Modulation of an Anagostic Interaction in SiPSi-Type Pincer Platinum

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Modulation of an Anagostic Interaction in SiPSi-Type Pincer Platinum Complexes Julio Zamora-Moreno,† Fernando Murillo,‡ Miguel A. Muñoz-Hernández,† Mary Grellier,§ Sudip Pan,‡ Said Jalife,‡ Gabriel Merino,*,‡ Sylviane Sabo-Etienne,*,§ and Virginia Montiel-Palma*,† †

Centro de Investigaciones Químicas, Instituto de Investigación en Ciencias Básicas y Aplicadas, Universidad Autónoma del Estado de Morelos, Avenida Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos C. P. 62209, Mexico ‡ Departamento de Física Aplicada, CINVESTAV Unidad Mérida, km 6, Antigua Carretera a Progreso, AP 73, Cordemex, Mérida 97310, Yucatán, Mexico § LCC-CNRS, Université de Toulouse, CNRS, UPS, 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France S Supporting Information *

ABSTRACT: The reactivities of tris(benzyldimethylsilyl)phosphine [P(o-C 6 H 4 -CH 2 SiMe 2 H) 3 ] (1) and tris(benzyldiphenylsilyl)phosphine [P(o-C6H4-CH2SiPh2H)3] (6) toward the same platinum precursor [Pt(PPh3)3] are strikingly different. The reaction with 1 renders the trans disilyl platinum(II) complex [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4CHSiMe2)}PPh3] (2) in which the ligand coordinates in a tridentate fashion while a new Si−C bond is formed from the third Si moiety. The most prominent feature is an anagostic interaction that is established at the apical position. In contrast, the reaction of [Pt(PPh3)3] with 6 yields the hexacoordinated hydrido trisilyl platinum(IV) complex [PtH{P(o-C6H4CH2SiPh2)3}PPh3] (7). We have studied the effect of the variation of the monodentate ligand in 2 by simple substitution reactions. We found a systematic variation of the chemical shift of the anagostic hydrogen in the 1H nuclear magnetic resonance spectrum of the corresponding PMe3, P(OPh)3, and CO complexes that can in principle be ascribed to a varying degree of the π acceptor character of the ancillary ligand. However, theoretical calculations at the density functional theory level show only slight changes in the frontier orbitals in line with predominantly closed-shell electrostatic interactions.

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electron subshells.8 However, as a result of the interplay between the orientation of the applied magnetic field B0 and the M−H bond vector, downfield shifts of hydrogen atoms attached to a metal center could result when B0 is oriented perpendicular to the bond vector instead of parallel to it.8,9 This latter situation takes place in anagostic systems in which a downfield hydrogen is observed in the 1H NMR spectra, yet the idea of being able to control the degree of an anagostic interaction, with a predominantly electrostatic character, in the complex framework has been sparingly explored.10−14 As part of our program for studying the chemistry of coordination of silylphosphine ligands to transition metals, we recently reported the quantitative reaction of tris(benzyldimethylsilyl)phosphine [P(o-C6H4-CH2SiMe2H)3] (1) with [Pt(PPh3)3] to render the trans silyl square planar platinum(II) complex [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4CHSiMe2)}PPh3] (2), in which two of the three silicon atoms were directly bonded to Pt while a Si−C bond has been

INTRODUCTION Bonding is at the root of chemistry, and the idea of being able to modulate the degree of bonding is one of the major aims of many chemists. Today, controlling C−H bond activation represents a major issue for applications in a variety of fields, particularly in catalysis. Much has been debated about the blurred line among agostic, anagostic, and even classical interactions.1 Their nature has been established in a variety of works by a number of different authors, and consensus has been nearly reached in the chemistry community about their implications in many transformations and the factors leading to the formation of such types of bonds.2−4 Undoubtedly, the study of these types of bonding can shed light on the fundamentals of C−H bond activation,5,6 and one can note that anagostic interactions have been much less studied than their agostic counterparts. The origin of upfield “hydric” 1H nuclear magnetic resonance (NMR) chemical shifts of hydrogen atoms directly attached to late transition metals has been explained by a number of different authors starting in 1964.7 There is a general consensus that the electronic contribution of transition metals can be explained in terms of paramagnetic shielding by incomplete d © XXXX American Chemical Society

Special Issue: In Honor of the Career of Ernesto Carmona Received: April 27, 2018

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DOI: 10.1021/acs.organomet.8b00269 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics created from the third Si atom (Scheme 1).15 We pointed out a C−H−Pt anagostic interaction at the apical position from one

Scheme 2. Reactivity of Complex 2 toward Different Neutral Ligands

Scheme 1. Reactions of [Pt(PPh3)3] with Tribenzylsilylphosphines 115 and 6 (this work)

P(OPh)3. Their formulation is supported by elemental analysis, multinuclear NMR data, and X-ray diffraction in the case of 4. Altogether, the results allow us to postulate that the anagostic interaction present in complex 2 has been preserved despite the substitution of the ancillary ligand. However, the extent of this interaction has been modified. Indeed, in the methylene region of the 1H NMR spectra of complexes 3 and 4, five signals are observed for the five inequivalent hydrogens of the “PSi3” ligand. In complex 3, two doublets of doublets at δ 4.57 and 2.10 are assigned to the anagostic hydrogen and its geminal hydrogen attached to the same carbon atom, respectively. The corresponding signals in complex 4 appear at δ 4.16 and 2.06, respectively. One can see that the anagostic signal is significantly shifted when going from 2 to 4. Table 1 gathers

hydrogen of the methylene attached to the noncoordinated Si. It was characterized by a distinct chemical shift in the 1H NMR spectrum, ∼2 ppm downfield of its diastereotopic counterpart. Herein, we report our results for substitution reactions of complex 2 that aim to preserve the general structure of the complex while replacing the neutral monodentate ligand, PPh3, with other two electron donor ligands. The resulting complexes bearing PMe3 (3), P(OPh)3 (4), and CO (5) were obtained. We found that the anagostic interaction in complexes 3−5 is preserved with systematic variations in the 1H NMR chemical shifts of the anagostic hydrogens. These variations are rationalized using a series of density functional theory (DFT) computations. On the other hand, replacing the methyl substituents on the silicon atoms of parent compound 1 with phenyl groups generates new compound 6 that turns to display a different coordination mode to the same platinum precursor. Indeed, the reaction of 6 with [Pt(PPh3)3] results in the formation of hexacoordinate Pt(IV) complex 7 (Scheme 1) with a tetradentate PSi3 ligand arising from 6.

Table 1. 1H NMR Chemical Shifts of the Anagostic and Geminal Hydrogen Atoms for Complexes 2−5 Recorded in C6D6 (400 MHz)a 1

complex 2 3 4 5 a

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RESULTS AND DISCUSSION The reactivity of platinum complex [Pt{P(o-C 6 H 4 CH2SiMe2)2(o-C6H4-CHSiMe2)}PPh3] (2) toward small molecules was probed with various solvents and at various stoichiometric ratios and temperatures. Complex 2 did not react in our hands with H2, Et3SiH, pyridine, or PCy3 even when the molar ratio of the reactants was increased (≤5 bar of H2 or 10 equiv of other reagents) and the reaction temperature was increased to 383 K in toluene. However, only mild reaction conditions are needed for substitution reactions to proceed with PMe3 and P(OPh)3, while an equilibrium takes place upon reaction with CO as described below (Scheme 2). Synthesis and Characterization of [Pt{P(o-C6H4CH2SiMe2)2(o-C6H4-CHSiMe2)}PMe3] (3) and [Pt{P(oC6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}P(OPh)3] (4). Addition of PMe3 or P(OPh)3 to equimolar benzene or toluene solutions of 2 at room temperature led to quantitative formation of yellow precipitates. After workup, platinum(II) complexes [Pt{P(o-C 6H4 -CH2SiMe2 )2 (o-C 6H 4-CHSiMe2 )}PMe3 ] (3) and [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}P(OPh)3] (4) were isolated in quantitative yields (99%) (Scheme 2). The two complexes result from the substitution of the originally coordinated triphenylphosphine ligand in 2 by PMe3 or

H NMR δ anagostic (ppm) 4.60 4.57 4.16 3.79

(4.76) (4.66) (4.29) (3.85)

1

H NMR δ geminal (ppm) 2.30 2.10 2.06 2.10

(2.33) (2.12) (1.97) (2.26)

Δδ (ppm) 2.30 2.47 2.10 1.69

(2.44) (2.54) (2.32) (1.59)

The values calculated by DFT are given in parentheses.

these findings, while Figure 1 shows the comparison of the methylene regions of the 1H NMR spectra of all the platinum complexes presented herein. The downfield shift of the

Figure 1. Methylene region of the 1H NMR spectra of complexes 2−5 recorded in C6D6 (400 MHz). B


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Organometallics

which is also comparable with the DFT value of 141.2°. These values lie within the proposed ranges of 2.3−2.9 Å and 110− 170°, respectively, for anagostic interactions as reported by several authors.1−3,16,17 Synthesis and Characterization of [Pt{P(o-C6H4CH2SiMe2)2(o-C6H4-CHSiMe2)}(CO)] (5). Exposure of complex 2 under 3 atm of CO at room temperature resulted in a change in the color of the solution from light to intense yellow within minutes. Previously, we had reported the reaction of the related complex [Pt{PhP(o-C6H4-CH2SiMe2)2}PPh3] with CO leading to the dicarbonyl [Pt{PhP(o-C6H4-CH2SiMe2)2}(CO)2] (A).15 However, in our case, the experimental and theoretical evidence is not consistent with the formation of a saturated species, and we propose the monocarbonyl formulation [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}(CO)] (5) (Scheme 2). As in the case of complex A, removal of the solvent upon vacuum or changing the CO atmosphere to argon resulted in the recovery of 2, which prevented the isolation of complex 5. The main 1H NMR features of complex 5 comprise the anagostic hydrogen as a doublet shifted to δ 3.79 (d, 2JH−H = 14.2 Hz), while the geminal hydrogen appears at δ 2.10 (dd, 2JH−H = 14.2 Hz, 4JH−P = 2.8 Hz). The anagostic hydrogen does not show the small 4JP−H coupling (1.2−3 Hz) that was characteristic of complexes 2−4. Five methyl signals are identified with integrations consistent with the proposed formulation (see the Supporting Information). In the 13C{1H} NMR spectrum, a large 2JC−P coupling could be identified for the carbonyl signal at δ 201.0, in agreement with the proposed structure. Finally, in the 31P{1H} NMR spectrum, a signal is observed at δ −1.43 with a 1JP−Pt of 2775 Hz. Bonding in Anagostic Complexes 2−5. Table 2 summarizes the most important results obtained at the PBE0-

anagostic hydrogen is well within the range proposed by several authors.1,3,16,17 As for complex 2, the 31P{1H} NMR spectra of 3 or 4 display two signals exhibiting large 2JP−P coupling constants indicative of a trans disposition of the two P ligands (357 and 552 Hz for 3 and 4, respectively). While the 2JP−P value in 3 is approximately the same in 2 (360 Hz), the much larger value in 4 suggests that, in solution, the P−Pt−P angle should be closer to the ideal value of 180° (vide inf ra for the discussion on the single-crystal X-ray diffraction of 4) than in 2 or 3. Moreover, the Pt−P coupling constants are approximately twice as large in complex 4 as in 2 or 3. The 1JPt−P values are 5370 and 2480 Hz in complex 4, while in complex 3, the corresponding values are 2838 and 2324 Hz, respectively, slightly smaller but yet comparable to those of complex 2 (3188 and 2503 Hz, respectively). The 1JP−Pt values in 4 are the largest reported for platinum complexes, even larger than those in the phosphinosilylcarborane trans-(CabP,Si)2Pt complexes that exhibit 1JP−Pt couplings between 2702 and 4049 Hz18 and certainly much larger than those found in related cis-P2PtSi2 (1300−1750 Hz).19−23 Crystals of 4 suitable for single-crystal X-ray diffraction analysis were grown from evaporation of a toluene/pentane solution at room temperature. As expected, the molecular structure (Figure 2, ESI) greatly resembles that of complex 2,15

Table 2. Computed Structural Parameters, Natural Charges (|e|), and Bond Critical Point (BCP) Properties for Pt···H Anagostic Interactions for Complexes 2−5 r(C−H···Pt) r(C−H) θ(Χ−Η···Pt) q(Pt) q(H) ρ(rc) ∇2ρ(rc) H(rc)

Figure 2. ORTEP diagram of complex 4 with thermal ellipsoids at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity except anagostic H212. Selected interatomic distances (angstroms) and angles (degrees): Pt1−H212, 2.42(2); Pt1−Si1, 2.4131(6); Pt1−Si2, 2.4471(6); Pt1−P1, 2.2994(6); Pt1−P2, 2.1887(6); Pt1−Si1, 2.4131(6); Pt1−Si2, 2.4471(6); Si1−Pt1−Si2, 174.04(2); P1−Pt1−P2, 176.96(2); P1−Pt1−Si1, 87.66(2); P1−Pt1− Si2, 87.25(2); P2−Pt1−Si1, 90.82(2); P2−Pt1−Si2, 94.12(2).

2

3

4

5

2.470 1.109 141.4 −0.653 0.273 0.0209 0.0541 −0.0007

2.389 1.111 141.4 −0.615 0.279 0.0244 0.0632 −0.0014

2.387 1.109 141.2 −0.713 0.271 0.0242 0.0640 −0.0013

2.413 1.109 139.6 −0.496 0.245 0.0231 0.0609 −0.0011

D3/def2-TZVP level for the computed geometries of complexes 2−5, concentrating on the C−H···Pt interaction. In the first place, it should be noticed that the computed 1H chemical shifts of both the anagostic and the geminal hydrogens, using benzene as a solvent, are in good agreement with the experimental values, allowing us to assume a good description of the geometrical and electronic structure of the complexes (Table 1). Complex 2 has the longest C−H···Pt interaction and the largest Χ−Η···Pt angle (2.470 Å and 141.4°, respectively), but the variations remain small within the series. The natural charges on the Pt atom (always negative) change in moving from one complex to another (from −0.713 |e| in 4 to −0.496 |e| in 5) as a result of the different substituents (Table 2). Charges on the anagostic hydrogens are positive (from 0.245 to 0.279 |e|), indicating that C−H···Pt interactions have an important electrostatic character. This is exactly what is

with bond distances and angles very similar for the “PSi3” ligand, the main difference being the substitution of PPh3 with P(OPh)3. The close to ideal square planar geometry around the platinum center is confirmed as well as the trans disposition of the Si atoms characterized by a Si1−Pt−Si2 angle of 174.04(2)°, even larger than the corresponding angle in 2 [169.43(4)°], to the best of our knowledge the largest experimentally measured in a Pt(II) system. The rest of the bond lengths and angles are similar to those of 2, one of the Pt−Si bond distances being slightly shorter than the other [2.4131(6) and 2.4471(6) Å]. With respect to the anagostic interaction, the C−H···Pt distance (from the localized H212 atom) accounts for 2.42(2) Å, while the computed value at the PBE0-D3/def2-TZVP level is found to be slightly shorter (2.387 Å). The experimental Pt−H−C angle is 148.13(2)°, C


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Organometallics

2136 cm−1, also shifted by comparison to that of the methyl analogue (νSi−H at 2119 cm−1 in 1). Synthesis and Characterization of [PtH{P(o-C6H4CH2SiPh2)3}PPh3] (7). The reaction between the platinum precursor [Pt(PPh3)3] and phenyl-Si-substituted compound 6 proceeded in a manner very different from that of analogous methyl-Si-substituted compound 1. The reaction did not occur at room temperature, only at 383 K, and led to the isolation of a white powder in good yield (86%). The spectroscopic data obtained for complex 7 are in agreement with a “PSi3” ligand coordinating in a tetradentate fashion through the phosphorus and the three silicon atoms. The remaining PPh3 ligand is disposed trans to a SiPh2 fragment, while a hydride is present in an axial position trans to the phosphorus atom. Thus, the resulting compound can be described as a hydrido(trisilyl) Pt(IV) species. The hydride signal appears only slightly upfield at δ −2.06 as a doublet of doublets with 2JP−H values of 22.0 and 150 Hz. The measured satellites exhibit a 1JPt−H of 1060 Hz in line with an oxidized Pt(IV) center. The 31P{1H} NMR spectrum shows two doublets with a small P−P coupling constant in agreement with a cis disposition of the phosphorus nuclei. The 29Si{1H} NMR spectrum displays two signals, one with a large 2JSi−P of 151 Hz, thus confirming the formulation shown in Scheme 1 (Figure 4).

reflected from the noncovalent interaction (NCI) plot in which the blue surface generated between anagostic hydrogens and platinum pictorially represents the interplay of electrostatic interaction therein (Figure 3). The consequence of such

Figure 3. Noncovalent index (NCI) plots of complexes 2−5. The anagostic interactions are denoted with arrows. For the color code, see the note in the Supporting Information.

interaction is a shorter bond distance, which in turn can induce some orbital participation. The electron density analysis shows the presence of a gradient path connecting the anagostic hydrogen with the platinum atom in each complex. As expected, the electron density [ρ(rc)] values (∼0.02 au) at the bond critical points (BCPs) related to the anagostic interactions are quite low and vary inversely with the C−H···Pt distances. The positive sign of the laplacian of ρ(rc), ∇2ρ(rc), at the BCPs and the shape of the ∇2ρ(r) distribution also corroborate the argument that there is no bonding electron pair between the anagostic hydrogen and the platinum atom. Table 2 and Table S4 list the values of different electron density-based descriptors, while Figure S36 shows the contour plots of ∇2ρ(r) plotted in the Si−Pt−H(anagostic) plane. Judging from the small negative values of H(rc), a small degree of orbital involvement can be suggested.10 It should be noticed that H(rc) correlates well with the Η···Pt distance as the complexes with shorter distances have more negative H(rc) values. Synthesis and Characterization of [P(o-C 6 H 4 CH2SiPh2)3] (6). New compound 6 was synthesized by a modification of the method previously reported for the synthesis of tris(o-benzyldimethylsilyl) phosphine (1).24 Polylithiation of tris(o-tolyl)phosphine in the presence of TMEDA and subsequent quenching with excess HSiPh2Cl led after workup to pure 6 as a white solid in excellent yield (94%). Compound 6 is characterized by a multiplet at δ 5.13 in the 1H NMR spectrum at 298 K in C6D6 for the Si hydride resonance with a 1JSi−H of 204 Hz. The signal shows a significant downfield shift of ∼1 ppm with respect to 1 (δ 4.28 with a 1 JSi−H of 189 Hz), as expected for a lower-σ donating nature of the phenyl substituents with respect to methyl groups. Compound 6 exhibits a νSi−H band in the IR spectrum at

Figure 4. 1H−29Si HSQC NMR spectrum of complex 7 (500 MHz, CD2Cl2, 298 K).

One possible explanation of the very different behavior of compounds 1 and 6 could be the increased level of steric crowding in 6 that could not allow C−Si bond formation in the restricted equatorial plane. In conclusion, the nature of the substituents on the Si atom of tri(silylbenzyl)phosphines 1 and 6 determines their reactivity toward Pt(PPh3)3, either leading to the formation of a modified tridentate ligand in a Pt(II) d8 anagostic complex or allowing tetracoordination to a Pt(IV) d6 complex. In both cases, two Si atoms are in a trans arrangement. In addition, although the chemical shift differences of the anagostic and geminal hydrogens in complexes 2−5 correspond with the π acceptor character of the ancillary ligands following the trend PPh3 < PMe3 < P(OPh)3 < CO,25 DFT-based computations clearly show the electrostatic character of the anagostic interactions. There is little variation in the frontier molecular orbitals of the four complexes, and electron density analysis corroborates a closed-shell interaction with slight covalent character for the Pt···H−C anagostic interaction. The synthesis of analogous D


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Organometallics

Synthesis of [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}P(OPh)3] (4). Complex 2 (50 mg, 0.05 mmol) and P(OPh)3 (7.1 μL, 0.05 mmol) were dissolved in 5 mL of toluene while being vigorously stirred for 30 min. After this time, the solution was evaporated under vacuum. The solid was washed three times with 0.5 mL of cold pentane and then dried under vacuum to afford a yellow powder (52 mg, 99% yield). Yellow crystals suitable for X-ray analysis were grown from toluene/pentane solutions at room temperature. For NMR assignment codes see the Supporting Information: 1H NMR (500 MHz, C6D6, 298 K) δ 7.62 (dd, 3JH−H = 9 Hz, 3JH−P = 18 Hz, 2H, mbenzyl), 7.40 (pseudo t, |3JH−H + 3JP−H| = 9 Hz, 1H, m-benzyl), 7.22 (d, 3 JH−H = 8 Hz, 6H, o-OPh), 6.86 (t, 3JH−H = 8 Hz, 6H, m-OPh), 6.81 (t, 3 JH−H = 7.5 Hz, 1H, m′-benzyl), 6.75 (t, 3H, p-OPh), 6.73 (d, overlapped, 3H, o-benzyl), 6.71 (t, overlapped, 2H, m′-benzyl), 6.68 (t, 3 JH−H = 7.5 Hz, 1H, p-benzyl), 6.65 (t, 3JH−H = 7 Hz, 1H, p-benzyl), 6.60 (t, 3JH−H = 6.5 Hz, 1H, p-benzyl), 4.16 (dd, 2JH−H = 14 Hz, 4JP−H = 1.2 Hz, 1H, CH2Si, anagostic), 2.62 (d, 2JH−H = 12.4 Hz, 1H, CH2Si), 2.55 (dd, 2JH−H = 12.4 Hz, 4JH−P = 4.8 Hz, 1H, CH2Si), 2.35 (d, 4JH−P = 6.8 Hz, 1H, SiCH), 2.06 (dd, 2JH−H = 14 Hz, 4JH−P = 2.8 Hz, 1H, CH2Si, geminal), 0.87 (s, 3H, SiMe2), 0.60 (s, 3H, SiMe2), 0.42 (s, 3H, SiMe2), −0.05 (s, 3H, SiMe2), −0.18 (s, 3H, SiMe2), −0.52 (s, 3H, SiMe2); 13C{1H} NMR (100 MHz, C6D6, 298 K) δ 152.19 (d, JC−P = 15.1 Hz, Carom), 152.03 (d, JC−P = 5.0 Hz, Carom), 150.31 (d, JC−P = 10.0 Hz, Carom), 143.15 (d, JC−P = 16.3 Hz, Carom), 134.31 (pseudo t, JC−P = 2.5 Hz, Carom), 134.09 (d, JC−P = 6.3 Hz, Carom), 133.66 (d, JC−P = 6.3 Hz, Carom), 133.07 (d, JC−P = 10.0 Hz, Carom), 132.61 (d, JC−P = 7.5 Hz, Carom), 132.44 (d, JC−P = 10.0 Hz, Carom), 131.04 (d, JC−P = 7.5 Hz, Carom), 130.19 (d, JC−P = 10.0 Hz, Carom), 130.06 (s, Carom), 129.81 (s, Carom), 129.62 (s, Carom), 129.14 (s, Carom), 128.59 (d, JC−P = 11.3 Hz, Carom), 128.00 (s, overlapped Carom), 127.07 (s, Carom) 126.60 (d, JC−P = 3.0 Hz, Carom), 125.18 (d, JC−P = 7.5 Hz, Carom), 124.40 (s, Carom), 123.76 (d, JC−P = 10.0 Hz, Carom), 35.8 (d, 3JC−P = 15 Hz, SiCH), 33.8 (d, 3JC−P = 11 Hz, SiCH2), 32.3 (d, 3 JC−P = 13 Hz, SiCH2), 7.98 (d, 2JC−P = 6.30 Hz, SiMe2), 7.65 (s, SiMe2), 7.25 (s, SiMe2), 5.55 (d, JC−P = 2.5 Hz, SiMe2), 0.23 (s, SiMe2), −3.36 (s, SiMe2); 31P{1H} NMR (161.9 MHz, C6D6) δ 122.3 [d, 2JP−P = 552 Hz, 1JP−Pt = 5394 Hz, sat, P(OPh)3], −1.62 (d, 2JP−P = 552 Hz, 1 JP−Pt = 2488 Hz, sat, P-ligand); 1H−29Si{1H}{31P} HMQC NMR (500−99.36 MHz, C6D6) δ 37.15 (s, Si-CH-Si-Pt), 22.50 (s, CH2SiPt), 5.30 (s, Si-CH-Si-Pt). Anal. Calcd for C45H50O3P2PtSi3: C, 55.14; H, 5.14. Found: C, 54.84; H, 5.07. Synthesis of [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}(CO)] (5). In a Fischer−Porter bottle, a degassed solution of complex 2 (50 mg, 0.05 mmol) dissolved in 0.6 mL of C6D6 was placed under 3 atm of CO while being vigorously stirred for 30 min. After this time, the solution was placed inside the drybox to prepare samples for NMR and IR analyses (99% conversion by NMR): 1H NMR (400 MHz, C6D6, 298 K) δ 7.72 (pseudo t, |3JH−H + 3JH−P| = 9.6 Hz, 1H, m-benzyl), 7.60 (dd, 3JH−H = 8 Hz, 3JH−P = 12 Hz, 1H, m-benzyl), 7.56 (pseudo t, 3 JH−H = 8.8 Hz, 1H, m-benzyl), 7.30 (dd, 3JH−H = 6.8 Hz, 3JH−H = 10.8 Hz, 1H, m′-benzyl), 7.04 (m, 1H, m′-benzyl), 6.85−6.80 (m, 2H, οbenzyl), 6.75−6.59 (m, overlapped, 3H, p-benzyl, 1H, m′-benzyl, 1H, ο-benzyl), 3.79 (d, 2JH−H = 14.2 Hz, 1H, CH2Si anagostic), 2.71 (dd, 2 JH−H = 12.8 Hz, 4JH−P = 4.8 Hz, 1H, CH2Si), 2.57 (d, 4JH−P = 6.0 Hz, 1H, SiCH), 2.40 (d, 2JH−H = 12.8 Hz, CH2Si), 2.10 (dd, 2JH−H = 14.2 Hz, 4JH−P = 2.8 Hz, 1H, CH2Si), 0.83 (s, 3H, 3JPt−H = 17.2 Hz, sat, SiMe2), 0.43 (s, 6H, 3JPt−H = 13.2 Hz, sat, SiMe2), 0.37 (s, 3H, 3JPt−H = 12.4 Hz, sat, SiMe2), 0.10 (s, 3H, SiMe2), −0.62 (s, 3H, SiMe2); 13 C{1H} NMR (50 MHz, C6D6, 298 K) δ 196.54 (s, CO), 191.52 (s, CO), 151.67 (d, JC−P = 14.0 Hz, Carom), 149.83 (d, JC−P = 10.5 Hz, Carom), 142.96 (d, JC−P = 15.5 Hz, Carom), 136.30 (s, Carom), 135.62 (s, Carom), 134.41 (d, JC−P = 3.5 Hz, Carom), 132.43 (d, JC−P = 9.5 Hz, Carom), 131.38 (d, JC−P = 9.0 Hz, Carom), 130.62 (br. s, Carom), 130.44 (d, JC−P = 10.0 Hz, Carom), 130.13 (s, Carom), 130.02 (s, Carom), 128.92 (s, Carom), 128.74 (s, Carom), 128.33 (s, Carom), 125.31 (d, JC−P = 8.0 Hz, Carom), 124.54 (d, JC−P = 10.0 Hz, Carom), 124.04 (d, JC−P = 8.0 Hz, Carom), 35.49 (d, 3JC−P = 13.5 Hz, SiCH), 32.22 (d, 3JC−P = 11.5 Hz, SiCH2), 32.06 (d, 3JC−P = 11.0 Hz, SiCH2), 7.29 (s, 5JC−P = 7.5 Hz, 2 JC−Pt = 40 Hz, 2-SiMe2), 6.24 (s, 2JC−Pt = 39.5 Hz, SiMe2), 3.72 (d,

phosphinosilane compounds bearing different substituents on the Si and P atoms is underway, and their reactivity will be reported in due course.

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EXPERIMENTAL SECTION

General Considerations. All experiments were performed under an argon atmosphere using standard Schlenck methods or in MBraun gloveboxes. Solvents were either dried and distilled from sodium using benzophenone ketyl as an indicator or purified over an MBraun column system. In either case, they were degassed prior to use. Deuterated solvents were either degassed via three freeze−pump− thaw cycles and stored over molecular sieves or stored over a freshly prepared potassium mirror in an ampule fitted with a J. Young’s valve. Pt(PPh3)3,26 and the phosphinosilane compound 1,24 were synthesized according to reported procedures. The other reagents were purchased from Sigma-Aldrich and used as received. NMR spectra in solution were recorded on Bruker Avance 300, 400, and 500 MHz and Varian Inova 400 MHz instruments. All chemical shifts for 1H, 29Si, and 13C are relative to TMS. 31P chemical shifts were referenced to an external 85% H3PO4 sample. Infrared spectra were recorded on a Nicolet 6700 instrument in absorbance mode either in a KBr disc or in solution using a demountable liquid cell. Single-Crystal X-ray Diffraction Analysis. Single crystals of 4 were covered with Paratone oil, mounted on a glass fiber, and measured at 100 K. X-ray intensity data were collected using CrysAlisPro27 on a four-circle SuperNova, Dual EosS2 CCD diffractometer with monochromatic Cu Kα radiation (λ = 1.54184 Å). Cell refinement, data reduction, incident beam, decay, and absorption corrections were performed with CrysAlisPro.27 Using Olex 2,28 the structure was determined by direct methods with SHELXT and refined by full-matrix least-squares techniques with SHELXL.29,30 Further details of experimental and structure analyses are given in CCDC 1835875. All hydrogen atoms were generated in calculated positions and constrained with the use of a riding model. The final model involved anisotropic displacement parameters for all non-hydrogen atoms. Synthesis of [Pt{P(o-C6H4-CH2SiMe2)2(o-C6H4-CHSiMe2)}PMe3] (3). Complex 2 (50 mg, 0.05 mmol) and PMe3 (6 μL, 0.06 mmol) were dissolved in 4 mL of C6H6 while being vigorously stirred for 30 min. Then, the solution was evaporated under vacuum. The solid was washed three times with 0.5 mL of cold pentane and then dried under vacuum to afford a pale yellow powder (99% yield by NMR). For NMR assignment codes, see the Supporting Information: 1 H NMR (400 MHz, C6D6, 298 K) δ 7.42 (pseudo t, |3JH−H + 3JP−H| = 9 Hz, 1H, m-benzyl), 7.17 (pseudo t, 3JH−H = 5.5 Hz, 3JH−P = 6 Hz, 1H, m-benzyl), 7.08 (pseudo t, |3JH−H + 3JP−H| = 7 Hz, 1H, m-benzyl), 6.84 (m, 3H, ο-benzyl), 6.72 (m, 3H, m′-benzyl + 2H p-benzyl), 6.63 (t, 3JH−H = 7.5 Hz, 1H, p-benzyl), 4.57 (dd, 2JH−H = 13.6 Hz, 4JH−P = 1.2 Hz, 1H, CH2Si, anagostic), 2.56 (d, 2JH−H = 12.4 Hz, 1H, CH2Si), 2.44 (dd, 2JH−H = 12.4 Hz, 4JH−P = 5.2 Hz, 1H, CH2Si), 2.35 (d, 4JH−P = 6 Hz, 1H, SiCH′), 2.10 (dd, 2JH−H = 13.2 Hz, 4JH−P = 2.8 Hz, 1H, CH2Si), 1.31−1.19 (m, 9H, PMe3), 0.57 (s, 3JPt−H = 10.0 Hz, 3H, SiMe2), 0.36 (s, 3H, SiMe2), 0.35 (s, 3H, SiMe2), 0.26 (s, 3H, SiMe2), 0.20 (s, 3H, SiMe2), −0.48 (s, 3H, SiMe2); 13C{1H} NMR (100 MHz, C6D6, 298 K) δ 151.84 (d, JC−P = 15.0 Hz, Carom), 149.08 (d, JC−P = 10.0 Hz, Carom), 142.58 (d, JC−P = 16.0 Hz, Carom), 137.72 (br. s, Carom), 134.01 (s, Carom), 132.67 (d, JC−P = 8.0 Hz, Carom), 132.09 (d, JC−P = 8.0 Hz, Carom), 132.00 (d, JC−P = 10.0 Hz, Carom), 131.06 (d, JC−P = 3.0 Hz, Carom), 130.36 (d, JC−P = 7.0 Hz, Carom), 129.74 (d, JC−P = 10.0 Hz, Carom), 129.33 (s, Carom), 128.73 (d, JC−P = 9.0 Hz, Carom), 128.37 (s, Carom), 128.07 (d, JC−P = 12.0 Hz, Carom), 124.46 (d, JC−P = 7.0 Hz, Carom), 123.36 (d, JC−P = 10.0 Hz, Carom), 123.03 (d, JC−P = 7 Hz, Carom), 35.72 (d, 3JC−P = 15.0 Hz, SiCH), 33.61 (d, 3JC−P = 13.0 Hz, SiCH2), 31.28 (d, 3JC−P = 11 Hz, SiCH2), 20.34 (d, 1JC−P = 35 Hz, PMe3), 8.46 (s, SiMe2), 7.81 (s, SiMe2), 7.06 (s, SiMe2) 5.69 (s, SiMe2), 0.94 (s, SiMe2), −3.80 (s, SiMe2); 31P{1H} NMR (202.46 MHz, C6D6) δ 0.49 (d, 2JP−P = 357 Hz, 1JP−Pt = 2324 Hz, sat, P-ligand), −24.18 (d, 2 JP−P = 357 Hz, 1JP−Pt = 2838 Hz, sat, PMe3). E


Article

Organometallics JC−Pt = 48 Hz, SiMe2), 0.85 (s, SiMe2), −3.67 (s, SiMe2); 31P{1H} NMR (161.9 MHz, C6D6) δ −1.44 (s, 1JP−Pt = 2782 Hz, sat); IR (C6D6) 2024 cm−1 (w, νCO). Synthesis of P{(o-C6H4)-CH2SiPh2H}3 (6). P{(o-C6H4)CH3}3 (1 g, 3.3 mmol) was dissolved in 30 mL of hexane, and then TMEDA (1.48 mL, 9.9 mmol) and a titrated hexane solution of nBuLi (3.96 mL, 9.9 mmol) were added. After being stirred for 20 h, the bright orange red reaction mixture was cooled to 195 K, and a stoichiometric amount of ClSiPh2H (1.9 mL, 9.9 mmol) was added via syringe. The off-white suspension was allowed to warm to room temperature and stirred for 12 h, after which the solvent was removed by distillation under a reduced pressure. The white solid was dissolved in 15 mL of toluene and washed with 15 mL of hexane: yield 94% (7.88 g, 9.3 mmol) from P{(o-C6H4)CH3}3; 1H NMR (400 MHz, C6D6, 298 K) δ 7.59−7.42 (m, 10H), 7.14−6.79 (m, 32H), 5.13 (pseudo q, |3JH−H + 3 JH−H + 3JP−H| = 2.8 Hz, 3H, |1JSi−H| = 204 Hz, sat, Si-H), 3.02 (d, 3 JH−H = 2.8 Hz, CH2); 13C{1H} NMR (100 MHz, C6D6, 298 K) δ 144.54 (d, JC−P = 26.0 Hz, Carom), 135.81 (s, Carom), 134.80 (s, Carom), 134.67 (s, Carom), 134.44 (d, JC−P = 10.0 Hz, Carom), 130.17 (d, JC−P = 5.0 Hz, Carom), 129.82 (s, Carom), 129.14 (s, Carom), 128.21 (s, Carom), 125.86 (s, Carom), 22.03 (d, JC−P = 21 Hz, CH2); 31P{1H} NMR (202.5 MHz, C6D6) δ −30.32 (s); IR (KBr) 2136 (s, νSi−H), 816 cm−1 (s, ωSi−H). Anal. Calcd for C57H51PSi3: C, 80.42; H, 6.04. Found: C, 80.14; H, 6.11. Synthesis of [PtH{P(o-C6H4-CH2SiPh2)3}PPh3] (7). Compound 6 (43.3 mg, 0.051 mmol) and [Pt(PPh3)3] (50 mg, 0.051 mmol) were dissolved in 10 mL of toluene and then refluxed overnight. Then, the volatiles were removed under reduced pressure, and the solid was washed three times with cold CH3CN and then dried under vacuum to yield a white powder (86%, 57.2 mg). The purity was verified by NMR in CD2Cl2. Subsequently, the sample was evaporated under vacuum and subjected to elemental analyses: 1H NMR (400 MHz, CD2Cl2, 298 K) δ 8.95 (dd, 3JH−H = 6.4 Hz, 3JH−P = 18 Hz, 1H, CHarom), 7.85 (dd, 3JH−H = 7.6 Hz, 3JH−P = 16.4 Hz, 1H, CHarom), 7.64 (dd, 3JH−H = 6.0 Hz, 3JH−P = 30.8 Hz, 5H, CHarom), 7.43−6.92 (m, 48H), 6.73 (pseudo t, |3JH−H + 3JH−P| = 9.2 Hz, 1H, CHarom), 6.65 (t, 3JH−H = 7.2 Hz, 1H, CHarom), 6.34 (br. d, 1H, CHarom), 6.25 (dd, 3JH−H = 3.6 Hz, 3 JH−H = 7.6 Hz, 5H, CHarom), 2.98 (d, 2JH−H = 12.8 Hz, 2H, overlapped with another CH2 signal), 2.08 (d, 2JH−H = 14 Hz, 1H, CH2), 2.06 (d, 2 JH−H = 13.6 Hz, 1H, CH2), 1.77 (d, 2JH−H = 13.2 Hz, 1H, CH2), 1.70 (d, 2JH−H = 13.6 Hz, 1H, CH2), −2.06 [dd, 2JP−H(cis) = 22.0 Hz, 2 JP−H(trans) = 150 Hz, 1JPt−H = 1060 Hz, sat, 1H, Pt-H]; 13C{1H} NMR (100 MHz, CD2Cl2, 298 K) δ 147.76 (d, JC−P = 13.6 Hz, Carom), 146.90 (d, JC−P = 3.8 Hz, Carom), 144.65 (ds, JC−Pt = 16.7 Hz, sat, Carom), 143.12 (s, Carom), 142.76 (s, Carom), 142.48 (s, Carom), 141.64 (s, Carom), 137.56 (s, Carom), 137.30 (d, JC−P = 4.0 Hz, Carom), 137.10 (s, Carom), 136.85 (d, JC−P = 15 Hz, Carom), 136.40 (s, Carom), 135.82 (s, Carom), 135.50 (s, Carom), 135.41 (s, Carom), 135.04 (s, Carom), 134.74 (s, Carom), 134.60 (d, JC−P = 12.4 Hz, Carom), 134.43 (s, Carom), 134.33 (s, Carom), 134.14 (s, Carom), 133.72 (d, JC−P = 5.1 Hz, Carom), 133.10 (s, Carom), 132.40 (d, JC−P = 8.0 Hz, Carom), 132.25 (d, JC−P = 5.8 Hz, Carom), 131.60 (s, Carom), 131.33 (d, JC−P = 5.1 Hz, Carom), 130. 92 (s, Carom), 130.82 (s, Carom), 130.65 (s, Carom), 129.88 (s, Carom), 129.81 (s, Carom), 129.30 (s, Carom), 129.02 (d, JC−P = 5.7 Hz, Carom), 128.84 (s, Carom), 128.53 (d, JC−P = 9.5 Hz, Carom), 128.15 (d, JC−P = 3.5 Hz, Carom), 127.99 (s, Carom), 127.62 (s, Carom), 127.53 (s, Carom), 124.39 (d, JC−P = 17.5 Hz, Carom), 124.05 (d, JC−P = 14.7 Hz, Carom), 123.80 (d, JC−P = 7.3 Hz, Carom), 25.46 (dd, 3JC−P = 4.8 Hz, 3JC−P = 15.7 Hz, CH2Si-Pt-PPh3), 22.17 (s, CH2Si-Pt-SiCH2), 20.64 (s, CH2Si-PtSiCH2); 31P{1H} NMR (202.5 MHz, CD2Cl2) δ 35.7 (d, 2JP−P = 15.2 Hz, 1JP−Pt = 1751 Hz, sat, PPh3), 29.09 (d, 2JP−P = 15.2 Hz, 1JP−Pt = 2443 Hz, sat, P-ligand); 1H−29Si{1H} HMQC NMR (500 to 99.4 MHz, CD2Cl2) δ 28.15 [d, 2JP−Si(trans) = 151 Hz, 1JPt−Si = 1230 Hz, sat, trans-Si-Pt-P], −4.90 (s, trans-Si-Pt-Si); IR (KBr) 2020 cm−1 (w-m, νPt−H). Anal. Calcd for C76H64P2PtSi3·CD2Cl2: C, 65.50; H, 4.92. Found: C, 65.58; H, 5.15. Computational Details. All geometries were fully optimized and characterized by frequency analysis using the PBE0 functional31,32 in conjunction with a def2-SVP basis set, including the dispersion effects

via the D3 version of Grimme’s approach,33 as implemented in Gaussian 09.34 To compute the chemical shifts, we employed a continuum solvation model called SMD,35 using benzene as a solvent. The real-space characteristics of the interaction were further examined via the evaluation of NCI indexes.36 The gradient isosurfaces in real space were visualized by NCIPLOT.37 Finally, the electron density analysis38 was also performed at the PBE0/def2-SVP/WTBS level (allelectron WTBS for Pt39) by using Multiwfn.40

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00269. NMR and IR spectra of all complexes, X-ray diffraction data (CCDC 1835875), and theoretical calculation details and optimizations (PDF) A text file of all computed molecule Cartesian coordinates for convenient visualization (XYZ) Accession Codes

CCDC 1835875 contains 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 data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Sudip Pan: 0000-0003-3172-926X Gabriel Merino: 0000-0003-1961-8321 Sylviane Sabo-Etienne: 0000-0001-7264-556X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by CONACyT (Ciencia Básica 242818 and 252356 and Ph.D. grant to J.Z.-M., F.M., and S.J.), ANR-CONACyT (274001), CNRS, and Université Paul Sabatier. The authors acknowledge the French-Mexican International Laboratory (LIA-LCMMC) for support.

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DEDICATION In honor of Prof. Ernesto Carmona, a charismatic colleague and great human being, for his outstanding contributions to organometallic chemistry and for being an inspiration to many.

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REFERENCES

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Modulation of an Anagostic Interaction in SiPSi-Type Pincer Platinum

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