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Synthesis and Structure of the First Gallium-Bridged Heterodimetallic Complexes, Cp*(dppe)FeGaM(CO)5 (Cp* ) η5-C5Me5, dppe ) Ph2P(CH2)2PPh2, M ) Cr, W) Takako Muraoka, Hideaki Motohashi, Yasuhiro Kazuie, Akira Takizawa, and Keiji Ueno* Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma UniVersity, Kiryu 376-8515, Japan ReceiVed December 25, 2008 Summary: The first Ga-bridged heterodimetallic complexes, Cp*(dppe)FeGaM(CO)5 (Cp* ) η5-C5Me5, dppe ) Ph2P(CH2)2PPh2, M ) Cr (3), W (4)), were synthesized by the reaction of Cp*(dppe)FeGaCl2 and K2[M(CO)5] (M ) Cr and W) in THF in 53 and 55% yield, respectiVely. Crystal structure analysis of 4 reVealed that both the Fe-Ga and Ga-W bonds are significantly shorter than the corresponding usual single bonds and comparable to those in gallylene metal complexes. Transition-metal dimetallic complexes bridged by a group 13 element, LnM-E-M′L′m (E ) group 13 elements; MLn, M′L′m ) transition metal fragments), are of growing interest because of their unique bonding, structures, and reactivity.1-5 The essentially linear arrangement of the M-E-M′ angle implies the sp-hybridization of the E atom and the contribution of π bonding in the metal-E bonds. However, the intrinsic insights into the bonding have been limited in this type of complexes due to the lack of systematic investigations on the electronic effect of the metal fragments on the M-E bonding. We have recently reported the synthesis and reactivity of the first gallium-bridged dimetallic complexes, Cp*(P2)Fe-GaFe(CO)4 (1: P2 ) Ph2P(CH2)2PPh2 (dppe), 2: P2 ) Me2P(CH2)2PMe2 (dmpe)), in which both of the iron-gallium bonds bear unsaturated bonding character.3a,e,f We have also found that the Fe-Ga bonds are quite sensitive to the electronic nature of the iron fragments.3e,f For example, substitution of one CO ligand of the Fe(CO)4 fragment in 1 with a more electron-releasing ligand PR3 shortens the Ga-Fe(CO)3(PR3) bond and elongates the Cp*(dppe)Fe-Ga bond, while substitution of dppe of 1 with * To whom correspondence should be addressed. Tel & Fax: +81-27730-1260. E-mail:
[email protected]. (1) (a) Braunschweig, H.; Whittell, G. R. Chem.-Eur. J. 2005, 11, 6128. (b) Ueno, K.; Muraoka, T. Bull. Jpn. Soc. Coord. Chem. 2007, 50, 18. (2) (a) Braunschweig, H.; Radacki, K.; Scheschkewitz, D.; Whittell, G. R. Angew. Chem., Int. Ed. 2005, 44, 1658. (b) Braunschweig, H.; Kraft, K.; Kupfer, T.; Radacki, K.; Seeler, F. Angew. Chem., Int. Ed. 2008, 47, 4931. (c) Braunschweig, H.; Burzler, M.; Dewhurst, R. D.; Radacki, K. Angew. Chem., Int. Ed. 2008, 47, 5650. (3) (a) Ueno, K.; Watanabe, T.; Tobita, H.; Ogino, H. Organometallics 2003, 22, 4375. (b) Bunn, N. R.; Aldridge, S.; Coombs, D. L.; Rossin, A.; Willock, D. J.; Jones, C.; Ooi, L. Chem. Commun. 2004, 1732. (c) Coombs, N. D.; Bunn, N. R.; Kays, D. L.; Day, J. K.; Ooi, L.-L.; Aldridge, S. Inorg. Chim. Acta 2006, 359, 3693. (d) Buchin, B.; Gemel, C.; Cadenbach, T.; Ferna´ndez, I.; Frenking, G.; Fischer, R. A. Angew. Chem., Int. Ed. 2006, 45, 5207. (e) Ueno, K.; Hirotsu, M.; Hatori, N. J. Organomet. Chem. 2007, 692, 88. (f) Muraoka, T.; Motohashi, H.; Ueno, K. Organometallics 2008, 27, 3918. (4) Bunn, N. R.; Aldridge, S.; Kays, D. L.; Coombs, N. D.; Rossin, A.; Willock, D. J.; Day, J. K.; Jones, C.; Ooi, L. Organometallics 2005, 24, 5891. (5) (a) Schiemenz, B.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1993, 32, 1772. (b) Uso´n, R.; Fornie´s, J.; Toma´s, M.; Garde, R. J. Am. Chem. Soc. 1995, 117, 1837. (c) Jeffery, J. C.; Jelliss, P. A.; Liao, Y.-H.; Stone, F. G. A. J. Organomet. Chem. 1998, 551, 27.
a more basic dmpe ligand, i.e., complex 2, causes the shortening of the Cp*Fe-Ga bond and lengthening of the Ga-Fe(CO)4 bond. These findings prompted us to investigate the electronic effect of metal fragments other than iron on the metal-gallium bonding. Although several groups including us have reported gallium-bridged dimetallic complexes, there is no report on the heterodimetallic complexes bridged by a gallium atom. Here, we report the synthesis and structures of the first heterodimetallic Ga-bridged complexes, Cp*(dppe)Fe-Ga-M(CO)5 (3: M ) Cr, 4: M ) W). The heterodimetallic complexes Cp*(dppe)Fe-Ga-M(CO)5 (3: M ) Cr, 4: M ) W) were synthesized by a salt elimination reaction of Cp*(dppe)FeGaCl26 with a corresponding dianionic complex, K2[M(CO)5], in THF (eq 1).
Complexes 3 and 4 were isolated as orange crystals in 53 and 55% yield, respectively.7 The 1H NMR spectrum of the Fe-Ga-Cr complex 3 showed a singlet signal assignable to a Cp* ligand at 1.44 ppm and several multiplet signals assignable to the Ph groups of dppe in the range 6.9-7.9 ppm. The inequivalent methylene protons of the dppe ligand are coincidentally overlapped and observed as a multiplet signal with 4H intensity at 2.16 ppm. The Fe-Ga-W complex 4 also gave an overlapped multiplet signal for the methylene protons at 2.10 ppm. In the 13C NMR spectrum, two CO signals were observed at 222.0 and 226.8 ppm for 3 and 203.0 and 204.2 ppm for 4, which are assignable to the cis- and the trans-CO to the bridging Ga atom, respectively, based on the signal intensities. Crystal structure analysis of 4 (Figure 1) revealed an almost linear arrangement of the Fe-Ga-W framework (173.78(4)°). (6) Ueno, K.; Watanabe, T.; Ogino, H. Appl. Organometal. Chem. 2003, 17, 403. (7) 3: 1H NMR (300 MHz, C6D6) δ 7.87 (m, 4H, Ph), 7.44 (m, 4H, Ph), 7.21 (m, 2H, Ph), 6.96 (m, 10H, Ph), 2.16 (m, 4H, PCH2CH2P), 1.44 (s, 15H, C5Me5); 13C{1H} NMR (125.7 MHz, C6D6) δ 226.8 (trans-CO), 222.0 (cis-CO), 139.8-127.4 (m, PPh), 86.8 (C5Me5), 33.4 (dd, 1JPC ) 23 Hz, 2JPC ) 23 Hz, PCH2), 10.5 (C5Me5); 31P{1H} NMR (202.5 MHz, C6D6) δ 93.0 (dppe); IR (KBr) νCO 2015, 1897 cm-1. Anal. Calcd for C41H39CrFeGaO5P2: C, 57.85; H, 4.62. Found: C, 57.62; H, 4.57. 4: 1H NMR (300 MHz, C6D6) δ 7.83 (m, 4H, Ph), 7.41 (m, 4H, Ph), 7.22-6.97 (m, 12H, Ph), 2.10 (m, 4H, PCH2CH2P), 1.43 (s, 15H, C5Me5); 13C{1H} NMR (125.7 MHz, C6D6) δ 204.2 (trans-CO), 203.0 (cis-CO), 139.6-127.4 (m, PPh), 86.6 (C5Me5), 32.6 (dd, 1JPC ) 22 Hz, 2JPC ) 22 Hz, PCH2), 10.1 (C5Me5); 31P{1H} NMR (202.5 MHz, C6D6) δ 91.2 (dppe); IR (KBr) νCO 2033, 1905 cm-1. Anal. Calcd for C41H39FeGaO5P2W: C, 50.09; H, 4.00. Found: C, 50.04; H, 4.13.
10.1021/om801219d CCC: $40.75 2009 American Chemical Society Publication on Web 02/18/2009
Communications
Figure 1. ORTEP drawing of 4 (thermal ellipsoids at the 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Fe-Ga, 2.2687(12); W-Ga, 2.5861(8); W-C3, 2.032(8); W-C1, 2.046(8); W-C2, 2.058(8); W-C4, 2.044(8); W-C5, 2.047(9); Fe-Ga-W, 173.78(4).
The linear arrangement suggests sp-hybridization of the Ga atom and the existence of two empty p-orbitals on Ga, which could accept electrons through π back-donation from the W and Fe fragments. The W-Ga and Fe-Ga bond lengths (2.5861(8) and 2.2687(12) Å, respectively) are significantly shorter than the corresponding usual single bonds (W-Ga, 2.71-2.76 Å;8 Fe-Ga, 2.36-2.46 Å3a,b,4,6,9) and are comparable to the those of gallylene metal complexes Cp*GaW(CO)5 (2.566(1) Å),10a (Cp*Ga)3W(CO)3 (av 2.521 Å),10b Ar*GaFe(CO)4 (2.2248(7) Å, Ar* ) 2,6-(2,4,6-iPr3C6H2)2C6H3),11a [Cp*Fe(dppe)GaI][BArf4] (2.2221(6) Å),11b and Cp*GaFe(CO)4 (2.2731(4) Å).11c The Cp*(dppe)Fe-Ga bond in 4 (2.2687(12) Å) is longer than that in Cp*(dppe)Fe-Ga-Fe(CO)4 (1, 2.2479(10) Å), comparable to that in Cp*(dppe)Fe-Ga-Fe(CO)3{P(OPh)3} (2.2690(8) Å), and shorter than that in Cp*(dppe)Fe-Ga-Fe(CO)3(PMe3) (2.2769(5) Å).3a,f This indicates that the electronic effect of W(CO)5 toward the Cp*(dppe)Fe-Ga fragment is comparable to that of Fe(CO)3{P(OPh)3}. Complexes 3 and 4 can be regarded as gallylene complexes with a metal-substituted gallylene ligand, Cp*(dppe)FeGa. Recent experimental and theoretical studies on the gallylene complexes LnMdGaR revealed that the gallylene ligand GaR (8) (a) Conway, A. J.; Hitchcock, P. B.; Smith, J. D. J. Chem. Soc., Dalton Trans. 1975, 1945. (b) Denis, J. N. S.; Butler, W.; Glick, M. D.; Oliver, J. P. J. Organomet. Chem. 1977, 129, 1. (9) (a) Fischer, R. A.; Weiss, J. Angew. Chem., Int. Ed. 1999, 38, 2830. (b) Ueno, K.; Watanabe, T.; Ogino, H. Organometallics 2000, 19, 5679. (c) Uhl, W.; El-Hamdan, A.; Petz, W.; Geiseler, G.; Harms, K. Z. Naturforsch. 2004, 59b, 789. (d) Bunn, N. R.; Aldridge, S.; Kays, D. L.; Coombs, N. D.; Day, J. K.; Ooi, L.; Coles, S. J.; Hursthouse, M. B. Organometallics 2005, 24, 5879. (e) Jones, C.; Aldridge, S.; Gans-Eichler, T.; Stasch, A. Dalton Trans. 2006, 5357.
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behaves as a electron-releasing ligand due to its strong σ-donor and relatively weak π-accepter character.9a,10-13 Indeed, the CO stretching bands of complex 3 (2015 and 1897 cm-1) and 4 (2033 and 1905 cm-1) appeared in the lower frequency region than those of the corresponding phosphine complex (Me3P)M(CO)5 (2063, 1949, and 1941 cm-1 for M ) Cr and 2071, 1947, and 1937 cm-1 for M ) W).14 The gallylene ligand Cp*(dppe)Fe-Ga is categorized as a donor-stabilized gallylene similar to η5-Cp*Ga and R2NGa, since the Ga p-orbitals are partially filled by the electrons supplemented by π back-donation from the Fe fragment.15 This decreases the π-acidity of the gallium center and suppresses the back-donation from the M(CO)5 fragment. The slightly long Ga-W bond and red-shift of ν(CO) in 4 (2.5861(8) Å, 2033 and 1905 cm-1) compared to those of Cp*Ga-W(CO)5 (2.566(1) Å, 2065, 1986, and 1910 cm-1) demonstrates the stronger electron-donating nature of the Cp*(dppe)Fe fragment than that of the Cp* group.10a
Acknowledgment. This work was supported by a Grantin-Aid for Scientific Research on Priority Areas (No. 20036011) and for Scientific Research (Nos. 17655022 and 20655011) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Supporting Information Available: Text, tables, figures, and a CIF file on experimental details and X-ray crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. OM801219D (10) (a) Leiner, E.; Scheer, M. J. Organomet. Chem. 2002, 646, 247. (b) Cokoja, M.; Steinke, T.; Gemel, C.; Welzel, T.; Winter, M.; Merz, K.; Fischer, R. A. J. Organomet. Chem. 2003, 684, 277. (11) (a) Su, J.; Li, X.-W.; Crittendon, R. C.; Campana, C. F.; Robinson, G. H. Organometallics 1997, 16, 4511. (b) Coombs, N. D.; Clegg, W.; Thompson, A. L.; Willock, D. J.; Aldridge, S. J. Am. Chem. Soc. 2008, 130, 5449. (c) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H.-G. Organometallics 1998, 17, 1305. (12) (a) Boehme, C.; Uddin, J.; Frenking, G. Coord. Chem. ReV. 2000, 197, 249. (b) Frenking, G.; Wichmann, K.; Frohlich, N.; Loschen, C.; Lein, M.; Frunzke, J.; Rayon, V. M. Coord. Chem. ReV. 2003, 238-239, 55 and references therein. (13) (a) Bollwein, T.; Brothers, P. J.; Hermann, H. L.; Schwerdtfeger, P. Organometallics 2002, 21, 5236. (b) Yang, X.-J.; Quillian, B.; Wang, Y.; Wei, P.; Robinson, G. H. Organometallics 2004, 23, 5119. (c) Yang, X.-J.; Wang, Y.; Quillian, B.; Wei, P.; Chen, Z.; Schleyer, P. R.; Robinson, G. H. Organometallics 2006, 25, 925. (d) Cadenbach, T.; Gemel, C.; Zacher, D.; Fischer, R. A. Angew. Chem., Int. Ed. 2008, 47, 3438. (e) Quillian, B.; Wang, Y.; Wei, P.; Robinson, G. H. New J. Chem. 2008, 32, 774. (14) (a) Mathieu, R.; Lenzi, M.; Poilblanc, R. Inorg. Chem. 1970, 9, 2030. (b) Cotton, F. A.; Darensbourg, D. J.; Kolthammer, B. W. S. Inorg. Chem. 1981, 20, 4440. (c) Lee, K. J.; Brown, T. L. Inorg. Chem. 1992, 31, 289. (d) Davis, M. S.; Pierens, R. K.; Aroney, M. J. J. Organomet. Chem. 1993, 458, 141. (15) Coombs, N. D.; Vidovic, D.; Day, J. K.; Thompson, A. L.; Le Pevelen, D. D.; Stasch, A.; Clegg, W.; Russo, L.; Male, L.; Hursthouse, M. B.; Willock, D.; Aldridge, S. J. Am. Chem. Soc. 2008, 130, 16111.
