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May 13, 2009 - Insertion of Carbodiimides and Organic Azides into. Actinide-Carbon Bonds. William J. Evans,*,† Justin R. Walensky,† Joseph W. Zill...
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Organometallics 2009, 28, 3350–3357

Insertion of Carbodiimides and Organic Azides into Actinide-Carbon Bonds William J. Evans,*,† Justin R. Walensky,† Joseph W. Ziller,† 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, La Jolla, California 92093-0358 ReceiVed February 19, 2009

Manipulation of steric crowding in organoactinide complexes has been explored by examining the insertion chemistry of carbodiimides, RNdCdNR, and organic azides, RN3, with actinide alkyl, alkynyl, and aryl complexes. iPrNdCdNiPr reacts with (C5Me5)2AnMe2 to produce the isomorphous methyl amidinates (C5Me5)2AnMe[(iPr)NC(Me)N(iPr)-κ2N,N′], An ) Th, 1; U, 2, in high yield. The reaction of i PrNdCdNiPr with (C5Me5)2U(CtCPh)2 forms a similar insertion product, (C5Me5)2U(CtCPh)[(iPr)NC(CtCPh)N(iPr)-κ2N,N′], 3. (C5Me5)2U(C6H5)2 does not generate an analogous product with iPrNdCdNiPr, but forms instead a complex formally derived from carbodiimide insertion into a “(C5Me5)2U(C6H4)” intermediate, (C5Me5)2U[(iPr)NCdN(iPr)(C6H4)-κN,κC], 4. Adamantyl azide, AdN3, inserts into the An-Me bonds in the (C5Me5)2AnMe2 complexes to make monomethyl actinide triazenido complexes that differ in the mode of triazenido coordination: (C5Me5)2ThMe[(Me)NNdN(Ad)-κ2N1,2], 5, and (C5Me5)2UMe[(Me)NNN(Ad)-κ2N1,3], 6. A κ2N1,3-triazenido complex of thorium was also isolated in a crystal comprised of a mixture of (C5Me5)2ThMe[(Me)NNN(Ad)-κ2N1,3] and (C5Me5)2Th(OH)[(Me)NNN(Ad)-κ2N1,3], 7. Introduction One of the powerful methods to manipulate reactivity in the relatively ionic complexes of the lanthanide and actinide metals is to vary the steric crowding in the coordination sphere of the metal.1 To enhance the capacity to change steric crowding in organoactinide complexes, the insertion reactivity of carbodiimides and organic azides into actinide-carbon bonds has been explored. These insertion reactions offer the potential to change a monohapto hydrocarbyl ligand into a group with more donor atoms and greater steric bulk by simple addition of a neutral ligand. Although an extensive insertion chemistry has been demonstrated for An-C bonds (An ) U, Th) with substrates such as CO,2 CO2,2d,3 isocyanides,2c,4 nitriles,2c,5 ketones,6 and diazoalkanes,7 carbodiimide insertion has not been investigated to our knowledge. However, the product of carbodiimide insertion into metal-alkyl bonds, namely, the amidinate moiety, has been shown to function as a useful ancillary ligand and can often replace cyclopentadienyl ligands.8 Hence, modification of steric bulk by carbodiimide insertion should provide a viable ligand for the new coordination sphere. * Corresponding author. E-mail: [email protected]. Fax: 949-824-2210. † University of California, Irvine. ‡ University of California, San Diego. (1) (a) Edelmann, F. T. In ComprehensiVe Organometallic Chemistry II 4; Lappert, M. F., Ed.; Pergamon: Oxford, 1995. (b) Anwander, R.; Herrmann, W. A. Top. Curr. Chem. 1996, 179, 1. (c) Evans, W. J.; Davis, B. L. Chem. ReV. 2002, 102, 2119. (2) (a) Manriquez, J. M.; Fagan, P. J.; Marks, T. J.; Day, C. S.; Day, V. W. J. Am. Chem. Soc. 1978, 100, 7112. (b) Fagan, P. J.; Manriquez, J. M.; Marks, T. J.; Day, V. W.; Vollmer, S. H.; Day, C. S. J. Am. Chem. Soc. 1980, 102, 5393. (c) Simpson, S. J.; Andersen, R. A. J. Am. Chem. Soc. 1981, 103, 4063. (d) Sonnenberger, D. C.; Mintz, E. A.; Marks, T. J. J. Am. Chem. Soc. 1984, 106, 3484. (3) Moloy, K. G.; Marks, T. J. Inorg. Chim. Acta 1985, 110, 127. (4) Zanella, P.; Paolucci, G.; Rossetto, G.; Benetollo, F.; Polo, A.; Fischer, R. D.; Bombieri, G. J. Chem. Soc., Chem. Commun. 1985, 96. Dormond, A.; Elbouadili, A. A.; Moise, C. J. Chem. Soc., Chem. Commun. 1984, 749.

Lanthanide9 and actinide10 amidinate complexes are known, but they are usually synthesized by ionic metathesis reactions using an amidinate salt. Carbodiimide insertion has been investigated with lanthanide and yttrium alkyl,11 amide,12 and alkynyl13 complexes, e.g., eq 1, but reactions of this type have not been reported for actinide complexes. (5) (a) Cramer, R. E.; Panchanatheswaran, K.; Gilje, J. W. J. Am. Chem. Soc. 1984, 106, 1853. (b) Dormond, A.; Aaliti, A.; El Bouadili, A.; Moise, C. J. Organomet. Chem. 1987, 329, 187. (c) Jantunen, K. C.; Burns, C. J.; Castro-Rodriguez, I.; Da Re, R. E.; Golden, J. T.; Morris, D. E.; Scott, B. L.; Taw, F. L.; Kiplinger, J. L. Organometallics 2004, 23, 4682. (d) Kiplinger, J. L.; Pool, J. A.; Schelter, E. J.; Thompson, J. D.; Scott, B. L.; Morris, D. E. Angew. Chem., Int. Ed. 2006, 45, 2036. (e) Schelter, E. J.; Yang, P.; Scott, B. L.; Da Re, R. E.; Jantunen, K. C.; Martin, R. L.; Hay, P. J.; Morris, D. E.; Kiplinger, J. L. J. Am. Chem. Soc. 2007, 129, 5139. (f) Schelter, E. J.; Morris, D. E.; Scott, B. L.; Kiplinger, J. L. Chem. Commun. 2007, 1029. (6) Dormond, A.; Aaliti, A.; El Bouadili, A.; Moise, C. Inorg. Chim. Acta 1987, 139, 171. (7) (a) Kiplinger, J. L.; John, K. D.; Morris, D. E.; Scott, B. L.; Burns, C. J. Organometallics 2002, 21, 4306. (b) Cantat, T.; Graves, C. R.; Jantunen, K. C.; Burns, C. J.; Scott, B. L.; Schelter, E. J.; Morris, D. E.; Hay, P. J.; Kiplinger, J. L. J. Am. Chem. Soc. 2008, 130, 17537. (8) See for example: (a) Barker, J.; Kilner, M. Coord. Chem. ReV. 1994, 133, 219. (b) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403. (c) Hagadorn, J. R.; Arnold, J. Organometallics 1998, 17, 1355. (d) Volkis, V.; Schmulinson, M.; Averbuj, C.; Lisovskii, A.; Edelmann, F. T.; Eisen, M. S. Organometallics 1998, 17, 3155. (e) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr. Organometallics 1998, 17, 4042. (f) Jayaratne, K. C.; Sita, L. R. J. Am. Chem. Soc. 2000, 122, 958. (g) Hirotsu, M.; Fontaine, P. P.; Epshteyn, A.; Zavalij, P. Y.; Sita, L. R. J. Am. Chem. Soc. 2007, 129, 9284. (9) (a) Schmidt, J. A. R.; Arnold, J. Chem. Commun. 1999, 2149. (b) Yao, Y.; Luo, Y.; Chen, J.; Zhang, Z.; Zhang, Y.; Shen, Q. J. Organomet. Chem. 2003, 679, 229. (c) Jing-Lei, C.; Ying-Ming, Y.; Yun-Jie, Luo; LiYing, Z.; Yong, Z.; Qi, S. J. Organomet. Chem. 2004, 689, 1019. (d) Trifonov, A. A.; Fedorova, E. A.; Fukin, G. K.; Bochkarev, M. N. Eur. J. Inorg. Chem. 2004, 4396. (e) Lyubov, D. M.; Bubnov, A. M.; Fukin, G. K.; Dolgushin, F. M.; Antipin, M. Y.; Pelce, O.; Schappacher, M.; Guillaume, S. M.; Trifonov, A. A. Eur. J. Inorg. Chem. 2008, 2090. (f) Zhang, W.-X.; Hou, Z. Org. Biomol. Chem. 2008, 6, 1720. (g) Luo, Y.; Wang, X.; Chen, J.; Luo, C.; Zhang, Z.; Yao, Y. J. Organomet. Chem. 2009, 694, 1289.

10.1021/om900135e CCC: $40.75  2009 American Chemical Society Publication on Web 05/13/2009

Insertion of Carbodiimides into Actinide-Carbon Bonds

Insertion reactivity is not as common for organic azides as for carbodiimides, but in some cases κ2-triazenido complexes can be isolated from η1-alkyl precursors.14 Triazenido complexes of f elements are known, but are usually obtained by either protonolysis or ionic metathesis methods.15 Recently, the insertion of mesityl azide, 2,4,6-Me3C6H2N3, into a lutetium alkyl bond was reported.16 In the organoactinide area, the reported reactivity of organic azides more commonly involves conversion to imides rather than insertion.17 We report here that carbodiimide and organic azide insertion into actinide-carbon bonds is facile and forms amidinate and triazenido metallocene products, respectively. The utility of this reactivity in derivatizing reactive intermediates containing An-C bonds is demonstrated with the ortho-metalated phenyl complex “(C5Me5)2U(C6H4),” derived from (C5Me5)2U(C6H5)2.18

Experimental Details General Experimental Procedures. The syntheses and manipulations described below were conducted with rigorous exclusion of air and water using Schlenk, vacuum line, and glovebox techniques. All reactions were conducted in a Vacuum Atmospheres inert-atmosphere (Ar) glovebox free of coordinating solvents. 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. Benzene-d6 (Cambridge Isotope Laboratories) was dried over NaK alloy and benzophenone, degassed by three freeze-pump-thaw cycles, and (10) (a) Wedler, M.; Roesky, H.; Edelmann, F. T. J. Organomet. Chem. 1988, 345, C1. (b) Wedler, M.; Kno¨sel, F.; Noltemeyer, M.; Edelmann, F. T.; Behrens, U. J. Organomet. Chem. 1990, 388, 21. (c) Edelmann, F. T.; Wedler, M.; Noltemeyer, M. Angew. Chem., Int. Ed. 1992, 31, 72. (d) Wedler, M.; Knosel, F.; Edelmann, F. T.; Behrens, U. Chem. Ber. 1992, 125, 1313. (e) Sarsfield, M. J.; Helliwell, M. J. Am. Chem. Soc. 2004, 126, 1036. (f) Sarsfield, M. J.; Helliwell, M.; Raftery, J. Inorg. Chem. 2004, 43, 3170. (g) Villiers, C.; Thuery, P.; Ephritikhine, M. Eur. J. Inorg. Chem. 2004, 4624. (h) Villiers, C.; Thuery, P.; Ephritikhine, M. Chem. Commun. 2006, 392. (11) (a) Zhang, J.; Ruan, R.; Shao, Z.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2002, 21, 1420. (b) Liu, B.; Yang, Y.; Cui, D.; Tang, T.; Chen, X.; Jing, X. Dalton Trans. 2007, 4252. (c) Masuda, J. D.; Jantunen, K. C.; Scott, B. L.; Kiplinger, J. L. Organometallics 2008, 27, 1299. (12) (a) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2004, 23, 3303. (b) Cui, P.; Chen, Y.; Li, G.; Xia, W. Angew. Chem., Int. Ed. 2008, 47, 9944. (13) Zhang, W.-X.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127, 16788. (14) (a) Hillhouse, G. L.; Goeden, G. V.; Haymore, B. L. Inorg. Chem. 1982, 21, 2064. (b) Heyduk, A. F.; Blackmore, K. J.; Ketterer, N. A.; Ziller, J. W. Inorg. Chem. 2005, 44, 468. (15) (a) Hillhouse, G. L.; Bercaw, J. E. Organometallics 1982, 1, 1025. (b) Chiu, K. W.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B. Polyhedron 1984, 3, 79. (c) Pfeiffer, D.; Guzei, I. A.; Liable-Sands, L. M.; Heeg, M. J.; Rheingold, A. L.; Winter, C. H. J. Organomet. Chem. 1999, 588, 167. (d) Hauber, S.-O.; Niemeyer, M. Inorg. Chem. 2005, 44, 8644. (e) Nimitsiriwat, N.; Gibson, V. C.; Marshall, E. L.; Takolpuckdee, P.; Tomov, A. K.; White, A. J. P.; Williams, D. J.; Elsegood, M. R. J.; Dale, S. H. Inorg. Chem. 2007, 46, 9988. (f) Barrett, A. G. M.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Kohn, G.; Procopiou, P. A. Inorg. Chem. 2008, 47, 7366. (16) Liu, B.; Cui, D. Dalton Trans 2009, 550. See also: Evans, W. J.; Mueller, T. J.; Ziller, J. W. J. Am. Chem. Soc. 2009, 131, 2678. (17) See for example: (a) Arney, D. S. J.; Burns, C. J. J. Am. Chem. Soc. 1995, 117, 9448. (b) Bart, S. C.; Anthon, C.; Heinemann, F. W.; Bill, E.; Edelstein, N. M.; Meyer, K. J. Am. Chem. Soc. 2008, 130, 12536. (18) Fagan, P. J.; Manriquez, J. M.; Maatta, E. A.; Seyam, A. M.; Marks, T. J. J. Am. Chem. Soc. 1981, 103, 6650.

Organometallics, Vol. 28, No. 12, 2009 3351 vacuum transferred before use. (C5Me5)2AnMe2,18 (C5Me5)2U(C6H5)2,18 and (C5Me5)2U(CtCPh)219 were prepared as previously described. iPrNdCdNiPr was purchased from Aldrich and dried over molecular sieves overnight and degassed by three freezepump-thaw cycles. AdN3, Me3SnN3, Me3SiN3, and CyNdCdNCy were purchased from Aldrich and placed under vacuum prior to use. NMR experiments were conducted with Bruker 400 or 500 MHz spectrometers. Infrared spectra were recorded as KBr pellets on a Perkin-Elmer Spectrum One FT-IR spectrometer. Elemental analyses were performed by Analytische Laboratorien (Lindlar, Germany) or with a Perkin-Elmer 2400 CHNS elemental analyzer. (C5Me5)2ThMe[(iPr)NC(Me)N(iPr)-K2N,N′], 1. iPrNdCdNiPr (100 µL, 0.646 mmol) was added to a stirred solution of (C5Me5)2ThMe2 (400 mg, 0.560 mmol) in toluene (10 mL). After 3 h, the solvent and excess carbodiimide were removed under vacuum to yield 1 as a white microcrystalline solid (480 mg, 97%). Crystals suitable for X-ray crystallography were obtained from a saturated toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 3.78 (sept, J ) 6.5 Hz, 1H, CHMe2), 3.65 (sept, J ) 6.5 Hz, 1H, CHMe2), 2.04 (s, 30H, C5Me5), 1.62 (s, 3H, Me), 1.26 (d, J ) 6.5 Hz, 6H, CHMe2), 1.16 (d, J ) 6.5 Hz, 6H, CHMe2), 0.30 (s, 3H, Me). 13C NMR (C6D6, 298 K): δ 12.5 (C5Me5), 18.4 (NC(Me)N), 25.4 (CHMe2), 26.3 (CHMe2), 47.2 (CHMe2), 49.5 (CHMe2), 63.4 (Th-Me), 122.1 (C5Me5), 176.5 (NC(Me)N). IR: 2960s, 2868s, 2722m, 1619w, 1479s, 1453s, 1412s, 1377s, 1359s, 1347s, 1321s, 1309s, 1218w, 1187s, 1099m, 1047m, 1020m, 809s cm-1. Anal. Calcd for C29H50N2Th: C, 52.87; H, 7.65; N, 4.25; Th, 35.22. Found: C, 52.44; H, 7.93; N, 3.89; Th, 35.10. (C5Me5)2UMe[(iPr)NC(Me)N(iPr)-K2N,N′], 2. Addition of i PrNdCdNiPr (180 µL, 1.16 mmol) to (C5Me5)2UMe2 (621 mg, 1.15 mmol) in pentane (15 mL) caused an immediate color change from orange to yellow-brown. After 5 h, the solvent was removed under vacuum to yield 2 as a yellow-brown powder (750 mg, 98%). Crystals suitable for X-ray diffraction were grown from a saturated pentane solution at -35 °C. 1H NMR (C6D6, 298 K): δ 39.3 (s, 6H, CHMe2), -1.8 (s, 30H, C5Me5), -6.9 (s, 1H, CHMe2), -9.7 (s, 3H, Me), -15.4 (s, 1H, CHMe2), -22.4 (s, 6H, CHMe2). The methyl group on uranium could not be located. 13C NMR (C6D6, 298 K): δ -55.28 (C5Me5). IR: 2965s, 2906s, 2857s, 2724w, 1655w, 1490m, 1435s, 1377s, 1347m, 1197m, 1143m, 1101m, 1058w, 1020m, 791w, 728w cm-1. Anal. Calcd for C29H50N2U: C, 52.40; H, 7.58; N, 4.21; U, 35.81. Found: C, 52.36; H, 7.40; N, 4.29; U, 35.95. (C5Me5)2U(CtCPh)[(iPr)NC(CtCPh)N(iPr)-K2N,N′], 3. iPrNd CdNiPr (55 µL, 0.36 mmol) was added to a stirred solution of (C5Me5)2U(CtCPh)2 (230 mg, 0.295 mmol) in methylcyclohexane (10 mL). The color changed from red to orange-red. After 30 min, the solvent was removed under vacuum to yield 3 as an orange microcrystalline solid (260 mg, 96%). Crystals suitable for X-ray crystallography were grown from a saturated toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 21.4 (s, 6H, CHMe2), 20.0 (d, J ) 9.5 Hz, 2H, C6H5), 12.8 (t, J ) 8.5 Hz, 1H, C6H5), 11.2 (t, J ) 8.5 Hz, 2H, C6H5), 6.3 (d, J ) 9.5 Hz, 2H, C6H5), 6.1 (t, J ) 9.5 Hz, 2H, C6H5), 3.3 (s, 30H, C5Me5), -13.0 (t, J ) 8.5 Hz, 1H, Ph), -21.3 (s, 6H, CHMe2). 13C NMR (C6D6, 298 K): δ 140.9 (C6H5), 137.4 (C6H5), 132.3 (C6H5), 124.9 (C6H5), 123.1 (C6H5), 34.8 (CHMe2), 32.3 (CHMe2), -45.4 (C5Me5). IR: 2924s, 2904s, 2720w, 2207s, 2062w, 1593s, 1492s, 1469s, 1452s, 1377s, 1186s, 1120s, 1052s, 1024m, 914w, 858w, 756s, 691s cm-1. Anal. Calcd for C47H68N2U: C, 62.79; H, 7.62; N, 3.12. Found: C, 62.63; H, 6.73; N, 3.30. (C5Me5)2U[(iPr)NCdN(iPr)(C6H4)-KN,KC], 4. iPrNdCdNiPr (50 µL, 0.32 mmol) was added to a solution of (C5Me5)2U(C6H5)2 (200 mg, 0.302 mmol) in toluene (8 mL) and allowed to stir for 2 h, after which time the solvent was removed under vacuum to (19) Straub, T.; Frank, W.; Reiss, G. J.; Eisen, M. S. J. Chem. Soc., Dalton Trans. 1996, 2541.

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EVans et al. 1177s, 1103s, 1059m, 1021m, 814w cm-1. Anal. Calcd for C32H51N3U: C, 53.69; H, 7.18; N, 5.87. Found: C, 53.71; H, 7.93; N, 5.70. X-ray Data Collection, Structure Solution, and Refinement for 1-7. This information is available in the Supporting Information.

Results Carbodiimide Insertion with (C5Me5)2AnMe2. The carbodiimide, iPrNdCdNiPr, reacts with the dimethyl actinide metallocenes, (C5Me5)2AnMe2, An ) Th, U, to form the monomethyl actinide amidinate complexes, (C5Me5)2AnMe[(iPr)NC(Me)N(iPr)-κ2N,N′] (An ) Th, 1; U, 2), as shown in eq 2. Both 1 and 2 can be isolated in greater than 95% yield and were characterized by elemental analysis and NMR and IR Figure 1. Thermal ellipsoid plot of (C5Me5)2ThMe[(iPr)NC(Me)N(iPr)κ2N,N′], 1, drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. The thermal ellipsoid plot of isomorphous (C5Me5)2UMe[(iPr)NC(Me)N(iPr)-κ2N,N′], 2, is in the Supporting Information. yield 4 as a tacky orange solid. Crystals suitable for X-ray diffraction were grown from a saturated pentane solution at -35 °C (118 mg, 55% crystalline). 1H NMR (C6D6, 298 K): δ 11.2 (s, 6H, CH(CH3)2), 6.1 (s, 30H, C5Me5), -6.2 (s, 6H, CH(CH3)2). The phenyl protons could not be assigned. Anal. Calcd for C33H48N2U: C, 55.76; H, 6.81; N, 3.94. Found: C, 56.03; H, 7.13; N, 3.74. An alternative method was used to synthesize 4. PhLi (18 mg, 0.21 mmol) was added to a stirred solution of [(C5Me5)2UMe(OTf)]2 (125 mg, 0.199 mmol) in benzene (10 mL). The color turned from red to orange with addition of PhLi. After 2 h, a white precipitate was removed by centrifugation, and iPrNdCdNiPr (30 µL, 0.19 mmol) was added. No color change was observed. The 1H NMR spectrum was consistent with the formation of 4. When the reaction was conducted in a sealed NMR tube, the presence of methane (δ 0.14 ppm in C6D6) was observed. The addition of PhCtCPh to the reaction of [(C5Me5)2UMe(OTf)]2 and PhLi matched the resonances obtained for (C5Me5)2U[C2(Ph)2C6H4].18 On the basis of the NMR spectrum, a 70% conversion was observed. (C5Me5)2ThMe[(Me)NNN(Ad)-K2N,N1,2], 5. Azidoadamantane, C10H15N3 (35 mg, 0.20 mmol), was added to a stirred solution of (C5Me5)2ThMe2 (105 mg, 0.197 mmol) in toluene (8 mL). No color change was observed. After 4 h, the solvent was removed, yielding 5 as a colorless powder (131 mg, 94%). Crystals suitable for X-ray diffraction were obtained from a saturated toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 3.2 (s, 3H, Ad), 2.1 (s, 3H, Ad), 2.1 (s, 6H, Ad), 1.98 (s, 3H, Ad), 1.91 (s, 30H, C5Me5), 0.3 (s, 3H, Me). 13C NMR (C6D6, 298 K): δ 123.3 (C5Me5), 65.5 (Th-Me), 59.1 (quat C Ad), 44.8 (Ad), 43.7 (Ad), 37.4 (Ad), 36.3 (Ad), 30.8 (Me), 11.5 (C5Me5). IR: 2902s, 2849s, 1492m, 1448s, 1421s, 1376s, 1272s, 1224m, 1181m, 1106s, 1088s, 993s, 972s, 798m, 695m cm-1. Anal. Calcd for C32H51N3Th: C, 54.15; H, 7.24; N, 5.92. Found: C, 54.43; H, 7.55; N, 5.59. (C5Me5)2UMe[(Me)NNN(Ad)-K2N1,3], 6. Azidoadamantane, C10H15N3 (102 mg, 0.575 mmol), was added to a stirred solution of (C5Me5)2UMe2 (300 mg, 0.557 mmol) in methylcyclohexane (10 mL). No color change was observed. After 14 h, the solvent was removed, quantitatively yielding 6 as an orange microcrystalline powder (397 mg). Crystals suitable for X-ray diffraction were obtained from a saturated pentane/toluene solution at -35 °C. 1H NMR (C6D6, 298 K): δ 2.3 (s, Me, 3H), -1.9 (s, C5Me5, 30H), -7.3 (s, 3H, Ad), -7.96 (s, 3H, Ad), -10.2 (s, 3H, Ad), -30.6 (s, 6H, Ad), -132.7 (s, Me, 3H). 13C NMR (C6D6, 298 K): δ 33.4 (Ad), 22.6 (Ad), -9.9 (Ad), -40.8 (Me), -59.0 (C5Me5). IR: 2977s, 2904s, 2849s, 2723m, 1491m, 1448s, 1434s, 1377s, 1268s, 1251s,

spectroscopy. The structures were established by X-ray crystallography, Figure 1. The remaining methyl groups in 1 and 2 do not react with excess carbodiimide to form bis(amidinate) complexes, even upon heating. Insertion reactions with cyclohexylcarbodiimide, CyNdCd NCy, were also investigated. CyNdCdNCy reacts with (C5Me5)2AnMe2 to make (C5Me5)2AnMe[CyNC(Me)NCyκ2N,N′] products similar to 1 and 2 with An ) U and Th. X-ray crystallography on (C5Me5)2UMe[CyNC(Me)NCy-κ2N,N′] revealed a product analogous to 2 (see Supporting Information, Figure B), but the data were not of sufficient quality for detailed analysis. Since the cyclohexyl-substituted analogues proved to be less crystalline than the isopropyl derivatives that allow definitive characterization by X-ray crystallography, subsequent reactions focused on iPrNdCdNiPr. The 1H NMR spectra of 1 and 2 each contain a single (C5Me5)- resonance that indicates that the added steric bulk from the carbodiimide insertion did not lock the metallocenes into a rigid conformation as was found for (C5Me5)2(C5Me4H)UMe, which displayed a unique resonance for each (C5Me5)- ligand.20 The 2.04 and -1.82 ppm resonances for the (C5Me5)- methyl groups of 1 and 2 can be compared to the 1.92 and 5.15 ppm resonances for (C5Me5)2ThMe2 and (C5Me5)2UMe2,18 respectively. The spectrum of 1 showed methyl resonances at 1.62 (amidinate methyl) and 0.30 ppm (Th-Me) (-0.19 ppm for (C5Me5)2ThMe2), but only one methyl resonance was observed in the 1H NMR spectrum of 2 at -9.8 ppm (-132 ppm for (C5Me5)2UMe2). The -9.8 ppm resonance is presumably due to the methyl on the amidinate that is further away from the paramagnetic metal center. Interestingly, each uranium complex characterized with the iPr amidinate ligand in this study has a 1 H NMR spectrum that contains one isopropyl methyl group downfield (e.g. 39.2 ppm in 2) and one isopropyl methyl group upfield (e.g. -15.4 ppm in 2). The crystallographic data on 1 and 2 showed that the An-(C5Me5 ring centroid) bond distances are longer than those in the (C5Me5)2AnMe2 complexes, 2.584 and 2.598 Å for 1, (20) Evans, W. J.; Walensky, J. R.; Furche, F.; Ziller, J. W.; DiPasquale, A. G.; Rheingold, A. L. Inorg. Chem. 2008, 47, 10169.

Insertion of Carbodiimides into Actinide-Carbon Bonds

2.518 and 2.518 Å for (C5Me5)2ThMe2,21 2.527 and 2.538 Å for 2, and 2.456 and 2.461 Å for (C5Me5)2UMe2,21 which is consistent with increased steric crowding. Concomitantly, the (C5Me5 ring centroid)-An-(C5Me5 ring centroid) angles in 1 and 2 are smaller than those in their precursors: 130.8° and 130.9° for 1 and 2, respectively, versus 133.9° and 140.5° for (C5Me5)2ThMe2 and (C5Me5)2UMe2, respectively.21 The U-C(Me) bond length of 2.442(3) Å in 2 compares well with other monomethyl uranium complexes such as 2.441(7) Å in [(C5Me5)2UMe(OTf)]2,7a 2.446(7) Å in [tBuNAr]3UMe, Ar ) 3,5-C6H3Me2,22 2.427(5) Å in (C5Me5)2UMe(SPh),23 2.438(5) Å of (C5Me5)2UMe(SePh),23 2.393(12) Å in [(C5Me5)2UMe][BPh3Me],24 and 2.41(1) Å in (Me2PCH2CH2PMe2)U(Me)(CH2C6H5)3.25 The Th-C(Me) bond length of 2.511(2) Å is also similar to other monomethyl thorium complexes such as 2.510(13) Å in (C5Me5)2ThMe[P(SiMe3)2],26 2.48(3) Å in (C11H11)3ThMe,27 2.479(3) Å in [(C5Me5)2ThMe][Fe(B9C2H11)],28 and 2.531(2) Å in (C5Me5)2ThMe[η2-(N,C)-6-CH3NC5H3].29 In both 1 and 2, the amidinate ligand coordinates through the two nitrogen atoms with similar An-N bond distances (1, 2.509(2), 2.515(2) Å; 2, 2.453(2), 2.462(2) Å). The central carbon, C(21), is much further away, 2.928(2) and 2.868(3) Å for 1 and 2, respectively. The An-N distances in 1 and 2 can be compared with analogues in the actinide amidinate complexes [2,4,6-(CF3)3C6H2C(NSiMe3)2]2AnCl2, which are 2.514(13) and 2.418(13) Å for An ) Th and 2.414(19) and 2.449(19) Å for An ) U.10a The actinide metal centers in 1 and 2 are 0.88 and 0.84 Å out of the NCN plane, respectively. Carbodiimide Insertion with (C5Me5)2U(CtCPh)2. i PrNdCdNiPr also reacts with the bis(alkynyl), (C5Me5)2U(CtCPh)2,19 to generate the insertion product (C5Me5)2U(CtCPh)[(iPr)NC(CtCPh)N(iPr)-κ2N,N′], 3, eq 3. As shown in Figure 2, the structure of complex 3, determined by X-ray

Organometallics, Vol. 28, No. 12, 2009 3353

Figure 2. Thermal ellipsoid plot of (C5Me5)2U(CtCPh)[(iPr)NC(Ct CPh)N(iPr)-κ2N,N′], 3, drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity.

Figure 3. Thermal ellipsoid plot of (C5Me5)2U[(iPr)NCdN(iPr)(C6H4)κN,κC], 4, drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity.

crystallography, is similar to that of 1 and 2. The IR spectrum of 3 contains two absorptions characteristic of C-C triple bonds. The 2207 cm-1 band is presumably due to the alkynyl amidinate since it is similar to the 2205 cm-1 CtC absorption observed for the yttrium carbodiimide phenyl alkynyl insertion product, {Me 2 Si(C 5 Me 4 )(NPh)}Y(THF){ t BuNC(CtCPh)N t Buκ2N,N′}.13 The 2062 cm-1 band is close to the 2056 cm-1 (21) Jantunen, K. C.; Burns, C. J.; Castro-Rodriguez, I.; Da Re, R. E.; Golden, J. T.; Morris, D. E.; Scott, B. L.; Taw, F. L.; Kiplinger, J. L. Organometallics 2004, 23, 4682. (22) Diaconescu, P.; Odom, A. L.; Agapie, T.; Cummins, C. C. Organometallics 2001, 20, 4993. (23) Evans, W. J.; Miller, K. A.; Ziller, J. W.; DiPasquale, A. G.; Heroux, K. J.; Rheingold, A. L. Organometallics 2007, 26, 4287. (24) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Organometallics 2005, 24, 3407. (25) Edwards, P. G.; Andersen, R. A.; Zalkin, A. Organometallics 1984, 3, 293. (26) 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. (27) Spirlet, M.-R.; Rebizant, J. Acta Crystallogr. 1993, C49, 1138. (28) Yang, X.; King, W. A.; Sabat, M.; Marks, T. J. Organometallics 1993, 12, 4254. (29) Kiplinger, J. L.; Scott, B. L.; Schelter, E. J.; Pool, J. A.; Tournear, D. J. Alloys Compd. 2007, 444, 445–477.

absorption displayed by (C5Me5)2U(CtCPh)2 and therefore is assigned to the (CtCPh)- ligand attached to the uranium. The U-(C5Me5 ring centroid) distances of 2.484 and 2.502 Å in 3 are in between those in (C5Me5)2UMe2 (2.456, 2.461 Å) and those in 2 (2.527, 2.538 Å). In contrast to 1 and 2, which have their two An-N(amidinate) distances equivalent within experimental error, the analogous U-N(amidinate) bond lengths in 3 are not as similar. The 2.482(1) Å U-N(1) distance furthest from the alkynyl ligand is longer than the 2.422(1) Å U-N(2) distances adjacent to the alkynyl. The same trend was observed in UCl[(Me3Si)NC(Ar)N(SiMe3)κ2N,N′]310b and UCl[(CyNC(Me)NCy-κ2N,N′]3.10g For example, the U-N distances adjacent to the chloride ligands in UCl[(CyNC(Me)NCy- κ2N,N′]3 are 0.1, 0.05, and 0.04 Å shorter than the U-N lengths farther from the chloride. This trend was rationalized on the basis of steric strain. The U-C(36) metal alkynyl bond distance of 2.433(1) Å in 3 is similar to the uranium methyl carbon bond in 2, 2.442(3) Å, and the 2.424(7) and 2.414(7) Å distances in (C5Me5)2UMe2. This distance can be compared to the U-terminal alkynyl distances of 2.409(4) Å in (C5Me5)2U(CtCPh)(NPh2)30 and 2.33(2) Å in (C5H5)3U(CtCPh).31 The 1.214(3) Å C(36)-C(37) bond distance in the CtCPh ligand and the 1.194(3) Å C(22)-C(23) distance of the alkyne substituent of the amidinate are consistent with CtC triple bonds.

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Carbodiimide Insertion with (C5Me5)2U(C6H5)2. Although PrNdCdNiPr reacts with the diphenyl metallocene (C5Me5)2U(C6H5)2, the product is not analogous to complexes 1-3. Instead, (C5Me5)2U[(iPr)NC(dNiPr)(C6H4)-κN,κC], 4, is isolated as shown in Figure 3. This result can be explained by carbodiimide insertion into an ortho-metalated phenyl complex, “(C5Me5)2U(C6H4)”, that is formed by elimination of benzene from (C5Me5)2U(C6H5)2, as shown in eq 4. When (C5Me5)2U(C6H5)2 was first reported,18 its decomposition to a “benzyne” i

complex of composition “(C5Me5)2U(C6H4)” was proposed. The evidence for this intermediate was the isolation of the PhCtCPh insertion product (C5Me5)2U[C2(Ph)2C6H4], a compound that was identified spectroscopically, eq 5.18 The isolation of 4 provides

whose 1H NMR spectrum matched that obtained for (C5Me5)2U[C2(Ph)2C6H4].18 The U-(C5Me5 ring centroid) bond distances in 4, 2.484 and 2.498 Å, are more similar to the 2.456 and 2.461 Å values in (C5Me5)2UMe221 than to those in 2. Similarly, the (C5Me5 ring centroid)-U-(C5Me5 ring centroid) angle in 4, 136.9°, is closer to that in (C5Me5)2UMe2, 140.5°, than to that in 2, 130.9°.21 This is consistent with less steric crowding in 4 due to the single chelating dianionic ligand. The 2.266(3) Å U-N(2) bond distance in 4 is equivalent to the 2.267(6) Å distance in (C5Me5)2U(NHR)2 (R ) 2,6-dimethylphenyl)19 and similar to the 2.221(8) Å in (C5Me5)2U[(o-C6H4)NPh-κN,κC].32 The 1.290(4) Å N(1)-C(7) bond distance is consistent with an NdC double bond,33 while the 1.408(4) Å N(2)-C(7) bond distance is in the N-C single bond range. The U-C(8) distance of 2.414(3) Å is similar to that observed for (C5Me5)2UMe2.21 Organic Azide Insertion with (C5Me5)2AnMe2. (C5Me5)2ThMe2 and (C5Me5)2UMe2 react with adamantyl azide, AdN3, to generate the triazenido monomethyl metallocene complexes (C5Me5)2ThMe[(Me)NNdN(Ad)-κ2N1,2], 5, eq 7, and (C5Me5)2UMe[(Me)NNN(Ad)-κ2N1,3], 6, eq 8, respectively. Both complexes were characterized by 1H and 13C NMR and IR spectroscopy and their structures determined by X-ray crystallography, Figures 4 and 5.

crystallographic support for this type of metalation and insertion chemistry. The 1H NMR spectrum of 4 contains a (C5Me5)- resonance at 6.08 ppm that is similar to the 6.14 ppm resonance assigned to the (C5Me5)- ligand in (C5Me5)2U[C2(Ph)2C6H4].18 Resonances between 0 and 6 ppm are present in the 1H NMR of 4 that could account for the phenyl protons, but they cannot be unambiguously assigned, even at lower temperature. It should be noted that the assignment of the phenyl protons in (C5Me5)2U(C6H5)2 was difficult as well.18 The methyl groups from the isopropyl group in 4 display the typical pattern of one downfield (11.2 ppm) and one upfield (-6.2 ppm) resonance. It is possible that 4 is formed not by the reaction shown in eq 4, but by carbodiimide insertion into a uranium phenyl linkage in (C5Me5)2U(C6H5)2 followed by a metalation that eliminates benzene. This was probed by examining an alternative route to 4 starting with the methyl triflate complex [(C5Me5)2UMe(OTf)]2.7a,20 This complex reacts with PhLi to form methane (observed by 1H NMR spectroscopy) and an orange solution with a 1H NMR spectrum that matches that of “(C5Me5)2U(C6H4)”.18 This reaction could involve formation of a “(C5Me5)2U(Ph)(Me)” intermediate that eliminates methane by methyl metalation of the phenyl ligand. Addition of i PrNdCdNiPr to this solution in situ produces identical resonances to those obtained for 4, eq 6. The formation of 4 in eq 6 is consistent with carbodiimide insertion into the “(C5Me5)2U(C6H4)” intermediate. Addition of PhCtCPh to the [(C5Me5)2UMe(OTf)]2/PhLi reaction product gave a compound

Addition of excess organic azide to 5 or 6 does not result in another insertion. Me3SiN3 does not react with (C5Me5)2AnMe2 (An ) Th, U) under analogous conditions, although it does react at 100 °C in toluene to form a complicated mixture of products from which an analogous insertion product has not been obtained. Me3SnN3 reacts to form a precipitate that could not be solubilized in alkanes, arenes, or ethers. In contrast to the isomorphous amidinate products, 1 and 2, the thorium complex 5 had a κ2N1,2-triazenido coordination

(30) Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. Organometallics 2008, 27, 3335. (31) Atwood, J. L.; Hains, C. F., Jr.; Tsutsui, M.; Gebala, A. E. J. Chem. Soc., Chem. Commun. 1973, 452.

(32) Graves, C. R.; Schelter, E. J.; Cantat, T.; Scott, B. L.; Kiplinger, J. L. Organometallics 2008, 27, 5371. (33) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1–S19.

Insertion of Carbodiimides into Actinide-Carbon Bonds

Figure 4. Thermal ellipsoid plot of (C5Me5)2ThMe[(Me)NNdN(Ad)κ2N1,2], 5, shown at the 50% probability level. Hydrogen atoms have been omitted for clarity.

Figure 5. Ball and stick diagram of (C5Me5)2UMe[(Ad)NNN(Me)κ2N1,3], 6.

mode that differs from the κ2N1,3-ligation in the uranium complex of analogous composition 6. Although the X-ray diffraction data on 6 provided connectivity, they were not of high enough quality to allow a detailed structural analysis. Hence, only the metrical data on 5 will be discussed. As observed for 3, the 2.537 and 2.534 Å Th-(C5Me5 ring centroid) distances in 5 (Table 5) are intermediate between those in (C5Me5)2ThMe2, 2.518 Å,21 and 1, 2.584 and 2.598 Å. Similarly, the 2.505(2) Å Th-C(Me) distance in 5 is similar to the 2.49(1) Å of [(C5Me5)2ThMe(THF)2][BPh4].34 Unlike 1-3, which have delocalized bonding in the amidinate ligands, complex 5 contains a localized double bond for N(1)-N(2), 1.243(3) Å, and a longer length for N(2)-N(3), 1.360(3) Å. Consistent with the lack of delocalization, the Th-N distances are also not equivalent. The 2.387(2) and 2.597(2) Å bond lengths for Th-N(3) and Th-N(2), respectively, are similar to the 2.339(7) and 2.571(7) Å in the bis(hydrazonato) complex (C5Me5)2Th[PhCH2-N-NdCPh2-κ2N,N′]2,7b which also has an “-N-Nd” moiety. While attempting to crystallize 5, the structure shown in Figure 6 was obtained. Superficially, this appeared to be (C5Me5)2ThMe[(Me)NNN(Ad)-κ2N1,2], but the structure differed in that the triazenido ligand was bound κ2N1,3 and not κ2N1,2. Closer examination of the bond distances revealed a 2.143(12) (34) Lin, Z.; Le Marechal, J.-F.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc. 1987, 109, 4127.

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Figure 6. Thermal ellipsoid plot of a 50:50 mixture of (C5Me5)2Th(CH3)[(Me)NNN(Ad)-κ2N1,3] and (C5Me5)2Th(OH)[(Me)NNN(Ad)κ2N1,3], 7, shown at the 50% probability level. Hydrogen atoms have been omitted for clarity.

Å distance to the position thought to be occupied by the methyl group. Since this distance is more appropriate for a Th-O(OH) bond (the Th-O(OH) distance in the terminal hydroxide {[Th(OAr)4(OH)THF][K(18-crown-6)(THF)2]} (Ar ) 2,6Ph2Ph) is 2.105(13) Å) than a Th-C(Me) bond, the data were refined for (C5Me5)2Th(OH)[(Me)NNN(Ad)-κ2N1,3]. This gave a model with a thermal parameter larger than expected for the hydroxyl oxygen. Subsequently, it was found that a model in which there is 50% occupancy of hydroxide and methyl at this position better matched the data. Hence, this crystal appears to contain a 50:50 mixture of a methyl complex and the hydroxide hydrolysis product. Evidently, the presence of the hydroxide component was a sufficient perturbation for the methyl complex to cocrystallize in the κ2N1,3 mode instead of the κ2N1,2 mode of complex 5. This suggests that the energy difference between these coordination modes is small enough to be influenced by crystal packing forces.

Discussion Insertion of carbodiimides and organic azides into actinide alkyl, alkynyl, and aryl bonds in metallocenes appears to be facile. These reactions provide direct routes to change the steric bulk of the η1-hydrocarbyl ligands to that of κ2N,N′-amidinate and κ2N1,2- and κ2N1,3-triazenido ligands. The reaction chemistry of the new complexes is consistent with increased steric crowding, since once one insertion occurs, the remaining alkyl group is unreactive toward additional substrate. The insertion reactions in this study can be compared to organoactinide reactions with related substrates.2-7 In general, smaller substrates such as CO2,2d,3 nitriles,5 and diazoalkanes7b can undergo double insertion into An-C bonds in (C5Me5)2AnR2 complexes. Hence, 1 and 2 equiv of CO2 react with (C5Me5)2UMe2 to form (C5Me5)2UMe(O2CMe) and (C5Me5)2U(O2CMe)2, respectively, both of which were characterized by NMR spectroscopy.3 Kiplinger has shown that nitriles and diazoalkanes doubly insert into the An-carbon bonds of (C5Me5)2AnR2 (An ) Th, U; R ) Me, CH2Ph) and (C5Me5)2Th(C6H5)2.7b Comparisons of the insertion chemistry reported here can also be made with group IV metals.35 The reactivity of (C5Me5)2(35) (a) Gambarotta, S.; Strologo, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1985, 24, 654. (b) Chiu, K. W.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B. Polyhedron 1984, 3, 79. (c) Hillhouse, G. L.; Bercaw, J. E. Organometallics 1982, 1, 1025.

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Table 1. X-ray Data Collection Parameters for Complexes 1-7

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 a

C29H50N2Th 1

C29H50N2U 2

C43H54N2U 3

C33H49N2U 4

C32H51N3Th · C7H8 5

C32H51N3U 6

C31.5H50N3O0.5Th 7

658.75 103(2) orthorhombic Pbca 18.2607(14) 16.5765(12) 18.3346(14) 90 90 90 5549.9(7) 8 1.577 5.392 0.0195 0.0469

664.74 143(2) orthorhombic Pbca 16.5291(12) 18.1347(14) 18.3817(14) 90 90 90 5509.9(7) 8 1.598 5.910 0.0233 0.0336

836.91 153(2) monoclinic P21/n 13.2684(7) 18.7110(10) 15.1098(8) 90 90.7735(6) 90 3750.9(3) 4 1.482 4.358 0.0165 0.0431

711.77 100(2) monoclinic P21/n 10.0405(6) 16.7741(10) 17.8447(11) 90 92.7800(10) 90 3001.9(3) 4 1.575 5.430 0.0218 0.0510

801.93 153(2) monoclinic P21/c 10.2096(6) 19.8762(11) 17.8379(10) 90 99.8160(10) 90 3566.8(4) 4 1.493 4.210 0.0196 0.0490

715.79 153(2) orthorhombic Pna21 19.7535(11) 14.2147(8) 10.6188(6) 90 90 90 2981.7(3) 4 1.595 5.468 0.0407 0.1071

710.78 153(2) triclinic P1j 9.9109(7) 10.7104(8) 14.9504(11) 85.5730(10) 72.4170(10) 75.4890(10) 1464.58(19) 2 1.612 5.117 0.0230 0.0537

Definitions: wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2] ]1/2, R1 ) ∑||Fo| - |Fc||/∑|Fo|. Table 2. Selected Bond Distances (Å) and Angles (deg) for (C5Me5)2ThMe[(iPr)NC(Me)N((iPr)-K2N,N′], 1, and (C5Me5)2UMe[(iPr)NC(Me)N(iPr)-K2N,N′], 2

An(1)-Cnt(C5Me5) An(1)-C(29) An(1)-N(1) An(1)-N(2) An(1)-C(21) Cnt(C5Me5)-An(1)-Cnt(C5Me5) Cnt(C5Me5)-An(1)-C(29) Cnt(C5Me5)-An(1)-N(1) Cnt(C5Me5)-An(1)-N(2) N(1)-An(1)-N(2) largest methyl displacement

1

2

2.584, 2.598 2.511(2) 2.509(2) 2.515(2) 2.928(2) 130.8 96.2, 94.6 103.1, 105.0 110.0, 119.1 53.20(7) 0.31

2.527, 2.538 2.442(3) 2.461(2) 2.453(2) 2.868(3) 130.9 95.8, 94.1 110.9, 118.2 103.0, 104.8 54.52(8) 0.34

Table 3. Selected Bond Distances (Å) and Angles (deg) for (C5Me5)2U(CtCPh[(iPr)NC(CtCPh)N(iPr)-K2N,N′], 3 U(1)-Cnt(C5Me5) U(1)-N(1) U(1)-N(2) U(1)-C(21) U(1)-C(36) Cnt(C5Me5)-U(1)-Cnt(C5Me5) Cnt(C5Me5)-U(1)-N(1) Cnt(C5Me5)-U(1)-N(2) Cnt(C5Me5)-U(1)-C(36) N(1)-U(1)-N(2) largest methyl displacement

2.484, 2.502 2.482(1) 2.422(1) 2.876(1) 2.433(1) 134.4 100.8, 103.9 111.5, 114.1 96.7, 91.6 54.82(5) 0.31

Table 4. Selected Bond Distances (Å) and Angles (deg) for (C5Me5)2U[(iPr)NCdN(iPr)(C6H4)-KN,KC], 4 U(1)-Cnt(C5Me5) U(1)-N(2) U(1)-C(8) Cnt(C5Me5)-U(1)-Cnt(C5Me5) Cnt(C5Me5)-U(1)-N(2) Cnt(C5Me5)-U(1)-C(8) N(1)-U(1)-C(8) largest methyl displacement

2.484, 2.498 2.266(3) 2.414(3) 136.9 111.8, 111.0 97.7, 100.2 71.8(1) 0.28

AnMe2 and (C5Me5)2U(CtCPh)2 complexes with carbodiimides is similar to that found with (C5H5)2ZrMe2 and (C5H5)2ZrPh2, compounds that react with only 1 equiv of p-tolylcarbodiimide even upon heating,35a In contrast, (C5H5)2Zr(CH2Ph)2 does not react with carbodiimides. The reaction of (C5H5)2ZrMe2 with Me3SiN3 gave (C5H5)2ZrMe(N3) by methyl abstraction. However, reactions of (C5H5)2ZrR2 (R ) Me, Ph) with phenylazide gave the monoalkyl insertion products (C5H5)2ZrR[(R)NNN(Ph)κ2N1,3],35b similar to what was observed with (C5Me5)2UMe2.

Table 5. Selected Bond Distances (Å) and Angles (deg) for (C5Me5)2ThMe[(Me)NNdN(Ad)-K2N1,2], 5 Th(1)-Cnt(C5Me5) 2.537, 2.534 Th(1)-N(2) 2.597(2) Th(1)-N(3) 2.387(2) Th(1)-C(32) 2.505(2) N(2)-N(3) 1.360(3) N(1)-N(2) 1.243(3) Cnt(C5Me5)-Th(1)-Cnt(C5Me5) 136.1 Cnt(C5Me5)-Th(1)-N(2) 110.1, 109.1 Cnt(C5Me5)-Th(1)-N(3) 102.1, 101.2 Cnt(C5Me5)-Th(1)-C(32) 99.5, 100.0 N(2)-Th(1)-N(3) 31.30(7) largest methyl displacement 0.27

Organic azides have also been shown to insert into (C5Me5)2Hf(H)2 to produce the monosubstituted triazenido complexes (C5Me5)2Hf(H)(NHNNR-κ2N1,3), R ) Ph, p-tolyl.35c In the reaction of iPrNdCdNiPr with (C5Me5)2U(C6H5)2, eq 5, not only was the coordination environment of the starting material changed, but crystallographic evidence was also provided in support of the NMR arguments previously made for the formation of an ortho-metalated intermediate “(C5Me5)2U(C6H4)”, a species that was described as a formal equivalent to a benzyne complex.18 The isolation of (C5Me5)2U[(iPr)NCdN(iPr)(C6H4)-κN,κC], 4, is consistent with the NMR-based PhCtCPh trapping experiments originally done with (C5Me5)2U(C6H5)2. The reaction of [(C5Me5)2UMe(OTf)]2 and PhLi, which was done to probe the mechanism of the formation of 4, has proven to be a new route to “(C5Me5)2U(C6H4)”. This reaction, with the identification of methane as a byproduct, provides further support for the formation of a metalated phenyl ligand in this system.

Conclusion The insertion chemistry reported here shows a facile method to change the coordination environment of bis(hydrocarbyl) actinide metallocenes. Since only one of the hydrocarbyl ligands in the (C5Me5)2AnMe2 and (C5Me5)2U(CtCPh)2 participates in insertion reactions, these reactions also provide a method to differentiate the two R groups and make a monohydrocarbyl product. In the case of (C5Me5)2U(C6H5)2, the insertion reaction proved to be useful in derivatizing an intermediate that was not readily isolated. Hence, this insertion chemistry could be used to trap

Insertion of Carbodiimides into Actinide-Carbon Bonds

hydrocarbyl actinide metallocenes that cannot be definitively characterized by other methods.

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.

Organometallics, Vol. 28, No. 12, 2009 3357 Supporting Information Available: X-ray diffraction details (CIF) and X-ray data collection, structure, solution, and refinement of compounds 1-7. This material is available free of charge via the Internet at http://pubs.acs.org.

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