Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H

Jun 16, 2010 - Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H for Selective Ethene Trimerization to 1-Hexene. Stephan Peitz†, Norm...
2 downloads 11 Views 2MB Size
Download PDF
Organometallics 2010, 29, 5263–5268 DOI: 10.1021/om100371f

5263

Metalation and Transmetalation Studies on Ph2PN(iPr)P(Ph)N(iPr)H for Selective Ethene Trimerization to 1-Hexene^ Stephan Peitz,† Normen Peulecke,† Bhaskar R. Aluri,† Bernd H. M€ uller,† † ,† ‡ Anke Spannenberg, Uwe Rosenthal,* Mohammed H. Al-Hazmi, Fuad M. Mosa,‡ Anina W€ ohl,§ and Wolfgang M€ uller*,§ †

Leibniz-Institut f€ ur Katalyse an der Universit€ at Rostock e.V., Albert-Einstein-Strasse 29 A, D-18059 Rostock, Germany, ‡Saudi Basic Industries Corporation, P.O. Box 42503, Riyadh 11551, Saudi Arabia, and § Linde AG, Linde Engineering Division, Dr.-Carl-von-Linde-Strasse 6-14, D-82049 Pullach, Germany Received April 29, 2010

Different organometallic compounds of the new aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)N(iPr)-H (1) are reported that are relevant model complexes for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)3, and Et3Al that produces 1-hexene in more than 90% yield and high purity. The lithiation of 1 by n-BuLi in the presence of tetramethylethylenediamine (tmeda) yields the mononuclear compound Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Without using tmeda the dinuclear species [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) was obtained. By addition of a Grignard reagent to the ligand solution the bis(aminodiphosphinoamide)magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) could be isolated. Reaction of Li[CpCrCl3] with 3 leads to the formation of the model compound CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5), which can be alkylated with Na[Et4Al] to form the corresponding ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). In THF the formation of EtCrCl2(THF)3 (8) directly from the reaction of CrCl3[Ph2PN(iPr)P(Ph)N(iPr)-H](THF) (6) with Et3Al could be observed. The organometallic chemistry of 1 gives hints on possible species and activation mechanisms in the catalysis, which have to be considered for a better understanding of the catalytic system.

Introduction In the last years industrial as well as academic research groups increased their activities in developing and improving novel on-purpose routes to 1-hexene and 1-octene. The main focus lies on homogeneous chromium-based catalyst systems.1,2 An important ligand class examined is based on mixed P and N donors.1-3 We also work in this field toward developing a new type of P,N donor ligand. First results of the new homogeneous chromium-based trimerization catalyst for ethene to 1-hexene, including detailed kinetic experiments and modeling, were very

recently published.4-6 Additionally, the coordination behavior of this ligand was examined.7 Here we describe the characteristics of this compound in organometallic reactions in more detail. Metalation and transmetalation model reactions that could occur under catalytic conditions were studied to gain a better understanding of the behavior and reactivity of this type of aminophosphorus ligand in the catalytic system. That is of great importance to understand the organometallic background leading to the outstanding catalytic selectivity to 1-hexene exhibited by this new ligand class. Depending on the desired variation of substituents, the synthesis of the ligand type can be carried out in two different ways (Scheme 1, a and b). In addition, the Ph2P N(iPr)P(Ph)Cl fragment of synthesis b (Scheme 1) can be used to immobilize the ligand on amino-functionalized styrene resins. Thus, advantages of homogeneous and heterogeneous catalysis can be merged.8

^ Dedicated to Professor Dietmar Seyferth in honor of his outstanding service as Editor-in-Chief of Organometallics. Part of the Dietmar Seyferth Festschrift. *To whom correspondence should be addressed. E-mail: Uwe. [email protected]; [email protected]. (1) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgen, D. H. J. Organomet. Chem. 2004, 689, 3641–3668. (2) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.; Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto, S.; Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J. Am. Chem. Soc. 2004, 126, 14712–14713. (3) W€ ohl, A.; M€ uller, W.; Peulecke, N.; M€ uller, B. H.; Peitz, S.; Heller, D.; Rosenthal, U. J. Mol. Catal. A 2009, 297, 1–8. (4) Fritz, P. M.; B€ olt, H.; W€ ohl, A.; M€ uller, W.; Winkler, F.; Wellenhofer, A.; Rosenthal, U.; Hapke, M.; Peulecke, N.; M€ uller, B. H.; Al-Hazmi, M. H.; Aliyev, V. O.; Mosa, F. M. (Linde AG/SABIC), WO 2009/006979-A2, 2009. (5) Peitz, S.; Peulecke, N.; Aluri, B. R.; Hansen, S.; M€ uller, B. H.; Spannenberg, A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.; W€ ohl, A.; M€ uller, W. Eur. J. Inorg. Chem. 2010, 1167–1171.

(6) (a) W€ ohl, A.; M€ uller, W.; Peitz, S.; Peulecke, N.; Aluri, B. R.; M€ uller, B. H.; Heller, D.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M. Chem.-Eur. J. 2010, DOI: 10.1002/chem.201000533. (b) M€uller, W.; W€ohl, A.; Peitz, S.; Peulecke, N.; Aluri, B. R.; M€uller, B. H.; Heller, D.; Rosenthal, U.; Al-Hazmi, H. H.; Mosa, F. M. ChemCatChem 2010, accepted. (7) Aluri, B. R.; Peulecke, N.; Peitz, S.; Spannenberg, A.; M€ uller, B. H.; Schulz, S.; Drexler, H.-J.; Heller, D.; Al-Hazmi, M. H.; Mosa, F. M.; A. W€ ohl, W. M€ uller, Rosenthal, U. Dalton Trans. 2010, accepted. (8) Peulecke, N.; M€ uller, B. H.; Peitz, S.; Aluri, B. R.; Rosenthal, U.; W€ ohl, A.; M€ uller, B. H.; Al-Hazmi, M. H.; Mosa, F. M. ChemCatChem 2010, DOI:10.1002/cctc.201000087.

r 2010 American Chemical Society

Published on Web 06/16/2010

pubs.acs.org/Organometallics

5264

Organometallics, Vol. 29, No. 21, 2010

Peitz et al.

Scheme 1. Different methods (a and b) for synthesizing Ph2PN(iPr)P(Ph)N(iPr)H5

Scheme 2. Metalation of Ph2PN(iPr)P(Ph)N(iPr)H (1) with n-BuLi to Give [Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2)

Figure 1. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2) with thermal ellipsoids set at 30% probability. All hydrogen atoms have been omitted for clarity. Important bond lengths [A˚] and angles [deg]: N1-P1 1.6411(13), P1-N2 1.7709(11), N2-P2 1.6850(12), N1-Li1 1.973(3), P2-Li1 2.774(3), N2-P1-N1 107.89(6), P2-N2-P1 117.77(7), P2Li1-N1 84.96(10).

Results and Discussion This work in addition to a short communication5 describes in detail metalation and transmetalation of a novel aminodiphosphinoamine compound. The ligand is characterized by a R2PN(R)P(R)N(R)H backbone (PNPN-H), which, in conjunction with a chromium compound and a suitable aluminum-alkyl activator, leads to a selective trimerization catalyst system that produces comonomer grade 1-hexene in more than 90% yield.4-6 An important aspect, regarding the elucidation of the catalytically active site, deals with the question of what kind of alteration the ligand undergoes in the catalytic system, where, due to its high complexity, several organometallic reactions could occur. It could be shown that, besides the usage of chromium as metal, the PNPN structure and in particular the terminal secondary amine function are crucial for C6 selectivity. Ph2PN(iPr)P(Ph)NR2 (R = Me, Et, iPr) as a ligand without the NH group, in combination with CrCl3(THF)3 and Et3Al, shows nearly no catalytic activity for ethylene trimerization (for R = Me, mainly PE production beside very low 1-hexene production; R = Et, low 1-hexene production of about 1 kg/ (gCr 3 h); R = iPr, no activity at all).5 First hints for a deprotonation of the ligand’s amine function, which is most likely under catalytic conditions,5,6 are given by the lithiation of 1 with n-BuLi in the presence of tetramethylethylenediamine (tmeda), giving [Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2) (Scheme 2), which could be crystallized from a mixture of diethyl ether and hexane. The molecular structure of 2 is depicted in Figure 1. The terminal amide function forms a covalent bond with the metal, and P2 acts as a donor to give a chelating [PNPN]fragment at the lithium ion. Without using tmeda in the reaction mixture the dinuclear species [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) as another Li-amide on the basis of the ligand (Figure 2) was formed. In complex 3 again a covalent amide bond and a coordinative bond of the terminal phosphorus atom to the metal center are observed. Additionally, a dinuclear motif is present and each amide function coordinates not only to one lithium but also to a second ion that already bears a deprotonated

Figure 2. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)-Li]2 (3) with thermal ellipsoids set at 30% probability. All hydrogen atoms have been omitted for clarity. Important bond lengths [A˚] and angles [deg]: N1-P1 1.6612(11), P1-N2 1.7783(10), N2-P2 1.6882(10), N1-Li1 2.049(2), P2-Li1 2.587(2), N1-Li1A 2.023(2), Li1-Li1A 2.362(4), N2-P1-N1 110.00(5), P2-N2-P1 120.32(6), P2-Li1-N1 88.66(8), Li1-N1-Li1A 70.92(11), N1-Li1-N1A 109.08(11).

ligand. Thus, the planar rhombic motif Li-N-Li-N is formed. Interestingly, in complex 3 the P2-Li1 bond length is shortened significantly by ca. 0.2 A˚ compared to 2, whereas the N1-Li1 bond is elongated by approximately 0.06 A˚. A similar dinuclear Li-N-Li-N motif from amidophosphine ligands is already known from Bauer et al., who reported on a comparable deprotonation of aminophosphines with n-BuLi.9 This provided a dimeric Li amidophosphine [tBuP(NH-tBu)N(tBu)-Li]2 that has similar Li-amide bond lengths of 1.997(4), 2.098(4), 2.096(4), and 2.012(4) A˚, respectively, compared to 3 (N1-Li1 2.049(2), N1-Li1A 2.023(2) A˚). The distance between both Li cations is, at Li1-Li1A = 2.362(4) A˚, in 3 a little bit longer than in Bauer’s molecule (Li1-Li2 = 2.296(5) A˚). This is most likely due to steric reasons because in 3 a larger bite angle (88.66(8) versus 78.9(2)) is observed for the angle donor-Li-amide caused by the elongated ligand backbone in 3. (9) Bauer, T.; Schulz, S.; Nieger, M.; Kessler, U. Organometallics 2003, 22, 3134–3142.

Article

Organometallics, Vol. 29, No. 21, 2010

5265

Scheme 4. Schlenk Equilibrium Including [Ph2PN(iPr)P(Ph)N(iPr)]2Mg (4)

Scheme 5. Formation of CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5)5 by Transmetalation of 3 and Formation of CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7) by Subsequent Alkylation

Figure 3. Molecular structure of [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) with thermal ellipsoids set at 30% probability. All hydrogen atoms have been omitted for clarity. Important bond lengths [A˚] and angles [deg]: Mg1-N1 1.998(2), Mg1-N3 2.005(2), Mg1-P2 2.7470(11), Mg1-P4 2.7126(11), N1-P1 1.666(2), N2-P1 1.762(2), N2-P2 1.676(2), N3-P3 1.662(3), N4-P3 1.765(2), N4-P4 1.675(2), N1-P1-N2 105.10(11), N3-P3-N4 106.45(11), P2-N2-P1 117.29(13), P4-N4-P3 115.42(13), N1-Mg1-P2 79.35(7), N3-Mg1-P4 79.50(7), N1-Mg1-N3 141.17(10). i

i

Scheme 3. Metalation of Ph2PN( Pr)P(Ph)N( Pr)-H (1) with i BuMgCl to Give [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4)

Switching to magnesium organic compounds in the reaction with 1, a different coordination sphere around the metal can be achieved. By addition of the Grignard reagent isobutylmagnesium chloride to the ligand solution the magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) could be isolated (Scheme 3). Few crystals of the compound could be grown from Et2O (Figure 3). The molecular structure reveals a Mg center coordinated by two deprotonated ligands in a distorted tetrahedral conformation. 31P NMR investigations of these crystals show two triplets. This could be due to coupling of the phosphorus atoms via the metal, resulting in overlapping doublets of doublets. The most material in this metalation reaction was obtained as a powder. Interestingly, the elemental analysis of this powder shows no exact correlation to the structure found by crystal structure analysis. Instead, we assume also a complex of the kind {[Ph2PN(iPr)P(Ph)N(iPr)-]2Mg 3 MgCl2} being present in the powder. A Schlenk equilibrium, as depicted in Scheme 4, could be the reason for this finding. Therefore, compound 4, as represented by the crystal structure, seems to be one species in a multicomponent mixture. The question arises whether the powder contains species a, b, or a mixture of 4 and MgCl2 (Scheme 4). To date, this could not fully be evaluated. 31P NMR investigation of the powder reveals two different species. One set of signals belongs to compound 4. The other signals represent a different species giving an indication for the mentioned adduct.

Similar to 4 a magnesium complex containing two amidophosphine ligands is known in the literature. Chivers et al.10 published the compound [Mg-{(NtBu)(NSiMe3)P(NHtBu)2}2], which has a quite similar backbone compared to Bauer’s molecule. Chiver’s complex has a Mg-NtBu bond (2.059(2) A˚) that is ca. 0.06 A˚ longer than that of 4, most likely due to steric reasons. The bite angle of [Mg-{(NtBu)(NSiMe3)P(NHtBu)2}2] is, at 72.4(1), smaller compared to 4 (79.35(7) and 79.50(7), respectively), which can be attributed to the elongated ligand backbone in 4. Reactions of the aforementioned isolated and characterized main group element amides 2, 3, and 4 of the PNPN-H ligand with CrCl3(THF)3, the preferred chromium salt in catalysis,5,6 were not successful so far in terms of isolating defined complexes. As can be seen in Scheme 5, if Li[CpCrCl3]11 is used instead of CrCl3(THF)3 in the reaction with [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3), transmetalation by elimination of two equivalents of LiCl leads to the formation of the desired model compound CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5).5 Its molecular structure is depicted in Figure 4 and shows that this chromium complex bears a chromium-amide bond that has almost the same length as the Li-N bond in complex 2. On the other hand, the Cr-Pterminal bond is shortened significantly by 0.26 A˚ compared to the Li-Pterminal bond in 2. To the best of our knowledge only two CpCr-amidophosphine complexes were described before. It was stated12a and proved by X-ray analysis12b respectively that the complexes contain chroma-heterocycles where both N and P are attached to Cr. In comparison to the chromium complex CrCl3[Ph2PN(iPr)P(Ph)N(iPr)-H](THF) (6)5 (Figure 5), which bears the original ligand, the strong amide bond in 5 does not lead to (10) Robertson, S. D.; Chivers, T.; Konu, J. J. Organomet. Chem. 2007, 692, 4327–4336. (11) Arndt, P.; Kurras, E.; Otto, J. Z. Chem. 1983, 443–445. (12) (a) Lindner, E.; Heckmann, M.; Fawzi, R.; Hiller, W. Chem. Ber. 1991, 124, 2171–2179. (b) Fryzuk, M. D.; Leznoff, D. B.; Rettig, S. J. Organometallics 1995, 14, 5193–5202.

5266

Organometallics, Vol. 29, No. 21, 2010

Peitz et al.

Figure 4. Molecular structure of 5 with thermal ellipsoids set at 30% probability.5 All hydrogen atoms have been omitted for clarity. Important bond lengths [A˚] and angles [deg]: N1-P1 1.6671(13), P1-N2 1.7558(14), N2-P2 1.6786(14), N1-Cr1 1.9650(13), P2-Cr1 2.5081(5), N2-P1-N1 102.74(7), P2-N2P1 118.08(7), P2-Cr1-N1 82.68(4).

Figure 6. Molecular structure of 7 with thermal ellipsoids set at 30% probability. The asymmetric unit contains two molecules, only one is depicted. All hydrogen atoms have been omitted for clarity. Important bond lengths [A˚] and angles [deg]: N1-P1 1.663(2), P1N2 1.745(2), N2-P2 1.681(2), N1-Cr1 2.002(2), P2-Cr1 2.4822(7), C30-Cr1 2.109(2), C30-C31 1.500(4), N2-P1-N1 102.71(9), P2-N2-P1 117.60(11), P2-Cr1-N1 81.42(6), N1-Cr1-C30 99.27(9), C30-Cr1-P2 91.20(7), C31-C30-Cr1 118.7(2).

Figure 5. Molecular structure of 6 with thermal ellipsoids set at 30% probability.5 The asymmetric unit contains (besides solvent molecules) two molecules of 6; only one molecule is depicted. Hydrogen atoms, except H1A, have been omitted for clarity. Selected bond lengths [A˚] and angles [deg]: N1-P1 1.643(4), N2-P2 1.694(4), N2-P1 1.717(4), Cr1-P1 2.3974(14), Cr1-P2 2.5158(14), N1-P1-N2 110.8(2), P2-N2-P1 104.9(2), P1Cr1-P2 66.74(4).

Figure 7. Molecular structure of EtCrCl2(THF)3 (8) with thermal ellipsoids set at 30% probability. All hydrogen atoms have been omitted for clarity. Important bond lengths [A˚] and angles [deg]: Cl1-Cr1 2.3281(5), Cl2-Cr1 2.3358(5), C13-Cr1 2.065 (2), C13-C14 1.507(3), Cr1-O3 2.0563(11), Cr1-O1 2.0604(11), Cr1-O2 2.2220(13), O3-Cr1-O1 171.97(5), O3-Cr1-O2 85.42 (5), O1-Cr1-O2 86.63(5), O3-Cr1-Cl1 89.93(3), O1-Cr1Cl1 90.87(3), O2-Cr1-Cl1 88.11(4), O3-Cr1-Cl2 89.65(3), O1-Cr1-Cl2 89.09(3), O2-Cr1-Cl2 88.62(4), Cl1-Cr1-Cl2 176.73(2), O1-Cr1-C13 95.49(6), C14-C13-Cr1 117.13(14).

a different terminal phosphorus-chromium bond length (Cr1-P2 2.5158(14) A˚ versus Cr1-P2 2.5081(5) A˚ in 5). The Cp ligand is recognized as the reason for the oligomerization behavior of 5 in catalytic tests. With AlEt3 mostly 1-butene (70.2 wt %) is formed, but a small amount of other oligomers following a Schulz-Flory distribution (14.3 wt %) and some polyethylene (15.5 wt %) were also present. Thus, dimerization based on a chromacyclopentane could be responsible for enhanced 1-butene formation, whereas the SchulzFlory distribution and the polymerization could be explained by an ethene insertion/β-elimination mechanism by chain growth that competes with the metallacyclic route. To find out if these suggestions are appropriate, 5 was alkylated with Na[Et4Al] (Scheme 5) to form the corresponding ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). Its molecular structure is depicted in Figure 6. The oligomerization test with AlEt3 as a cocatalyst resulted in a similar product distribution compared to the oligomerization experiment with 5. Compared to 5, the Cr-N bond in 7 is elongated slightly by 0.04 A˚ and the Cr-P bond is shortened by 0.02 A˚, whereas the P-Cr-N angle is reduced by ca. 1.3. Complex 7, with an ethyl group, is stable at room temperature.

To prove whether alkylation of 6 gives a complex analogous to 7, we reacted 6 with Et3Al in THF. Surprisingly, this led to the formation of EtCrCl2(THF)3 (8). It is thermally less stable compared to the corresponding phenyl PhCrCl2(THF)313 and methyl MeCrCl2(THF)314 compounds. Obviously, the weak ligand coordination via both phosphorus atoms on the chromium site of 6 is not favored in the presence of THF and AlEt3. One can discuss whether first alkylation of chromium takes place and the ligand is then replaced by THF molecules or the ligand is displaced in a first step by THF and afterward the chromium is alkylated. By fast crystallization complex 6 can be obtained from a mixture of THF/hexane, but after some days in solution these blue crystals decompose under formation of violet CrCl3(THF)3 and free ligand can be observed by NMR. Hence, this reaction behavior is one reason that THF is not a suitable solvent for the new ethene trimerization system.5 Complex 8 was described before,15 but via a different reaction and without a molecular structure, which is shown (13) Kurras, E. Naturwissenschaften 1959, 46, 171. (14) Kurras, E. Monatsber. Akad. Wiss. 1963, 5, 378. (15) Nishimura, K.; Kuribayashi, H.; Yamamoto, A.; Ikeda, S. J. Organomet. Chem. 1972, 37, 317–329.

Article

Organometallics, Vol. 29, No. 21, 2010

Table 1. Summary of Important Bond Lengths and Angles

complex

metal

2 3 4

Li Li Mg

5 6 7

Cr Cr Cr

distance M-N(A˚)

distance M-Pterminal (A˚)

angle N--MPterminal (deg)

1.973(3) 2.049(2) 1.998(2) 2.005(2) 1.9650(13)

2.774(3) 2.587(2) 2.7470(11) 2.7126(11) 2.5081(5) 2.5158(14) 2.4822(7)

84.96(19) 88.66(8) 79.35(7) 79.50(7) 82.68(4)

2.002(2)

81.42(6)

here in Figure 7. Its coordination sphere is nearly perfect octahedral. The ethyl group is located trans to one THF molecule. Both chlorine atoms are situated trans to each other. The chromium-carbon bond, at 2.065 A˚, is slightly shorter than that in complex 7.

Conclusion We herein present different metal amide complexes of Ph2PN(iPr)P(Ph)N(iPr)H (1), obtained by deprotonation of the amine function. Lithiation of compound 1 under stabilization with tetramethylenediamine (tmeda) forms a tmedalithium-amide complex. Without tmeda, a dinuclear lithiumamide complex can be isolated. Reaction of a Grignard reagent with 1 yields a magnesium bis-amide compound, which represents only a minor part of the reaction mixture. Cr-amide complexes were prepared, showing a coordination motif that could be part of a catalytically active species in ethene trimerization. After storing a reaction mixture of a Cr-ligand complex and AlEt3 in THF for several days the ligand is replaced by solvent molecules and EtCrCl2(THF)3 can be isolated. For the first time a crystal structure of this compound is presented. In conclusion, the compounds show how metalation and transmetalation of the new ligand in catalysis can look alike, which is of major interest concerning its coordination chemistry as well as activation processes of the precatalyst mixture in ethene trimerization.

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: Mass spectra: MAT 95-XP and Finnigan Polaris Q. 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) and THF-d8 (δH =2.73, δC =25.2). Chemical shifts for 31P are given relative to 85% H3PO4. The spectra were assigned with the help of DEPT. Melting points: sealed capillaries, B€ uchi 535 apparatus. Elemental analyses: Leco CHNS932 elemental analyzer. Compounds 1, 5, and 6 were prepared according to published literature procedures.5 Oligomerization experiments were conducted as published before.3,4 Analytical details of compound 8 were published before.15 Preparation of [Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Ph2PN(iPr)P(Ph)N(iPr)-H (1) (204 mg, 0.5 mmol) and 90 μL of tetramethylethylenediamine (tmeda, 0.6 mmol) were dissolved in 10 mL of THF. After cooling to -40 C n-butyllithium

5267

(0.35 mL, 1.6 M n-BuLi in n-hexane, 0.56 mmol) was added to the solution, whereupon the color changed immediately to orange-yellow. The solution was stirred for an additional two hours at room temperature. Subsequently, half the solvent was removed by distillation. For crystallization 2 mL of n-hexane was added and the solution was stored at -78 C. Yield: 120 mg (45%). Molecular weight: 530.59 g/mol [C30H45LiN4P2]. Elementary analysis was impossible because of dissociation of tmeda. Melting point: 128-129 C. 1H NMR (THF-d8): δ 7.587.48 (m, 6H, aryl-H), 7.36-7.17 (m, 6H, aryl-H), 7.04-6.91 (m, 3H, aryl-H), 3.71 (m, 1H, CHCH3), 3.57 (m, 1H, CHCH3), 2.30 (s, 4H, CH2), 2.13 (br s, 12H, NCH3), 1.38 (d, J = 6.5 Hz, 3H, CHCH3), 1.24 (d, J = 6.40 Hz, 3H, CHCH3), 1.23 (d, J = 6.4 Hz, 3H, CHCH3), 1.02 (d, J = 6.5 Hz, 3H, CHCH3). 13C NMR (THF-d8): δ 157.1, 143.4, 141.9, 134.9, 133.3, 132.4, 129.4, 128.6, 127.9, 127.1, 125.2, (18C, arom.) 58.7 (2C, CH2), 54.4, 50.6 (2C, CHCH3), 46.2 (4C, NCH3), 30.1, 25.8, 24.5, 24.2 (4C, CHCH3). 31P{H} NMR (THF-d8): δ 40.6 (br), 100.4 ppm (d, 2JP-P = 20.5 Hz). Preparation of [Ph2PN(iPr)P(Ph)N(iPr)-Li]2 (3). Ph2PN(iPr)P (Ph)N(iPr)-H (1) (8.70 g, 21.35 mmol) was dissolved in 15 mL of toluene. After cooling to -78 C n-butyllithium (12.8 mL, 2.5 M n-BuLi in n-heptane, 32.0 mmol) was added to the solution, causing the color to change immediately to orange-yellow. The solution was stirred for an additional two hours at room temperature, and a colorless solid precipitated. The precipitate was filtered and washed three times with 5 mL of toluene. Remaining solvent was removed under vacuum to give a colorless powder. Crystals could be grown from the mother liquor at room temperature. Yield: 6.73 g (76%). Molecular weight: 414.39 g/mol [C24H29LiN2P2]. Anal. Calcd: C 69.56, H 7.05, N 6.76. Found: C 69.25, H 7.06, N 6.87. Melting point: 187189 C. 1H NMR (THF-d8): δ 7.50-7.57 (m, 6H, aryl-H), 7.20-7.34 (m, 6H, aryl-H), 7.02 (m, 2H, arom.), 6.93 (m, 1H, aryl-H), 3.70 (m, 1H, CHCH3), 3.58 (m, 1H, CHCH3), 1.39 (d, J = 6.5 Hz, 3H, CHCH3), 1.25 (d, J = 6.2 Hz, 3H, CHCH3), 1.22 (d, J = 6.2 Hz, 3H, CHCH3), 1.04 (d, J = 6.5 Hz, 3H, CHCH3). 13C NMR (THF-d8): 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.), 54.6, 54.0 (CHCH3), 31.0, 26.7 (CHCH3). 31P{H} NMR (THF-d8): δ 40.6 (br), 100.1 ppm (d, 2JP-P = 24.6 Hz). Preparation of [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4). Ph2PN(iPr) P(Ph)N(iPr)-H (1) (3.00 g, 7.34 mmol) was dissolved in 50 mL of diethyl ether. At room temperature a solution of isobutylmagnesium chloride (3.7 mL, 2.0 M C4H9ClMg in diethyl ether, 7.40 mmol) was added to the solution. The solution was stirred for an additional two hours. After cooling to -30 C a colorless precipitate of the composition Ph2PN(iPr)P(Ph)N(iPr)-MgCl was isolated. Yield: 2.01 g (58%). Recrystallization from diethyl ether resulted in amorphous powders with unchanged analytical data. Few single crystals were obtained by this method, revealing the structure of [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg. Yield: 0.46 g (15%). 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 CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). CpCrCl [-N(iPr)P(Ph)N(iPr)PPh2] (5)5 (0.030 g, 0.054 mmol) and Na [Et4Al] (0.009 g, 0.054 mmol) were suspended in 5 mL of Et2O at room temperature. The color changed immediately to greenbrown, and a colorless precipitate occurred. After stirring overnight all volatiles were removed under vacuum, and the residue was extracted with toluene. The brown solution was reduced to 1 mL. Brown crystals suitable for X-ray analysis formed

5268

Organometallics, Vol. 29, No. 21, 2010

within two weeks storing time at room temperature. Molecular weight: 553.60 g/mol [C31H39CrN2P2]. Yield: 18 mg (60%). Anal. Calcd: C 67.26, H 7.10, N 5.06. Found: C 66.49, H 7.04, N 4.69. Melting point: 132-134 C (dec). Preparation of EtCrCl2(THF)3 (8). CrCl3[Ph2PN(iPr)P(Ph)N i ( Pr)-H](THF) (6)5 (0.20 g, 0.357 mmol) was solved in 10 mL of THF. AlEt3 (0.28 mL, 1.9 M in toluene, 0.536 mmol) was added to the blue solution, which turned green immediately. The solution was mixed with 10 mL of n-hexane and stored one week at -40 C. In that time green crystals suitable for X-ray analysis formed. Molecular weight: 368.28 g/mol [C14H29CrO3]. Yield: 21 mg (16%). Crystallographic Details. Diffraction data were collected on a STOE IPDS diffractometer using graphite-monochromated Mo KR radiation. The structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares techni-

Peitz et al. ques on F2 (SHELXL-97). DIAMOND was used for graphical representations.

Acknowledgment. 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 technical staff at LIKAT. Supporting Information Available: Tables of crystallographic data in cif file format, including bond lengths and angles of compounds 2, 3, 4, 7, and 8. This material is available free of charge via the Internet at http://pubs.acs.org.