Reductive Reactivity of the Tetravalent Uranium ... - ACS Publications

236

Organometallics 2009, 28, 236–243

Reductive Reactivity of the Tetravalent Uranium Complex [(η5-C5Me5)(η8-C8H8)U]2(µ-η3:η3-C8H8) William J. Evans,*,† Michael K. Takase,† Joseph W. Ziller,† Antonio G. DiPasquale,‡ and Arnold L. Rheingold‡ Department of Chemistry, UniVersity of California, IrVine, California 92697-2025, and Department of Chemistry and Biochemistry, UniVersity of California, San Diego, 9500 Gilman DriVe, MC 0358, La Jolla, California 92093-0358 ReceiVed August 1, 2008

The reductive reactivity of the cyclooctatetraenide ligands in [(η5-C5Me5)(η8-C8H8)U]2(µ-η3:η3-C8H8), 1, was examined with polycyclic hydrocarbons, phenazine, and the diphenyldichalcogenide compounds PhEEPh (E ) S, Se, Te). Complex 1 does not reduce anthracene, acenaphthylene, or benzanthracene, but it acts as a two-electron reductant with phenazine to form 1 equiv of C8H8 and the bimetallic complex [(η5-C5Me5)(η8-C8H8)U]2(µ-η1:η1-C12H8N2), 2. X-ray crystallography showed that the heteroleptic metallocene unit [(C5Me5)(C8H8)U]1+ adopted an η1-coordination mode with the phenazine dianion rather than the η3-coordination previously found with the homoleptic f element metallocene cations [(C5Me5)2M]1+. Complex 1 also reacts as a two-electron reductant with PhEEPh (E ) S, Se, Te) to form C8H8 and the heteroleptic complexes [(η5-C5Me5)(η8-C8H8)U]2(µ-EPh)2 (E ) S, 3; Se, 4; Te, 5). Introduction Recent studies of the reductive chemistry of organoactinides have shown that traditional metal-based reduction reactions can be coupled with ligand-based reductions to accomplish multielectron reductions.1-6 Equation 1 shows an example in which

H1– canalsoeffectreductionalongwithmetal-basedprocesses.4,8-10 Equation 2 shows a four-electron reduction8 involving (BPh4)1– and eq 3 shows a six-electron process10 involving both hydride

a U3+ complex, (C5Me5)3U, functions as a three-electron reductant to make a U4+ product by combining a one-electron U3+/U4+ redox couple with two (C5Me5)1–/(C5Me5) reductions.1-3 In efforts to better define this sterically induced reduction (SIR),1-3,7 control reactions with sterically “normal” complexes were examined and revealed that ligands such as (BPh4)1– and

* Corresponding author. Fax: 949-824-2210. E-mail: [email protected]. † University of California, Irvine. ‡ University of California, San Diego. (1) Evans, W. J.; Davis, B. L. Chem. ReV. 2002, 102, 2119–2136. (2) Evans, W. J.; Nyce, G. W.; Johnston, M. A.; Ziller, J. W. J. Am. Chem. Soc. 2000, 122, 12019–12020. (3) Evans, W. J.; Nyce, G. W.; Ziller, J. W. Angew. Chem., Int. Ed. 2000, 39, 240–242. (4) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Chem. Commun. 2005, 4681–4683. (5) Evans, W. J.; Kozimor, S. A.; Ziller, J. W.; Kaltsoyannis, N. J. Am. Chem. Soc. 2004, 126, 14533–14547. (6) Diaconescu, P. L.; Arnold, P. L.; Baker, T. A.; Mindiola, D. J.; Cummins, C. C. J. Am. Chem. Soc. 2000, 122, 6108–6109. (7) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Inorg. Chem. 2005, 44, 7960–7969. (8) Evans, W. J.; Miller, K. A.; Hillman, W. R.; Ziller, J. W. J. Organomet. Chem. 2007, 692, 3649–3654.

and (C5Me5)1– ligands. The reductive reactivity of ligands in sterically normal organoactinide complexes suggested that a wider variety of ligands should be studied. The reductive chemistry of sterically normal [(η5-C5Me5)(η8C8H8)U]2(µ-η3:η3-C8H8), 1,3 was of interest since this molecule contained three cyclooctatetraenide dianions. Each of these could potentially function as a two-electron reductant to provide ligand-based reduction chemistry according to eq 4. The combination of the three (C8H8)2- ligands could make bimetallic 1 a six-electron reductant that could deliver two [(C5Me5)U]3+ units. (9) Evans, W. J.; Nyce, G. W.; Forrestal, K. J.; Ziller, J. W. Organometallics 2002, 21, 1050–1055. (10) Evans, W. J.; Miller, K. A.; Kozimor, S. A.; Ziller, J. W.; DiPasquale, A. G.; Rheingold, A. L. Organometallics 2007, 26, 3568–3576.

10.1021/om800747s CCC: $40.75  2009 American Chemical Society Publication on Web 11/20/2008

TetraValent Uranium Complex

(C8H8)2- 98 C8H8 + 2e1-

Organometallics, Vol. 28, No. 1, 2009 237

(4)

Complex 1 was also an interesting reagent since it contained two different types of cyclooctatetraenide ligands both in solution and in the solid state. As shown in Figure 1, the crystal structure contains two terminal (C8H8)2- ligands that are planar, as expected for an aromatic system, and bind as η8-ligands, as is typical in organo-f-element chemistry. However, the bridging (C8H8)2- ligand is nonplanar and coordinates to the two uranium centers in a bis η3-fashion. Reactivity studies could determine if this structural difference in the solid state would translate into reactivity differences for the ligands in solution, where a 2:1 ratio of (C8H8)2- resonances is observed. Complex 1 was also unusual in that the 1H NMR resonances of the (C8H8)2ligands, at -41.7 and -42.2 ppm, are at the far end of the range of values observed for U4+ complexes and are closer to values usually observed for (C8H8)2- ligands in U3+ complexes, Table 1. The reductive chemistry of 1 is also of interest in comparison to uranocene, (C8H8)2U, which contains only planar (η8-C8H8)2ligands.11-15 Uranocene has not been reported to have extensive reductive chemistry,16,17 but it is air sensitive, and reactions have been reported with iodine18 to form (C8H8)UI2(THF)2 and with silanols.19 A mono-n-butyl-substituted derivative has been reported to react with nitrobenzene, forming PhNdNPh, UO2, and free n-butylcyclooctatetraene, eq 5.20 To our knowledge, this is the only reductive reaction currently known for uranocenes in which the ligand is oxidized to form a free substituted cyclooctatetraene.

Although complex 1 was an attractive reagent for further studies of organoactinide reduction chemistry, its original synthesis according to eq 1 was challenging. The recent discovery of a synthetic pathway to 1 via eq 310 made complex 1 readily accessible for reactivity studies. We report here that 1 has extensive reduction chemistry and functions primarily as a two-electron reductant with the substrates that have given characterizable products.

Experimental Section The syntheses and manipulations described below were conducted under argon with rigorous exclusion of air and water using (11) Streitwieser, A., Jr.; Mueller-Westerhoff, U. J. Am. Chem. Soc. 1968, 90, 7364. (12) Streitwieser, A., Jr.; Muller-Westerhoff, U.; Sonnichsen, G.; Mares, F.; Morrell, D. G.; Hodgson, K. O.; Harmon, C. A. J. Am. Chem. Soc. 1973, 95, 8644. (13) Zalkin, A.; Raymond, K. N. J. Am. Chem. Soc. 1969, 91, 5667– 5668. (14) Avdeef, A.; Raymond, K. N.; Hodgson, K. O.; Zalkin, A. Inorg. Chem. 1972, 11, 1083–1088. (15) Seyferth, D. Organometallics 2004, 23, 3562–3583. (16) Butcher, J. A., Jr.; Chambers, J. Q.; Pagni, R. M. J. Am. Chem. Soc. 1978, 100, 1012–1013. (17) Butcher, J. A., Jr.; Pagni, R. M.; Chambers, J. Q. J. Organomet. Chem. 1980, 199, 223–227. (18) Berthet, J. C.; Le Marechal, J. F.; Ephritikhine, M. J. Organomet. Chem. 1990, 393, C47–C48. (19) Lorenz, V.; Fischer, A.; Bruser, W.; Edelmann, F. T.; Jacob, K.; Gelbrich, T.; Jones, P. G. Chem. Commun. 1998, 2217–2218. (20) Grant, C. B.; Streitwieser, A., Jr. J. Am. Chem. Soc. 1978, 100, 2433–2440.

Figure 1. Molecular structure of [(C5Me5)(C8H8)U]2(C8H8), 1,3 showing the η3:η3 binding and nonplanarity of the bridging (C8H8)2ligand. Thermal ellipsoids are drawn at the 50% probability level and hydrogen atoms have been omitted for clarity. glovebox, vacuum line, and Schlenk techniques. All glovebox manipulations were done in an argon-filled glovebox free of coordinating solvents. Solvents were dried over columns containing Q-5 and molecular sieves. NMR solvents were dried over sodium potassium alloy, degassed, and vacuum transferred prior to use. 1 H NMR spectra were recorded with a Bruker DRX 500 MHz spectrometer. [(C5Me5)(C8H8)U]2(C8H8), 1, was prepared as previously described.10 1,3,5,7-C8H8 was distilled over molecular sieves and degassed by three freeze-pump-thaw cycles before use. PhSSPh, PhSeSePh, PhTeTePh, and phenazine were purchased from Aldrich and sublimed before use. Elemental analyses were performed by Analytische Laboratorien (Lindlar, Germany) or on a Perkin-Elmer 2400 CHNS elemental analyzer. [(C5Me5)(C8H8)U]2(µ-η1:η1-C12H8N2), 2. A yellow solution of phenazine (43 mg, 0.24 mmol) in toluene (4 mL) was added to a dark brown solution of 1 (251 mg, 0.237 mmol) in toluene (6 mL) and stirred for 2 days. The solvent was evaporated under vacuum, leaving a tacky brown solid, which was washed with hexanes and dried under vacuum to yield 2 as a dark brown solid (215 mg, 80%). In an NMR scale experiment, free C8H8 was observed at 5.6 ppm in a 1:1 molar ratio with 2 by 1H NMR spectroscopy. Crystals of 2 suitable for X-ray diffraction were grown at room temperature from a concentrated benzene solution. 1H NMR (C6D6): δ 6.9 (s, C5Me5, ∆ν1/2 ) 5 Hz, 30H), -20.7 (s, C12H8N2, ∆ν1/2 ) 10 Hz, 4H), -33.3 (s, C8H8, ∆ν1/2 ) 6 Hz, 16H). 13C NMR (C6D6): δ -26.2 (s, C5Me5), 227.7 (s, C8H8). All of the phenazine resonances could not be identified. IR: 3383m, 3261m, 3190m, 3047m, 2966s, 2899s, 2853s, 1591m, 1514s, 1501m, 1457s, 1376w, 1302s, 1279s, 1193w, 1124w, 889s, 726s cm-1. Anal. Calcd for C48H54N2U2: C, 50.79; H, 4.80; N, 2.47. Found: C, 51.46; H, 4.48; N, 2.72. [(C5Me5)(C8H8)U]2(µ-SPh)2, 3. A colorless solution of PhSSPh (43 mg, 0.197 mmol) in toluene (4 mL) was added to a dark brown solution of 1 (208 mg, 0.197 mmol) in toluene (6 mL). After the solution was allowed to stir for 3 h, it was evaporated to dryness under vacuum. The resulting tacky brown solid was washed with hexanes and dried under vacuum to yield 3 as a light brown powder (189 mg, 82%). Free C8H8 was observed in a 1:1 molar ratio with 3 in a 1H NMR experiment. 1H NMR (C6D6): δ 7.7 (s, C5Me5, ∆ν1/2 ) 17 Hz, 30H), 5.2 (s, SPh, ∆ν1/2 ) 43 Hz, 2H), 4.3 (s, SPh, ∆ν1/2 ) 60 Hz, 4H), -20.6 (s, SPh, ∆ν1/2 ) 82 Hz, 4H), -38.2 (s, C8H8, ∆ν1/2 ) 34 Hz, 16H). 13C NMR (C6D6): δ -23.9 (s, C5Me5), 113 (s, SPh), 134 (s, SPh), 147 (s, SPh), 277 (s, C8H8). IR: 2907s, 2856s, 1774w, 1574m, 1471s, 1433m, 1373m, 1082m, 1021w, 921w, 902w, 725s, 691s cm-1. Anal. Calcd for C48H56S2U2: C, 49.14; H, 4.81; S, 5.47; U, 40.58. Found: C, 48.85; H, 4.88; S, 5.32; U, 41.1. [(C5Me5)(C8H8)U]2(µ-SePh)2, 4. In a manner analogous to the preparation of 3, 4 was isolated as a red powder (121 mg, 92%)

238 Organometallics, Vol. 28, No. 1, 2009

EVans et al.

Table 1. 1H NMR Shifts of the (C8H8)2- Ligands in Organouranium Complexes Arranged in Order of Increasing Oxidation State and Chemical Shift complex

oxidation state

shift (ppm)

(C5Me5)(C8H8)U(THF) (C5Me5)(C8H8)U(HMPA)b,58 [(C8H8)U(HMPA)3][BPh4]b,59 (C8H8)U(tmp)(HMPA)2b,e,58 [Zr2(OiPr)9][(C8H8)U]60 K[(C8H8)U(tmp)2(BH4)(THF)]e,61 (C5H5)(C8H8)U(BH4)(THF)62 [(C5Me5)(C8H8)U]2(C8H8)3

3 3 3 3 3 4 4 4

(µ-η8,η8-C8H8)[U(NC[tBu]Mes)3]244 (C5Me5)(C8H8)UI18,63

4 4

(C8H8)U(O3SCF3)2(py)f,64 (C8H8)U[C5H4(SiMe3)]257 (C5H5)(C8H8)U(NEt2)41 (C8H8)U(BH4)2(PPh3)62 (C5Me5)(C8H8)U(NEt2)41 (C5Me5)(C8H8)U[N(SiMe3)2]31

4 4 4 4 4 4

(C8H8)UI2(THF)218,63 (C8H8)U(NEt2)265,66

4 4

(C5Me5)(C8H8)U[CH2(SiMe3)]63 (C8H8)U(NEt2)[CH(SiMe3)2]43 [(C5H5)(C8H8)U(THF)2][BPh4]41 (C8H8)U(NEt2)[N(SiMe3)2]43 (C5H5)(C8H8)U[N(SiMe3)2]63 [(C8H8)U(S2CNEt2)(THF)2][BPh4]43 (C5H5)(C8H8)UI63 [(C8H8)U(BH4)(THF)2][BPh4]67

4 4 4 4 4 4 4 4

(C8H8)U(BH4)2(THF)62 (C8H8)U(tmp)(BH4)(THF)e,61 (C8H8)U(BH4)(OiPr)33

4 4 4

-52.3 -50.18c -47.4d -43.16c -39.8a -53.27d -47.60c -42.2a -41.7a -39.19a -38.5c -34.02d -37.5d -37.18a -36.20a -35.88c -35.78a -35.5a -35.0c -35.43d -35.18c -27.76d -35.07a -35.0a -34.87g -34.3a -34.23c -34.0d -33.97c -33.64d -33.40h -33.35a -33.27d -33.19c -30.63d -33.14d -33.0h -32.88h -32.77d -32.7a -32.7c -30.64d -32.60d -32.31d -32.09d -32.07h -32.07h -31.7d -31.6d -31.5d -31.50d -24.04h

57

e,61

(C8H8)U(tmp)(OEt) [(C8H8)UCl(THF)2][BPh4]43 [(C5Me5)(C8H8)U(THF)2][BPh4]41 [(C8H8)U(BH4)(OPPh3)3][BPh4]67 (C5Me5)(C8H8)UCl(OCNH(CH2)531 (C8H8)U(BH4)(OtBu)33

4 4 4 4 4 4

[(C8H8)U(tmp)(HMPA)2][(BPh4)]b,e,61 (C8H8)UI2(HMPA)2b,18,63 [(C8H8)U(BH4)(HMPA)3][BPh4]b,67 (C8H8)U(dmio)(py)f,i,68 (C8H8)U(dmio)(py)2f,i,69 [(C8H8)U(O2CNEt2)(THF)2][BPh4]43 (C8H8)UCl2(py)2f,70 (C8H8)UCl2(THF)270 (C8H8)U(OiPr)233

4 4 4 4 4 4 4 4 4

a

complex

oxidation state

shift (ppm)

(C8H8)U(dmio)(OPPh ) (C8H8)U(C5H3(SiMe3)2)I(HMPA)b,63 (C8H8)UI(acac)j,63 (C5H5)(C8H8)UI(HMPA)b,63 (C8H8)U(dddt)(py)f,k,68 (C8H8)U(dddt)(py)2f,k,69 (C8H8)U(NEt2)(BH4)(THF)443 (C8H8)U(dmio)(HMPA)2b,i,69 (C8H8)U(BH4)(OEt)33 [Na(THF)][(C8H8)U(StBu)3]71 (C5H5)(C8H8)U(BH4)(OPPh3)62 (C8H8)U(acac)2j,18,63,70

4 4 4 4 4 4 4 4 4 4 4 4

(C8H8)U(mdt)(OPPh3)2l,69 (C5Me5)(C8H8)ClU(Cl)U(C5Me5)(C8H8)31 (C8H8)U(NEt2)2(THF)65 [Na(18-crown-6)]2[(C8H8)U(dddt)2]k,72 (C8H8)U(OtBu)233 (C8H8)U(BH4)2(OPPh3)62 (C8H8)U(mdt)(HMPA)2b,l,69 Na[(C8H8)U(BH4)2(OEt)]33 [(C8H8)U(NC{Me}NEt2)(THF)2][BPh4]43 (C8H8)U(CH2Ph)2(HMPA)2b,63 (C8H8)U(OEt)233

4 4 4 4 4 4 4 4 4 4 4

[(C8H8)U(NEt2)(THF)2][BPh4]41 (C8H8)U(CH2SiMe3)2(HMPA)b,63 (C8H8)U(dddt)(HMPA)2b,k,69 (C8H8)U(mdt)(py)2f,l,69 [K(18-crown-6)][(C8H8)U(BH4)3]33 (C8H8)U(SnBu)271

4 4 4 4 4 4

(C8H8)U(SiPr)271

4

71 2

(C8H8)U(s Bu)

4

(C8H8)U(O2CNEt2)265 [Li(THF)3][(C8H8)U(CH2SiMe3)3]63 Li[(C8H8)U(NEt2)3]66 K[(C8H8)U(NEt2)3]65 [(C8H8)U(HMPA)3][(BPh4)2]b,67 [(C8H8)U(NEt2)2(THF)2][BPh4]66 [Na(18-crown-6)][(C8H8)U(dddt)2]k,72 [(C8H8)U(NEt2)2(THF)][BPh4]65,66 (C5H5)(C8H8)U(NEt2)265 (C8H8)U(NEt2)365,66 (C8H8)U(NMe2)365 (C8H8)U(OiPr)365

4 4 4 4 5 5 5 5 5 5 5 5

-31.46d -31.45c -31.37d -31.36a -30.98h -30.98h -30.6d -30.44d -30.25d -30.05d -29.99d -29.6c -29.18a,c -29.52d -29.3a -29.20a -29.17d -28.86d -28.82d -28.78d -28.72d -28.3h -27.95c -27.8d -24.02h -27.13h -26.57c -26.13d -24.82h -24.09d -23.48c -23.36h,m -26.62h,n -23.22h -23.20c -22.96c -22.88h,m -28.99h,n -21.06d -19.96a -15.84d -15.84d -32.48h -29.71d -27.35d -15.3d -12.5a -9.5a,c -8.9a -6.6a

i,69 3 2

t

a Solvent ) benzene. b HMPA ) hexamethyl phosphorus triamide. c Solvent ) toluene. d Solvent ) THF. e tmp ) C4Me4P. f py ) pyridine. Solvent ) acetonitrile. h Solvent ) pyridine. i dmio ) 1,3-dithiole-2-one-4,5-dithiolate. j acac ) acetoacetonate. k dddt ) 5,6-dihydro-1,4dithiine-2,3-dithiolate. l mdt ) 1,3-dithiole-4,5-dithiolate. m Dimeric form. n Monomeric form. g

from a yellow solution of PhSeSePh (33 mg, 0.104 mmol) in toluene (4 mL) and a dark brown solution of 1 (111 mg, 0.104 mmol) in toluene (6 mL). 1H NMR (C6D6): δ 8.6 (s, C5Me5, ∆ν1/2 ) 40 Hz, 30H), 6.7 (s, SePh, ∆ν1/2 ) 86 Hz, 2H), 5.9 (s, SePh, ∆ν1/2 ) 122 Hz, 4H), -16.7 (s, SePh, ∆ν1/2 ) 111 Hz, 4H), -37.8 (s, C8H8, ∆ν1/2 ) 60 Hz, 16H). 13C NMR (C6D6): δ -23.9 (s, C5Me5), 154 (s, SePh), 285 (s, C8H8). IR: 3048m, 2984m, 2901s, 2855m, 1576m, 1471s, 1449m, 1435m, 1379m, 1069m, 1021s, 999w, 736s, 693m, 667m cm-1. Anal. Calcd for C48H56Se2U2: C, 45.50; H, 4.46; Se, 12.46; U, 37.58. Found: C, 44.93; H, 4.34; Se, 12.3; U, 38.4. [(C5Me5)(C8H8)U]2(µ-TePh)2, 5. In a manner analogous to the preparation of 3, 5 was isolated as a light red powder (228 mg, 86%) from an orange solution of PhTeTePh (80 mg, 0.194 mmol) in toluene (4 mL) and a dark brown solution of 1 (206 mg, 0.194 mmol) in toluene (6 mL). 1H NMR (C6D6): δ 9.7 (s, C5Me5, ∆ν1/2 ) 18 Hz, 30H), 8.3 (s, TePh, ∆ν1/2 ) 33 Hz, 2H), 7.8 (s, TePh,

∆ν1/2 ) 34 Hz, 4H), -10.9 (s, TePh, ∆ν1/2 ) 38 Hz, 4H), -39.1 (s, C8H8, ∆ν1/2 ) 29 Hz, 16H). 13C NMR (C6D6): δ -24 (s, C5Me5), 119 (s, TePh), 135 (s, TePh), 165 (s, TePh), 297 (s, C8H8). IR: 3053m, 2898s, 2851m, 1570s, 1468s, 1430s, 1378m, 1016s, 900w, 722s, 695m, 650w cm-1. Anal. Calcd for C48H56Te2U2: C, 42.26; H, 4.14; Te, 18.71; U, 34.90. Found: C, 42.52; H, 4.10; Te, 18.9; U, 34.0. X-ray Data Collection, Structure Solution, and Refinement for 2. A brown crystal of approximate dimensions 0.10 × 0.10 × 0.20 mm was mounted on a glass fiber and transferred to a Bruker CCD platform diffractometer. The SMART21 program package was used to determine the unit-cell parameters and for data collection (30 s/frame scan time for a sphere of diffraction data). The raw (21) SMART Software Users Guide, Version 5.1; Bruker Analytical X-Ray Systems, Inc.: Madison, WI, 1999.



Table 2. X-ray Data Collection Parameters for [(C5Me5)(C8H8)U]2(C12H8N2), 2, [(C5Me5)(C8H8)U]2(SePh)2, 4, and [(C5Me5)(C8H8)U]2(TePh)2, 5 C48H54N2U2 · (C6H6) 2 C48H56Se2U2 4 C48H56Te2U2 5 fw temperature (K) cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) volume (Å3) Z Fcalcd (Mg/m3) µ (mm-1) R1 [I > 2.0σ(I)]a wR2 (all data)a

1213.10 158(2) monoclinic P21/n 18.183(3) 12.9333(19) 19.487(3) 90 105.644(2) 90 4412.9(11) 4 1.826 7.369 0.0391 0.0861

1266.91 208(2) orthorhombic Pbca 12.191(4) 17.707(8) 19.051(5) 90 90 90 4113(3) 4 2.046 9.669 0.0424 0.01066

1364.19 155(2) orthorhombic Pbca 19.204(6) 9.975(3) 22.158(7) 90 90 90 4245(2) 4 2.135 9.000 0.0328 0.0665

Figure 2. Molecular structure of [(C5Me5)(C8H8)U]2(C12H8N2), 2, with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity.

a Definitions: wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2] ]1/2, R1 ) ∑|Fo| - |Fc|/∑|Fo|.

frame data were processed using SAINT22 and SADABS23 to yield the reflection data file. Subsequent calculations were carried out using the SHELXTL24 program. The diffraction symmetry was 2/m, and the systematic absences were consistent with the centrosymmetric monoclinic space group P21/n, which was later determined to be correct. The structure was solved by direct methods and refined on F2 by full-matrix least-squares techniques. The analytical scattering factors25 for neutral atoms were used throughout the analysis. Hydrogen atoms were included using a riding model. There was one molecule of benzene solvent present per formula unit. The solvent was refined as a regular hexagon with equal isotropic displacement parameters (EADP). Details are given in Table 2. X-ray Data Collection, Structure Solution, and Refinement for 4. A black block 0.13 × 0.10 × 0.06 mm in size was mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 208(2) K using phi and omega scans. Crystal-todetector distance was 60 mm and exposure time was 10 s per frame using a scan width of 0.3°. Data collection was 99.9% complete to 25.00° in θ. A total of 20739 reflections were collected covering the indices -15 e h e 16, -22 e k e 20, -11 e l e 25. 4958 reflections were found to be symmetry independent, with an Rint of 0.0585. Indexing and unit cell refinement indicated a primitive, orthorhombic lattice. The space group was found to be Pbca (No. 61). The data were integrated using the Bruker SAINT22 software program and scaled using the SADABS23 software program. Solution by direct methods (SIR-2004) produced a complete heavyatom phasing model consistent with the proposed structure. All nonhydrogen atoms were refined anisotropically by full-matrix leastsquares (SHELXL-97). All hydrogen atoms were placed using a riding model. Their positions were constrained relative to their parent atom using the appropriate HFIX command in SHELXL97. X-ray Data Collection, Structure Solution, and Refinement for 5. A red crystal of approximate dimensions 0.12 × 0.21 × 0.25 mm was handled as described for 2. The diffraction symmetry was mmm, and the systematic absences were consistent with the orthorhombic space group Pbca, which was later determined to be correct. The molecule was located about an inversion center. The (22) SAINT Software Users Guide, Version 6.0; Bruker Analytical X-Ray Systems, Inc.: Madison, WI, 1999. (23) Sheldrick, G. M. SADABS, Version 2.10; Bruker Analytical X-Ray Systems, Inc.: Madison, WI, 2002. (24) Sheldrick, G. M. SHELXTL, Version 6.12; Bruker Analytical X-Ray Systems, Inc.: Madison, WI, 2001. (25) International Tables for X-Ray Crystallography; Kluwer Academic Publishers: Dordrecht, 1992; Vol. C.

Figure 3. Molecular structure of [(C5Me5)(C8H8)U]2(SePh)2, 4, with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. uranium atom was disordered and included using two components with site-occupancy factors of 0.955 and 0.045. The distance between the two components was 1.044 Å. The distances and angles reported refer only to those related to the major component U(1).

Results Phenazine. C12H8N2 was initially examined as a substrate since it is easily reducible (-0.364 V vs SCE)26 and has been used successfully to test other f element reduction systems.27-29 Complex 1 reacts with phenazine in a 1:1 ratio to form the complex [(C5Me5)(C8H8)U]2(µ-η1:η1-C12H8N2), 2, which was characterized by 1H and 13C NMR spectroscopy and identified by X-ray crystallography, eq 6, Figure 2. One equivalent of free C8H8 per equivalent of 2 was observed in an NMR scale reaction.

(26) Nechaeva, O. N.; Pushkareva, Z. V. Zh. Obshch. Khim. 1958, 28, 2693–2701. (27) Evans, W. J.; Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1994, 116, 2600–2608.


Figure 4. Molecular structure of [(C5Me5)(C8H8)U]2(TePh)2, 5, with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity.

In this two-electron reduction reaction, only one of the (C8H8)2- ligands in 1 was needed to reduce phenazine to the dianion (C12H8N2)2-. As a consequence, the net reaction generates two monocationic [(C5Me5)(C8H8)U]1+ heteroleptic metallocene units along with the doubly reduced phenazine dianion. Isolation of 2 allows direct comparison of the mixed ligand [(C5Me5)(C8H8)U]1+ metallocene with the more common homoleptic f element metallocene, [(C5Me5)2M]1+. The solid-state structure of 2 revealed that the [(C5Me5)(C8H8)U]1+ unit coordinates to the phenazine dianion in a bonding mode not previously seen in f element chemistry.27,28,30 Specifically, the (C12H8N2)2- ligand bridges the uranium centers with an η1-bonding mode to each nitrogen. There are no other crystallographically characterized uranium (C12H8N2)2- complexes in the literature, but the structure of 2 can be compared to the lanthanide complexes [(C5Me5)2Ln]2(µ-η3:η3-C12H8N2) (Ln ) Sm, 6;27 La, 728,30). In the lanthanide complexes, the phenazine dianion bridges the metals using three adjacent atoms in an aza-allyl mode on each side, Scheme 1. The X-ray diffraction study also revealed that in the solid state the heteroleptic metallocene units are arranged so that the two (C5Me5)1– ligands are in a cis rather than trans orientation with respect to each other, and concomitantly the same is true for the (C8H8)2- ligands. Heteroleptic bimetallic f element complexes more often have a trans arrangement of ligands: (C5Me5)(C8H8)ClU(µ-Cl)U(C8H8)(C5Me5)31 and {(C5Me5)[C8H6(SiiPr3)2]U}2(µ-η1:η2-C3O3)32 are two examples. However, both cis and trans structures are found for [(C8H8)UX]2(µ-OR)2 (X ) BH4, R ) Et; X ) OiPr, R ) iPr).33 It is possible that isomers exist in this case also since two pairs of (C5Me5)1– and (C8H8)2resonances are observed in the crude reaction mixture before recrystallization. Table 3 shows a comparison of selected bond distances and angles for 2 versus the [(C5Me5)2Ln]2(C12H8N2) complexes in order to evaluate how the heteroleptic [(C5Me5)(C8H8)U]1+ metallocene cation compares with the homoleptic metallocene (28) Evans, W. J.; Perotti, J. M.; Kozimor, S. A.; Champagne, T. M.; Davis, B. L.; Nyce, G. W.; Fujimoto, C. H.; Clark, R. D.; Johnston, M. A.; Ziller, J. W. Organometallics 2005, 24, 3916–3931. (29) Evans, W. J.; Lee, D. S.; Ziller, J. W.; Kaltsoyannis, N. J. Am. Chem. Soc. 2006, 128, 14176–14184. (30) Scholz, J.; Scholz, A.; Weimann, R.; Janiak, C.; Schumann, H. Angew. Chem., Int. Ed. Engl. 1994, 1233, 1171–1174. (31) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Polyhedron 2006, 25, 484–492. (32) Summerscales, O. T.; Cloke, F. G. N.; Hitchcock Peter, B.; Green Jennifer, C.; Hazari, N. Science 2006, 311, 829–831. (33) Arliguie, T.; Baudry, D.; Ephritikhine, M.; Nierlich, M.; Lance, M.; Vigner, J. J. Chem. Soc., Dalton Trans. 1992, 1019–1024.

EVans et al.

cations [(C5Me5)2Ln]1+. The similarities in effective size of (C5Me5)1- and(C8H8)2- ligandshavebeendescribedpreviously.34,35 The 139.1° (C5Me5 ring centroid)-U-(C8H8 ring centroid) angle in 2 is similar to the 135.9° analogue in 6 and 136.4° and 136.3° analogues in 7. The U-N distances are more difficult to compare using Shannon ionic radii36 since the coordination numbers differ in these complexes. Seven-coordinate U4+ is 0.07 Å smaller than seven-coordinate Sm3+ and 0.182 Å smaller than nine-coordinate Sm3+. By either metric, the 2.323(5) and 2.333(6) Å U-N bonds in 2 seem to be longer than expected in comparison to the 2.360(2) Å distance in the samarium complex 6. The U-N bonds in 2 also seem long in comparison to other U4+-N distances in the literature, e.g., (C5Me5)(C8H8)U[N(SiMe3)2] [2.284(4) Å],31 (C5Me5)2U[NH(C6H3Me2-2,6)]2 [2.267(6) Å],37 (C5Me5)2U(NEt2)2 [2.167(9) and 2.162(9) Å],38 and [(C5Me5)2U(NMe2)(CNtBu)2][BPh4] [2.22(1) Å].39,40 However, the U-N distances in 2 are similar to the 2.318(4) Å U-N distance in tetravalent [(Me3SiC5H4)3U]2(µ-pyrazine).45 The U-N distances in tetravalent 2 are more similar to those in the trivalent uranium complexes (C5Me5)2U[N(SiMe3)2] [2.352(2) Å],9 (C5Me5)U[N(SiMe3)2]2 [2.358(19) and 2.23(3) Å],46 U[N(SiMe3)2]3 [2.330(4) Å],47 and {[(Me3Si)2N](C5Me5)U}2(C6H6) [2.306 (2) Å],5 all of which contain anionic N-donor ligands. In comparison, the trivalent complexes of neutral N-donor ligands such as (Me3SiC5H4)3U(lutidine)48 and (Me3SiC5H4)3U(pyrimidine)48 have U-N distances of 2.646(4) and 2.688 (7) Å. This argues against the possibility that 2 contains U3+ and neutral phenazine. The atoms comprising the phenazine dianion in 2 are coplanar to within 0.09 Å. In a comparison, the dianions in 6 and 7 are planar to within 0.06 Å. Anthracene and Related Polycyclic Aromatic Hydrocarbons. The reactivity of anthracene with 1 was also examined, since it too has proven to be a viable substrate with f element reductants.27,29 When it was determined that 1 does not reduce anthracene (-1.98 and -2.44 V vs SCE),49 reactions with acenaphthylene (-1.65 and -1.89 V vs SCE)49 and benzan(34) Evans, W. J.; Clark, R. D.; Ansari, M. A.; Ziller, J. W. J. Am. Chem. Soc. 1998, 120, 9555–9563. (35) Evans, W. J.; Johnston, M. A.; Greci, M. A.; Ziller, J. W. Organometallics 1999, 18, 1460–1464. (36) Shannon, R. D. Acta Crystallogr., Sect. A 1976, A32, 751–767. (37) Straub, T.; Frank, W.; Reiss, G. J.; Eisen, M. S. J. Chem. Soc., Dalton Trans. 1996, 2541–2546. (38) Boisson, C.; Berthet, J.-C.; Lance, M.; Nierlich, M.; Vigner, J.; Ephritikhine, M. J. Chem. Soc., Chem. Commun. 1995, 543–544. (39) Boisson, C.; Berthet, J. C.; Lance, M.; Nierlich, M.; Ephritikhine, M. J. Organomet. Chem. 1997, 548, 9–16. (40) Other examples include [(C5Me5)U(NEt2)2(THF)2][BPh4] [2.17(1) and 2.18(1) Å],41 (C5Me5)U[N(CH2CH2NSiMe3)3] [2.264(15), 2.28(2), 2.25(2), and 2.61(2) Å],42 (C5Me5)U(NMe2)3(THF) [2.25(2), 2.31(3), and 2.35(5) Å],38 [(C8H8)U(NEt2)(THF)3][BPh4] [2.18(2) Å],43 Na(C8H8)U[NC(tBu)(Mes)]3 [2.225(5), 2.295(4), and 2.286(5) Å],44 (C8H8)U2[NC(tBu)(Mes)]6 [2.161(3), 2.174(4), and 2.186(3)].44 (41) Berthet, J.-C.; Boisson, C.; Lance, M.; Vigner, J.; Nierlich, M.; Ephritikhine, M. J. Chem. Soc., Dalton Trans. 1995, 3027–3033. (42) Scott, P.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1995, 603– 609. (43) Boisson, C.; Berthet, J. C.; Ephritikhine, M.; Lance, M.; Nierlich, M. J. Organomet. Chem. 1996, 522, 249–257. (44) Diaconescu, P. L.; Cummins, C. C. J. Am. Chem. Soc. 2002, 124, 7660–7661. (45) Mehdoui, T.; Berthet, J.-C.; Thuery, P.; Ephritikhine, M. Eur. J. Inorg. Chem. 2004, 199, 6–2000. (46) Avens, L. R.; Burns, C. J.; Butcher, R. J.; Clark, D. L.; Gordon, J. C.; Schake, A. R.; Scott, B. L.; Watkin, J. G.; Zwick, B. D. Organometallics 2000, 19, 451–457. (47) Stewart, J. L.; Andersen, R. A. Polyhedron 1998, 17, 953–958. (48) Mehdoui, T.; Berthet, J.-C.; Thuery, P.; Ephritikhine, M. Dalton Trans. 2004, 579–590. (49) De Boer, E. AdV. Organomet. Chem. 1964, 2, 115–155.



Table 3. Selected Bond Distances (Å) and Angles (deg) for [(C5Me5)(C8H8)U]2(C12H8N2), 2, [(C5Me5)2Sm]2(C12H8N2), 6,27 and [(C5Me5)2La]2(C12H8N2), 728,30 2 a

U(1)-Cnt1(C5Me5) a

2.436

b

M(1)-Cnt1(C5Me5)

U(1)-Cnt2(C8H8)

1.936

M(1)-Cnt2(C5Me5)

2.421

U(2)-Cnt3(C5Me5)a U(2)-Cnt4(C8H8)a U(1)-N(1)

2.472 1.971 2.333(6)

M(1)-N(1)

2.360(2)

U(2)-N(2)

2.323(5)

M(1)-C(21)

U(1)-C(C5Me5) range

2.716(7)-2.769(6)

M(1)-C(22)

U(2)-C(C5Me5) range U(1)-C(C8H8) range U(2)-C(C8H8) range U(1)-C(C5Me5) av U(2)-C(C5Me5) av U(1)-C(C8H8) av U(2)-C(C8H8) av U-C(C5Me5) av U-C(C8H8) av Cnt1-U(1)-N(1)a Cnt2-U(1)-N(1)a Cnt1-U(1)-Cnt2a

2.718(7)-2.767(7) 2.627(8)-2.670(8) 2.648(8)-2.732(7) 2.751 2.688 2.654 2.7466 2.7489 2.671 102.1 118.5 139.1

M(1)-C(25A) M(1)-C(26A)

2.866(3) 2.877(2)

Cnt1-M(1)-Cnt2b

136.4

a

Cnt3-U(2)-N(2) Cnt4-U(2)-N(2)a Cnt3-U(2)-Cnt4a a

2.478

6 b

7 2.525(1) 2.529 2.541(1) 2.536 2.452(2) 2.447(2) 2.920(2) 2.910(2) 2.931(2) 2.929(3)

135.9(1) 136.3

100.6 120.7 138.6

Cnt1 is C(1)-C(5); Cnt2 is C(21)-C(28); Cnt3 is C(11)-C(15); Cnt4 is C(29)-C(36). b Cnt1 is C(1)-C(5); Cnt2 is C(11)-C(15).

thracene (-1.58 and -1.93 V vs SCE)49 were examined. Neither of these substrates are reduced. Diphenyldichalcogenides. Another class of substrates that has proven useful in characterizing f element reduction chemistry are the PhEEPh compounds (E ) S, Se, Te), which have reduction potentials of -1.75,50 -1.20,50 and -1.06 V51 vs SCE, respectively. Although PhSSPh has a more negative reduction potential than the first reduction potential of benzanthracene, it is reduced by 1, as are PhSeSePh and PhTeTePh. Hence, kinetic factors including precoordination may be important in determining which substrates can be reduced by 1. The reaction of 1 with the PhEEPh substrates in a 1:1 ratio produced crystalline solids of the formula [(C5Me5)(C8H8)U]2(µEPh)2 in each case (E ) S, 3; Se, 4; Te, 5), eq 7, Figures 3 and 4. One equivalent of free C8H8 per equivalent of 3, 4, and 5 was observed in each reaction mixture by 1H NMR spectros-

copy. In these reactions, as in eq 6 above, 1 functions as a twoelectron reductant to convert 1 equiv of PhEEPh to two (EPh)1ligands. (50) Bradbury, J. R.; Masters, A. F.; McDonell, A. C.; Brunette, A. A.; Bond, A. M.; Wedd, A. C. J. Am. Chem. Soc. 1981, 103, 1959–1964. (51) Liftman, Y.; Albeck, M. Electrochim. Acta 1984, 29, 95–98.

Table 4. 1H NMR Spectral Data of [(C5Me5)(C8H8)U]2(SPh)2, 3,52 [(C5Me5)(C8H8)U]2(SePh)2, 4,10 and [(C5Me5)(C8H8)U]2(TePh)2, 553 complex

(C5Me5)1shift

[(C5Me5)(C8H8)U]2(SPh)2, 3 [(C5Me5)(C8H8)U]2(SePh)2, 4 [(C5Me5)(C8H8)U]2(TePh)2, 5 (C5Me5)2U(SPh)Me (C5Me5)2U(SePh)Me (C5Me5)2U(TePh)Me

7.7 8.6 9.7 9.4 9.7 9.8

complex

(C5Me5)1shift

(C5Me5)2U(SPh)2 (C5Me5)2U(SePh)2 (C5Me5)2U(TePh)2

13.3 14.0 15.1

Complexes 3-5 were characterized by 1H and 13C NMR spectroscopy, and 4 and 5 were definitively characterized by X-ray crystallography, Figures 3 and 4. The 1H NMR spectra of 3, 4, and 5 show a progressive downfield shift for each of the (C5Me5)1-, (C8H8)2-, and (EPh)1- resonances as the chalcogen is changed from S to Se to Te, Table 4. Such a trend is also observed for (C5Me5)2U(EPh)2 (E ) S,52 Se,10 and Te53) and (C5Me5)2U(EPh)Me (E ) S, Se, Te).53 In both 4 and 5, two [(C5Me5)(C8H8)U]1+ moieties are connected by two bridging (EPh)1- ligands. In contrast to 2, the (C5Me5)1- and (C8H8)2- ligands are in a trans orientation around the bridging groups. Selected bond distances and angles are given in Table 5. The 3.058(1) and 3.070(1) Å U-(µ-Se) distances in 4 are similar to those in [(C5Me5)2Sm(µ-SePh)]2 [3.0478(4) and 3.0558(4) Å].54 The similarity of the M-Se distances in these complexes is consistent with the similarity of the eight-coordinate Shannon radius of Sm3+, 1.079 Å,36 and the extrapolated value for 10-coordinate U4+, ca. 1.09 Å. The U-(µ-Se) distances in 4 are longer than the 2.7997(7), 2.8011(7), and 2.8432(7) Å U-(terminal Se) distances in (52) Lescop, C.; Arliguie, T.; Lance, M.; Nierlich, M.; Ephritikhine, M. J. Organomet. Chem. 1999, 580, 137–144. (53) Evans, W. J.; Miller, K. A.; Ziller, J. W.; DiPasquale, A. G.; Heroux, K. J.; Rheingold, A. L. Organometallics 2007, 26, 4287–4293. (54) Evans, W. J.; Miller, K. A.; Lee, D. S.; Ziller, J. W. Inorg. Chem. 2005, 44, 4326–4332.


EVans et al. Scheme 1

(C5Me5)2U(SePh)210 and (C5Me5)2U(SePh)Me,53 respectively, as expected for bridging versus terminal ligands. The structure of 5 is only the third crystallographically characterized example of a molecular complex containing a U-Te bond.53,55 The U-(µ-Te) distances in 5 are about 0.30 Å longer than those in 4, a difference that is larger than the 0.23 Å difference in Shannon radii of Te2- and Se2-. In comparison, the U-E distances in (C5Me5)2U(SePh)2 and (C5Me5)2U(TePh)2 differed by 0.24 Å,54 and the Sm-E distances in [(C5Me5)2Sm(µ-SePh)]2 and [(C5Me5)2Sm(µ-TePh)]2 differed by 0.17-0.20 Å. Although 4 and 5 have nearly identical (C5Me5 ring centroid)-U-(C8H8 ring centroid) and U-E-U′ angles, these complexes differ in the orientation of the phenyl rings, as shown in Figures 3 and 4. In 4, the plane of the phenyl rings displays a 21.3° angle with respect to the U2Se2 plane. This puts the phenyl rings in the middle of the (C5Me5)-U-(C8H8) wedge and keeps the phenyl substituents away from the (C5Me5)1- and (C8H8)2- rings. The longer U-Te distances in 5 may allow the phenyl rings to adopt the 77.7° average angle between the planes of the phenyl rings and the U2Te2 plane. Nitrobenzene. The reaction of 1 with nitrobenzene (-1.15 V vs SCE)56 was examined for comparison with the (nBu(55) Gaunt, A. J.; Scott, B. L.; Neu, M. P. Angew. Chem., Int. Ed. 2006, 45, 1638–1641. (56) Maki, A. K.; Geske, D. H. J. Am. Chem. Soc. 1961, 83, 1852– 1860. (57) Schake, A. R.; Avens, L. R.; Burns, C. J.; Clark, D. L.; Sattelberger, A. P.; Smith, W. H. Organometallics 1993, 12, 1497–1498. (58) Cendrowski-Guillaume, S. M.; Le Gland, G.; Nierlich, M.; Ephritikhine, M. Eur. J. Inorg. Chem. 2003, 1388–1393. (59) Cendrowski-Guillaume, S. M.; Nierlich, M.; Ephritikhine, M. Eur. J. Inorg. Chem. 2001, 1495–1498. (60) Evans, W. J.; Nyce, G. W.; Greci, M. A.; Ziller, J. W. Inorg. Chem. 2001, 40, 6725–6730. (61) Cendrowski-Guillaume, S. M.; Nierlich, M.; Ephritikhine, M. J. Organomet. Chem. 2002, 643-644, 209–213. (62) Baudry, D.; Bulot, E.; Ephritikhine, M.; Nierlich, M.; Lance, M.; Vigner, J. J. Organomet. Chem. 1990, 388, 279–287. (63) Berthet, J.-C.; Le Marechal, J.-F.; Ephritikhine, M. J. Organomet. Chem. 1994, 480, 155–161. (64) Berthet, J. C.; Nierlich, M.; Ephritikhine, M. Eur. J. Inorg. Chem. 2002, 850–858. (65) Boisson, C.; Berthet, J.-C.; Lance, M.; Vigner, J.; Nierlich, M.; Ephritikhine, M. J. Chem. Soc., Dalton Trans. 1996, 947–953. (66) Berthet, J. C.; Ephritikhine, M. J. Chem. Soc., Chem. Commun. 1993, 1566–1567. (67) Cendrowski-Guillaume, S. M.; Lance, M.; Nierlich, M.; Ephritikhine, M. Organometallics 2000, 19, 3257–3259. (68) Arliguie, T.; Thuery, P.; Fourmigue, M.; Ephritikhine, M. Organometallics 2003, 22, 3000–3003. (69) Arliguie, T.; Thuery, P.; Fourmigue, M.; Ephritikhine, M. Eur. J. Inorg. Chem. 2004, 4502–4509. (70) Boussie, T. R.; Moore, R. M., Jr.; Streitwieser, A.; Zalkin, A.; Brennan, J.; Smith, K. A. Organometallics 1990, 9, 2010–2016.

Table 5. Selected Bond Distances (Å) and Angles (deg) for [(C5Me5)(C8H8)U]2(SePh)2, 4, and [(C5Me5)(C8H8)U]2(TePh)2, 5 a

U(1)-Cnt1(C5Me5) U(1)-Cnt2(C8H8)a U(1)-E(1) U(1)-E(1A) U(1)-C(C5Me5) range U(1)-C(C8H8) range U(1)-C(C5Me5) av U(1)-C(C8H8) av Cnt1-U(1)-E(1)a Cnt1-U(1)-E(1)a Cnt2-U(1)-E(1A)a Cnt2-U(1)-E(1A)a Cnt1-U(1)-Cnt2a U(1A)-E(1)-U(1)a a

4

5

2.482 1.968 3.0575(11) 3.0704(9) 2.744(7)-2.774(7) 2.641(8)-2.714(7) 2.7576 2.676 105.8 113.1 100.6 117.5 135.3 120.74(3)

2.472 1.969 3.3589(7) 3.3725(10) 2.728(6)-2.773(6) 2.653(7)-2.718(6) 2.752 2.6861 98.0 107.0 119.1 112.1 135.8 120.810(18)

Cnt1 is C(1)-C(5); Cnt2 is C(11)-C(18).

C8H8)U reaction, eq 5. Reduction occurs and free C8H8 is observed, but the other reaction products were not readily identifiable.

Discussion [(C5Me5)(C8H8)U]2(C8H8), 1, has been shown to act as a twoelectron reductant with substrates such as phenazine and the PhEEPh compounds (E ) S, Se, Te). In these reductions, one of the (C8H8)2- ligands per molecule is oxidized to free C8H8 and two (C8H8)2- ligands are retained in the bimetallic product. Since the 1:2 ratio of bridging to terminal (C8H8)2- ligands in 1 is the same as the 1:2 ratio of reactive (C8H8)2- and unreactive (C8H8)2- species in the reductions, it is attractive to assign the reductive reactivity to the bridging (C8H8)2- species. Moreover, since the bridging (C8H8)2- ligand is unusual in its nonplanar solid-state structure, it could have enhanced reactivity. However, there is no hard evidence to support these correlations. In solution, the full asymmetry of the bridging ligand of 1 is not observed by 1H NMR spectroscopy, although two (C8H8)2resonances are observable in a 2:1 ratio. Complex 1 provides a facile synthetic route to the heteroleptic metallocene moiety [(C5Me5)(C8H8)U]1+ through reactions like eq 6 and 7. This provides an opportunity to compare a mixed ligand monocationic metallocene to the more common [(C5Me5)2M]1+ monocationic moiety. If the central (C8H8)2functions as a two-electron reductant, this allows 1 to react equivalently to two trivalent (C5Me5)(C8H8)U moieties. (71) Leverd, P. C.; Arliguie, T.; Lance, M.; Nierlich, M.; Vigner, J.; Ephritikhine, M. J. Chem. Soc., Dalton Trans. 1994, 501–504. (72) Arliguie, T.; Fourmigue, M.; Ephritikhine, M. Organometallics 2000, 19, 109–111.


The chemistry of (C5Me5)(C8H8)U has previously been explored only through its solvated derivative (C5Me5)(C8H8)U(THF).57 (C5Me5)(C8H8)U(THF) and 1 differ in that the former complex would derive its reductive reactivity from U3+, whereas the latter formally uses the reductive capacity of (C8H8)2-.

Conclusion Tetravalent [(C5Me5)(C8H8)U]2(C8H8), 1, functions as a twoelectron reductant with phenazine and PhEEPh substrates to make bimetallic heteroleptic tetravalent complexes containing one (C5Me5)1- ligand and one (C8H8)2- ligand per uranium. The mixed ligand metallocene unit, [(C5Me5)(C8H8)U]1+, offers an alternative to the common [(C5Me5)2U]2+ moiety and is ef-


fectively the actinide equivalent of [(C5Me5)2Ln]1+. Reductive chemistry with solvent-free [(C5Me5)(C8H8)U]1+ is readily accessible synthetically through 1.

Acknowledgment. We thank the National Science Foundation for support of this research. Supporting Information Available: X-ray data collection, structure solution, and refinement (PDF) and X-ray diffraction details of compounds 2, 3, and 5 (CIF, CCDC No. 697218-697200). This material is available free of charge via the Internet at http://pubs.acs.org. OM800747S

Reductive Reactivity of the Tetravalent Uranium ... - ACS Publications

Recommend Documents