Reactivity of Methyl Groups in Actinide ... - ACS Publications

Dec 8, 2009 - Andrew C. Behrle , Andrew Kerridge , and Justin R. Walensky .... Reactivity of Tuck-in and Tuck-over Uranium Metallocene Complexes...
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Organometallics 2010, 29, 101–107 DOI: 10.1021/om9008179

101

Reactivity of Methyl Groups in Actinide Metallocene Amidinate and Triazenido Complexes with Silver and Copper Salts William J. Evans,* Justin R. Walensky, and Joseph W. Ziller Department of Chemistry, University of California Irvine, California 92697-2025 Received September 19, 2009

The effect of the heteroleptic ligand sets {(C5Me5)2[iPrNC(Me)NiPr]}3- and {(C5Me5)2[(Me)NNN(Ad)]}3- on actinide-carbon bond reactivity has been evaluated by examining the monomethyl actinide metallocene amidinate complexes (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]AnMe (An = U, 1; Th, 2) and the triazenido complex (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UMe, 3. This has led to a facile method to convert methyl groups in U4þ and Th4þ complexes to halide and pseudo-halide ligands. Complexes 1 and 3 react with AgOSO2CF3 (AgOTf) to produce (C5Me5)2[iPrNC(Me)NiPrκ2N,N0 ]U(OTf), 4, and (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(OTf), 5, respectively. The methyl complexes are also reactive with copper reagents, as demonstrated by the reactions of CuI with 1 and 2 to make (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]UI, 6, and (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]ThI, 7, respectively. Similarly, reactions of CuBr with 1 and 3 generate (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]UBr, 8, and (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UBr, 9, respectively. These triflate and halide complexes are good precursors to other complexes with these ligand sets, as exemplified by their reactions with NaN3, which produce (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U(N3), 10, and (C5Me5)2[(Me)NNN(Ad)κ2N1,3]U(N3), 11, respectively. However, the reactions of 4 and 6 with LiCH2SiMe3 lead to reduction and the formation of the trivalent uranium heteroleptic metallocene (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U, 12. LiCH2SiMe3 does not cause reduction with the triazenido ligand set, and the monoalkyl complex (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(CH2SiMe3), 13, can be isolated. Introduction Recent studies of actinide metallocenes have shown that carbodiimides, RNdCdNR, can be inserted into actinide alkyl bonds to significantly change the coordination environment of the actinide,1 e.g., eq 1. In the case shown, a

{(C5Me5)2[iPrNC(Me)NiPr]}3- heteroleptic ligand set is generated that allows U4þ to bind to just one additional ligand. Monoalkyl bis(pentamethylcyclopentadienyl) metallocene *Corresponding author. Fax: 949-824-2210. E-mail: wevans@uci. edu. (1) Evans, W. J.; Walensky, J. R.; Ziller, J. W.; Rheingold, A. L. Organometallics 2009, 28, 3350. (2) See for example: (a) Fagan, P. J.; Manriquez, J. M.; Maatta, E. A.; Seyam, A. M.; Marks, T. J. J. Am. Chem. Soc. 1981, 103, 6650. (b) Lin, Z.; Le Marechal, J.-F.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc. 1987, 109, 4127. (c) Yang, X.; Stern, C. L.; Marks, T. J. Organometallics 1991, 10, 840. (d) Hall, S. W.; Huffman, J. C.; Miller, M. M.; Avens, L. R.; Burns, C. J.; Arney, D. S. J.; England, A. F.; Sattelberger, A. P. Organometallics 1993, 12, 752. (e) Yang, X.; King, W. A.; Sabat, M.; Marks, T. J. Organometallics 1993, 12, 4254. (f) England, A. F.; Burns, C. J.; Buchwald, S. L. Organometallics 1994, 13, 3491. (g) Jia, L.; Yang, X.; Stern, C. L.; Marks, T. J. Organometallics 1997, 16, 842. (3) Kiplinger, J. L.; John, K. D.; Morris, D. E.; Scott, B. L.; Burns, C. J. Organometallics 2002, 21, 4306. r 2009 American Chemical Society

actinide complexes are known in the literature,2,3 but when the common [(C5Me5)2]2- ligand set complexes with An4þ ions, dialkyl compounds are the most prevalent class, i.e., (C5Me5)2AnR2.4 Preliminary studies on the effect of the {(C5Me5)2[iPrNC(Me)NiPr]}3- ligand set on the reactivity of the An-Me bonds revealed that the methyl group in this coordination environment is not very reactive. Typical reactions for (C5Me5)2AnMe2 such as σ-bond metathesis and insertion were not observed with substrates such as HCtCPh, HNPh2, H2, Me3CCtN, and MeCtN. However, we report here that the methyl group in the (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]AnMe complexes can be removed to form (C5Me5)2[iPrNC(Me)NiPrκ2N,N0 ]AnX compounds in which X can be a halide or triflate ligand. These can in turn be further derivatized by ionic metathesis to complexes not easily accessible from the usual (C5Me5)2AnCl2 starting materials that predominate in actinide metallocene chemistry.4 Methyl to halide and pseudo-halide conversion was accomplished in this study not only by silver salts, which have been previously used to remove alkyl and amide groups from electropositive metals,5 but also by copper salts. Copper reagents are less expensive and generally less light sensitive. Copper reagents have recently been shown by Kiplinger and (4) Sharma, M.; Eisen, M. S. Struct. Bonding (Berlin) 2008, 127, 1. (5) (a) Jordan, R. F.; Bajgur, C. S.; Dasher, W. E. Organometallics 1987, 6, 1041. (b) Berthet, J.-C.; Ephritikhine, M. Coord. Chem. Rev. 1998, 178-180, 83. (c) Evans, W. J.; Walensky, J. R.; Furche, F.; Ziller, J. W.; DiPasquale, A. G.; Rheingold, A. L. Inorg. Chem. 2008, 47, 10169. Published on Web 12/08/2009

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co-workers to be very effective for oxidation of actinide metallocene complexes in reactions involving U3þ to U4þ and U4þ to U5þ reactions.6 Conversion of An4þ alkyls to An4þ halides and pseudo-halides by copper reagents has not been previously reported to our knowledge. In addition to examining the effects of the mixed cyclopentadienyl amidinate ligand set on organoactinide chemistry, the reaction chemistry of the methyl group in the related complex (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UMe, 3, obtained by insertion of adamantyl azide into one U-Me bond of (C5Me5)2UMe2,1 was studied. The {(C5Me5)2[(Me)NNN(Ad)]}3- ligands in 3 provide another trianionic ancillary ligand set for evaluation of the reactivity of monoalkyl uranium complexes. The reactivity of 3 shows the generality of this methyl to halide conversion, but emphasizes the importance of the detailed nature of the ancillary ligand set on organoactinide reactivity.

Experimental Details The syntheses and manipulations described here were conducted with rigorous exclusion of air and water using Schlenk, vacuum line, and glovebox techniques. Solvents were sparged with UHP argon, dried by passage through columns containing Q-5 and molecular sieves, and delivered directly to the glovebox through stainless steel tubing. All reactions were conducted under argon in a glovebox free of coordinating solvents, unless otherwise specified. Benzene-d6 and toluene-d8 (Cambridge Isotope Laboratories) were dried over NaK alloy and benzophenone, degassed by three freeze-pump-thaw cycles, and vacuum transferred before use. (C5Me5)2[iPrNC(Me)NiPrκ2N,N0 ]AnMe,1 An = U, 1; Th, 2, (C5Me5)2[(Me)NNN(Ad)κ2N1,3]UMe, 3,1 and [(C5Me5)2UMe(OTf)]25c were prepared as previously described. Silver trifluoromethanesulfonate, AgOTf (Strem), was used as received. CuBr, CuI, and NaN3 (Aldrich) were degassed under vacuum prior to use. LiCH2SiMe3 was purchased from Aldrich as a 1.0 M solution in pentane, and the solvent was removed prior to use. iPrNdCdNiPr (Aldrich) was dried over activated molecular sieves overnight and degassed by three freeze-pump-thaw cycles. NMR experiments were conducted with Bruker DRX 400 and GN 500 MHz spectrometers. Due to the paramagnetism of uranium, only resonances that could be unambiguously assigned in the NMR spectra are reported. 19F NMR spectra were referenced against CFCl3 in CDCl3. Infrared spectra were recorded as KBr pellets on a Perkin-Elmer Spectrum One FT-IR spectrometer. Elemental analyses for C, H, and N were performed on a Perkin-Elmer 2400 CHN elemental analyzer. Analyses for other elements were obtained from Analytische Laboratorien (Lindlar, Germany). (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]U(OTf), 4. In a glovebox with the light turned off, (C5Me5)2[iPrNC(Me)NiPr-κ2 N,N0 ]UMe, 1 (285 mg, 0.429 mmol), and AgOTf (110 mg, 0.428 mmol) were combined in toluene (10 mL). After 4 h, metallic insoluble material was removed by centrifugation and the solvent was removed under vacuum to yield a red oil. Extraction of the oil with pentane followed by removal of pentane from this extract gave 4 as a red powder (290 mg, 90%), which was identified by 1H NMR spectroscopy (see below). Complex 4 can also be synthesized by addition of iPrNdCd NiPr (75 μL, 0.475 mmol) to [(C5Me5)2UMe(OTf)]2 (298 mg, 0.475 mmol) in toluene (6 mL), which caused an immediate color (6) (a) Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. J. Am. Chem. Soc. 2007, 129, 11914. (b) Graves, C. R.; Yang, P.; Kozimor, S. A.; Vaughn, A. E.; Clark, D. L.; Conradson, S. D.; Schelter, E. J.; Scott, B. L.; Thompson, J. D.; Hay, P. J.; Morris, D. E.; Kiplinger, J. L. J. Am. Chem. Soc. 2008, 130, 5272. (c) Graves, C. R.; Schelter, E. J.; Cantat, T.; Scott, B. L.; Kiplinger, J. L. Organometallics 2008, 27, 5371. (d) Graves, C. R.; Kiplinger, J. L. Chem. Commun. 2009, 3831.

Evans et al. change from yellow-brown to red. After 12 h, solvent was removed under vacuum to obtain 4 as a red powder (275 mg, 77%). Crystals suitable for X-ray diffraction were grown from a saturated pentane solution at room temperature. 1H NMR (C6D6, 298 K): δ 12.9 (s, 1H, CHMe2), 8.64 (s, 30H, C5Me5), 2.49 (s, 1H, CHMe2), 0.59 (br s, 6H, CHMe2), -5.21 (s, 3H, Me), -9.43 (br s, 6H, CHMe2). IR: 2976s, 2935s, 2731m, 1654s, 1491s, 1453s, 1414s, 1384s, 1324s, 1227s, 1140s, 1005s, 795s cm-1. Anal. Calcd for C29H47F3N2O3SU: C, 43.60; H, 5.93; N, 3.51. Found: C, 43.57; H, 5.72; N, 3.31. (C5Me5)2[(Me)NNN(Ad)-K2N1,3]U(OTf), 5. AgOTf (130 mg, 0.506 mmol) was added to a stirred solution of 3 (365 mg, 0.429 mmol) in toluene (10 mL). The color turned from orange to dark red. After 14 h, a dark insoluble material (presumably Ag) was removed by centrifugation and the solvent removed under vacuum to yield 5 as a red powder (395 mg, 91%). Crystals suitable for X-ray diffraction were obtained from a saturated toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 28.9 (s, 3H, Ad), 8.20 (s, 30H, C5Me5), -5.62 (d, 3H, Ad), -6.31 (s, 3H, Me), -7.90 (d, 3H, Ad), -24.49 (s, 6H, Ad). 19F NMR (C6D6, 298 K): δ -67.40. IR: 2908s, 2850s, 2088m, 1492m, 1451m, 1382m, 1337s, 1270s, 1230s, 1191s, 989s, 632s cm-1. Anal. Calcd for C32H48F3N3O3SU: C, 45.23; H, 5.69; N, 4.94. Found: C, 45.07; H, 5.42; N, 4.77. (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]UI, 6. CuI (124 mg, 0.651 mmol) was added to a stirred solution of 1 (430 mg, 0.647 mmol) in toluene (10 mL). After 24 h, metallic insoluble material was removed by centrifugation and the solvent was removed under vacuum to yield 6 as a dark red microcrystalline solid (495 mg, 98%). Crystals suitable for X-ray diffraction were grown from slow evaporation of solvent in an NMR tube at room temperature. 1H NMR (C6D6, 298 K): δ 8.33 (s, 30H, C5Me5), -4.76 (s, 3H, Me). IR: 2927s, 2896s, 2720m, 1638w, 1494s, 1436s, 1414s, 1379s, 1359s, 1349s, 1195s, 1140s, 1126s, 1055m, 1018m, 1000m, 808w, 790m cm-1. Anal. Calcd for C28H47N2IU: C, 43.30; H, 6.10; N, 3.61; I, 16.34; U, 30.65. Found: C, 43.73; H, 5.68; N, 3.34; I, 16.03; U, 30.84. (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]ThI, 7. CuI (100 mg, 0.525 mmol) was added to a stirred solution of (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]ThMe, 2 (200 mg, 0.303 mmol), in toluene (6 mL). After 24 h, metallic insoluble material was removed by centrifugation, and a white powder, 7, was obtained upon removing the solvent under vacuum (215 mg, 85%). Crystals suitable for X-ray crystallography were obtained from a saturated toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 3.82 (sept, J = 7 Hz, 1H, CH(CH3)2), 3.45 (sept, J = 7 Hz, 1H, CH(CH3)2), 2.15 (s, 30H, C5Me5), 1.63 (s, 3H, Me), 1.32 (d, J = 7 Hz, 6H, CH(CH3)2), 1.28 (d, J = 7 Hz, 6H, CH(CH3)2). 13 C NMR (C6D6, 298 K): δ 176.89 [NC(Me)N], 125.96 (C5Me5), 46.92 (CHMe2), 27.64 (CHMe2), 26.12 (CHMe2), 25.18 [NC(Me)N], 13.81 (C5Me5). IR: 2972s, 2901s, 2723m, 1608w, 1501s, 1418s, 1380s, 1351s, 1194s, 1177s, 1127s, 1055m, 1019m, 1002m, 814m, 792m, 771m cm-1. Anal. Calcd for C28H47N2ITh: C, 43.64; H, 6.15; N, 3.64; I, 16.47; Th, 30.11. Found: C, 43.81; H, 6.01; N, 3.72; I, 15.88; Th, 30.10. (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]UBr, 8. CuBr (120 mg, 0.837 mmol) was added to a stirred solution of 1 (100 mg, 0.150 mmol) in toluene (8 mL). The solution turned from yellow-brown to red. After 14 h, an insoluble metallic material was removed by centrifugation, and the solvent was removed under vacuum to yield 8 as a red powder (100 mg, 91%). 1H NMR (C6D6, 298 K): δ 5.84 (s, 30H, C5Me5), -5.08 (s, 3H, Me). IR: 2931s, 2893s, 1642 m, 1476s, 1442s, 1418s, 1383s, 1347s, 1339s, 1203s, 1143s, 1126s, 1047m, 1019m, 993s, 790m cm-1. Anal. Calcd for C28H47N2BrU: C, 46.09; H, 6.49; N, 3.84. Found: C, 46.15; H, 6.68; N, 3.76. (C5Me5)2[(Me)NNN(Ad)-K2N1,3]UBr, 9. CuBr (88 mg, 0.61 mmol) was added to a stirred solution of 3 (182 mg, 0.254 mmol) in toluene (8 mL). The solution slowly changed color from orange to dark red. After 13 h, metallic insoluble

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Table 1. X-ray Data Collection Parameters for 4-7, 9, and 13

empirical formula

4

5

6

7

9

13

C29H47F3N2O3SU

C32H48F3N3O3SU 3 C7H8

C28H47N2IU

C28H47N2ITh

C31H48N3BrU

C35H59N3SiU

770.62 143(2) monoclinic P21/n 9.5437(6) 17.1372(11) 17.9011(11) 90 101.1260(10) 90 2872.7(3) 4 1.782 6.283 0.0229 0.0560

780.66 103(2) rhombohedral R3 31.8275(7) 31.8275(7) 15.0874(6) 90 90 120 13235.8(7) 18 1.763 6.901 0.0191 0.0452

787.97 103(2) monoclinic P21/n 10.5241(9) 17.2620(15) 19.3260(17) 90 97.4100(10) 90 3481.6(5) 4 1.530 4.723 0.0368 0.0929

)

798.78 941.96 776.61 143(2) 148(2) 143(2) monoclinic monoclinic monoclinic P21/n P21/n P21/n 10.2738(10) 10.4415(9) 9.4249(7) 18.6761(19) 19.6597(18) 17.1517(13) 16.4915(16) 18.7144(17) 17.8315(13) 90 90 90 93.435(2) 91.6880(10) 101.2720(10) 90 90 90 3158.6(5) 3840.0(6) 2826.9(4) 4 4 4 1.680 1.629 1.825 5.254 4.336 6.851 0.0245 0.0418 0.0300 0.0502 0.1110 0.0758 P P P a 2 2 2 P Definitions: R1 = Fo|-|Fc / |Fo|, wR2 = [ [w(Fo - Fc ) ]/ [w(Fo2)2] ]1/2. )

fw temperature (K) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) volume (A˚3) Z Fcalcd (Mg/m3) μ (mm-1) R1 [I > 2.0σ(I)]a wR2 (all data)a

material was removed by centrifugation and the solvent was removed under vacuum to yield 9 as a red microcrystalline solid (194 mg, 98%). Crystals suitable for X-ray diffraction were obtained from a saturated pentane/toluene solution at -35 °C. 1 H NMR (C6D6, 298 K): δ 50.77 (s, 3H, Me), 4.87 (s, 30H, C5Me5), -6.18 (s, 6H), -8.63 (s, 3H), -26.74 (s, 6H). IR: 2982s, 2903s, 2849s, 2724m, 1489m, 1447s, 1432s, 1378s, 1265s, 1177s, 1103m, 1059m, 1021m, 814w cm-1. Anal. Calcd for C31H48N3BrU: C, 47.69; H, 6.20; N, 5.38. Found: C, 47.79; H, 6.17; N, 5.26. (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]U(N3), 10. NaN3 (100 mg, 1.54 mmol) was added to a stirred solution of 4 (501 mg, 0.552 mmol) in THF (10 mL). The solution changed from red to orange. After 16 h, white insoluble material was removed by centrifugation and the solvent was removed under vacuum to yield 10 as an orange microcrystalline solid (375 mg, 98%). 1H NMR (C6D6, 298 K): δ 27.10 (s, 6H, CHMe2), 1.48 (s, 30H, C5Me5), -6.84 (s, 3H, Me), -11.21 (s, 1H, CHMe2), -20.55 (s, 6H, CHMe2). IR: 2971s, 2902s, 2723m, 2082s, 1644m, 1485s, 1430s, 1412s, 1367s, 1189s, 1127m, 1019m, 806w, 790w, 705w cm-1. Anal. Calcd for C28H47N5U: C, 48.62; H, 6.85; N, 10.12. Found: C, 49.23; H, 6.88; N, 9.42. (C5Me5)2[(Me)NNN(Ad)-K2N1,3]U(N3), 11. NaN3 (30 mg, 0.46 mmol) was added to a stirred solution of 9 (350 mg, 0.448 mmol) in THF (10 mL). The color slowly changed from red to orange-brown. After 16 h, a white precipitate was removed by centrifugation and the solvent was removed under vacuum to yield 11 as an orange-brown powder (275 mg, 83%). 1 H NMR (C6D6, 298 K): δ 1.70 (s, 30H, C5Me5), -1.93 (s, 6H, Ad), -6.55 (s, 3H, Ad), -6.94 (s, 3H, Ad), -9.28 (s, 3H, Ad), -27.62 (s, 3H, Me). IR: 2905s, 2851s, 2115s, 2085s, 1451m, 1377m, 1266m, 1242m, 1179m, 1089m, 1058m, 1021m cm-1. Anal. Calcd for C62H96N9U2: C, 51.59; H, 6.70; N, 8.73. Found: C, 51.92; H, 7.10; N, 8.59. (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]U, 12, from 4 and LiCH2SiMe3. On an NMR scale, LiCH2SiMe3 (3 mg, 0.03 mmol) was added to a stirred solution of 4 (20 mg, 0.025 mmol) in C6D6. The 1H NMR spectrum showed only resonances consistent with (C5Me5)2[(iPr)NC(Me)N(iPr)]U, 12.7 Complex 12 is also obtained from the reaction of 6 (25 mg, 0.032 mmol) and LiCH2SiMe3 (5 mg, 0.05 mmol) in C6D6. (C5Me5)2U[iPrNC(Me)NiPr-K2N,N0 ], 12, from 4 and KC8. On an NMR scale, KC8 (5 mg, 0.13 mmol) was added to a stirred solution of 4 (20 mg, 0.025 mmol) in C6D6. A color change from red to green-brown was observed. The 1H NMR spectrum showed only resonances consistent with 12. Complex 12 is also (7) Evans, W. J.; Walensky, J. R.; Ziller, J. W. Chem.-Eur. J. 2009, 15, 12204.

obtained from the reaction of 6 (25 mg, 0.032 mmol) and KC8 (5 mg, 0.13 mmol) in C6D6. (C5Me5)2[(Me)NNN(Ad)-K2N1,3]U(CH2SiMe3), 13. LiCH2SiMe3 (30 mg, 0.32 mmol) was added to a stirred solution of 9 (152 mg, 0.195 mmol) in toluene (8 mL). The color changed from red to orange after a few minutes. After 1 h, a white precipitate was removed by centrifugation and the solvent was removed from the orange solution under vacuum to yield 13 as an orange powder (128 mg, 83%). Crystals suitable for X-ray diffraction were grown from a saturated toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 32.92 (s, 9H, SiMe3), 5.17 (s, 6H, Ad), 4.86 (s, 6H, Ad), -2.30 (s, 30H, C5Me5), -6.45 (s, 2H, CH2SiMe3), -10.14 (s, 3H, Ad). IR: 2904s, 2850s, 1450s, 1377m, 1269s, 1241s, 1180m, 1088m, 846s, 818s, 719m, 673 m cm-1. Anal. Calcd for C35H59N3U: C, 53.35; H, 7.55; N, 5.33. Found: C, 53.52; H, 7.85; N, 4.97. 9 from 13 and CuBr. On an NMR scale, 13 (10 mg, 0.013 mmol) was dissolved in C6D6 (1 mL) and CuBr (5 mg, 0.03 mmol) was added. After 1 h, the solution was filtered into an NMR tube to remove any insoluble material. The 1H NMR was consistent with the formation of 9. The presence of SiMe4 was confirmed in the 1H NMR spectrum. X-ray Data Collection, Structure Solution, and Refinement for 4-7, 9, and 13. This information is available in the Supporting Information. Selected X-ray collection parameters are found in Table 1.

Results Methyl to Triflate Conversions with AgOTf. The methyl complex (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]UMe, 1, reacts with silver triflate to form the triflate derivative (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U(OTf), 4, eq 2, in 90%

yield. In this reaction as well as all the subsequent methyl complex reactions described, methane was observed as a byproduct by 1H NMR spectroscopy. After 4 was isolated by this abstraction method, an alternative synthesis was explored starting from the methyl triflate3 [(C5Me5)2UMe(OTf)]2, prepared from (C5Me5)2UMe2 and AgOTf.5c Carbodiimide insertion with

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Figure 1. Thermal ellipsoid plot of (C5Me5)2[iPrNC(Me)NiPrκ2N,N0 ]U(OTf), 4, drawn at the 50% probability level. The hydrogen atoms have been omitted for clarity.

[(C5Me5)2UMe(OTf)]2 is as facile as it is with (C5Me5)2AnMe2 such that 4 can be synthesized as shown in eq 3.

Complex 4 was characterized by analytical and spectroscopic methods as well as by X-ray crystallography, Figure 1. Since the low reactivity of the methyl group in 1 compared to (C5Me5)2UMe2 could arise from increased steric crowding, it was conceivable that replacement of the methyl group in 1 by triflate would form a complex with an outer-sphere triflate counteranion. However, 4 crystallizes with triflate in the inner coordination sphere. Structural details are discussed in a later section. Complex 4 has an infrared absorption at 1384 cm-1 characteristic of a monodentate triflate ligand,3,8 and a single resonance was observed in the 19F NMR spectrum at -66.51 ppm. In comparison, the triflate in [(C5Me5)2UMe(OTf)]2 resonates at -77.44 ppm.3 Silver triflate also converts the methyl complex (C5Me5)2[(Me)NNN(Ad)]UMe, 3, to an inner-sphere triflate complex, (C5Me5)2[(Me)NNN(Ad)]U(OTf), 5, eq 4. Like 4, complex

5 has an IR absorption at 1382 cm-1 characteristic of a monodentate triflate ligand8 and a 19F NMR resonance at -67.39 ppm. The structure of 5 was determined by X-ray crystallography, Figure 2, and is discussed in a later section. Reactions with Copper Reagents. The reaction of 1 with CuI revealed that conversions of the type shown in eq 2 could also be accomplished with copper reagents. A red product was isolated from this reaction in high yield, eq 5, and identified as (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]UI, 6, by X-ray crystallography, Figure 3.

(8) Lawrence, G. A. Chem. Rev. 1986, 86, 17.

Evans et al.

Figure 2. Thermal ellipsoid plot of (C5Me5)2[(Me)NNN(Ad)κ2N1,3]U(OTf), 5, shown at the 30% probability level. The hydrogen atoms and the toluene solvent molecule have been omitted for clarity.

Examination of the CuI reaction in eq 5 with the thorium analogue gave a similar result: (C5Me5)2[iPrNC(Me)NiPrκ2N,N0 ]ThI, 7, can be isolated from the reaction between (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]ThMe, 2, and CuI in 85% yield. The thorium complex was also characterized by X-ray crystallography and is isomorphous with 6. CuBr was also examined as a reagent and was found to generate the analogous bromide, (C5Me5)2[iPrNC(Me)NiPr]UBr, 8, from 1 faster than the CuI reaction. Complex 8 was characterized by elemental analysis and spectroscopic methods. The 1H NMR and IR spectra of 8 are very similar to crystallographically characterized 6. Copper bromide reactions were also examined with 3. As shown in eq 6, complex 3 reacts with CuBr to produce (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UBr, 9. The solid-state structure of 9 is

shown in Figure 4. As in the parent compound, the adamantyl group lies in the middle of the wedge of the metallocene adjacent to the bromide ligand. Ionic Metathesis Reactions. Complexes 4, 6, and 8 react with NaN3 in THF (but not in arene solvents) to produce (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U(N3), 10, eq 7. The IR spectrum of 10 has a strong absorption at 2082 cm-1, which is similar to

those in other terminal azide uranium complexes: 2080 cm-1 in [{(ArO)3tacn}U(N3)] ((ArOH)3tacn =

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The reactions of 4, 6, and 8 with LiCH2SiMe3 do not lead to substitution and formation of trimethylsilylmethyl complexes. Instead, reduction is observed and the previously identified (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U, 12,7 is isolated, eq 8. LiCH2SiMe3 has recently been reported to reduce U6þ to U5þ.13 The organic byproduct in eq 8 has not been identified. The reaction of 4 or 6 with KC8 also produces 12.

Figure 3. Thermal ellipsoid plot of (C5Me5)2[iPrNC(Me)NiPrκ2N,N0 ]UI, 6, drawn at the 30% probability level. The hydrogen atoms have been omitted for clarity. A thermal ellipsoid plot of the isomorphous thorium analogue 7 is given in the Supporting Information.

In contrast to the reaction in eq 8, an isolable U4þ alkyl complex, (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(CH2SiMe3), 13, was obtained from the reaction of 9 with LiCH2SiMe3, eq 9. The solid-state structure of 13 was determined by X-ray

crystallography, but the data were only sufficient to establish atomic connectivity in the molecule (see Supporting Information). To check the generality of the copper bromide reaction, complex 13 was treated with CuBr. Complex 9 was re-formed in 80% yield, eq 10. When done in a sealed NMR tube, SiMe4 was observed.

Figure 4. Thermal ellipsoid plot of (C5Me5)2[(Me)NNN(Ad)κ2N1,3]UBr, 9, shown at the 50% probability level. The hydrogen atoms have been omitted for clarity.

1,4,7-tris(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane),9 2073 cm-1 in [(C5Me5)2UN3(μ-N3)]3,10 and 2055 cm-1 in (Bu4N)3[U(N3)7].11 This can be compared to bridging azides that are found at 2111 cm-1 in [(C5Me5)2UN3(μ-N3)]310 and 2100 cm-1 in [(C5Me5)2U(μ-N)U(μ-N3)U(C5Me5)2]4.12 The reactions of 5 and 9 with NaN3 produce an orangebrown solid, which has been identified by 1H NMR and IR spectroscopy and elemental analysis as (C5Me5)2[(Me)NNN(Ad)]U(N3), 11. The IR spectrum of 11 shows one strong band at 2085 cm-1, which, if similar to other uranium compounds listed above, is consistent with a terminal azide. (9) Castro-Rodriguez, I.; Olsen, K.; Gantzel, P.; Meyer, K. J. Am. Chem. Soc. 2003, 125, 4565. (10) Evans, W. J.; Miller, K. A.; Ziller, J. W.; Greaves, J. Inorg. Chem. 2007, 46, 8008. (11) Crawford, M.-J.; Ellern, A.; Mayer, P. Angew. Chem., Int. Ed. 2005, 44, 7874. (12) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Science 2005, 309, 1835.

Structural Analyses. Bond lengths and angles for the {(C5Me5)2[iPrNC(Me)NiPr]}3- complexes 4, 6, and 7 are compared with those of 1 in Table 2. Similar comparisons for the {(C5Me5)2[(Me)NNN(Ad)]}3- complexes 5 and 9 are given in Table 3. The structural parameters for the {(C5Me5)2[iPrNC(Me)NiPr]}3- ligand set in 4 and 6 are similar and have slightly smaller U-ligand distances compared to 1. The U-(C5Me5 ring centroid) distances in 4, 2.482 and 2.497 A˚, and 6, 2.498 and 2.500 A˚, are slightly smaller than those in 1, 2.527 and 2.538 A˚, and the 2.333(2) A˚ U-N(1) and 2.448(2) A˚ U-N(2) A˚ distances in 4 and the 2.371(4) A˚ U-N(1) and 2.480(3) A˚ U-N(2) distances in 6 have one U-N distance shorter than the 2.453(2) and 2.461(2) A˚ U-N distances in 1. In each case, the shorter U-N(amidinate) distance involves the nitrogen in the center of the molecule closest to the triflate and iodide ligands. The 2.470(2) A˚ U-O(1)(triflate) bond distance in 4 is slightly longer than the 2.442(3) A˚ U-C(Me) distance in 1, as is found in [(C5Me5)2UMe(OTf)]2: the U-C(Me) distances are 2.403(7)-2.441(7) A˚ compared to 2.496(5)-2.544(5) A˚ for the U-O(OTf) lengths. The (13) Berthet, J.-C.; Siffredi, G.; Thuery, P.; Ephritikhine, M. Dalton Trans. 2009, 3478.

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Table 2. Selected Bond Distances (A˚) and Angles (deg) for (C5Me5)2[iPrNC(Me)NiPr-K2N,N0 ]AnX, An = U, X = Me, 1; OTf, 4; I, 6; and An = Th, X = I, 7 bond distance/angle

1 (X = Me)1

4 (X = OTf)

6 (X = I)

7 (X = I)

An(1)-(C5Me5 ring centroid) An(1)-X(1) An(1)-N(1) An(1)-N(2) An(1)-C(21) (C5Me5 ring centroid)-An(1)-(C5Me5 ring centroid) (C5Me5 ring centroid)-An(1)-X(1) (C5Me5 ring centroid)-An(1)-N(1) (C5Me5 ring centroid)-An(1)-N(2) N(1)-An(1)-N(2)

2.527, 2.538 2.442(3) 2.453(2) 2.461(2) 2.868(3) 130.9 95.8, 94.1 110.9, 118.2 103.0, 104.8 54.52(8)

2.482, 2.497 2.470(2) 2.333(2) 2.448(2) 2.847(3) 130.3 94.7, 100.7 108.0, 121.2 101.7, 100.5 55.63(8)

2.500, 2.498 3.1118(4) 2.371(4) 2.480(3) 2.880(5) 133.0 97.2, 97.1 99.3, 99.2 112.1, 113.8 54.45(14)

2.570, 2.560 3.1717(3) 2.465(2) 2.524(2) 2.950(3) 132.8 96.8, 97.3 113.3, 112.7 99.6, 98.9 53.30(8)

Table 3. Selected Bond Distances (A˚) and Angles (deg) for (C5Me5)2[(Me)NNN(Ad)-K2N1,3]UX, where X = OTf, 5; Br, 9 bond distance/angle

5 (X = OTf)

9 (X = Br)

An(1)-(C5Me5 ring centroid) An(1)-X(1) An(1)-N(1) An(1)-N(2) An(1)-N(3) (C5Me5 ring centroid)An(1)-(C5Me5 ring centroid) (C5Me5 ring centroid)-An(1)-X(1) (C5Me5 ring centroid)-An(1)-N(1) (C5Me5 ring centroid)-An(1)-N(2) N(1)-An(1)-N(3)

2.454, 2.467 2.404(4) 2.415(5) 2.903(5) 2.452(5) 135.1

2.482, 2.474 2.7852(3) 2.435(2) 2.914(2) 2.460(2) 134.6

99.6, 97.3 95.8, 95.2 104.2, 104.7 52.8(2)

99.0, 100.5 97.6, 96.1 107.1, 104.1 52.21(8)

3.1118(4) A˚ U(1)-I(1) distance in 6 is typical for terminal uranium-iodide bonds.10 For example, distances from 2.953(2) A˚ in [C5H3(SiMe3)2]2UI214 to 3.264(1) A˚ in (tpza)UI3(THF)15 (tpza = tris[(2-pyrazinyl)methyl]amine) have been reported. The longer U-O(OTf) and U-I distances may allow the cyclopentadienyl and amidinate ligands to approach closer to the uranium center. Complex 7 is isomorphous with 6. The distances in 7 are longer than those in 6 due to the greater size of thorium versus uranium.16 Very few structures are known with Th-I bonds, but the 3.1717(3) A˚ Th-I bond distance in 7 is between the 3.008(2) A˚ in (C5Me5)2ThI217 and 3.226(1) A˚ in ThI(OCHiPr2)3(py)2.18 (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(OTf), 5, has normal bonding parameters for a nine-coordinate tetravalent uranium metallocene. The U(1)-O(1)(triflate) bond distance of 2.404(4) A˚ is shorter than the 2.470(2) A˚ in 4, but compares well with the 2.40(1) and 2.36(1) A˚ distances in (C5Me5)2U(OTf)2(H2O).19 The 2.415(5) and 2.452(5) A˚ U-N bond lengths in 5 can be compared to the 2.453(2) and 2.461(2) A˚ analogues in 1.1 Complex 5 seems less crowded than 4 since the U-O and U-N bond distances are shorter and the (C5Me5 ring centroid)-U(1)-(C5Me5 ring centroid) angle has opened to 135.1° compared to 130.9° in 4. Selected bond lengths and angles for (C5Me5)2[(Me)NNN(Ad)κ2N1,3]UBr, 9, are shown in Table 3. The 2.435(2) and (14) Blake, P. C.; Lappert, M. F.; Taylor, R. G.; Atwood, J. L.; Hunter, W. E.; Zhang, H. Dalton Trans. 1995, 3335. (15) Berthet, J.-C.; Thuery, P.; Ephritikhine, M. Inorg. Chem. 2005, 44, 1142. (16) Shannon, R. D. Acta Crystallogr. 1976, A32, 751. (17) Rabinovich, D.; Bott, S. G.; Nielsen, J. B.; Abney, K. D. Inorg. Chim. Acta 1998, 274, 232. (18) Barnhart, D. M.; Clark, D. L.; Gordon, J. C.; Huffman, J. C.; Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1995, 34, 5416. (19) Berthet, J.-C.; Ephritikhine, M.; Lance, M.; Nierlich, M. Chem. Commun. 1998, 1373.

2.460(2) A˚ U-N(1) and U-N(3) bond distances in 9, respectively, are similar to those in 5. The U-Br(1) distance of 2.7852(3) A˚ is comparable to the 2.747(2) A˚ bond length in (C9H7)3UBr,20 2.823(2) A˚ in (NN0 3)UBr,21 NN0 3 = [N(CH2CH2NSiMe2But)3], and 2.794(1) A˚ in (C5Me5)2(η2-t BuNSPh)UBr.22

Discussion The reactions of (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]UMe, 1, and (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UMe, 3, with AgOTf, eqs 2 and 4, show that silver salts provide a viable method to activate relatively unreactive methyl ligands in An4þ complexes. AgOTf has previously been shown to replace one methyl group in (C5Me5)2UMe2 with triflate to form [(C5Me5)2UMe(OTf)]2.5c Equations 2 and 4 show that this reaction also occurs with ligand sets such as {(C5Me5)2[iPrNC(Me)NiPr]}3- and {(C5Me5)2[(Me)NNN(Ad)]}3- that protect reactive ligands and reduce their reactivity. When such protective ligand environments are present, synthetic manipulation of the complex can be achieved by this silver-based reaction. The reactions of 1-3 with CuI and CuBr, eqs 5 and 6, show that An4þ methyl groups can also be replaced with halides using copper reagents. The synthesis of triflate and halide (C5Me5)2[iPrNC(Me)i N Pr]UX and (C5Me5)2[(Me)NNN(Ad)]UX complexes allows further variation of the X groups in these coordination environments. Equation 7 shows that these complexes can be converted to azides. Hence, with copper reagents, it is possible to convert methyl ligands to halides and then to other anionic ligands in organoactinide complexes. However, attempts to accomplish this type of ionic metathesis with alkyllithium reagents to form other U-alkyl complexes are highly dependent on the ancillary ligand set. Although (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UBr, 9, can be cleanly converted to (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(CH2SiMe3), 13, eq 9, the analogous reaction with (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U(OTf), 4, and (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]UI, 6, gives reduction and a U3þ product, (C5Me5)2[iPrNC(Me)NiPr-κ2N,N0 ]U, 12, eq 8. Hence, the balance of LiR reduction reactivity versus the U4þ/U3þ redox potential can be finely tuned by changing an ancillary amidinate to a triazenido ligand.

(20) Spirlet, M. R.; Rebizant, J.; Goffart, J. Acta Crystallogr. 1987, C43, 354. (21) Roussel, P.; Alcock, N. W.; Boaretto, R.; Kingsley, A. J.; Munslow, I. J.; Sanders, C. J.; Scott, P. Inorg. Chem. 1999, 38, 3651. (22) Danopoulos, A. A.; Hankin, D. M.; Cafferkey, S. M.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 2000, 1613.

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Conclusion Copper salts can be as effective as the more expensive silver reagents, such as AgOTf, in replacing methyl groups in An4þ complexes with halide or pseudo-halide ligands that provide reactive derivatives suitable for further synthetic manipulation. For the heteroleptic complexes such as (C5Me5)2[(iPr)NC(Me)N(iPr)]UMe, 1, and (C5Me5)2[(Me)NNN(Ad)]UMe, 3, which are easily accessible from the common organoactinide methyl precursor (C5Me5)2UMe2, these copper reactions allow the methyl group to be replaced with considerable synthetic variation that would be difficult to achieve starting from other common precursors. The synthetic capacity with some reagents must be balanced by the ability of the

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{(C5Me5)2[iPrNC(Me)NiPr]}3- versus {(C5Me5)2[(Me)NNN(Ad)]}3- ligand sets to stabilize U4þ versus U3þ.

Acknowledgment. We thank the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences of the Department of Energy for support of this research. We thank Michael K. Takase for assistance with X-ray crystallography. Supporting Information Available: X-ray diffraction details (CIF) and X-ray data collection, structure solution, and refinement of compounds 4-7, 9, and 13. This material is available free of charge via the Internet at http://pubs.acs. org.