Thiopyridazine-Based Palladium and Platinum ... - ACS Publications

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

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Thiopyridazine-Based Palladium and Platinum Boratrane Complexes Stefan Holler,†,# Michael Tüchler,†,# Beate G. Steller,† Ferdinand Belaj,† Luis F. Veiros,‡ Karl Kirchner,§ and Nadia C. Mösch-Zanetti*,† †

Institute of Chemistry, University of Graz, Schubertstrasse 1, 8010 Graz, Austria Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais No. 1, 1049-001 Lisboa, Portugal § Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria ‡

S Supporting Information *

ABSTRACT: Palladium and platinum boratrane complexes of the type [M{B(PnMe,tBu)3}(PPh3)] (M = Pd 1, Pt 2b) have been prepared via the reaction of the soft scorpionate ligand potassium tris(4-methyl-6-tert-butyl-3-thiopyridazinyl)borate KTnMe,tBu with bis(triphenylphosphine)metal(II) dichloride. While reaction with the Pd precursor allowed direct isolation of a symmetric boratrane complex, the Pt analogue led to the hydrido compound [Pt{B(PnMe,tBu)3}(PPh3)H]Cl (2a), which after reaction with a base gave 2b. Subsequent oxidation with Br2 and I2, respectively, led to the dihalide compounds of the molecular formula [M{B(PnMe,tBu)3}X2] (3a,b−4a,b). Halide abstraction with Ag(SbF6) further gave interesting cationic compounds of either dimeric [Pd{B(PnMe,tBu)3}X]2(SbF6)2 (5a,b) or monomeric [Pd{B(PnMe,tBu)3}(NCMe)2](SbF6) (6) nature. All compounds were spectroscopically and Xray crystallographically characterized revealing strong metal to boron interactions. DFT calculations of 1, 2a, and 2b confirm the strong M−B interaction and a high positive charge on the metal centers.

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INTRODUCTION Ambiphilic ligands consisting of Lewis acidic as well as Lewis basic moieties have gained considerable attention in coordination chemistry during the past decade.1−4 Within those molecules, the Lewis base as well as the Lewis acid are capable to coordinate to the metal with the latter exhibiting a Z-type bond where the electrons are provided formally by the metal rather than by the ligand.4 Fine-tuning of both moieties provides the opportunity to develop unique complexes with respect to their electronic properties at the metal center. For this reason, metal complexes with ambiphilic ligands have developed from unusual coordination chemistry into more applied chemistry. Interesting examples of Z-type complexes were found to reduce dinitrogen5−8 and to reversibly migrate hydrides.9−12 While metal complexes with unsupported Z-type ligands are known, ambiphilic ligands in which a Lewis acid and base are linked by an organic backbone leading to cage-like structures have been particularly well investigated. Upon coordination, complexes are formed with the metal and the Lewis acid being in the bridgehead positions. Most of such ambiphilic ligands contain a boron atom as Lewis acid, but examples with other electron-deficient elements such as aluminum have likewise been described.1 The respective metal complexes are generally referred to as metallatranes and specifically with boron as metallaboratranes. Many borane ligands with various structural motifs capable for boratrane formation were developed © XXXX American Chemical Society

including nitrogen, sulfur, selenium, or phosphorus donor sites.8,13−30 Typically, such metallaboratrane complexes can either be formed by direct reaction of the respective neutral borane [Me2P(CH2)2]3B31 or [o-(R2P)C6H4]3B20 with a metal precursor or via the more general reaction of a hydroborate ligand HB(Het)3¯ (Het = 2-thiomethimidazole,28 7-azaindol,11 2-thiopyridine,32 5-thiotriazol,33 6-tert-butyl-3-thiopyridazine)27,30,34,35 with a metal precursor under elimination of the hydride at boron (Figure 1). For an efficient M−B bond, electron-rich metal centers are beneficial which is why most Z-type complexes contain late transition metals in low oxidations states. While the majority of boratrane complexes described to date contain copper, iron, cobalt, and nickel metals (first row) or rhodium, ruthenium, and iridium (second and third rows), palladium and platinum complexes with a Z-type ligand are rather scarce,20,24,36−40 and only a few of them can be classified as metallaboratrane complexes (Figure 2).20,24,38,39 The Z-type bond between M and B leads to ambiguity regarding the formal oxidation state of the metal.41−43 Upon considering the boron ligand neutral, the electron count at the metal remains dn. However, as the two electrons for the bond are formally provided by the metal, the ligand may be considered −2, thereby decreasing the metal to dn−2. While Received: February 28, 2018

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DOI: 10.1021/acs.inorgchem.8b00530 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. General structure of metallaboratrane complexes derived from neutral borane ligands (top) and hydroborate ligands (bottom).

been investigated. Thus, cationic Pd boratrane complexes would be of particular interest as they are expected to be highly electrophilic, a feature beneficial for various reactions catalyzed by cationic palladium complexes such as the oxidation of terminal olefins,47 hetero Diels−Alder reactions,48 or C−H activation followed Suzuki−Miyaura coupling.49 We have recently developed thiopyridazine-based borate ligands K[HB(PnR,tBu)3] (KTnR,tBu) which form boratrane complexes with metal halide precursors (as shown in Scheme 1).27,30,34,35,41,50 Thiopyridazine belongs to the electrondeficient heterocycles and is thus expected to promote a strong Z-type interaction. Our observed high tendency for boratrane formation goes along with this expectation. In addition, variation of substituent R in ortho-position to sulfur allows for fine-tuning of the properties.35,41 This combination of a strong M−B interaction with the option of introducing R groups ortho to the donor site prompted us to investigate palladium and platinum chemistry with the thiopyridazine borates. Here we present the synthesis and characterization of a palladium and platinum boratrane complexes of the general formula [M{B(PnMe,tBu)3}(PPh3)]. Furthermore, we show that oxidation exclusively occurs at the metal center, indicating strong B−M bonds. The reactivity of the oxidized complexes is demonstrated by the stepwise abstraction of the halides with Ag(SbF6) leading to stable cationic complexes.

Figure 2. Literature-known metallaboratrane complexes containing palladium and platinum.

the degree of the actual electron shift may only be determined by theoretical calculations, it influences the reactivity in the position trans to boron. Research described by the groups of Parkin and Hill demonstrated the different reactivity of higher homologues toward oxidizing agents by comparing nickel (and iron) to platinum boratranes.38,44,45 While tris-methimazolylborane compounds with the first row transition metals iron and nickel undergo 1,2-addition of halides across the M−B bond forming haloborate metal-halides, the respective platinum complexes reveal oxidative addition at the metal center, with the Pt−B bond being retained. For example, [Pt{Bmt)3}(PPh3)] was found to react with HCl to form the respective cationic Pthydrido compound [Pt{Bmt)3}(PPh3)H]Cl.38,46 While a few oxidative reactions have been reported with palladium containing Z-type complexes,1 reactions with palladium boratranes are yet elusive. DFT calculations on a Pd boratrane suggest that the B−Pd bond orbital is not the HOMO, possibly explaining the resistance to cleave this bond.38 However, the strength of the M−B bond allows for high and selective reactivity at the trans-position. It is therefore surprising that further reactivity of the Pd and Pt boratrane complexes has not

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RESULTS AND DISCUSSION Complex Synthesis. Reaction of the literature-known41 scorpionate ligand KTnMe,tBu with [PdCl2(PPh3)2] in CH2Cl2 under exclusion of light led to formation of the diamagnetic boratrane compound [Pd{B(PnMe,tBu)3}(PPh3)] (1) as shown in Scheme 2. The very dark colored crude product was purified via recrystallization to obtain deep purple crystals in 85% yield. In contrast to 1 where a C3 symmetric product is obtained, reaction of KTnMe,tBu with [PtCl2(PPh3)2] led to the isolation

Scheme 1. Thiopyridazine-Based Borate Ligand K[HB(PnR,tBu)3] (KTnR,tBu) and Boratrane Formation27,30,34,35,41

B


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Inorganic Chemistry Scheme 2. Synthesis of the Palladium and Platinum Boratrane Complexes 1, 2a, and 2b

of a yellow solid in 87% yield (2a, Scheme 2). Subsequent 1H NMR spectroscopy revealed two sets of ligand signals in a 2:1 ratio indicating loss of C3 symmetry. Furthermore, a prominent one hydrogen singlet with characteristic platinum satellites at −13.21 ppm strongly suggests the formation of the hydrido compound [Pt{B(PnMe,tBu)3} (PPh3)H]Cl (2a). This is also supported by the IR spectrum where a band for the Pt−H stretching frequency at 2147 cm−1 is prominently observed, which is in perfect agreement with the calculated IR spectrum (Figure S26). A similar observation has previously been described by Hill and co-workers with the methimidazolebased scorpionate ligand Na[HB(mt)3] which forms the respective hydrido compound [Pt{Bmt)3}(PPh3)H]Cl.46 Upon addition of the base 1,8-diazabicyclo[5.4.0]undec-7-en (DBU), conversion to the symmetric [Pt{Bmt)3}(PPh3)] is reported.46 Furthermore, this reaction was also found to be reversible by addition of HCl, regenerating the hydrido complex [Pt{Bmt)3}(PPh3)H]Cl. Accordingly, we also investigated the properties toward a base finding a similar behavior: addition of a slight excess of DBU to Pt hydrido complex 2a leads to an immediate color change from yellow to deep purple. After workup, C3 symmetric compound [Pt{B(PnMe,tBu)3}(PPh3)] (2b) could be isolated in 72% yield (Scheme 2). Characterization by 1H NMR spectroscopy revealed the absence of the hydride resonance at −13.21 ppm and the presence of only one set of ligand resonances indicating C3 symmetry. For example in CD2Cl2, the two tBu groups in 2a appear at 1.07 and 1.30 ppm (9:18 ratio), while those of 2b are found as one singlet at 1.15 ppm (27 H). Similar to the Pt complex reported by Hill,46 addition of HCl to 2b also leads to a color change from black to yellow, regenerating 2a, as demonstrated by 1H NMR spectroscopy (Figure S10). In the first step of the reaction sequence, the hydride is transferred from boron to palladium or platinum, respectively, forming the hydrido complexes in a formally redox neutral process. In the second step, the H atom at M is removed as a protic hydrogen either by spontaneous elimination of HCl (palladium) or with the help of the base (platinum) whereupon formal reduction of the metal centers occurs. The isolation of the Pt hydrido complex, and not the Pd analog, might suggest that the complex is better described with the metal being in higher oxidation state as their stability is increasing in higher homologues. Our theoretical calculations also support the metals being in higher oxidations states (vide infra). Single crystals suitable for X-ray diffraction analysis could be obtained by cooling of a CH2Cl2/pentane solution of 1 or a CH2Cl2/heptane solution of 2a and by slow diffusion of pentane into a CH2Cl2/heptane solution of 2b, respectively. Molecular views are shown in Figures 3 and 4; selected bond

lengths and angles are given in Tables 2 and 3. Crystallographic data is given in Tables S1 and S2.

Figure 3. Molecular view of [Pd{B(PnMe,tBu)3}(PPh3)] (1). Hydrogen atoms and solvent molecules are omitted for clarity.

In 1 and 2b, the metal atoms exhibit distorted trigonalbipyramidal geometries with C3 symmetry along the B−M−P axis in 1 and distorted C3 symmetry in 2b. Thus, the Pd−S bond lengths in 1 are at 2.4373(9) Å equally long and together with the Pd1−P1 bond length of 2.408(2) Å in the same range of the other three structurally characterized palladium boratrane

Figure 4. Molecular view of [Pt{B(PnMe,tBu)3}(PPh3)H]Cl (2a, left) and [Pt{B(PnMe,tBu)3}(PPh3)] (2b, right). Solvent molecules, noncoordinating Cl− in 2a, and hydrogen atoms except for Pt−H in 2a were omitted for clarity. C


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Inorganic Chemistry Table 1. 1H NMR Resonances of Palladium Boratrane Complexes in CD2Cl2 (ppm)a arom. A arom. B Me A Me B tBu A tBu B

Table 3. Selected Bond Lengths (Å) and Angles (deg) of Pt Complexes 2a,b and 4aa

1b

3a

3b

5a

5b

6

7.02

7.32 7.22 2.44 2.43 1.32 1.12

7.27 7.11 2.42 2.39 1.30 1.09

7.52 7.39 2.56 2.39 1.34 1.15

7.52 7.35 2.56 2.37 1.34 1.14

7.83 7.48 2.53 2.47 1.34 1.15

2.36 1.09

Pt−B Pt−L (ax.) Pt−L (eq ) Pt−S1 Pt−S2 Pt−S3 B−Pt−P/X/L B-pyramidalization

a Thiopyridazine trans to halide or acetonitrile A; thiopyridazine cis to halide or acetonitrile B. bAll three thiopyridazine are equivalent.

2a

2b

4a

2.098(4) 2.4751(10) 1.559b 2.3338(11) 2.4337(11) 2.3755(11) 176.04(13) 0.524(19)

2.092(4) 2.3638(8)

2.069(4) 2.6710(4) 2.5001(4) 2.3178(9) 2.3037(10) 2.3558(9) 175.25(11) 0.50(3)

2.3263(10) 2.4311(9) 2.3853(9) 178.93(10) 0.56(4)

a

Only for complex 2a is the geometry of molecule B listed. bThe Pt− H distance was restrained to 1.559 Å according to DFT calculations.

complexes (2.328 Å−2.536 Å for Pd−S; 2.360 for Pd−PMe3 and 2.412 Å for Pd−PPh3, respectively).20,36,39 The Pd1−B1 bond length of 2.075(7) Å is slightly longer compared to those of the thiomethimidazolyl-based palladium boratrane complex (2.050(8) Å) and the thiopyridine-based analogue (2.065(3) Å).36,39 In contrast to 1, in 2b the Pt−S bond lengths vary from 2.3263(10) to 2.4311(9) Å, which is the result of the slight asymmetric nature of the complex. It is furthermore noteworthy that the asymmetric unit contains two molecules A and B of 2b exhibiting rather different geometries. This is particularly distinct in the S1−Pt1−S3 angle which is enlarged to 153.72(3)° in B compared to 127.40(4)° in A (Figure S13). The flexibility in geometry in the Pt compound possibly explains the intermediate stability of hydride complex 2a. The slightly higher degree of boron pyramidalization of Δ = 0.56(4) Å in 2b compared to Δ = 0.55(2) Å in 1 might indicate a stronger B−M interaction in 2b, which is not reflected by the B−M bond lengths of 2.075(7) Å for 1 and 2.092(4) Å for 2b.51 In contrast to the trigonal bipyramidal coordination of Pt in 2b, the platinum atom in 2a exhibits an octahedral geometry with the Pt1−B1 bond length of 2.098(4) Å and the Pt1−P1 bond length of 2.4752(10) Å. The pyramidalization at boron Δ = 0.524(19) Å is slightly lower compared to that of 1 (0.55(2) Å), or 2b (Δ = 0.56(4) Å) indicating less B−M interaction, which could be due to the higher oxidation state in 2a. Due to the asymmetry of the complex, the Pt1−S distances vary between 2.3339(11) Å (Pt1−S3) and 2.4338(11) Å (Pt1−S2). The hydride H1 could not be found in a difference Fourier map, but was included with the Pt1−H1 bond length restrained to 1.559 Å, a number taken from our theoretical calculations. Furthermore, a noncoordinating Cl− molecule occupies a void of approximately 21 Å3. The structural parameters of 2a are very similar to those of the platinum hydrido boratrane complex obtained by Hill and co-workers (Pt−H 1.53(2) Å, Pt−P 2.4626(9) Å);38 however, the observed Pt1−B1 bond

length in 2a is the shortest of all other three structurally characterized platinum boratrane complexes that vary between 2.119(4) and 2.224(4) Å.24,38 Oxidation and Ligand Exchange. According to 1H NMR spectroscopy, we found that Pt hydrido complex 2a is not stable in chlorinated solvents under ambient atmosphere and decomposes within several days to yet unidentified species. In an attempt to elucidate the nature of this decomposition product, a solution of the latter in CHCl3 was allowed to crystallize for several days under ambient atmosphere, after which few single crystals appeared in the flask. X-ray diffraction analysis revealed them to be the dichlorido compound [Pt{B(PnMe,tBu)3}Cl2] as shown in Figure 5. The structure is

Figure 5. Molecular view of [Pt{B(PnMe,tBu)3}Cl2]. Hydrogen atoms and solvent molecules were omitted for clarity.

Table 2. Selected Bond Lengths (Å) and Angles (deg) of Pd Complexes 1, 3a,b, 5b, and 6a Pd−B Pd−L (ax.) Pd−L (eq ) Pd−S1 Pd−S2 Pd−S3 B−Pd−P/X/L B-pyramidalization a

1

3a

3b

5b

6

2.075(7) 2.408(2)

2.089(4) 2.6703(4) 2.4677(5) 2.3065(8) 2.3039(9) 2.3512(8) 172.62(10) 0.48(2)

2.097(6) 2.8779(7) 2.6589(7) 2.3161(17) 2.3247(17) 2.3491(17) 174.9(2) 0.48(6)

2.088(6) 2.9325(6) 2.6807(6) 2.3195(16) 2.3335(14) 2.3666(16) 177.27(16) 0.46(7)

2.092(6) 2.267(6) 2.030(6) 2.312(2) 2.2804(19) 2.367(2) 178.1(2) 0.47(7)

2.4373(9) 2.4373(9) 2.4373(9) 180.0 0.55(2)

Only for complex 5b is the geometry around Pd1 listed. D


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Inorganic Chemistry

palladium occurred, while the respective reaction with 2a represents a ligand exchange from hydride to halogenide. After workup, all compounds were isolated in good yields (60 to 99%) as red (3a), brown (3b), or orange (4a and 4b) solids. NMR spectroscopy revealed all four compounds to be asymmetric species with two sets of resonances for the pyridazine rings in a 2:1 ratio. The chemical shifts are influenced by the oxidation: For example, the 1H NMR shifts in CD2Cl2 at 7.32 and 7.22 (for 3a) and 7.27 and 7.11 (for 3b) assignable for the aromatic proton at the heterocyclic rings are downfield shifted by 0.09−0.40 ppm compared to those of 1 pointing to a more electron-deficient compound, which is in accordance with the higher oxidation state of the metal (Table 1). Single crystals suitable for X-ray diffraction analysis could be obtained by slow evaporation of the corresponding CHCl3 or CH2Cl2/heptane solutions. Molecular views are shown in Figure 6. Selected bond lengths and angles are given in Table 2, and crystallographic data are given in Tables S2 and S3. The solid state structure of 4a shows a similar octahedral environment at platinum compared to the chlorido compound with a relatively short Pt−B bond length of 2.069(4) Å (0.011 Å shorter than that for the chlorine compound) but a similar degree of boron pyramidalization (0.49(3) Å) in the chlorido complex vs 0.50(3) Å in 4a. This might be due to the stronger electron withdrawing effect of chlorine compared to bromine resulting in a weaker M−B interaction. While there has been previously described one structurally characterized platinum boratrane diiodide complex,38 3a and 3b are the first palladium boratrane halides. The Pd−B distances are 2.089(4) Å (for 3a) and 2.097(6) Å (for 3b), slightly longer than in the platinum derivatives, indicating a weaker bonding interaction. This is also supported by the slightly smaller boron pyramidalization of Δ =

similar to the only other structurally characterized platinaboratrane halide [Pt{B(mt)3}I2] described by Hill and co-workers which was obtained via treatment of tris-methimazolyl borane complex [Pt{B(mt)3}(PPh3)] with elemental iodine.38 The platinum atom in [Pt{B(PnMe,tBu)3}Cl2] is found in an octahedral environment with a platinum−boron bond length of 2.080(6) Å and a boron pyramidalization of Δ = 0.49(3) Å. This is slightly shorter compared to that of 2a (2.098(4)Å or Δ = 0.524(19) Å), which is likely attributed to the increased electrophilicity of the metal center. As anticipated, the platinum-chloride bond in trans position to the boron atom (Pt1−Cl1) is with 2.5348(12) Å significantly longer than the cis chlorine bond (Pt1−Cl2) with 2.3528(11) Å, indicating a transinfluence of the boron atom.52 The structural evidence of the dichloride compound prompted us to investigate the reactivity of 1 and 2a, respectively, toward bromine and iodine. Therefore, treatment with excess Br2 or I2 led to selective formation of the dihalido complexes [M{B(PnMe,tBu)3}X2] (M = Pd, X = Br 3a, I 3b; M = Pt, X = Br 4a, I 4b) as shown in Scheme 3. With 1, oxidation of Scheme 3. Reaction of Boratrane Complexes 1 and 2a with Br2 and I2

Figure 6. Molecular view of [Pd{B(PnMe,tBu)3}Br2] (3a, left), [Pd{B(PnMe,tBu)3}I2] (3b, right), and [Pt{B(PnMe,tBu)3}Br2] (4a, bottom). Hydrogen atoms and solvent molecules were omitted for clarity. E


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Inorganic Chemistry 0.48(2) Å for 3a and Δ = 0.48(6) Å for 3b. Both the palladium as well as the platinum complexes show significantly elongated metal−halide bond lengths in trans position to the boron atom (2.6703(4) vs 2.4677(5) Å for 3a, 2.8779(7) vs 2.6589(7) Å for 3b, and 2.3178(9) vs 2.3037(10) Å for 4a). Cationic Complexes. Given the fact that no cationic palladium and platinum boratrane complexes are known in the literature, we were interested whether the observed high transinfluence of the boron atom and the resulting long metal− halide bond lengths could lead to these as yet elusive compounds. Due to the larger abundance of reactions catalyzed by cationic palladium complexes47−49 compared to those by platinum,53,54 we limited our investigation to the reactivity of the palladium halogenido complexes toward a silver(I) salt with a weakly coordinating counterion. Addition of 1 equiv of Ag(SbF6) to 3a and 3b in CH2Cl2 led to the formation of dimeric, cationic complexes of the general formula [Pd{B(PnMe,tBu)3}X]2(SbF6)2 (X = Br 5a, I 5b) as shown in Scheme 4. They can be isolated as red solids in good yields up to 87%

for 6) indicating strong established M−B bonds and possibly explaining the high stability of these compounds. Single crystals of 5b and 6 suitable for X-ray diffraction analysis could be obtained by slow evaporation of a benzene/ methylene chloride (for 5b) and an acetonitrile solution (for 6). Molecular views are shown in Figure 7. Selected bond lengths and angles are given in Table 2, and crystallographic data are given in Table S5.

Scheme 4. Synthesis of Cationic Complexes 5a,b and 6 via Reaction with AgSbF6

Figure 7. Molecular view of [Pd{B(PnMe,tBu)3}I]2(SbF6)2 (5b) (left) and [Pd{B(PnMe,tBu)3}(NCMe)2](SbF6) (6) (right). Counter ions, tBu groups, hydrogen atoms, and solvent molecules were omitted for clarity.

The molecular structure of 5b reveals the formation of a dinuclear boratrane complex with bridging iodine atoms. According to the applied stoichiometry in the reaction, only one halogen atom is abstracted from the complex. In the absence of a coordinating solvent the monocationic complexes dimerizes forming an octahedrally coordinated bis-μ-iodine bridged dimer, as displayed in Figure 7. The Pd1−B1 bond lengths of 2.088(6) Å for 5b and the boron pyramidalization of Δ = 0.47(7) Å are only slightly shorter compared to those of precursor complex 3b (2.097(6) Å), which might be attributed to the cationic character of the complex. As already observed for 3a and 3b, again the iodine trans to the boron atom shows a significantly longer bonding distance compared to the cis counterparts (2.9325(6) vs 2.6807(6) Å). The molecular structure of dicationic complex 6 is displayed in Figure 7, revealing an octahedral Pd center, coordinated by the boratrane ligand and two neutral acetonitrile solvent molecules. The Pd1−B1 bond length of 2.092(6) Å and the boron pyramidalization of Δ = 0.49(3) Å is similar to those of precursor complexes 3a (2.089 Å) and 3b (2.097 Å), indicating similar bonding interactions. Again, the coordinated acetonitrile trans to the boron atom reveals a significantly longer bonding distance compared to the cis-coordinated analogue (2.267(6) vs 2.030(6) Å), indicative for a trans influence of the boron atom.52 Density Functional Theory Calculations. Boratrane complexes can be described, according to Green’s rule, as Ztype compounds where the electrons for the B−M bond are supplied by the metal rendering the latter in a high oxidation state.55 However, many reports find disputing arguments for such a description.42,43,56 We have previously gained theoretical support that our Z-type complexes indeed can be better described as oxidized metals with significant back-donation to

and are stable at ambient atmosphere, both in solution and in the solid state. 1H NMR spectroscopy in CD2Cl2 revealed a 2:1 ratio for the resonances of the ligand, indicative of an asymmetric coordination. Furthermore, the signals for the aromatic protons at 7.52 ppm in 5a are shifted to lower fields compared to those in 3a, indicating lower electron density on the heterocycle (Table 1). Moreover, addition of 2 equiv of Ag(SbF6) to 3a and 3b in acetonitrile leads to the dicationic complex [Pd{B(PnMe,tBu)3}(NCMe)2](SbF6)2 (6), which can be isolated as a red solid in almost quantitative yield. This complex was also found to be stable at ambient atmosphere in solution and in the solid state. We find this rather surprising as its increased electrophilicity compared to neutral dihalide complexes 3a and 3b might lead to enhanced hydrolysis reactivity at the Lewis acidic platinum center. Similar to 5a and 5b, in 6, 1H NMR spectroscopy reveals a 2:1 ratio for the resonances of the ligand. As expected for a dicationic complex, the aromatic resonances are significantly shifted to lower fields, demonstrated by the shift of the aromatic signals from 7.32 and 7.22 ppm in 3a to 7.83 and 7.48 ppm in 6 (Table 1). In addition, 11B NMR spectroscopy reveals upfield shifts going from neutral to mono- and dicationic complexes (e.g., 21.62 ppm for 1, 18.21 ppm for 3b, 17.85 ppm for 4b, and 15.07 ppm F


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Inorganic Chemistry

Figure 8. Frontier orbitals (d-splitting) for 2a (left) and for 2b (right). Energy values in atomic units.

the boron atom.35 We were therefore interested whether this holds true in the here presented compounds so that we performed DFT/PBE0 calculation in order to elucidate the nature of the palladium/platinum boron bond. The optimized structures of 1, 2a, and 2b, supporting the experimental findings, are provided in Figure S23. The corresponding frontier orbitals of 2a and 2b are represented in Figure 8. For complexes 1 and 2b, in the d-splitting there is one empty d orbital (z2 if the B−M−P direction is the z axis) representing the M−B σ antibonding orbital, based on metal z2. That means that the orbitals point toward d8 metals, i.e., Pt(II) and Pd(II). With respect to the atomic charges (NPA population analysis) of the metal centers, these are clearly positive (0.28 for both metals) indicating a +II oxidation state. The B−M bonds are well-established meaning a very strong coordination of the B atom: WI(M−B) = 0.56 (Pd) and 0.59 (Pt). Thus, the here-provided calculation support the idea that in analogy to density functional theory calculations we performed at a similar copper boratrane compound 41 compounds 1 and 2b are also better described in the oxidation state +II possessing a d8 rather than a d10 electron configuration in line with calculations on a structurally related palladium mercaptoimidazolylboratrane compound.39 In contrast to 1 and 2b, the d-splitting of 2a (Figure 8, right) reveal that the frontier orbitals have less contribution of d, but especially the very strong Pt−B bond (WI = 0.51) points toward a formal Pt−B two electron back-donation. In combination to the d-splitting, revealing a d6 octahedral

complex, again this points to a higher oxidized Pt(IV) hydrido species rather than Pt(II). Additionally, oxidized dibromide complexes 3a and 4a were calculated revealing a similar d-splitting of octahedral d6 complexes, with an empty eg set (z2 and x2−y2) and a filled t2g set (xy, xz, and yz; Figure S25). Also, the M−B bonds were found to be well-established with WI = 0.52 for Pt and 0.44 for Pd indicating significant back-donation from the metal to boron. As a result of these calculations, we assume 3a,b and 4a,b are Pd(IV) and Pt(IV) complexes rather than Pd(II) or Pt(II).

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CONCLUSION In the present study, we report the synthesis of Z-type palladium and platinum boratrane complexes [M{B(PnMe,tBu)3}(PPh3)] (M = Pd (1), Pt(2b)]. While the Pd complex is formed spontaneously, 2b is synthesized via reaction of [Pt{B(PnMe,tBu)3}(PPh3)H]Cl (2a) with a base. Further reactivity studies led to isolation of palladium and platinum boratrane halides [M{B(PnMe,tBu)3}X2] (M = Pd, X = Br (3a), I (3b); M = Pt, X = Br (4a), I (4b)). Particularly, the facile ligand exchange in compound 2a represents an interesting starting point for possible further reactivity. Abstraction of the halide ions with and without acetonitrile as a coordinating solvent yields surprisingly stable cationic Pd boratranes [Pd{B(PnMe,tBu)3}X]2(SbF6)2 (X = Br (5a), I (5b)) and [Pd{B(PnMe,tBu)3}(NCMe)2](SbF6)2 (6). Spectroscopic data as well as theoretical calculations point toward well-established meta−boron bonds explaining the high stability of the G


Article

Inorganic Chemistry

P NMR (CDCl3) δ 0,4 (bs) ppm. 1H NMR (CD2Cl2) δ 7.53−7.50 (m, 15H, PPh3), 7.38 (q, J = 1.2 Hz, 2H, aromatic H cis to Pt−H), 7.22 (q, J = 1.2 Hz, 1H, aromatic H trans to Pt−H), 2.37 (d, J = 1.1 Hz, 3H, Me trans to Pt−H), 2.34 (d, J = 1.1 Hz, 6H, Me trans to Pt− H), 1.30 (s, 18H, tBu cis to Pt−H), 1.07 (s, 9H, tBu trans to Pt−H), −13.21 (d, J = 9.0 Hz, 1H, Pt−H) ppm. 31P NMR (CD2Cl2) δ 0,00 (bs) ppm. 11B NMR (CD2Cl2): 19.73 (JPt−B 93.3 Hz) ppm. 13C NMR (CDCl3) δ 177.5, 177.3, 164.8, 163.3, 145.6, 145.0, 133.7, 133.5, 133.7, 133.5, 129.1, 128.9, 36.9, 36.4, 29.5, 29.0, 20.8, 19.5 ppm. IR (ATR, cm−1): 2956, 2147 (Pt−H), 1597, 1514, 1478, 1433, 1376, 1308, 1189, 1178, 1094, 1016, 922, 892, 808, 693, 521, 498, 465. HRMS-ESI (m/ z): [Pt{B(Pn Me,tBu ) 3 }ClPPh 3 ] + calcd for C 45 H 54 BClN 6 PPtS 3 : 1046.2739, found: 1046.2720. b) An NMR tube, equipped with a Young valve, was charged with 35 mg (0.035 mmol) of 2b and dissolved in 0.5 mL of CD2Cl2. Concentrated HCl (aqueous) (10 μL, 3.4 equiv) was added, whereupon the black solution turned yellow. Subsequent 1H NMR spectroscopy reveals full conversion to 2a. [Pt{B(PnMe,tBu)3}(PPh3)] (2b). A Schlenk flask was charged with 50 mg (0.048 mmol) of 2a then dissolved in 4 mL of methylene chloride. To the yellow solution was added 8.5 μL (0.057 mmol, 1.2 equiv) of 1,8-diazabicyclo[5.4.0]undec-7-en dissolved in 2 mL of methylene chloride, resulting in an immediate color change to deep purple. After stirring for 10 min, the formed suspension was eluted over a pad of Celite, and to the dark solution was added 4 mL of heptane. CH2Cl2 was allowed to evaporate slowly over a period of 4 days yielding 33 mg (72%) of dark purple crystals. 1H NMR (CD2Cl2) δ 7.67−7.61 (m, 5H, PPh3), 7.40−7.34 (m, 10H, PPh3), 6.92 (d, J = 1.0 Hz, 3H, aromatic H), 2.34 (d, J = 0.8 Hz 9H, Me), 1.15 (s, 27H, tBu) ppm. 31P NMR (CD2Cl2) δ 16.81 (bs) ppm. 11B NMR (CD2Cl2): 23.14 (bs) ppm. 13C NMR (CD2Cl2) δ 176.18, 160.28, 145.60, 134.62, 134.44, 128.60, 128.49, 121.64, 36.49, 29.79, 20.95. HRMS-ESI (m/z): [Pt{B(Pn Me,tBu ) 3 }(PPh 3 )] + H + calcd for C 45 H 55 BN 6 PPtS 3 : 1012.3123, found: 1012.3095. [Pd{B(PnMe,tBu)3}Br2] (3a). To a solution of 1 (600 mg, 0.65 mmol) in toluene (10 mL) was added bromine at room temperature via a syringe until the reaction mixture turned into a red suspension (2 droplets, about 2 equiv) The precipitate was isolated via filtration at ambient conditions and washed with toluene (2 × 5 mL) and pentane (5 mL). For purification, the residue was taken up in CH2Cl2 (10 mL) and toluene (10 mL), and the former was evaporated under reduced pressure. The resulting red precipitate was then again isolated via filtration and washed with toluene (2 × 5 mL) and pentane (5 mL) to obtain 3a as a red crystalline solid (530 mg, 99%). Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a CHCl3 solution. 1H NMR (CD2Cl2) δ 7.32 (s, 2H, aromatic H cis to Br), 7.22 (s, 1H, aromatic H trans to Br), 2.44 (s, 6H, Me cis to Br), 2.43 (s, 3H, Me trans to Br), 1.32 (s, 18H, tBu cis to Br), 1.12 (s, 9H, tBu trans to Br) ppm. 11B NMR (CD2Cl2): 18.06 ppm. 13 C NMR (CD2Cl2) δ 180.8, 178.2, 165.1, 164.4, 145.3, 143.3, 125.5, 125.3, 36.8, 36.6, 29.1, 28.6, 19.5, 19.4 ppm. IR (ATR, cm−1): 2955, 2924, 2848, 1596, 1514, 1478, 1389, 1168, 1171, 1012, 928, 909, 621. HRMS-ESI (m/z): [Pd{B(PnMe,tBu)3}Br]+ calcd for C27H39BrN6BPdS3: 741.0699, found: 741.0726. [Pd{B(PnMe,tBu)3}I2] (3b). To a solution of 1 (100 mg, 0.11 mmol) in toluene (10 mL) was added iodine (55 mg, 0.22 mmol), whereupon a color change from deep purple to brown occurred. After stirring for 7 h, all volatiles were removed under reduced pressure and recrystallized from a CH2Cl2/heptane mixture to isolate 3b as dark brown crystals (94 mg, 95%). Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a CHCl3 solution. 1H NMR (CD2Cl2) δ 7.27 (q, J = 1.0 Hz, 2H, aromatic H cis to I), 7.11 (t, J = 1.1 Hz, 1H, aromatic H trans to I), 2.42 (d, J = 1.1 Hz, 6H, Me cis to I), 2.39 (d, J = 1.1 Hz, 3H, Me trans to I), 1.30 (s, 18H, tBu cis to I), 1.09 (s, 9H, tBu trans to I) ppm. 11B NMR (CD2Cl2): 18.21 ppm. 13C NMR (CD2Cl2) δ 181.6, 165.6, 165.1, 145.9, 144.0, 37.4, 37.1, 29.7, 29.1, 20.0, 19.9 ppm. IR (ATR, cm−1): 2963, 2931, 2866, 1600, 1476, 1436, 1378, 1368, 1316, 1191, 1163, 1119, 722, 689. HRMS-ESI (m/ z): [Pd{B(PnMe,tBu)3}I]+ calcd for C27H39IN6BPdS3: 787.0578, found: 787.0616. 31

complexes. The electron-deficient nature in combination with the robustness of the ligand (oxidation without breaking the M−B bond) and the generally accepted two electron mechanism in palladium catalyzed reactions render these complexes potentially interesting for catalytic applications.

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EXPERIMENTAL SECTION

General Information. Reactions were carried out under N2 atmosphere using standard Schlenk-technique or a glovebox. KTnMe,tBu was synthesized according to a published procedure.41 All other chemicals were purchased from commercial sources and used without purification. Acetonitrile, methylene chloride, heptane, pentane, and toluene were purified via a Pure-Solv MD-4-EN solvent purification system from Innovative Technology, Inc. NMR spectra were measured on a Bruker Avance III 300 MHz spectrometer at 25 °C if not otherwise stated. Chemical shifts are given in ppm and are referenced to residual protons in the solvent. Electrospray mass spectra were recorded using a Thermo Scientific Q-Exactive mass spectrometer. Spectra were obtained using flow injection of approximately 1 μM solutions of compounds in acetonitrile/acetone mixtures. Both positive and negative mode was employed. Infrared spectra were recorded on a Bruker Alpha Platinum ATR spectrometer. X-ray Structure Determination. X-ray data collection was performed with a Bruker AXS SMART APEX 2 CCD diffractometer by using graphite-monochromated Mo−Kα radiation (0.71073 Å) from a Incoatec microfocus sealed tube at 100(2) K. SHELXS-9757 was used as the structure solution and SHELXL-2014/658 as the structure refinement program. Refinement details and results are given in the Supporting Information. Crystallographic data for this paper (CCDC reference numbers 1826214−1826223) can be obtained free of charge from the Cambridge Crystallographic Data Centre via ww. ccdc.cam.ac.uk/data_request/cif. Further details on the solution of the structures can be found in the Supporting Information. [Pd{B(PnMe,tBu)3}(PPh3)] (1). An aluminum-wrapped 100 mL Schlenk flask was charged with KTnMe,tBu (1.00 g, 1.68 mmol), [PdCl2(PPh3)2] (1.18 g, 1.68 mmol), and 25 mL of CH2Cl2. The deep purple reaction mixture was stirred at room temperature for 3 h, thereafter filtered through a pad of Celite, and the residue washed twice with 10 mL of CH2Cl2. The solvent was evaporated under reduced pressure to yield a deep purple solid. The crude product was purified via inert recrystallization from 25 mL of hot acetonitrile to yield 1 as a deep purple solid (1.32 g, 85%). Single crystals suitable for X-ray diffraction analysis were obtained by cooling of a CH2Cl2/ pentane solution to −20 °C. 1H NMR (C6D6) δ 8.16−8.06 (m, 6H, PPh3), 7.13−7.04 (m, 6H, PPh3), 7.03−6.95 (m, 3H, PPh3), 6.42 (q, J = 1.2 Hz, 3H, aromatic H), 2.19 (d, J = 1.2 Hz, 9H, Me), 0.96 (s, 27H, tBu) ppm. 1H NMR (CD2Cl2) δ 7.66−7.60(m, 6H, PPh3), 7.38−7.35 (m, 9H, PPh3), 7.02 (q, J = 1.1 Hz, 3H, aromatic H), 2.36 (d, J = 1.1 Hz, 9H, Me), 1.09 (s, 27H, tBu) ppm. 31P NMR (C6D6): 14.58 (bs) ppm. 11B NMR (C6D6): 21.62 ppm. 13C NMR (C6D6) δ 179.40 (d, J = 8.6 Hz), 158.61, 146.33, 136.92 (d, J = 19.7 Hz), 135.00 (d, J = 15.5 Hz), 129.17, 121.09 (d, J = 2.2 Hz), 35.87, 29.46, 20.93 (d, J = 2.4 Hz); IR (ATR, cm−1): 2958, 1592, 1511, 1476, 1445, 1433, 1371, 1195, 1167, 696, 514, 502. HRMS-ESI (m/z): [Pd{B(PnMe,tBu)3}(PPh3)]+ calcd for C45H54BN6PPdS3: 922.2448, found: 922.2495. [Pt{B(Pn Me,tBu ) 3 }(PPh 3 )H]Cl (2a). a) To a solution of [PtCl2(PPh3)2] (152 mg, 0.192 mmol) in 2 mL CH2Cl2 KTnMe,tBu (114 mg, 0.192 mmol) in 2 mL CH2Cl2 was added slowly under light exclusion. The reaction mixture turned into a brown suspension during some minutes and was further stirred for 18 h. All solids were removed via filtration and heptane (5 mL) was added to the filtrate. At −40 °C yellow crystals formed which were isolated and washed with pentane (2 mL) to yield 175 mg of 2a (87%). Single crystals suitable for X-ray diffraction analysis could be obtained by cooling of a CH2Cl2/heptane solution to −20 °C. 1H NMR (CDCl3) δ 7.52−7.49 (m, 15H, PPh3), 7.42 (q, J = 1.0 Hz, 2H, aromatic H cis to Pt−H), 7.21 (q, J = 0.9 Hz, 1H, aromatic H trans to Pt−H), 2.39 (d, J = 0.9 Hz, 3H, Me trans to Pt−H), 2.37 (d, J = 1.0 Hz, 6H, Me cis to Pt−H), 1.29 (s, 18H, tBu cis to Pt−H), 1.07 (s, 9H, tBu trans to Pt−H) ppm. H


Article

Inorganic Chemistry [Pt{B(PnMe,tBu)3}Br2] (4a). To a solution of 2a (51 mg, 0.049 mmol) in CH2Cl2 (3 mL) was added bromine via a syringe (2 droplets), whereupon a color change from yellow to red occurred. After stirring for 2 h, additional CH2Cl2 (2 mL) and heptane (4 mL) were added, and the solution was filtrated over a pad of Celite. CH2Cl2 was allowed to evaporate slowly over a couple of days to yield orange crystals. The solvent was decanted and the crystals washed with pentane to isolate 34 mg of 4a (74%). 1H NMR (CD2Cl2) δ 7.28 (q, J = 1.0 Hz, 2H, aromatic H cis to Br), 7.15 (s, 1H, aromatic H trans to Br), 2.44−2.43 (m, 9H, Me), 1.35 (s, 18H, tBu cis to Br), 1.12 (s, 9H, tBu trans to Br) ppm. 11B NMR (CD2Cl2): 13.18 (JPt−B 219.5 Hz) ppm. 13C NMR (CD2Cl2) δ 180.2, 165.7, 165.0, 146.0, 135.0, 37.3, 37.1, 29.8, 29.2, 20.2, 19.9 ppm. IR (ATR, cm−1): 2958, 2926, 2861, 1600, 1518, 1478, 1378, 1190, 1171, 1010, 929, 895, 815, 692, 540. HRMS-ESI (m/z): [Pt{B(PnMe,tBu)3}Br]+ calcd for C27H39BBrN6PtS3: 828.1324, found: 828.1311. [Pt{B(PnMe,tBu)3}I2] (4b). To a solution of 2a (52 mg, 0.050 mmol) in CH2Cl2 (3 mL) was added iodine (30 mg, 0.118 mmol), whereupon a color change from yellow to orange occurred. After stirring for 16 h, heptane (5 mL) was added whereupon a precipitate formed. The solid was isolated via filtration and dried under vacuum to obtain 31 mg of 4b (60%). 1H NMR (CD2Cl2) δ 7.26 (q, J = 1.1 Hz, 2H, aromatic H cis to I), 7.12 (q, J = 1.1 Hz, 1H, aromatic H trans to I), 2.43 (d, J = 1.1 Hz, 6H, Me cis to I), 2.42 (d, J = 1.1 Hz, 3H, Me trans to I) 1.35 (s, 18H, tBu cis to I), 1.12 (s, 9H, tBu trans to I) ppm. 11B NMR (CD2Cl2): 16.40 (JPt−B 217.9 Hz) ppm. 13C NMR (CD2Cl2) δ 165.69, 165.00, 145.83, 143.86, 125.49, 37.32, 37.09, 29.83, 29.20, 20.15, 19.91. IR (ATR, cm−1): 2960, 2928, 2867, 1598, 1581, 1478, 1447, 1368, 1317, 1194, 1168, 1120, 929, 898, 812, 723, 693, 622, 541. HRMS-ESI (m/z): [Pt{B(PnMe,tBu)3}I]+ calcd for C27H39BIN6PtS3: 879.1187, found: 876.1172. [Pd{B(PnMe,tBu)3}Br]2(SbF6)2 (5a). 3a (50 mg, 0,061 mmol) and AgSbF6 (21 mg, 0.061 mmol) were transferred inside a glovebox into a glass vial, and CH2Cl2 (1 mL) was added, whereupon a dark colored suspension resulted. After 15 min of stirring, the reaction mixture was filtered over a pad of Celite before heptane was added to the filtrate (1 mL). After storing the solution at −40 °C for 1 week, dark red crystals formed, which were isolated and washed with pentane (1 mL) to obtain 5a (52 mg, 87%). 1H NMR (CD2Cl2) δ 7.52 (q, J = 1.2 Hz, 4H, aromatic H cis to Br), 7.39 (q, J = 1.2 Hz, 2H, aromatic H trans to Br), 2.56 (bs, 12H, Me cis to Br), 2.39 (bs, 6H, Me trans to Br), 1.34 (s, 36H, tBu cis to Br), 1.15 (s, 18H, tBu trans to Br) ppm. 11B NMR (CD2Cl2): 17.95 ppm. 13C NMR (CD2Cl2) δ 179.83, 178.08, 166.46, 166.22, 146.10, 144.20, 127.60, 127.02, 37.48, 37.34, 29.26, 28.94, 20.01, 19.86 ppm. HRMS-ESI (m/z): [Pd{B(PnMe,tBu)3}Br]+ calcd for C27H39BrN6BPdS3: 741.0699, found: 741.0735. [Pd{B(PnMe,tBu)3}I]2(SbF6)2 (5b). To a solution of 3b (50 mg, 0,055 mmol) in CH2Cl2 (1 mL) was added AgSbF6 (25 mg, 0.073 mmoL). After stirring for 40 min, the reaction mixture was filtered, and all volatiles were removed under reduced pressure. The resulting crude product was purified via recrystallization from a CH2Cl2/heptane mixture to obtain 3b as dark red crystals (45 mg, 95%). Single crystals suitable for X-ray diffraction analysis were obtained by recrystallization of a benzene/methylene chloride solution. 1H NMR (CD2Cl2) δ 7.52 (q, J = 1.2 Hz, 4H, aromatic H cis to I), 7.35 (q, J = 1.2 Hz, 2H, aromatic H trans to I), 2.56 (d, J = 1.1 Hz, 12H, Me cis to I), 2.37 (d, J = 1.1 Hz, 6H, Me trans to I), 1.37 (s, 36H, tBu cis to I), 1.14 (s, 18H, tBu trans to I) ppm. 11B NMR (CD2Cl2): 17.85 ppm. 13C NMR (CD2Cl2) δ 180.0, 176.4, 166.8, 166.0, 146.0, 143.5, 126.7, 37.1, 36.8, 28.9, 28.4, 19.3, 18.8 ppm. IR (ATR, cm−1): 2995, 2931, 2869, 1716, 1596, 1478, 1444, 1381, 1193, 1122, 733, 654. HRMS-ESI (m/z): [Pd{B(PnMe,tBu)3}I]+ calcd for C27H39IN6BPdS3: 787.0578, found: 787.0609. [Pd{B(PnMe,tBu)3}(NCMe)2](SbF6)2 (6). 3a (415 mg, 0,506 mmol) and AgSbF6 (382 mg, 1.11 mmol) were transferred inside a glovebox into a 25 mL Schlenk-type round-bottomed flask. At room temperature, 10 mL of acetonitrile was added to yield a red suspension. After 5 min of stirring, the reaction mixture was filtrated through Celite to remove precipitated AgBr and washed with acetonitrile (5 mL). The filtrate was concentrated under reduced

pressure and the residue was dried under vacuum to yield 6 as a red solid (590 mg, 96%). Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of an acetonitrile solution. 1 H NMR (CD3CN) δ 7.81 (s, 2H, aromatic H cis to NCMe), 7.68 (s, 1H, aromatic H trans to NCMe), 2.45 (s, 6H, Me cis to NCMe), 2.39 (s, 3H, Me trans to NCMe), 2.23 (bs, 6H, NCMe), 1.31 (s, 18H, tBu cis to NCMe), 1.12 (s, 9H, tBu trans to NCMe) ppm. 1H NMR (CD2Cl2) δ 7.83 (s, 2H, aromatic H cis to NCMe), 7.48 (s, 1H, aromatic H trans to NCMe), 2.53 (s, 6H, Me cis to NCMe), 2.47 (s, 3H, Me trans to NCMe), 2.17 (s, 6H, NCMe), 1.34 (s, 18H, tBu cis to NCMe), 1.15 (s, 9H, tBu trans to NCMe) ppm. 11B NMR (CD3CN): 15.07 ppm. 13C NMR (CD3CN) δ 179.2, 175.1, 168.6, 167.7, 146.9, 144.3, 129.7, 129.2, 38.0, 37.7, 29.3, 28.7, 19.3 (d, J = 3.6 Hz), 18.4 (d, J = 3.8 Hz) ppm. 19F NMR (CD3CN) δ 124.0 ppm. IR (ATR, cm−1): 2970, 2936, 2875, 2324, 2300, 1653, 1596, 1480, 1446, 1382, 1324, 1197, 1169, 1041, 1015, 984, 931, 813, 754, 652. HRMS-ESI (m/z): [Pd{B(PnMe,tBu)3}(NCMe)]2+ calcd for C29H42N7BPdS3: 350.5897, found: 350.5918.

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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.inorgchem.8b00530. 1 H NMR spectra, crystallographic and computational data (PDF) Accession Codes

CCDC 1826214−1826223 and 1839208 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, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +43 (0)316 380-5286. Fax: +43 (0)316 380-9835. Email: [email protected]. ORCID

Luis F. Veiros: 0000-0001-5841-3519 Nadia C. Mösch-Zanetti: 0000-0002-1349-6725 Author Contributions #

S.H. and M.T. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the reviewers for their assistance and help in identifying the nature of the platinum hydrido compound.

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REFERENCES

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