Bi- and Trinuclear Complexes of Group 4 Metal and Palladium

Dec 2, 2008 - The early−late heterobinuclear complexes Cp2M(μ-OPPh2)2PdMe2 (M = Ti (1), Zr (2), and Hf (3)) were synthesized by the reaction of PdM...
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Organometallics 2009, 28, 539–546

539

Bi- and Trinuclear Complexes of Group 4 Metal and Palladium Bridged by OPPh2 Groups: Synthesis and High Catalytic Activities in Double Hydrophosphinylation of 1-Octyne Tsutomu Mizuta,* Chihiro Miyaji, Takafumi Katayama, Jun-ichi Ushio, Kazuyuki Kubo, and Katsuhiko Miyoshi Department of Chemistry, Graduate School of Science, Hiroshima UniVersity, Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan ReceiVed August 26, 2008

The early-late heterobinuclear complexes Cp2M(µ-OPPh2)2PdMe2 (M ) Ti (1), Zr (2), and Hf (3)) were synthesized by the reaction of PdMe2(tmeda) (tmeda ) Me2NCH2CH2NMe2) with respective metallocene diphosphinite ligands Cp2M(OPPh2)2 prepared from Cp2MCl2 (M ) Ti, Zr, and Hf) and LiOPPh2. The complexes 1-3 catalyzed the addition (hydrophosphinylation) of HP(O)Ph2 to 1-octyne to give mainly not the single-addition product n-Hex-CHdCHP(O)Ph2 (4a) or n-Hex-C{P(O)Ph2}dCH2 (4b) but the double-addition product n-Hex-CH{P(O)Ph2}CH2P(O)Ph2 (5) at 40 °C in low yields. The yield of 5 was, however, substantially improved to >95% for 2 and 3 when tertiary phosphine PR3 such as PMePh2 was added to the catalytic system. The stoichiometric reaction of the complexes 1-3 with the phosphorus substrate HP(O)Ph2 and PMePh2 afforded in situ the trinuclear complexes H(PMePh2)Pd(µOPPh2)3M(µ-OPPh2)3PdH(PMePh2), which were found to exhibit the high catalytic activities similar to those of their parent complexes 1-3 in the presence of PR3 and were thus proposed to be a practical catalyst. On the basis of the above findings, simple mixtures of mononuclear Cp2MCl2 and PdMe2(tmeda) complexes together with PMePh2 could be used successfully as precatalysts for the double hydrophosphinylation of 1-octyne with HP(O)Ph2 to give satisfactory results comparable to those attained with the preorganized binuclear complexes 2 and 3 with PMePh2 added. Introduction Early-late heterobinuclear complexes have long been recognized to have new and valuable reactivities brought about through the combination of different properties that respective metal centers assume.1,2 Lewis-acidic early-transition-metal and electron-rich latetransition-metal catalysts are both well-established mononuclear systems used widely for conjugate additions and coupling reactions, respectively, in organic synthesis.3,4 Hence, their combinations have been believed to exhibit a promising cooperative catalytic activity, and actually dramatic effects on the reactivity were demonstrated simply by using these two different types of catalysts together.5 If early- and late-transition-metal catalysts are intentionally linked in advance so as to interact cooperatively with a substrate, the resulting preorganized heterobinuclear complex would exhibit a higher efficiency and/or novel function in catalytic reactions. However, a fairly limited number of systems have attained outstanding catalytic activities so far.1,6 A Pd-catalyzed hydrophosphinylation of terminal alkynes was first reported by Tanaka’s group in 1996.7 Since then, it has been intensively investigated by several research groups and has become a useful synthetic method to give monohydrophosphinylated alkene, i.e., a single addition product, under mild reaction conditions.8-10 However, the second addition to give the double-addition product proceeded to a limited extent, because the steric demand of the single-addition product prevents its alkene part from coordinating to the Pd center of the catalyst. It is only under enforcing conditions (above 100 °C) that the double-addition product was obtained in * To whom correspondence should be addressed. Fax: +81-82-424-0729. E-mail: [email protected]. (1) (a) Stephan, D. W. Coord. Chem. ReV. 1989, 95, 41–107. (b) Wheatley, N.; Kalck, P. Chem. ReV. 1999, 99, 3379–3419.

Figure 1. Cooperative interaction of group 4 metal-Pd binuclear complexes with olefin bearing a hard functional group.

a good yield.11 Thus, development of a metal catalyst that promotes the double addition “under mild conditions” is an important subject in view of the delicate tuning of catalyst-substrate interactions. On the other hand, as a part of our ongoing research on heterobinuclear complexes,12 we have recently obtained a bidentate Cp2Ti(OPPh2)2 metallo ligand having two OPPh2 arms as P-donor groups, which allowed us to synthesize a bifunctional Ti-Pd binuclear complex to catalyze the hydrophosphinylation. Since the hard Ti(IV) center of the preorganized binuclear complex is expected to hold firmly the single-addition product bearing a hard OdP group through the concurrent interaction as illustrated in Figure 1, otherwise inaccessible double addition would be promoted. With this expectation in mind, we examined the hydrophosphinylation of 1-octyne with the M-Pd (M ) Ti, Zr, Hf) binuclear complexes as catalysts.

Results and Discussion Preparation of Binuclear Complexes. The binuclear complexes 1a, 2, and 3 were prepared according to eq 1, in which metallocene diphosphinite ligands Cp2M(OPPh2)2 were obtained in advance from Cp2MCl2 (M ) Ti, Zr, Hf) and LiOPPh2, according to a method similar to that reported for the analogue

10.1021/om8008298 CCC: $40.75  2009 American Chemical Society Publication on Web 12/02/2008

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Cp2Zr(CH2PPh2)2, having CH2PPh2 arms.13,14 The formation of these metallo ligands was confirmed by the appearance of 31P NMR signals at 126.7, 114.1, and 112.2 ppm for the Ti, Zr, and Hf ligands, respectively. Out of these, Cp2Ti(OPPh2)2 was found to decompose gradually to give an arm-coupling product Ph2P(O)-PPh2 in addition to a white precipitate, which was probably a polymeric species (Cp2TiO)n. Hence the Ti ligand prepared in situ was immediately used for the subsequent (2) Selected recent examples: (a) Edelmanna, F. T.; Blaurock, S.; Lorenz, V.; Chivers, T. Z. Anorg. Allg. Chem. 2008, 634, 413–415. (b) Arashiba, K.; Iizuka, H.; Matsukawa, S.; Kuwata, S.; Tanabe, Y.; Iwasaki, M.; Ishii, Y. Inorg. Chem. 2008, 47, 4264–4274. (c) Hernandez-Gruel, M. A. F.; Dobrinovitch, I. T.; Lahoz, F. J.; Oro, L. A.; Perez-Torrente, J. J. Organometallics 2007, 26, 6437–6446. (d) Packheiser, R.; Lang, H. Inorg. Chem. Commun. 2007, 10, 580–582. (e) Hernandez-Gruel, M. A. F.; Lahoz, F. J.; Dobrinovich, I. T.; Modrego, F. J.; Oro, L. A.; Perez-Torrente, J. J. Organometallics 2007, 26, 2616–2622. (f) Sisak, A.; Halmos, E. J. Organomet. Chem. 2007, 692, 1817–1824. (g) Kuwabara, J.; Takeuchi, D.; Osakada, K. Chem. Commun. 2006, 36, 3815–3817. (h) Arashiba, K.; Matsukawa, S.; Kuwata, S.; Tanabe, Y.; Iwasaki, M.; Ishii, Y. Organometallics 2006, 25, 560–562. (i) Alvarez-Vergara, M. C.; Casado, M. A.; Martin, M. L.; Lahoz, F. J.; Oro, L. A.; Perez-Torrente, J. J. Organometallics 2005, 24, 5929–5936. (j) Comte, V.; Le Gendre, P.; Richard, P.; Moiese, C. Organometallics 2005, 24, 1439–1444. (k) Cornelissen, C.; Erker, G.; Kehr, G.; Froehlich, R. Organometallics 2005, 24, 214–225. (l) Cornelissen, C.; Erker, G.; Kehr, G.; Fro¨hlich, R, Dalton Trans 2004, 405, 9–4063. (m) Braunstein, P.; Morise, X.; Benard, M.; Rohmer, M.-M.; Welter, R. Chem. Commun 2003, 5, 610–611. (n) Takeuchi, D.; Kuwabara, J.; Osakada, K. Organometallics 2003, 22, 2305. (o) Hernandez-Gruel, M. A. F.; PerezTorrente, J. J.; Ciriano, M. A.; Rivas, A. B.; Lahoz, F. J.; Dobrinovitch, I. T.; Oro, L. A. Organometallics 2003, 22, 1237–1249. (p) Lang, H.; Meichel, E.; Stein, T.; Weber, C.; Kralik, J.; Rheinwald, G.; Pritzkow, H. J. Organomet. Chem. 2002, 664, 150–160. (q) Back, S.; Stein, T.; Kralik, J.; Weber, C.; Rheinwald, G.; Zsolnai, L.; Huttner, G.; Lang, H. J. Organomet. Chem. 2002, 664, 123–129. (r) Kuwata, S.; Nagano, T.; Matsubayashi, A.; Ishii, Y.; Hidai, M. Inorg. Chem. 2002, 41, 4324–4330. (s) Fong, S.-W. A.; Yap, W. T.; Vittal, J. J.; Henderson, W.; Hor, T. S. A. J. Chem. Soc., Dalton Trans. 2002, 8, 1826–1831. (t) Meichel, E.; Stein, T.; Kralik, J.; Rheinwald, G.; Lang, H. J. Organomet. Chem. 2002, 649, 191–198. (u) Kato, H.; Seino, H.; Mizobe, Y.; Hidai, M. J. Chem. Soc., Dalton Trans. 2002, 1494–1499. (v) Wenzel, B.; Loennecke, P.; Stender, M.; Hey-Hawkins, E. J. Chem. Soc., Dalton Trans. 2002, 4, 478–480. (w) Ikada, T.; Mizobe, Y.; Hidai, M. Organometallics 2001, 20, 4441–4444. (x) Lutz, M.; Haukka, M.; Pakkanen, T. A.; Gade, L. H. Organometallics 2001, 20, 2631. (y) Mokuolu, Q. F.; Avent, A. G.; Hitchcock, P. B.; Love, J. B. J. Chem. Soc., Dalton Trans. 2001, 18, 2551–2553. (z) Takayama, C.; Yamaguchi, Y.; Mise, T.; Suzuki, N. J. Chem. Soc., Dalton Trans. 2001, 94, 8–953. (3) For recent reviews, see: (a) Krause, N.; Hoffmann-Roder, A. Synthesis 2001, 2, 171-196. (b) Christoffers, J.; Koripelly, G.; Rosiak, A.; Roessle, M. Synthesis 2007, 9, 1279–1300. (4) (a) Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi, E., Ed.; Wiley-Interscience: New York, 2002; Vols. 1 and 2. (b) Tsuji, J. Palladium Reagents and Catalysts: New PerspectiVes for the 21st Century; John Wiley & Sons: Chichester, 2004. (c) Harrington, P. J. In ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 12, Chapter 8.2, pp 798-903. (5) (a) Lou, S.; Westbrook, J. A.; Schaus, S. E. J. Am. Chem. Soc. 2004, 126, 11440–11441. (b) Poli, G.; Giambastiani, G.; Mordini, A. J. Org. Chem. 1999, 64, 2962–2965. (c) Shen, Q.; Hartwig, J. F. J. Am. Chem. Soc. 2007, 129, 7734–7735. (d) Nakao, Y.; Yada, A.; Ebata, S.; Hiyama, T. J. Am. Chem. Soc. 2007, 129, 2428–2429. (6) Handa, S.; Gnanadesikan, V.; Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc. 2007, 129, 4900–4901. (7) (a) Han, L.-B.; Tanaka, M. J. Am. Chem. Soc. 1996, 118, 1571– 1572. (b) Han, L.-B.; Choi, N.; Tanaka, M. Organometallics 1996, 15, 3259– 3261. (8) (a) Tanaka, M. Top. Curr. Chem. 2004, 232, 25–54. (b) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. ReV. 2004, 104, 3079–3159.

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reaction with PdMe2(tmeda) (tmeda ) Me2NCH2CH2NMe2), which gave Cp2Ti(µ-OPPh2)2PdMe2 (1a) in a moderate yield. On the other hand, the Zr and Hf ligands were stable at ambient temperature to give the corresponding M-Pd (M ) Zr 2 and Hf 3) complexes in better yields. For the Ti-Pd complex, the analogue Cp′2Ti(µ-OPPh2)2PdMe (1b), having C5H4Me (Cp′) in place of Cp, was also prepared in hopes of its increased solubility (vide infra). The characterization of the binuclear complexes was carried out by 31P{1H}, 1H, and 13C{1H} NMR as well as X-ray crystal structure analysis, as follows. The 31 P{1H} NMR signals of 1a, 1b, 2, and 3 were observed at 166.7, 164.1, 151.2, and 149.2 ppm, respectively, which were all at a lower field by ca. 40 ppm than those of the corresponding (9) (a) Alnasleh, B. K.; Sherrill, W. M.; Rubin, M. Org. Lett. 2008, 10, 3231–3234. (b) Dobashi, N.; Fuse, K.; Hoshino, T.; Kanada, J.; Kashiwabara, T.; Kobata, C.; Nune, S. K.; Tanaka, M. Tetrahedron Lett. 2007, 48, 4669–4673. (c) Nune, S. K.; Tanaka, M. Chem. Commun. 2007, 27, 2858– 2860. (d) Stockland, R. A.; Lipman, A. J.; Bawiec, J. A.; Morrison, P. E.; Guzei, I. A.; Findeis, P. M.; Tamblin, J. F. J. Organomet. Chem. 2006, 691, 4042–4053. (e) Van Rooy, S.; Cao, C.; Patrick, B. O.; Lam, A.; Love, J. A. Inorg. Chim. Acta 2006, 359, 2918–2923. (f) Montchamp, J.-L. J. Organomet. Chem. 2005, 690, 2388–2406. (g) Stockland, R. A. J.; Taylor, R. I.; Thompson, L. E.; Patel, P. B. Org. Lett. 2005, 7, 851–853. (h) Deprele, S.; Montchamp, J.-L. J. Am. Chem. Soc. 2002, 124, 9386–9387. (i) Deprele, S.; Montchamp, J.-L. J. Am. Chem. Soc. 2002, 124, 9386–9387. (j) Levine, A. M.; Stockland, R. A. J.; Clark, R.; Guzei, I. Organometallics 2002, 21, 3278–3284. (k) Zhao, C.-Q.; Han, L.-B.; Tanaka, M. Organometallics 2000, 19, 4196–4198. (l) Han, L.-B.; Hua, R.; Tanaka, M. Angew. Chem., Int. Ed. 1998, 37, 94–96. (10) (a) Kondoh, A.; Yorimitsu, H.; Oshima, K. Bull. Chem. Soc. Jpn. 2008, 81, 502–505. (b) Niu, M.; Fu, H.; Jiang, Y.; Zhao, Y. Chem. Commun. 2007, 3, 272–274. (c) Ribiere, P.; Bravo-Altamirano, K.; Antczak, M. I.; Hawkins, J. D.; Montchamp, J.-L. J. Org. Chem. 2005, 70, 4064–4072. (d) Han, L.-B.; Zhao, C.-Q.; Onozawa, S.; Goto, M.; Tanaka, M. J. Am. Chem. Soc. 2002, 124, 3842–3843. (e) Han, L.-B.; Zhao, C.-Q.; Tanaka, M. J. Org. Chem. 2001, 66, 5929–5932. (f) Zhao, C.-Q.; Han, L.-B.; Goto, M.; Tanaka, M. Angew. Chem., Int. Ed. 2001, 40, 1929–1932. (g) Reichwein, J. F.; Patel, M. C.; Pagenkopf, B. L. Org. Lett. 2001, 3, 4303–4306. (11) (a) Han, L.-B.; Ono, Y.; Shimada, S. J. Am. Chem. Soc. 2008, 130, 2752–2753. (b) Dobashi, N.; Fuse, K.; Hoshino, T.; Kanada, J.; Kashiwabara, T.; Kobata, C.; Nune, S. K.; Tanaka, M. Tetrahedron Lett. 2007, 48, 4669–4673. (c) Stone, J. J.; Stockland, R. A.; Reyes, J. M.; Kovach, J.; Goodman, C. C.; Tillman, E. S. J. Mol. Catal. A, Chem. 2005, 226, 11–21. (d) Allen, A. J.; Ma, L.; Lin, W. Tetrahedron Lett. 2002, 43, 3707–3710. (e) Allen, A. J.; Manke, D. R.; Lin, W. Tetrahedron Lett. 2000, 41, 151– 154. (12) (a) Mizuta, T.; Nakazono, T.; Miyoshi, K. Angew. Chem., Int. Ed. 2002, 41, 3897–3898. (b) Imamura, Y.; Kubo, K.; Mizuta, T.; Miyoshi, K. Organometallics 2006, 25, 2301–2307. (c) Mizuta, T.; Iwakuni, Y.; Nakazono, T.; Kubo, K.; Miyoshi, K. J. Organomet. Chem. 2007, 692, 184– 193. (d) Kubo, K.; Akimoto, T.; Mizuta, T.; Miyoshi, K. Chem. Lett. 2008, 37, 166–167. (13) (a) Schore, N. E.; Hope, H. J. Am. Chem. Soc. 1980, 102, 4251– 4253. (b) Schore, N. E.; Young, S. J.; Olmstead, M.; Hofmann, P. Organometallics 1983, 2, 1769–1780. (c) Etienne, M.; Choukroun, R.; Gervais, D. J. Chem. Soc., Dalton Trans. 1984, 5, 915–917. (d) Choukroun, R.; Gervais, D.; Rifai, C. E. J. Organomet. Chem. 1989, 368, C11–C14. (e) Cuenca, T.; Flores, J. C.; Royo, P.; Larsonneur, A. M.; Choukroun, R.; Dahan, F. Organometallics 1992, 11, 777–780. (f) Tueting, D. R.; Olmstead, M. M.; Schore, N. E. 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Bi- and Trinuclear Complexes of Group 4 Metal and Pd

Organometallics, Vol. 28, No. 2, 2009 541

the corresponding phosphine (PRAr2).17 In addition, the P-Pd-P bite angles of the metallo chelates forming six-membered rings are 97.15(8)°, 98.44(4)°, and 98.28(4)° for 1b, 2, and 3, respectively, which are somewhat greater than 93.18(9)° of dppp in [PdMe2(dppp)], having a similar six-membered chelate ring. The wider bite angles adopted are attributable both to longer M-O bonds (1.93-1.99 Å) in 1b, 2, and 3 than C-C bonds in dppp and to the considerably wide P-O-M angles (140.7-145.3°), leading to favorable π-donation from O to M. Catalytic Double-Hydrophosphinylation Reaction. The M-Pd complexes 1-3 were used as catalysts for hydrophosphinylation (eq 2) of 1-octyne with HP(O)Ph2. The results obtained are summarized in Table 2. In these reactions, the complexes 2 (Zr) and 3 (Hf) were dissolved completely in the reaction mixture, whereas the Ti complexes 1a and1b had to

Figure 2. Molecular structure of Cp′2Ti(µ-OPPh2)2PdMe2 (1b) with thermal ellipsoids given at the 50% probability level.

Figure 3. Molecular structure of Cp2Zr(µ-OPPh2)2PdMe2 (2) with thermal ellipsoids given at the 50% probability level. Note that only one of two crystallographically independent molecules per asymmetric unit is shown.

free ligands. The Me groups on the Pd centers of all the complexes showed multiplet 1H NMR signals at ca. 0.9 ppm and double-doublet 13C{1H} NMR signals coupled with both cis and trans phosphorus nuclei. The molecular structures determined by X-ray analysis are shown in Figures 2-4 for 1b, 2, and 3, respectively, where each metallocene diphosphinite ligand coordinates to a PdMe2 fragment to form a standard square-planar geometry. The selected geometric parameters are summarized in Table 1. The average Pd-P bond distances are 2.287(2), 2.283(1), and 2.282(1) Å for 1b, 2, and 3, respectively, which are slightly smaller than those of the corresponding [PdMe2L2]-type (L ) PRPh2) complexes, e.g., 2.324(1) Å in cis-[PdMe2(PMePh2)2] and 2.304(3) Å in [PdMe2(dppp)] (dppp ) 1,3-bis(diphenylphosphino)propane).15,16 The shorter Pd-P bonds observed for 1b, 2, and 3 are in line with the observation that the usual phosphinite (P(OR)Ar2) forms a shorter Pd-P bond than does

be used as a suspension owing to their low solubilities. After the reaction mixtures were kept at 40 °C for 20 h, the Ti (1b), Zr (2), and Hf (3) complexes all gave the double-addition product 5 as a main product, with the yield increasing in the order Hf > Zr > Ti (entries 2-4). The poorest activity of 1a (entry 1) is probably due to its much lower solubility. The same holds more or less for 1b. In each reaction, 1-octyne was used in excess, since use of its stoichiometric amount lowered the reaction rate, resulting in the decreased yield. All these complexes work rather poorly under the present mild conditions; the yields in entries 2-4 are at an unsatisfactory level. However, we fortunately found that addition of tertiary phosphine such as PMePh2 brought about much better results (entries 5, 7, and 11). For the Zr (2) and Hf (3) complexes, in particular, the yields of 5 as well as the required reaction times were significantly improved; the yields were >95% for 1 h at 40 °C. Similar effects were also observed when related phosphines were used as an additive (entries 6-14).18 In this way, the present double hydrophosphinylation of 1-octyne with HP(O)Ph2 became highly efficient by using the preorganized heterobinuclear M-Pd complexes 1-3 with tertiary phosphines added. The role of the phosphine added will be mentioned later. Catalytically Active Trinuclear Complex. To obtain information about the catalytically active species promoting the present double addition, the reaction was monitored with 31 P{1H} NMR. Complex 1a was selected, because its catalytic reaction with added PMePh2 proceeded slowly, and thus it was easy to follow. After 10 h, new transient signals different from those of the substrate and the final products were observed at 8.0 and 112.9 ppm as a mutually coupled quartet and doublet (JP-P ) 114 Hz), respectively. These peculiar signals were observed with much higher intensities when a stoichiometric amount of 1a was treated similarly with HP(O)Ph2 and PMePh2 (eq 3). The product of this stoichiometric reaction was isolated

and characterized by X-ray analysis to be the Pd-Ti-Pd trinuclear complex 6, shown in Figure 5, in which the six OPPh2

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Table 1. Selected Bond Distances (Å) and Bond Angles (deg) 2 Pd-C1 Pd-C2 Pd-P1 Pd-P2 M-O1 M-O2 P1-O1 P2-O2 C1-Pd-C2 P1-Pd-P2 O1-M-O2 O1-P1-Pd O2-P2-Pd P1-O1-M P2-O2-M

molecule 1

molecule 2

molecule 1

molecule 2

2.13(5) 2.169(6) 2.2955(19) 2.278(2) 1.927(5) 1.925(5) 1.573(5) 1.574(5) 85.2(14) 97.15(8) 91.6(2) 117.4(2) 119.1(2) 143.2(3) 143.8(3)

2.130(5) 2.126(5) 2.2895(12) 2.2718(13) 1.987(3) 2.005(3) 1.596(3) 1.589(3) 83.4(2) 98.10(4) 90.36(14) 119.40(14) 118.73(14) 145.3(2) 145.2(2)

2.124(4) 2.135(4) 2.2802(10) 2.2900(10) 2.012(3) 2.001(3) 1.592(3) 1.586(3) 84.69(18) 98.78(4) 90.90(11) 117.98(11) 119.45(11) 141.05(17) 142.54(18)

2.114(4) 2.117(4) 2.2867(10) 2.2733(10) 1.975(3) 1.982(3) 1.594(3) 1.596(3) 83.94(18) 97.95(4) 90.95(11) 119.47(11) 118.68(11) 144.98(18) 145.05(17)

2.114(3) 2.111(4) 2.2793(8) 2.2893(9) 2.002(2) 1.988(2) 1.590(2) 1.590(3) 85.33(16) 98.61(3) 91.66(10) 118.07(9) 119.81(10) 140.70(15) 141.71(15)

Table 2. Hydrophosphinylation of 1-Octyne with HP(O)Ph2a yield (%)b entry

catalyst

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

1a 1b 2 3 1b 2 2 2 3 3 3 3 3 3 [Ti] + [Pd]d [Zr] + [Pd]d [Hf] + [Pd]d

3

1b

phosphine (mol %)

time (h)

5 (PMePh2) 5 (PMe2Ph) 5 (PMePh2) 5 (PPh3) 5 (PMe3) 5 (PMe2Ph) 5 (PMePh2) 5 (PPh3) 2.5 (PMePh2) 10 (PMePh2) 5 (PMePh2) 5 (PMePh2) 5 (PMePh2)

20 20 20 20 20 2 1 9 5 1 1 5 2 1 20 3 1

4c

7 4 2 3 3 2 2 3 3 7 4

5 trace 7 27 36 19 >99 95 97 97 99 97 98 97 97 76 88 94

a Conditions: toluene solution of HP(O)Ph2 (0.5 M) and 1-octyne (0.5 M), 5 mol % catalyst, 40 °C. b Yields are based on intensities of 31P NMR signals of the crude reaction mixture. c Total yield of 4a and 4b. d [Ti] ) Cp2TiCl2, [Zr] ) Cp2ZrCl2, [Hf] ) Cp2HfCl2, [Pd] ) PdMe2(tmeda).

arms bridge the Ti center with the two terminal Pd atoms. Each Pd center has the added tertiary phosphine PMePh2 coordinated, which is responsible for 31P{1H} NMR signals observed at 8.0 ppm. The remaining signal at 112.9 ppm is thus assigned to the bridging OPPh2 ligands. Each Pd center has, in addition to these four phosphorus groups, a hydride ligand, which was found on a difference Fourier map and was refined isotropically, to form a pentacoordinate [Pd(H)P4]+-type complex,19 which is characterized by X-ray analysis for the first time. Selected geometric parameters for 6 are given in Table 3. The Pd-H bond lengths of Pd1 and Pd2 centers are 1.50(5) and 1.67(8) Å, respectively. Though their standard deviations are large, they are close to 1.58 Å, estimated by a QM/MM calculation for [PdH(dppe)2]+ (dppe ) 1,2-bis(diphenylphosphino)ethane) having a similar [Pd(H)P4]+ coordination (15) Ledford, J.; Shultz, C. S.; Gates, D. P.; White, P. S.; DeSimone, J. M.; Brookhart, M. Organometallics 2001, 20, 5266–5276. (16) Wisner, J. M.; Bartczak, T. J.; Ibers, J. A. Organometallics 1986, 5, 2044–2050. (17) Trzeciak, A. M.; Bartosz-Bechowski, H.; Ciunik, Z.; Niesyty, K.; Ziolkowski, J. J. Can. J. Chem. 2001, 79, 752–759. (18) We used PMePh2 mainly, because liquid phosphine (usually a few mg) was easy to measure out using a microsyringe in a glovebox.

Table 3. Selected Bond Distances (Å) and Bond Angles (deg) for 6 Pd1-P1 Pd1-P2 Pd1-P3 Pd1-P4 Pd1-H1 Ti1-O1 Ti1-O2 Ti1-O3 P1-O1 P2-O2 P3-O3 P1-Pd1-P2 P1-Pd1-P3 P1-Pd1-P4 P2-Pd1-P3 P2-Pd1-P4 P3-Pd1-P4 P1-Pd1-H1 O1-Ti1-O6 O3-Ti1-O5

2.3309(11) 2.3715(11) 2.4594(12) 2.3055(12) 1.50(5) 1.960(3) 1.966(3) 1.924(3) 1.555(3) 1.568(3) 1.576(3) 87.32(4) 92.60(4) 101.90(4) 88.69(4) 142.14(5) 126.81(4) 178(2) 177.47(13) 176.95(13)

Pd2-P5 Pd2-P6 Pd2-P7 Pd2-P8 Pd2-H2 Ti1-O4 Ti1-O5 Ti1-O6 P5-O4 P6-O5 P7-O6 P5-Pd2-P6 P5-Pd2-P7 P5-Pd2-P8 P6-Pd2-P7 P6-Pd2-P8 P7-Pd2-P8 P5-Pd2-H2 O2-Ti1-O4

2.3434(12) 2.3463(12) 2.5031(13) 2.3176(13) 1.67(8) 1.949(3) 1.961(3) 1.919(3) 1.564(3) 1.564(3) 1.582(3) 90.53(4) 91.62(4) 102.28(5) 87.70(4) 142.05(5) 126.81(5) 173(2) 176.64(13)

sphere.19g Each of the hydride ligands H1 and H2 occupies the position trans to one of the three OPPh2 groups with the P1-Pd1-H1 and P5-Pd2-H2 angles of 178(2)° and 173(2)° close to 180°, respectively. Other noteworthy bond angles are P2-Pd1-P4 and P6-Pd2-P8, which are 142.14(5)° and 142.14(5)°, respectively. Since they are in an intermediate range between 120° for an equatorial bond angle of a trigonal bipyramid and 180° for a trans bond angle of a square pyramid, the geometry around each Pd center can be understood to be an intermediate between a trigonal bipyramid with the hydride in an axial position and a square pyramid with P3 or P7 in an apical position for the Pd1 or Pd2 center, respectively. For the Ti(IV) center, its geometry is an almost ideal octahedron with the three trans O-Ti-O angles all close to 180° but the Ti-O3 and Ti-O6 bonds somewhat shorter than other Ti-O bonds. For 6, several tautomeric structures are conceivable, but only tautomers having cationic or neutral Pd centers are depicted in (19) (a) Nimlos, M. R.; Chang, C. H.; Curtis, C. J.; Miedaner, A.; Pilath, H. M.; DuBois, D. L. Organometallics 2008, 27, 2715–2722. (b) Qi, X.-J.; Fu, Y.; Liu, L.; Guo, Q.-X. Organometallics 2007, 26, 4197–4203. (c) Kovacs, G.; Papai, I. Organometallics 2006, 25, 820–825. (d) Aresta, M.; Dibenedetto, A.; Papai, I.; Schubert, G.; MacChioni, A.; Zuccaccia, D. Chem.-Eur. J. 2004, 10, 3708–3716. (e) Raebiger, J. W.; Miedaner, A.; Curtis, C. J.; Miller, S. M.; Anderson, O. P.; DuBois, D. L. J. Am. Chem. Soc. 2004, 126, 5502–5514. (f) Curtis, C. J.; Miedaner, A.; Raebiger, J. W.; DuBois, D. L. Organometallics 2004, 23, 511–516. (g) Aresta, M.; Dibenedetto, A.; Amodio, E.; Papai, I.; Schubert, G. Inorg. Chem. 2002, 41, 6550–6552. (h) Aresta, M.; Quaranta, E. J. Organomet. Chem. 2002, 662, 112–119. (i) Miedaner, A.; DuBois, D. L.; Curtis, C. J.; Haltiwanger, R. C. Organometallics 1993, 12, 299–303. (j) Brueggeller, P. Inorg. Chem. 1990, 29, 1742–1750.

Bi- and Trinuclear Complexes of Group 4 Metal and Pd

Organometallics, Vol. 28, No. 2, 2009 543

Figure 6. Two tautomeric forms of the trinuclear complex 6, where dative bonds are indicated by arrows: a zwitterion form (left 6a) and a neutral form with two OdPPh2 groups (right 6b).

Figure 4. Molecular structure of Cp2Hf(µ-OPPh2)2PdMe2 (3) with thermal ellipsoids given at the 50% probability level. Note that only one of two crystallographically independent molecules per asymmetric unit is shown.

Figure 5. Molecular structure of (PMePh2)(H)Pd(µ-OPPh2)3Ti(µOPPh2)3Pd(H)(PMePh2) (6) with thermal ellipsoids given at the 50% probability level. Hydrogen atoms except those on Pd centers are omitted for clarity.

Figure 6, because a number of cationic and neutral fivecoordinate Pd(II) complexes are known to be thermodynamically stable, while only a few anionic five-coordinate Pd(II) complexes have been described so far.20 In Figure 6, 6a (left) is a zwitterion form in which the six -O-PPh2 groups are all monoanionic trivalent phosphorus ligands. Each half of them bridges the Ti(IV) with each Pd(II) center triply to leave the dianionic Ti and monocationic Pd centers to which each -O-PPh2 coordinates as an anionic O- and neutral P-donor, respectively. The other tautomer 6b (right) is different from 6a in that two of the six groups adopt a pentavalent form, OdPPh2-, which coordinates to the Ti center as a neutral O-donor, but as an anionic P-donor to the Pd center, leading overall to the neutral Ti and Pd centers. If the trivalent OPPh2 group bridges the Ti and Pd centers, the resulting three bonds in the Ti-O-PfPd sequence should be shorter-longer-longer, respectively, than the corresponding three bonds in the TirOdP–Pd sequence formed by the pentavalent form, because a covalent bond formed by an anionic (20) (a) Vendilo, A. G.; Dyatlova, N. M.; Fridman, A. Y. Zh. Neorg. Khim. 1987, 32, 3006–3010. (b) Parthasarathy, V.; Joergensen, C. K. Chimia 1975, 29, 210–212. (c) Gonzalez Garcia, S.; Gonzalez Vilchez, F. An. Quim. 1970, 66, 875–890.

O- or P-donor is generally shorter than a dative bond formed by the corresponding neutral donor and also because an O-P single bond is no doubt longer than an OdP double bond. Detailed comparison of the bond lengths given in Table 3 shows that the three bonds in the Ti-O3-P3-Pd1 and Ti-O6-P7-Pd2 sequences are somewhat but definitely shorter-longer-longer, respectively,thanthoseintheotherfoursequencesTi-O1-P1-Pd1, Ti-O2-P2-Pd1, Ti-O4-P5-Pd2, and Ti-O5-P6-Pd2, suggesting that the former two sequences are comprised of the trivalent form. This inference is supported by a close similarity of their Ti-O and O-P distances to those of the metallo ligand in 1b, where the OPPh2 groups are apparently the trivalent forms (Figure 2 and Table 1), and it is reasonable that the weakly coordinating neutral P3 and P7 atoms occupy the equatorial (trigonal bipyramid) or apical (square pyramid) position around the d8 Pd(II) center. The remaining four sequences have the opposite bond-length trend to the above, indicating appreciable contribution of the pentavalent form to these four sequences. If these four OPPh groups all adopt the pentavalent form OdPPh2-, each fivecoordinate Pd center would carry an anionic charge (and the Ti center a dicationic one), which is unlikely as mentioned above. Therefore, only two of the four groups are depicted as the pentavalent form in 6b (Figure 6). However, which group adopts the pentavalent form cannot be settled, because the four groups actually have comparable bond lengths owing to a possible conjugation between the trivalent and pentavalent forms, but the pentavalent form obviously contributes to the opposite trend observed. In short, the tautomer 6b plays an important role in the present bridging system. On the other hand, the three OPPh2 groups on each Pd center were observed as equivalent in 31P NMR (vide supra), indicating a dynamic exchange between PMePh2 and hydride in solution through a turnstyle rotation or pseudorotation, that is, an accompanying complete averaging of the six Ti-O-P-Pd sequences. In accordance with the exchange, the hydride signal in the 1H NMR was observed at -8.50 ppm as a doublet of quartets due to couplings with phosphorus centers of both PMePh2 and three now equivalent OPPh2 groups. In the course of the reaction in eq 3, the Ti center has lost Cp rings as CpH, which was detected when the reaction was monitored with 1H NMR. Marks et al. reported similar liberation of Cp from Cp2TiCl2 under acidic conditions.21 Since HP(O)Ph2 added in eq 3 is known to isomerize partially to its tautomer P(OH)Ph2, the proton dissociated from this phosphinous acid might attack Cp- ligands on Ti to liberate CpH. The vacant sites thus left were probably occupied by OPPh2-. In addition, formation of the trinuclear complex implies disproportionation of the starting 1:1 Ti-Pd complex having taken place, but the fate of the remaining half of the Ti species is not known at present. (21) Toney, J. H.; Marks, T. J. J. Am. Chem. Soc. 1985, 107, 947–953.

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When the Zr (or Hf)-Pd complex in place of the Ti-Pd complex 1a was treated similarly (eq 3), the corresponding Zr or Hf trinuclear complex 7 or 8, respectively, was also formed in situ, as confirmed by the characteristic doublet and quartet observed in the 31P{1H} NMR as for 6. These reaction mixtures were found to have a high catalytic activity comparable to those of the starting Zr-Pd and Hf-Pd binuclear complexes with PMePh2 as an additive. These results suggest that the preorganized binuclear complexes must have been converted to their corresponding trinuclear complexes with the aid of the added tertiary phosphine in the reaction mixture so as to exhibit a practical catalytic activity. Since each of the trinuclear complexes in eq 3 was obtained from the binuclear M-Pd complex prepared in advance according to eq 1, the direct preparation of the trinuclear complex was tried using Cp2MCl2 (M ) Zr, Hf) and PdMe2(tmeda) as the starting materials. The reaction of a 2:2 equiv mixture of these two metal complexes with HP(O)Ph2 (10 equiv) and PMePh2 (2 equiv) gave successfully the corresponding trinuclear complex 7 or 8 as a major product after initial formation of the binuclear complex 2 or 3, respectively (eq 4). These results prompted us to examine the double addition using a simple mixture of Cp2MCl2 (M ) Zr, Hf) and

Figure 7. Catalytic cycle proposed for the double hydrophosphynation catalyzed by trinuclear complexes 7 and 8. [M] denotes the remaining half of the starting trinuclear complex, as shown at the bottom of the figure, and all Ph groups of the complexes are eliminated for clarity.

PdMe2(tmeda) as the metal sources. The results (entries 16 and 17 in Table 2) demonstrate that satisfactory yields are obtained with the combination of these non-elaborately designed earlyand late-metal complexes. In addition, the yield obtained with Cp2TiCl2 (entry 15) is also improved substantially compared to that given in entry 5, where the preorganized Ti-Pd catalyst 1b was used. A homogeneous reaction mixture attained for the former case is probably responsible for the better yield, while a limited amount of 1b was dissolved for the latter case. In this way, we need not procure either the preorganized binuclear complexes or the trinuclear complexes prepared therefrom. Reaction Mechanism of Double Hydrophosphinylation. It is worth noting that the trinuclear complexes 6-8 possess structural similarities to the mononuclear Pd complex 9, which has been reported as an active catalyst for the single-addition

reaction;7b complex 9 has one hydride, one phosphine ligand, and two OPPh2 groups linked with a proton. These structural features are common also to the trinuclear complexes 6-8, though the proton in the chelate-like part of 9 is replaced with the group 4 metals and the third OPPh2 group coordinates additionally to the Pd center to form the five-coordinate structure. The hydrophosphinylation catalyzed by complex 9 has been reported to proceed via insertion of terminal alkyne

to the Pd-H bond and succeeding reductive elimination of the vinyl group with the OdPPh2 moiety, followed by regeneration of 9 by oxidative addition of HP(O)Ph2 to the Pd(0) center.8 Judging from the common structural features between 9 and the present catalysts, it is reasonable to assume a similar mechanism in the present catalysis. Actually, a preliminary cross experiment using the Zr-Pd binuclear complex 2 and HP(O)(pTol)2 as a substrate gave the double-addition products having not only the P(O)(p-Tol)2 but also the P(O)Ph2 groups. Therefore, it is highly plausible that the OPPh2 bridges incorporated into the catalyst are transferred to 1-octyne to give the double-addition product. In addition, when these reactions were monitored with 31P{1H} NMR, consumption of HP(O)Ph2 was observed with the growth of the two doublets due to the double-addition product 5. Notably, even at the early stage of the reaction, the signals assigned to the single addition products 4a and 4b were much smaller in intensity. This reveals that both 4a and 4b once formed undergo promptly the second addition reaction to give 5, indicating that the present catalysts add HP(O)Ph2 preferentially to phosphinoalkene 4 rather than to intact 1-octyne, probably through the cooperative interaction assumed in Figure 1. Details of the reaction mechanism are not clear at this stage, but a tentative one is given in Figure 7. The reaction starts from the top left of the figure, where one of the three OPPh2 groups is depicted as the pentavalent form (OdP) as in 6b (Figure 6), since the OPPh2 group transferred to 1-octyne is eventually the pentavalent form. Before the insertion of alkyne, one of the phosphorus ligands, particularly L in the figure, dissociates from the Pd center to incorporate alkyne onto the Pd center. After a usual insertion followed by a reductive elimination, the monophosphinoalkene 4 formed does not leave the catalyst but is firmly held on both the Zr(IV) (or Hf(IV)) and Pd(0) centers via OdP and alkene groups, respectively, as shown in the middle of the right side. Even if partial dissociation

Bi- and Trinuclear Complexes of Group 4 Metal and Pd

of 4 takes place here, dissociated 4 recoordinates to the catalyst much more readily than 1-octyne present in excess coordinates to it, probably because the strong attractive interaction between the group 4 metal and the OdP group of 4 prevails over the steric repulsion between the catalyst and the bulky P(O)Ph2 group of 4. Then, the subsequent oxidative addition of HP(O)Ph2 followed by insertion leads to the second addition, to liberate the double-addition product by reductive elimination. Finally, the second oxidative addition of HP(O)Ph2 regenerates the starting catalyst. In conclusion, the double addition of HP(O)Ph2 to 1-octyne was accomplished under mild conditions using the Zr (or Hf)-Pd heterobinuclear system, while mononuclear Pd complexes such as 9 reported so far gave the double-addition product only under enforcing conditions. The present reaction is catalyzed by the trinuclear Zr (or Hf)-Pd2 complexes formed in situ through the reaction of the preorganized Zr (or Hf)-Pd binuclear complexes with HP(O)Ph2 and PMePh2 or through the direct self-assembling of the simple Cp2MCl2 (M ) Zr, Hf) and PdMe2(tmeda) complexes in the presence of HP(O)Ph2 and PMePh2. Concurrent interactions of the group 4 metal and Pd centers with the OdP and alkene groups, respectively, are proposed to play a key role in the catalytic cycle, which effects the unusually facile double hydrophosphinylation of 1-octyne with HP(O)Ph2.

Experimental Section General Remarks. All reactions were carried out under an atmosphere of dry nitrogen using Schlenk tube techniques or an MBraun Labmaster 130 glovebox. All solvents were dried and distilled from sodium (for hexane) or sodium/benzophenone (for benzene, ether, THF, and toluene). These purified solvents were stored under an N2 atmosphere. Cp2TiCl2 was purified by vacuum sublimation. Cp2HfCl2,22 HP(O)Ph2,23 PMe3,24 PMe2Ph,25 and PMePh226 were prepared according to literature methods. Other reagents were used as received. NMR spectra were recorded on JEOL LA-300 and LA-500 spectrometers. 1H and 13C NMR chemical shifts were reported relative to Me4Si and were determined by reference to the residual solvent peaks. 31P NMR chemical shifts were reported relative to H3PO4 (85%) used as an external reference. Elemental analyses were performed with a Perkin-Elmer 2400CHN elemental analyzer. Preparation of Cp2Ti(µ-OPPh2)2PdMe2, 1a. To a THF (10 mL) solution of HP(O)Ph2 (560 mg, 2.78 mmol) in a Schlenk tube was added BuLi (1.60 M in hexane; 1.74 mL, 2.78 mmol) at -78 °C. The yellow solution was stirred for 4 h with warming gradually to room temperature. The LiOPPh2 solution thus obtained was added to a THF (10 mL) solution of Cp2TiCl2 (346 mg, 1.39 mmol). After stirring for 5 min, the formation of Cp2Ti(OPPh2)2 was confirmed with a 31P{1H} NMR spectrum, and then PdMe2(tmeda) (351 mg, 1.39 mmol) dissolved in THF (10 mL) was added dropwise to the solution containing Cp2Ti(OPPh2)2. After the solution was stirred for 2 h, THF was removed under reduced pressure, and the residue was dried in vacuo. This residue was extracted repeatedly with benzene (10 mL × 5), until the benzene solution became colorless. After the extract obtained was filtered, benzene was removed under reduced pressure, and then the residue was washed with ether (5 (22) Druce, P. M.; Kingston, B. M.; Lappert, M. F.; Spalding, T. R.; Srivastava, R. C. J. Chem. Soc., A 1969, 2106. (23) Hunt, B. B.; Saunders, B. C. J. Chem. Soc. 1957, 2413–14. (24) Luetkens, M. L.; Sattelberger, A. P.; Murray, H. H.; Basil, J. D.; Fackler, J. P. Inorg. Synth. 1989, 26, 7–12. (25) Benn, F. R.; Briggs, J. C.; McAuliffe, C. A. J. Chem. Soc., Dalton Trans. 1984, 293–295. (26) Mikolajczyk, M.; Graczyk, P. P. J. Org. Chem. 1995, 60, 5190– 208.

Organometallics, Vol. 28, No. 2, 2009 545 mL × 6) and dried in vacuo to give a reddish-orange powder of 1a. Yield: 580 mg (58%). 1H NMR (300.5 MHz, C6D6): δ 0.96 (m, 6H, Pd-CH3), 5.67 (s, 10H, Cp), 7.15-7.25 (m, 12H, Ph), 8.07 (dd, 8H, Ph). 13C{1H} NMR (75.6 MHz, C6D6): δ 117.2 (s, Cp), 130.3 (s, Ph), 133.6 (t, JC-P ) 7.2 Hz, Ph). Owing to the poor solubility of the sample, other carbons did not have signal intensities enough to be observed. 31P{1H} NMR (121.7 MHz, C6D6): δ 166.7 (s). The elemental analysis of 1a did not give satisfactory and reproducible results, because its low solubility precluded complete purification. Preparation of (C5H4Me)2Ti(µ-OPPh2)2PdMe2, 1b. Preparation of 1b was carried out in a manner similar to that described for 1a starting with Cp′2TiCl2 (300 mg, 1.08 mmol), HP(O)Ph2 (438 mg, 2.17 mmol), BuLi (1.60 M in hexane; 1.30 mL, 2.17 mmol), and PdMe2(tmeda) (274 mg, 1.08 mmol). An orange powder of 1b (469 mg, 58%) was obtained. 1H NMR (300.5 MHz, C6D6): δ 0.92 (m, 6H, Pd-CH3), 1.49 (s, 6H, C5H4-CH3), 5.55-5.64 (m, 8H, C5H4), 7.10-7.21 (m, 12H, Ph), 8.10 (dd, 8H, Ph). 13C{1H} NMR (75.6 MHz, C6D6): δ 6.2 (dd, JC-P ) 14 Hz, JC-P ) 121 Hz, Pd-CH3), 15.8 (s, C5H4-CH3), 115.9 (s, Cp), 119.1 (s, Cp), 128.5 (m, Ph), 130.1 (s, Ph), 133.9 (m, Ph), 142.6 (m, ipso-Ph). 31P{1H} NMR (121.7 MHz, C6D6): δ 164.1 (s). Anal. Calcd for C38H40O2P2PdTi · 2/ 3LiCl: C, 59.03; H, 5.21. Found: C, 58.73; H, 5.03. Preparation of Cp2Zr(µ-OPPh2)2PdMe2, 2. Preparation of 2 was carried out in a manner similar to that described for 1a starting with Cp2ZrCl2 (219 mg, 0.75 mmol), HP(O)Ph2 (303 mg, 1.50 mmol), BuLi (1.6 M in hexane; 0.93 mL, 1.50 mmol), and PdMe2(tmeda) (189 mg, 0.75 mmol). A pale pink powder of 2 (423 mg, 74%) was obtained. 1H NMR (300.5 MHz, C6D6): δ 0.87 (m, 6H, Pd-CH3), 5.67 (s, 10H, Cp), 7.11-7.21 (m, 12H, Ph), 7.98 (dd, 8H, Ph). 13C{1H} NMR (75.6 MHz, C6D6): δ 6.3 (dd, JC-P ) 16 Hz, JC-P ) 122 Hz, Pd-CH3), 114.4 (s, Cp), 128.5 (m, Ph), 130.2 (s, Ph), 133.4 (m, Ph), 142.2 (m, ipso-Ph). 31P{1H} NMR (121.7 MHz, C6D6): δ 151.2 (s). Anal. Calcd for C36H36O2P2PdZr · 2/ 3LiCl: C, 54.83; H, 4.60. Found: C, 55.06; H, 4.39. Preparation of Cp2Hf(µ-OPPh2)2PdMe2, 3. Preparation of 3 was carried out in a manner similar to that described for 1a starting with Cp2HfCl2 (300 mg, 0.79 mmol), HP(O)Ph2 (320 mg, 1.58 mmol), BuLi (1.6 M in hexane; 0.99 mL, 1.58 mmol), and PdMe2(tmeda) (200 mg, 0.79 mmol). A pale pink powder of 3 (447 mg, 67%) was obtained. 1H NMR (300.5 MHz, C6D6): δ 0.86 (m, 6H, Pd-CH3), 5.63 (s, 10H, Cp), 7.11-7.21 (m, 12H, Ph), 7.99 (dd, 8H, Ph). 13C{1H} NMR (75.6 MHz, C6D6): δ 6.4 (dd, JC-P ) 16 Hz, JC-P ) 123 Hz, Pd-CH3), 113.2 (s, Cp), 128.5 (m, Ph), 130.3 (s, Ph), 133.4 (m, Ph), 142.2 (m, ipso-Ph). 31P{1H} NMR (121.7 MHz, C6D6): δ 149.2 (s). Anal. Calcd for C36H36HfO2P2Pd: C, 51.02; H, 4.28. Found: C, 50.80; H, 4.00. Preparation and Isolation of the Pd-Ti-Pd Complex 6 from 1a. The complex 1a (200 mg, 0.28 mmol), HP(O)Ph2 (112 mg, 0.56 mmol), PMePh2 (52 µL, 0.28 mmol), and toluene (10 mL) were put in a vial. The suspension was stirred for 17 h at 40 °C. The dark red reaction mixture was filtered to remove a small amount of the remaining Ti-Pd complex, then the solvent was removed under reduced pressure. The residue was washed with hexane (5 mL × 3) and ether (5 mL × 10) and dried in vacuo to give (PMePh2)(H)Pd(µ-OPPh2)3Ti(µ-OPPh2)3Pd(H)(PMePh2) (6). Yield: 123 mg (49%). 1H NMR (300.5 MHz, C6D6): δ -8.50 (dq, 2H, 2 JH-P ) 9.7, 76.3 Hz), 1.45 (d, 6H, PMe), 6.91-7.85 (m, 80H, Ph). 31P{1H} NMR (121.7 MHz, C6D6): δ 8.0 (q, 2P, 2JP-P ) 114 Hz, PMePh2), 112.7 (d, 6P, 2JP-P ) 114 Hz, OPPh2). Anal. Calcd for C98H88O6P8Pd2Ti · 1/2LiCl: C, 62.23; H, 4.69. Found: C, 62.23; H, 4.59. Preparation of the Pd-Zr-Pd Complex 7 from 2. The Zr-Pd complex 2 (20 mg, 0.026 mmol), HP(O)Ph2 (22 mg, 0.109 mmol), PMePh2 (4.9 µL, 0.026 mmol), and toluene (0.5 mL) were put in an NMR tube and kept at 40 °C. After 3 h, the 31P{1H} NMR spectrum recorded (Figure S2) showed major signals of (PMePh2)-

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Mizuta et al. Table 4. Crystallographic Data

formula cryst color, habit cryst syst space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Z temp/K µ(Mo KR)/mm-1 no. of rflns measd obsd (I > 2.00σ(I), 2θ < 55°) R1 (I > 2σ(I)) wR2 GOF a/ba a

1b

2

3

6

C43.7H45.1Cl0.3O2P2PdTi dark red, cubic monoclinic P21/a (No. 14) 19.889(1) 10.1284(6) 20.030(1) 90.00 102.708(2) 90.00 3936.0(4) 4 293 0.797 8987 5180

C36H36O2P2PdZr pale pink, plate monoclinic P21/a (No. 14) 19.9260(2) 10.2770(1) 32.4970(3) 90.00 93.170(1) 90.00 6644.5(1) 8 200 0.981 15 216 12 905

C36H36HfO2P2Pd pale pink, plate monoclinic P21/a (No. 14) 19.8990(1) 10.2630(1) 32.4220(1) 90.00 93.088(1) 90.00 6611.72(8) 8 200 3.809 15 644 14 605

C105H96O6P8Pd2Ti pale pink, plate triclinic P1j (No. 2) 13.4700(1) 15.2910(1) 24.5460(1) 95.029(1) 102.054(1) 107.525(2) 4652.9(2) 2 200 0.659 19 971 14 723

0.0975 0.1822 1.154 0.0310/18.1773

0.0521 0.1507 1.054 0.0820/21.2224

0.0310 0.0807 1.040 0.0387/27.6883

0.0623 0.1809 1.027 0.1035/6.2869

wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2; w ) 1/[σ2(Fo2) + (ap)2 + bp]; p ) (Fo2 + 2Fc2)/3.

(H)Pd(µ-OPPh2)3Zr(µ-OPPh2)3Pd(H)(PMePh2) (7) as well as those of remaining HP(O)Ph2 and PMePh2. 31P{1H} NMR (121.7 MHz, toluene): δ 7.4 (q, 2P, 2JP-P ) 117 Hz, PMePh2), 116.4 (d, 6P, 2 JP-P ) 116 Hz, OPPh2). Preparation of the Pd-Hf-Pd Complex 8 from 3. The Hf-Pd complex 3 (40 mg, 0.047 mmol), HP(O)Ph2 (28 mg, 0.14 mmol), PMePh2 (8.8 µL, 0.047 mmol), and toluene (2.0 mL) were put in an NMR tube and kept at 40 °C. After 3 h, the 31P{1H} NMR spectrumrecorded(FigureS3)showedmajorsignalsof(PMePh2)(H)Pd(µOPPh2)3Hf(µ-OPPh2)3Pd(H)(PMePh2) (8) as a major product as well as those of remaining HP(O)Ph2 and PMePh2 and some unidentified products. 31P{1H} NMR (121.7 MHz, toluene): δ 7.3 (q, 2P, 2JP-P ) 117 Hz, PMePh2), 101.9 (d, 6P, 2JP-P ) 117 Hz, OPPh2). Preparation of 7 from Cp2ZrCl2 and PdMe2(tmeda). Cp2ZrCl2 (5.8 mg, 0.020 mmol), PdMe2(tmeda) (5.0 mg, 0.020 mmol), HP(O)Ph2 (20 mg, 0.099 mmol), PMePh2 (7.4 µL, 0.040 mmol), and toluene (0.5 mL) were put in an NMR tube and kept at 40 °C. After 23 h, the 31P{1H} NMR spectrum recorded (Figure S4) showed major signals of 7 as well as those of remaining HP(O)Ph2 and PMePh2. Preparation of 8 from Cp2HfCl2 and PdMe2(tmeda). Cp2HfCl2 (7.5 mg, 0.020 mmol), PdMe2(tmeda) (5.0 mg, 0.020 mmol), HP(O)Ph2 (20 mg, 0.099 mmol), PMePh2 (7.4 µL, 0.040 mmol), and toluene (0.5 mL) were put in an NMR tube and kept at 40 °C. After 5 h, the 31P{1H} NMR spectrum recorded (Figure S5) showed major signals of 8 as well as those of remaining PMePh2 and some unidentified products. Catalysis. The catalyst 1, 2, or 3 (0.014 mmol), HP(O)Ph2 (56.6 mg, 0.280 mmol), 1-octyne (41.1 µL, 0.280 mmol), toluene (0.5 mL), and phosphine (its amount is given in Table 1) were all put in an NMR tube and kept at 40 °C. After the reaction time specified in Table 2, the reaction mixture was mixed with CHCl3 (2 mL) to quench the reaction and then extracted with ether (5 mL × 5). The extracts were combined, and the solvents were removed under reduced pressure. The residue thus obtained was redissolved in CHCl3 (0.50 mL), and the amounts of the phosphorus compounds were estimated by 31P{1H} NMR spectra. Similar procedures were applied when the mixture of Cp2MCl2 and PdMe2(tmeda) was used as a catalyst. X-ray Crystallography. Suitable crystals of 1b, 2, 3, and 6 were mounted separately on glass fibers. The measurements were made on a Rigaku SCXmini at room temperature for 1b and on a Mac Science

DIP2030 imaging plate area detector at 200 K for 2, 3, and 6. Cell parameters and intensities for the reflections were estimated using the program packages of CrystalClear for 1b and HKL for 2, 3, and 6.27,28 The structures were solved by direct methods and expanded using Fourier techniques. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms except the hydrides of 6 were located at ideal positions, while the hydride ligands of 6 were located on a difference Fourier map and refined isotropically. All calculations were performed using a SHELXL-97 crystallographic software package.29 After several cycles of least-squares refinement for the crystal structure of 1b, the crystal analyzed was found to be mixed with a PdClMe analogue, Cp′2Ti(µ-OPh2)2PdClMe. Thus one of the two Me groups on the Pd atom of 1b was treated as a disordered group with a chloride anion in a 70:30 occupancy ratio. For crystal structures of 2 and 3, each asymmetric unit was comprised of two independent molecules. In the crystal of 6, considerably disordered solvent molecules were refined as molecules having rigid ideal structures. The molecular structures are depicted in Figures 2-5 for 1b, 2, 3, and 6, respectively. Details of data collection and refinement for these crystals are listed in Table 4 and CIF files, which include bond distances and angles, atomic coordinates, and anisotropic thermal parameters.

Acknowledgment. This work was supported by Grants-inAid for Scientific Research (Nos. 19350032, 19550066, and 19550067) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. We thank the Natural Science Center for Basic Research and Development (N-BARD), Hiroshima University, for the measurement of NMR. Supporting Information Available: 31P{1H} NMR spectra of complexes 6, 7, and 8, and CIF files giving full crystallographic data for complexes 1b, 2, 3, and 6. This material is available free of charge via the Internet at http://pubs.acs.org. OM8008298 (27) CrystalClear 1.3.6; Rigaku/MXC, Inc.: The Woodlands, TX, 2004. (28) Otwinowski, Z.; Minor, W. In Processing of X-ray Diffraction Data Collected in Oscillation Mode; Carter,C. W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276 (Macromolecular Crystallography, Part A), pp 307-326. (29) Scheldrick, G. M. SHELX-97: Programs for Crystal Structure Analysis; University of Go¨ttingen: Germany, 1997.