Preparation and Thermal Reaction of

Jul 23, 2010 - Preparation and Thermal Reaction of Tetrastannapalladacyclopentane. Sn−Sn Bond Formation and Cleavage. Makoto Tanabe, Masaya ...
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Organometallics 2010, 29, 3535–3540 DOI: 10.1021/om100281t

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Preparation and Thermal Reaction of Tetrastannapalladacyclopentane. Sn-Sn Bond Formation and Cleavage Makoto Tanabe, Masaya Hanzawa, and Kohtaro Osakada* Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan Received April 7, 2010

Reaction of H2SnPh2 with [Pd(dmpe)2]n (n = 1 or 2; dmpe = 1,2-bis(dimethylphosphino)ethane) in 4:1 ratio produces a tetrastannapalladacyclopentane, [Pd(SnPh2SnPh2SnPh2SnPh2)(dmpe)] (1), via dehydrogenative Sn-Sn bond formation. Heating of 1 in toluene at 70 °C cleaves the Sn-Sn bonds, which is accompanied by migration of Ph groups, to form a bis(triphenylstannyl)palladium complex, [Pd(SnPh3)2(dmpe)] (2). A similar reaction of H2SnPh2 with [Pd(PCy3)2] yields a dipalladium(I ) complex with bridging diphenylstannyl ligands, [{Pd(PCy3)}2(μ-η2-HSnPh2)2] (3).

Introduction Transition metal complexes catalyze dehydrogenative coupling reactions of hydrostannanes to produce distannanes and dehydropolymerization of secondary stannanes.1 A diverse set of the transition metals, Zr,2 Hf,3 Fe,4 Ru,5 Pd,6 Pt,7 Cu,8 and Au,9 have been employed in the catalysis of the dimerization. Braunstein et al. designed a heterobimetallic catalyst that contains Fe and Pd centers bridged by alkoxysilyl ligands.10 Several mechanisms were proposed for the *To whom correspondence should be addressed. E-mail: kosakada@ res.titech.ac.jp. (1) (a) Braunstein, P.; Morise, X. Chem. Rev. 2000, 100, 3541–3552. (b) Clark, T. J.; Lee, K.; Manners, I. Chem. Eur. J. 2006, 12, 8634–8648. (2) (a) Imori, T.; Tilley, T. D. J. Chem. Soc., Chem. Commun. 1993, 1607–1609. (b) Imori, T.; Lu, V.; Cai, H.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117, 9931–9940. (c) Lu, V.; Tilley, T. D. Macromolecules 1996, 29, 5763–5764. (d) Woo, H.-G.; Song, S.-J.; Kim, B.-H. Bull. Korean Chem. Soc. 1998, 19, 1161–1164. (e) Lu, V. Y.; Tilley, T. D. Macromolecules 2000, 33, 2403–2412. (3) (a) Neale, N. R.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124, 3802– 3803. (b) Neale, N. R.; Tilley, T. D. Tetrahedron 2004, 60, 7247–7260. (4) Sharma, H. K.; Arias-Ugarte, R.; Metta-Magana, A. J.; Pannell, K. H. Angew. Chem., Int. Ed. 2009, 48, 6309–6312. (5) Maddock, S. M.; Finn, M. G. Angew. Chem., Int. Ed. 2001, 40, 2138–2141. (6) (a) Mitchell, T. N.; Amamria, A.; Killing, H.; Rutschow, D. J. Organomet. Chem. 1986, 304, 257–265. (b) Rupnicki, L.; UrbanczykLipkowska, Z.; Ste-pien, A.; Cmoch, P.; Pianowski, Z.; Stalinski, K. J. Organomet. Chem. 2005, 690, 3690–3696. (7) (a) Thompson, S. M.; Schubert, U. Inorg. Chim. Acta 2003, 350, 329–338. (b) Thompson, S. M.; Schubert, U. Inorg. Chim. Acta 2004, 357, 1959–1964. (8) Schubert, U.; Mayer, B.; Russ, C. Chem. Ber. 1994, 127, 2189– 2190. (9) Ito, H.; Yajima, T.; Tateiwa, J.; Hosomi, A. Tetrahedron Lett. 1999, 40, 7807–7810. (10) (a) Braunstein, P.; Morise, X.; Blin, J. J. Chem. Soc., Chem. Commun. 1995, 1455–1456. (b) Braunstein, P.; Morise, X. Organometallics 1998, 17, 540–550. (c) Braunstein, P.; Durand, J.; Morise, X.; Tiripicchio, A.; Ugozzoli, F. Organometallics 2000, 19, 444–450. (11) (a) Woo, H.-G.; Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114, 5698–5707. (b) Woo, H.-G.; Walzer, J. F.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114, 7047–7055. (c) Tilley, T. D. Acc. Chem. Res. 1993, 26, 22–29. r 2010 American Chemical Society

Sn-Sn bond-forming reactions. Dehydrogenative dimerization of organosilanes catalyzed by early transition metal complexes was believed to involve σ-bond metathesis.11 A similar mechanism was proposed also in Ru-catalyzed reaction of Bu3SnH to form Bu3SnSnBu3.5 Tilley et al. investigated the dimerization of Mes2SnH2 catalyzed by hafnocene derivatives and proposed the mechanism involving a stannylene intermediate formed by R-elimination of the stannylhafnium complexes.3 The SnSn bond formation catalyzed by Fe and Mo complexes was attributed to double oxidative addition of the Sn-H bonds to the metal center.4 Active transition metal catalysts, such as zirconocenes, promote dehydropolymerization of secondary stannanes to afford high molecular weight polystannanes.2 [RhH(CO)(PPh3)3] and [RhCl(PPh3)3] catalyzed polymerization of dibutylstannane to give branched and linear poly(dibutylstannane)s, respectively.12,13 The latter polymer displayed a reversible phase transition at 1 °C and showed liquid-crystalline properties above that temperature. In this paper, we present a new type of Sn-Sn bond formation promoted by a Pd(0) complex to yield a stannapalladacycle and its Sn-Sn bond cleavage induced by heating in solution.

Results and Discussion [Pd(dmpe)2]n (n = 1 or 2; dmpe = 1,2-bis(dimethylphosphino)ethane) was prepared by the method reported by Hitchcock with slight modification.14 X-ray crystallographic measurement revealed a dinuclear structure containing two tetrahedral Pd(0) centers and two bridging dmpe ligands, [{Pd(dmpe)}2( μ-dmpe)2] (Chart 1A), as shown in Figure 1. The 31P{1H} NMR measurements in toluene-d8 showed a (12) Babcock, J. R.; Sita, L. R. J. Am. Chem. Soc. 1996, 118, 12481– 12482. (13) Choffat, F.; Smith, P.; Caseri, W. J. Mater. Chem. 2005, 15, 1789–1792. (14) Broadwood-Strong, G. T. L.; Chaloner, P. A.; Hitchcock, P. B. Polyhedron 1993, 12, 721–729 The dimeric structure of [{Pd(dmpe)}2( μ-dmpe)2] was proposed, but was not characterized by X-ray crystallography. Published on Web 07/23/2010

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Chart 1

single signal at δ 0.17 even at -80 °C, indicating the existence of the mononuclear species [Pd(dmpe)2] (Chart 1B) in solution or rapid mutual exchange between the mononuclear and dinuclear species. Reaction of H2SnPh2 with [Pd(dmpe)2]n in 4:1 ratio at room temperature for 30 min produces tetrastannapalladacyclopentane [Pd(SnPh2SnPh2SnPh2 SnPh2)(dmpe)] (1) in 89% yield (eq 1). H2 gas evolution was immediately observed upon addition of the Pd(0) complex to the solution of H2SnPh2. Complex 1 was obtained also by exchange of silyl ligands of [Pd(SiHPh2)2(dmpe)]15 with stannyl groups on addition of excess H2SnPh2 (eq 2). Silyl- and germylplatinum complexes, [Pt(SiMe3)2(dppe)] and [Pt(GeMe3)2(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane), were reported to react smoothly with HSnMe3 to produce the stannylplatinum complex [Pt(SnMe3)2(dppe)].16

The structure of 1 was determined by multinuclear NMR spectroscopy and elemental analyses. The 1H NMR spectrum shows two doublets with Sn satellites due to the ortho hydrogen of the SnPh2 groups at δ 7.48 (J117/119Sn-H = 36 Hz) and 7.17 (J117/119Sn-H = 43 Hz) with equal intensity. No signals due to Sn-H hydrogens were observed. The 13C{1H} NMR spectrum in the aromatic region contains four pairs of signals assigned to ipso, ortho, meta, and para carbons of two magnetically inequivalent Ph groups. The 119Sn{1H} and 31P{1H} NMR spectra of 1 are shown in Figures 2 and 3. The 119Sn{1H} NMR spectrum of 1 (Figure 2) shows two doublets of doublets at δ -3.8 and -198.2 (SnMe4 standard). The former signal (δ -3.8) exhibits large 2J119Sn-P values (1682, 184 Hz) and is assigned to the Sn atom directly bonded to the Pd center. Coupling constants of the latter signal (δ -198.2) are much smaller (3J119Sn-P = 169, 22 Hz). The Sn-Sn coupling constants between the two signals (3487 and 980 Hz) also suggest the presence of two kinds of Sn nuclei, which are coupled with each other. 1,2,3-Tristanna[3]ferrocenophane

Figure 1. ORTEP drawing of [{Pd(dmpe)}2( μ-dmpe)2] with thermal ellipsoids shown at the 50% probability level. The complex has an inversion center at the midpoint between the two Pd atoms. Atoms with asterisks are crystallographically equivalent to those having the same number without asterisks. Four methylene carbons of the chelating dmpe ligands were disordered. Selected bond distances (A˚) and angles (deg): Pd-P1* 2.3148(6), Pd-P2 2.3127(7), Pd-P3 2.3114(7), Pd-P4 2.3005(9), P1*-Pd-P2 107.20(2), P1*-Pd-P4 114.54(2), P2-Pd-P3 115.04(2), P3-Pd-P4 88.20(2).

Figure 2. 119Sn{1H} NMR spectra of 1 in THF-d8 at rt (a) assigned as the terminal Sn and (b) assigned as the internal Sn atoms. Peaks with asterisks are due to Sn satellite signals.

having a Fe-Sn-Sn- Sn ring showed two different 117Sn-119Sn coupling constants (J117Sn-119Sn = 3224 Hz, 2J117Sn-119Sn =

537 Hz), which were attributed to the two magnetically different Sn nuclei in the FeSn3 ring system.17 The 31P{1H} NMR spectrum of 1 shows a single signal at δ 27.1, which is flanked with 117Sn and 119Sn satellite signals (Figure 3a). Bistrimethylstannyl)palladium complex cis-[Pd(SnMe3)2(PMe3)2] was reported to show two different 2J119/117Sn-P coupling constants, 1618 and 203 Hz, which were assigned to coupling of the coordinated Sn nuclei with P nuclei at the trans and cis positions, respectively.18 Large 2J119Sn-P and 2J117Sn-P values

(15) Tanabe, M.; Mawatari, A.; Osakada, K. Organometallics 2007, 26, 2937–2940. (16) (a) Clemmit, A. F.; Glockling, F. Chem. Commun. 1970, 705– 706. (b) Clemmit, A. F.; Glockling, F. J. Chem. Soc. (A) 1971, 1164–1169.

(17) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Angew. Chem., Int. Ed. Engl. 1996, 35, 1803–1804. (18) Tsuji, Y.; Nishiyama, K.; Hori, S.; Ebihara, M.; Kawamura, T. Organometallics 1998, 17, 507–512.

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Figure 3. (a) Experimental 31P{1H} NMR spectra of 1 in THF-d8 at rt and the expand region around the central peak. (b) Simulated 31 P{1H} NMR spectra and the corresponding expand region.

(1682 and 1607 Hz) of 1 are similarly assigned to the coupling constants between the Sn and P nuclei bonded at trans positions, while the coupling constants of 184 and 176 Hz are attributed to the coupling of cis P and Sn nuclei. The 117Sn and 119Sn isotopes exist in natural abundance (7.67% and 8.68%, respectively) and whose gyromagnetic ratio is equal to that of the J119Sn-P and J117Sn-P values. The appearance of two small signals due to the presence of the isotopomers suggests JP-P = 22 Hz. The coupling patterns in the 31P{1H} NMR spectrum of 1 show good agreement with the simulated spectrum on the basis of the above spin system (Figure 3b). Thus, we concluded that complex 1 has a five-membered ring composed of a Pd and four Sn atoms, although X-ray crystallography was not feasible. Braddock-Wilking et al. reported the preparation of tetrasilaand tetragermaplatinacyclopentane, [Pt(ER2ER2ER2ER2)(dppe)] (ER2 = SiC12H8 or GeC12H8), via the dehydrogenative Si-Si and Ge-Ge bond-forming reactions of sila- and germafluorene H2ER2 with [PtMe2(dppe)] in 4:1 ratio.19 Marschner et al. reported that metallocene-containing silacyclopentanes

Chart 2

Pd, Pt: Chart 2C) prepared from the reactions of H2GePh2 from bis(germyl)palladium22 and -platinum23 complexes. Plati-

cyclopentane [M(GePh2GePh2GePh2GePh2)(dmpe)] (M =

nacyclobutane [Pt(GePh2GePh2GePh2)(dmpe)] (Chart 2D) also reacts with H2GePh2 to produce the tetragermaplatinacyclopentane via formal insertion of a diphenylgermylene to a Pt-Ge bond. Reaction 1 should involve formation of stannylpalladium complexes such as [Pd(SnHPh2)2(dmpe)] or [PdH(SnHPh2)(dmpe)] as the intermediates. Complex 1, however, was obtained in high yields after a short reaction (30 min). Even the reaction of H2SnPh2 with [Pd(dmpe)2]n in 2:1 molar ratio produces 1 and a small amount of unidentified byproduct (δ 19.6 and 20.2 in the 31P{1H} NMR spectrum). Thus, the Sn-Sn bond-forming reactions24 occur rapidly to form the five-membered palladacycles in high selectively. Group 10

(19) Braddock-Wilking, J.; Bandrowsky, T.; Praingam, N.; Rath, N. P. Organometallics 2009, 28, 4098–4105. (20) Kayser, C.; Kickelbick, G.; Marschner, C. Angew. Chem., Int. Ed. 2002, 41, 989–992. (21) Zirngast, M.; Flock, M.; Baumgartner, J.; Marschner, C. J. Am. Chem. Soc. 2009, 131, 15952–15962.

(22) Tanabe, M.; Ishikawa, N.; Hanzawa, M.; Osakada, K. Organometallics 2008, 27, 5152–5158. (23) Tanabe, M.; Hanzawa, M.; Ishikawa, N.; Osakada, K. Organometallics 2009, 28, 6014–6019. (24) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. Rev. 1989, 89, 11–49.

[M{Si(SiMe3)2SiMe2SiMe2Si(SiMe3)2}(C5H5)2]20 and stannacyclobutanes [M{Sn(SiMe3)2Sn(SiMe3)2Sn(SiMe3)2}(C5H5)2]21 (M=Zr, Hf) were prepared from the metathesis reactions of oligosilyl or oligostannyl dianions with Cp2MCl2 (Chart 2A,B). We also reported tetragermapalladacyclopentane and -platina-

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Figure 4. ORTEP drawing of 2 with thermal ellipsoids shown at the 50% probability level. Selected bond distances (A˚) and angles (deg): Sn1-Pd 2.5984(2), Sn2-Pd 2.6079(2), Pd-P1 2.3110(8), Pd-P2 2.3111(8), Sn1-Pd-Sn2 86.848(8), Sn1Pd-P2 96.07(2), Sn2-Pd-P1 91.34(2), P1-Pd1-P2 85.41(2).

metallacycles composed of oligosilyl25 and oligogermyl26 groups have been suggested as one of possible intermediates for catalytic dehydrocoupling condensation to prepare polysilanes and polygermanes. Heating a toluene solution of 1 at 70 °C for 20 h converted it into bis(triphenylstannyl)palladium complex [Pd(SnPh3)2(dmpe)] (2) (87%), which is soluble in toluene (eq 3). The reaction is considered to involve cleavage of the Sn-Sn bonds in the PdSn4 rings and migration of the Ph groups from internal Sn atoms to those bonded to the Pd center. The reaction mixture produces a gray insoluble solid also. It may be assigned to polymeric organotin products and/or metallic tin, but was not characterized.

Figure 4 shows the ORTEP drawing of 2, which was characterized by X-ray crystallography. The Pd-Sn bond distances of 2 (2.5984(2), 2.6079(2) A˚) are similar to those of [Pd(1-PPh2-2-SnMe2-1,2-C2B10H10)2] (2.5743(5), 2.5760(5) A˚),27 cis-[Pd(SnMe3)2(PMe3)2] (2.607(1), 2.604(1) A˚),18 and [Bu3MeN]2[(dppp)Pd(SnB11H11)2] (2.578(1) A˚).28 Bis(stannyl)palladium(II)18 and -platinum(II)29-31 complexes with monodentate phosphine ligands undergo twisted rotation at the metal center via a pseudotetrahedral transition state in solution. The crystal structure of cis-[Pd(SnMe3)2(PMe3)2], which has negligible steric congestion between the ligands, is distorted from square-planar coordination around Pd (dihedral angle = 16.8°).18 The chelating diphosphine ligand of 2 reduces the dihedral angle to 6.4°. The 31P{1H} and (25) Lemanski, M. F.; Schram, E. P. Inorg. Chem. 1976, 15, 1489–1492. (26) Usui, Y.; Hosotani, S.; Ogawa, A.; Nanjo, M.; Mochida, K. Organometallics 2005, 24, 4337–4339. (27) Lee, T.; Lee, S. W.; Jang, H. G.; Kang, S. O.; Ko, J. Organometallics 2001, 20, 741–748. (28) Marx, T.; Mosel, B.; Pantenburg, I.; Hagen, S.; Schulze, H.; Wesemann, L. Chem. Eur. J. 2003, 9, 4472–4478. (29) (a) Obora, Y.; Tsuji, Y.; Nishiyama, K.; Ebihara, M.; Kawamura, T. J. Am. Chem. Soc. 1996, 118, 10922–10923. (b) Tsuji, Y.; Obora, Y. J. Organomet. Chem. 2000, 611, 343–348. (30) (a) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Angew. Chem., Int. Ed. Engl. 1997, 36, 1508–1510. (b) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Chem. Eur. J. 1998, 4, 1027–1032. (31) Sagawa, T.; Ohtsuki, K.; Ishiyama, T.; Ozawa, F. Organometallics 2005, 24, 1670–1677.

Sn{1H} NMR spectra of 2 display more simple coupling patterns than 1. The 119Sn{1H} NMR spectrum of 2 (δ -40.4) shows a doublet of doublets by couplings with trans and cis 31P atoms (1791 and 157 Hz). The 31P{1H} NMR signal at δ 24.5 is observed with the typical coupling patterns of bis(stannyl)palladium(II) complexes.27,32 Reaction of [Pd(PCy3)2] with equimolar H2SnPh2 gave a dipalladium(I) complex with bridging stannyl ligands, [{Pd(PCy3)}2( μ-η2-HSnPh2)2] (3), in 26% yield (eq 4). An excess amount of H2SnPh2 in the presence of [Pd(PCy3)2] forms 3 together with cyclic oligostannanes (SnPh2)5 and (SnPh2)6 (119Sn NMR signals at δ -206.0 and -217.2).33

Braddock-Wilking prepared the diplatinum complex with bridging stannyl ligands, [(Ph3P)2(H)Pt( μ-SnPh2)( μ-η2HSnPh2)Pt(PPh3)], from the reaction of a Pt(0)-PPh3 complex with H2SnPh2.34 Analogous dipalladium complexes with bridging silyl and germyl ligands, [{Pd(PCy3)}2( μ-η2HEPh2)2] (E = Si,35,36 Ge37), and their Pt analogues were also reported.38,39 The 1H NMR signal of 3 at δ 0.20 is observed as an apparent triplet with virtual couplings due to two phosphorus atoms, which is assigned to the bridging hydrogens in 3c-2e Pd-H-Sn bonds. The observed chemical shift of 3 is similar to the corresponding peak of the dipalladium with bridging germyl ligands [{Pd(PCy3)}2( μHGePh2)2] (δ 0.42).37 In summary, this study revealed formation of a tetrastannapalladacyclopentane via Sn-Sn bond formation and demonstrated generality of the reactions shown previously for the formation of the Ge analogues.22,23 The dehydrogenative coupling reaction is dependent strongly on the nature of the phosphine ligands and is limited to the complex with dmpe at present. Complex 1 undergoes thermally induced Sn-Sn bond cleavages in the PdSn4 ring and Sn-C bond formations. (32) Lee, C.; Lee, J.; Lee, S. W.; Kang, S. O.; Ko, J. Inorg. Chem. 2002, 41, 3084–3090. (33) Neale, N. R.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127, 14745–14755. (34) White, C. P.; Braddock-Wilking, J.; Corey, J. Y.; Xu, H.; Redekop, E.; Sedinkin, S.; Rath, N. P. Organometallics 2007, 26, 1996–2004. (35) Tanabe, M.; Yamada, T.; Osakada, K. Organometallics 2003, 22, 2190–2192. (36) (a) Kim, Y.-J.; Lee, S.-C.; Park, J.-I.; Osakada, K.; Choi, J.-C.; Yamamoto, T. Organometallics 1998, 17, 4929–4931. (b) Kim, Y.-J.; Lee, S.-C.; Park, J.-I.; Osakada, K.; Choi, J.-C.; Yamamoto, T. Dalton Trans. 2000, 417–421. (37) Tanabe, M.; Ishikawa, N.; Osakada, K. Organometallics 2006, 25, 796–798. (38) (a) Auburn, M.; Ciriano, M.; Howard, J. A. K.; Murray, M.; Pugh, N. J.; Spencer, J. L.; Stone, F. G. A.; Woodward, P. J. Chem. Soc., Dalton Trans. 1980, 659–666. (b) Sanow, L. M.; Chai, M.; McConnville, D. B.; Galat, K. J.; Simons, R. S.; Rinaldi, P. L.; Youngs, W. J.; Tessier, C. A. Organometallics 2000, 19, 192–205. (c) Braddock-Wilking, J.; Levchinsky, Y.; Rath, N. P. Organometallics 2000, 19, 5500–5510. (d) BraddockWilking, J.; Corey, J. Y.; Trankler, K. A.; Dill, K. M.; French, L. M.; Rath, N. P. Organometallics 2004, 23, 4576–4584. (e) Arii, H.; Takahashi, M.; Noda, A.; Nanjo, M.; Mochida, K. Organometallics 2008, 27, 1929–1935. (f ) Tanabe, M.; Ito, D.; Osakada, K. Organometallics 2008, 27, 2258–2267. (39) (a) Braddock-Wilking, J.; Corey, J. Y.; White, C.; Xu, H.; Rath, N. P. Organometallics 2005, 24, 4113–4115. (b) Arii, H.; Nanjo, M.; Mochida, K. Organometallics 2008, 27, 4147–4151.

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Experimental Section General Procedures. All manipulations of the complexes were carried out using standard Schlenk techniques under an argon or nitrogen atmosphere. Hexane and toluene were purified by using a solvent purification system (Glass Contour). The 1H, 13 C{1H}, 31P{1H}, and 119Sn{1H} NMR spectra were recorded on Varian Mercury 300 and JEOL JNM-500 spectrometers. Chemical shifts in 1H and 13C{1H} NMR spectra were referenced to the residual peaks of the solvents used. The peak positions of the 31P{1H} and 119Sn{1H} NMR spectra were referenced to external 85% H3PO4 (δ 0) and external SnMe4 (δ 0) in the deuterated solvents. IR absorption spectra were recorded on a Shimadzu FT/IR-8100 spectrometer. Elemental analysis was carried out using a LECO CHNS-932 or Yanaco MT-5 CHN autorecorder. H2SnPh2 was obtained from reduction of Cl2SnPh2 (Aldrich) with LiAlH4.40 [Pd(PCy3)2]37 and [Pd(SiHPh2)2(dmpe)]15 were prepared according to the reported procedure. Preparation of [Pd(dmpe)2]n (n = 1 or 2). The reported preparation method was modified.14 To a toluene solution (5 mL) of [Pd(PCy3)2] (227 mg, 0.34 mmol) was added a twice molar amount of dmpe (113 μL, 0.68 mmol). The reaction mixture was stirred at room temperature for 2 h in a glovebox. The volatiles were removed under reduced pressure to give a white solid, which was washed with 3  3 mL of hexane and dried in vacuo to produce [Pd(dmpe)2]n (100 mg, 72%). Colorless crystals of [Pd(dmpe)2]n suitable for X-ray crystallography were obtained by recrystallization from a toluene/hexane solution (1:7) in a freezer. X-ray crystallography of the crystals indicated the dimer structure [{Pd(dmpe)}2( μ-dmpe)2]. The NMR spectra showed much more simple peaks than expected from the crystallographic results. The 31P{1H} NMR spectrum in toluene-d8 even at -80 °C was recorded as a single signal. 1H NMR (300 MHz, C6D6, rt): δ 1.36 (br, 8H, PCH2), 1.31 (s, 24H, PCH3). 31P{1H} NMR (121 MHz, C7D8): δ -1.21 (rt) and 0.17 (-80 °C). Preparation of [Pd(SnPh2SnPh2SnPh2 SnPh2)(dmpe)] (1) from Pd(0) Complex. To a hexane solution (3 mL) of [Pd(dmpe)2]n (71.5 mg, 0.18 mmol) was added a 4-fold amount of H2SnPh2 (193 mg, 0.70 mmol). Rapid H2 gas evolution was observed, and the reaction mixture produced a yellow precipitate, which continued to stir for 30 min at room temperature. The yellow solid was collected by filtration, washed with hexane (3  2 mL), and dried in vacuo to produce complex 1 (210 mg, 89%). Anal. Calcd for C54H56P2PdSn4: C, 48.11; H, 4.19. Found: C, 48.02; H, 4.03. 1H NMR (500 MHz, THF-d8, rt): δ 7.48 (d, 8H, C6H5 ortho, JH-H = 7.9 Hz, J117/119Sn-H = 36 Hz), 7.17 (d, 8H, C6H5 ortho, JH-H = 7.9 Hz, J117/119Sn-H = 43 Hz), 7.07 (t, 4H, C6H5 para, JH-H = 7.3 Hz), 7.01-6.98 (m, 12H, C6H5 meta and para), 6.91 (t, 8H, C6H5 meta, JH-H = 7.3 Hz), 1.76 (d, 4H, PCH2, 2 JP-H = 20 Hz), 1.14 (d, 12H, PCH3, 2JP-H = 8.6 Hz). 13C{1H} NMR (126 MHz, THF-d8, rt): δ 149.0 (t, C6H5 ipso, 3JP-C = 8.3 Hz), 142.5 (s, C6H5 ipso), 139.8 (C6H5 ortho, 2J117/119Sn-C = 39 Hz), 139.5 (C6H5 ortho, 2J117/119Sn-C = 38 Hz), 128.4 (C6H5 meta, 2J117/119Sn-C = 39 Hz), 128.3 (C6H5 meta, 2J117/119Sn-C = 30 Hz), 127.5 (C6H5 para), 127.3 (C6H5 para), 30.3 (apparent triplet, PCH2, J = 24 Hz), 14.1 (dd, PCH3, 2JP-C = 9.3, 12.4 Hz). 31P{1H} NMR (122 MHz, THF-d8, rt): δ 27.1 (s, 2 J119Sn(trans)-P = 1682 Hz, 2J117Sn(trans)-P = 1607 Hz, 2J119Sn(cis)-P = 184 Hz, 2J117Sn(cis)-P = 176 Hz, 3J119Sn-P = 169 Hz, 3J117Sn-P = 162 Hz, 2JP-P = 22 Hz). 119Sn{1H} NMR (186 MHz, THF-d8, rt): δ -3.8 (dd, Pd-Sn, 2JP(trans)-Sn = 1682 Hz, 2JP(cis)-Sn = 184 Hz, JSn-117/119Sn = 3487 Hz, 2JSn-117/119Sn = 980 Hz), -198.2 (dd, Pd-Sn-Sn, 3JP(trans)-Sn = 169 Hz, 3JP(cis)-Sn = 22 Hz, JSn-117/119Sn = 3487 Hz, 2JSn-117/119Sn = 980 Hz). When the reaction of [Pd(dmpe)2]n (30 mg, 0.074 mmol) with H2SnPh2 (41 mg, 0.148 (40) Kuivila, H. G.; Sawyer, A. K.; Armour, A. G. J. Org. Chem. 1961, 26, 1426–1429.

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Table 1. Crystallographic Data and Details of Refinement of [{Pd(dmpe)}2( μ-dmpe)2] and 2

formula fw cryst size/mm cryst syst cryst color space group a/A˚ b/A˚ c/A˚ β/deg V/A˚3 Z Dcalcd/g cm-3 F(000) μ/mm-1 no. of reflns measd no. of unique reflns Rint no. of obsd reflns (I > 2σ(I )) no. of variables R, Rw (I > 2σ(I )) R, Rw (all data) GOF on F2

[{Pd(dmpe)}2( μ-dmpe)2]

2

C24H64P8Pd2 813.36 0.35  0.50  0.60 monoclinic colorless P21/n (No. 14) 11.778(3) 11.869(3) 14.363(3) 92.983(3) 2005.1(7) 2 1.347 840 1.2291 12 680 4304 0.016 4071

C42H46PdP2Sn2 956.55 0.42  0.28  0.13 monoclinic yellow P21/n (No. 14) 11.652(2) 27.857(4) 12.180(2) 96.006(2) 3932(1) 4 1.616 1896 1.8224 31 694 8991 0.033 7599

173 0.0344, 0.0947 0.0366, 0.0966 1.027

425 0.0312, 0.0769 0.0382, 0.0818 0.992

mmol) in 1:2 ratio was conducted in C6D6 (0.8 mL), complex 1 was formed mainly, together with a small amount of unidentified products (δ 19.6 and 20.2 in the 31P{1H} NMR spectrum). Addition of excess H2SnPh2 (76 mg, 0.278 mmol) to a solution of [Pd(dmpe)2]n (11 mg, 0.028 mmol) in C6D6 (0.6 mL) caused H2 gas evolution and rapid oligomerization of H2SnPh2 to yield an insoluble yellow solid. The GPC measurements of the THF soluble part of the obtained solid revealed formation of the oligostannanes with Mn = 700. Preparation of 1 from [Pd(SiHPh2)2(dmpe)]. A reaction mixture of [Pd(SiHPh2)2(dmpe)] (263 mg, 0.37 mmol) and a 4-fold amount of H2SnPh2 (403 mg, 1.47 mmol) in toluene (3 mL) was stirred for 2 h at room temperature. The solvent was removed under reduced pressure, and the pale yellow residue was washed with hexane (2  3 mL) and dried in vacuo to give complex 1 (314 mg, 64%). Preparation of [Pd(SnPh3)2(dmpe)] (2). Heating of a toluene solution (7 mL) of 1 (275 mg, 0.20 mmol) was conducted at 70 °C for 20 h. The reaction mixture turned into a dark brown solution, and a gray solid was precipitated. The solvent was removed under reduced pressure to give a gray solid, which was washed with ether (3  3 mL) and dried in vacuo to form complex 2 (169 mg, 87%). Recrystallization of 2 from slow diffusion of hexane into a toluene solution afforded pale yellow crystals for X-ray crystallography. Anal. Calcd for C42H46P2PdSn2: C, 52.73; H, 4.85. Found: C, 49.66; H, 4.21. 1H NMR (300 MHz, C6D6, rt): δ 7.73 (m, 12H, C6H5 ortho, 2J119/117Sn-H = 38 Hz), 7.11-6.97 (m, 18H, C6H5 meta and para), 0.73 (m, 4H, PCH2), 0.67 (m, 12H, PCH3). 13C{1H} NMR (125 MHz, THF-d8, rt): δ 150.1 (t, C6H5 ipso, JP-C = 8.8 Hz), 138.8 (C6H5 ortho, 2 J119/117Sn-C =39 Hz), 127.9 (C6H5 meta, 2J119/117Sn-C = 36 Hz), 127.1 (C6H5 para), 30.1 (apparent triplet, PCH2, J=23 Hz), 13.8 (m, PCH3, JP-C = 10 Hz). 31P{1H} NMR (202 MHz, THF-d8, rt): δ 24.5 (s, 2J119Sn(trans)-P=1791 Hz, 2J117Sn(trans)-P= 1710 Hz, 2 J119/117Sn(cis)-P =153 Hz, 2JP-P =31 Hz). 119Sn{1H} NMR (186 MHz, THF-d8, rt): δ -40.4 (dd, 2JP(cis)-Sn=157 Hz, 2JP(trans)-Sn= 1791 Hz). Preparation of [{Pd(PCy3)}2( μ-η2-HSnPh2)2] (3). Reaction of [Pd(PCy3)2] (448 mg, 0.67 mmol) with equimolar H2SnPh2 (184 mg, 0.67 mmol) in toluene solution (12 mL) was stirred for 4 h at room temperature. Removal of the solvent under reduced pressure produced a yellow solid, which was washed with hexane

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Organometallics, Vol. 29, No. 16, 2010

(5  4 mL) and dried in vacuo to give complex 3 (114 mg, 26%). Anal. Calcd for C60H88P2Pd2Sn2 3 1/4C7H8: C, 55.16; H, 6.75. Found: C, 55.29; H, 6.33. 1H NMR (500 MHz, THF-d8, rt): δ 8.10 (d, 8H, C6H5 ortho, JH-H=7.5 Hz), 7.34 (t, 8H, C6H5 meta, JH-H=7.5 Hz), 7.19 (t, 4H, C6H5 para, JH-H=7.5 Hz), 1.99 (br, 6H, C6H11), 1.79 (d, 12H, C6H11, J=12 Hz), 1.52-1.47 (m, 18H, C6H11, J=12 Hz), 1.35 (d, 12H, C6H11, J=12 Hz), 1.07 (m, 12H, C6H11), 0.96 (m, 6H, C6H11), 0.20 (apparent triplet, 2H, SnH, J = 5.6 Hz). The Sn satellite signals of the Pd-H-Sn hydrogens are not observed. 13C{1H} NMR (126 MHz, THF-d8, rt): δ 154.3 (C6H5 ipso), 138.3 (C6H5 ortho), 128.6 (C6H5 meta), 127.9 (C6H5 para), 38.7 (apparent triplet, PCH, J = 8.3 Hz), 31.6 (PCHCH2), 28.1 (apparent triplet, PCHCH2CH2, J = 5.2 Hz), 26.9 (PCHCH2CH2CH2). 31P{1H} NMR (202 MHz, THFd8, rt): δ 62.6 (s, 2JSn(trans)-P = 817 Hz, 2JSn(cis)-P = 182 Hz). The 119Sn NMR signal of 3 was not observed. IR (KBr): 1576 (νSnH) cm-1. The reaction of [Pd(PCy3)2] (20 mg, 0.030 mmol) with H2SnPh2 (33 mg, 0.120 mmol) in 1:4 ratio in C6D6 (0.8 mL) gave a mixture of dipalladium complex 3 and cyclic oligostannanes, which showed 119Sn{1H} NMR signals at δ -206.0 and -217.2, respectively. These chemical shifts were consistent with the spectroscopic data of (SnPh2)5 and (SnPh2)6.33 (41) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure Refinement; University of Gottingen: Germany, 1997.

Tanabe et al. X-ray Crystallography. Crystals of [{Pd(dmpe)}2( μ-dmpe)2] and 2 suitable for X-ray diffraction study were mounted on MicroMounts (MiTeGen). The crystallographic data for [{Pd(dmpe)}2( μ-dmpe)2] and 2 were collected on a Rigaku Saturn CCD area detector equipped with monochromated Mo KR radiation (λ = 0.71073 A˚) at 150 K. Calculations were carried out using the program package Crystal Structure, version 3.8, for Windows. The positional and thermal parameters of nonhydrogen atoms were refined anisotropically on F2 by the fullmatrix least-squares method using SHELXL-97.41 Hydrogen atoms were placed at calculated positions and refined with a riding mode on their corresponding carbon atoms. Crystallographic data and details of refinement of [{Pd(dmpe)}2( μ-dmpe)2] and 2 are summarized in Table 1.

Acknowledgment. This work was financially supported by Grants-in-Aid for Scientific Research for Young Chemists (No. 21750057), for Scientific Research (No. 1925008), and for Scientific Research on Priority Areas (No. 19027018), from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. Supporting Information Available: Crystallographic data for [{Pd(dmpe)}2( μ-dmpe)2] and 2 as a CIF file. This material is available free of charge via the Internet at http://pubs.acs.org.