12 mmol) were dissolved in CH2Cl2 (15 mL), and 2 (100 mg, 0.25 mmol) was added, followed by KOAc (30 mg, 0.30 mmol).After stirring for 24 h at room temperature, the color changed from orange to yellow (for Ir) or from red to orange (for Rh), and the solution was filtrated through Celite ® .Then, the volatiles were removed by vacuum.Later, pentane (3 × 5 mL) was added.For the rhodium complexes, products were washed with pentane, while for iridium, a partial extraction of them with pentane was achieved.In the latter case, the volatiles of pentane solution were, again, removed by vacuum, leading to a mixture of [IrCp*Cl(2-py-SBF)] (Ir6) and [IrCp*(OCOCH3)(2-py-SBF)] (Ir2) in a 1:3 ratio.Meanwhile, the solid that precipitates with pentane was dried in a vacuum, giving a mixture of [MCp*Cl(2-py-SBF)] (M = Rh (Rh6), Ir (Ir6)) and [MCp*(OCOCH3)(2-py-SBF)] (M = Rh (Rh7), Ir (Ir7)) in a 1:1.5 ratio for both Ir and Rh complexes.Crystals of Ir6, Ir7, and Rh6 were obtained from the slow evaporation of a CH2Cl2:hexane mixture.Isolated mass of Ir6 + Ir7: 168 mg.Isolated mass of Rh6 + Rh7: 149 mg.

Crystallography
Crystallographic data for complexes Ir6, Ir7, and Rh6 were collected on a Bruker D8 Venture Photon 100 CMOS diffractometer at 100 K using Mo-Kα radiation (λ = 0.71073 Å).The frames were integrated with the Bruker SAINT 6.01 [32] software package, and the data were corrected for absorption using the program SADABS-2016/2 [33].The structures were solved by direct methods using the program SHELXL-2018/3 [34].All nonhydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares calculations on F 2 using the program SHELXL-2018/3 [35].Hydrogen atoms were inserted at calculated positions and were constrained with isotropic thermal parameters.For Ir7, the high disorder was found in the nonsubstituted SBF branch, which does not allow data publication but supports the structure provided by the rest of the characterization data.The crystal data and structure refinement table can be found at the Supplementary Materials.

Conclusions
Iridium and rhodium metallacyclic complexes bearing spirobifluorene moiety [MCp*X(2-py-SBF)] (M = Rh, Ir; X = Cl, OAc)(6,7) have been synthesized and fully characterized.While these complexes cannot react towards amines, the inclusion of one or two aldehyde groups at the spirobifluorene moiety to give complexes 8 and 9 allowed such reactivity.The reaction took place through the condensation reaction of an aldehyde with aromatic or aliphatic amines leading to imine complexes (R,M)/(R,P)-[MCp*Cl(2 -CH=NR-2-py-SBF)] (M = Rh, Ir)(10-12) and (R,M)/(R,P)-[IrCp*Cl(2 , 7-di(CH=NPh)-2-py-SBF)](13) under mild conditions.Interestingly, the reactivity of these complexes toward each type of amine depends on the transition metal coordinated.Thus, rhodium complex Rh8 reacts with aliphatic amines, while both Ir8 and Ir9 react with aromatic ones.This selectivity could be the grounds for the synthesis of organometallic complexes based on C-N bidentate spirobifluorene ligands for the detection of aliphatic amines with rhodium and aromatic amines with iridium.

Figure 3 .
Figure 3. Section of the 1 H, 13 C HSQC NMR spectrum of complex Rh10.

Figure 3 .
Figure 3. Section of the 1 H, 13 C HSQC NMR spectrum of complex Rh10.
a Conversion of the organometallic complex determined by 1 H NMR spectroscopy in the presence of excess amine.

Table 3 .
Characteristic NMR and IR data of imine complexes.

Table 3 .
Characteristic NMR and IR data of imine complexes.
a Measured at 400 MHz in CD 2 Cl 2 , b In an ATR-diamond IR spectrometer.