Organoplatinum Chemistry Related to Alkane Oxidation: The Effect of a Nitro Substituent in Ligands Having an Appended Phenol Group

: The organoplatinum chemistry of the ligands 2-C 5 H 4 N-CH 2 -NH-C 6 H 3 -2-OH-5-X ( L1 , X = H; L3 , X = NO 2 ) and 2-C 5 H 4 N-CH=N-C 6 H 3 -2-OH-5-X ( L2 , X = H; L4 , X = NO 2 ), which contain an appended phenol substituent, is described. Comparisons are made between the ligands with amine or imine groups ( L1 , L3 vs. L2 , L4 ) and ligands with X = H or NO 2 ( L1 , L2 vs. L3 , L4 ), and major differences are observed. Thus, on reaction with the cycloneophylplatinum(II) complex [{Pt(CH 2 CMe 2 C 6 H 4 )( µ -SMe 2 )} 2 ], ligands L1 , L2 and L4 give the corresponding platinum(II) complexes [Pt(CH 2 CMe 2 C 6 H 4 )( κ 2 - N , N ′ - L )], containing a Pt ·· HO hydrogen bond, whereas L3 gives a mixture of isomeric platinum(IV) hydride complexes [PtH(CH 2 CMe 2 C 6 H 4 )( κ 3 - N , N ′ , O - L3-H )], which are formed by oxidative addition of the phenol O-H bond and which react further with oxygen to give [Pt(OH)(CH 2 CMe 2 C 6 H 4 )( κ 3 - N , N ′ , O - L3-H )]. The differences in reactivity are proposed to be due to the greater acidity of the nitro-substituted phenol groups in L3 and L4 and to the greater ability of the deprotonated amine ligand L3 over L4 to stabilize platinum(IV) by adopting the fac - κ 3 - N , N ′ , O - L3-H coordination mode.

Scheme 1.The ligands used in this work.
Scheme 1.The ligands used in this work.

The Ligand L4
The ligand L4 is known to form coordination complexes, but it has usually been prepared and used in situ [55][56][57] and, since several related imine derivatives are known to cyclize to the corresponding oxazoline [58][59][60][61], it was prepared and studied in solution.
In most solvents (CD 2 Cl 2 , CDCl 3 , (CD 3 ) 2 CO, (CD 3 ) 2 SO and CD 3 CN), L4 was present in the imine form as shown by the prominent singlet resonance for the imine N=CH proton (δ = 8.96 in CD 2 Cl 2 ) in the 1 H NMR spectrum.However, in CD 3 OD solution, an equilibrium mixture of L4 and the oxazoline isomer L5 was present in a ratio L4:L5 = 1:4 (Figure 1).The imine resonance for L4 was at δ = 8.93 and the corresponding proton for the oxazoline derivative L5 was at δ = 5.86.Following the evaporation of the solution and the dissolution of the solid in CD 2 Cl 2 , the 1 H NMR spectrum showed that complete isomerization of L5 back to L4 had occurred.DFT calculations predict that the preferred structure of L4 is the E-isomer [33], with the two nitrogen donor atoms (pyridyl and imine) in the anti conformation, whereas the syn conformation is required for chelation (calculated E-anti − E-syn = 3 kJ mol −1 ).In the gas phase, L4 is predicted to be more stable than L5 by 23 kJ mol −1 , but the difference in energy is less in polar solvents and L5 is calculated to be slightly more stable than L4 in methanol, consistent with the experimental observations.The calculations take no account of specific intermolecular hydrogen bonding interactions so are not expected to be accurate, but the trend is clear.

The Ligand L4
The ligand L4 is known to form coordination complexes, but it has usually been prepared and used in situ [55][56][57] and, since several related imine derivatives are known to cyclize to the corresponding oxazoline [58][59][60][61], it was prepared and studied in solution.
In most solvents (CD2Cl2, CDCl3, (CD3)2CO, (CD3)2SO and CD3CN), L4 was present in the imine form as shown by the prominent singlet resonance for the imine N=CH proton (δ = 8.96 in CD2Cl2) in the 1 H NMR spectrum.However, in CD3OD solution, an equilibrium mixture of L4 and the oxazoline isomer L5 was present in a ratio L4:L5 = 1:4 (Figure 1).The imine resonance for L4 was at δ = 8.93 and the corresponding proton for the oxazoline derivative L5 was at δ = 5.86.Following the evaporation of the solution and the dissolution of the solid in CD2Cl2, the 1 H NMR spectrum showed that complete isomerization of L5 back to L4 had occurred.DFT calculations predict that the preferred structure of L4 is the E-isomer [33], with the two nitrogen donor atoms (pyridyl and imine) in the anti conformation, whereas the syn conformation is required for chelation (calculated E-anti − E-syn = 3 kJ mol −1 ).In the gas phase, L4 is predicted to be more stable than L5 by 23 kJ mol −1 , but the difference in energy is less in polar solvents and L5 is calculated to be slightly more stable than L4 in methanol, consistent with the experimental observations.The calculations take no account of specific intermolecular hydrogen bonding interactions so are not expected to be accurate, but the trend is clear.

Model Platinum(IV) Complexes with Imine Ligand L2
The reaction of the complex [PtMe 2 (L2)], B (Scheme 2) [33] with methyl iodide or 3,5-di-t-butylbenzyl bromide gave the platinum(IV) complexes [PtIMe 3 (L2)], 1, or [PtBrMe 2 (CH 2 C 6 H 3 -3,5-t-Bu 2 )(L2)], 2, respectively (Scheme 3).The structures of complexes 1 and 2 (Figures 2 and 3) show that the L2 remains as a bidentate ligand and that the phenol forms an intramolecular hydrogen bond OH••IPt in 1 and OH••BrPt in 2. The geometrical constraints of the imine group make it difficult for the deprotonated L2 to act as a fac-N,N,O-tridentate ligand, as is often observed with the corresponding amine ligand L1 [40,41].This feature, which is established by the reactions of Scheme 2, will be important in later studies of reactivity with dioxygen.The platinum(IV) complexes 1 and 2 are chiral and this leads to non-equivalence of the benzylic CH 2 protons of complex 2, which appear as an AB multiplet in the 1 H NMR spectrum.
Inorganics 2024, 12, x FOR PEER REVIEW 4 of 1 L1 [40,41].This feature, which is established by the reactions of Scheme 2, will be im portant in later studies of reactivity with dioxygen.The platinum(IV) complexes 1 and are chiral and this leads to non-equivalence of the benzylic CH2 protons of complex 2 which appear as an AB multiplet in the 1 H NMR spectrum.Inorganics 2024, 12, x FOR PEER REVIEW 4 of 1 L1 [40,41].This feature, which is established by the reactions of Scheme 2, will be im portant in later studies of reactivity with dioxygen.The platinum(IV) complexes 1 and are chiral and this leads to non-equivalence of the benzylic CH2 protons of complex 2 which appear as an AB multiplet in the 1 H NMR spectrum.

Cycloneophyl Complexes with Imine Ligand L4
The reaction of [Pt2(CH2CMe2C6H4)2(μ-SMe2)2] [44] with ligand L4 gave the plati num(II) complex [Pt(CH2CMe2C6H4)(L4)], 3, as a single isomer (Scheme 4a).Complex was isolated as an orange-red solid, this color being characteristic of a platinum(II) com plex, and it was stable in dichloromethane solution for at least one day.The correspondin complex of the ligand L2, [Pt(CH2CMe2C6H4)(L2)], H, was reported previously and ha similar spectroscopic properties [38].The observation of the imine proton in the 1 H NMR spectrum of 3 [δ( 1 H) = 9.58 (s, 3 J(PtH) = 25 Hz)] proves that the imine structure is main tained.Both complexes 3 and H give very broad resonances for the PtCH2 protons of th cycloneophyl group due to fluxionality.The formation of the OH .. Pt hydrogen bond lead to a loss of the effective plane of symmetry and thus to non-equivalence of the PtCH A H protons of the cycloneophyl group, and cleavage of the hydrogen bond is required t make them equivalent (Scheme 4b).As seen in variable-temperature NMR studies, th value of the activation energy for fluxionality for 3 was ΔG † = 60(1) kJ mol −1 , compared t the value of ΔG † = 55(1) kJ mol −1 for complex H [38].The difference can be attributed to th greater acidity of L4 compared to L2, leading to a stronger OH .. Pt hydrogen bond in 3 tha in H.However, this nitro group effect is not great enough to cause complete proton trans fer to platinum to form a platinum(IV) hydride.

Cycloneophyl Complexes with Imine Ligand L4
The reaction of [Pt 2 (CH 2 CMe 2 C 6 H 4 ) 2 (µ-SMe 2 ) 2 ] [44] with ligand L4 gave the platinum(II) complex [Pt(CH 2 CMe 2 C 6 H 4 )(L4)], 3, as a single isomer (Scheme 4a).Complex 3 was isolated as an orange-red solid, this color being characteristic of a platinum(II) complex, and it was stable in dichloromethane solution for at least one day.The corresponding complex of the ligand L2, [Pt(CH 2 CMe 2 C 6 H 4 )(L2)], H, was reported previously and has similar spectroscopic properties [38].The observation of the imine proton in the 1 H NMR spectrum of 3 [δ( 1 H) = 9.58 (s, 3 J(PtH) = 25 Hz)] proves that the imine structure is maintained.Both complexes 3 and H give very broad resonances for the PtCH 2 protons of the cycloneophyl group due to fluxionality.The formation of the OH••Pt hydrogen bond leads to a loss of the effective plane of symmetry and thus to non-equivalence of the PtCH A H B protons of the cycloneophyl group, and cleavage of the hydrogen bond is required to make them equivalent (Scheme 4b).As seen in variable-temperature NMR studies, the value of the activation energy for fluxionality for 3 was ∆G † = 60(1) kJ mol −1 , compared to the value of ∆G † = 55(1) kJ mol −1 for complex H [38].The difference can be attributed to the greater acidity of L4 compared to L2, leading to a stronger OH••Pt hydrogen bond in 3 than in H.However, this nitro group effect is not great enough to cause complete proton transfer to platinum to form a platinum(IV) hydride.
The reaction of complex 3 with methyl iodide gave the platinum(IV) complex [PtIMe (CH 2 CMe 2 C 6 H 4 )(L4)], 4, as a mixture of two isomers 4a and 4b (Scheme 4a), with a ratio 4a:4b of approximately 1:2.When the reaction was monitored by 1 H NMR spectroscopy, the first product formed was 4a and it equilibrated with 4b over a period of one hour.The methylplatinum resonances were observed at δ 1.81, 2 J(PtH) = 72 Hz, and at δ 1.22, 2 J(PtH) = 72 Hz, for 4a and 4b, respectively.Both isomers are chiral and so the methylene protons of the cycloneophyl group appear as AB multiplets.The imine protons were observed at δ 8.84, 3 J(PtH) = 20 Hz, and at δ 9.07, 3 J(PtH) = 18 Hz, for 4a and 4b, respectively.

Cycloneophyl Complexes with Ligand L3
The reaction of [Pt2(CH2CMe2C6H4)2(μ-SMe2)2] with ligand L3 was more complex and was solvent-dependent.The reaction in acetone solution gave a mixture of five com pounds, perhaps isomers, in a ratio of about 10:6:1:1:0.4,characterized in the 1 H NMR spectrum of the mixture by the ortho pyridyl proton resonance at δ(H6) = 8.77, 9.06, 9.18 8.88 and 8.92, respectively.The compounds could not be identified by their NMR spectra but recrystallisation from methanol gave crystals of the major isomer, which was identi fied as [Pt(OH)(CH2CMe2C6H4)(L3-H)], 5, as the methanol solvate, via X-ray structure de termination (Scheme 5, Figures 4 and 5).The formation of complex 5 involves the activa tion of dioxygen and is analogous to the formation of complex F (Scheme 2), although in that case it was a different isomer that crystallized [37].As in related systems, the reaction is likely to involve a shortlived hydroperoxide complex intermediate [21][22][23][24][62][63][64], which might be formed either by the direct reaction of dioxygen with the platinum(II) precurso or by the insertion of dioxygen into a hydridoplatinum(IV) intermediate [24,28,32,62].In both complexes 5 and F, the deprotonated ligand L3-H acts as a fac-κ 3 -N,N′,O tridentat ligand, a geometry that has not been observed with platinum(IV) complexes of the imin ligand L4.In the crystal, complex 5 forms a hydrogen-bonded supramolecular polymeri structure.There are dimer units formed by complementary hydrogen bonding N(2)H .. O(2B) and N(2A)H .. O(2) groups, with NH groups as H-bond donors and PtOH groups as acceptors (Figure 5).These dimer units were connected to neighbors by inter

Cycloneophyl Complexes with Ligand L3
The reaction of [Pt 2 (CH 2 CMe 2 C 6 H 4 ) 2 (µ-SMe 2 ) 2 ] with ligand L3 was more complex and was solvent-dependent.The reaction in acetone solution gave a mixture of five compounds, perhaps isomers, in a ratio of about 10:6:1:1:0.4,characterized in the 1 H NMR spectrum of the mixture by the ortho pyridyl proton resonance at δ(H6) = 8.77, 9.06, 9.18, 8.88 and 8.92, respectively.The compounds could not be identified by their NMR spectra, but recrystallisation from methanol gave crystals of the major isomer, which was identified as [Pt(OH)(CH 2 CMe 2 C 6 H 4 )(L3-H)], 5, as the methanol solvate, via X-ray structure determination (Scheme 5, Figures 4 and 5).The formation of complex 5 involves the activation of dioxygen and is analogous to the formation of complex F (Scheme 2), although in that case it was a different isomer that crystallized [37].As in related systems, the reaction is likely to involve a shortlived hydroperoxide complex intermediate [21][22][23][24][62][63][64], which might be formed either by the direct reaction of dioxygen with the platinum(II) precursor or by the insertion of dioxygen into a hydridoplatinum(IV) intermediate [24,28,32,62].In both complexes 5 and F, the deprotonated ligand L3-H acts as a fac-κ 3 -N,N ′ ,O tridentate ligand, a geometry that has not been observed with platinum(IV) complexes of the imine ligand L4.In the crystal, complex 5 forms a hydrogen-bonded supramolecular polymeric structure.There are dimer units formed by complementary hydrogen bonding N( 2     The reaction of [Pt 2 (CH 2 CMe 2 C 6 H 4 ) 2 (µ-SMe 2 ) 2 ] with ligand L3 in CD 2 Cl 2 solution, as monitored by 1 H NMR spectroscopy under nitrogen, was also complex (Figure 6).After five minutes reaction time, the dimethylsulfide ligands had been displaced to give a mixture of four isomeric platinum(IV) hydride complexes [PtH(CH 2 CMe 2 C 6 H 4 )(L3-H)], 7.These isomers were initially formed in abundances 7a (72%), 7b (21%), 7c (4%) and 7d (3%) as determined by the integration of the characteristic PtH resonances for 7a (δ = −18.81, 1 J(PtH) = 1479 Hz), 7b (δ = −21.23, 1 J(PtH) = 1449 Hz), 7c (δ = −18.86, 1 J(PtH) = 1480 Hz) and 7d (δ = −19.42, 1 J(PtH) = 1434 Hz).After 40 min and after 24 h, these isomers remained but the abundances changed to 7a (20%), 7b (60%), 7c (10%) and 7d (10%) and to 7a (10%), 7b (60%), 7c (10%) and 7d (20%), respectively.No further change in isomer ratio occurred, but slow decomposition occurred over a period of weeks.What is clear from these data is that 7a and 7b are the major isomers of kinetic and thermodynamic control, respectively, and that the interconversion of isomers is relatively slow at room temperature.However, it is more challenging to assign the structures of the isomers or to determine the mechanisms of both the initial reaction and the subsequent isomerization steps.The reaction of [Pt2(CH2CMe2C6H4)2(μ-SMe2)2] with ligand L3 in CD2Cl2 solution, a monitored by 1 H NMR spectroscopy under nitrogen, was also complex (Figure 6).Afte five minutes reaction time, the dimethylsulfide ligands had been displaced to give a mix ture of four isomeric platinum(IV) hydride complexes [PtH(CH2CMe2C6H4)(L3-H)], 7 These isomers were initially formed in abundances 7a (72%), 7b (21%), 7c (4%) and 7d (3%) as determined by the integration of the characteristic PtH resonances for 7a (δ −18.81, 1 J(PtH) = 1479 Hz), 7b (δ = −21.23, 1 J(PtH) = 1449 Hz), 7c (δ = −18.86, 1 J(PtH) = 148 Hz) and 7d (δ = −19.42, 1 J(PtH) = 1434 Hz).After 40 min and after 24 h, these isomers re mained but the abundances changed to 7a (20%), 7b (60%), 7c (10%) and 7d (10%) and t 7a (10%), 7b (60%), 7c (10%) and 7d (20%), respectively.No further change in isomer rati occurred, but slow decomposition occurred over a period of weeks.What is clear from these data is that 7a and 7b are the major isomers of kinetic and thermodynamic contro respectively, and that the interconversion of isomers is relatively slow at room tempera ture.However, it is more challenging to assign the structures of the isomers or to deter mine the mechanisms of both the initial reaction and the subsequent isomerization steps Some suggestions of likely mechanisms, based on the experimental observations and on DFT calculations (see experimental section for details), are summarized in Schemes 6 and 7. I is likely that the first step is the displacement of the dimethylsulfide ligands from [Pt 2 (CH 2 CMe 2 C 6 H 4 ) 2 (µ-SMe 2 ) 2 ] by the ligand L3 to give [Pt(CH 2 CMe 2 C 6 H 4 )(L3)], which may exist as isomers 6 and 6a (Scheme 6).In most analogous complexes (e.g., complexes 3 and H), the isomer with the aryl group trans to the pyridyl group is preferred, but the presence of strong OH••Pt hydrogen bond leads to the distortion of the square planar stereochemistry so that 6 and 6a are calculated to have the same energy.Concerted oxidative addition of the O-H bond to platinum(II) might then give isomers 7a-7d, with 7a predicted to be the kinetically favored product (Scheme 6).Complexes 7a-7c are predicted to be accessible directly from 6 or 6a, but the activation energy for the formation of 7d from 6 is predicted to be too high to allow the formation of 7d at room temperature (Scheme 6).A subsequent pairwise exchange between hydride and alkyl or aryl groups can lead to subsequent isomerization steps, as illustrated in Scheme 7 [37].The lowest energy isomers are predicted to be 7b and 7d, with CH 2 trans to O, while the highest energy isomers are 7e and 7f, with hydride trans to O.These isomers 7e and 7f were not observed, and they are expected to be present in only very low concentration at equilibrium.There are also potential isomers with hydride trans to CH 2 or C 6 H 4 , but these are predicted to lie at a higher energy and are not accessible.Some suggestions of likely mechanisms, based on the experimental observations and on DFT calculations (see experimental section for details), are summarized in Schemes 6 and 7.It is likely that the first step is the displacement of the dimethylsulfide ligands from [Pt2(CH2CMe2C6H4)2(μ-SMe2)2] by the ligand L3 to give [Pt(CH2CMe2C6H4)(L3)], which may exist as isomers 6 and 6a (Scheme 6).In most analogous complexes (e.g., complexes 3 and H), the isomer with the aryl group trans to the pyridyl group is preferred, but the presence of strong OH .. Pt hydrogen bond leads to the distortion of the square planar ste reochemistry so that 6 and 6a are calculated to have the same energy.Concerted oxidative addition of the O-H bond to platinum(II) might then give isomers 7a-7d, with 7a predicted to be the kinetically favored product (Scheme 6).Complexes 7a-7c are predicted to be accessible directly from 6 or 6a, but the activation energy for the formation of 7d from 6 is predicted to be too high to allow the formation of 7d at room temperature (Scheme 6).A subsequent pairwise exchange between hydride and alkyl or aryl groups can lead to sub sequent isomerization steps, as illustrated in Scheme 7 [37].The lowest energy isomers are predicted to be 7b and 7d, with CH2 trans to O, while the highest energy isomers are 7e and 7f, with hydride trans to O.These isomers 7e and 7f were not observed, and they are expected to be present in only very low concentration at equilibrium.There are also po tential isomers with hydride trans to CH2 or C6H4, but these are predicted to lie at a highe energy and are not accessible.

A Comparison of Complexes with L3 and L4
In complexes such as 7, in Schemes 6 and 7, the hydride and carbon donors have a strong preference for the fac stereochemistry and so, to accommodate this, the deprotonated ligand L3-H must also take the fac stereochemistry.This is easily achieved with the amine ligand L3 but not with the imine ligand L4, in which the planar imine unit leads to strain in the fac-PtN,N',O coordination mode.In stable organoplatinum(IV) complexes with the imine ligands L2 and L4, there is typically a halide ligand and the intact phenol unit forms a hydrogen bond OH••XPt, as in complexes 1, 2 and 4 (Schemes 3 and 4).On the other hand, the deprotonated imine ligands are better suited to act as tridentate pincer ligands in platinum(II) complexes.These trends are supported by DFT calculations illustrated in Figure 7.The intramolecular oxidative addition of the O-H bond of complex 6 to give isomers of 7 (illustrated by 7c in Figure 7, see also Scheme 7) is favorable, but a similar reaction of the imine complex 3 is unfavorable, in agreement with the observation that the hydridoplatinum(IV) complex [PtH(CH 2 CMe 2 C 6 H 4 )(L4-H)], J, or its isomers, is not observed.The potential reductive elimination from complex 7 might give either [Pt(CH 2 CMe 2 Ph)(L3-H)] or [Pt(C 6 H 4 -2-t-Bu)(L3-H)], I, by a combination of the hydride with sp 2 or sp 3 carbon donors, respectively.Complex I is calculated to be more stable, but its formation from 7 is still not favored, consistent with the observation that isomers of 7 are stable at room temperature.In contrast, the reductive elimination of J to give [Pt(C 6 H 4 -2-t-Bu)(L3-H)], K, is calculated to be strongly favored as the strained fac stereochemistry of L3-H in J is replaced by the planar pincer stereochemistry in K.Although K is the most stable isomer, it is not formed at room temperature due to the high activation energy needed to reach the likely intermediate J (Figure 7).Scheme 7. A possible sequence of isomerization of isomers of complex 7 from the kinetic produc 7a, and the calculated relative energies of the isomers.

A Comparison of Complexes with L3 and L4
In complexes such as 7, in Schemes 6 and 7, the hydride and carbon donors have a strong preference for the fac stereochemistry and so, to accommodate this, the deproto nated ligand L3-H must also take the fac stereochemistry.This is easily achieved with th amine ligand L3 but not with the imine ligand L4, in which the planar imine unit leads to strain in the fac-PtN,N',O coordination mode.In stable organoplatinum(IV) complexe with the imine ligands L2 and L4, there is typically a halide ligand and the intact pheno unit forms a hydrogen bond OH .. XPt, as in complexes 1, 2 and 4 (Schemes 3 and 4).On th other hand, the deprotonated imine ligands are better suited to act as tridentate pince ligands in platinum(II) complexes.These trends are supported by DFT calculations illus trated in Figure 7.The intramolecular oxidative addition of the O-H bond of complex 6 to give isomers of 7 (illustrated by 7c in Figure 7, see also Scheme 7) is favorable, but a simila Scheme 7. A possible sequence of isomerization of isomers of complex 7 from the kinetic product 7a, and the calculated relative energies of the isomers.
its formation from 7 is still not favored, consistent with the observation that isomers of 7 are stable at room temperature.In contrast, the reductive elimination of J to give [Pt(C6H4-2-t-Bu)(L3-H)], K, is calculated to be strongly favored as the strained fac stereochemistry of L3-H in J is replaced by the planar pincer stereochemistry in K.Although K is the most stable isomer, it is not formed at room temperature due to the high activation energy needed to reach the likely intermediate J (Figure 7).

Materials and Methods
The , and ligands L1-L4 [34,37,38,55] were prepared using the literature methods.NMR spectra were recorded using a Varian Inova 400 NMR or a Varian Inova 600 NMR spectrometer at room temperature and were reported using the labeling system of Scheme 8. Assignments were assisted by recording the COSY spectra.

Materials and Methods
The compounds , and ligands L1-L4 [34,37,38,55] were prepared using the literature methods.NMR spectra were recorded using a Varian Inova 400 NMR or a Varian Inova 600 NMR spectrometer at room temperature and were reported using the labeling system of Scheme 8. Assignments were assisted by recording the COSY spectra.

Structure determinations.
Typically, a sample single crystal was mounted on a Mitegen polyimide micromount with a small amount of Paratone N oil.All X-ray measurements were made by using a Bruker Kappa Axis Apex2 diffractometer at a temperature of 110 K.The data collection strategy was a number of ω and φ scans and frame integration was performed using SAINT [66].The resulting raw data were scaled and absorption corrected using a multiscan averaging of symmetry-equivalent data using SADABS [67].The structures were solved by using a dual space methodology using the SHELXT program [68].The hydrogen atoms were introduced at idealized positions and were allowed to ride on the parent atom.The structures were refined using the SHELXL program from the SHELX-2014 suite of crystallographic software [69].Details of individual structure determinations are given in the cif files (CCDC 2243128-2243130).
The DFT calculations were carried out using the NEB (nudged elastic band) method Scheme 8. NMR labeling scheme.

Structure determinations.
Typically, a sample single crystal was mounted on a Mitegen polyimide micromount with a small amount of Paratone N oil.All X-ray measurements were made by using a Bruker Kappa Axis Apex2 diffractometer at a temperature of 110 K.The data collection strategy was a number of ω and φ scans and frame integration was performed using SAINT [66].The resulting raw data were scaled and absorption corrected using a multiscan averaging of symmetry-equivalent data using SADABS [67].The structures were solved by using a dual space methodology using the SHELXT program [68].The hydrogen atoms were introduced at idealized positions and were allowed to ride on the parent atom.
The structures were refined using the SHELXL program from the SHELX-2014 suite of crystallographic software [69].Details of individual structure determinations are given in the cif files (CCDC 2243128-2243130).
The DFT calculations were carried out using the NEB (nudged elastic band) method for finding the minimum energy reaction paths because this method can roughly track the reaction coordinate and gives good insight into the reaction mechanism [70,71].The BLYP functional was used, with double-zeta basis set and first-order scalar relativistic corrections [72].The solvent effect of dichloromethane was modeled by using COSMO [73], all as implemented in ADF-2020 [74].Details of the calculated ground state and transition state structures are given in the Supporting Information.

Inorganics 2024 , 18 Scheme 6 .
Scheme 6.A possible route for the formation of isomers of complex 7, and their calculated relative energies.The signs * or ** indicate a transition state structure.Scheme 6.A possible route for the formation of isomers of complex 7, and their calculated relative energies.The signs * or ** indicate a transition state structure.