Organometallics 2010, 29, 945–950 DOI: 10.1021/om901006t
945
Insertion Reactivity of CO2, PhNCO, Me3CCtN, and Me3CNtC with the Uranium-Alkynyl Bonds in (C5Me5)2U(CtCPh)2 William J. Evans,* Justin R. Walensky, and Joseph W. Ziller Department of Chemistry, University of California, Irvine, California 92697-2025 Received November 17, 2009
The insertion reactivity of (C5Me5)2U(CtCPh)2, 1, has been studied with CO2, PhNCO, Me3CCtN, and Me3CNtC. Insertion into both U-CtCPh bonds of 1 occurs with the first three substrates to form (C5Me5)2U(O2CCtCPh)2, 2, (C5Me5)2U[PhNC(CtCPh)O-κ2N,O]2, 3, and (C5Me5)2U[NdC(CMe3)(CtCPh)]2, 4, respectively. Only 1 equiv of Me3CNtC reacts with 1 to form (C5Me5)2[(PhCtC)CdN(CMe3)-η2C,N]U(CtCPh), 5, a result similar to the iPrNdCdNiPr insertion that forms (C5Me5)2[iPrNC(CtCPh)NiPr-κ2N,N0 ]U(CtCPh), 6.
Introduction The reactivity of actinide-carbon bonds has been heavily studied as a method to probe fundamental actinide-element bond making and breaking chemistry as well as a platform to define new options in catalysis1 including oligomerization,2 hydroamination,3 and hydrosilylation.4 Insertion of a substrate into the actinide-carbon bond is an important component of these transformations.5 The insertion chemistry of the common metallocene dialkyl complexes, (C5Me5)2AnMe2 (An= Th, U), has been established with substrates such as Me3CNtC,6 CO2,7 PhCtN,8 and Ph2CN2.9 Insertion reactions between (C5Me5)2An(CH2Ph)2 and PhCtN8 and Ph2CN29 have also been reported in the literature. Insertion reactivity for the bis(alkynyl) metallocene analogues, (C5Me5)2An(CtCPh)2, *Corresponding author. E-mail:
[email protected]. Fax: 949-8242210. (1) (a) Barnea, E.; Eisen, M. S. Coord. Chem. Rev. 2006, 250, 855. (b) Castro-Rodriguez, I.; Meyer, K. Chem. Commun. 2006, 1353. (c) Andrea, T.; Eisen, M. S. Chem. Soc. Rev. 2008, 37, 550. (d) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Nature 2008, 455, 341. (2) (a) Haskel, A.; Straub, T.; Dash, A. K.; Eisen, M. S. J. Am. Chem. Soc. 1999, 121, 3014. (b) Haskel, A.; Wang, J. Q.; Straub, T.; Neyroud, T. G.; Eisen, M. S. J. Am. Chem. Soc. 1999, 121, 3025. (c) Wang, J.; Dash, A. K.; Kapon, M.; Berthet, J.-C.; Ephritikhine, M.; Eisen, M. S. Chem.;Eur. J. 2002, 8, 5384. (3) (a) Stubbert, B. D.; Stern, C. L.; Marks, T. J. Organometallics 2003, 22, 4836. (b) Stubbert, B. D.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 6149. (4) (a) Dash, A. K.; Wang, J. Q.; Eisen, M. S. Organometallics 1999, 18, 4724. (b) Dash, A. K.; Gourevich, I.; Wang, J. Q.; Wang, J.; Kapon, M.; Eisen, M. S. Organometallics 2001, 20, 5084. (5) See for example: (a) Barnea, E.; Andrea, T.; Kapon, M.; Berthet, J.-C.; Ephritikhine, M.; Eisen, M. S. J. Am. Chem. Soc. 2004, 126, 10860. (b) Barnea, E.; Andrea, T.; Berthet, J.-C.; Ephritikhine, M.; Eisen, M. S. Organometallics 2008, 27, 3103. (6) Dormond, A.; Elbouadili, A. A.; Moise, C. J. Chem. Soc., Chem. Commun. 1984, 749. (7) Moloy, K. G.; Marks, T. J. Inorg. Chim. Acta 1985, 110, 127. (8) 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. (9) 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. r 2010 American Chemical Society
has been demonstrated by Eisen and co-workers in a series of papers on catalytic alkyne oligomerization2 and isocyanidealkyne coupling.10 (C5Me5)2U(CtCPh)2, 1, generated in situ from (C5Me5)2UMe2 and HCtCPh, is often used in these catalyses. Insertion into U-C(alkynyl) bonds has also been reported with the amide complexes [(Me3Si)2N]3U(CtCR) [R = (CH2)xCH3 (x = 2-5) and C(CH3)3], which react with Me2CdO to form [(Me3Si)2N]3U[OC(Me2)Ct CR].11 Although alkynyl actinides are reactive in insertion chemistry, crystallographic data on insertion products are limited. Recently, structural data were reported on the insertion of the carbodiimide iPrNdCdNiPr, into a uranium-alkynyl bond of 1 to form (C5Me5)2[iPrNC(CtCPh)NiPr-κ2N,N0 ]U(CtCPh), eq 1.12 Since few results were in the literature to
allow detailed comparisons with this result, a study of the insertion chemistry of 1 was initiated to obtain such data. We report here double insertion reactivity for CO2, PhNCO, and Me3CCtN and single insertion for Me3CNtC. Crystallographic data are reported on the products of the last three insertions as well as the structure of (C5Me5)2U(CtCPh)2 for comparison. Since insertion into metal-carbon bonds is an important reaction throughout the periodic table, considerable literature exists to compare the CO2, PhNCO, Me3CCtN, and Me3CNtC insertions reported here. Insertions with early transition metal and lanthanide metallocenes are most (10) Wang, J. Q.; Eisen, M. S. J. Organomet. Chem. 2003, 670, 97. (11) Baudry, D.; Dormond, A.; Hafid, A. J. Organomet. Chem. 1995, 494, C22. (12) Evans, W. J.; Walensky, J. R.; Ziller, J. W.; Rheingold, A. L. Organometallics 2009, 28, 3350. Published on Web 01/22/2010
pubs.acs.org/Organometallics
946
Organometallics, Vol. 29, No. 4, 2010
pertinent. The lanthanide insertion literature has recently been reviewed,13 and the following examples give leading references to early transition metal insertion reactions.14 CO2 insertion into metal-carbon bonds is well established and produces carboxylates.15 A recent PhNCO insertion example involves the ansa metallocene complex [(nBu)(C5Me4)(C5H4)]ZrMe2, which reacts to produce the monoinsertion product [(nBu)(C5Me4)(C5H4)][PhNC(Me)O-κ2N,O]ZrMe,16 just as (C5H5)2ZrMe2 reacts to form (C5H5)2[PhNC(Me)O-κ2N,O]ZrMe.17 Nitrile insertion produces ketimide complexes as demonstrated by reactions of the allyl complexes (C5H5)2Ti(C3H5) and (C5H5)2Ti(C4H7) with MeCtN to form (C5H5)2Ti[NdC(Me)C(R)C=CH2], R=H or Me.18 Examples of isocyanide insertions include the reactions of [(C5H5)2TaMe2]þ with RNtC to form [(C5H5)2(RNdCMe-η2C,N)TaMe]þ, R = Me3C, C6H11, CH2Ph.19 Additionally, the reaction of (C5H5)2ZrRR0 with pTolNtC yields a single insertion, (C5H5)2ZrR0 [(pTol)NdCR], R = CH2CMe3, CH2SiMe3, CH(SiMe3)2; R0 = Cl, CH2SiMe3, CH2CMe3, Me.20 Insertion chemistry with early transition metal metallocenes alkynides is less common. An example is the reaction of (C5Me5)2Ti(CtCCMe3) with CO2 to make (C5Me5)2Ti(O2CCtCCMe3).21 Interestingly, the “ate” salt (C5Me5)2Ti(CtCCPh)2Li(THF)2 reacts with CO2 to make (C5Me5)2Ti(CtCCPh)2,21 and the titanocene alkynide CO2 insertion appears to be quite sensitive to the specific substituents on the alkynide and the ring.21,22
Experimental Section The syntheses and manipulations described below 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. Benzene-d6 (Cambridge Isotope Laboratories) was dried over NaK alloy and benzophenone, degassed by three freeze-pump-thaw cycles, and vacuum transferred before use. Phenyl isocyanate, tert-butyl nitrile, and tert-butyl isocyanide were obtained from Aldrich and distilled prior to use. CO2 (Airgas) was used as received. NMR experiments were conducted with Bruker 400 or 500 MHz spectrometers. Infrared spectra were recorded as KBr pellets (13) (a) Zhou, X.; Zhu, M. J. Organomet. Chem. 2002, 647, 28. (b) Liu, R.; Zhou, X. J. Organomet. Chem. 2007, 692, 4424. (14) (a) Lappert, M. F., Vol. Ed. In Comprehensive Organometallic Chemistry; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: New York, 1995; Vol. 4. (b) Anti~nolo, A.; Garcia-Yuste, S.; Otero, A.; Villase~ nor, E. J. Organomet. Chem. 2007, 692, 4436. (15) (a) Darensbourg, D. J.; Kudaroski, R. A. In Advances in Organometallic Chemistry; Stone, F. G. A., Ed.; Academic Press, Inc.: New York, 1983; Vol. 22, p 136. (b) Correa, A.; Martin, R. Angew. Chem., Int. Ed. 2009, 48, 6201. (16) Antinolo, A.; Fernandez-Galan, R.; Molina, N.; Otero, A.; Rivilla, I.; Rodriguez, A. M. J. Organomet. Chem. 2009, 694, 1959. (17) Gambarotta, S.; Strologo, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1985, 24, 654. (18) (a) Ferreira, M. J.; Martins, A. M. Coord. Chem. Rev. 2006, 250, 118. (b) Klei, E.; Teuben, J. H.; De Liefde Meijer, H. J.; Kwak, E. J. J. Organomet. Chem. 1982, 224, 327. (19) Cook, K. S.; Piers, W. E.; Patrick, B. O.; McDonald, R. Can. J. Chem. 2003, 81, 1137. (20) Lappert, M. F.; Luong-Thi, N. T.; Milne, C. R. C. J. Organomet. Chem. 1979, 174, C35. (21) Kirchbauer, F. G.; Pellny, P.-M.; Sun, H.; Burlakov, V. V.; Ardnt, P.; Baumann, W.; Spannenberg, A.; Rosenthal, U. Organometallics 2001, 20, 5289. (22) Burlakov, V. V.; Yanovsky, A. I.; Struchkov, Yu. T.; Rosenthal, U.; Spannenberg, A.; Kempe, R.; Ellert, O. G.; Shur, V. B. J. Organomet. Chem. 1997, 542, 105.
Evans et al. on a Perkin-Elmer Spectrum One FT-IR spectrometer. Elemental analyses were performed with a Perkin-Elmer 2400 CHN elemental analyzer. (C5Me5)2U(CtCPh)2, 1. (C5Me5)2U(CtCPh)2 was prepared as previously described.23 Crystals suitable for X-ray crystallography were grown from a saturated solution of methylcyclohexane at -35 °C. 1H NMR (C6D6, 298 K): δ 10.3 (s, 30H, C5Me5), 3.6 (t, J = 7 Hz, 2H, C6H5), -1.9 (t, J = 7 Hz, 4H, C6H5), -10.9 (d, J=7 Hz, 4H, C6H5) (ref 23 gives the 1H NMR spectrum in d8-THF). (C5Me5)2U(O2CCtCPh)2, 2. In a glovebox, 1 (285 mg, 0.402 mmol) was dissolved in toluene (8 mL) and placed in a FisherPorter vessel. On a pressure manifold, CO2 was added at a pressure of 80 psi to the vessel and allowed to react for 24 h, during which the color turned from red-orange to orange. The apparatus was brought back into the glovebox, where the solvent was removed under vacuum to yield an orange powder (290 mg, 91%). 1H NMR (C6D6, 298 K): δ 7.6 (s, 30H, C5Me5), 7.5 (d, J = 6 Hz, 4H, C6H5), 7.3 (t, J = 6 Hz, 2H, C6H5), 6.6 (t, J = 6 Hz, 4H, C6H5). IR: 2902s, 2214s, 1544 m, 1491s, 1408s, 1226m, 1026m, 944s, 781s, 771w, 757s, 689s cm-1. Anal. Calcd for C38H40O4U: C, 57.29; H, 5.06. Found: C, 56.61; H, 5.26. (C5Me5)2U[PhNC(CtCPh)O-K2N,O]2, 3. PhNCO (40 μL, 0.37 mmol) was added to a stirred solution of 1 (122 mg, 0.172 mmol) in diethyl ether (8 mL). The color immediately turned from red-orange to orange. After 10 min, the solvent was removed to yield 3 as an orange powder (155 mg, 95%). Crystals suitable for X-ray diffraction were grown from a saturated diethyl ether solution at -35 °C. 1H NMR (C6D6, 298 K): δ 11.4 (d, J=7.5 Hz, 4H, C6H5), 8.7 (t, J=7 Hz, 2H, C6H5), 8.0 (t, J=7.5 Hz, 4H, C6H5), 4.3 (t, J=7 Hz, 4H, C6H5), 4.1 (d, J= 7.5 Hz, 2H, C6H5), 1.9 (s, 30H, C5Me5), -4.8 (d, J = 7 Hz, 4H, C6H5). IR: 2901s, 2205s, 1778w, 1712w, 1575s, 1504s, 1443m, 1403s, 1307s, 1187s, 1026w, 952m, 757s, 691s cm-1. Anal. Calcd for C50H50N2O2U: C, 63.28; H, 5.31; N, 2.95. Found: C, 63.93; H, 5.25; N, 3.05. (C5Me5)2U[NdC(CMe3)(CtCPh)]2, 4. Me3CCtN (100 μL, 0.884 mmol) was added to a stirred solution of 1 (250 mg, 0.352 mmol) in diethyl ether (10 mL). The solution turned from redorange to brown. After 1 h, the solvent was removed under vacuum to yield a brown powder (295 mg, 96%). Crystals suitable for X-ray diffraction were obtained from a saturated diethyl ether solution at room temperature. 1H NMR (C6D6, 298 K): δ 13.8 (t, J = 7 Hz, 4H, C6H5), 10.1 (d, J = 7 Hz, 4H, C6H5), 7.6 (t, J=7 Hz, 2H, C6H5), -2.1 (s, 30H, C5Me5), -14.2 (s, 18H, CMe3). IR: 2964s, 2897s, 2861s, 2191s, 1579s, 1488s, 1440m, 1383w, 1272w, 1216w, 1057s, 1009m, 858w, 755s, 689s cm-1. Anal. Calcd for C46H58N2U: C, 63.00; H, 6.67; N, 3.19. Found: C, 62.88; H, 6.27; N, 2.79. (C5Me5)2[(PhCtC)CdN(CMe3)-η2C,N]U(CtCPh), 5. Me3CNtC (100 μL, 0.884 mmol) was added to a stirred solution of 1 (300 mg, 0.423 mmol) in diethyl ether (10 mL). The solution immediately turned from red-orange to dark red-brown. After 12 h, the solvent was removed to yield 5 as a brown-red tacky solid. Upon crystallization from a saturated diethyl ether solution at -35 °C, red crystals suitable for X-ray diffraction were obtained (325 mg, 97%). 1H NMR (C6D6, 298 K): δ 12.6 (d, J= 6.8 Hz, 2H, C6H5), 12.1 (d, J = 6.8 Hz, 2H, C6H5), 10.6 (t, J = 7.6 Hz, 1H, C6H5), 9.1 (t, 2H, J=7.6 Hz, C6H5), 8.6 (t, J=6.8 Hz, 1H, C6H5), 8.3 (t, J = 7.6 Hz, 2H, C6H5), 0.9 (s, 30H, C5Me5), -8.9 (s, 9H, CMe3). IR: 2973s, 2900s, 2154s, 2059s, 1594m, 1535m, 1484s, 1441s, 1359m, 1199s, 1068m, 1025m, 980w, 778m, 757s, 690s cm-1. Anal. Calcd for C41H49NU: C, 62.03; H, 6.22; N, 1.76. Found: C, 62.15; H, 6.03; N, 1.88. X-ray Data Collection, Structure Solution, and Refinement for 1 and 3-5. This is available in the Supporting Information.
(23) Straub, T.; Frank, W.; Reiss, G. J.; Eisen, M. S. J. Chem. Soc., Dalton Trans. 1996, 2541.
Article
Organometallics, Vol. 29, No. 4, 2010
947
Table 1. X-ray Data Collection Parameters for Complexes 1 and 3-5 1
3
4
5
empirical formula
C36H40U 3 1 /2 C6H6
C46H58N2U 3 C50H50N2O2U 3 C41H49NU 1 C4H10O /2 C4H10O
fw temp (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
749.76 148(2) monoclinic P21/c 8.8439(8) 10.7190(10) 34.967(3) 90 94.5480(10) 90 3304.4(5) 4 1.507 4.936 0.0342 0.0789
914.30 148(2) triclinic P1 10.2805(11) 14.6471(15) 15.5586(16) 76.1631(13) 87.8792(14) 73.2747(13) 2177.3(4) 2 1.394 3.761 0.0419 0.1134
630.70 153(2) monoclinic P21/n 10.7666(8) 10.3076(8) 32.170(3) 90 96.4510(10) 90 3547.5(5) 4 1.486 4.603 0.0285 0.0594
P P Fo|-|Fc / |Fo|; wR2 = [ [w(Fo2 - Fc2)2]/ )
R1 = P Definitions: [w(Fo2)2]]1/2.
P
)
a
1023.07 153(2) triclinic P1 12.060(2) 12.865(2) 15.663(3) 76.5252(19) 76.9840(19) 81.9283(18) 2292.4(7) 2 1.482 3.585 0.0254 0.0675
Table 2. Selected Bond Distances (A˚) and Angles (deg) for 1, 3, 4, and 5 1 U(1)-(C5Me5 ring centroid) U(1)-N(1) U(1)-N(2) U(1)-C(21) U(1)-C(29) U(1)-C(36) U(1)-O(1) U(1)-O(2) (C5Me5 ring centroid)U-(C5Me5 ring centroid) (C5Me5 ring centroid)U(1)-N(1) (C5Me5 ring centroid)U(1)-N(2) C(29)-U(1)-N(1) N(1)-U(1)-N(2) O(1)-U(1)-N(1) O(1)-U(1)-O(2)
3
4
2.421, 2.458 2.495, 2.513 2.471 2.194(4) 2.195(4) 2.398(5) 2.398(5)
141.7
140.3
2.544(2) 2.535(2) 2.881(3) 2.879(3) 2.406(2) 2.424(2) 137.0
100.4, 100.7 110.2 101.9, 99.9
5 2.465, 2.470 2.386(3) 2.436(4) 2.380(4)
135.5
Figure 1. Thermal ellipsoid plot of (C5Me5)2U(CtCPh)2, 1, shown at the 50% probability level. Hydrogen atoms and solvent molecule have been omitted for clarity.
is larger than the 94.5(3)° value in the dimethyl complex.8 Both U-C(CCPh) bond lengths in 1 were measured to be 2.398(5) A˚, which is within the 3σ range of the 2.414(7) and 2.424(7) A˚ U-C(Me) distances in (C5Me5)2UMe2.8 Other U4þ-alkynide distances in the literature include 2.33(2) A˚ in (C5H5)3U(CtCPh),24 2.36(3) A˚ in (C5H5)3U(CtCH),25 2.409(4) A˚ in (C5Me5)2U(NPh2)(CtCPh),26 and 2.433(1) A˚ in (C5Me5)2[iPrNC(CtCPh)NiPr-κ2(N,N0 )]U(CtCPh),12 6. CO2 Insertion. Since the bulky carbodiimide iPrNdCd i N Pr had been found to insert as shown in eq 1, it was anticipated that the smaller isoelectronic CO2 could also insert with the possibility that a double insertion could occur with this small substrate. Indeed, as shown in eq 2, 1 reacts with excess CO2 at 80 psi to form the double-insertion product (C5Me5)2U(O2CCtCPh)2, 2. Complex 2 was characterized by spectroscopic and analytical techniques, but single
111.5
108.3 31.56(11)
113.75(17) 53.37(8) 177.80(7)
Table 1 contains selected X-ray data collection information. Metrical parameters are in Table 2.
Results Structure of (C5Me5)2U(CtCPh)2, 1. The synthesis of (C5Me5)2U(CtCPh)2, 1, has been previously reported from the reaction of (C5Me5)2UMe2 and 2 equiv of HCtCPh,23 but to our knowledge the complex has never been characterized by X-ray crystallography. Single crystals were obtained as part of this study and the structure was determined, Figure 1. Complex 1 has metrical parameters similar to those of (C5Me5)2UMe2, Table 2. The 2.421 and 2.458 A˚ U-(C5Me5 ring centroid) bond distances and 141.7° (C5Me5 ring centroid)-U-(C5Me5 ring centroid) angle in 1 are close to the 2.456 and 2.461 A˚ distances and 140.5° angle in the dimethyl complex.8 The 100.99(16)° C(21)-U-C(29) angle
crystals were elusive. The 1H NMR spectrum of 2 showed a single resonance for the (C5Me5)- protons at 7.6 ppm, shifted from the 10.3 ppm of 1, as well as one set of three resonances for the phenyl groups at 7.5, 7.3, and 6.6 ppm, which are significantly shifted from the 3.6, -1.9, and -10.9 ppm resonances in 1. The stretching frequencies of the CtC bonds, summarized in Table 3, are also indicative of double insertion in 2. A single absorption at 2214 cm-1 is found in the 2190-2260 cm-1 range, which is typical for disubstituted alkynes not bound to a metal center,27 as exemplified by complexes 2-6. In comparison, the (CtCPh)- ligands bound to uranium in the bis(alkynide) 1 exhibit a stretch at 2056 cm-1, as is typical for uranium alkynyl (24) Atwood, J. L.; Hains, C. F., Jr.; Tsutsui, M.; Gebala, A. E. J. Chem. Soc., Chem. Commun. 1973, 452. (25) Atwood, J. L.; Tsutsui, M.; Ely, N.; Gebala, A. E. J. Coord. Chem. 1976, 5, 209. (26) Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. Organometallics 2008, 27, 3335. (27) Bellamy, L. J. The Infrared Spectra of Complex Molecules; John Wiley: New York, 1964.
948
Organometallics, Vol. 29, No. 4, 2010
Evans et al.
Table 3. CtC Stretching Frequencies and 1H NMR Shifts (in C6D6) for the Phenyl Resonances in 1-6 ν(CtC) (cm-1) 1 2 3 4 5 6
2056 2214 2191 2205 2154, 2059 2207, 2062
1 H NMR phenyl resonances (ppm)
3.6, -1.9, -10.9 7.5, 7.3, 6.6 11.4, 8.7, 8.0, 4.3, 4.1, -4.8 13.8, 10.1, 7.6 12.6, 12.1, 10.6, 9.1, 8.6, 8.3 20.0, 12.8, 11.2, 6.3, 6.1, -13.0
complexes, e.g., 2059 cm-1 in (C5Me5)2U(NPh2)(CtCC6H4CH3-4)28 and 2062 cm-1 in (C5Me5)2U(NPh2)(CtCPh).26,28 The monoinsertion product, 6,12 exhibits absorptions at 2062 and 2207 cm-1, and a similar pattern would be expected if only a single CO2 insertion had occurred in eq 2. Absorptions at 1544 and 1408 cm-1 are in the range characteristic of symmetric and asymmetric stretches for carboxylate ligands.29 Phenylisocyanate Insertion. To obtain structural data on insertion substrates isoelectronic with CO2, the reaction of 1 with PhNCO was examined. Phenylisocyanate insertion has previously been observed in f element chemistry with Ln-butyl,30 Ln-naphthyl,30 Ln-pentamethylcyclopentadienyl,31 and UdCHPMePhR32 bonds (Ln = lanthanide). As shown in eq 3, 2 equiv of PhNCO reacts with 1 to form (C5Me5)2U[PhNC(CtCPh)O-κ2N,O]2, 3. Spectroscopic data were consistent with this assignment. For example, the IR
Figure 2. Thermal ellipsoid plot of (C5Me5)2U[PhNC(Ct CPh)O-κ2N,O]2, 3, shown at the 50% probability level. Hydrogen atoms and solvent molecule have been omitted for clarity.
Figure 3. Thermal ellipsoid plot of (C5Me5)2U[NdC(CMe3)(CtCPh)]2, 4, shown at the 30% probability level. Hydrogen atoms and solvent molecule have been omitted for clarity.
spectrum of 3 contains a single CtC absorption (Table 3) in the region of an alkynyl unit not coordinated to uranium. IR stretching frequencies at 1712 and 1575 cm-1 are similar to the 1705 and 1660 cm-1 in [(nBu)(C5Me4)(C5H4)][PhNC(Me)O-κ2N,O]ZrMe, which have been assigned to the C-O and C-N stretches, respectively.16 The identity of 3 was confirmed by X-ray crystallography, Figure 2. The metrical parameters of the metallocene fragment of 3 (Table 2) are similar to those in previous examples33 with typical U-(C5Me5 ring centroid) bond distances of 2.495 and 2.513 A˚ and a (C5Me5 ring centroid)-U-(C5Me5 ring centroid) angle of 137.0°. However, the insertion of two large PhNCO substrates into the U-CtCPh bonds spreads out the ligands in the metallocene wedge to such an extent that the O(1)-U-O(2) bond angle is nearly linear: 177.80(7)°. Complex 3 contains a metallocene and two κ2-type ligands. To our knowledge, crystallographic data on only one other (28) Thomson, R. K.; Graves, C. R.; Scott, B. L.; Kiplinger, J. L. Eur. J. Inorg. Chem. 2009, 1451. (29) Gibson, D. H. Chem. Rev. 1996, 96, 2063. (30) Zhou, X.; Zhang, L.; Zhu, M.; Cai, R.; Weng, L. Organometallics 2001, 20, 5700. (31) Evans, W. J.; Forrestal, K. J.; Ziller, J. W. J. Am. Chem. Soc. 1998, 120, 9273. (32) Cramer, R. E.; Jeong, J. H.; Gilje, J. W. Organometallics 1987, 6, 2010. (33) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Inorg. Chem. 2005, 44, 7960.
f element metallocene with two κ2-ligands has been reported in the literature, (C5Me5)2U(2-mercaptobenzothiazolateκ2N,S)2, 7.34 However, the S(1)-U-S(2) angle in 7 is only 146.64(4)°. The C(36)-N(2) and C(21)-N(1) distances of 1.308(4) and 1.313(4) A˚, respectively, and C(36)-O(2) and C(21)-O(1) bond lengths of 1.280(4) and 1.287(4) A˚, respectively, in 3 are intermediate between single and double bonds35 and indicate delocalized bonding in the N-C-O unit, as is typical in the lanthanide insertion products cited above. The 2.535(2) A˚ U-N(2) and 2.544(2) A˚ U-N(1) bond distances, as well as the 2.406(2) A˚ U-O(1) and 2.424(2) A˚ U-O(2) bond lengths are quite long compared to simple bis(amide) and bis(aryloxide) uranium metallocenes. For example, the U-N bond distances in (C5Me5)2U[NH(C6H3Me2-2,6)]2 are 2.267(6) A˚23 and the U-O distances in (C5Me5)2U(OPh)2 are 2.119(11) and 2.140(13) A˚.36 The U-O bond lengths in 3 are also longer than the 2.361(9) and 2.34(1) A˚ distances in the κ2 complexes (C5Me5)2U(CH2Ph)[ONC5H4-κ2O,C]37 and (C5H5)3U[PhNC(CCHPMe2Ph)O-κ2N,O],32 respectively. However, the U-N distances in 3 are shorter than the 2.589(4) A˚ U-N bond length in 7. (34) Roger, M.; Belkhiri, L.; Arliguie, T.; Thuery, P.; Boucekkine, A.; Ephritikhine, M. Organometallics 2008, 27, 33. (35) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1. (36) Evans, W. J.; Miller, K. A.; DiPasquale, A. G.; Rheingold, A. L.; Stewart, T. J.; Bau, R. Angew. Chem., Int. Ed. 2008, 47, 5075. (37) Pool, J. A.; Scott, B. L.; Kiplinger, J. L. J. Am. Chem. Soc. 2005, 127, 1338.
Article
Organometallics, Vol. 29, No. 4, 2010
949
outside and the phenyl groups are inside. The 2.194(4) and 2.195(4) A˚ U-N bond distances in 4 are similar to those in 8, 2.184(3) A˚, and 9, 2.179(6) A˚, but the 113.75(17)° N(1)U-N(2) bond angle in 4 is larger than the 102.40(15)° and 107.2(2)° analogues in 8 and 9, respectively. The large N-U-N angle in 4 is probably a result of steric crowding between the tert-butyl groups. Isocyanide Insertion. In contrast to the CO2, PhNCO, and Me3CCtN reactions above, only 1 equiv of tert-butyl isocyanide undergoes insertion with 1 to yield (C5Me5)2[(PhCtC)CdN(CMe3)-η2C,N]U(CtCPh), 5, eq 5. Complex 5 was previously reported as an intermediate in the catalytic
Figure 4. Thermal ellipsoid plot of (C5Me5)2[(PhCtC)Cd N(CMe3)-η2C,N]U(CtCPh), 5, shown at the 50% probability level. Hydrogen atoms have been omitted for clarity.
Nitrile Insertion. Double insertion reactivity is also observed in the reaction of 1 with tert-butyl nitrile as shown in eq 4. The product, (C5Me5)2U[NdC(CMe3)(CtCPh)]2, 4, was
identified by X-ray crystallography, Figure 3. The double insertion of tert-butyl nitrile to form the diketimide was expected since Kiplinger and co-workers have shown that nitriles will do similar insertions with dialkyl and diaryl actinide metallocenes.8 The ketimide linkage has been postulated as an intermediate in hydroamination reactions with alkynes.38 The infrared spectrum of 4 contains a single absorption in the CtC triple bond region at 2191 cm-1, consistent with double insertion and movement of the alkynyl ligands away from uranium. The CdN stretch observed at 1579 cm-1 in 4 is similar to the double-bond stretches in the diketimides, such as (C5Me5)2U(NdCPh2)2,39 8, 1605 cm-1, (C5Me5)2U[NdC(Ph)(CH2Ph)]2,8 9, 1631 and 1615 cm-1, and (C5Me5)2U[NdC(Ph)(Me)]2,40 1623 and 1612 cm-1. There is disorder in the uranium position in the structure of 4, but this shows no discernible effect on the light atom positions. The metrical parameters of the metallocene part of 4 are similar to those of the diketimide complexes 8 and 9. For example, the U-(C5Me5 ring centroid) bond distances are 2.471 A˚ in 4, 2.479 A˚ in 8, and 2.483 and 2.506 A˚ in 9. Both tert-butyl substituents in 4 are in the center of the metallocene wedge, and the CtCPh substituents are oriented away from the center. In 9, the benzyl groups are both (38) (a) Haskel, A.; Straub, T.; Eisen, M. S. Organometallics 1996, 15, 3773. (b) Straub, T.; Haskel, A.; Neyroud, T. G.; Kapon, M.; Botoshansky, M.; Eisen, M. S. Organometallics 2001, 20, 5017. (39) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J. Organometallics 2002, 21, 3073. (40) Da Re, R. E.; Jantunen, K. C.; Golden, J. T.; Kiplinger, J. L.; Morris, D. E. J. Am. Chem. Soc. 2005, 127, 682.
coupling of alkynes and tert-butyl isocyanide.10 In the present study, the structure of 5 was determined by X-ray crystallography, Figure 4. Single insertion was also reported on the basis of spectroscopic information in the reaction of (C5Me5)2UMe2 with Me3CNtC,6 and it was argued that steric crowding prevented a second insertion. The dihapto iminoacyl ligand that forms in these reactions is more sterically demanding than the ketimide ligands in (C5Me5)2U(NdCR2)2, but the double insertions of CO2 and PhNCO demonstrate that there is room to accommodate two large ligands in the metallocene wedge. As expected for a monoinsertion product, two CtC alkynide stretching absorptions are observed in the infrared spectrum at 2059 and 2154 cm-1. The CdN stretch at 1594 cm-1 is consistent with the 1610 and 1608 cm-1 stretches found for the iminoacyl complexes (C5Me5)2[Me3CNdCMe-η2C,N]UX, X = Me, Cl, respectively,6 and matches the 1594 cm-1 absorption observed for (C5Me5)(C8H8)U[Me3CNdCPh-η2C,N].41 There is disorder in the structure of 5 in the position of the uranium, in one of the (C5Me5)- ligands, and in the tertbutyl group. The data reported in Table 3 refer to the major metal component (95%), and distances for the disordered ring are averages over the disorder. In any case, the metrical parameters of the metallocene unit in 5 are not unusual and do not suggest steric crowding. The 2.436(4) A˚ U-C(21) metal-alkynyl bond in 5 is almost identical to the 2.433(1) A˚ distance in 6. These are both longer than the 2.398(5) A˚ distance in 1. In the iminoacyl ligand, the 2.380(4) A˚ UC(29) and 2.386(3) A˚ U-N bond lengths are equivalent.
Discussion The sp-hybridized carbon to uranium bonds in (C5Me5)2U(CtCPh)2, 1, readily participate in insertion chemistry with a variety of substrates to form structurally characterizable products. The double-insertion reactivity of CO2, PhNCO, and Me3CCtN displayed in eqs 2-4 generates new metallocene bis(ligand) insertion products that have phenylethynyl substituents. Since the CtCPh group has substantial size, these reactions form metallocenes in which (41) Evans, W. J.; Takase, M. K.; Ziller, J. W.; Rheingold, A. L. Organometallics 2009, 28, 5802.
950
Organometallics, Vol. 29, No. 4, 2010
considerable ligand bulk expands out from the wedge area. This is particularly evident in Figures 2 and 3. The double-insertion chemistry is quite reasonable for the small substrate, CO2, which can generate chelating carboxylate ligands with small bite angles. Double insertion is also normal for nitrile substrates based on the studies of the Kiplinger group in making diketimide actinide metallocenes.8 The PhNCO double insertion in eq 3 is the most remarkable given the large size of the two [PhNC(CtCPh)O-κ2N,O]- ligands that are formed. The resulting nearly linear O-U-O linkage that results is unique for a U4þ bis(oxygen donor ligand) metallocene. Linear (OdUdO)2þ units are ubiquitous in U6þ chemistry, but they have much shorter U-O bonds, usually in the range 1.6-1.8 A˚.42 For example, in [(C5Me5)UO2(CN)3]2-,43 each U-O bond distance is 1.784(2) A˚ and the uranyl moiety has an oxygen to oxygen distance of 3.57(1) A˚. In 3, the O-U-O unit spans 4.83(1) A˚. The double insertion of PhNCO could be facilitated by π-stacking of the phenyl rings. Indeed, the two phenyl groups in 3 are oriented planar to one another with interphenyl C-C distances ranging from 3.396 to 4.158 A˚. These distances are (42) Denning, R. G. J. Phys. Chem. A 2007, 111, 4125. (43) Maynadie, J.; Berthet, J.-C.; Thuery, P.; Ephritikhine, M. Chem. Commun. 2007, 486. (44) See for example: Miyamura, K.; Mihara, A.; Fujii, T.; Gohshi, Y.; Ishii, Y. J. Am. Chem. Soc. 1995, 117, 2377.
Evans et al.
in the range found for π-stacking.44 In contrast, the tertbutyl groups of Me3CNtC are three-dimensional and may lead to steric congestion that does not allow a second insertion to occur in 5.
Conclusion Unsaturated substrates such as CO2, RNCO, RCtN, and RNtC readily insert into the U-C(sp) bonds of (C5Me5)2U(CtCPh)2 to make metallocenes of ligands that incorporate the CtCPh unit as a substituent. Both single and double insertion can occur depending on the substrate. The [(C5Me5)2U]2þ metallocene unit displays considerable flexibility in accommodating these reactions and product structures. Supporting Information Available: X-ray diffraction details (CIF) and X-ray data collection, structure, solution, and refinement of compounds 1 and 3-5. This material is available free of charge via the Internet at http://pubs.acs.org.
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 and the reviewers for their helpful suggestions.
