Synthesis of Quinoline-Based Pt–Sb Complexes with L- or Z-Type Interaction: Ligand-Controlled Redox via Anion Transfer

A series of Pt–Sb complexes with two or three L-type quinoline side arms were prepared and studied. Two ligands, tri(8-quinolinyl)stibane (SbQ3, Q = 8-quinolinyl, 1) and 8,8′-(phenylstibanediyl)diquinoline (SbQ2Ph, 2), were used to synthesize the PtII–SbIII complexes (SbQ3)PtCl2 (3) and (SbQ2Ph)PtCl2 (4). Chloride abstraction with AgOAc provided the bis-acetate complexes (SbQ3)Pt(OAc)2 (5) and (SbQ2Ph)Pt(OAc)2 (6). To better understand the electronic effects of the Sb moiety, analogous bis-chloride complexes were oxidized to an overall formal oxidation state of +7 (i.e., Pt + Sb formal oxidation states = 7) using dichloro(phenyl)-λ3-iodane (PhICl2) and 3,4,5,6-tetrachloro-1,2-dibenzoquinone (o-chloranil) as two-electron oxidants. Depending on the oxidant, different conformational changes occur within the coordination sphere of Pt as confirmed by single-crystal X-ray diffraction and NMR spectroscopy. In addition, the nature of Pt–Sb interactions was evaluated via molecular and localized orbital calculations.


■ INTRODUCTION
−43 Based on the covalent bond classification (CBC) method published by Green, in general, the 2-center-2electron bonding interactions between the metal center and the ligand can be classified into three types, which are known as the L-type, X-type, and Z-type interactions. 44Ligands of Ltype are considered neutral two-electron donors to the metal center, and X-type ligands are defined as forming a bond with one electron from the metal center and one electron from the ligand to form a covalent bond. 44Z-type ligands are defined to form bonds with a metal through the donation of an electron pair from the metal center to an empty ligand orbital. 44,45In this article, we specifically discuss the Z-type interactions in σsymmetry, for which a Z-type ligand is referred to as a σacceptor ligand.Among examples of Z-type ligands, side-arm ligands with P and S donors are common auxiliary chelating functional groups used to position the Z-type moiety. 19ompared to these, N-based donors, such as quinoline and amines, appear to be less common; however, examples of cisbidentate ligands with one amine/quinoline arm that position the L-type Sb III center within the coordination sphere of ligated metals have been reported (Figure 1b). 40,41,46eviously, examples of Sb-based ligands with redox and coordination non-innocent features have been demonstrated. 17,47,48−51 In addition, their studies have demonstrated that by abstracting the halides from Sb V , the lowest unoccupied molecular orbital (LUMO) on Sb can be stabilized, which results in an increase in Lewis acidity of the Sb center that leads to differences in the catalytic activity of Pt complexes (Figure 1c). 42The Wagler group has utilized Mossbauer spectroscopy coupled with DFT calculations to fully characterize and assign the full spectrum of L-, X-and Z-type bonding interactions between Pt and Sb with pyridine-2-thiolate supporting ligands (Figure 1d). 43−64 By synthesizing different capping arene motifs, M−arene distances can be  controlled and thus offer tunable steric bulk and metal−arene interactions (Figure 2, left).For example, we reported the influence of the capping arene ligand structure on the rate of reductive elimination from Rh III , 53 Rh-catalyzed olefin hydrogenation, 55 and Co-catalyzed water oxidation. 57uilding on the "capping arene" structure and the notion of tuning reactivity with the donor/withdrawing ability of the arene group, we found an analogy to Sb III /Sb V donor (L-type) or acceptor (Z-type) motifs (Figure 2, right).Antimony was selected for our studies due to its strong Lewis acidity (based on the fluoride ion affinity) 65,66 and tunable σ-donation/ accepting ability (varied by control of the Sb oxidation state, e.g., Sb III vs Sb V ).
8][49][50]67 Herein, we report a series of Pt−Sb complexes with the ligands bonding in bi-, tri-, and tetradentate coordination modes in which the Sb center is in +3 to +5 formal oxidation states.

■ RESULTS AND DISCUSSION
Synthesis and Characterization of Sb III Ligands.Two quinoline-appended Sb III ligands with a variable number of Ndonor side arms, tri(quinolin-8-yl)-λ 3 -stibane (SbQ 3 , 1) and di(quinolin-8-yl)-phenyl-λ 3 -stibane (SbQ 2 Ph, 2), were synthesized (Scheme 1a).The proligands 1 and 2 offer potential tetradentate and tridentate coordination, respectively.The use of quinoline-based Sb ligands has been explored previously by the Wright group who utilized 2-methylquinoline Sb ligands to bind various coinage metals including Ag I , Au I , and Cu I . 68ompound 1 was isolated in multigram scale with an isolated yield of 57% from the treatment of SbCl 3 with three equivalents of 8-lithio-quinoline.Compound 2 was synthesized in a similar manner using SbPhCl 2 and two equivalents of 8lithio-quinoline with a 45% isolated yield.
Both proligands exhibited stability in the presence of air and moisture (a characteristic also indicated by quinolineappended Sb ligands from the Wright group) 68 and could be washed with water quickly with no significant impurity formation.The solid-state structures of compounds 1 and 2 indicated trigonal pyramidal geometries, which is consistent with the presence of a Sb III center (Scheme 1b).The solid-state structures of 3 and 4 were determined by single-crystal X-ray diffraction (Figure 3).The Pt−Sb bond distances for 3 and 4 are 2.4556(4) and 2.4500(8) Å, respectively, which are shorter than the sum of Sb and Pt covalent radii (i.e., 2.75 Å).Thus, the Pt−Sb distances are consistent with a bonding interaction.The Pt−Cl bond length of the chloride trans to Sb is slightly longer than that of the cis-Scheme 2. Synthetic Routes for Pt−Sb Complexes (SbQ 3 )PtCl 2 (3), (SbQ 2 Ph)PtCl 2 (4), (SbQ 3 )Pt(OAc) 2 (5), and (SbQ 2 Ph)Pt(OAc) 2 (6) from SbQ 3 (1) and SbQ 2 Ph (2) (OAc = acetate) Figure 3. ORTEPs of (SbQ 3 )PtCl 2 (3) and (SbQ 2 Ph)PtCl 2 (4).Ellipsoids are drawn at 50% probability level, and hydrogen atoms and noncoordinating solvents are omitted for clarity.chloride with distances of 2.3818(14) versus 2.2962(13) Å for complex 3 and 2.370(2) versus 2.297(2) Å for complex 4 (Table 1).For complexes 3 and 4, both ligands coordinate to the Pt center in a bidentate fashion, with Pt bound to Sb and the nitrogen atom from one of the quinoline side arms, while the other quinoline side arm(s) is uncoordinated.This results in a square planar geometry for the Pt center, which is commonly observed for L-type bidentate pnictogen Pt II complexes. 69he 1 H NMR spectrum of complex 3 shows two groups of proton resonances attributed to the quinolines with an approximate 2-to-1 integrated ratio.This observation is consistent with the solid-state structure, which includes one coordinated quinoline side arm and two chemically equivalent uncoordinated quinoline groups.The proton resonances belonging to the coordinated quinoline are shifted downfield, while the chemical shifts of the uncoordinated quinoline groups are similar to the free ligand.The 1 H NMR spectrum of 4 is consistent with the X-ray structure that includes an uncoordinated quinoline side arm.
The Pt carboxylate complexes (SbQ 3 )Pt(OAc) 2 ( 5) and (SbQ 2 Ph)Pt(OAc) 2 (6) were synthesized by the treatment of complex 3 or 4, respectively, with 2.1 equiv of AgOAc in dichloromethane (DCM) at room temperature (Scheme 2).The X-ray structures of both 5 and 6 indicate similar acetate binding modes except for an apparent interaction between one acetate bridging Pt and Sb in 6 (Figure 4).Complex 6 has disordered Pt−Sb atoms, resulting in two separate bond distances in the structure.In complexes 5 and 6, the lengths of the Pt−O bonds trans to the Sb center are 2.1104(14) and 2.141(5)/2.103(3)Å, respectively.In contrast, the acetate ligands cis to Sb have slightly shorter Pt−O bond distances ranging from 1.979(5) to 2.0037(14) Å, which suggests a stronger trans influence of Sb compared to quinoline.The distance between the Sb and O2 atom is 2.6948(14) Å for 5 and ranged from 2.457(7) to 2.531(3) Å for 6 (Table 2), and both Sb1•••O2 distances are longer than the sum of Sb and oxygen covalent radii (i.e., 2.05 Å).The distinct bond lengths in the crystal structures between O1−C and O2−C (Table 2) suggest that there is little resonance delocalization across the acetate ligand.We speculate that the acetate ligand can transfer between Pt and Sb centers via the formation of a paddlewheeltype structure.Similar examples have been reported before with bridging pyS ligands. 43n the 1 H NMR spectra of complexes 5 and 6, the most downfield-shifted resonance, assigned as the quinoline proton ortho to the nitrogen (H a ), has a chemical shift of ∼10 ppm.However, in complexes 3 and 4, the corresponding proton resonances exhibit an uncommon downfield chemical shift >11 ppm, as shown in Figure 5 labeled with a blue arrow (complex 3 vs 5).The downfield shifts for 3 and 4 are likely attributable to the close through-space distance between H a and Cl2 on Pt that is trans to the Sb center (Table 1).In the 1 H NMR spectra of 5 and 6, two proton resonances have been observed for the coordinated acetate (2.26 and 1.96 ppm for 5; 2.37 and 2.10    5) and (SbQ 2 Ph)Pt(OAc) 2 (6).Ellipsoids are drawn at the 50% probability level.Some of the hydrogen atoms, the non-coordinating solvents, and the minor position of the disordered atoms (6) are omitted for clarity.ppm for 6).In addition, EXSY experiments have been completed, and the data are consistent with no exchange between the two coordinated acetates (Supporting Information, Section 8).Reactions with Chemical Oxidants.To obtain Pt → Sb complexes with a formal Sb V center, iodobenzene dichloride (PhICl 2 ) and 3,4,5,6-tetrachloro-1,2-dibenzoquinone (o-chloranil) were tested as oxidants with complexes 3 and 4 (Scheme 3).Using PhICl 2 as the oxidant with either complex 3 or 4 generated a mixture of products due to the redox of both the Pt and Sb centers in which the Sb center served as either a Z-, X-, or L-type ligand; in contrast, the chelating oxidant, ochloranil, led to the formation of single products with selective oxidation of solely the Sb center (see below).
Reacting complex 3 with PhICl 2 in DCM or chloroform at room temperature resulted in the formation of a white solid precipitate, Cl 2 SbQ 3 PtCl 2 (7), as the major isolated product.During the in situ 1 H NMR studies, an intermediate, likely ClSbQ 3 PtCl 3 (8), was observed.This complex converts to complex 7 (see Supporting Information, Section 2).Complex 7 has poor solubility in most NMR solvents, but with dimethyl sulfoxide (DMSO) it results in the conversion to a different complex likely due to the solvent (i.e., DMSO) coordination.By using CDCl 3 , in which complex 7 is slightly soluble, a 1 H NMR spectrum of 7 was obtained; however, a small amount of complex 8 remains in the solution as an impurity.The solidstate structures of complexes 7 (Figure 6, left) and 8 (Figure S2) have been confirmed by X-ray crystallography.The observed 1 H NMR spectrum of complex 7 is consistent with the solid-state crystal structure in which two groups of quinoline proton resonances are observed with a 2-to-1 integration ratio.
Similar to complex 3, the oxidation of complex 4 using PhICl 2 results in two products based on 1 H NMR spectroscopy (Scheme 3).One of the formed products, which we propose is (Cl 2 SbQ 2 Ph)PtCl 2 (9), is soluble in CDCl 3 , while the other product, (ClSbQ 2 Ph)PtCl 3 (10), has poor solubility and forms a white precipitate during the reaction in DCM or chloroform.The crystal structure of complex 10 (Figure 6, right) shows a coordination mode similar to that of complex 8 for which three chlorides coordinate to the Pt center and one chloride coordinates to the Sb center.The observed 1 H NMR spectrum of complex 10 is consistent with the solid-state crystal structure in which only one group of quinoline proton resonances is observed due to symmetry.Although we were unable to characterize 9 with single-crystal X-ray diffraction, due to the conversion from 9 to 10, we propose that 9 has two chlorides bonded to Sb and two are coordinated to Pt (see Supporting Information, Section 3).The 1 H NMR spectrum of complex 9 shows one group of quinoline proton resonances that suggest the phenyl ring is likely trans to the Pt center.In addition, the presence of a more downfield-shifted proton in complex 10 (11.5 ppm) than in 9 (11.0 ppm) in CDCl 3 (Figure S6) is consistent with the proposed structure of 9 without an axial chloride trans to the Sb center.The conversion from complex 9 to 10 is potentially initiated by the chloride transfer from the Sb to Pt center, while the conversion from 8 to 7 likely involves a chloride transfer from Pt to Sb.To better understand this difference in coordination mode, the relative energies of complex 7 versus 8 and complex 9 versus 10 were examined via DFT calculations, which suggests that the isolated products (7 and 10) were relatively more stable in energy (see Supporting Information, Section 4).
For complex 10, the Sb center is bonded to only one chloride and three carbon atoms, which gives formal Pt IV and Sb III or Pt III and Sb IV oxidation states (if Sb−Cl is considered as a formal bond).Complexes 7 and 10 each have much longer Pt−Cl distances trans to Sb (2.6842(15) and 2.6164(18) Å, respectively, Table 3) compared to complexes 3 or 4 (2.3818(14) and 2.370(2) Å, Table 1), which are longer than the sum of covalent radii of Pt and Cl (i.e., 2.38 Å).In contrast, the Pt−Cl bond cis to Sb is similar between the oxidized complexes (2.3189(15) Å for 7 and 2.3094(12) Å for 10) and the Sb III complexes (2.2962(13) Å for 3 and 2.297(2) Å for 4).These distances are consistent with the chloride trans to Sb more closely resembling a non-coordinating anion.Anion transfers between Sb-bound metals have been explored previously, and tuning the electronic nature of Sb has been reported to elicit changes in coordination modes. 70,71gure 6.ORTEPs of (Cl 2 SbQ 3 )PtCl 2 (7) and (ClSbQ 2 Ph)PtCl 3 (10).Ellipsoids are drawn at the 50% probability level and hydrogen atoms and non-coordinating solvents are omitted for clarity.To address the chloride transfer between Pt and Sb, ochloranil was selected as the oxidant due to its bidentate chelating nature, which could kinetically inhibit transfer from Sb to the Pt center.Stirring either 3 or 4 in DCM with 1.1 equivalents of o-chloranil led to a single Pt II −Sb V product (complexes 11 and 12, respectively) with o-chloranil coordinated to the Sb center (Scheme 3).Similar to complex 7, the 1 H NMR spectrum of complex 11 includes two groups of quinoline proton resonances with a 2-to-1 integration ratio as well as of two downfield-shifted resonances due to H a (>12 ppm), which both suggest that the Sb ligand coordinated to Pt in a tetradentate fashion.
The crystal structure of complex 11 shows octahedral geometries for both Pt and Sb (Figure 7, left).Based on the structures, Sb can be assigned a formal oxidation state of +5 with bonding to the Pt II center as a Z-type ligand.However, transition metal complexes with d 8 configuration (e.g., Pt II ) normally favor a square planar geometry to minimize the energy.Similar to complex 7, in complex 11, the chloride trans to Sb might be better described as a counterion given the long Pt−Cl bond relative to the cis chloride (2.7792(14) vs 2.2938(14) Å, Table 4) as well as the sum of covalent radii of Pt and Cl (i.e., 2.38 Å).Therefore, the Pt II center could potentially be considered to be in a square planar geometry with three quinoline and one chloride donor or in a square pyramidal geometry if the Pt−Sb interaction is considered, while the Sb serves as a σ-acceptor that increases the Lewis acidity of the Pt center thus causing close Pt contact with the chloride counterion in a position trans to the Sb center.However, in the crystal structure of complex 11, the Sb1−O1 bond is longer than Sb1−O2 (2.208(5) vs 2.048(4) Å, Table 4), while O1−C is shorter than a typical O−C single bond and different from O2−C (1.268(8) vs 1.332(8) Å, Table 4).This suggests that a covalent bonding interaction may not be the best way to describe the interaction between Sb1 and O1 atoms and, thus, raises the question about the oxidation states of Pt and Sb in complex 11 (Pt II −Sb V vs Pt III −Sb IV , see below for more discussion).
The 1 H NMR spectrum of complex 12 is consistent with the solid-state structure (Figure 7, right) for which the two quinoline groups are equivalent due to symmetry.The Pt center in complex 12 shows a square pyramidal geometry, while the Sb center is in an octahedral geometry.Different from complex 11, the two Sb−O bonds in complex 12 have similar bond lengths (∼2.06(1)Å, Table 4) as well as two O− C bonds (1.343(11) and 1.333(12) Å, Table 4).Furthermore, the Pt−Sb bond length of 2.8375(12) Å (Table 4) is longer than the sum of covalent radii (i.e., 2.75 Å), which likely indicates only a weak interaction between Pt and Sb.Based on these observations, it seems reasonable to conclude that complex 12 can be considered as a "square planar" Pt II complex with two quinoline and two chloride donor ligands, while the Sb V moiety serves as a Z-type ligand withdrawing electron density from the Pt center through a σ-interaction.We speculate that the geometrical differences between complexes 12 and 11 or 7 are caused by the lack of the third quinoline side arm.
Pt−Sb Bonding Analysis.With the synthesis of several unique Pt−Sb complexes, we wanted to understand the bonding between the Pt and Sb centers.To do this, we examined both molecular (MO) and natural localized (NLMO) orbitals, which provide the ability to differentiate the X-, L-, and Z-type bonding scenarios.We were most interested in complexes 7 and 11 because they have a unique formal Pt II coordination environment and geometry in which the Pt−Cl distance for the axial chloride connected to the Pt was found to be much longer than that for the equatorial  chloride.Also, the absence of the axial chloride in 12 presented a much longer Pt−Sb distance.
Figure 8 provides an overview of the MOs and NLMOs for Pt−Sb interactions in complexes 7 and 11.A complementary intrinsic bond orbital (IBO) analysis, which gave a similar bonding description, can be found in the Supporting Information.The MO for complex 7 shows multicentered σbonding with some bonding between the Pt and Sb centers.This orbital extends to the chloride ligand attached to the Sb center.Because it was unclear from visual inspection the contribution from Pt and Sb, we carried out NLMO calculations.This revealed that the Pt−Sb interaction is mostly a donor−acceptor type interaction for which Pt acts as an Ltype ligand donating a pair of electrons to the vacant orbital on Sb.For complex 7, the Pt−Sb interaction consists of an 84% electronic contribution from Pt and 10% contribution from Sb.A nearly identical bonding description was found for complex 11.For complex 12, the Pt contribution increases to 91% and Sb contribution decreases to 5%, which is likely due to the absence of the axial chloride ligand that polarizes the Pt-lone pair electrons more toward the Sb in complexes 7 and 11.In the absence of such an axial push in complex 12, electron density is more localized on the Pt.
Based on the above orbital analysis, a simplified bonding model can be developed for complexes 7, 11, and 12.If we consider the axial chloride ligand in complexes 7 and 11 as a counterion chloride and only held together with Pt through an electrostatic, nonorbital interaction, then its complementary positive charge on Pt makes the Pt fragment a stable square planar 16-electron complex and the Sb fragment a fivecoordinate structure with a vacant sixth coordination site.The 16-electron Pt II fragment can then donate to the vacant orbital on the Sb V fragment, which makes the Pt−Sb interaction a donor−acceptor type bonding (Pt fragment as L-type and Sb fragment as Z-type).As mentioned above, in complexes 7 and 11, electron polarization induced by the negatively charged chloride ligand makes the Pt−Sb bond stronger and shorter.Absence of such an axial push in complex 12 makes the Pt−Sb bond longer with an axial lone pair more localized on the Pt center.Importantly, the Pt−Sb interaction in these complexes is mostly due to the geometrical constraints induced by the bridging quinoline ligand and this relatively weak donor− acceptor interaction would unlikely result in a stable intermolecular bond.
The above bonding perspective is further supported by a second-order perturbative natural bond orbital (NBO) analysis of donor−acceptor interaction energy based on the overlap and energy difference between the donor and acceptor orbitals (see the Supporting Information for values).Importantly, it is well known that this type of analysis likely overestimates the absolute interaction energies but can be used for qualitative relative values.The interaction energies computed for complexes 7 and 11 were 111.2 and 71.9 kcal/mol, respectively.These interactions showed electron delocalization between the Pt lone pair and the vacant acceptor orbital on the Sb fragment.In contrast, the interaction energy in complex 12 was calculated to be only 14.7 kcal/mol, which supports the description of a much weaker bonding interaction between Pt and Sb.The difference between 7 and 11 compared to that of 12 can be traced to the difference in Pt to Sb orbital overlap.For complexes 7 and 11, the overlap was calculated to be 0.13 and 0.12 au, while for 12 the overlap was calculated to be 0.05 au.

■ CONCLUSIONS
In conclusion, we synthesized a variety of Pt−Sb complexes with the Sb center in +3 to +5 oxidation states.Depending on the Pt and Sb oxidation states, the ligand moiety can bond in bi-, tri-, or tetradentate fashions.Oxidizing the Pt II −Sb III complexes (3 or 4) with PhICl 2 leads to a mixture of Pt−Sb complexes with different bonding interactions between the Pt and Sb centers (7 and 8 or 9 and 10) due to the transfer of chloride(s) from the Sb to the Pt center.The bidentate oxidant o-chloranil was found to circumvent the potential substrate(s) transfer from Sb to Pt center and thus selectively produce the Z-type Pt−Sb complexes (11 or 12).X-ray crystal structures and NLMO modeling of complexes 7, 11, and 12 suggested a Z-type Pt → Sb interaction, while the axial chloride in complexes 7 and 11 is better described as an anion.
■ EXPERIMENTAL SECTION General Information.All reactions were performed in air under ambient conditions, unless otherwise noted.The synthesis of ligands SbQ 3 and SbQ 2 Ph was performed under a dinitrogen atmosphere using Schlenk line techniques.Synthesis of complexes 5 and 6 was performed in a nitrogen-filled glovebox.
All NMR reactions were performed using Wilmad medium wall precision low pressure/vacuum (LPV) NMR tubes.Tetrahydrofuran (THF) and diethyl ether (Et 2 O) were dried via a potassiumbenzophenone/ketyl still under a dinitrogen atmosphere and stored over activated 4 Å molecular sieves inside a glovebox.Pentane and methylene chloride were dried using a solvent purification system with activated alumina and stored under activated 3 Å molecular sieves inside a dinitrogen-filled glovebox.Chloroform-d and methylene chloride-d 2 were stored over activated 4 Å molecular sieves inside a glovebox.SbPhCl 2 and iodobenzene dichloride were synthesized as previously reported. 72,73All other chemicals were purchased from commercial sources and used as received.

Di(quinolin-8-yl)-phenyl-λ 3 -stibane (SbQ 2 Ph, 2).
A mixture of Ph 3 Sb (0.43 g, 1.22 mmol) and SbCl 3 (0.56 g, 2.45 mmol) was stirred under dinitrogen without solvent for approximately 1 day; at the end, the solid mixture had changed to liquid (PhSbCl 2 ).Then, 10 mL of distilled Et 2 O was added.To a solution of 8-bromoquinoline (1.5 g, 7.32 mmol) in 20 mL of distilled Et 2 O under a dinitrogen atmosphere, a 2.5 M solution of n-BuLi in hexanes (2.9 mL, 7.32 mmol) was syringed slowly at −78 °C.The mixture was allowed to warm to room temperature and stirred for about 1 h.The solution of 8-lithio-quinoline was both cooled to −78 °C and cannulated slowly into the solution of PhSbCl 2 , during which the formation of a solid precipitate was observed.The mixture was allowed to warm to room temperature and stirred overnight.The reaction mixture was concentrated using a rotavap until about 10 mL of solvent remained.The solid mixture was collected by vacuum filtration and is a mixture of LiCl with Q 2 SbPh.The solid was redissolved using DCM and washed with water to remove the LiCl.The organic layer was concentrated to dryness to yield a light-yellow solid product, which can be further purified via reprecipitation from DCM and pentanes (0.75 g, 45% yield in the presence of small amounts of 1).**The solid can be used directly for the synthesis of Pt complexes without further purification.Small amounts of 1 as an impurity could be purified by column chromatography using EtOAc/hexanes with triethylamine.However, some of the product is lost using this method (approximately 40−50% recovery from the column).X-ray quality crystals of SbQ 2 Ph were obtained by vapor diffusion of diethyl ether into a DCM solution of product. 1 H NMR (800 MHz, CD 2 Cl 2 ) δ 8.83 (dd, 3 J HH = 4 Hz, 4 J HH = 1 Hz, 2H, 1-position), 8.22 (dd, 3 J HH = 8 Hz, 4 J HH = 2 Hz, 2H, 3-position), 7.84 (dd, 3 J HH = 8 Hz, 4 J HH = 1 Hz, 2H, 4-or 6-position), 7.42 (dd, 3 J HH = 8 Hz, 4 J HH = 4 Hz, 2H), 7.39−7.35(m, 2H, 7-or 8-position), 7.35 (dd, 3 J HH = 8, 7 Hz, 2H, 5position), 7.31−7.27(m, 1H, 9-position), 7.27−7.22(m, 4H, 4-or 6position and 7-or 8-position). 13

Figure 1 .
Figure 1.(a) Selected examples of transition metal complexes with Z-type ligands.(b) Previously reported Pt II −Sb III complex (L-type Sb ligand) supported by nitrogen-based side arms.(c) Examples of tunable Lewis acidity of Pt−Sb complexes.(d) Pt−Sb complexes exhibiting a variety of bonding types.36−39,41−43

a
H a is based on the calculated position of the quinoline proton ortho to the nitrogen.

Figure 8 .
Figure 8. Structural features and relevant molecular orbitals (MOs) and natural localized molecular orbitals (NLMOs) of the Pt−Sb interaction in complexes 7, 11, and 12.

Table 3 .
Selected Bond Lengths for Complexes (Cl 2 SbQ 3 )PtCl 2(7)and (ClSbQ 2 Ph)PtCl 3(10)Based on Single-Crystal X-ray Structures a Sb−Cl A is trans to Pt. b Sb−Cl B is cis to Pt. c H a is the calculated position of the quinoline proton ortho to the nitrogen.