Synthesis and Protonolysis of Tungsten− and Molybdenum

Reactions of tungsten- and molybdenum−dinitrogen complexes bearing ruthenocenyldiphosphines with an excess amount of sulfuric acid in methanol at ro...
0 downloads 0 Views 905KB Size
Download PDF
Organometallics 2009, 28, 4741–4746 DOI: 10.1021/om900298g

4741

Synthesis and Protonolysis of Tungsten- and Molybdenum-Dinitrogen Complexes Bearing Ruthenocenyldiphosphines Masahiro Yuki, Tatsuya Midorikawa, Yoshihiro Miyake, and Yoshiaki Nishibayashi* Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan Received April 21, 2009

Tungsten- and molybdenum-dinitrogen complexes bearing 1,10 -bis(diethylphosphino)ruthenocene (depr) or 1,10 -bis(dimethylphosphino)ruthenocene (dmpr) have been prepared and characterized spectroscopically. Reactions of tungsten- and molybdenum-dinitrogen complexes bearing ruthenocenyldiphosphines with an excess amount of sulfuric acid in methanol at room temperature give ammonia in good yields. Ferrocene and its derivatives are widely used in organometallic chemistry and material sciences.1 Ferrocene-based ligands are also of increasing importance in transition-metal-catalyzed organic syntheses, including asymmetric transformations.2,3 Ferrocenyldiphosphines such as 1,10 -bis(diphenylphosphino)ferrocene (dppf) are common diphosphine ligands because of their relatively large bite angle, capacity for dative bond formation with electron-deficient metal centers, and chemical robustness of the ferrocene skeleton.3 It is also known that the catalytic behavior of complexes can be fine-tuned by replacing the ferrocenyldiphosphines with ruthenocenyldiphosphines.4 In general, a ruthenocenyldiphosphine such as 1,10 -bis(diphenylphosphino)ruthenocene (dppr) gives a slightly larger bite angle compared to dppf, as a consequence of the larger atomic radii of ruthenium.5 In addition, it is also possible that the difference in electronic properties between ferrocene and ruthenocene moieties modifies the electronic

and structural properties of the corresponding complexes bearing these metallocenes.6 Recently, we have reported the preparation of tungstenand molybdenum-dinitrogen complexes bearing ferrocenyldiphosphines as auxiliary ligands, [M(N2)2(depf)2] (M = W, Mo; depf = 1,10 -bis(diethylphosphino)ferrocene).7 Reactions of these dinitrogen complexes with an excess amount of sulfuric acid afforded ammonia in good yields. It is noteworthy that the ferrocene moiety in these complexes plays an important role in the conversion of the coordinated dinitrogen into ammonia.8 This result is in sharp contrast to the previous result that protonolysis of tungsten- and molybdenum-dinitrogen complexes bearing conventional diphosphines such as [M(N2)2(dppe)2] and [M(N2)2(depe)2] did not produce ammonia. In the

*To whom correspondence should be addressed. E-mail: ynishiba@ sogo.t.u-tokyo.ac.jp. (1) (a) Hudson, R. D. A. J. Organomet. Chem. 2001, 637-639, 47. (b) Nishihara, H. Adv. Inorg. Chem. 2002, 53, 41. (c) Nakamura, E. Pure Appl. Chem. 2003, 75, 427. (d) van Staveren, D. R.; Metzler-Nolte, N. Chem. Rev. 2004, 104, 5931. (e) Nakamura, E. J. Organomet. Chem. 2004, 689, 4630. (f) J. Inorg. Organomet. Polym. Mater. 2005, 15(1) (the special issue celebrating the 50th anniversary of polyferrocenes). (g) Fouda, M. F. R.; Abd-Elzaher, M. M.; Abdelsamaia, R. A.; Labib, A. A. Appl. Organomet. Chem. 2007, 21, 613. (h) Gao, Y.; Shreeve, J. M. J. Inorg. Organomet. Polym. Mater. 2007, 17, 19. (i) Seiwert, B.; Karst, U. Anal. Bioanal. Chem. 2008, 390, 181. (2) (a) Colacot, T. J. Chem. Rev. 2003, 103, 3101. (b) Barbaro, P.; Bianchini, C.; Giambastiani, G.; Parisel, S. L. Coord. Chem. Rev. 2004, 248, 2131. (c) G omez Arrayas, R.; Adrio, J.; Carretero, J. C. Angew. Chem., Int. Ed. 2006, 45, 7674. (d) Fihri, A.; Meunier, P.; Hierso, J.-C. Coord. Chem. Rev. 2007, 251, 2017. (3) (a) Ferrocenes. Homogenous Catalysis, Organic Synthesis, Material Science; Togni, A., Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995. (b) Ferrocenes. Ligands, Materials and Biomolecules; Stepnicka, P., Ed.; Wiley: Sussex, England, 2008. (4) (a) Hayashi, T.; Ohno, A.; Lu, S.; Matsumoto, Y.; Fukuyo, E.; Yanagi, K. J. Am. Chem. Soc. 1994, 116, 4221. (b) Li, Sihai; Wei, B.; Low, P. M. N.; Lee, H. K.; Hor, T. S. A.; Xue, F.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 1997, 1289. (c) Hamann, B. C.; Hartwig, J. F. J. Am. Chem. Soc. 1998, 120, 3694. (d) Mendez, M.; Cuerva, J. M.; Gomez-Bengoa, E.; Cardenas, D. J.; Echavarren, A. M. Chem. Eur. J. 2002, 8, 3620. (e) Gusev, O. V.; Peganova, T. A.; Kalsin, A. M.; Vologdin, N. V.; Petrovskii, P. V.; Lyssenko, K. A.; Tsvetkov, A. V.; Beletskaya, I. P. Organometallics 2006, 25, 2750. (5) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes, P. Chem. Rev. 2000, 100, 2741.

(6) (a) Barlow, S.; Marder, S. R. Chem. Commun. 2000, 1555. (b) Nataro, C.; Campbell, A. N.; Ferguson, M. A.; Incarvito, C. D.; Rheingold, A. L. J. Organomet. Chem. 2003, 673, 47. (c) Gusev, O. V.; Peterleitner, M. G.; Kal0 sin, A. M.; Vologdin, N. V. Russ. J. Electrochem. 2003, 39, 1293. (d) Kinnibrugh, T. L.; Salman, S.; Getmanenko, Y. A.; Coropceanu, V.; Porter, W. W.III; Timofeeva, T. V.; Matzger, A. J.; Bredas, J.-L.; Marder, S. R.; Barlow, S. Organometallics 2009, 28, 1350. (7) Yuki, M.; Miyake, Y.; Nishibayashi, Y.; Wakiji, I.; Hidai, M. Organometallics 2008, 27, 3947. (8) George, T. A.; Tisdale, R. C. J. Am. Chem. Soc. 1985, 107, 5157. (9) (a) Nishibayashi, Y.; Iwai, S.; Hidai, M. Science 1998, 279, 506. (b) Nishibayashi, Y.; Takemoto, S.; Iwai, S.; Hidai, M. Inorg. Chem. 2000, 39, 5946. (c) Nishibayashi, Y; Saito, M.; Uemura, S.; Takekuma, S.; Takekuma, H.; Yoshida, Z. Nature 2004, 428, 279. (10) For recent reviews on dinitrogen fixation, see: (a) Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 1115. (b) Gambarotta, S. J. Organomet. Chem. 1995, 500, 117. (c) Fryzuk, M. D.; Johnson, S. A. Coord. Chem. Rev. 2000, 200-202, 379. (d) MacKay, B. A.; Fryzuk, M. D. Chem. Rev. 2004, 104, 385. (e) Gambarotta, S.; Scott, J. Angew. Chem., Int. Ed. 2004, 43, 5298. (f) Hidai, M.; Mizobe, Y. Can. J. Chem. 2005, 83, 358. (g) Himmel, H.J.; Reiher, M. Angew. Chem., Int. Ed. 2006, 45, 6264. (11) For recent examples of dinitrogen complexes, see: (a) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76. (b) Pool, J. A.; Lobkovsky, E.; Chirik, P. J. Nature 2004, 427, 527. (c) Curley, J. J.; Sceats, E. L.; Cummins, C. C. J. Am. Chem. Soc. 2006, 128, 14036. (d) Smythe, N. C.; Schrock, R. R.; Muller, P.; Weare, W. W. Inorg. Chem. 2006, 45, 9197. (e) Bart, S. C.; Chleopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky, E.; Neese, F.; Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 13901. (f) Mori, H.; Seino, H.; Hidai, M.; Mizobe, Y. Angew. Chem., Int. Ed. 2007, 46, 5431. (g) Akagi, F.; Matsuo, T.; Kawaguchi, H. Angew. Chem., Int. Ed. 2007, 46, 8778. (h) Scott, J.; Vidyaratne, I.; Korobkov, I.; Gambarotta, S.; Budzelaar, P. H. M. Inorg. Chem. 2008, 47, 896. (i) Knobloch, D. J.; Toomey, H. E.; Chirik, P. J. J. Am. Chem. Soc. 2008, 130, 4248. (j) Morello, L.; Ferreira, M. J.; Patrick, B. O.; Fryzuk, M. D. Inorg. Chem. 2008, 47, 1319. (k) R€omer, R.; Stephan, G.; Habeck, C.; Hoberg, C.; Peters, G.; N€ather, C.; Tuczek, F. Eur. J. Inorg. Chem. 2008, 3258.

r 2009 American Chemical Society

Published on Web 07/24/2009

pubs.acs.org/Organometallics

4742

Organometallics, Vol. 28, No. 16, 2009

Yuki et al.

Scheme 1

Scheme 2

Figure 1. ORTEP view of trans-[W(N2)2(depr)(PPh2Me)2] (1) with 50% thermal ellipsoids. Selected interatomic distances (A˚) and bond angles (deg): W-P(1)=2.512(2), W-P(2)=2.518(2), W-P(3)=2.479(2), W-P(4)=2.461(2), W-N(1)=1.967(5), WN(3)= 1.972(6), N(1)-N(2) = 1.161(8), N(3)-N(4) = 1.138(9), W 3 3 3 Ru=4.5775(7); P(1)-W-P(2)=98.72(6), P(2)-W-P(3) = 88.93(6), P(3)-W-P(4) = 85.23(7), P(4)-W-P(1) = 90.32(7), N(1)-W-N(3)=178.7(2).

course of our continuing interest in dinitrogen fixation chemistry,7-11 we now report the preparation and protonation of tungsten- and molybdenum-dinitrogen complexes bearing ruthenocenyldiphosphines as auxiliary ligands.

Results and Discussion Ruthenocenyldiphosphines were prepared by a procedure similar to that for ferrocenyldiphosphines.7 Dilithiation of ruthenocene with n-butyllithium-TMEDA in hexane at room temperature afforded a white powder of 1,10 dilithioruthenocene, which was treated with PEt2Cl to give 1,10 -bis(diethylphosphino)ruthenocene (depr) in 25% yield (Scheme 1). Similarly, 1,10 -bis(dimethylphosphino)ruthenocene (dmpr) was also prepared in 22% yield by using PMe2Cl instead of PEt2Cl. The reaction of trans-[W(N2)2(PPh2Me)4] with 2 equiv of depr at 60 °C for 12 h gave trans-[W(N2)2(depr)(PPh2Me)2] (1) as a major complex together with a trace amount of trans-[W(N2)2(depr)2] (2) (Scheme 2). Recrystallization of the mixture of two complexes from THF-hexane afforded 1 in 29% isolated yield as orange-red plates. The IR spectrum of 1 exhibited one absorption band for νNN at 1895 cm-1, indicating the trans arrangement of two dinitrogen ligands. In the 31P{1H} NMR spectrum, four phosphorus atoms displayed an AA0 BB0 spectrum centered at -8.5 ppm, due to two pairs of chemically equivalent but magnetically inequivalent phosphorus atoms bound to a tungsten center. The molecular structure of 1 was unequivocally determined by X-ray crystallography. An ORTEP drawing of 1 is shown in Figure 1. Around the octahedrally coordinated tungsten center, two dinitrogen ligands occupied positions trans to each other. The ruthenocene moiety adopts a staggered conformation with a rotation angle of 46.4°. The bite angle of depr in 1 is 98.72(6)°. This value is slightly larger than that (12) Yuki, M.; Miyake, Y.; Nishibayashi, Y. Unpublished results. Crystal data for trans-[W(N2)2(depf)(PPh2Me)2] are given in the Supporting Information.

Figure 2. Structures of trans-[W(N2)2(depr)(PPh2Me)2] (1) (left) and trans-[W(N2)2(depf)(PPh2Me)2]12 (right).

of depf in trans-[W(N2)2(depf)(PPh2Me)2] (96.72(6)°)12 (Figure 2). The W-Ru distance of 4.5775(7) A˚ indicated no bonding interaction between ruthenium and tungsten atoms and was almost the same as the W-Fe distance of trans-[W(N2)2(depf)(PPh2Me)2] (4.5631(11) A˚). Next, we carried out the reaction of trans-[W(N2)2(PPh2Me)4] with an excess amount of depr at a higher reaction temperature such as 70 °C for 4 h to afford trans-[W(N2)2(depr)2] (2) in 29% yield as a pink powder (Scheme 2). The 1H NMR spectrum of 2 was very similar to that of trans-[W(N2)2(depf)2] (3). In the 31P{1H} NMR spectrum of 2, four equivalent phosphorus atoms were observed at -6.8 ppm as a singlet with 183W satellites (1JPW = 319 Hz). The IR spectrum of 2 showed a strong absorption band for νNN at 1879 cm-1, which was almost the same frequency as that of 3 (νNN 1883 cm-1). These observations were consistent with the trans configuration of 2, as in the case of 3. A cyclic voltammogram (CV) of 2 showed a reversible one-electron-oxidation wave at -0.97 V assignable to the W(0/I) redox couple. This value was very close to the values observed for 3 and trans-[W(N2)2(depe)2], as shown in Table 1. Both the IR and CV data of 2 display the same strongly electron donating properties of depr as for depf. The reaction of trans-[W(N2)2(PPh2Me)4] with 1 equiv of dmpr at 60 °C for 3 h afforded trans-[W(N2)2(dmpr)(PPh2Me)2] (4) in 39% yield (Scheme 3). The IR spectrum

Article

Organometallics, Vol. 28, No. 16, 2009 Scheme 3

4743

Scheme 5

Scheme 4

of 4 exhibited one absorption band of νNN at 1899 cm-1. A cyclic voltammogram of 4 showed a reversible W(0/I) redox wave at -0.80 V, close to that of 1. On the other hand, we could not obtain a complex such as trans-[W(N2)2(dmpr)2], even if the reaction was carried out with an excess amount of dmpr for a longer reaction time. The reaction of trans-[Mo(N2)2(PPh2Me)4] with 2 equiv of depr proceeded even at room temperature to give a mixture of trans-[Mo(N2)2(depr)(PPh2Me)2] (5) and trans-[Mo(N2)2(depr)2] (6) as an orange powder (Scheme 4). The 1H NMR spectrum of the powder exhibited signals assignable to 5 and 6 in a ratio of ca. 15:1. The chemical shifts were almost same as for the corresponding tungsten complexes 1 and 2, respectively. The 31P{1H} NMR spectrum showed a set of symmetric multiplet signals centered at 20.5 ppm consistent with the AA0 BB0 spin system of 5 due to four phosphorus atoms bound to the molybdenum center. A singlet signal of 6 was also observed at 21.6 ppm. When the reaction was carried out with an excess amount of depr, complex 6 was observed as a major product in benzene-d6 solution by NMR. However, we have not yet isolated 5 or 6 in pure form.

The reaction of trans-[Mo(N2)2(PPh2Me)4] with 1 equiv of dmpr gave trans-[Mo(N2)2(dmpr)(PPh2Me)2] (7) in 56% yield (Scheme 5). The IR and NMR spectra of 7 supported the structure of 7. The molecular structure of 7 was confirmed by X-ray crystallography, as shown in Figure 3. The ruthenocene moiety of 7 adopts an eclipsed conformation with a rotation angle of 11.1°, in contrast to the staggered structure of 1. This conformation is due to the remarkably small bite angle of the dmpr ligand (88.33(3)°). The bond angle betweenthe two PPh2Me ligands is rather large (P(3)Mo-P(4)=92.66(2)°). These structural differences indicate that the conformations of ruthenocene moieties are determined by the subtle balance of steric repulsion between the coordinated ligands in these complexes. Both eclipsed and staggered conformations were previously observed for two ferrocene moieties in one molecule of trans-[M(N2)2(depf)2] (M=W, Mo).7 When the reaction was carried out with an excess amount of dmpr, the formation of the possible complex trans-[Mo(N2)2(dmpr)2] (8) was observed in solution by NMR spectra.14 Unfortunately, any effort to isolate 8 has been in vain at the present. Finally, we investigated the reactivity of novel tungstenand molybdenum-dinitrogen complexes toward protonolysis.15,16 Reactions of dinitrogen complexes with an excess amount of sulfuric acid in methanol at room temperature for 24 h gave ammonia in all cases (Scheme 6). In no case was hydrazine detected. Similar to the previous results of the protonation of dinitrogen complexes,15 dinitrogen complexes bearing monodentate phosphines as auxiliary ligands such as 1, 4, 5, and 7 gave ammonia in good to high yields. Interestingly, protonation of 2 with sulfuric acid also gave ammonia in 68% yield based on the tungsten atom. This result is in sharp contrast with those for molybdenum- and tungsten-dinitrogen complexes bearing chelating diphosphines as auxiliary ligands [M(N2)2L2] (M = Mo, W; L = dppe, depe), where ammonia was not found and only the

Table 1. IR and Electrochemical Data of Tungsten- and Molybdenum-Dinitrogen Complexes complexa trans-[W(N2)2(depr)(PPh2Me)2] (1) trans-[W(N2)2(depr)2] (2) trans-[W(N2)2(dmpr)(PPh2Me)2] (4) trans-[W(N2)2(depf)2] trans-[W(N2)2(depe)2] trans-[W(N2)2(dppe)2] trans-[W(N2)2(dchpe)2] trans-[W(N2)2(dppe)(PPh2Me)2] trans-[W(N2)2(PPh2Me)4] trans-[W(N2)2(PPhMe2)4] trans-[Mo(N2)2(dmpr)(PPh2Me)2] (7) trans-[Mo(N2)2(depf)2] trans-[Mo(N2)2(depe)2] trans-[Mo(N2)2(dppe)2] trans-[Mo(N2)2(dppe)(PPh2Me)2] trans-[Mo(N2)2(PPh2Me)4]

νNN(asym)/cm-1b

E1/2/V c

1895 1879 1899 1883 1895 1943 1880d 1920d 1899 1898 1925 1907 1928 1975 1943d 1922

-0.83 -0.97 -0.80 -0.95 -0.96 -0.68 -1.02 -0.71 -0.83 -0.80 -0.97 -0.97 -0.70 -0.71

ref this work this work this work 7 13a,13b 13a,13b 13b 13c 7,13c 13d this work 7 13b,13e 13b 13c 13f,13g

Abbreviations: dppe=1,10 -bis(diphenylphosphino)ethane; depe=1,10 -bis(diethylphosphino)ethane; dchpe=1,10 -bis(dicyclohexylphosphino)ethane. b Asymmetric NN stretching bands in KBr pellets. c Relative to ferrocene-ferrocenium couple in THF. d Nujol mull. a

4744

Organometallics, Vol. 28, No. 16, 2009

Yuki et al. Scheme 6

Figure 3. ORTEP view of trans-[Mo(N2)2(dmpr)(PPh2Me)2] (7) with 50% thermal ellipsoids. Selected interatomic distances (A˚) and bond angles (deg): Mo-P(1) = 2.4635(10), Mo-P(2) = 2.4881(9), Mo-P(3) = 2.4856(8), Mo-P(4) = 2.4763(9), Mo-N(1) = 2.012(2), Mo-N(3) =2.009(2), N(1)-N(2) =1.128(3), N(3)-N(4)=1.126(3), Mo 3 3 3 Ru=4.5215(3); P(1)-Mo-P(2)=88.33(3), P(2)-Mo-P(3) = 92.17(3), P(3)-Mo-P(4) = 92.66(2), P(4)Mo-P(1)=89.21(3), N(1)-Mo-N(3)=175.02(11).

formation of the corresponding hydrazido complexes was observed.16 On the other hand, the result described in this paper is similar to those for protonation of tungsten- and molybdenum-dinitrogen complexes bearing ferrocenyldiphosphines such as trans-[M(N2)2(depf)2] (M=W, Mo) with sulfuric acid, where ammonia was obtained in 129% and 48% yields, respectively.7 Although we previously isolated the corresponding hydrazido complexes as reactive intermediates in the protonation of trans-[M(N2)2(depf)2] (M = W, Mo) with 2 equiv of HOTf,7 we cannot isolate similar hydrazido complexes in the protonation of trans-[W(13) (a) Nordwig, B. L.; Ohlsen, D. J.; Beyer, K. D.; Brummer, J. G. Inorg. Chem. 2006, 45, 858. (b) Hussain, W.; Leigh, G. J.; Mohd.-Ali, H.; Pickett, C. J.; Rankin, D. A. J. Chem. Soc., Dalton Trans. 1984, 1703. (c) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton Trans. 1977, 2139. (d) George, T. A.; DeBord, J. R. D.; Kaul, B. B.; Pickett, C. J.; Rose, D. J. Inorg. Chem. 1992, 31, 1295. (e) Filippou, A. C.; Schnakenburg, G.; Philippopoulos, A. I.; Weidemann, N. Angew. Chem., Int. Ed. 2005, 44, 5979. (f) George, T. A.; Noble, M. E. Inorg. Chem. 1978, 17, 1678. (g) Lazarowych, N. J.; Morris, R. H.; Ressner, J. M. Inorg. Chem. 1986, 25, 3926. (14) NMR data for trans-[Mo(N2)2(dmpr)2] (8) are as follows. 1H NMR (270 MHz, C6D6): δ 4.80 (t, J = 2 Hz, 8H, C5H4), 4.61 (t, J = 2 Hz, 8H, C5H4), 1.62 (br s, 24H, Me). 31P{1H} NMR (C6D6): δ 4.4 (s). (15) (a) Chatt, J.; Heath, G. A.; Richards, R. L. J. Chem. Soc., Dalton Trans. 1974, 2074. (b) Chatt, J.; Pearman, A. J.; Richards, R. L. Nature 1975, 253, 39. (c) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton Trans. 1977, 1852. (d) Hidai, M.; Mizobe, Y.; Takahashi, T.; Uchida, Y. Chem. Lett. 1978, 1187. (e) Takahashi, T.; Mizobe, Y.; Sato, M.; Uchida, Y.; Hidai, M. J. Am. Chem. Soc. 1979, 101, 3405. (f) Baumann, J. A.; George, T. A. J. Am. Chem. Soc. 1980, 102, 6153. (g) George, T. A.; Kovar, R. A. Inorg. Chem. 1981, 20, 285. (h) Anderson, S. N.; Fakley, M. E.; Richards, R. L.; Chatt, J. J. Chem. Soc., Dalton Trans. 1981, 1973. (i) Bossard, G. E.; George, T. A.; Lester, R. K. Inorg. Chim. Acta 1982, 64, L227. (j) Anderson, S. N.; Richards, R. L.; Hughes, D. L. J. Chem. Soc., Dalton Trans. 1986, 245. (16) (a) Heath, G. A.; Mason, R.; Thomas, K. M. J. Am. Chem. Soc. 1974, 96, 259. (b) Hidai, M.; Kodama, T.; Sato, M.; Hirakawa, M.; Uchida, Y. Inorg. Chem. 1976, 15, 2694. (c) Chatt, J.; Leigh, G. J.; Neukomm, H.; Pickett, C. J.; Stanley, D. R. J. Chem. Soc., Dalton Trans. 1980, 121. (d) Nishihara, H.; Mori, Y.; Nakano, K.; Saito, T.; Sasaki, Y. J. Am. Chem. Soc. 1982, 104, 4367. (e) Henderson, R. A. J. Chem. Soc., Dalton Trans. 1982, 917. (f) Bakar, M. A.; Hughes, D. L.; Hussain, W.; Leigh, G. J.; Macdonald, C. J.; Mohd.-Ali, H. J. Chem. Soc., Dalton Trans. 1988, 2545. (g) Barclay, J. E.; Hills, A.; Hughes, D. L.; Leigh, G. J.; Macdonald, C. J.; Bakar, M. A.; Mohd.-Ali, H. J. Chem. Soc., Dalton Trans. 1990, 2503.

(N2)2(depr)2] with 2 equiv of HOTf. At present, we have not yet clarified the exact role of ruthenocenyldiphosphines in these dinitrogen complexes, but it may be possible to assume that the electron transfer process from ruthenocene units to the tungsten or molybdenum center assists the reduction of the dinitrogen molecule to ammonia. A similar electron transfer has been previously proposed in the protonation of tungsten- and molybdenum-dinitrogen complexes bearing ferrocenyldiphosphines.7 In summary, we have prepared novel tungsten- and molybdenum-dinitrogen complexes bearing ruthenocenyldiphosphines as auxiliary ligands. Reactions of these complexes with an excess amount of sulfuric acid in methanol at room temperature gave ammonia in good yields. Although the details are not yet clear, the ruthenocene moiety in these complexes plays an important role in the facile conversion of the coordinated dinitrogen into ammonia.

Experimental Section General Method. 1H NMR (270 MHz) and 31P{1H} NMR (109 MHz) spectra were measured on a JEOL Excalibur 270 spectrometer, and 31P chemical shifts were quoted relative to an external standard of 85% H3PO4. The chemical shifts and the coupling constants of AA0 BB0 spin systems were determined by line shape analysis.17 IR spectra were recorded on a JASCO FT/ IR 4100 Fourier transform infrared spectrophotometer. Elemental analyses were performed on an Exeter Analytical CE440 elemental analyzer or at the Microanalytical Center of The University of Tokyo. Cyclic voltammograms were recorded on an ALS/Chi Model 610C electrochemical analyzer with a platinum working electrode in THF containing 0.1 M nBu4NBF4 as a supporting electrolyte. The potentials were quoted relative to the ferrocene/ferrocenium couple. All manipulations were performed under a dry nitrogen atmosphere. Solvents were dried over appropriate reagents and distilled prior to use. N,N,N0 ,N0 Tetramethylethylenediamine (TMEDA) was distilled from calcium hydride. The complexes trans-[W(N2)2(PPh2Me)4] 3 1.5THF13c and trans-[Mo(N2)2(PPh2Me)4]18 were prepared by the literature methods. Other reagents were purchased and used as received. Preparation of 1,10 -Bis(diethylphosphino)ruthenocene (depr). A mixture of ruthenocene (4.00 g, 17.3 mmol), TMEDA (5.2 mL, 34.5 mmol), and nBuLi (1.58 M, 22.0 mL, 34.8 mmol) in n(17) Reich, H. J. WINDNMR: NMR Spectrum Calculations, version 7.1.12; Department of Chemistry, University of Wisconsin, Madison, WI, 2005. (18) Lazarowych, N. J.; Morris, R. H.; Ressner, J. M. Inorg. Chem. 1986, 25, 3926.

Article hexane (25 mL) was stirred at room temperature overnight. The pale yellow precipitates were separated from the supernatant by decantation and were washed with n-hexane (50 mL). After removal of the washings, the precipitates were suspended into hexane (30 mL). To the suspension was added PEt2Cl (5.0 g, 40.1 mmol), and the mixture was stirred at room temperature overnight. The reaction mixture was filtered through a Celite pad, and the filtrate was concentrated in vacuo. The pale yellow residue was subjected to silica gel column chromatography. Elution with n-hexane-benzene (1/1) afforded depr (1.38 g, 25%) as a pale yellow solid. 1H NMR (C6D6): δ 4.59-4.56 (m, 4H, C5H4), 4.55-4.53 (m, 4H, C5H4), 1.50 (q, 3JHH=8 Hz, 8H, CH2), 1.06 (dt, 3JPH=15 Hz, 3JHH=8 Hz, 12H, CH3). 31P{1H} NMR (C6D6): δ -27.2 (s). Anal. Calcd for C18H28P2Ru: C, 53.06; H, 6.93. Found: C, 53.06; H, 6.99. Preparation of 1,10 -Bis(dimethylphosphino)ruthenocene (dmpr). The compound was obtained in 22% yield by a procedure similar to that for depr, using Me2PCl in place of Et2PCl. 1H NMR (C6D6): δ 4.54 (t, 3JHH =1 Hz, 4H, C5H4), 4.51 (t, 3JHH = 1 Hz, 4H, C5H4), 1.06 (d, 2JPH = 3 Hz, 12H, Me). 31P{1H} NMR (C6D6): δ -56.9 (s). Anal. Calcd for C14H20P2Ru: C, 47.86; H, 5.74. Found: C, 47.67; H, 5.73. Preparation of trans-[W(N2)2(depr)(PPh2Me)2] (1). A solution of trans-[W(N2)2(PMePh2)4] 3 1.5THF (500 mg, 0.435 mmol) and depr (397 mg, 0.974 mmol) in THF (15 mL) was stirred at 60 °C for 12 h. After removal of the solvent under reduced pressure, the residue was washed with hexane and recrystallized from THF-hexane, affording red plates of 1 (132 mg, 0.126 mmol, 29%). 1H NMR (270 MHz, C6D6): δ 7.62 (br t, J=7 Hz, 8H, Ph), 7.07 (t, J=7 Hz, 8H, Ph), 6.98 (t, J = 7 Hz, 4H, Ph), 4.80 (br, 4H, C5H4), 4.61 (t, J=1 Hz, 4H, C5H4), 2.14-1.98 (m, 4H, CH2), 2.03 (br, 6H, PPh2Me), 1.80-1.62 (m, 4H, CH2), 1.04-0.91 (m, 12H, PCH2CH3). 31P NMR (109 MHz, C6D6): δ -8.2 (1JPW=318 Hz), -8.7 (1JPW = 314 Hz) (AA0 BB0 spin system with 183W satellites, JAB(trans) = 123 Hz, JAB0 = -17 Hz, JAA0 and JBB0 = -24 and -42 Hz). IR (KBr): νNN 1961 vw, 1895 vs cm-1. Anal. Calcd for C44H54N4P4RuW: C, 50.44; H, 5.19; N, 5.35. Found: C, 50.18; H, 5.34; N, 5.43. Preparation of trans-[W(N2)2(depr)2] (2). A solution of trans-[W(N2)2(PMePh2)4] 3 1.5THF (206 mg, 0.179 mmol) and depr (463 mg, 1.14 mmol) in toluene (10 mL) was heated at 70 °C for 4 h. After concentration, the dark orange oily residue was washed with hexane (15 mL) to give a red solid. The solid was dissolved in THF, followed by precipitation with hexane, to give 2 as a pink powder (54 mg, 29%). 1H NMR (C6D6): δ 4.89 (t, J=2 Hz, 8H, C5H4), 4.64 (t, J = 2 Hz, 8H, C5H4), 2.45-2.18 (m, 16H, CH2), 1.25-1.11 (m, 24H, Me). 31P{1H} NMR (C6D6): δ 6.8 (s with 183W satellites, 1JP-W=319 Hz). IR (KBr): νNN 1960 vw, 1879 vs cm-1. Anal. Calcd for C36H56N4P4Ru2W: C, 40.99; H, 5.35; N, 5.31. Found: C, 41.02; H, 5.40; N, 5.06. Preparation of trans-[W(N2)2(dmpr)(PPh2Me)2] (4). A mixture of trans-[W(N2)2(PMePh2)4] 3 1.5THF (230 mg, 0.200 mmol) and dmpr (77 mg, 0.219 mmol) in THF (10 mL) was heated at 60 °C for 3 h. The solution was concentrated to ca. 1 mL, and hexane (15 mL) was added to the solution. After the resulting orange precipitate was removed by filtration, the solution was concentrated to dryness. The orange oily residue was triturated with hexane to give an orange powder of 4 (78 mg, 39%). 1H NMR (C6D6): δ, 7.47 (t, J=8 Hz, 8H, Ph), 7.03 (t, J=8 Hz, 8H, Ph), 6.94 (t, J=8 Hz, 4H, Ph), 4.90 (q, J=2 Hz, 4H, C5H4), 4.53 (t, J=2 Hz, 4H, C5H4), 2.30 (br d, 2JPH=5 Hz, 8H, PPh2Me), 1.46 (d, 2JPH=6 Hz, 12H, PMe2). 31P NMR (C6D6): δ -4.6 (dt with 183W satellites, 2JPP=111 and 7 Hz, 1JPW=319 Hz, PPh2Me), -26.3 (dt with 183W satellites, 2JPP =111 and 7 Hz, 1 JPW =322 Hz, dmpr). IR (KBr): νNN 1970 vw, 1899 vs cm-1. Anal. Calcd for C40H46N4P4RuW: C, 48.45; H, 4.68; N, 5.65. Found: C, 48.76; H, 4.51; N, 5.38. Reaction of trans-[Mo(N2)2(PPh2Me)4] with depr. A solution of trans-[Mo(N2)2(PPh2Me)4] (203 mg, 0.213 mmol) and depr (178 mg, 0.437 mmol) in toluene (10 mL) was stirred at room

Organometallics, Vol. 28, No. 16, 2009

4745

Table 2. Summary of Crystallographic Data for 1 and 7 1

7

formula C44H54N4P4RuW C40H46N4P4MoRu formula wt 1047.75 903.73 cryst size/mm 0.15  0.10  0.02 0.30  0.30  0.15 color, habit orange plate orange plate cryst syst monoclinic monoclinic P21/n (No. 14) space group P21/n (No. 14) a/A˚ 10.4793(7) 12.9067(5) b/A˚ 19.8614(12) 22.0993(7) c/A˚ 20.6273(13) 14.0746(6) β/deg 99.581(4) 104.0972(13) 3 4233.4(5) 3893.6(2) V/A˚ Z 4 4 1.644 1.542 dc/g cm-3 -1 3.263 9.085 μ(Mo KR)/mm no. of data collected 30 497 (2θ < 50°) 37 334 (2θ < 55°) 7470 (0.118) 8861 (0.053) no. of unique data (Rint) no. of params refined 541 497 a 2 0.046 0.034 R1 (F > 2σ) b wR2 (all data) 0.061 0.072 0.94 1.02 goodness of fit indicatorc þ1.71 to -1.86 þ0.97 to -1.09 residual electron density/e A˚-3 P P P P a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(F2o - F2c )2/ w(Fo)2]1/2. c P 1/2 2 2 2 [ w(Fo - Fc ) /(Nobservns - Nparams)] .

temperature for 24 h. After removal of the volatiles in vacuo, the residue was washed with hexane (10 mL  2) and extracted with toluene (40 mL). The extract was concentrated under vacuum, giving a mixture of trans-[Mo(N2)2(depr)(PPh2Me)2] (5) and trans-[Mo(N2)2(depr)2] (6) as an orange powder (165 mg). The 1 H NMR spectrum indicated that the powder contains 5 and 6 in a ratio of ca. 15:1. Further purification of the products was not successful. NMR data for 5 are as follows. 1H NMR (270 MHz, C6D6): δ 7.61 (t, J=7 Hz, 8H, Ph), 7.07 (t, J=7 Hz, 8H, Ph), 6.99 (t, J = 7 Hz, 4H, Ph), 4.80 (br, 4H, C5H4), 4.62 (t, J = 1 Hz, 4H, C5H4), 1.95-1.82 (m, 4H, CH2), 1.88 (d, 2JHP =3 Hz, 6H, PPh2Me), 1.65-1.47 (m, 4H, CH2), 1.05-0.93 (m, 12H, CH2Me). 31P NMR (109 MHz, C6D6): δ 21.8 and 19.2 (AA0 BB0 spin system, JAB(trans)=105 Hz, JAB0 =-8 Hz, JAA0 and JBB0=-13 and -21 Hz, PPh2Me and depr). NMR data for 6 are as follows. 1H NMR (C6D6): δ 4.90 (t, J=2 Hz, 8H, C5H4), 4.64 (t, J = 2 Hz, 8H, C5H4), 2.45-2.10 (m, 16H, CH2), 1.251.10 (m, 24H, Me). 31P{1H} NMR (C6D6): δ 21.6 (s). Preparation of trans-[Mo(N2)2(dmpr)(PPh2Me)2] (7). A solution of trans-[Mo(N2)2(PPh2Me)4] (191 mg, 0.200 mmol) and dmpr (71 mg, 0.203 mmol) in toluene (15 mL) was stirred at room temperature for 3 h. The solvent was removed under reduced pressure. Recrystallization from THF-hexane afforded orange plates of 7 (101 mg, 56%). 1H NMR (270 MHz, C6D6): δ 7.49 (t, J=8 Hz, 8H, Ph), 7.03 (t, J=8 Hz, 8H, Ph), 6.95 (t, J = 8 Hz, 4H, Ph), 4.90 (q, J = 1 Hz, 4H, C5H4), 4.54 (t, J=1 Hz, 4H, C5H4), 1.89 (d, 2JPH=4 Hz, 6H, PPh2Me), 1.35 (d, 2JPH =4 Hz, 12H, PMe2). 31P{1H} NMR (C6D6): δ 23.0 (d, 3JPP=95 Hz, PPh2Me), 1.70 (d, 3JPP=95 Hz, dmpr). IR (KBr): νNN 2000 vw, 1925 vs cm-1. Anal. Calcd for C40H46N4MoP4Ru: C, 53.16; H, 5.13; N, 6.20. Found: C, 53.12; H, 5.26; N, 6.02. Protonation of Dinitrogen Complexes with Sulfuric Acid. To a methanol (5 mL) suspension of dinitrogen complex (ca. 40 μmol) was added H2SO4 (0.05 mL). After 24 h of stirring at room temperature, ammonia was base-distilled and quantified by the indophenol method.19 Hydrazine was also analyzed with p-(dimethylamino)benzaldehyde reagent.20 X-ray Crystallography of 1 and 7. Crystallographic data for complexes 1 and 7 are summarized in Table 2. A paraffin-coated (19) Chaney, A. L.; Marbach, E. P. Clin. Chem. 1962, 8, 130. (20) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1952, 24, 2006.

4746

Organometallics, Vol. 28, No. 16, 2009

crystal was placed on a nylon loop and mounted on a Rigaku RAXIS RAPID imaging plate system. Data were collected at -100 °C under a cold nitrogen stream using graphite-monochromated Mo KR radiation (λ = 0.710 69 A˚). Data were corrected for absorption, Lorentz, and polarization effects. The structures were solved by direct methods21 and expanded using Fourier techniques.22 Anisotropic thermal parameters were introduced for the other non-hydrogen atoms. Hydrogen atoms were generated at calculated positions (dC-H = 0.97 A˚) and treated as riding atoms with isotropic thermal factors. (21) SIR97: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. C.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115. (22) DIRDIF99: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-99 program system, Technical Report of the Crystallography Laboratory; University of Nijmegen, Nijmegen, The Netherlands, 1999. (23) Carruthers, J. R.; Rollett, J. S.; Betteridge, P. W.; Kinna, D.; Pearce, L.; Larsen, A.; Gabe, E. CRYSTALS Issue 11; Chemical Crystallography Laboratory, Oxford, U.K., 1999. (24) CrystalStructure 3.8: Crystal Structure Analysis Package; Rigaku and Rigaku Americas, 2000-2007.

Yuki et al. Full-matrix least-squares refinement on F2 was carried out until the maximum parameter shift/esd converged to less than 0.001.23 All calculations were performed using the Crystal Structure software package.24

Acknowledgment. This work was supported by Grants-in-Aid for Scientific Research for Young Scientists (S) (No. 19675002) and for Scientific Research on Priority Areas (No. 18066003) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Y.N. thanks the Tonen General Sekiyu Foundation for the Promotion of Science, Technology, the Mazda Science and Technology Foundation, and the Iwatani Naoji Foundation. Supporting Information Available: CIF files giving crystallographic data for 1, trans-[W(N2)2(depf)(PPh2Me)2], and 7. This material is available free of charge via the Internet at http:// pubs.acs.org.