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Organometallics 2010, 29, 4702–4710 DOI: 10.1021/om100445a
Sila- and Germametallacycles of Late Transition Metals† Makoto Tanabe and Kohtaro Osakada* Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan Received May 9, 2010
This article reviews recent advances in late-transition-metal complexes with chelating Si and Ge ligands. Compounds with two Si-H bonds, such as bis(silyl)alkanes, bis(silyl)arenes, and tetramethyldisiloxanes, react with Re, Rh, Ir, Pd, and Pt complexes to form disilametallacycles with five- or six-membered chelate rings. Four- and five-membered disilacycloalkanes and disilanyldiylcarboranes undergo Si-Si bond cleavage promoted by Pd(0) and Pt(0) complexes to produce the corresponding disilametallacycles. High reactivity of the Si-Si bond toward oxidative addition facilitates the above ring enlargement, even for compounds with stable five-membered rings. Platinum complexes with a η2-silene ligand react with small molecules having electronegative atoms, such as O2 and NH3, to produce metallacycles formed via addition of the electronegative atom to the Si-Si bond. The above disilametallacycles undergo insertion of alkynes and carbonyl compounds into the M-Si bonds of the disilametallacycles. The persilyl metallacycle [Pt(SiPh2SiPh2SiPh2SiPh2)(PPh3)2] is obtained by the double oxidative addition of tetrakis(diphenylsilane) with two Si-H groups and via a metathesis reaction of its dilithio derivative with [PtCl2(PPh3)2]. Reactions of H2GeAr2 with Pd(II) and Pt(II) complexes having diphenylgermyl ligands yield the tetragerampalladacyclopentane and its Pt analogue. Trigermaplatinacyclobutane reacts with Ph2GeH2 to produce the tetragermaplatinacyclopentane via formal insertion of GePh2 into a Pt-Ge bond. 1. C versus Si or Ge Metallacycles The chemistry of metallacycles1 has been a major area of organometallic chemistry because of their role as key intermediates in the metathesis2 and oligomerization3 of alkenes catalyzed by transition-metal complexes. Five- and six-membered metallacycles are common, and they are stabilized kinetically in many cases. Their M-C bonds undergo various reactions such as insertion of small molecules, reductive elimination of cycloalkanes, and β-hydrogen elimination, but the reactions occur more slowly than for the usual alkyl complexes due to ring strain of the intermediates or the products. Metallacyclobutanes of Mo, W, and Ru with a four-membered-ring structure are known as the actual intermediates of olefin metathesis catalyzed by the transition-metal complexes.4 Silyl and germyl complexes of late transition metals exhibit different reactivity from the alkyl metal complexes. For example, they prefer R-hydrogen elimination rather than β-hydrogen elimination, which is common as a † Part of the Dietmar Seyferth Festschrift. *To whom correspondence should be addressed. E-mail: kosakada@ res.titech.ac.jp. (1) (a) Puddephatt, R. J. Coord. Chem. Rev. 1980, 33, 149–194. (b) Chappell, S, D.; Cole-Hamilton, D. J. Polyhedron 1982, 1, 739–777. (c) Campora, J.; Palma, P.; Carmona, E. Coord. Chem. Rev. 1999, 193-195, 207–281. (d) Blom, B.; Clayton, H.; Kilkenny, M.; Moss, J. R. Adv. Organomet. Chem. 2006, 54, 149–205. (e) Zheng, F.; Sivaramakrishna, A.; Moss, J. R. Coord. Chem. Rev. 2007, 251, 2056–2071. (2) (a) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997, 119, 3887–3897. (b) Grubbs, R. H. Tetrahedron 2004, 60, 7117–7140. (c) Schrock, R. R. J. Mol. Catal. A: Chem. 2004, 213, 21–30. (3) (a) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. J. Organomet. Chem. 2004, 689, 3641–3668. (b) Wass, D. F. Dalton Trans. 2007, 816–819. (4) Jennings, P. W.; Johnson, L. L. Chem. Rev. 1994, 94, 2241–2290.
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decomposition pathway of the alkyl complexes. Chemical properties of the metallacycles, having Si or Ge as the coordinating atoms, are expected to be unique, being cyclic versions of the silyl and germyl complexes. Many research groups have investigated the preparation, structures, and chemical properties of such sila- or germametallacycles. Pd and Pt, in particular, are employed as the major elements among late transition metals, probably because the σ-bonds between Si or Ge and these metals are common and stable in noncyclic complexes and because the square-planar structures of Pd(II) and Pt(II) with d8 configuration are suited for cis coordination of the chelating ligands. The sila- and germametallacycles are classified into two categories, shown in Chart 1. One contains Si (or Ge) as the coordinating atoms only (type A), while another has the ring system composed of the heavy group 14 elements and transition metals (type B). Scheme 1 summarizes the synthetic reactions of the Si- or Ge-containing metallacycles. The metathesis reaction of a disilyl or digermyl dianion with dihalo complexes of transition metals (reaction i in Scheme 1) produces metallacycles having Si or Ge as the coordinating atoms. Oxidative addition of the compounds with two Si-H bonds to lowvalent metal complexes (reaction ii in Scheme 1), however, is more common than reaction i. The reaction of alkylene or arylene dianions with dihalo complexes of the transition metals is the most common method to prepare metallacycles with two M-C bonds, while reaction ii is more important for the synthesis of the disilametallacycles because Si-H bonds undergo oxidative addition more easily than C-H bonds. The latter reactions are employed as the synthetic method of the C-metallacycles mostly in the cyclometalation of the phosphine r 2010 American Chemical Society
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Chart 2
Chart 3 Scheme 1
by oxidative dimerization of alkynes or by oxidative addition of dihaloalkanes and -arenes to the metal centers, but the reactions have not been used in syntheses of the Si- and Ge-containing metallacycles.
2. Disilylated and Digermylated Metallacycles
(5) (a) Miyashita, A.; Takahashi, M.; Takaya, H. J. Am. Chem. Soc. 1981, 103, 6257–6259. (b) Miyashita, A.; Watanabe, Y.; Takaya, H. Tetrahedron Lett. 1983, 24, 2595–2598. (6) (a) Eisch, J. J.; Piotrowski, A. M.; Han, K. I.; Kr€ uger, C.; Tsay, Y. H. Organometallics 1985, 4, 224–231. (b) Schwager, H.; Spyroudis, S.; Vollhardt, K. P. C. J. Organomet. Chem. 1990, 382, 191–200. (c) Edelbach, B. L.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc. 1998, 120, 2843– 2853. (d) Satoh, T.; Jones, W. D. Organometallics 2001, 20, 2916–2919. (7) (a) Dewar, M. J. S. Bull. Soc. Chim. Fr. 1951, 18, C79. (b) Chatt, J.; Duncanson, L. A. J. Chem. Soc. 1953, 2939–2947. (8) Pham, E. K.; West, R. Organometallics 1990, 9, 1517–1523.
ing Si ligands, [M{SiMe2(CH2)2 SiMe2}(CO)4] (5; M = Fe,
Ru, Os) (Chart 4).10 [Rh(SiMe2O SiMe2)(H)(PPh3)3] (6)
and amine ligands. Ring expansion of the cyclic carbon compounds was reported to lead to the C-metallacycles, although the substrates are limited to strained molecules such as bicyclobutane5 and diphenylene.6 Oxidative addition of the Si-Si bonds to late transition metals occurs more easily than addition of C-C bonds. Consequently, the reactions of cyclic compounds having an Si-Si bond in the ring system with low-valent latetransition-metal complexes lead to selective cleavage of the Si-Si bond and provide metallacycles having two M-Si bonds (reaction iii in Scheme 1). The three-membered metallacycles of late transition metals are often regarded as a canonical form of olefin complexes because of significant back-donation, as suggested by the Dewar-Chatt-Duncanson model.7 The C-C bonds of these metallacycles are stable and are not cleaved by common organic and inorganic reagents. Similar complexes with π-coordinated disilene (R2SidSiR2) ligands have been isolated in the case of Pt.8 The bond between the two Si atoms, however, is activated upon addition of small molecules such as O2, NH3, and S8 to produce the four-membered disilametallacycles classified into type A in Chart 1 (reaction iv in Scheme 1). The metallacycles composed of carbon and metal are prepared also
1,2-Bis(dimethylsilyl)benzene (dmsbH2), 1,2-bis(dimethylsilyl)ethane (dmseH2), and 1,1,3,3-tetramethyldisiloxane (tmdsH2) (Chart 2) undergo double oxidative addition of the two Si-H bonds to late-transition-metal complexes to afford a variety of five-membered disilametallacycles. Eaborn prepared four-, five-, and six-membered disilaplatinacycles 1-3 from the double oxidative addition of the bifunctional molecules to [Pt(CH2dCH2)(PPh3)2] under mild conditions (Chart 3).9 Oxidative addition of Si-H bonds to the Pt(0) complex probably forms a hydrido(silyl)platinum complex with a pendant Si-H group, [PtH(SiMe2-X-SiMe2H)(PPh3)2], as an intermediate for formation of the disilaplatinacycles (Scheme 2). The reaction of HMe2SiCH2C6H4CH2SiMe2H with [Pt(CH2d CH2)(PPh3)2] yields the hydrido(silyl)platinum(II) complex 4 rather than the seven-membered platinacycle. The complex is not converted further into the metallacycle, due to oxidative addition of the second Si-H bond being much slower than the intermolecular Si-H bond activation of the first Si-H bond. Double oxidative addition of dmseH2 toward group 8 transition-metal carbonyls, Fe(CO)5, Ru3(CO)12, and Os3(CO)12, produces mononuclear complexes with chelat-
and [Ir(SiMe2O SiMe2)(H)(CO)(PPh3)2] (7) are prepared similarly from Wilkinson and Vaska complexes and tmdsH2 and catalyze disproportionation of tmdsH2 into Me2SiH2 and the linear or cyclic polysiloxanes (OSiMe2)n.11 Cleavage (9) (a) Eaborn, C.; Metham, T. N.; Pidcock, A. J. Organomet. Chem. 1973, 54, C3–C4. (b) Eaborn, C.; Metham, T. N.; Pidcock, A. J. Organomet. Chem. 1973, 63, 107–117. (10) Vancea, L.; Graham, W. A. G. Inorg. Chem. 1974, 13, 511–513. (11) (a) Greene, J.; Curtis, M. D. J. Am. Chem. Soc. 1977, 99, 5176–5177. (b) Curtis, M. D.; Greene, J. J. Am. Chem. Soc. 1978, 100, 6362–6367. (c) Curtis, M. D.; Greene, J.; Butler, W. M. J. Organomet. Chem. 1979, 164, 371–380.
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dehydrogenation of cyclooctane to cyclooctene compared to ReH7(PPh3)2.
Scheme 2
Chart 4
two dmsb ligands, [Rh(SiMe2C6H4 SiMe2)(H)(PPh3)2] (9) and [Rh(SiMe2C6H4 SiMe2)(η1-SiMe2C6H4SiHMe2)(PPh3)] (10) (eq 2). The remaining Si-H group of 10 is weakly coordinated to the Rh center. The strong trans influence of the organosilyl ligand may prevent further oxidative addition of the remaining Si-H group to produce a Rh(V) complex. Polyhydrides of Re(VII) and Ir(V), [ReH7(PPh3)2] and [IrH5(PPh3)2], react with dmsbH2 and dmseH2 to produce complexes with chelating Si ligands.14 [ReH5(dmse)(PPh3)2], thus obtained, shows a much higher catalytic activity for
(12) Osakada, K.; Hataya, K.; Nakamura, Y.; Tanaka, M.; Yamamoto, T. J. Chem. Soc., Chem. Commun. 1993, 576–577. (13) (a) Nagashima, H.; Tatebe, K.; Itoh, K. J. Chem. Soc., Perkin Trans. 1 1989, 1707–1708. (b) Nagashima, H.; Tatebe, K.; Ishibashi, T.; Sakakibara, J.; Itoh, K. Organometallcs 1989, 8, 2495–2496. (c) Nagashima, H.; Tatebe, K.; Ishibashi, T.; Nakaoka, A.; Sakakibara, J.; Itoh, K. Organometallics 1995, 14, 2868–2879. (d) Sunada, Y.; Fujimura, Y.; Nagashima, H. Organometallics 2008, 27, 3502–3513. (14) (a) Loza, M. L.; de Gala, S. R.; Crabtree, R. H. Inorg. Chem. 1994, 33, 5073–5078. (b) Loza, M.; Faller, J. W.; Crabtree, R. H. Inorg. Chem. 1995, 34, 2937–2941. (15) (a) Bourg, S.; Boury, B.; Carre, F.; Corriu, R. J. P. Organometallics 1997, 16, 3097–3099. (b) Bourg, S.; Boury, B.; Carre, F. H.; Corriu, R. J. P. Organometallics 1998, 17, 167–172.
Kang and Ko prepared transition-metal complexes with ancillary silyl-o-carborane ligands. Disilametallacycles with a bulky
with a hydride ligand, fac-[RhH(SiMe2CH2CH2 SiMe2)(PMe3)3] (8).12 Nagashima reported enhancement of Rh(I) complex catalyzed hydrosilylation by using the bifunctional organosilanes dmsbH2 and dmseH2, affording the monohydrosilylation products selectively (eq 1).13 Hydrosilylation of acetone with HMe2Si(CH2)nSiMe2H (n = 2, 3) catalyzed by RhCl(PPh3)3 is 50-120 times faster than that with trialkylsilanes and with HMe2Si(CH2)nSiMe2H (n = 1, 4). These results suggest that Rh complexes with chelating Si ligands show much higher catalytic activity than complexes with monosilyl ligands or monocoordinated silyl ligands having an uncoordinated SiMe2H group. The reactions of dmsbH2 with RhCl(PPh3)3 or RhH(PPh3)4 in a 10:1 ratio provided a mixture of Rh(III) complexes with one or
Scheme 3
of a stable Si-O bond should occur during the reaction, and a mechanism involving an intermediate silylene complex was proposed. Oxidative addition of dmseH2 to the Rh(I) thiolato complex [Rh(SPh)(PMe3)3] produces a disilarhodacycle
Compounds with two secondary silyl groups, H2SiPh(CH2)2SiPhH2 and H2SiMe(C6H4)SiMeH2, react with Co2(CO)8 to form the butterfly-shaped dinuclear complexes [{Co(CO)3}2{μ(SiR-X-SiR)}] (11, X=(CH2)2, R=Ph; 12, X=C6H4, R= Me) (Scheme 3).15 The molecules have two distorted-octahedral Co atoms bridged with a metal-metal bond and two silylene groups. The crystallographic results suggested short contacts between the two Si atoms and weak Si 3 3 3 Si interactions.
carborane group, [M(SiMe2(C2B10H10) SiMe2)(PR3)2] (13, M = Pt, R = Ph; 14, M = Ni, R = Et), are obtained from oxidative addition of two Si-H bonds with zerovalent metal complexes (eq 3). The complexes are stabilized kinetically due to the unique electronic and steric effects of the carborane.16
Tanaka and Shimada prepared group 10 metal complexes with high oxidation state by using chelating 1,2-disilylbenzene ligands.17 Equimolar reactions of H3SiC6H4SiH3 with Ni(0), Pd(0), and Pt(0) complexes yield common square-planar (16) (a) Kang, Y.; Kang, S. O.; Ko, J. Organometallics 2000, 19, 1216– 1224. (b) Kang, Y.; Lee, J.; Kong, Y. K.; Kang, S. O.; Ko, J. Organometallics 2000, 19, 1722–1728. (c) Lee, Y.-J.; Lee, J.-D.; Kim, S.-J.; Ko, J.; Suh, I.-H.; Cheong, M.; Kang, S. O. Organometallics 2004, 23, 135–143. (d) Lee, Y.-J.; Lee, J.-D.; Kim, S.-J.; Yoo, B. W.; Ko, J.; Suh, I.-H.; Cheong, M.; Kang, S. O. Organometallics 2004, 23, 490–497. (17) (a) Yamashita, H.; Tanaka, M. Bull. Chem. Soc. Jpn. 1995, 68, 403– 419. (b) Shimada, S.; Tanaka, M. Coord. Chem. Rev. 2006, 250, 991–1011.
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BuNC. Passing H2 gas through its solution for a few minutes regenerates the starting complex with dihydrogen ligands.
complexes of divalent metals with chelating disilyl ligands. Further reactions of disilylbenzene produce complexes with a tetravalent octahedral metal and two chelating disilanyl ligands: 15,18
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16,19 and 1720 (eq 4). Themolysis of [Pd(H2SiC6H4SiH2){PR2(CH2)2PR2}] (R=Me, Et) converts it into the unprecedented tripalladium complex 18, with three disilylbenzene ligands (Chart 5).21 The central Pd atom of 18 is coordinated by six Si atoms. Theoretical calculations suggested a possible interaction between the two Si atoms at positions close to each other, as shown in 180 .22 Aromatic trisilane reacts with Ni(0) or Pt(0) complexes to form a hydrido(trisilyl)nickel(IV) (19) and -platinum(IV) complexes (20), as shown in eq 5.23 The reaction with the Pd(0) complex, however, does not produce the corresponding Pd(IV) complex, probably due to reductive elimination of the compound with an Si-Si bond.
Si-Si bond activation of a compound containing two disilyl groups also yields the disilametallacycles. Ito prepared the disilapalladacycle [Pd(dmsb)(CNtBu)2] (22) starting from bis(disilanyl)benzene and a Pd(0) complex, as shown in eq 7.24 The reaction should involve initial oxidative addition of an Si-Si bond to form the intermediate 23 (Chart 6). Subsequent reaction can be intramolecular σ-bond metathesis of the formed Pd-SiMe2Ph bond and the remaining Si-Si bond or further oxidative addition of the disilyl group to Pd, giving the Pd(IV) intermediate 24, followed by reductive elimination of PhMe2Si-SiMe2Ph. Both pathways rationalize formation of the disilapalladacycle.
Chart 5
Chart 6
1,2-disilaplatinacyclobutanes [Pt(SiPh2(NCH2R) SiPh2)(PMe3)2] (25; R = Me, Ph) (eq 8).25 Insertion of the CtN bond into the Pt-Si bond did not take place in this case. Insertion of dimethyl acetylenedicarboxylate (ZCtCZ, Z = COOMe) into the Pt-Si bond of bis(silyl)platinum complexes produces the four-mem
Sabo-Etienne conducted the reaction of dmseH2, dmsbH2, etc. with Ru complexes with hydride and dihydrogen ligands and obtained complexes with bis(silane) li-
Double silylation of the CtN triple bond by Si-H groups of bis(silyl)platinum complexes yields the four-membered 3-aza-
(18) Shimada, S.; Rao, M. L. N.; Tanaka, M. Organometallics 1999, 18, 291–293. (19) Shimada, S.; Tanaka, M.; Shiro, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 1856–1858. (20) Shimada, S.; Tanaka, M.; Honda, K. J. Am. Chem. Soc. 1995, 117, 8289–8290. (21) Chen, W.; Shimada, S.; Tanaka, M. Science 2002, 295, 308–310. (22) (a) Sherer, E. C.; Kinsinger, C. R.; Kormos, B. L.; Thompson, J. D.; Cramer, C. J. Angew. Chem., Int. Ed. 2002, 41, 1953–1956. (b) Aull€on, G.; Lled€ os, A.; Alvarez, S. Angew. Chem., Int. Ed. 2002, 41, 1956–1959. (23) Chen, W.; Shimada, S.; Tanaka, M.; Kobayashi, Y.; Saigo, K. J. Am. Chem. Soc. 2004, 126, 8072–8073.
(24) Suginome, M.; Oike, H.; Park, S.-S; Ito, Y. Bull. Chem. Soc. Jpn. 1996, 69, 289–299. (25) Tanabe, M.; Osakada, K. Organometallics 2001, 20, 2118–2120. (26) (a) Tanabe, M.; Osakada, K. J. Am. Chem. Soc. 2002, 124, 4550– 4551. (b) Tanabe, M.; Osakada, K. Chem. Eur. J. 2004, 10, 416–424. (27) Yamamoto, K.; Okinoshima, H.; Kumada, M. J. Organomet. Chem. 1971, 27, C31–C32. (28) (a) Seyferth, D.; Duncan, D. P.; Vick, S. C. J. Organomet. Chem. 1977, 125, C5–C10. (b) Seyferth, D.; Shannon, M. L.; Vick, S. C.; Lim, T. F. O. Organometallics 1985, 4, 57–62. (c) Sakurai, H.; Kamiyama, Y.; Nakadaira, Y. J. Am. Chem. Soc. 1977, 99, 3879–3880.
bered 4-sila-3-platinacyclobutene [Pt(CZdCZSiPh2)(PMe3)2] (26) in high yield, accompanied by elimination of H2SiPh2, as shown in Scheme 4.26 A detailed study of the reaction revealed that 26 is equilibrated with the 3-sila-1-propenyl platinum complex cis-[Pt(CZdCZSiPh2H)(SiHPh2)(PMe3)2] (27) in solution. Complex 26 is the first isolated silacyclometallabutene, although the silametallacyclobutenes of group 10 transition metals have been proposed as intermediates for cycloaddition of disilanes to
gands, [RuH2{η2-(HMe2Si-X- SiMe2H)}(PCy3)2] (21, X = (CH2)2, (CH2)3, C6H4, OSiMe2O) (eq 6). Crystallographic and 1H NMR results of 21 indicated coordination of two σ-Si-H bonds of the bis(silane) ligand to the Ru center. JSi-H values (65-82 Hz) smaller than those for uncoordinated Si-H bonds are diagnostic to determine the coordination in solution. The Si ligands of 21 are easily replaced with CO and
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Scheme 4
Scheme 5
alkynes (Pt),27 addition of silacyclopropanes to alkynes (Pd),28 cyclodimerization of alkynyl disilanes (Ni),29 and reaction of siliranes with alkynes to give silirenes (Pd).30 Tanaka isolated 4platina-2,5-cyclohexadiene from disilane, alkyne, and Pt(PEt3)4, and the reaction was proposed to involve four-membered intermediates.31 Ohshita and Ishikawa reported preparation of a silanickelacyclobutene, which was identified by a detailed NMR study of the solution, although it was too unstable to be isolated.32
Scheme 6
The reactions in Scheme 4 are summarized as above. Insertion of acetylene into a Pt-Si bond of the bis(silyl)platinum complex forms the silapropenylplatinum complex 27 initially. Complex 27 has weak coordination of the Si-H group of the ligand with an apical site of the Pt center, as is evident by the NMR results of 27 and the X-ray structure of an analogous complex with a dmpe (1,2-bis(dimethylphosphino)ethane) ligand. It rendered oxidative addition of the Si-H bond to the Pt center and subsequent reductive elimination of H2SiPh2 smoothly. Seyferth,33 Ishikawa,34 and Ko16a and their respective coworkers reported addition of the Si-Si bond to unsaturated compounds containing CdC, CdO, and CtC, CtN bonds, giving compounds with enlarged rings. The stoichiometric reactions of disilacyclopentane, disilacyclobenezene, and 2,3disilanyldiylcarborane cause smooth oxidative addition of the Si-Si bonds onto zerovalent group 10 metal complexes to form the five- and six-membered disilametallacycles 28, 29, and 13 (Scheme 5). Complex 13 reacts with carbonyl compounds to form 30 and 31, as shown in Scheme 6. Double insertion of the (29) (a) Ishikawa, M.; Sugisawa, H.; Harata, O.; Kumada, M. J. Organomet. Chem. 1981, 217, 43–50. (b) Ishikawa, M.; Matsuzawa, S.; Hirotsu, K.; Kamitori, S.; Higuchi, T. Organometallics 1984, 3, 1930–1932. (c) Ishikawa, M.; Matsuzawa, S.; Higuchi, T.; Kamitori, S.; Hirotsu, K. Organometallics 1985, 4, 2040–2046. (30) (a) Palmer, W. S.; Woerpel, K. A. Organometallics 1997, 16, 1097–1099. (b) Palmer, W. S.; Woerpel, K. A. Organometallics 1997, 16, 4824–4827. (31) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1992, 11, 3227–3232. (32) (a) Ishikawa, M.; Ohshita, J.; Ito, Y.; Iyoda, J. J. Am. Chem. Soc. 1986, 108, 7417–7419. (b) Ohshita, J.; Isomura, Y.; Ishikawa, M. Organometallics 1989, 8, 2050–2054. (33) Seyferth, D.; Goldman, E. W.; Escudie, J. J. Organomet. Chem. 1984, 271, 337–352. (34) Naka, A.; Hayashi, M.; Okazaki, S.; Ishikawa, M. Organometallics 1994, 13, 4994–5001.
Scheme 7
carbonyl groups of the cyclic 1,2-dione into the Pt-Si bond forms the former product. Oxophilic nature of the silyl ligand renders the reaction smooth. The latter reaction in Scheme 6, however, should involve insertion of the CdO bond of transcinnamaldehyde into the two Si-C bonds of the complex. Ito and Suginome reported ring-enlargement oligomerization of 1,2-disilacyclopropanes catalyzed by a Pd(0) isonitrile complex.35 The formal σ-bond metathesis of two Si-Si bonds yields another pair of Si-Si linkages. As an extension of mechanistic studies of the reaction, they found that bicyclic (35) (a) Suginome, M.; Oike, H.; Shuff, P. H.; Ito, Y. Organometallics 1996, 15, 2170–2178. (b) Suginome, M.; Kato, Y.; Takeda, N.; Oike, H.; Ito, Y. Organometallics 1998, 17, 495–497.
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Scheme 10
Scheme 9
Si-Si bond, leading to M-Si-E- Si (M = Mo, W; E = O, S,
Se) type four-membered cyclic metallacycles [M(SiMe2-S-SiMe2)Cp2] (34), as shown in eq 9.36 The η2-coordinated disilene ligand in [Pt(η2-Si2Me4)(dppe)]8 (dppe = 1,2-bis(diphenylphosphino)ethane) forms new Si-O and Si-N bonds upon contact
with oxygen and NH3 to give [Pt(SiMe2-O- SiMe2)(dppe)] (35)
and [Pt(SiMe2-NH- SiMe2)(dppe)] (36), respectively (Scheme 8). Cleavage of the Pt-Si bonds was not observed in the reaction. The former complex shows a short Si 3 3 3 Si contact (2.549(2) A˚) in the M-Si-O- Si four-membered-ring structure due to a weak interaction, which is supported by theoretical calculations.37
Corriu reported double addition of dmsb to nitrile to form the five-membered disilazane under photoirradiation.38 The reaction (36) (a) Berry, D. H.; Chey, J. H.; Zipin, H. S.; Carroll, P. J. J. Am. Chem. Soc. 1990, 112, 452–453. (b) Berry, D. H.; Chey, J.; Zipin, H. S.; Carroll, P. J. Polyhedron 1991, 10, 1189–1201. (c) Hong, P.; Damrauer, N. H.; Carroll, P. J.; Berry, D. H. Organometallics 1993, 12, 3698–3704. (37) Nikonov, G. I.; Vyboishchikov, S. F.; Kuzmina, L. G.; Howard, J. A. K. Chem. Commun. 2002, 568–569. (38) (a) Corriu, R. J. P.; Moreau, J. J. E. J. Chem. Soc., Chem. Commun. 1980, 278–279. (b) Corriu, R. J. P.; Moreau, J. J. E.; Pataud-Sat, M. J. Org. Chem. 1981, 46, 3372–3374. (c) Corriu, R. J. P.; Moreau, J. J. E.; Pataud-Sat, M. Organometallics 1985, 4, 623–629.
as [Pt(GeMe2(CH2)2 GeMe2)(PPh3)2]n (38) on the basis of IR spectroscopic data (Scheme 10).40 Subsequent coordination of the chelating diphosphine to 38 produces the mononu-
clear digermaplatinacyclopentane [Pt{GeMe2(CH2)2GeMe2}(dppe)] (39). A similar reaction of (Z)-R,β-bis(dimethylgermyl)styrene with a Pt(0)-PPh3 complex forms the digerma
compounds having two Si-Si bonds undergo oxidative addition to Pd(0) complexes to afford 32, a dinuclear palladium complex with bridging tridentate Si ligand (Scheme 7). Allyl(cyclopentadienyl)palladium is employed as a precursor of Pd(0) species because of the facile reductive elimination of allylcyclopentadiene. The reaction of the spirotrisilane, however, converts it to complex 33 with the cyclopentadienyl ligand being kept at the Pd center. Reductive elimination of allylsilane takes place from the coupling of the allyl ligand and central silyl atom of the ligand instead. A molybdenum and tungsten complex with a η2-tetramethyldisilene ligand undergoes addition of elemental chalcogens to the
involves initial formation of the disilaferracyclopentane [Fe(dmsb)(CO)4] (37), originally prepared by Fink,39 and subsequent reaction of the nitrile with the formed metallacycle (Scheme 9). Digermylated metallacycles were prepared by methods similar to those for the silametallacycles mentioned above. Double oxidative addition of HMe2Ge(CH2)2GeMe2H to [Pt(CH2dCH2)(PPh3)2] gave an insoluble solid, which was suggested as the polymeric complex formulated
platinacyclopentene [Pt{GeMe2(CHdCPh) GeMe2}(PPh3)2] (40) directly.41 Complexes 39 and 40 undergo insertion of CtC bonds of terminal alkynes into the Pt-Ge bonds, whereas treatment of 40 with CO and CNtBu causes substitution of a PPh3 ligand with ligands having π-acidic character. Ni(PEt3)4 reacts with digermyl-o-carborane and with carboranylene digermacyclobutane to cause activation of the two Ge-H bonds and of the Ge-Ge bond, respectively, to yield the digermanickellacycle, similarly to the case for silyl carboranes (eq 3, Scheme 5).42 Cycloaddition of digermacyclopropane43 and digermacyclobutene44 to alkyne catalyzed by Pd complexes was proposed to involve digermametallacycles as the intermediates. The stoichiometric reactions of these ring-strained digermanes with Pd(PPh3)4 produce the isolable palladium complexes 41 and 42, which are formed by insertion of a palladium atom into the Ge-Ge bond (Scheme 11). Suginome and Ito conducted the reaction of bis(silylgermyl)dithiane with Pd- and Pt-CNtBu complexes (39) Fink, W. Helv. Chim. Acta 1976, 59, 606–613. (40) (a) Barrau, J.; Rima, G.; Cassano, V.; Satge, J. Inorg. Chim. Acta 1992, 198-200, 461–467. (b) Barrau, J.; Rima, G.; Cassano, V.; Satge, J. Organometallics 1995, 14, 5700–5703. (c) Barrau, J.; Rima, G.; Cassano, V. Main Group Met. Chem. 1996, 19, 283–299. (41) Mochida, K.; Karube, H.; Nanjo, M.; Nakadaira, Y. Organometallics 2005, 24, 4734–4741. (42) (a) Lee, J.; Lee, C.; Lee, S. S.; Kang, S, O.; Ko, J. Chem. Commun. 2001, 1730–1731. (b) Lee, C.; Lee, J.; Lee, S. W.; Kang, S, O.; Ko, J. Inorg. Chem. 2002, 41, 3084–3090. (c) Lee, J.; Lee, T.; Lee, S. S.; Park, K.-M.; Kang, S. O.; Ko, J. Organometallics 2002, 21, 3922–3929. (43) Tsumuraya, T.; Ando, W. Organometallics 1989, 8, 2286–2288. (44) (a) Komoriya, H.; Kako, M.; Nakadaira, Y.; Mochida, K. J. Organomet. Chem. 2000, 611, 420–432. (b) Mochida, K.; Karube, H.; Nanjo, M.; Nakadaira, Y. J. Organomet. Chem. 2005, 690, 2967–2974.
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Scheme 11
Scheme 13
Scheme 14 Scheme 12
Chart 7
cycles [Pt(GePh2(SiMe2)n GePh2)(PPh3)2] (49; n = 1, 2), as shown in Scheme 13.47
3. Persilylated and Pergermylated Metallacycles Schram
prepared
the
tetrasilaplatinacyclopen-
The reactions of HGePh2(SiMe2)nGePh2H (n = 0-2) with a Pt(0)-PPh3 complex form the hydrido(germyl)platinum complexes [PtH{GePh2(SiMe2)nGeHPh2}(PPh3)2] (48; n = (45) Suginome, M.; Oike, H.; Shuff, P. H.; Ito, Y. J. Organomet. Chem. 1996, 521, 405–408. (46) (a) Litz, K. E.; Henderson, K.; Gourley, R. W.; Banaszak Holl, M. M. Organometallics 1995, 14, 5008–5010. (b) Litz, K. E.; Kampf, J. W.; Banaszak Holl, M. M. J. Am. Chem. Soc. 1998, 120, 7484–7492. (c) Litz, K. E.; Bender, J. E.; Sweeder, R. D.; Banaszak Holl, M. M.; Kampf, J. W. Organometallics 2000, 19, 1186–1189.
tane [Pt(SiPh2SiPh2SiPh2 SiPh2)(PPh3)2] (50) from two independent reactions, as shown in Scheme 14.48 Metathesis of [PtCl2(PPh3)2] with Li2[SiPh2SiPh2SiPh2SiPh2] yields 50, while double oxidative addition of the 1,4-dihydro(octaphenyl)tetrasilane to [Pt(C2H4)(PPh3)2] also affords the same complex. These two reactions correspond to those shown as (i) and (ii) in Scheme 1, respectively.
tinacycle [PtC(O)O Ge{N(SiMe3)2}2(PEt3)2] (47) via [2 þ 2] cycloaddition of the CdO and PtdGe double bonds (eq 10).46 46 and 47 are equilibrated, and heating of 47 regenerates 46, which is accompanied by elimination of CO2. The reversibility of the reaction enables formation of either complex depending on the temperature.
0-2) as the initial products, and subsequent cyclometalation of the ligand produces the four- and five-membered metalla-
and obtained digermametallacycles of Pd(II) and Pt(IV), as shown in Scheme 12.45 The digermapallacycles 43 were produced through double oxidative addition of the Ge-Si bonds to Pd(CNtBu)2, accompanied by elimination of the disilanes. Reaction with the Pt(0) complex forms two Pt(IV) complexes. The double oxidative addition yields 44, a digermaplatinacyclobutane having two silyl ligands. Reductive elimination of disilane from 44 causes further double oxidative addition of a new substrate molecule to afford 45. Exposure of a solution of the isolated platinumgermylene complex [(PEt3)2PtdGe{N(SiMe3)2}2] (46) to CO2 results in formation of the four-membered germapla-
The tetragermaytterbiacyclopentane [Yb(GePh2GePh2GePh2GePh2)(thf)4] (51) was obtained from the direct reaction of Ph2GeCl2 with metallic Yb, which was characterized by X-ray crystallography (Chart 7).49 Mochida studied the palladium-catalyzed insertion of alkynes into the Ge-Ge bond of cyclic oligogermanes to produce a cyclic compound with a Ge-CdC-Ge bond. They (47) Usui, Y.; Hosotani, S.; Ogawa, A.; Nanjo, M.; Mochida, K. Organometallics 2005, 24, 4337–4339. (48) Lemanski, M. F.; Schram, E. P. Inorg. Chem. 1976, 15, 1489– 1492. (49) Bochkarev, L. N.; Makarov, V. M.; Zakharov, L. N.; Fukin, G. K.; Yanovsky, A. I.; Struchkov, Y. T. J. Organomet. Chem. 1995, 490, C29–C31.
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Organometallics, Vol. 29, No. 21, 2010 Scheme 15
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Scheme 16
Scheme 17
proposed a mechanism which involves the tetragermapalladacyclopentane 52 as one of the intermediates, on the basis of results of bisgermylation of alkynes.50 The corresponding tetragermapalladacyclopentane, however, was not isolated from the reaction mixture, probably due to the rapid catalytic reaction. More recently, Braddock-Wilking conducted the reaction of sila- and germafluorenes H2ER2 (ER2 = SiC12H8, GeC12H8) with a Pt(II)-dppe complex and isolated the persilyl- and pergermyl-
platinacyclopentanes [Pt(ER2ER2ER2ER2)(dppe)] (53).51 Dehydrocondensation of the secondary germane forms the cyclic compounds in this reaction. The reactions of H2GePh2 with the Pd(II) and Pt(II) complexes with germyl ligands also produce a tetragermametallacycle. The Pd- and Pt-containing
tetragermacyclopentanes [M(GePh2GePh2GePh2GePh2)(dmpe)] (54, M=Pd;52 55, M=Pt53) were obtained from the reaction of excess H2GePh2 with [M(GeHPh2)2(dmpe)] (M = Pd, Pt), as shown in Scheme 15. An equimolar reaction of H2GePh2 with the bis(germyl)platinum complex forms the four-membered
germaplatinacycle [Pt(GePh2GePh2GePh2)(dmpe)] (56), and further addition of excess H2GePh2 causes ring enlargement of the germametallacycle to give 55. Thus, formation of the tetragermaplatinacyclopentane 55 involves the trigermaplatinacyclobutane 56 as the intermediate. The tetragermapalladacyclopentane 54 is also produced via a similar ring enlargement process. The tetrastannapalladacyclopentane [Pd(SnPh2SnPh2SnPh2SnPh2)(dmpe)] (57) was also prepared by starting from the Pd(0) complex by treatment with H2SnPh2 in 1:4 ratio (eq 11). Sn-H bonds are easily activated in comparison to Ge-H or Si-H bonds, leading to the formation of a five-membered ring under mild conditions.54
Treatment of 55 and 56 with excess PhGeH3 results in the Pt-Ge bond cleavage of the germacycles to release the tetra(50) Mochida, K.; Hirakue, K.; Suzuki, K. Bull. Chem. Soc. Jpn. 2003, 76, 1023–1028. (51) Braddock-Wilking, J.; Bandrowsky, T.; Praingam, N.; Rath, N. P. Organometallics 2009, 28, 4098–4105. (52) Tanabe, M.; Ishikawa, N.; Hanzawa, M.; Osakada, K. Organometallics 2008, 27, 5152–5158. (53) Tanabe, M.; Hanzawa, M.; Ishikawa, N.; Osakada, K. Organometallics 2009, 28, 6014–6019. (54) Tanabe, M.; Hanzawa, M.; Osakada, K. Organometallics 2010, in press.
and trigermanes, as shown in Scheme 16. These reactions provide a new route to prepare a linear oligogermane directly from the diarylgermanes. Banaszak Holl,55 Mochida,56 and Ishii57 reported isomerization of the bis(germyl)platinum to (digermyl)hydridoplatinum complexes via facile rearrangement of the primary or secondary germyl ligands, as shown in reaction i in Scheme 17. The Ge-Ge bond formation promoted by the Pt atom proceeds through a PtdGe intermediate formed by R-hydrogen elimination of a GeHAr2 ligand and migratory insertion of the formed GeAr2 ligand into the Pt-Ge bond (Scheme 17, reaction iia), or to occur reductive elimination to form Ge-Ge bond and subsequent reoxidative addition of the Ge-H bond (Scheme 17, reaction iib). Scheme 18 shows a plausible pathway for preparation of germametallacycles starting from the digermyl and hydrido complex A. Excess H2GePh2 causes exchange of the hydride ligand of A with the GeHPh2 ligand to form the digermyl and germyl complex B. Rearrangement of the digermyl and germyl ligands of B, similar to the case in reaction ii of Scheme 17, gives the hydrido(trigermyl)metal complex C. Repeated exchange of the hydrido with GePh2H ligands and migration of the germylene moiety afford the hydrido(tetragermyl)metal complex (D), (55) Bender, J. E.; Litz, K. E.; Giarikos, D.; Wells, N. J.; Banaszak Holl, M. M.; Kampf, J. W. Chem. Eur. J. 1997, 3, 1793–1796. (56) Arii, H.; Nanjo, M.; Mochida, K. Organometallics 2008, 27, 4147–4151. (57) Nakata, N.; Fukazawa, S.; Ishii, A. Organometallics 2009, 28, 534–538.
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Tanabe and Osakada
cently, Ni complexes were reported to produce the cyclic polysilane from primary silanes in part.59 This may be ascribed to the formation of Ni-containing metallacycles and their ring enlargement reaction shown above for the condensation of H2GeAr2 promoted by Pt complexes.
4. Conclusions
Scheme 19
propagating the (GePh2)n unit. Trigerma- and tetragermametallacycles 56 and 54, 55 are formed by intramolecular cyclization of C or D, respectively. Thus, the Ge-Ge bond-forming reaction proceeds successively during the formation of the germaplatinacycle and its Pd analogue. The cyclization via H2 extrusion occurs not only for formation of the stable five-membered ring but also for the less stable four-membered ring. Ring enlargement occurs smoothly, although it may contain ring expansion and re-formation of the ring during it. Ring expansion of the four-membered 56 into five-membered cycles 55 occurs via a similar pathway (Scheme 19). Treatment of the ring-strained complex 56 with H2GePh2 undergoes a ring-opening reaction by cleavage of the Pt-Ge bond to form F. Intramolecular migration of the GePh2 group into the Pt-Ge bond gives the hydrido(tetragermyl)platinum complex D, followed by cyclometalation with a dehydrogenation process to form the five-membered germaplatinacycle 55. Transition-metal complexes catalyze the polycondensation of organosilanes to produce polysilanes. Early-transition-metal complexes catalyze the dehydrogenative polycondensation of diorganosilanes probably via σ-bond metathesis and often produce the cyclic polysilanes.58 Re(58) (a) Tilley, T. D. Acc. Chem. Res. 1993, 26, 22–29. (b) Gauvin, F.; Harrod, J. F.; Woo, H. G. Adv. Organomet. Chem. 1998, 42, 363–405. (c) Corey, J. Y. Adv. Organomet. Chem. 2004, 51, 1–52. (59) (a) Fontaine, F.-G.; Zargarian, D. Organometallics 2002, 21, 401–408. (b) Fontaine, F.-G.; Zargarian, D. J. Am. Chem. Soc. 2004, 126, 8786–8794.
Sila- and germametallacycles of late transition metals were synthesized by several kinds of reactions which form the M-Si and M-Ge bonds smoothly. The most common one is double oxidative addition of the bifunctional organosilicon compounds to low valent transition metal complexes. Reversibility of activation of E-H and E-E bond (E = Si, Ge) in the oxidative addition and formation of these bonds in concerted reductive elimination probably renders these synthetic reactions smoothly and selectively. The metallacycles undergo insertion of small molecules into the M-Si and M-Ge bonds, but chemical properties of these complexes have not been widely investigated yet. More concern should be added to this area to understand the reactivity of the coordination bonds and new findings of the reactions of organic compounds having heavy elements promoted by transition metal complexes. Activation of the E-H and E-E bonds by electron-rich late transition metals is the more useful methods to form M-Si bonds, compared to the corresponding M-C bonds. The study of the four- and five-membered persilyl- and pergermyl- metallacycles provided us details of the Si-Si and Ge-Ge bond-forming reactions using organosilanes and organogermanes. Dehydrocoupling polymerization of organosilanes catalyzed by late transition metal complexes seems to be related to the Ge-Ge bond formation shown in this article because the catalytic process often produces the cyclic oligo- and polysilanes and because the Ge-Ge bond forming reaction tends to involve the cyclic intermediate which may undergo ring enlargement easily upon addition of H2GeAr2. Further studies of the sila- and germa-metallacylces will provide the results and obsevation which are general and important in understanding of properties of the transition metal complexes with Si- and Ge- ligands. The silametallacycles with apparently weak bonds within the cycle were reported to show unique and important chemical properties.60 These compounds as well as the complexes related to intermediate of the synthetic organic reactions are not conducted to this article.
Acknowledgment. This article is dedicated to Prof. Dietmar Seyferth for his great contribution as the first chief editor of Organometallics, his continuous efforts to build up and strengthen the journal and the research field as well as his kindness and patience donated to younger foreign scientists throughout these three decades. We are grateful to Prof. Akihiko Ishii and Dr. Norio Nakata of Saitama University for helpful discussion. The studies of our group cited in this article were done with help of Mr. Masaya Hanzawa and Ms. Naoko Ishikawa and with financial support 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. (60) (a) Ueno, K.; Tobita, H.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc. 1988, 110, 4092–4093. (b) Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc. 1990, 112, 3415–3420.
