Synthesis and Reactions of the Homoleptic Chromium(II) Bis-amide

Article pubs.acs.org/Organometallics

Synthesis and Reactions of the Homoleptic Chromium(II) Bis-amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr with Relevance to a Selective Catalytic Ethene Trimerization System to 1-Hexene Bernd H. Müller,† Normen Peulecke,† Anke Spannenberg,† Uwe Rosenthal,*,† Mohammed H. Al-Hazmi,‡ Roland Schmidt,‡ Anina Wöhl,§ and Wolfgang Müller*,§ †

Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert-Einstein-Straße 29 A, D-18059 Rostock, Germany Saudi Basic Industries Corporation, P.O. Box 42503, Riyadh 11551, Saudi Arabia § Linde Engineering Division, Linde AG, Dr.-Carl-von-Linde-Straße 6-14, D-82049 Pullach, Germany ‡

S Supporting Information *

ABSTRACT: New organometallic compounds were obtained on the basis of the aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)N(iPr)-H (1), which is relevant for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)3, and Et3Al. This catalytic system produces 1-hexene in more than 90% yield and high purity. Here, we report a more efficient, high-yield synthesis of the recently published homoleptic magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) by reaction of n-butylethylmagnesium and 1 in Et2O. Compound 2 can be used as a reagent to transfer the amide moiety [Ph2PN(iPr)P(Ph)N(iPr)−] effectively to a chromium or aluminum center. In situ synthesis of the magnesium amide 2 followed by addition of CrCl2(THF)2 results in the formation of the homoleptic chromium(II)bis-amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) by transmetalation. The structure of chromium compound 3 is in some aspects similar to that of the corresponding homoleptic magnesium complex 2. Reacting 2 with ethylaluminum dichloride results in the formation of the respective aluminum amide [Ph2PN(iPr)P(Ph)N(iPr)−][AlEtCl] (4), for which the direct synthesis of 1 with diethylaluminum chloride was unsuccessful. Additionally, we investigated compound 3 with potentially interesting activators such as Et2Zn, Et3Al, and Et3B to obtain more information about the catalytic properties of these systems.

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INTRODUCTION During the past few years, several research groups developed selective catalytic routes to 1-hexene and 1-octene focusing on homogeneous chromium-based catalyst systems.1−5 P and N donor ligands yielded the most promising results.1−5 Our contribution was a new PNPNH donor ligand system, used as new, selective homogeneous chromium-based trimerization catalysts of ethene to 1-hexene. For this system, detailed kinetic experiments and modeling were very recently published.6−15 Additionally, the ligand's coordination behavior and chemistry with relevance for the activation and deactivation of the catalyst were reported elsewere.7 The synthesis of the PNPNH ligand type was described and can be carried out in two different ways (Scheme 1, a and b). The Ph2PN(iPr)P(Ph)Cl fragment of synthesis b (Scheme 1) was useful to immobilize the ligand.11 Metalation of 1 by nBuLi in the presence of tetramethylethylenediamine (tmeda) yields the mononuclear compound [Ph2PN(iPr)P(Ph)N(iPr)−][Li(tmeda)]. Without tmeda, the dinuclear species [Ph2N(iPr)P(Ph)N(iPr)−Li]2 was formed.8 Reaction of 1 with Grignard reagent iPrMgCl gave only very poor yields of the magnesium diamide [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2). Consequently, only lithium compounds were used as starting materials to obtain chromium amides. Reaction of Li[CpCrCl3] with [Ph2N(iPr)P(Ph)N(iPr)−Li]2 leads to © XXXX American Chemical Society

Scheme 1. Different Methods (a and b) for Synthesizing Ph2PN(iPr)P(Ph)N(iPr)H (1)6

CpCrCl[−N(iPr)P(Ph)N(iPr)PPh2]; reaction with Na[Et4Al], to the ethyl compound CpCrEt[−N(iPr)P(Ph)N(iPr)PPh2]. Additionally, reaction of CrCl3[Ph2PN(iPr)P(Ph)N(iPr)− H](THF) with Et3Al formed EtCrCl2(THF)3 directly. The organometallic chemistry of 1 hints at potential species and activation mechanisms, which have to be considered for a better understanding of the catalytic system. Here, we describe more characteristics of the PNPNH compound in organometallic reactions. Metalation and transReceived: March 6, 2012

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dx.doi.org/10.1021/om300186a | Organometallics XXXX, XXX, XXX−XXX

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metalation model reactions were studied that could occur under catalytic conditions to better understand the behavior and reactivity of this type of aminophosphorus ligands. This knowledge is of great importance to understand the outstanding catalytic selectivity to 1-hexene exhibited by this new ligand class.

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RESULTS AND DISCUSSION Stoichiometric Reactions. The above-mentioned synthesis of [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) via the addition of isobutylmagnesium chloride to 1 yielded only a few crystals that could be isolated from Et2O (Scheme 2).8 Here we Figure 1. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) with thermal ellipsoids set at 50% probability. All hydrogen atoms have been omitted for clarity. Important bond lengths [Å] and angles [deg]: Cr−N1 2.0063(19), Cr−N3 2.0182(19), Cr−P2 2.5208(7), Cr−P4 2.4955(7), N1−P1 1.657(2), N2−P1 1.765(2), N2−P2 1.679(2), N3−P3 1.655(2), N4−P3 1.7586(19), N4−P4 1.679(2), N1−P1−N2 104.04(10), N3−P3−N4 103.42(9), P2−N2−P1 116.40(11), P4− N4−P3 115.14(11), N1−Cr−P2 82.61(6), N3−Cr−P4 81.95(6), N1−Cr−N3 96.79(8).

Scheme 2. Alternative Approaches for the Synthesis of [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2)

Table 1. Summary of Important Bond Lengths and Angles complex

describe the high-yield synthesis of this compound from nbutylethylmagnesium and the ligand in Et2O (Scheme 2). The reaction of 1 with n-butylethylmagnesium with the in situ formed magnesium complex 2 followed by addition of CrCl2(THF)2 results in the formation of the homoleptic chromium(II) amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) by transmetalation (Scheme 3). Scheme 3. Transmetalation of [Ph2PN(iPr)P(Ph)N(iPr) −]2Mg (2) to [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3)

The molecular structure of the chromium amide 3 was investigated by X-ray crystal structure analysis. It is in some aspects similar to that of the magnesium amide 2, but having a distorted square-planar coordination geometry with a cisorientation of the amide function. Table 1 gives an overview of several similar compounds. A comparison of [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) with the new chromium compound [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) shows similarities but also significant differences (Figure 2). Instead of the square-planar coordination geometry in 3 compound 2 exhibits a distorted tetrahedral coordination. The smallest angles found are PMgN and P′MgN′, at 79.3° and 79.5°, respectively. The angle between the planes PMgN and P′MgN′ is 71.83(7)°. Comparable structures are well known, e.g., for Mg{N[Si(CH3)3](CH2)3N(CH3)2}2.16 Complex 3 has a distorted square-planar geometry (sum of angles at chromium is 361°). The angles PCrN and P′CrN′ are

metal

distance M− N− (Å)

distance M− Pterminal (Å)

angle N−− M−Pterminal (deg)

Ph2PN(iPr)P(Ph) N(iPr)−] [Li(tmeda)] [Ph2N(iPr)P(Ph) N(iPr)-Li]2 [Ph2PN(iPr)P(Ph) N(iPr)−]2Mg (2)

Li

1.973(3)

2.774(3)

84.95(10)

Li

2.049(2)

2.587(2)

88.66(8)

Mg

1.998(2)

2.7470(11)

79.35(7)

CpCrCl[−N(iPr) P(Ph)N(iPr)PPh2], CpCrEt[−N(iPr) P(Ph)N(iPr)PPh2]. CrCl3[Ph2PN(iPr) P(Ph)N(iPr)−H] (THF) [Ph2PN(iPr)P(Ph) N(iPr)−]2Cr (3)

Cr

2.005(2) 1.9650(13)

2.7126(11) 2.5081(5)

79.50(7) 82.68(4)

Cr

2.002(2)

2.4822(7)

81.42(6)

Cr Cr

2.5161(14) 2.0063(19)

2.4955(7)

81.95(6)

2.0182(19)

2.5208(7)

82.61(6)

Figure 2. Selected angles for the molecular structures of [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) and [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3).

82.6° and 81.9°, respectively. The angle between the planes PCrN and P′CrN′ is 13.44(7)°. The planar complex [Cr(NPh2)2(py)2] shows a trans-coordination, to be expected for 3.17 Another comparable complex, [Ni(Ph2PN(PPh2)NPh]2, exhibits a square-planar cis-coordination.18 Discussions about a B


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conceivable trans-effect during complexation would result in an energetically unfavored coordination, as in the case of 3. [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) can be used as a transfer reagent for [Ph2PN(iPr)P(Ph)N(iPr)−]− to an aluminum center by reaction with ethylaluminum dichloride (Scheme 4). Interestingly, the formation of the aluminum Scheme 4. Formation of [Ph2PN(iPr)P(Ph)N(iPr) −][AlEtCl] (4) by Addition of EtAlCl2 to [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2)

Figure 3. Molecular structure of [(μ(Cr,Cr)-Cl)-(μ(Cr,Al)-Cl)Cr{κ2P,P-P(Ph2)N(iPr)P(Ph)N(iPr)Al(EtCl)}]2 (5) with thermal ellipsoids set at 50% probability. All hydrogen atoms have been omitted for clarity. Important bond lengths [Å] and angles [deg]: Cr−P1 2.4271(6), Cr−P2 2.4489(7), Cr−Cl1 2.5810(6), Cr−Cl2 2.3609(6), Al−N1 1.8771(19), Al−Cl1 2.2305(8), Al−Cl3 2.1545(9), N1−P1 1.6366(18), P1−N2 1.7140(18), N2−P2 1.7000(18), P1−Cr−P2 67.25(2), P1−N2−P2 104.55(10), N1−P1− N2 114.42(9), Cl1−Al−N1 106.85(6), Al−N1−P1 117.77(10), Cl1− Cr−Cl2 96.75(2), Cl2−Cr−Cl2′ 92.64(2).

amide [Ph2PN(iPr)P(Ph)N(iPr)−][AlEtCl] (4) was not possible by direct synthesis of Ph2PN(iPr)P(Ph)N(iPr)H (1) with diethylaluminum chloride. Similar compounds were obtained before when reacting Ph2PN(iPr)P(Ph)N(iPr)H (1) with trimethyl- and triethylaluminum.12 Because for one of these compounds, namely, [Ph2 PN( iPr)P(Ph)N(iPr)−][AlMe2], a mononuclear molecular structure was established by X-ray crystal structure analysis, it is reasonable to assume 4 is a monomer, too.12 To study the influence of other cocatalysts, the interaction of 3 with EtAlCl2 was investigated. As a result, the dinuclear Cr− Al compound 5 was obtained (Scheme 5, Figure 3).

Scheme 6. Different Approaches to the Synthesis of Dinuclear Cr−Al Compounds

Scheme 5. Formation of the Dinuclear Cr−Al Compound 5

We very recently described similar complexes (Scheme 6).15 By the reaction of 1 with Et2Zn in Et2O or toluene [Ph2PN(iPr)P(Ph)N(iPr)−][ZnEt] (6) is formed. (Scheme 7). Analogously as discussed for the aluminum amide [Ph2PN(iPr)P(Ph)N(iPr)−][AlEtCl] (4), a mononuclear molecular structure is assumed for the zinc amide [Ph2PN(iPr)P(Ph)N(iPr)−][ZnEt] (6). The mass spectrum shows a mole peak m/e = 502. The reaction of 1 with Et3B led to a mixture of different products, which could not yet be identified. Catalytic Reactions. Without a cocatalyst complex [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) is not catalytically active for the oligomerization of ethene (83 mg of 3 in 100 mL of toluene; 30 bar, 50−100 °C: 0 kg/(gCr·h). Addition of triethylaluminum as cocatalyst and tetraphenylphosphonum chloride as modifier yields an effective ethylene trimerization catalyst (26 mg of 3; 56 mg of [PPh4]Cl, 0.7 mL (1.9 M) of AlEt3 in 100 mL of toluene; 30 bar, 50 °C: 12.5 kg/(gCr·h)).

Compared with the catalytic trimerization standard results for the trimerization (11 mg Cr(acac)3; 15 mg 1; 56 mg Scheme 7. Synthesis of the Zn Compound [Ph2PN(iPr)P(Ph)N(iPr)−][ZnEt] (6)

C


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tetraphenylphosphonium chloride as modifier yields an effective ethylene trimerization catalyst. Additionally, we investigated other potentially interesting activators such as Et2Zn, Et3Al, and Et3B. These did not exhibit any activation of the chromium compounds for the selective ethene oligomerization. This result is particularly important with respect to Et3Al and shows that “chloride” is an essential part of the catalytic system.

[PPh4]Cl, 0.5 mL (1.9 M) AlEt3 in 100 mL of toluene; 30 bar, 50 °C: 50 kg/(gCr·h) ZnEt2 as cocatalyst (11 mg of Cr(acac)3, 15 mg of 1, 56 mg [PPh4]Cl, 1.0 mL (1.5 M) of ZnEt2 in 100 mL of toluene; 30 bar, 50−100 °C: 0 kg/(gCr·h) did not show any activity as in the case of BEt3 (11 mg of Cr(acac)3, 15 mg of 1, 56 mg of [PPh4]Cl, 1.0 mL (1.0 M) of BEt3 in 100 mL of toluene; 30 bar, 50−100 °C: 0 kg/(gCr·h)). Only if in addition to BEt3 also AlEt3 was used (11 mg Cr(acac)3, 15 mg of 1, 56 mg of [PPh4]Cl, 1.0 mL (1.0 M) of BEt3, 0.5 mL (1.9 M) of AlEt3 in 100 mL of toluene; 30 bar, 50 °C: 25 kg/(gCr·h)) was such an activity observed, which is lower compared to the standard system.

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Table 2. Results of the Oligomerization of Ethene complex as precatalyst [Ph2PN(iPr)P(Ph) N(iPr)−]2Cr (3) [Ph2PN(iPr)P(Ph) N(iPr)−]2Cr (3) Cr(acac)3 Cr(acac)3 Cr(acac)3 Cr(acac)3

ligand

activity kg/ (gCr·h)

cocatalyst

modifier

Ph2PN(iPr)P(Ph) N(iPr)−H (1) no additional

no

no

Et3Al

12.5

Ph2PN(iPr)P(Ph) N(iPr)−H (1) Ph2PN(iPr)P(Ph) N(iPr)−H (1) Ph2PN(iPr)P(Ph) N(iPr)−H (1) Ph2PN(iPr)P(Ph) N(iPr)−H (1)

Et3Al

BEt3

[PPh4] Cl [PPh4] Cl [PPh4] Cl no

BEt3/ Et3Al

[PPh4] Cl

25

ZnEt2

EXPERIMENTAL SECTION

General Procedures. All operations were carried out under argon with standard Schlenk techniques or in a glovebox. Prior to use, nonhalogenated solvents (including deuterated solvents benzene-d6 and THF-d8) were freshly distilled from sodium tetraethylaluminate and stored under argon. All other chemical reagents and solvents were obtained from commercial sources and used without further purification. The following spectrometers were used. MS: Finnigan MAT 95-XP from Thermo-Electron. NMR spectra: Bruker AV 300, AV 400, and AMX 400. Chemical shifts (1H, 13C) are given relative to SiMe4 and are referenced to signals of the used solvent: benzene-d6 (δH = 7.16, δC = 128.0). Chemical shifts for 31P are given relative to 85% H3PO4. The spectra were assigned with the help of DEPT. Melting points: sealed capillaries, Büchi 535 apparatus. Elemental analyses: Leco CHNS-932 elemental analyzer. Compound 1 was prepared according to a published literature procedure.5 Oligomerization experiments were conducted as published before.3,4 Analytical details of compound 2 were published before.15 Preparation of [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2). (Ph2PN(iPr)P(Ph)(iPr)−H (1) (4.00 g, 9.79 mmol) was dissolved in 50 mL of diethyl ether. At room temperature a solution of n-butylethylmagnesium (5.5 mL, 0.9 M nBuEtMg in heptane, 4.95 mmol) was added to the solution. The solution was stirred for an additional 2 h. After cooling to −30 °C colorless crystals with satisfying elementary analysis were obtained. Yield: 3.70 g (90%). Molecular weight: 839.20 g/mol [C48H58MgN4P4]. Anal. Calcd: C, 68.70; H, 6.97; N, 6.68. Found: C, 68.93; H, 7.07; N, 6.91. Melting point: 202 °C. 1H NMR (C6D6): δ 6.83−7.66 (m, 30H, aryl-H), 3.54−3.62 (m, 2H, CHCH3), 3.38−3.48 (m, 2H, CHCH3), 1.51 (d, J = 6.5 Hz, 6H, CHCH3), 1.19 (d, J = 6.5 Hz, 6H, CHCH3), 1.15 (d, J = 6.5 Hz, 6H, CHCH3), 1.10 (m, 6H, CHCH3). 13C NMR (C6D6): δ 143.4, 142.0, 134.9, 133.4, 132.5, 131.5, 129.4, 128.6, 128.0, 127.9, 127.1, 125.2 (arom.), 52.0, 51.5 (CHCH3), 29.5, 28.6, 25.9, 24.1 (CHCH3). 31P{H} NMR (C6D6): δ 87.05 (tr, J = 10.4 Hz), 28.32 (tr, J = 10.4 Hz). Preparation of [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3). Ph2PN(iPr)P(Ph)(iPr)−H (1) (4.00 g, 9.79 mmol) was dissolved in 40 mL of toluene. At room temperature a solution of n-butylethylmagnesium (5.5 mL, 0.9 M nBuEtMg in heptane, 4.95 mmol) was added to the solution. The solution was stirred for two more hours and thereafter filtered to a suspension of CrCl2(THF)2 (1.31 g, 4.90 mmol) in 10 mL of toluene. Stirring for two days results in a brownish-red suspension. After filtration and concentrating to 10 mL dark crystals were obtained upon crystallization at −78 °C. Satisfying elementary analysis was obtained by washing the powdered crystals with pentane. Yield: 2.76 g (65%). Molecular weight: 866.89 g/mol [C48H58CrN4P4]. Anal. Calcd: C, 66.50; H, 6.74; Cr, 6.00; N, 6.46; P, 14.29. Found: C, 66.28; H, 6.43; Cr, 6.20; N, 6.31; P, 14.69. Melting point: 161 °C (dec). Preparation of [Ph2PN(iPr)P(Ph)N-(iPr)][AlEtCl] (4). [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg (2) was prepared in situ from Ph2PN(iPr)P(Ph)(iPr)−-H (5.00 g, 12.24 mmol) and n-butylethylmagnesium (7.0 mL, 0.9 M nBuEtMg in heptane, 6.30 mmol) in 50 mL of toluene. After stirring for 2 h a solution of ethylaluminum dichloride in toluene (6.8 mL, 1.8 M AlEtCl2 in toluene, 12.24 mmol) was added. After an additional 2 h the suspension was filtered. The filtrate was condensed to approximately 20 mL. Cooling to −30 °C resulted in a colorless solid. Yield: 3.60 g (59%). Molecular weight: 498.94 g/mol [C26H34AlClN2P2]. Anal. Calcd: C, 62.59; H, 6.87; N, 5.61; Cl, 7.11. Found: C, 62.32; H, 6.76; N, 5.51; Cl, 7.36. Melting point: 121 °C. 1H NMR (C6D6): δ 7.80−7.63 (m, H, aryl-H), 7.56−7.28 (m, 5H, arylH), 7.14−6.90 (m, 9H, aryl-H), 4.23−4.02 (m, 0.7H, CHCH3), 3.91−

0

50 0 0

Complex [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) is inactive without or with addition of triethylaluminum. This indicates that there is a need for chloride to form a catalytically active system.13b The combination of [PPh4]Cl and AlEt3 proves to be the most effective to achieve this goal, while other potential cocatalysts such as ZnEt2 and BEt3 failed. Additionally, dinuclear chromium(II) compounds such as 5 failed. The dinuclear chromium(II) compound with AlEtCl units [μ(Cr,Cr)-Cl-(μ(Cr,Al)-Cl)Cr{κ2P,P-P(Ph2)N(iPr)P(Ph)N(iPr)Al(EtCl)}]2 (5) did not show any activity without a cocatalyst. Similar results were obtained for the corresponding complexes with AlEt2 groups, [(μ(Cr,Cr)-Cl)-(μ(Cr,Al)-Cl)Cr{κ2P,P-P(Ph2)N(R)P(Ph)N(R)(AlEt2)}]2 (Scheme 6, R = i Pr, Cy).15 Obviously there is a need for further reduction of Cr(II) to Cr(I) by the cocatalyst, as discussed by Gambarotta and co-workers.19

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CONCLUSION We presented a more effective, high-yield synthesis of the recently reported homoleptic magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)−]2Mg, which can be used as an effective amide [Ph2PN(iPr)P(Ph)N(iPr)−]− transfer reagent. Using this magnesium compound, synthesis of the homoleptic chromium(II) bis-amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr by transmetalation was realized. Reaction of this magnesium compound with ethylaluminum dichloride results in the formation of the aluminum amide [Ph2PN(iPr)P(Ph)N(iPr) −][AlEtCl]. Reaction of chromium(II) bis-amide [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr with ethylaluminum dichloride results in the formation of a dinuclear Cr−Al compound. Without a cocatalyst, complex [Ph2PN(iPr)P(Ph)N(iPr) −]2Cr (3) is not catalytically active for the oligomerization of ethene, but addition of triethylaluminum as cocatalyst and D


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3.71 (m, 0.3H, CHCH3), 3.64−3.38 (m, H, CHCH3), 1.80−0.84 (m, 15H, CHCH3, CH2CH3), 0.45-(−0.40) (m, 2H, CH2CH3). 13C NMR (C6D6): δ 134.1 (d, J = 15 Hz), 133.7 (d, J = 11 Hz), 133.2 (d, J = 15 Hz), 132.7, 132,6 131.7, 131.4 131.3, 131.1, 131.0, 128.9, 128.9 128.8, 128.6, 128.5 (arom.), 52.4, 51.9 (CHCH3), 28.2 (d, 5 Hz), 26.5 (d, 16 Hz), 25.7 (d, 8 Hz), 23.7 (d, 16 Hz) (CHCH3,), 8.9 (CH2CH3), 2.9 (CH2CH3). 31P{H} NMR (C6D6): isomer A δ 95.3 (d, J = 25.0 Hz), 24.9 (d, J = 25.0 Hz); isomer B δ 87.8 (d, J = 25.0 Hz), 24.9 (d, J = 25.0 Hz). MS (EI, 70 eV): m/z (%) 365 (100) [Ph2P-N(iPr)-P(Ph)NH]+, 308 (42), 149 (84) [N(iPr)-Al(EtCl)]+. Preparation of [(μ(Cr,Cr)-Cl)-(μ(Cr,Al)-Cl)Cr{κ2P,P-P(Ph2)N(iPr)P(Ph)N(iPr)Al(EtCl)}]2 (5). [Ph2PN(iPr)P(Ph)N(iPr)−]2Cr (3) (0.75 g, 0.865 mmol) was dissolved in 10 mL of toluene. A solution of ethylaluminum dichloride in toluene (1.20 mL, 1.8 M AlEtCl2 in toluene, 2.16 mmol) was added. After stirring for 12 h the suspension was filtered. Upon cooling to −78 °C, blue crystals were obtained, which contained one equivalent of toluene. Satisfying elementary analysis was obtained by drying thoroughly under vacuum. Yield: 0.280 g (52%). Molecular weight: 1243.69 g/mol [C52H68Al2Cl6Cr2N4P4]. Anal. Calcd: C, 50.22; H, 5.51; N, 4.50; Cl, 17.10. Found: C, 50.39; H, 5.80; N, 3.84; Cl, 14.0. Melting point: decomposition above 90 °C. Preparation of [Ph2PN(iPr)P(Ph)N(iPr)−][ZnEt] (6). Ph2PN(iPr)P(Ph)(iPr)−H (1) (1.00 g, 2.45 mmol) was dissolved in 40 mL of diethyl ether. At room temperature a solution of diethylzinc (2.0 mL, 1.5 M ZnEt2 in toluene, 3.00 mmol) was added to the solution. After stirring for 12 h the solution was condensed to 20 mL. Cooling to −30 °C resulted in a colorless solid. Yield: 0.800 g (65%). Molecular weight: 501.92 g/mol [C26H34N2P2Zn]. Anal. Calcd: C, 62.22; H, 6.83; N, 5.58; P, 12.34. Found: C, 62.71; H, 6.80; N, 6.03; P, 12.29. Melting point: 95 °C. 1H NMR (C6D6): δ 7.75−7.68 (m, 2H, aryl-H), 7.65−7.56 (m, H, aryl-H), 7.44−7.35 (m, 2H, aryl-H), 7.26−7.16 (m, 2H, aryl-H), 7.10−6.90 (m, 8H, aryl-H), 4.03−3.88 (m, H, CHCH3), 3.66−3.53 (m, H, CHCH3), 1.56−1.39 (m, 9H, CHCH3) 1.38−1.31 (m, 3H, CH2CH3), 1.31−1.27 (m, 3H CHCH3), 0.73−0.62 (m, 2H, CH2CH3). 13C NMR (C6D6): δ 151.3, 134.1, 133.4, 132.2, 130.9, 130.1, 129.5, 128.5, 128.1 (arom.), 51.6, 50.2 (CHCH3), 31.0, 29.9, 26.5, 24.4 (CHCH3), 12.8 (CH2CH3), 2.9 (CH2CH3); 31P{H} NMR (C6D6): δ 87.50 (d, J = 16.5 Hz), 28.00 (d, J = 16.5 Hz). MS (EI, 70 eV): m/z (%) 502 (1.24) [M]+, 407 (39) [M − ZnEt]+, 365 (83) [Ph2P-N(iPr)-P(Ph)-NH]+, 308 (51), 185 [Ph2P]+ (100). Crystallographic Details. Diffraction data were collected on a STOE IPDS diffractometer and on a Bruker APEX II DUO diffractometer, respectively, using graphite-monochromated Mo Kα radiation. The structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares techniques on F2 (SHELXL96).20 DIAMOND was used for graphical representations.21

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technical staff at LIKAT. Marc Gongoll is thanked for excellent and skillful support of the experimental work.

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ASSOCIATED CONTENT

S Supporting Information *

Tables of crystallographic data in cif file format, including bond lengths and angles, of compounds 1, 2, 3, and 5. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Linde Engineering and SABIC for the permission to publish this work. Furthermore, we wish to thank Linde Engineering’s R&D Chemistry Department for their valuable contributions as well as the analytical service and the E


Synthesis and Reactions of the Homoleptic Chromium(II) Bis-amide

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