Synthesis, properties and group 10 metal complexes of a bis(dipyridylphosphinomethyl)phenyl pincer ligand

Inorganica Chimica Acta 442 (2016) 24–29

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Synthesis, properties and group 10 metal complexes of a bis (dipyridylphosphinomethyl)phenyl pincer ligand Teresa F. Vaughan, John L. Spencer ⇑ School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand

a r t i c l e

i n f o

Article history: Received 6 September 2015 Received in revised form 16 November 2015 Accepted 17 November 2015 Available online 2 December 2015 Keywords: Pyridylphosphine Pincer Phosphine selenide Platinum(II) complexes Palladium(II) complexes

a b s t r a c t The synthesis, properties and coordination behaviour of the bis(dipyridylphosphinomethyl)phenyl pincer ligand 1,3-C6H4(CH2PPy2)2 (Py = 2-pyridyl) are reported. The basicity of the phosphorus atoms in the ligand is explored through the synthesis of the phosphine selenide and a protonation study. The 1 JPSe value of 742 Hz indicates that this ligand is less basic than PPh3 and the protonation study confirms the nitrogen atoms are more basic than the phosphorus atoms. Protonation of the ligand also renders it water-soluble. The ligand reacts with [PtXY(hex)] (X = Y = Me; X = Cl Y = Me, hex = hexa-1,5-diene) at 50 °C to give pincer [PtX(PCP)] complexes (X = Me, Cl). In contrast, when reaction with [PtXY(hex)] (X = Y = Me, Cl; X = Cl Y = Me) occurs at ambient temperature, dimeric complexes of the type [PtXY(l-PP)]2 are observed in the NMR spectra. The presence of a methyl ligand appears to facilitate metalation: when there is no methyl ligand present formation of the platinum pincer complex does not occur even after prolonged thermolysis. However, reaction with [PdCl2(MeCN)2] proceeds readily at 50 °C from the dimer to the [PdCl(PCP)] complex. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction Polydentate ligands containing phosphorus and nitrogen donor atoms continue to attract attention due to their diverse coordination chemistry. One of the important features of P,N ligands is their ability to stabilise metals in a range of oxidation states and geometries. The phosphorus donor is considered to be a soft Lewis base and can stabilise soft Lewis acids, such as metal centres in low oxidation states. In contrast, nitrogen donors are hard ligands and therefore are better ligands for hard metal centres like those high oxidation states [1]. Thus this hard/soft combination can lead to selective binding to metal ions of different types [2] and the potential for hemilability [3]. Tertiary phosphines with pyridyl substituents (pyridylphosphines) are among the most widely studied P,N ligands and are attractive ligands for coordination chemistry [4–6]. They have been important in the development of water-soluble catalysts [7] and their silver(I) and gold(I) complexes have proven useful in inorganic medicinal chemistry [8]. While pyridylphosphines of the type PPh3-nPyn have been extensively studied, pyridyldiphosphines have received far less attention [4–6]. There are two distinct types of pyridyldiphosphines: those with the pyridyl ring as part of the ⇑ Corresponding author. Tel.: +64 4 463 5119. E-mail address: [email protected] (J.L. Spencer). http://dx.doi.org/10.1016/j.ica.2015.11.018 0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

ligand backbone, such as type I in Fig. 1, and those with pyridyl rings as substituents on the phosphorus atoms, type II. While type I ligands have been found to act as pincer ligands forming complexes that are catalytically active in a range of reactions [9,10], ligands of type II have received far less attention. In particular pincer type ligands with pyridyl substituents on the phosphorus donor atoms have not been reported. Pincer ligands refer to tridentate chelating ligands which usually coordinate to metal centres in a meridional fashion. There has been a large variety of structures reported. Pincer ligands are often named based on the ligating atoms present. Thus the type I ligand in Fig. 1 would be referred to as a PNP ligand. A major reason why pincer ligands receive so much attention is due to the high catalytic activity of their complexes. For example, palladium complexes of pincer ligands have been shown to be active catalysts in a range of reactions [11]. In particular, pincer complexes have been found to be highly active catalysts for Heck and Suzuki crosscoupling reactions. One of the reasons these complexes are attractive catalysts is because they show high thermal stability. This is a consequence of the rigid tridentate coordination typically forming two five-membered rings [11]. Herein, we report the synthesis, properties and coordination chemistry, with platinum(II) and palladium(II), of the bis (dipyridylphosphinomethyl)phenyl pincer ligand 1,3-C6H4(CH2PPy2)2 (1) (Py = 2-pyridyl).

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frequencies has been reported to be indicative of protonation of the nitrogen in a pyridyl ring [18] or coordination of a metal to the nitrogen atom [2,19]. Thus the shift of the C@N stretch could be concluded to indicate that the proton was bound to the nitrogen. In the reaction with six equivalents of acid N–H stretches and C@N stretches consistent with the nitrogen atoms being protonated were observed at 3100 and 1606 cm1 as well as P–H stretches at 2361 and 2363 cm1 in the IR spectrum. This confirmed that reaction with six equivalents of H2C(SO2CF3)2 protonated all of the nitrogen and phosphorus atoms in ligand 1. This reactivity meant that the proton basicity of the phosphorus in 1 could not be investigated through direct titration. Instead, the basicity of the phosphine was explored indirectly through the synthesis of a phosphine selenide. The measurement of 1JPSe has been found to be a reliable method to probe the basicity of a phosphine and is particularly useful for determining the basicity of heteroatom-containing phosphines for which direct titration is not possible [20,21]. It has been established that the larger the value of 1JPSe the greater the ‘s’ character of the phosphorus lone pair, meaning that phosphines with electron-withdrawing substituents will have larger 1JPSe values than electron-rich phosphines [22]. For example the phosphine selenides of PMe3 and PPh3 have 1 JPSe values of 684 and 732 Hz respectively [22,23]. The reaction between ligand 1 and excess elemental selenium was complete after refluxing overnight in chloroform. The 31P NMR spectrum of the phosphine selenide product 2 (Scheme 1) showed a singlet at 34.0 ppm with a 1JPSe value of 742 Hz. Given this it was concluded that ligand 1 was slightly less basic than PPh3 and that 2-pyridyl substituents are more electron withdrawing than phenyl groups.

N PR2

PR2

Py2P

I

PPy2 II

Fig. 1. Types of pyridyldiphosphines.

2. Results and discussion 2.1. Ligand synthesis and properties The synthesis of 2-pyridylphosphines usually involves lithiation of 2-bromopyridine and subsequent reaction with a chlorophosphine. For example, tris(2-pyridyl)phosphine is synthesised via the reaction of 2-pyridyllithium with phosphorus trichloride and the most widely used pyridyldiphosphine, 1,2-bis(di-2pyridylphosphino)ethane, is formed when 2-pyridyllithium is reacted with 1,2-bis(dichlorophosphino)ethane [12]. However, the disadvantage of this methodology is the use of chlorophosphine reagents which often require a complicated multi-step synthesis or, when commercially available, are expensive. Given this, the new ligand 1 was synthesised using an adaptation of the alternative method reported by Berners-Price et al. [12]. Reaction of dibromo-m-xylene with two equivalents of lithium bis(2-pyridyl)phosphide, generated in situ from the reaction of tris(2-pyridyl)phosphine with a lithium dispersion, gave ligand 1 (Scheme 1). Ligand 1 was isolated as a pale yellow solid 0 after the 2,2 -bipyridine formed as a byproduct in this reaction was removed via sublimation [13]. While the presence of the pyridyl rings in ligand 1 did not render the ligand water-soluble, when the pyridyl nitrogens were protonated through reaction with HCl(aq) the resulting protonated ligand was soluble in water. When ligand 1 was reacted with 1–6 equivalents of the strong acid H2C(SO2CF3)2 the pyridyl nitrogen atoms were protonated before the phosphorus atoms in 1. In the 31P NMR spectra of the reactions of compound 1 with one to four equivalents of acid the signal of the product appeared between 24.5 and 22.5 ppm. Usually when a phosphorus atom is protonated to form a phosphonium ion the signal in the 31P NMR spectrum shifts downfield [14–17]. However, the shift observed in these reactions was in the opposite direction, which suggests that the proton was not bound to the phosphorus but rather to the nitrogen atoms. Infrared spectroscopy (IR) was used to confirm that the protons were bound to the nitrogens in these reactions. In the IR spectra, recorded of the products of the reactions of one and four equivalents of H2C (SO2CF3)2 with 1, N–H stretches were observed at 3081 and 3100 cm1 and the m(C@N) stretching vibration had shifted to 1607 cm1 compared to 1580 cm1 in the free ligand. A shift of 10–30 cm1 of the m(C@N) stretching vibration to higher

2.2. Platinum(II) and palladium(II) complexes The reaction of ligand 1 with dimethyl(hexa-1,5-diene) platinum at 50 °C for 16 h led to the formation of the [PtMe (PCP)] complex 3 (Scheme 2). The 31P NMR spectrum of complex 3 consisted of a singlet at 38.3 ppm with platinum-195 satellites, 1 JPtP = 2969 Hz. In the 1H NMR spectrum of 3 the signal for the methylene protons appeared as a virtual triplet at 4.46 ppm (2JPH + 4JPH = 5.9 Hz). This triplet is characteristic of complexes of this type with strong phosphorus–phosphorus coupling between trans phosphorus donor atoms that are magnetically equivalent [24]. This was consistent with the NMR data of the analogous diphenylphosphino pincer complex [25]. The signal for the methyl ligand in the 1H NMR spectrum appeared as a singlet at 0.48 ppm with 195Pt satellites, 2JPtH = 75 Hz. When ligand 1 was reacted with chloromethyl(hexa-1,5-diene)platinum under the same conditions as above, the [PtCl(PCP)] complex 4 was formed (Scheme 2). The signal in the 31P NMR spectrum of 4 was very similar to that of 3, appearing as a singlet at 38.0 ppm with 1JPtP = 2916 Hz. As the pincer core is the same for complexes 3 and 4 the difference in the 1JPtP values is due to the difference in cis influence of the methyl and chloride ligands. As

Se P(2-Py)2

P N

P(2-Py)2 (iv)

(i),(ii),(iii)

3 P(2-Py)2

P(2-Py)2

1

Se 2

Scheme 1. Synthesis of ligand 1 and phosphine selenide 2. Reagents and conditions: (i) Li, THF, 78 °C ? rt, 40 min; (ii) NH4Cl, 78 °C ? rt, 30 min; (iii) dibromo-m-xylene, THF, 78 °C ? rt, 30 min; (iv) excess Se, CHCl3, reflux, overnight.

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Me

PPy2

Py2P

Me

Me Pt

Pt PPy2

Py2P

Me (ii)

(i) PPy2

PPy2 5 Pt

PPy2 1

X

+ CH4

PPy2

(iii)

(iv)

Cl

PPy2

Cl

Pt

3 X = Me 4 X = Cl

PPy2 Pt

Me

Me

Py2P

Py2P

6 Scheme 2. Synthesis of platinum pincer complexes. Reagents and conditions: (i) Dimethyl(hexa-1,5-diene)platinum, CHCl3; (ii) 50 °C, 16 h; (iii) chloromethyl(hexa-1,5diene)platinum, CHCl3; (iv) 50 °C, 16 h.

methyl ligands have a lower cis influence than chloride ligands the 1 JPtP value for complex 3 is higher than that of complex 4 [26,27]. The 1 H NMR spectrum of complex 4 also contained a virtual triplet at 4.47 ppm, 2JPH + 4JPH = 5.8 Hz, due to the methylene protons. The [PtCl(PCP)] complex 4 was reacted with one equivalent of the sodium salt NaCH(SO2CF3)2. It was predicted that when the chloride ligand was abstracted the pyridyl nitrogen atoms may coordinate to the platinum centre. However, this was not the case. Instead, an intractable mixture of products was formed. Often pyridyl substituents are included in the design of phosphine ligands to impart water-solubility to the ligands and thus the complexes formed with those ligands [7]. While ligand 1 was insoluble in water, it was found that protonation of 1 rendered it soluble in water. Thus the protonation of the [PtCl(PCP)] complex 4 was investigated as a means to impart water-solubility to complex 4. However, reaction of complex 4 with an excess of either H2C(SO2CF3)2 or HCl did not result in a water-soluble product. When the reactions between ligand 1 and the platinum precursors were carried out on an NMR scale, intermediates were observed in the 31P and 1H NMR spectra of the reaction mixtures. The signals for these intermediates in the 31P NMR spectra appeared at 31.0 and 29.5 ppm with 1JPtP values of 1922 and 3070 Hz for the dimethyl and chloromethyl reactions respectively. As the signals for these complexes were quite broad it was not possible to fully characterise these complexes by NMR spectroscopy. The IR spectra of these complexes showed a C@N stretch at 1573 cm1 indicating that the pyridyl nitrogens were not coordinated to the platinum. Based on 31P NMR and IR data it is proposed that these complexes were the cis-[PtMe2(l-PP)]2 complex 5 and the trans-[PtClMe(l-PP)]2 complex 6 (PP = 1) (Scheme 2). There are many examples in the literature of dimeric complexes similar to 5 and 6 forming when pincer ligands are reacted with platinum precursor complexes, several of which have the crystal structures

reported [28–30]. The mechanism through which these dimers could react to form pincer complexes has been investigated [31,32]. Whether cis or trans dimers are formed in these reactions depends on several factors: the size of the ligand, antisymbiotic effects, electrostatic interactions and solvation [33]. In this system antisymbiotic effects dominate [34]. Thus in these reactions the high trans influence of the methyl ligands meant that they preferred to coordinate trans to the ligand with the lowest trans influence. This led to the formation of the cis-[PtMe2(l-PP)]2 complex 5, where the methyl ligands are trans to the phosphine ligands, and the trans-[PtClMe(l-PP)]2 complex 6, where the methyl ligand preferred to bind trans to the chloride ligand. When ligand 1 is reacted with either dichloro(hexa-1,5-diene)platinum or dichlorobis(diethylsulfide)platinum the dimeric cis[PtCl2(l-PP)]2 complex 7 is formed (Scheme 3). Complex 7 appears as a broad singlet at 20.2 ppm in the 31P NMR spectrum with 1 JPtP = 3902 Hz. However, in contrast to the reactivity observed with the other platinum(II) methyl complexes, prolonged heating of the reaction mixture does not form a pincer complex. This difference in reactivity is ascribed to the C–H activation required to form a pincer complex being more facile from the chlormethyl starting material than the dichloride complexes, as the elimination of methane is more favourable than the elimination of HCl [35]. In contrast, when dichlorobis(acetonitrile)palladium is reacted with one equivalent of ligand 1 at 50 °C for 16 h the [PdCl(PCP)] complex 8 is formed (Scheme 3). The signal in the 31P NMR spectrum appears as a singlet at 39.7 ppm and the 1H NMR data is basically identical to that of the analogous platinum complex 4. While there is evidence for the formation of a dimeric intermediate in the 31P NMR spectrum of the reaction mixture, most likely cis-[PdCl2(l-PP)]2 complex 9, in this case the intermediate was reactive enough to form the pincer complex.

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PPy2

PPy2 (i)

Cl

PPy2

Py2P

Cl

Cl M

M PPy2

Py2P

(ii)

Pd

Cl

+ HCl

Cl

PPy2

PPy2

1

8 7 M = Pt 9 M = Pd

Scheme 3. Reaction of ligand 1 with dichloroplatinum and palladium complexes. Reagents and conditions: (i) Dichloro(hexa-1,5-diene)platinum, dichlorobis(diethylsulfide)platinum or dichlorobis(acetonitrile)palladium, CHCl3; (ii) 50 °C, 16 h.

3. Conclusion The new pyridyldiphosphine ligand 1 was synthesised via an adapted literature method. Reaction of 1 with acid protonated the pyridyl nitrogen atoms before the phosphorus atoms and the resulting protonated ligand was found to be water-soluble. Evaluation of the 1JPSe value of the phosphine selenide 2 indicated that ligand 1 had a similar basicity to PPh3. Reaction of ligand 1 with platinum(II) and palladium(II) complexes initially gave dimeric [MXY(l-PP)]2 complexes (M = Pt, X = Y = Me, Cl, X = Cl, Y = Me; M = Pd, X = Y = Cl). In the platinum(II) complexes the presence of a methyl ligand was found to be essential to the ability of the dimer to react to form the desired pincer complex. Protonation of [PtCl(PCP)] complex 4 did not render the complex soluble in water and abstraction of the chloride ligand did not result in chelation of a pyridyl nitrogen atom. The ligand synthesis method outlined in this report provides a facile and reliable route to a class of pyridylphosphine ligands that has not received a great deal of attention to date. These ligands have several useful properties, including potential hemilabile coordination of the pyridyl nitrogen atoms to metal centres, which could stabilise intermediates in catalytic cycles without significant loss of catalytic activity. The presence of the pyridyl rings on these ligands make the new ligand 1 and complexes derived from this ligand useful potential starting materials in the synthesis of multimetallic complexes. A subsequent report will outline the ability of this ligand to bridge more than one metal centre. 4. Experimental 4.1. General methods All reactions were carried out using degassed solvents and standard Schlenk techniques under an argon atmosphere unless stated otherwise. The starting materials used in this work were obtained from Sigma-Aldrich and Thermo Fisher Scientific, and were used without further purification unless stated otherwise. Tetrahydrofuran (THF) and diethyl ether (Et2O) were distilled under an argon atmosphere from sodium benzophenone ketyl immediately prior to use. All other solvents used were of analytical grade and were degassed and dried over molecular sieves. Tris(2-pyridyl)phosphine [36], [PtClMe(hexa-1,5-diene)] [35], [PtCl2(hexa-1,5-diene)] [37], [PtCl2(SEt2)2] [38], [PtMe2(hexa-1,5-diene)] [39], [PdCl2(NCMe)2] [40], H2C(SO2CF3)2 [41] and NaCH(SO2CF3)2 [42] were synthesised using standard literature methods. Nuclear Magnetic Resonance (NMR) spectra were recorded using a Varian Unity Inova spectrometer operating at 300 and 121 MHz for 1H and 31P spectra respectively, a Varian Unity Inova spectrometer operating at 500, 125 and 95 MHz for 1H, 13C and 77Se spectra respectively and a Varian

DirectDrive spectrometer operating at 600 and 150 for 1H and 13C spectra respectively. All direct-detected 1H and 13C chemical shifts, d (ppm), were referenced to the residual solvent peak of the deuterated solvent [43]. 31P NMR spectra were referenced to H3PO4. 13C and 31P NMR spectra were measured with 1H-decoupling. Infrared spectra were obtained using a Perkin Elmer Spectrum One FT-IR spectrophotometer (resolution 4 cm1) in absorbance mode. All spectral data were obtained at ambient temperature, unless otherwise stated. Electrospray ionisation mass spectroscopy was recorded using an Agilent 6530 Q-TOF mass spectrometer or performed by the Carbohydrate Chemistry Group at Industrial Research Limited, Lower Hutt, using a Waters Q-TOF Premier Tandem mass spectrometer. Elemental analysis was performed at the Campbell Microanalytical Laboratory at Otago University, Dunedin. 4.2. Synthesis of ligand 1 A solution of tris(2-pyridyl)phosphine (1.110 g, 4.18 mmol) in THF (10 mL) was added dropwise to a dispersion of lithium (0.116 g, 16.7 mmol) in THF (5 mL) at 78 °C. The reaction mixture was allowed to warm to room temperature with vigorous stirring for 40 min. The excess lithium was removed by filtration. The resulting filtrate was cooled to 78 °C and ammonium chloride (0.224 g, 4.18 mmol) was added. The reaction mixture was allowed to warm to room temperature and stirred for 30 min. It was then once again cooled to 78 °C and a solution of dibromo-m-xylene (0.501 g, 1.90 mmol) in THF (5 mL) was added dropwise. This was then allowed to warm to room temperature over 30 min. The solvent was removed under reduced pressure to give a yellow oil. Dichloromethane (35 mL) and water (25 mL) were added and stirred for 5 min. The resulting emulsion was allowed to separate and the lower organic layer was isolated. The solvent was removed and the resulting oil was washed with pentane (3  10 mL). The bipyridine was removed via sublimation to give 1 as a pale yellow solid (0.591, 65%). 7 1 3 4

P

2

8

6

N

9 10

2

5

P(2-Py)2 1

H NMR (500 MHz, CDCl3): d/ppm 8.70 (d, J = 5.0 Hz, 4H, H10), 7.52 (t, J = 7.5 Hz, 4H, H8), 7.34 (dd, J = 7.5, 4.5 Hz, 4H, H7), 7.16 (tm, J = 6.0 Hz, 4H, H9), 6.99 (s, 1H, H5), 6.94 (d, 3JHH = 7.5 Hz, 1H, H4), 6.88 (d, 3JHH = 7.5 Hz, 2H, H3), 3.66 (s, 4H, H1). 13C NMR (125 MHz, CDCl3): d/ppm 162.79 (d, 1JPC = 5.8 Hz, C6), 150.46 (d, 3JPC = 8.2 Hz, C10), 137.85 (d, 2JPC = 7.2 Hz, C2), 135.54 (d, 3JPC = 6.2 Hz, C8), 130.64 (t, 3JPC = 6.8 Hz, C5), 129.40 (d,

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2

JPC = 28 Hz, C7), 128.26 (s, C4), 127.04 (dd, JPC = 6.7, 2.4 Hz, C3), 122.85 (s, C9), 33.33 (d, 1JPC = 13 Hz, C1). 31P NMR (121 MHz, CDCl3): d/ppm 3.84 (s). IR (film from CH2Cl2): mmax/cm1 3041 (sp2 C–H stretch), 2954 (sp3 C–H stretch), 1573, 1559 (C@N stretch). HRMS calc. for C28H25N4O2P2 [M+2O+H]+: m/z = 511.1453. Found: 511.1454. HRMS calc. for C28H24N4NaO2P2 [M+2O+Na]+: m/z = 533.1272. Found: 533.1271. 4.3. Synthesis of phosphine selenide 2

Excess selenium (182 mg, 2.3 mmol) was added to a solution of the phosphine 1 (110 mg, 0.23 mmol) in chloroform (10 mL). The reaction mixture was refluxed overnight. The reaction mixture was filtered, to remove the unreacted selenium, and the solvent removed under vacuum. This gave the phosphine selenide 2 as a brown solid (quantitative conversion). 1 H NMR (500 MHz, CDCl3): d/ppm 8.75 (d, J = 4.8 Hz, 4H, H10), 8.11 (t, J = 7.2 Hz, 4H, H7), 7.71 (m, 4H, H8), 7.31 (m, 4H, H9), 6.92 (br s, 1H, H5), 6.88 (s, 3H, H3+4), 4.26 (d, 2JPH = 15.3 Hz, 4H, H1). 13C NMR (125 MHz, CDCl3): d/ppm 154.41 (d, 1JPC = 97 Hz, C6), 149.66 (d, 3JPC = 18 Hz, C10), 136.49 (d, 3JPC = 11 Hz, C8), 133.20 (t, 3JPC = 5.8 Hz, C5), 130.86 (vt, 2JPC + 4JPC = 5.0 Hz, C2), 129.51 (vt, 3JPC + 5JPC = 4.6 Hz, C3), 129.30 (d, 2JPC = 26 Hz, C7), 127.45 (t, 4JPC = 3.6 Hz, C4), 125.10 (s, C9), 36.23 (d, 1JPC = 46 Hz, C1). 31P NMR (121 MHz, CDCl3): d/ppm 34.92 (s, 1JPSe = 742, 6 JPP = 3.6 Hz). 77Se NMR (95 MHz, CDCl3): d/ppm 363.52 (d, 1JPSe = 741 Hz). HRMS calc. for C28H25N4P2Se2 [M+H]+: m/z = 638.9885. Found: 638.9884. HRMS calc. for C28H24N4NaP2Se2 [M+Na]+: m/z = 660.9704. Found: 660.9699. 4.4. Reaction with HCl to acheive water-solubility Degassed water (2 mL) was added to 1 (50 mg, 0.10 mmol). To this concentrated hydrochloric acid was added dropwise until all of the solid had dissolved. The water and acid were removed under reduced pressure to give a brown oil which was dissolved in D2O to allow characterisation by NMR methods. 1 H NMR (500 MHz, D2O): d/ppm 8.67 (d, J = 5.6 Hz, 4H, H10), 8.49 (t, J = 7.7 Hz, 4H, H8), 8.12 (t, J = 7.3 Hz, 4H, H7), 7.99 (m, 4H, H9), 6.95 (dd, J = 7.6, 3.3 Hz, 2H, H3), 6.77 (d, J = 7.6 Hz, 1H, H4), 6.72 (s, 1H, H5), 3.81 (s, 4H, H1). 13C NMR (125 MHz, D2O): d/ppm 151.75 (d, 1JPC = 32 Hz, C6), 146.68 (s, C8), 144.03 (s, C10), 134.52 (d, 2 JPC = 12 Hz, C2), 132.72 (d, 2JPC = 5.8 Hz, C7), 129.97 (s, C3), 129.64 (d, 3JPC = 6.6 Hz, C5), 128.35 (br s, C9), 128.30 (m, C4), 31.70 (d, 1 JPC = 15 Hz, C1). 31P NMR (121 MHz, D2O): d/ppm 16.08 (s). 4.5. Synthesis of [PtMe(PCP)] (3) Dimethyl(hexa-1,5-diene)platinum (114 mg, 0.37 mmol) was added to a solution of ligand 1 (177 mg, 0.37 mmol) in chloroform (5 mL, degassed). The reaction mixture was heated to 50 °C over 16 h, after which the reaction mixture was filtered and the solid washed with CH2Cl2 (2  5 mL). The filtrate was isolated and the solvent removed to give 3 as a brown oil (232 mg, 92%). Inwards diffusion of hexane into CH2Cl2 gave crystals that were unsuitable for crystallography. 7 1 3 4

2 5

P

8 9

6

N Pt Me

10

2

PPy2 1

H NMR (500 MHz, CDCl3): d/ppm 8.72 (d, J = 4.5 Hz, 4H, H10), 8.53 (m, 4H, H7), 7.72 (tq, J = 7.8, 2.0 Hz, 4H, H8), 7.28 (m, 4H,

H9), 7.15 (d, 3JHH = 7.5 Hz, 2H, H3), 7.03 (t, 3JHH = 7.5 Hz, 1H, H4), 4.46 (vt, 2JPH + 4JPH = 5.9 Hz, 4H, H1), 0.48 (s, 2JPtH = 75 Hz, 3H, Pt–Me). 13C NMR (125 MHz, CDCl3): d/ppm 154.93 (vt, 1 JPC + 3JPC = 37 Hz, C6), 150.61 (vt, 3JPC + 5JPC = 7.2 Hz, C10), 147.99 (vt, 2JPC + 4JPC = 11 Hz, C2), 146.19 (s, C5), 136.23 (vt, 3 JPC + 5JPC = 4.8 Hz, C8), 131.59 (vt, 2JPC + 4JPC = 15 Hz, C7), 125.62 (s, C4), 124.79 (s, C9), 123.35 (vt, 3JPC + 5JPC = 11 Hz, C3), 37.44 (vt, 1 JPC + 3JPC = 21 Hz, C1), 4.72 (s, 1JPtC = 690 Hz, Pt–Me). 31P NMR (121 MHz, CDCl3): d/ppm 38.08 (s, 1JPtP = 2913 Hz). IR (film from CH2Cl2): mmax/cm1 1573, 1563 (C@N stretch). HRMS calc. for C28H23N4P2Pt [M–CH3]+: m/z = 672.1043. Found: 672.1048. HRMS calc. for C30H26N5P2Pt [M–CH3+CH3CN]+: m/z = 713.1308. Found: 713.1304. Elemental Analysis: C, 50.9; H, 3.9; N, 8.4% (C29H26N4P2Pt requires C, 50.7; H, 3.8; N, 8.2%). 4.6. Synthesis of [PtCl(PCP)] (4) A mixture of chloromethyl(hexa-1,5-diene)platinum (70 mg, 0.21 mmol) and ligand 1 (102 mg, 0.21 mmol) in chloroform (5 mL, degassed) was heated to 50 °C with stirring for 16 h. The reaction mixture was filtered and the brown solid washed with CH2Cl2 (15 mL). The filtrate was isolated and the solvent removed under vacuum. The resulting solid was washed with hexane (2  5 mL) and then dried under vacuum to give 4 as a yellow solid (126 mg, 84%). 1 H NMR (500 MHz, CDCl3): d/ppm 8.72 (d, J = 4.8 Hz, 4H, H10), 8.54 (m, 4H, H7), 7.72 (td, J = 7.7, 1.7 Hz, 4H, H8), 7.28 (m, 4H, H9), 7.15 (d, 3JHH = 7.4 Hz, 2H, H3), 7.03 (t, 3JHH = 7.4 Hz, 1H, H4), 4.47 (vt, 2JPH + 4JPH = 5.8 Hz, 4H, H1). 13C NMR (125 MHz, CDCl3): d/ppm 154.98 (vt, 1JPC + 3JPC = 37 Hz, C6), 150.56 (vt, 3 JPC + 5JPC = 6.7 Hz, C10), 147.93 (vt, 2JPC + 4JPC = 11 Hz, C2), 146.16 (s, C5), 136.37 (m, C8), 131.61 (vt, 2JPC + 4JPC = 14 Hz, C7), 125.68 (br s, C4), 124.84 (br s, C9), 123.42 (vt, 3JPC + 5JPC = 11 Hz, C3), 37.42 (vt, 1JPC + 3JPC = 20 Hz, C1). 31P NMR (121 MHz, CDCl3): d/ppm 38.05 (s, 1JPtP = 2916 Hz). HRMS calc. for C28H24ClN4P2Pt [M+H]+: m/z = 709.0805. Found: 709.0799. HRMS calc. for C28H23ClN4NaP2Pt [M+Na]+: m/z = 731.0625. Found: 731.0614. Elemental Analysis: C, 47.4; H, 3.4; N, 7.8% (C28H23ClN4P2Pt requires C, 47.5; H, 3.3; N, 7.9%). 4.7. Synthesis of [PdCl(PCP)] (8) Dichlorobis(acetonitrile)palladium (104 mg, 0.40 mmol) was added to a solution of 1 (191 mg, 0.40 mmol) in chloroform (5 mL, degassed). The reaction mixture was heated to 50 °C over 16 h. After which the reaction mixture was allowed to cool to room temperature and then the solution was filtered and the solid washed with CH2Cl2 (2  5 mL). The filtrate was isolated and the solvent removed to give 8 as an orange oil (141 mg, 57%). 1 H NMR (500 MHz, CDCl3): d/ppm 8.71 (d, J = 4.1 Hz, 4H, H10), 8.50 (m, 4H, H7), 7.71 (t, J = 7.3 Hz, 4H, H8), 7.28 (m, 4H, H9), 7.16 (d, 3JHH = 7.5 Hz, 2H, H3), 7.03 (t, 3JHH = 7.5 Hz, 1H, H4), 4.53 (vt, 2JPH + 4JPH = 5.8 Hz, 4H, H1). 13C NMR (125 MHz, CDCl3): d/ppm 155.17 (vt, 1JPC + 3JPC = 31 Hz, C6), 150.61 (vt, 3JPC + 5JPC = 6.7 Hz, C10), 149.33 (vt, 2JPC + 4JPC = 13 Hz, C2), 136.37 (vt, 3 JPC + 5JPC = 4.8 Hz, C8), 131.93 (vt, 2JPC + 4JPC = 15 Hz, C7), 126.31 (s, C4), 124.71 (s, C9), 124.00 (vt, 3JPC + 5JPC = 13 Hz, C3), 37.41 (vt, 1 JPC + 3JPC = 16 Hz, C1). 31P NMR (121 MHz, CDCl3): d/ppm 39.70 (s). HRMS calc. for C28H23N4P2Pd [M–Cl]+: m/z = 579.0454. Found: 579.0453. Elemental Analysis: C, 54.1; H, 3.5; N, 8.8% (C28H23ClN4P2Pd requires C, 54.3; H, 3.7; N, 9.0%). Acknowledgments T.F.V. would like to acknowledge the award of a Curtis Gordon Research Scholarship and a Top Achiever Doctoral Scholarship.

T.F. Vaughan, J.L. Spencer / Inorganica Chimica Acta 442 (2016) 24–29

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