Sterically Demanding Phosphines with 2,6-Dibenzhydryl-4

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Sterically Demanding Phosphines with 2,6-Dibenzhydryl-4methylphenyl Core: Synthesis of RuII, PdII, and PtII Complexes, and Structural and Catalytic Studies Madhusudan K. Pandey,† Joel T. Mague,‡ and Maravanji S. Balakrishna*,† †

Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States

‡

S Supporting Information *

ABSTRACT: The synthesis of sterically demanding aminophosphine and phosphinite ligands Ar*NHPPh2 (1) and Ar*OPPh2 (2), based on 2,6-dibenzhydryl-4-methylphenyl core having bulky benzhydryl groups, and their RuII, PdII and PtII complexes is described. The reactions of 1 and 2 with [Ru(η6-p-cymene)Cl2]2 in 2:1 molar ratios produced mononuclear complexes [RuCl2{(η6-p-cymene)PPh2-EAr*}-κ1-P] (E = NH (3) and O (4)). Interestingly, complexes 3 and 4, upon refluxing in chlorobenzene, displace the p-cymene ring by one of the phenyl rings of side arms, forming rare η6-arene coordinated tethered complexes [RuCl2{(PPh2-EAr*)-κ1-P-η6arene}] (E = NH (5) and O (6)). Treatment of 1 and 2 with [M(COD)Cl 2 ] [M = Pd, Pt] in 2:1 ratios afforded mononuclear complexes [MCl2{(PPh2EAr*)-κ1-P}2] (E = NH, M= Pd (7), Pt (8); E = O, M= Pd (9), Pt (10)). Similarly, 1:1 reactions of 1 and 2 with [Pd(COD)Cl2] produced chloro-bridged dinuclear complexes [PdCl2{(PPh2EAr*)-κ1-P}]2 (E = NH (11) and O (12)), whereas [Pt(COD)Cl2] yielded only the mononuclear complexes 8 and 10. The reactions of 1 and 2 with [Pd(η3-C3H5)Cl]2 in 2:1 molar ratios produced the mononuclear complexes [PdCl{(η3-C3H5)(PPh2EAr*)-κ1-P}] (E = NH (13) and O (14)). Many of these complexes have been structurally characterized, which show C−H···π interactions between the methine hydrogen of the benzhydryl and with one of the carbon atoms of the phenyl ring attached to the phosphorus center. The complex [RuCl2{(η6-p-cymene)PPh2-NHAr*}-κ1-P] (3) shows very short C−H···π interactions of 2.36 Å; in addition, C−H···M interactions were observed between the methine hydrogen of one of the benzhydryl groups and palladium centers in 11 and 13. The tethered ruthenium complex 5 is found to be an excellent catalyst for the catalytic oxidation of various styrene derivatives.

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example, κ1-P-η6-arene, where P is the σ-donor atom, along with η6-coordinated arene as a π-donor.5 A few known tethered complexes of ruthenium are shown in Chart 1. Most of these complexes typically contain two- or three-carbon tethers (I− VII),5,6 whereas the complexes having heteroatoms in their spacers are scarce. Alain and co-workers have reported methylenaminophosphine ligands of the type R1(Ph)CN− PR2 (R1 = H, Ph, iPr2N), which form tethered complexes of the type VIII.7 Herein, we report the synthesis of new phosphines 1 and 2 having bulky benzhydryl group at 2,6 positions as pendant arms and their RuII, PdII, and PtII complexes. The tethered ruthenium complex 5 shows excellent catalytic activity toward the oxidation of various styrene derivatives.

INTRODUCTION Ligand design plays an important role in coordination chemistry and catalysis.1 Phosphines with sterically bulky groups in the ligand framework are particularly interesting, because of their catalytic efficiency in a range of organic transformations.2 Buchwald and co-workers have reported several dialkylbiarylphosphine ligands bearing sterically bulky groups2a−c that can stabilize metals in their low-valent and lowcoordination states and promote organic transformations efficiently.2a,d,f Although several bulky phosphines are known in the literature, reports on bulky phosphines with direct P−N and P−O bonds3 or having bulky aryl groups with 2,6-aryl substituents are scarce.4 Phosphines having pendant aromatic groups in close proximity to the P atoms are particularly interesting, because of their ability to exhibit η2, η3, η4, or η6 binding modes, depending on the electronic situation at the metal center. If such ligands form complexes of the type [MX2(κ-P-η6-arene)] (mostly in the case of ruthenium), they are usually called tethered complexes and the ligands can also be termed as polydentate ligands (most often tetradentate), for © XXXX American Chemical Society

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RESULTS AND DISCUSSION Synthesis of N-(2,6-dibenzhydryl-4-methylphenyl)diphenylphosphinamine (1) and (2,6-dibenzhydryl-4Received: April 20, 2018

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DOI: 10.1021/acs.inorgchem.8b01095 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Chart 1. η6-Arene Tethered Ruthenium Complexes Known in the Literature

methylphenoxy)diphenylphosphine (2). The reactions of lithiated amide [Li{NH(Ar*)}] or lithium phenoxide [Li{O(Ar*)}] generated in situ with 1 equiv of chlorodiphenylphosphine resulted in the formation of Ar*NHPPh2 (1) and Ar*OPPh2 (2) as white solids, as shown in Scheme 1. Because

Figure 1. Molecular structure of Ar*NHPPh2 (1). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except (H1A and H21) have been omitted for clarity. Selected bond lengths: P1− N1, 1.702(13) Å; P1−C34, 1.821(16) Å; P1−C40, 1.838(16) Å; and C1−N1, 1.419(19) Å. Selected bond angles: ∠P1−N1−C1, 123.78(11)°; ∠N1−P1−C34, 100.41(7)°; and ∠N1−P1−C40, 100.24(7)°.

Scheme 1. Synthesis of Phosphines 1 and 2

that observed in terpy-C6H4N(PPh2)2 (P−N = 1.721(2)− 1.731(2) Å),8 N-(2,6-dibenzhydryl-4-isopropylphenyl)-1,1-diphenylphosphanamine (1.711(2) Å)4b and longer than that in the 2,6-{μ-(tBuN)2P(tBuHN)PO}2C6H3I (P−N = 1.666(3)− 1.686(3) Å) system.8,9 The C21−H21···P1 distance of 2.84 Å in 1 suggests the phosphorus lone pair pointing toward the methine hydrogen (see Figure 1). Synthesis of RuII, PdII, and PtII Complexes. The bulky phosphines 1 and 2, having benzhydryl substituents in close proximity to P atom, which can freely rotate around C−C single bonds, can coordinate and thus influence the coordination behavior. Hence, it would be interesting to explore their coordination behavior with various transitionmetal precursors. The possible coordination modes of 1 and 2 are depicted in Chart 2. Although simple κ1-coordination via

of the presence of bulky groups, phosphines 1 and 2 are found to be highly air stable and also soluble in most of the organic solvents. The spectroscopic and structural features of 1 is similar to the aminophosphine analogue reported by Jones and co-workers;4b however, the chemical shifts of NH and CH protons of benzhydryl groups in 1 are more shielded, compared to the Jones ligand. The 31P{1H} NMR spectra of 1 and 2 showed single resonances at 38.5 and 115.1 ppm, respectively. In the 1H NMR spectra of 1 and 2, methyl protons appear as a singlet around 2.0 ppm and aromatic protons display multiplets at ∼6.80−7.50 ppm, while the CH protons of methine groups show a doublet at ∼5.50 ppm, possibly due to the throughspace coupling (JPH = 3.1 and 2.1 Hz, respectively) with the P atom. The NH proton of 1 appeared as a doublet at 3.23 ppm with a 1JPH coupling of 7.6 Hz. The molecular compositions were confirmed by mass spectrometry, and the structure was confirmed by X-ray analysis in the case of 1. The perspective view of the molecular structure of 1, along with the selected bond lengths and the bond angles, are shown in Figure 1. The pyramidal geometry around the P atom (∠N1−P1−C34 = 100.40(7)°, ∠N1−P1−C40 = 100.25(7)°, ∠C34−P1−C40 = 99.15(7)°) is slightly distorted. The geometry around nitrogen (∠C1−N1−P1 = 123.78(11)°, ∠P1−N1−H1 = 117.4(13)°, ∠C1−N1−H1 = 110.3(13)°) is also distorted, with a significantly larger ∠C1−N1−P1 bond angle of 123.78(11)°, probably to overcome the steric congestion. The two phenyl rings on P atoms are nearly orthogonal to each other, as observed from their torsion angles (∠P1−C40−C45−C44 = 168.92(13)°, ∠P1−C34−C39−C38 = 176.28(13)°). The P−N bond distance of 1.702(13) Å in 1 is in the expected range with partial N2Pπ → Pσ* multiple bonding, but slightly shorter than

Chart 2. Possible Coordination Modes for Phosphines 1 and 2

the P atom (I, II, and III) is the most common and preferred mode for both ligands 1 and 2, the bulky phosphines 1 and 2, upon treatment with suitable metal precursors, can give rise to type IV complexes. The coordination behavior of 1 and 2 with various transition-metal derivatives has been investigated in detail. The reactions of 1 and 2 with [Ru(η6-p-cymene)Cl2]2 in 2:1 ratios in dichloromethane resulted in mononuclear complexes [RuCl 2 {(η 6 -p-cymene)PPh 2 -NHAr*}-κ 1 -P] (3) and [RuCl2{(η6-p-cymene)PPh2-OAr*}-κ1-P] (4) in good yield as B


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Inorganic Chemistry

observed in related arene ruthenium(II) complexes and is attributed to the bond-lengthening effect of the phosphine ligands.5,12 The Ru−P (2.366(7) Å) and Ru−Cl (2.415(7) Å) bond distances are similar to those in [Ru(η6-p-cymene)Cl2{DippNH-PPh2}-κ1-P] (2.372(5) and 2.418(6) Å),10 [{Ru(η6-p-cymene)Cl2}2{(μ-DPEphos)-κ1 -P}] (2.370(10) and 2.410(8) Å),12c and [Ru(η6-p-cymene)Cl2{(PPh3)-κ1-P}] (2.343(6) and 2.415(6) Å).11 The objective of making ligands 1 and 2 with bulky benzhydryl pendant arms was to form tethered complexes involving phenyl groups as (η2−η6) donors. Since the reactions of 1 and 2 with [Ru(η6-p-cymene)Cl2]2 did not yield anticipated tethered complexes of the type [RuCl2{PPh2EAr*}(κ1-P-η6-arene)], complex 3 was heated to 120 °C in chlorobenzene for 16 h, which resulted in tethered complex 5, as confirmed from spectroscopic and structural studies. Alternately, the reactions of 1 and 2 with [Ru(η6-p-cymene)Cl2]2 in chlorobenzene at 120 °C produced the same tethered complexes 5 and 6 in good yield. Arene exchange reactions are known in the case of (arene)tricarbonylchromium complexes.13 These reactions proceed at very high temperature (150−170 °C) and require aromatic reagents as solvents. In order to assess the arene exchange reactions, the ruthenium complexes 3−6 were heated at 150 °C in xylene or mesitylene for 24−48 h; arene exchange was not observed, but cymene complexes 3 and 4 were converted to tethered complexes 5 and 6. The 1H NMR spectrum of 5 showed triplets at δ 6.24 and 6.14 ppm, with a coupling of 6.0 Hz; doublets at δ 5.81 and 4.73 ppm, with a coupling of 4.3 and 5.6 Hz; and a triplet at δ 5.01 ppm, with a coupling of 5.6 Hz. These observations supported the presence of a η6-coordinated phenyl ring, hence confirming the formation of a tethered complex [RuCl2(PPh2-NHAr*)(κ1-Pη6-arene)] (5). Under identical reaction conditions, 4 produced tethered complex [RuCl2(PPh2-OAr*)(κ1-P-η6-arene)] (6) (see Scheme 2). The 31P{1H} NMR spectra of 5 and 6 showed singlets at 64.3 and 118.7 ppm, with shifts of 7.3 and 5.2 ppm, with respect to complexes 3 and 4. In the 1H NMR spectrum of 5, the NH proton appears as a doublet at 3.78 ppm with a 1JPH coupling of 5.0 Hz, which is more shielded, compared to that of complex 3 (5.25 ppm). The structures of 5 and 6 were confirmed by single-crystal X-ray analysis. The perspective views of molecular structures of 5 and 6, along with the atom labeling scheme, are shown in Figure 3. The crystallographic data and the details of the structure

red solids (see Scheme 2). Complexes 3 and 4 showed singlets at 57 and 124 ppm, respectively, in their 31P{1H} NMR spectra. Scheme 2. Synthesis of Ruthenium Complexes 3−6

The 1H NMR spectra of 3 and 4 are consistent with the proposed structures. The NH proton of 3 appeared as a doublet at 5.25 ppm with a 1JPH coupling of 14.9 Hz. The large downfield shift (2.02 ppm) of NH proton in 3, compared to that of the free ligand 1, is due to its hydrogen bonding with the Cl− ion, as evident from its X-ray structure. Complex 3 adopts the three-legged “piano stool” geometry with the ruthenium atom in a pseudo-octahedral environment (Figure 2). The

Figure 2. Molecular structure of [RuCl2{(η6-p-cymene)PPh2NHAr*}-κ1-P] (3). Hydrogen atoms except (H1 and H21) have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

∠C1−N1−P1 bond angle (125.48(18)°) is slightly larger than the same in 1 (123.78(11)°) due to the steric interactions between the p-cymene and the Ph2CH moieties of the ligand backbone. As a result, the p-cymene group is pushed away from the metal center, which is evident from the slightly longer Ru− C(cymene) distances in 3 (2.175(3)−2.249(3) Å). However, the average Ru−C(cymene) distance of 2.219 Å in 3 is in the range observed in complexes such as [Ru(η6-p-cymene)Cl2{DippNH-PPh2}-κ1-P] (2.211(2) Å)10 and [RuCl2(η6-pcymene){(PPh3)-κ1-P}] (2.218(2) Å).11 The Ru−C bonds trans to the P atom (Ru(1)−C(53) = 2.241(3) Å and Ru(1)− C(54) = 2.249(3) Å) are slightly longer than those trans to the two Cl− ions (2.175(3)−2.231(3) Å). Similar trends were

Figure 3. Molecular structures of [RuCl2(PPh2-NHAr*)-(κ1-P-η6arene)] (5) and [RuCl2(PPh2-OAr*)-(κ1-P-η6-arene)] (6). Hydrogen atoms except for (H1 and H8 in 5 and H8 and H21 in 6) have been omitted for the sake of clarity. Displacement ellipsoids are drawn at the 50% probability level. C


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Inorganic Chemistry

in the range observed in complexes [CpRuCl(PPh3)(PPh2N(H)Ph)] and [CpRuCl(PPh2N(H)Ph)2].9 The P−O distance of 1.625(2) Å in 6 is similar to that found in [{RuCl2(η6-pcymene)} 2 (Ph 2 POC 6 H 4 OPPh 2 )] (1.635(2) Å) 15 and [RuCl2(η6-p-cymene){Ph2P(OAr)}] (1.627(2) Å).16 The ∠C1−E1−P1 bond angles of 129.6(3)° and 128.7(2)° in 5 and 6 are larger than the same in 3 (125.4(8)°). The larger ∠C1−E1−P1 angles in 5 and 6 push the PPh2 group away from the methine hydrogen of benzhydryl, and, as a result, the C− H···π interactions in these complexes become considerably weaker than the same in 3. The molecular structure of 3 shows very short C−H···π interactions of 2.36 and 2.69 Å between the methine hydrogen of the benzhydryl group with the ortho and ipso carbons (C39 and C34) of one of the phenyl rings of PPh2 moiety (see Figure 2). The analogous arene complexes 5 and 6 have slightly longer C−H···π interactions between the methine hydrogen of the benzhydryl group and with the ipso carbon of one of the phenyl rings of the PPh2 group (H8···C34 = 2.88 Å in 5, H8···C34 = 2.88 Å, and H21···C40 = 2.83 Å in 6) (see Figure 3). The C−H···π interactions found in these complexes are very comparable to the same in analogous complexes reported in the literature.4a,17 NMR spectroscopy is a powerful method for studying the weak interactions in solution; the 1 H−1H NOESY experiments are very useful for the detection of C−H···π interactions in solutions.18 Two-dimensional nuclear magnetic resonance (2-D) NMR (1H−1H COSY and 1H−1H NOESY) and NOE experiments were carried out in order to gain some insight into the C−H···π interactions. The 1H−1H COSY and NOE spectra of 3 and the 1H−1H NOESY spectrum are presented in Figure 4, as well as Figure S12 in the ESI, respectively. All the protons of 3 have been identified based on their location, integration, coupling constants, and cross-peak correlations using 1H−1H COSY and 1H−1H NOESY NMR spectra. The aromatic protons of the side arms of benzhydryl groups appear in two sets (6.6 and. 7.0 ppm) and show correlation with each other, whereas the aromatic protons attached to phosphorus-bound phenyl groups appear as three sets of multiplets in which Hf protons show correlation with He protons, which, in turn, show correlation with Hd protons. The methine protons of benzhydryl groups observed at 6.15 ppm show NOE correlation with Hd protons

determination are given in Table S2 (in the Supporting Information (ESI)), and the selected bond lengths (Å) and the bond angles (deg) are listed in Table 1. Complexes 5 and 6 Table 1. Selected Bond Lengths and Bond Angles for Compounds 3, 5, and 6 3 M1−P1 M1−Cl1 M1−Cl2 P1−E C1−E1−P1 Cl2−M1−Cl1 Cl2−M1−P1 Cl1−M1−P1 C34−P1−C40

5

Bond Lengths (Å) 2.366(7) 2.312(11) 2.416(7) 2.401(11) 2.415(7) 2.410(10) 1.693(2) 1.690(3) Bond Angles (deg) 125.48(18) 129.6(3) 86.59(2) 90.14(4) 87.62(2) 88.46(4) 90.70(2) 85.90(4) 100.50(13) 99.78(18)

6 2.278(9) 2.382(9) 2.386(9) 1.625(2) 128.7(2) 89.86(3) 88.56(3) 85.09(3) 100.71(16)

adopt the three-legged “piano stool” geometry with a Ru atom in a pseudo-octahedral environment with the tethered phenyl ring of the ligand backbone, two Cl− ions, and the P atom completing the coordination sphere. The Ru−P bond lengths of 2.312(11) and 2.2787(9) Å in complexes 5 and 6 are shorter than the same in 3 (2.3663(7) Å). The Ru−P and Ru−Cl bond distances in 3 and 5 are unexceptional and are found to be in the range of previously reported complexes.7,14 The ∠P1− Ru1−Cl1 bond angles in complexes 5 (85.90(4)°) and 6 (85.09(3)°) are smaller than the same in 3 (90.70(2))°, whereas the ∠P1−Ru1−Cl2 and ∠Cl1−Ru1−Cl2 bond angles in 5 and 6 lie within a fairly narrow range and are surprisingly close to the corresponding angles in 3, suggesting that constraining the coordinated phosphine moiety and arene ring via unsaturated tether does not have a marked influence on the coordination geometry at the metal center. The molecular structures of complexes 3, 5, and 6 show that the distance between the Ru center and the centroid of p-cymene or proximal phenyl ring of ligand backbone is 1.70 Å and is independent of coordination geometry around the metal. The P−N bond lengths of 1.693(2) and 1.690(3) Å in 3 and 5 are

Figure 4. 1H−1H COSY and NOE spectra of 3 recorded in CDCl3. D


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Inorganic Chemistry of phenyl groups bonded to the P atom. In the 1H−1H NOESY spectrum, the Ha protons show through-space correlation with Hd protons. Therefore, the NOE and 1H−1H NOESY experiments clearly demonstrate the existence of intramolecular CH···π interactions in 3. Synthesis of PdII and PtII Complexes. The reactions of [M(COD)Cl2] (M = Pd or Pt) with 1 and 2 in 1:2 molar ratios in dichloromethane afforded the trans complexes [MCl2{(PPh2EAr*)-κ1-P}2] (7−10) as shown in Scheme 3.

The metal center in complexes 7, 8, and 10 adopt slightly distorted square-planar geometries. The Pd−P and Pd−Cl bond distances of 2.3138(8) and 2.299(8) Å in 7 are similar to those in [PdCl2{(DippNH-PPh2)2}-κ1-P] (2.3124(4) and 2.3014(8) Å)20 and lie within the normal range expected for trans-[PdCl2(PR3)2]21 complexes, as well as the Pt−P and Pt− Cl bond distances in 8 (2.297(13), 2.3066(11) Å) and 10 (2.3071(2), 2.3065(9) Å).21b The solid-state molecular structures of 7, 8, and 10 confirm the trans arrangement of the bulky phosphines around the metal center. These complexes have a center of symmetry lying at the metal center. In addition, they also have a crystallographically imposed 2-fold rotation axis passing through the metal center. In complexes 7 and 8, the 2-fold rotation axis is passing through the metal center and is perpendicular to the square plane formed by two Cl− ions and two P atoms. In contrast, the 2-fold rotation axis in complex 10 is passing through the PtCl2 moiety along the plane formed by the two Cl− ions and two P atoms. The pendant phenyl rings are disposed above and below the 4methylphenyl moiety and, although pointed away from the PPh2 group, provide enough steric hindrance (hence, the trans conformations around the metal center). Complexes 8 and 10 show C−H···π type intramolecular interactions. The C−H···π interactions between the methine hydrogen of the benzhydryl and the ipso carbon of the PPh2 group (H8···C40 = 2.56 Å in 7, H21···C34 = 2.57 Å in 8, and H21···C40 = 2.76 Å in 10) are in the range found in the ruthenium complexes 3, 5, and 6 (2.36− 2.88 Å), as well as in other similar complexes.4a The ∠E1−P1− M1 angles of 110.55(10)° and 110.81(16)° in 7 and 8 (Figure 5) are considerably smaller than the same in complex 10 (117.11(7)°) (Figure 6). The larger ∠E1−P1−M1 bond angle in 10 allows the PPh2 and benzhydryl groups to stay away from each other; as a result, the C−H···π interaction becomes weaker in complex 10. [Selected bond lengths and bond angles for compounds 7, 8, and 10 are shown in Table 2.] The molecular structures of complexes 11 and 12 are confirmed by single-crystal X-ray analysis. Both complexes 11 and 12 have similar bond parameters. Complexes 11 and 12 have crystallographically imposed 2-fold rotation axis passing through the bridging chloride (μ2-Cl) atoms. The palladium center in these complexes adopt slightly distorted square planar geometries. Complexes 11 and 12, by virtue of their bulkiness, showed C−H···π as well as C−H···M type intramolecular

Scheme 3. Synthesis of PdII and PtII Complexes

However, the equimolar reactions of 1 and 2 with [Pd(COD)Cl2] under similar reaction conditions produced chloro-bridged dimers [PdCl2{(PPh2EAr*)-κ1-P}]2 (11 and 12) (see Scheme 3). Similar reactions of 1 and 2 with [Pt(COD)Cl2] in 1:1 molar ratios yielded only the mononuclear complexes 8 and 10. The 31P{1H} NMR spectra of palladium complexes 7 and 9 showed singlets at 54.5 and 100.6 ppm, whereas the platinum complexes 8 and 10 also showed singlets at 46.0 and 90.4 ppm, but with characteristic 195Pt satellites with 1JPtP couplings of 2611 and 2887 Hz, respectively. The lower 1JPtP coupling values support the trans disposition of P atoms.19 The dimeric palladium complexes 11 and 12 showed 31P{1H} chemical shifts at 61.2 and 102.6 ppm, respectively, which are slightly deshielded, compared to the same in complexes 7 and 9. The 1 H NMR spectra and mass spectrometry also support the product formation. The identity of complexes 7, 8, and 10−12 were established by single-crystal X-ray studies.

Figure 5. Molecular structures of [PdCl2{(PPh2NHAr*)2-κ1-P}] (7) and [PtCl2{(PPh2NHAr*)2-κ1-P}] (8). All hydrogen atoms (except H8 in 7, and H21 in 8) are omitted for the sake of clarity. Displacement ellipsoids are drawn at the 50% probability level. E


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Inorganic Chemistry

distances are as expected.23 [Selected bond lengths and bond angles for compounds 11 and 12 are shown in Table 3.] Table 3. Selected Bond Lengths and Bond Angles for Compounds 11 and 12 11 E1−P1 P1−Pd1 Cl1−Pd1 Cl1−Pd11 Cl2−Pd1 C1−E1 Pd1−P1−C34 Pd1−P1−E1 Cl1−Pd1−P1 Cl11−Pd1−P1 Cl2−Pd1−P1 Cl2−Pd1−Cl11

Figure 6. Molecular structure of [PtCl2{(PPh2OAr*)2-κ1-P}] (10). All hydrogen atoms except H21 are omitted for the sake of clarity. Displacement ellipsoids are drawn at the 50% probability level.

M1−P1 M1−Cl1 P1−E1 Cl11−M1−Cl1 Cl1−M1−P11 P11−M1−Cl1 P1−M1−P11

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Bond Lengths (Å) 2.313(8) 2.297(17) 2.299(8) 2.306(17) 1.680(3) 1.681(4) Bond Angles (deg) 180.0 180.0 86.68(3) 86.66(4) 93.32(3) 93.34(4) 180.0 180.0

1.610(5) 2.208(2) 2.327(17) 2.428(18) 2.273(18) 1.415(8) 116.5(2) 113.9(2) 95.96(7) 177.80(7) 86.98(6) 91.06(6)

Treatment of 1 and 2 with 0.5 equiv [Pd(η3-C3H5)Cl]2 afforded [PdCl{(η3-C3H5)(PPh2EAr*)-κ1-P}] (13 and 14), as shown in Scheme 4. The 31P{1H} NMR spectra of 13 and 14

Table 2. Selected Bond Lengths and Bond Angles for Compounds 7, 8, and 10 7

12

Bond Lengths (Å) 1.675(4) 2.203(12) 2.307(12) 2.432(12) 2.283(11) 1.438(6) Bond Angles (deg) 116.42(16) 110.01(14) 97.27(4) 172.83(5) 84.58(4) 91.68(4)

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Scheme 4. Synthesis of Palladium Allyl Complexes 13 and 14 2.307(7) 2.288(9) 1.626(19) 180.0 93.79(17) 86.20(17) 172.40(3)

interactions. The C−H···π interactions between the methine hydrogen of the benzhydryl and the ipso carbon of the PPh2 group (H21···C34 = 2.82 Å in 11 and H8···C40 = 2.87 Å in 12) are slightly weaker than the same observed in mononuclear complex (H8···C40 = 2.56 Å) 7. In addition to the C−H···π interaction, complex 11 also shows C−H···M interaction between the methine hydrogen of the benzhydryl group and palladium atom (H8···Pd1 = 2.61 Å) (see Figure 7). The relatively long M···H bond distance of 2.61 Å and nearly linear ∠M···H−C bond angle of 176.92° in 11 suggests it to be an anagostic interaction.22 The Pd−P, Pd−Cl, and Pd−Pd bond

showed singlets at 69.0 and 132.1 ppm, respectively. The allylic group in square planar palladium complexes are known to undergo η3 to η1 conversion influenced by the ligand steric attributes. Sterically bulky phosphines retard the η3-to-η1 conversion process.24 Similar phenomena were observed in 13 and 14, as evidenced by the 1H NMR spectral data. The allylic protons showed five distinct signals for each proton of the allyl group ruling out the possibility of η3 to η1 exchange in solution. The 1H NMR spectra of 13 and 14 showed five allylic signals due to the presence of an unsymmetrical η3-allyl group. The two upfield resonances at ∼3.0 and 1.9 ppm can probably

Figure 7. Molecular structures of [PdCl2{(PPh2NHAr*)-κ1-P}]2 (11) and [PdCl2{(PPh2OAr*)-κ1-P}]2 (12). All hydrogen atoms (except H8 and H21 in 11 and H8 in 12) are omitted for the sake of clarity. Displacement ellipsoids are drawn at the 50% probability level. F


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Inorganic Chemistry be assigned to the CH2 group anti to the Cl− ion, which lies in the anisotropic cone of the phenyl core of the ligand backbone. The metal center in these complexes adopt slightly distorted square-planar geometries. The Pd−C(allyl), Pd−P, and Pd−Cl bond lengths are typical for these types of complexes.25 The ∠Cl1−Pd1−P1 bond angles in 13 and 14 are 96.95(7)° and 93.65(2)°, respectively. The molecular structure of [PdCl{(η3C3H5)(Ar*NHPPh2)-κ1-P}] (13) shows a C−H···π interaction between the methine hydrogen of the benzhydryl and the ipso carbon (C40) of the PPh2 group (H8···C40 = 2.70 Å). Interestingly, the complex [PdCl{(η3-C3H5)(Ar*OPPh2)-κ1P}] (14) shows C−H···π interactions between both the methine hydrogen of the benzhydryl groups and both the ipso carbons (C40 and C34) of the PPh2 group (H8···C40 = 2.58 Å and H21···C34 = 2.76 Å). In addition, complex 13 also displays a C−H···M interaction (H21···Pd = 2.98 Å) between the methine hydrogen of the benzhydryl side arm and the palladium center (see Figure 8). The longer C−H···M bond

is an important reaction in the organic synthesis, because it leads to the addition of oxygen functionality. Generally, it is carried out with highly toxic OsO4 and a variety of co-oxidants [H2O2, TBHP, PhI(OAc)2, NaIO4] in different solvent systems.26 RuCl3 with NaIO4 as the oxidant was used by Sharpless for oxidative cleavage of olefins.27 Subsequently, a significant number of RuCl3/oxidant/solvent combinations have been explored.28 However, high catalyst loading and overoxidation of aldehydes to the corresponding acids is the major drawback. Apart from RuCl3/oxidant/solvent combinations, abnormal NHC-based ruthenium complexes that show moderate to good conversion also have been used. 29 Surprisingly, to the best of our knowledge, ruthenium complexes of phosphine ligands have not been explored in the catalytic oxidation of olefin. Complexes 3, 4, and 6 showed only moderate conversion (up to 85%) at room temperature, whereas the arene complex 5 afforded quantitative conversion to aldehydes. During the process, the formation of dihydroxy, epoxide, α-hydroxy ketone, or α-dione are not observed. Acid formation was observed in a few cases. Quantitative conversion to benzaldehyde was achieved at room temperature within 20 min in a 1:1 acetonitrile/water solvent combination. The substrate scope was examined under the optimized conditions at room temperature (see Chart 3). Styrene and the electronChart 3. Substrate Scope for Catalytic Oxidation of Various Styrene Derivativesa

Figure 8. Molecular structures of [PdCl{(PPh2NHAr*)(η3-C3H5)-κ1P}] (13) and [PdCl{(PPh2OAr*)(η3-C3H5)-κ1-P}] (14). All hydrogen atoms except H8 and H21 are omitted for the sake of clarity. Displacement ellipsoids are drawn at the 50% probability level.

distance and the relatively larger ∠C−H···M bond angle of 129.91° in [PdCl{(η3−C3H5)(Ar*NHPPh2)-κ1-P}] (13) suggest this interaction to be weakly anagostic in nature.22 [Selected bond lengths and bond angles for compounds 13 and 14 are shown in Table 4.] Catalytic Oxidation of Styrene Derivatives Using Ruthenium Complexes 3−6. Oxidative cleavage of olefins

a Conditions: olefins, 0.4 mmol; catalyst 5 (1 mol %); solvent (CH3CN:H2O), (1:1, 4 mL); NaIO4, 1.2 mmol; RT. bBased on GCMS.

rich styrene derivatives p-methyl and tert-butylstyrene afforded quantitative conversions to the corresponding aldehydes (entries b and c in Chart 3) but required longer time. The electron-deficient styrenes took less time than the electron-rich styrenes (entries d−h in Chart 3). Optimization of the reaction conditions for the catalytic oxidation of styrene is detailed in Table 5. To assess and compare the catalytic efficiency of 5 with other ligands, catalytic oxidation reactions were performed using a mixture of [Ru(η6-p-cymene)Cl2]2 and PPh3, PPh2(NHPh), or PPh2(OPh) with NaIO4 as an oxidant. In all of these cases, moderate conversion to benzaldehyde was observed (up to 60%), along with the formation of some overoxidation products (see in the ESI, Table S1). Under identical conditions, ligands 1 and 2 showed conversions of 65% and 60%. However, isolated complex 5 in the presence of NaIO4 showed almost quantitative conversions. To probe the actual catalyst involved in the catalysis, we carried out the reaction of complex 5 with an excess NaIO4(aq) at room temperature in acetonitrile. Acetonitrile solution was

Table 4. Selected Bond Lengths and Bond Angles for Compounds 13 and 14 13 M1−P1 M1−Cl1 P1−E1 M1−C46 M1−C47 M1−C48 P1−M1−Cl1 C(46)−M1−P(1) E(1)−P(1)−C(34) E(1)−P(1)−M(1) E(1)−P(1)−C(40)

Bond Lengths (Å) 2.309(5) 2.3545(6) 1.700(17) 2.139(2) 2.148(4) 2.190(2) Bond Angles (deg) 96.95(2) 101.33(7) 104.05(10) 112.63(6) 106.08(9)

14 2.291(17) 2.361(19) 1.657(5) 2.179(9) 2.161(9) 2.147(10) 93.62(7) 172.9(3) 99.9(3) 123.15(19) 99.4(3) G


Article

Inorganic Chemistry Table 5. Optimization of the Reaction Conditions for the Catalytic Oxidation of Styrene

a

No.

substrate

NaIO4 (equiv)

1 2 3 4 5 6 7 8

styrene styrene styrene styrene styrene styrene styrene styrene

2 3 3 3 3

precatalyst (mol %) 3 3 5 4 6 5

(5) (1) (1) (1) (1) (1)

3 4

time (min)

product

conversiona (%)

10 10 10 10 10 10 10 30

benzaldehyde benzaldehyde benzaldehyde benzaldehyde benzaldehyde not observed not observed benzaldehyde

48 70 100 75 85 NCb NCb 10

Based on GC-MS. bNC = no conversion. acquired using broadband decoupling methods. The spectra were recorded in CDCl3 solutions with CDCl3 as an internal lock; chemical shifts of 1H and 13C{1H} NMR spectra are reported in ppm downfield from TMS, which was used as an internal standard. The chemical shifts of 31P{1H} NMR spectra were referred to 85% H3PO4 as an external standard. Positive values indicate downfield shifts. Mass spectra were recorded using a Bruker Maxis Impact LC-q-TOF mass spectrometer. Infrared spectra were recorded on a PerkinElmer Spectrum One FTIR spectrometer (Model No. 73465) in KBr disk. The microanalyses were performed using a Thermo Finnigan FLASH EA 1112 Series CHNS Analyzer. The melting points of all compounds were determined on a Veego melting point apparatus and were uncorrected. Synthesis of (Ar*NHPPh2) (1). To a solution of 2,6-bis(benzhydrylmethyl)-4-methylaniline (1.92 g, 4.36 mmol) in toluene (40 mL) was added, dropwise, a solution of nBuLi (3.0 mL, 1.6 M in hexanes) at −50 °C; the mixture was allowed to warm to room temperature and additional stirring occurred for 4 h. A solution of PPh2Cl (0.970 g, 4.40 mmol) in toluene (20 mL) was added dropwise at −70 °C and the reaction mixture was allowed to come to room temperature and additional stirring was performed for a period of 16 h. The reaction mixture was filtered using a Celite bed to remove LiCl and toluene was removed under reduced pressure to give the crude product. Petroleum ether (50 mL) was added and sonicated for 30 min to give a white solid, which was filtered to give analytically pure product 1 as a white crystalline solid. The colorless crystals of 1 suitable for single-crystal X-ray diffraction (XRD) study were obtained by slow diffusion of petroleum ether into the dichloromethane solution of 1 at room temperature. Yield 66.4% (1.8 g). Melting point (mp) 200−203 °C. Anal. Calcd for C45H38NP: C, 86.64; H, 6.14; N, 2.24. Found: C, 86.36; H, 5.83; N, 2.21. 1H NMR (400 MHz, CDCl3): δ 7.29−7.07 (m, 20H, ArH), 6.78 (dd, J = 7.5, 1.6 Hz, 10H, ArH), 6.43 (s, 2H, ArH), 5.52 (d, J = 3.1 Hz, 2H, Ph2CH), 3.23 (d, J = 7.6 Hz, 1H, NH), 2.03 (s, 3H, ArCH3). 13C NMR (101 MHz, CDCl3): δ 143.78 (s), 142.45 (s), 139.27 (d, J = 3.2 Hz), 131.84 (s), 131.63 (s), 129.89 (s), 129.81 (s), 129.14 (s), 128.55 (d, J = 6.7 Hz), 128.19 (s), 126.25 (s), 51.94 (d, J = 4.3 Hz), 21.50 (s). 31P{1H} NMR (162 MHz, CDCl3): δ 38.54 (s). FT−IR (KBr disk, cm−1): 3320 s, 3053 m, 3019 m, 2911 w, 2863 w, 1594 w, 1456 s, 1443 s, 1265 m, 1077 w, 1026 w, 878 w, 727 s, 693 s. ESI-MS: m/z calcd. for C45H39NP (M+H)+: 624.2815. Found: 624.2806. Synthesis of (Ar*OPPh2) (2). To a solution of 2,6-bis(benzhydrylmethyl)-4-methylphenol (1.87 g, 4.20 mmol) in toluene (50 mL) was added, dropwise, a solution of nBuLi (2.9 mL, 1.6 M in hexanes) at −50 °C, and the mixture was allowed to warm to room temperature and was stirred for 4 h. A solution of PPh2Cl (0.936 g, 4.20 mmol) in toluene (20 mL) was added, dropwise, to the reaction mixture at −70 °C stirred for an additional period of 16 h at room temperature. The solution was filtered and the crude product obtained was dissolved in petroleum ether (30 mL) and sonicated for 30 min to give analytically pure microcrystalline product 2 as a white solid. Yield 69.4% (1.82 g). mp = 168 °C. Anal. Calcd for C45H37OP: C, 86.51; H, 5.97. Found: C, 86.71; H, 6.13. 1H NMR (400 MHz, CDCl3): δ 7.46

subjected to ESI-MS analysis, which showed a signal for [MCl]+ at m/z 792.1339 (z = 1) corresponding to [RuVI(1)Cl2(O)2] (1 = Ligand) [see ESI Figure S57]. The presence of metal-bound 1 suggests that the molecular integrity of the catalyst is maintained during the catalysis. Therefore, the complex 5 acts as a pre-catalyst and the RuVI dioxo compound [RuVI(1)Cl2(O)2] might be the active catalyst.

■

CONCLUSIONS

■

EXPERIMENTAL SECTION

The coordination behavior of sterically demanding phosphines 1 and 2 toward RuII, PdII, and PtII has been described. Phosphines 1 and 2 form mononuclear (κ1-P) complexes with [RuCl2(η6-p-cymene)]2 and [Pd(η3-C3H5)Cl]2, whereas with [M(COD)Cl2], both mononuclear as well as chloro-bridged dinuclear complexes were isolated. The ruthenium p-cymene complexes afforded tethered η6-arene complexes on refluxing in chlorobenzene. In mononuclear as well as dinuclear palladium complexes, ligands 1 and 2 occupy the trans position, because of their steric bulk, while in η6-arene complexes, the ligands act as 8e− donors. The catalytic activity of ruthenium complexes 3−6 has been evaluated in olefin oxidation reactions. In the case of tethered ruthenium complex 5, quantitative conversions were observed, whereas complexes 3, 4, and 6 showed moderate conversions, similar to other ligands, such as PPh3, PPh2(NHPh), or PPh2(OPh) under identical conditions. Interestingly, tethered complex 5, even in the presence of oxidant NaIO4, did not decompose, which indicated its robustness. Currently, we are looking into the reactivity of group 10 complexes and also other catalytic reactions using tethered complex 5. Furthermore, because of the rotational fluxionality of the phosphine moiety, the acidic methine C−H bond(s) of the pendant arms of the ligands can be activated to form interesting complexes.

General Procedures. All of the air-sensitive compounds were handled and stored in an MBRAUN glove box. All manipulations were performed under an inert atmosphere of dry nitrogen or argon, using standard Schlenk techniques. All the solvents were dried by conventional methods and distilled prior to use. [Ar*NH2],30 [Ar*OH],31 [Ru(η6-cymene)Cl2]2,32 [M(COD)Cl2] (M = Pd or Pt),33 [Pd(η3-C3H5)Cl]2,34 [PhNHPPh2],35 and [PhOPPh2]36 were prepared according to the published procedures. Other reagents were obtained from commercial sources and used after purification. Instrumentation. The solution NMR spectra were recorded on Bruker FT spectrometers (Model Avance-400 or 500) MHz at ambient probe temperatures. 13C{1H} and 31P{1H} NMR spectra were H


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Inorganic Chemistry

ArH), 7.29−7.18 (m, 7H, ArH), 7.15 (t, J = 7.6 Hz, 2H, ArH), 7.08 (dt, J = 10.7, 7.5 Hz, 2H, ArH), 7.05−6.99 (m, 5H, ArH), 6.33 (d, J = 15.9 Hz, 2H), 6.28 (d, J = 7.6 Hz, 2H), 6.24 (t, J = 6.0 Hz, 1H), 6.14 (t, J = 5.9 Hz, 1H, η6-C6H6), 5.81 (d, J = 4.3 Hz, 1H, η6-C6H6), 5.01 (t, J = 5.6 Hz, 1H, η6-C6H6), 4.73 (d, J = 5.6 Hz, 1H, η6-C6H6), 4.00−3.95 (m, 1H, η6-C6H6), 3.78 (d, J = 5.0 Hz, 1H, NH), 1.95 (s, 3H, ArCH3).13C NMR (126 MHz, CDCl3): δ 143.33 (s), 141.33 (s), 140.70 (s), 138.62 (s), 134.55 (d, J = 10.2 Hz), 131.11(s), 130.80 (s), 130.63 (s), 130.00 (s), 129.65 (s), 129.16 (s), 128.89 (s), 128.35 (s), 127.54 (s), 127.02 (s), 126.33 (s), 94.60 (s), 91.87 (s), 85.21 (s), 83.86 (s), 53.06 (s), 48.74 (s), 21.42 (s). 31P{1H} NMR (202 MHz, CDCl3): δ 64.3 (s). FT−IR (KBr disk, cm−1): 3056 m, 3035 w, 2961 m, 2921 w, 1437 m, 1348 w, 1260 m, 1098 m, 1030 w, 802 m, 701 s. ESI-MS: m/z calcd. for C45H38ClNPRu (M−C1)+: 760.1477. Found: 760.1474. Synthesis of Complex [RuCl2(PPh2-OAr*)-κ1-P] (6). Compound 6 was prepared according to the procedure described for 5 on the same scale and isolated as an orange-red crystalline solid. A 1:1 solution (dichloromethane and petroleum ether) of 6 stored at room temperature for 24 h gave X-ray-quality crystals of 6 as an orange-red crystalline solid. Yield 78.4% (0.02 g). mp = 253−255 °C (dec). Anal. Calcd for C45H37OPRuCl2: C, 67.84; H, 4.68. Found: C, 67.92; H, 4.42. 1H NMR (500 MHz, CDCl3): δ 8.10−8.07 (m, 2H, ArH), 8.02− 7.98 (m, 2H, ArH), 7.48 (s, 4H, ArH), 7.35 (t, J = 7.5 Hz, 3H, ArH), 7.31 (d, J = 7.0 Hz, 2H, ArH), 7.16 (dd, J = 12.8, 6.1 Hz, 5H, ArH), 7.10 (t, J = 7.4 Hz, 3H, ArH), 7.01 (d, J = 7.4 Hz, 2H, ArH), 6.51 (s, 1H, Ph2CH), 6.47−6.41 (m, 2H, ArH), 6.36 (d, J = 11.8 Hz, 2H, ArH), 6.29 (t, J = 6.3 Hz, 1H, η6-C6H6), 5.74 (d, J = 3.8 Hz, 1H, η6C6H6), 5.24 (t, J = 5.6 Hz, 1H, η6-C6H6), 5.05 (s, 1H, Ph2CH) 4.90 (d, J = 5.3 Hz, 1H, η6-C6H6), 4.31−4.26 (m, 1H, η6-C6H6), 2.05 (s, 3H, ArCH3). 13C NMR (101 MHz, CDCl3) δ 143.30 (s), 142.89 (s), 141.22 (s), 140.97 (d, J = 4.5 Hz), 140.64 (s), 138.57 (s), 134.46 (t, J = 9.7 Hz), 133.63 (s), 133.06 (s), 131.05 (s), 130.67 (d, J = 19.3 Hz), 129.76 (dd, J = 26.9, 8.4 Hz), 129.04 (dd, J = 39.7, 13.9 Hz), 128.84 (d, J = 3.5 Hz), 128.75 (dd, J = 19.4, 9.2 Hz), 128.27 (d, J = 6.9 Hz), 127.51 (s), 126.99 (s), 126.62 (d, J = 13.8 Hz), 126.29 (s), 102.21 (d, J = 10.8 Hz), 99.34 (d, J = 11.0 Hz), 94.54 (s), 91.82 (s), 85.18 (s), 83.80 (s), 53.02 (s), 48.69 (s), 21.38 (s). 31P{1H} NMR (202 MHz, CDCl3): δ 118.7 (s). FT−IR (KBr disk, cm−1): 3057 w, 2964 m, 2883 m, 2852 w, 1454 w, 1433 m, 1262 s, 1112 w, 1004 m, 871 w, 804 m, 736 m, 702 m. ESI-MS: m/z calcd. for C45H37ClOPRu (M−C1)+: 761.1318. Found: 761.1312. Synthesis of Complex [RuCl2(PPh2-NHAr*)-κ1-P] (5) (Method B). A mixture of 1 (0.024 g, 0.038 mmol) and [Ru(η6-p-cymene)Cl2]2 (0.012 g, 0.019 mmol) in chlorobenzene (16 mL) was heated to reflux for 16 h. The reaction mixture then was allowed to attain room temperature and was filtered through Celite, and the solvents were removed under vacuum to give analytically pure product of 5 as an orange crystalline solid. Yield 86% (0.026 g). Synthesis of Complex [RuCl2(PPh2-OAr*)-κ1-P] (6) (Method B). A mixture of 2 (0.021 g, 0.0336 mmol) and [Ru(η6-pcymene)Cl2]2 (0.010 g, 0.0168 mmol) in chlorobenzene (16 mL) was heated to reflux for 16 h. The reaction mixture was cooled to room temperature and filtered through Celite, and the solvents were removed under vacuum to give analytically pure product of 6 as an orange-red solid. Yield 82.2% (0.022 g). Synthesis of [PdCl2{(PPh2NHAr*)-κ1-P}2] (7). A solution of Pd(COD)Cl2 (0.0137 g, 0.048 mmol) in dichloromethane (10 mL) was added dropwise to a solution of 1 (0.06 g, 0.096 mmol) also in dichloromethane (8 mL) with constant stirring. The reaction mixture was allowed to be subjected to stirring for 4 h. After removal of solvent completely under reduced pressure, the residue was obtained as a yellow solid, which was washed with petroleum ether (2 × 8 mL) and dried under vacuum to give compound 7 as a yellow crystalline solid. Yield 76% (0.052 g). mp = 210−212 °C. Anal. Calcd for C90H76N2P2PdCl2·2CH2Cl2: C, 69.29; H, 5.06; N, 1.76. Found: C, 68.91; H, 5.14; N, 1.57. 1H NMR (500 MHz, CDCl3): δ 7.47 (dd, J = 12.6, 5.5 Hz, 4H, ArH), 7.36−7.25 (m, 3H, ArH), 7.14−7.03 (m, 15H, ArH), 6.54 (d, J = 6.8 Hz, 8H, ArH), 6.36 (s, 2H, ArH), 5.82 (s, 2H, Ph2CH), 4.99 (t, J = 6.7 Hz, 1H, NH), 1.98 (s, 3H, ArCH3). 13C NMR

(dd, J = 11.2, 4.7 Hz, 4H, ArH), 7.41−7.29 (m, 8H, ArH), 7.29−7.19 (m, 10H, ArH), 6.88−6.85 (m, 8H, ArH), 6.62 (s, 2H, ArH), 5.69 (d, J = 2.1 Hz, 2H, Ph2CH), 2.17 (s, 3H, ArCH3). 13C NMR (126 MHz, CDCl3): δ 143.93 (s), 135.69 (s), 131.07 (s), 130.88 (s), 130.24 (s), 129.83 (s), 129.72 (s), 128.65 (s), 128.46 (d, J = 7.8 Hz), 128.24 (s), 127.99 (s), 126.01 (s), 50.43 (d, J = 3.6 Hz), 21.37 (s). 31P{1H} NMR (162 MHz, CDCl3): δ 115.13 (s). FT−IR (KBr disk, cm−1): 3056 m, 3023 m, 2855 w, 1596 w, 1458 s, 1447 s, 1263 m, 1250 m, 1203 w, 863 m, 850 m, 716 s, 693 s. ESI-MS: m/z calcd. for C45H38OP (M+H)+: 625.2655. Found: 625.2658. Synthesis of Complex [RuCl2{(η6-p-cymene)PPh2-NHAr*}-κ1P] (3). A solution of [Ru(η6-p-cymene)Cl2]2 (0.015 g, 0.024 mmol) in dichloromethane (8 mL) was added, dropwise, to a solution of 1 (0.03 g, 0.048 mmol) also in dichloromethane (7 mL). The reaction mixture was stirred at room temperature for 4 h, and the solvent was removed under reduced pressure; the residue obtained was washed with petroleum ether (1 × 10 mL) to remove free p-cymene and dried under vacuum to give 3 as a red solid. Single crystals of 3, suitable for X-ray studies, were grown from a (1:1) mixture of dichloromethane and petroleum ether over 24 h. Yield 89.6% (0.040 g). mp = 220−223 °C (dec). Anal. Calcd for C55H52Cl2NPRu·CH2Cl2: C, 66.27; H, 5.36; N, 1.38. Found: C, 66.38; H, 5.67; N, 1.57. 1H NMR (400 MHz, CDCl3): δ 7.84−7.74 (m, 4H, ArH), 7.36 (d, J = 7.0 Hz, 2H, ArH), 7.29 (d, J = 6.6 Hz, 4H, ArH), 7.07 (s, 12H, ArH), 6.61 (s, 8H, ArH), 6.41 (s, 2H, ArH), 6.15 (s, 2H, Ph2CH), 5.25 (d, J = 14.9 Hz, 1H, NH), 4.78 (dd, J = 27.6, 5.8 Hz, 4H, p-cymene), 2.79−2.71 (m, 1H, (CH3)2CH), 1.98 (s, 3H, ArCH3), 1.89 (s, 3H, ArCH3), 1.13 (d, J = 6.9 Hz, 6H, (CH3)2CH). 13C NMR (101 MHz, CDCl3): δ 144.49 (s), 143.84 (s), 135.08 (s), 134.35 (d, J = 10.5 Hz), 130.77 (s), 129.85 (s), 129.40 (s), 127.81 (s), 127.77 (s), 127.71(s), 125.65 (s), 95.90 (s), 90.54 (s), 86.78 (d, J = 6.1 Hz), 50.41 (s), 30.51 (s), 22.44 (s), 21.49 (s), 18.16 (s). 31P{1H} NMR (202 MHz, CDCl3): δ 57.0 (s). FT−IR (KBr disk, cm−1): 3056 w, 3019 w, 2961 m, 2920 m, 2851 w, 1260 m, 1099 s, 1030 w, 803 s, 702 s. ESI-MS: m/z calcd. for C55H52Cl2NNaPRu (M+Na)+: 952.2159. Found: 952.2331. Synthesis of Complex [RuCl2{(η6-p-cymene)PPh2-OAr*}-κ1-P] (4). A solution of [Ru(η6-p-cymene)Cl2]2 (0.010 g, 0.016 mmol) in dichloromethane (9 mL) was added dropwise to a solution of 2 (0.02 g, 0.032 mmol) in the same solvent (6 mL) and the reaction mixture was stirred at room temperature for 4 h. After the removal of solvent completely under reduced pressure, the residue obtained was washed with petroleum ether (2 × 5 mL) to remove the free p-cymene and the residue was dried under vacuum to give compound 4 as a red solid. Yield 77.2% (0.023 g). mp = 230−233 °C (dec). Anal. Calcd for C55H51Cl2OPRu·CH2Cl2: C, 66.21; H, 5.26. Found: C, 66.61; H, 5.05. 1 H NMR (500 MHz, CDCl3): δ 7.79 (t, J = 8.7 Hz, 4H, ArH), 7.34 (t, J = 7.3 Hz, 3H, ArH), 7.19 (qd, J = 14.5, 7.6 Hz, 15H, ArH), 6.78 (d, J = 7.2 Hz, 8H, ArH), 6.52 (s, 2H, ArH), 6.19 (s, 2H, Ph2CH), 5.10 (d, J = 5.7 Hz, 2H, p-cymene), 4.73 (d, J = 5.8 Hz, 2H, p-cymene), 2.89 (m, 1H, (CH3)2CH), 2.02 (s, 3H, ArCH3), 1.17 (d, J = 6.9 Hz, 6H, (CH3)2CH), 1.09 (s, 3H, p-cymene CH3). 13C NMR (101 MHz, CDCl3): δ 144.59 (s), 135.94 (s), 134.72 (s), 131.03 (s), 130.81 (s), 130.16 (s), 129.73 (d, J = 8.3 Hz), 128.23 (s), 127.96 (s), 127.14 (d, J = 9.5 Hz), 126.22 (s), 103.82 (s), 100.33 (s), 89.26 (s), 86.47 (s), 49.94 (s), 30.21 (s), 21.99 (s), 21.29 (s), 17.63 (s). 31P{1H} NMR (162 MHz, CDCl3): δ 123.9 (s). FT−IR (KBr disk, cm−1): 3060 w, 3024 w, 2964 m, 2923 m, 2853 w, 1494 w, 1433 m, 1261 m, 1110 s, 1030 w, 871 w, 803 w, 737 s, 703 s. ESI-MS: m/z calcd. for C55H51ClOPRu (M−C1)+: 895.2416. Found: 895.2402. Synthesis of Complex [RuCl2(PPh2-NHAr*)-κ1-P] (5) (Method A). A solution of 3 (0.03 g, 0.032 mmol) in chlorobenzene was heated at 120 °C for 16 h. The resulting solution was filtered through Celite, washed with diethyl ether (2 × 5 mL), and dried under vacuum to give analytically pure product of 5 as an orange solid. Crystals suitable for X-ray analysis were obtained by slow diffusion of dichloromethane into the petroleum ether solution of 5 at room temperature. Yield 82.5% (0.021 g). mp = 262−267 °C (dec). Anal. Calcd for C45H38Cl2NPRu: C, 67.92; H, 4.81; N, 1.76. Found: C, 67.87; H, 4.47; N, 1.80. 1H NMR (500 MHz, CDCl3): δ 8.03−8.01 (m, 2H, ArH), 7.84−7.77 (m, 2H, ArH), 7.40 (d, J = 6.7 Hz, 3H, ArH), 7.32 (d, J = 7.3 Hz, 1H, I


Article

Inorganic Chemistry (126 MHz, CDCl3): δ 143.91 (s), 142.52 (s), 135.19 (s), 134.23 (t, J = 6.8 Hz), 130.73 (s), 129.95 (d, J = 12.5 Hz), 128.27 (s), 127.98 (s), 126.10 (s), 51.88 (s), 21.54 (s). 31P{1H} NMR (202 MHz, CDCl3): δ 54.56 (s). FT-IR (KBr disk, cm−1): 3324 s, 3053 m, 3023 w, 2960 w, 1596 w, 1440 s, 1259 s, 1097 s, 1026 w, 800 s, 697 s. ESI-MS: m/z calcd. for C90H76Cl2KN2P2Pd (M+K)+: 1463.3543. Found: 1463.3505. Synthesis of [PtCl2{(PPh2NHAr*)-κ1-P}2] (8). A solution of Pt(COD)Cl2 (0.018 g, 0.048 mmol) in dichloromethane (10 mL) was added dropwise to a solution of 1 (0.06 g, 0.096 mmol) in the same solvent (15 mL) and stirred for 4 h. After the removal of solvent under reduced pressure, the residue obtained was washed with petroleum ether (2 × 6 mL) and dried under vacuum to give 8 as a colorless crystalline solid. X-ray-quality crystals were grown from a 1:1 mixture of CH2Cl2 and petroleum ether. Yield 80% (0.058 g). mp = 223−228 °C. Anal. Calcd for C90H76N2P2PtCl2: C, 71.42; H, 5.06; N, 1.85. Found: C, 71.34; H, 4.88; N, 1.76. 1H NMR (500 MHz, CDCl3): δ 7.50 (d, J = 6.0 Hz, 4H, ArH), 7.32−7.26 (m, 4H, ArH), 7.08 (td, J = 14.2, 6.5 Hz, 14H, ArH), 6.55 (d, J = 7.3 Hz, 8H, ArH), 6.37 (s, 2H, ArH), 5.87 (s, 2H, Ph2CH), 4.95 (s, 1H, NH), 2.01 (s, 3H, ArCH3). 13 C NMR (126 MHz, CDCl3): δ 143.97 (s), 142.71 (s), 134.33 (s), 133.94 (s), 130.69 (s), 129.90 (s), 129.65 (s), 128.58 (s), 128.03(s), 127.80 (t, J = 5.4 Hz), 126.20 (s), 126.04 (s), 51.80 (s), 21.52 (s). 31 1 P{ H} NMR (162 MHz, CDCl3): δ 46.00 (s, 1JPtP = 2611.44 Hz). FT-IR (KBr disk, cm−1): 3250 m, 3053 m, 3023 m, 2960 m, 1631 m, 1451 m, 1259 s, 1099 s, 1030 m, 801 s, 699 s. ESI-MS: m/z calcd. for C90H76ClN2P2Pt (M−C1)+: 1477.4831. Found: 1477.4814. Synthesis of [PdCl2{(PPh2OAr*)-κ1-P}2] (9). A solution of Pd(COD)Cl2 (0.014 g, 0.048 mmol) in dichloromethane (15 mL) was added dropwise to a solution of 2 (0.06 g, 0.096 mmol) in the same solvent (12 mL), and the reaction was stirred for 4 h. The solvent was removed under reduced pressure and the residue obtained was washed with petroleum ether (1 × 10 mL) dried under vacuum to give 9 as a yellow solid. Yield 73% (0.050 g). mp = 215−218 °C (dec). Anal. Calcd for C90H74O2P2PdCl2: C, 75.76; H, 5.23. Found: C, 75.43; H, 5.02. 1H NMR (400 MHz, CDCl3): δ 7.23 (m, 2H, ArH), 7.19− 7.11 (m, 3H, ArH), 7.07 (d, J = 7.1 Hz, 5H, ArH), 7.01 (t, J = 7.3 Hz, 8H, ArH), 6.90 (d, J = 7.3 Hz, 12H, ArH), 6.73 (s, 2H, ArH), 5.69 (s, 2H, Ph2CH), 2.28 (s, 3H, ArCH3). 13C NMR (126 MHz, CDCl3): δ 150.98 (s), 143.92 (s), 136.20 (s), 134.23 (s), 133.89 (d, J = 31.3 Hz), 133.68 (d, J = 7.3 Hz), 130.85 (s), 130.46 (s), 129.88 (s), 129.79 (d, J = 22.7 Hz), 127.98 (s), 127.73 (s), 127.44 (s), 127.39 (s), 127.35 (s), 126.04 (s), 51.36 (s), 21.73 (s). 31P{1H} NMR (162 MHz, CDCl3): δ 100.71 (s). FT-IR (KBr disk, cm−1): 3053 m, 3023 m, 2956 w, 1596 w, 1436 m, 1255 m, 1196 m, 1116 m, 1097 m, 801 m, 699 s. ESI-MS: m/ z calcd. for C 90 H74 ClO2P 2 Pd (M−C1) +: 1391.3905. Found: 1391.3903. Synthesis of [PtCl2{(PPh2OAr*)-κ1-P}2] (10). A solution of Pt(COD)Cl2 (0.009 g, 0.024 mmol) in dichloromethane (8 mL) was added dropwise to a solution of 2 (0.03 g, 0.048 mmol) in the same solvent (9 mL), and the reaction mixture was stirred for 4 h. The solvent was removed under vacuo to give 10 as white solid. The product was washed with petroleum ether (1 × 10 mL) to remove the free cyclooctadiene. The crystals of 10 suitable for X-ray analysis were obtained by recrystallizing 10 in a 1:1 mixture of dichloromethane and petroleum ether at room temperature. Yield 85.2% (0.031 g). mp = 245−248 °C (dec). Anal. Calcd for C90H74O2P2PtCl2·2CH2Cl2: C, 65.56; H, 4.66. Found: C, 65.44; H, 4.25. 1H NMR (400 MHz, CDCl3) δ 7.24 (s, 2H, ArH), 7.15 (d, J = 7.4 Hz, 4H, ArH), 7.12−7.06 (m, 6H, ArH), 7.02 (t, J = 7.3 Hz, 8H, ArH), 6.90 (d, J = 7.1 Hz, 12H, ArH), 6.71 (s, 2H, ArH), 5.72 (s, 2H, Ph2CH), 2.28 (s, 3H, ArCH3). 13 C NMR (126 MHz, CDCl3): δ 150.64 (s), 143.99 (s), 136.31 (s), 133.70 (s), 130.81 (s), 130.46 (s), 129.86 (s), 127.72 (s), 127.35 (s), 126.04 (s), 100.15 (s), 51.30 (s), 31.04 (s), 21.73 (s). 31P{1H} NMR (162 MHz, CDCl3): δ 90.36 (s, 1JPtP = 2887.94 Hz). FT-IR (KBr disk, cm−1): 3083 w, 3056 m, 3024 w, 2961 w, 1436 m, 1260 m, 1118 s, 1099 s, 1030 w, 801 s, 699 s. ESI-MS: m/z calcd. for C90H74Cl2KO2P2Pt (M+K)+: 1553.3828. Found: 1553.3811. Synthesis of [PdCl2{(PPh2NHAr*)-κ1-P}]2 (11). A solution of Pd(COD)Cl2 (0.013 g, 0.048 mmol) in dichloromethane (8 mL) was added dropwise to a solution of 1 (0.03 g, 0.048 mmol) also in

dichloromethane (10 mL) with constant stirring. The reaction mixture was allowed to be subjected to stirring for 4 h. After removal of solvent completely under reduced pressure, the residue obtained was washed with petroleum ether (1 × 10 mL) and dried under vacuum to give 11 as a yellow solid. Single crystals suitable for X-ray diffraction were grown from a (1:1) mixture of CHCl3 and petroleum ether over 24 h. Yield 83% (0.032 g). mp = 188 °C (dec). Anal. Calcd for C90H76N2P2Pd2Cl4·CHCl3: C, 63.48; H, 4.50; N, 1.62. Found: C, 64.34; H, 4.50; N, 1.62. 1H NMR (500 MHz, CDCl3): δ 7.42 (s, 5H, ArH), 7.21 (dd, J = 26.2, 19.9 Hz, 17H, ArH), 6.86 (d, J = 6.3 Hz, 8H, ArH), 6.46 (s, 2H, ArH), 6.27 (s, 2H, Ph2CH), 2.37 (s, 1H, NH), 2.03 (s, 3H, ArCH3). 13C NMR (126 MHz, CDCl3): δ 143.45 (s), 142.55 (s), 133.69 (t, J = 12.7 Hz), 132.12 (s), 130.47 (s), 130.03 (d, J = 13.3 Hz), 128.56 (s), 128.53 (s), 128.45 (s), 128.31 (s), 126.60 (s), 116.73 (s), 52.36 (s), 31.09 (s), 21.62 (s). 31P{1H} NMR (CDCl3): δ 61.21 (s). FT-IR (KBr disk, cm−1): 2963 m, 1261 s, 1098 s, 1019 m, 863 m, 802 s, 700 m. ESI-MS: m/z calcd. for C45H38ClNPPd (M+H)+: 764.1473. Found: 764.1406. Synthesis of [PdCl2{(PPh2OAr*)-κ1-P}]2 (12). A solution of Pd(COD)Cl2 (0.010 g, 0.035 mmol) in dichloromethane (5 mL) was added dropwise to a solution of 2 (0.022 g, 0.035 mmol) also in dichloromethane (6 mL), and the clear solution obtained was stirred for 4 h. After the removal of solvent under reduced pressure, the residue obtained was washed with petroleum ether (2 × 8 mL) and dried under vacuum to give 12 as a yellow solid. Single crystals suitable for X-ray diffraction were grown from a 1:1 mixture of CHCl3 and toluene over 48 h at room temperature. Yield 73.3% (0.022 g). mp = 228−232 °C (dec). Anal. Calcd for C90H74O2P2Pd2Cl4·CHCl3: C, 63.42; H, 4.38. Found: C, 63.53; H, 4.78. 1H NMR (400 MHz, CDCl3): δ 7.36−7.31 (m, 4H, ArH), 7.23−7.17 (m, 12H, ArH), 7.12 (d, J = 5.0 Hz, 6H, ArH), 7.06 (d, J = 6.8 Hz, 8H, ArH), 6.48 (s, 2H, ArH), 6.19 (s, 2H, Ph2CH), 2.04 (s, 3H, ArCH3). 31P{1H} NMR (CDCl3): δ 102.60 (s). FT-IR (KBr disk, cm−1): 3053 m, 3019 m, 2952 w, 2915 w, 1598 m, 1434 s, 1257 m, 1192 m, 1099 s, 928 m, 800 m, 701 s. ESI-MS: m/z calcd. for C90H74Cl4NaO2P2Pd2 (M+Na)+: 1627.1894. Found: 1627.1509. Synthesis of [PdCl{(η3-C3H5)(PPh2NHAr*)-κ1-P}] (13). A solution of [Pd(η3-C3H5)Cl]2 (0.012 g, 0.032 mmol) in dichloromethane (6 mL) was added dropwise to a solution of 1 (0.04 g, 0.062 mmol) also in dichloromethane (6 mL) and stirred for 4 h. The solvent was removed under reduced pressure to give compound 13 as a yellow solid. X-ray-quality crystals were grown from a 1:1 mixture of CH2Cl2 and petroleum ether at room temperature over 24 h. Yield 88% (0.044 g). mp = 174 °C (dec.). Anal. Calcd for C48H43NPPdCl: C, 71.47; H, 5.37; N, 1.74. Found: C, 71.53; H, 5.27; N, 1.82. 1H NMR (500 MHz, CDCl3): δ 7.36 (dt, J = 11.4, 7.0 Hz, 6H, ArH), 7.30 (d, J = 6.9 Hz, 4H, ArH), 7.24−7.16 (m, 12H, ArH), 6.83 (t, J = 6.5 Hz, 8H, ArH), 6.56 (s, 2H, ArH), 5.69 (s, 2H, Ph2CH), 5.17−5.07 (m, 1H, η3-C3H5), 4.78 (t, J = 7.5 Hz, 1H, η3-C3H5), 3.62 (dd, J = 13.5, 10.9 Hz, 1H, η3C3H5), 3.35 (d, J = 4.2 Hz, 1H, NH), 3.03 (d, J = 5.5 Hz, 1H, η3C3H5), 2.10 (s, 3H), 1.94 (d, J = 12.2 Hz, 1H, η3-C3H5). 13C NMR (126 MHz, CDCl3): δ 143.60 (s), 142.45 (s), 138.20 (s), 136.00 (s), 132.64 (s), 130.83 (s), 129.90 (s), 129.89 (d, J = 11.6 Hz), 128.36 (s), 126.54 (s), 117.69 (s), 80.46 (d, J = 31.1 Hz), 56.76 (s), 52.44 (s), 21.79 (s). 31P{1H} NMR (202 MHz, CDCl3): δ 69.05 (s). FT-IR (KBr disk, cm−1): 3048 w, 3024 w, 2961 m, 2919 w, 1449 m, 1435 m, 1261 s, 1093 m, 1029 m, 802 s, 707 s, 699 s. ESI-MS: m/z calcd. for C48H43NPPd (M−Cl)+: 770.2180. Found: 770.2180. Synthesis of [PdCl{(η3-C3H5)(PPh2OAr*)-κ1-P}] (14). A solution of [Pd(η3-C3H5)Cl]2 (0.012 g, 0.032 mmol) in dichloromethane (9 mL) was added, dropwise, to a solution of 2 (0.04 g, 0.062 mmol) also in dichloromethane (7 mL) with constant stirring. The reaction mixture was allowed to be subjected to stirring for 4 h. The solvent was evaporated under reduced pressure to afford 14 as a yellow solid. Single crystals suitable for X-ray diffraction were grown from a 1:1 mixture of CH2Cl2 and petroleum ether. Yield 72% (0.036 g). mp = 152 °C (dec.). Anal. Calcd for C48H42OPPdCl: C, 71.37; H, 5.24; Found: C, 71.48; H, 5.51. 1H NMR (500 MHz, CDCl3): δ 7.71−7.62 (m, 4H, ArH), 7.43 (d, J = 6.7 Hz, 2H, ArH), 7.34 (d, J = 5.2 Hz, 4H, ArH), 7.26 (s, 12H, ArH), 6.95−6.81 (m, 8H, ArH), 6.72 (s, 2H, J


Article

Inorganic Chemistry ArH), 5.67 (s, 2H, Ph2CH), 5.30−5.20 (m, 1H, η3-C3H5), 4.97 (t, J = 7.5 Hz, 1H, η3-C3H5), 3.84−3.76 (m, 1H, η3-C3H5), 3.07 (d, J = 5.0 Hz, 1H, η3-C3H5), 2.21 (s, 3H, ArCH3), 2.03 (d, J = 12.2 Hz, 1H, η3C3H5). 13C NMR (126 MHz, CDCl3): δ 151.23 (s), 143.40 (s), 136.04 (s), 134.49 (s), 132.65 (s), 132.52 (s), 132.30 (s), 132.16 (s), 131.49 (s), 131.28 (s), 130.37 (s), 129.76 (s), 128.43 (s), 128.17 (d, J = 32.0 Hz), 126.38 (s), 118.15 (s), 83.08 (d, J = 32.5 Hz), 56.70 (s), 50.99 (s), 21.51(s). 31P{1H} NMR (CDCl3): δ 132.11 (s). FT−IR (KBr disk, cm−1): 3054 w, 3019 m, 2924 m, 2852 w, 1260 w, 1199 w, 1097 m, 1028 w, 875 w, 707 s, 695 s. ESI-MS: m/z calcd. for C48H42OPPd (M−Cl)+: 771.2020. Found: 771.2016. General Procedure for the Catalytic Oxidation of Olefins. Styrene (0.4 mmol) and catalyst 5 (1 mol %) were placed in a roundbottom flask. Two mL of acetonitrile and 1 mL of H2O were added to it. NaIO4 (256 mg, 1.2 mmol) was dissolved in 1 mL of H2O and transferred to the reaction mixture. The reaction mixture was stirred at room temperature for ∼15−360 min. The reaction products and unreacted substrates were analyzed by gas chromatography/mass spectroscopy (GC/MS). The conversion of the products were calculated via GC/MS analyses.

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Nixon, J. F.; Laurent, J. C. T. R. B. S. Coordination chemistry of diphosphinoamine and cyclodiphosphazane ligands. Coord. Chem. Rev. 1994, 129, 1−90. (d) Grabulosa, A.; Granell, J.; Muller, G. Preparation of optically pure P-stereogenic trivalent phosphorus compounds. Coord. Chem. Rev. 2007, 251, 25−90. (2) (a) Walker, S. D.; Barder, T. E.; Martinelli, J. R.; Buchwald, S. L. A Rationally Designed Universal Catalyst for Suzuki−Miyaura Coupling Processes. Angew. Chem., Int. Ed. 2004, 43, 1871−1876. (b) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. Catalysts for Suzuki−Miyaura Coupling Processes: Scope and Studies of the Effect of Ligand Structure. J. Am. Chem. Soc. 2005, 127, 4685− 4696. (c) Surry, D. S.; Buchwald, S. L. Dialkylbiaryl phosphines in Pdcatalyzed amination: a user’s guide. Chem. Sci. 2011, 2, 27−50. (d) Arrechea, P. L.; Buchwald, S. L. Biaryl Phosphine Based Pd(II) Amido Complexes: The Effect of Ligand Structure on Reductive Elimination. J. Am. Chem. Soc. 2016, 138, 12486−12493. (e) Sather, A. C.; Buchwald, S. L. The Evolution of Pd0/PdII-Catalyzed Aromatic Fluorination. Acc. Chem. Res. 2016, 49, 2146−2157. (f) Ingoglia, B. T.; Buchwald, S. L. Oxidative Addition Complexes as Precatalysts for Cross-Coupling Reactions Requiring Extremely Bulky Biarylphosphine Ligands. Org. Lett. 2017, 19, 2853−2856. (g) Doherty, S.; Smyth, C. H.; Knight, J. G.; Hashmi, S. A. K. Synthesis of an electron-rich KITPHOS monophosphine, preparation of derived metal complexes and applications in catalysis. Nat. Protoc. 2012, 7, 1870−1883. (h) Doherty, S.; Knight, J. G.; McGrady, J. P.; Ferguson, A. M.; Ward, N. A. B.; Harrington, R. W.; Clegg, W. ortho,ortho′-Substituted KITPHOS Monophosphines: Highly Efficient Ligands for PalladiumCatalyzed C−C and C−N Bond Formation. Adv. Synth. Catal. 2010, 352, 201−211. (3) (a) Aydemir, M.; Baysal, A.; Gürbüz, N.; Ö zdemir, I.̇ ; Gümgüm, B.; Ö zkar, S.; Ç aylak, N.; Yıldırım, L. T. Synthesis and characterization of new (N-diphenylphosphino)-isopropylanilines and their complexes: crystal structure of (Ph2PS)NH−C6H4−4-CH(CH3)2 and catalytic activity of palladium(II) complexes in the Heck and Suzuki crosscoupling reactions. Appl. Organomet. Chem. 2010, 24, 17−24. (b) Poetschke, N.; Nieger, M.; Khan, M. A.; Niecke, E.; Ashby, M. T. Synthesis and Crystal Structures of Lithium Salts of New Iminophosphide/Phosphinoamide Anions. Inorg. Chem. 1997, 36, 4087−4093. (c) Rivard, E.; Lough, A. J.; Manners, I. Synthesis, characterization and thermolysis of phosphinite-borane adducts: Investigation of an unusual thermally-induced phenol elimination reaction. J. Chem. Soc., Dalton Trans. 2002, 2966−2972. (4) (a) Iwai, T.; Tanaka, R.; Sawamura, M. Synthesis, Coordination Properties, and Catalytic Application of Triarylmethane-Monophosphines. Organometallics 2016, 35, 3959−3969. (b) Bottcher, T.; Jones, C. Extremely bulky secondary phosphinoamines as substituents for sterically hindered aminosilanes. Dalton Trans. 2015, 44, 14842− 14853. (5) Doherty, S.; Knight, J. G.; Addyman, C. R.; Smyth, C. H.; Ward, N. A. B.; Harrington, R. W. Ruthenium Complexes of κ(P)- and κ(P)η6-Coordinated KITPHOS Monophosphines: Efficient Catalysts for the Direct Ortho Arylation of 2-Phenylpyridine and N-Phenylpyrazole with Aryl Chlorides. Organometallics 2011, 30, 6010−6016. (6) (a) Ghebreyessus, K. Y.; Nelson, J. H. Base-Promoted Hydroalkylation Reactions of 1,3,5-Me3C6H3, p-MeC6H4CHMe2, C6Me6, p-MeC6H4Me, and MeC6H5 Ligands Coordinated to Ruthenium(II). Organometallics 2000, 19, 3387−3392. (b) Umezawa-Vizzini, K.; Guzman-Jimenez, I. Y.; Whitmire, K. H.; Lee, T. R. Synthesis, Characterization, and Thermal Stability of (η6 :η1C6H5CH2CH2PR2)Ru(CH3)2 (R = Cy, Ph, Et). Organometallics 2003, 22, 3059−3065. (c) Pinto, P.; Marconi, G.; Heinemann, F. W.; Zenneck, U. Chiral Arene Ruthenium Complexes. 6. Diastereoselective Formation of Chiral-At-Metal P-Tethered Arene Ruthenium(II) Complexes. Organometallics 2004, 23, 374−380. (d) Navarro, M.; Vidal, D.; Clavero, P.; Grabulosa, A.; Muller, G. Mild Photochemical Tethering of [RuCl2(η6-arene)P*] Complexes with P-Stereogenic 2-Biphenylylphosphines. Organometallics 2015, 34, 973−994. (e) Faller, J. W.; Fontaine, P. P. Resolution and Diels−Alder Catalysis with Planar Chiral Arene-Tethered Ruthenium Complexes.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01095. NMR and HRMS data for 1−14 (PDF) Accession Codes

CCDC 1836869−1836879 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: + 44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*Fax:+91-22-5172-3480/2576-7152. E-mail addresses: [email protected], [email protected]. ORCID

Maravanji S. Balakrishna: 0000-0003-3736-6148 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Science & Engineering Research Board, New Delhi, for financial support of this work through Grant No. SB/S1/IC-108/2014. We also thank the Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, for instrumentation facilities, as well as spectral and analytical data. M.K.P. thanks UGC, New Delhi for SRF fellowship. J.T.M. thanks the Louisiana Board of Regents for the purchase of the APEX CCD diffractometer, an NSF-MRI grant (No. 1228232) for the purchase of the D8 VENTURE diffractometer, and the Chemistry Department of Tulane University for support of the X-ray laboratory.

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