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Organometallics 2010, 29, 6608–6611 DOI: 10.1021/om100917w
Facile Insertion of N2O into Metal-Carbon Bonds of Metallocene Allyl Complexes to Form (RN2O)- Ligands Selvan Demir,†,‡ Elizabeth Montalvo,† Joseph W. Ziller,† Gerd Meyer,‡ and William J. Evans*,† †
Department of Chemistry, University of California, Irvine, California 92697-2025, United States, and ‡ Institut f€ ur Anorganische Chemie, Universit€ at zu K€ oln, Greinstrasse 6, D-50939 K€ oln, Germany Received September 23, 2010
Summary: Attempts to generate a scandium metallocene oxide using N2O have revealed that N2O undergoes facile insertion into metal-carbon bonds of allyl metallocene complexes to form (RN2O)- ligands where R = C3H5. This has been demonstrated in reactions with the tetramethylcyclopentadienyl allyl complexes (C5Me4H)2M(η3-C3H5) (M = Sc, Y) and the pentamethylcyclopentadienyl allyl compounds (C5Me5)2M(η3-C3H5) (M = Y, Sm, La), which generate the insertion products [(C5Me4H)2M( μ-η1:η2-ONdNC3H5)]2 (M = Sc, 1; Y, 2) and [(C5Me5)2M( μ-η1:η2-ONdNC3H5)]2 (M = Y, 3; Sm, 4; La, 5), respectively.
Introduction One of the characteristics of organometallic complexes of electropositive metals is that they can readily react with oxygen-containing compounds to make oxide derivatives. In many cases, the source of the oxygen is unknown, and it is difficult to isolate and characterize molecular products from these reactions since intractable or insoluble products often form. However, for the metallocenes of yttrium and the lanthanides, oxide complexes of formula [(C5Me5)2Ln]2( μ-O) are often formed that are isolable and fully characterizable.1-7 Crystallographic data have been obtainable on examples with Ln = La,3 Ce,4 Nd,5 Sm,1 Y,2 and Lu5 as well as several analogues of formula [(C5R5)2LnL]2( μ-O), where L = a Lewis base.6,7 When a new metallocene system of metals of this type is investigated, it is often useful to generate the [(C5R5)2Ln]2( μ-O) oxide complex to facilitate identification by NMR spectroscopy in case it is formed as a byproduct. In the case of [(C5Me5)2Sm]2( μ-O), the oxide complex was deliberately made with reagents such as pyNO, epoxides, NO, and N2O.1 Recent studies of tetramethylcyclopentadienyl complexes of *To whom correspondence should be addressed. E-mail: wevans@ uci.edu. (1) Evans, W. J.; Grate, J. W.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem. Soc. 1985, 107, 405. (2) Ringelberg, S. N.; Meetsma, A.; Troyanov, S. I.; Hessen, B.; Teuben, J. H. Organometallics 2002, 21, 1759. (3) Evans, W. J.; Davis, B. L.; Nyce, G. W.; Perotti, J. M.; Ziller, J. W. J. Organomet. Chem. 2003, 677, 89. (4) Evans, W. J.; Rego, D. B.; Ziller, J. W. Inorg. Chem. 2006, 45, 10790. (5) Deposited in the Cambridge Crystallographic Data Base CCDC 623043. (6) Evans, W. J.; Drummond, D. K.; Hughes, L. A.; Zhang, H.; Atwood, J. L. Polyhedron 1988, 7, 1693. (7) Deelman, B. J.; Booij, M.; Meetsma, A.; Teuben, J. H.; Kooijman, H.; Spek, A. L. Organometallics 1995, 14, 2306. pubs.acs.org/Organometallics
Published on Web 11/03/2010
scandium generated a byproduct identified by NMR spectroscopy that was thought to be the analogous oxide in this system, namely, [(C5Me4H)2Sc]2( μ-O).8 In efforts to make this complex independently, the reaction of the allyl complex (C5Me4H)2Sc(η3-C3H5)8 with N2O was investigated. However, instead of forming the oxide, N2O inserted into the Sc-C(allyl) bond. This paper reports the details of this reaction as well as its extension to allyl yttrium and lanthanide metallocenes. N2O has been extensively studied since it is a thermodynamically powerful oxidant, a potent greenhouse gas, and a component in the global nitrogen cycle with its own metalloenzyme, nitrous oxide reductase, that converts it to dinitrogen and water.9-11 In reactions with metal complexes, N2O often functions as an oxo transfer reagent, either providing metal oxides or inserting oxygen into metal-ligand bonds.12-18 Hence, the N2O insertion reported here is not common. To our knowledge only two isolated examples of N2O insertion with organometallic complexes of electropositive metals have been reported. In one case, N2O reacted with (C5Me5)2M(C2Ph2) (M = Ti, Zr) to make (C5Me5)2M[N(O)NCPhdCPh], in which the [N(O)NCPhdCPh]- ligand surprisingly binds to Ti and Zr only with the nitrogen atoms.19 In the other example, the samarium complex (C5Me5)2Sm(CH2C6H5)(THF)21 reacted with N2O to generate the dimer shown in eq 1.20
(8) Demir, S.; Lorenz, S. E.; Fang, M.; Furche, F.; Meyer, G.; Ziller, J. W.; Evans, W. J. J. Am. Chem. Soc. 2010, 132, 11151. (9) Tolman, W. B. Angew. Chem., Int. Ed. 2010, 49, 2. (10) Trogler, W. C. Coord. Chem. Rev. 1999, 187, 303. (11) Leont’ev, A. V.; Fomicheva, O. A.; Proskurnina, M. V.; Zefirov, N. S. Russ. Chem. Rev. 2001, 37, 91. (12) Bottomley, F.; Paez, D. E.; White, P. S. J. Am. Chem. Soc. 1982, 104, 5651. (13) Hall, K. A.; Mayer, J. M. J. Am. Chem. Soc. 1992, 114, 10402. (14) Smith, M. R., III; Matsunaga, P. T.; Andersen, R. A. J. Am. Chem. Soc. 1993, 115, 7049. (15) Howard, W. A.; Parkin, G. J. Am. Chem. Soc. 1994, 116, 606. (16) Baranger, A. M.; Hanna, T. A.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 10041. (17) List, A. K.; Koo, K.; Rheingold, A. L.; Hillhouse, G. L. Inorg. Chim. Acta 1998, 270, 399. r 2010 American Chemical Society
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Experimental Section The manipulations described below were performed under argon with rigorous exclusion of air and water using Schlenk, vacuum line, and glovebox techniques. Solvents were saturated with UHP grade argon (Airgas) and dried by passage through Glasscontour27 drying columns before use. NMR solvents (Cambridge Isotope Laboratories) were dried over sodium-potassium alloy, degassed, and vacuum-transferred before use. (C5Me5)2M(η3-C3H5) (M = Sm,22 La, Y23) and (C5Me4H)2M(η3-C3H5) (M=Sc,8 Y24) complexes were prepared according to literature methods. Nitrous oxide (99% SigmaAldrich) was used as received. 1H NMR and 13C NMR spectra were recorded on a Bruker DRX500 spectrometer at 25 °C. Due to the paramagnetism of samarium, only resonances that could be unambiguously identified are reported. Infrared spectra were recorded as KBr pellets on a Varian 1000 FTIR spectrophotometer at 25 °C. Elemental analyses were performed on a PerkinElmer 2400 Series II CHNS elemental analyzer. [(C5Me4H)2Sc( μ-η1:η2-ONdNC3H5)]2, 1. A sealable Schlenk flask outfitted with a Teflon stopcock was charged with (C5Me4H)2Sc(η3-C3H5) (143 mg, 0.435 mmol) in toluene (10 mL) and a stir bar. The flask was attached to a high vacuum line, and the reaction mixture was frozen in liquid nitrogen and placed under vacuum (10-5 Torr) for 30 min. One equivalent of N2O was measured into a second, similar Schlenk tube of known volume using a manometer and was subsequently condensed into the first tube. The reaction vessel was sealed and rapidly warmed to room temperature, which caused a color change from bright yellow to yellow. Once at room temperature, the reaction flask was returned to the glovebox and the mixture was stirred at room temperature for 4 h. Evaporation of solvent yielded a yellow crystalline material, which was washed with hexane until the supernatant was colorless. Complex 1 remained as a yellow crystalline powder (126 mg, 78%). Colorless crystals of 1 suitable for X-ray diffraction were grown over the course of three days from toluene at -35 °C. 1H NMR (C6D6): δ 6.31 (m, 2H, CH2CHCH2), 5.95 (s, 4H, C5Me4H), 5.44 (d, 2H, 3Jtrans = 17.0 Hz, CH2CHdCH2 trans CH2), 5.18 (d, 2H, 3Jcis=10.3 Hz, CH2CHdCH2 cis CH2), 4.51 (d, 4H, 3JH-H = 5.8 Hz, CH2CHdCH2), 1.89 (s, 24H, C5Me4H), 1.69 (s, 24H, C5Me4H). 13 C NMR (C6D6): δ 134.8 (CH2CHCH2), 123.4 (C5Me4H), 119.3 (C5Me4H), 112.9 (C5Me4H), 117.7 (CH2CHdCH2), 56.7 (CH2CHdCH2), 13.3 (C5Me4H), 10.9 (C5Me4H). IR: 3083m, 3054m, 3021m, 2969s, 2943s, 2907s, 2860s, 2722m, 2064w, 1941w, 1856w, 1647m, 1603m, 1510m, 1494s, 1451s, 1403s, 1381s, 1331m, 1305m, 1287m, 1184s, 1128s, 1082m, 1021m, 990s, 927s, 823s, 806s, 777s, 730s, 694s, 615m cm-1. Anal. Calcd for C46H74N4O2Sc2: C, 67.72; H, 8.39; N, 7.52. Found: C, 67.68; H, 8.85; N, 7.41. The 1H NMR spectrum of 1 is shown in the Supporting Information. [(C5Me4H)2Y( μ-η1:η2-ONdNC3H5)]2, 2. As described for 1, 2 was obtained as a colorless crystalline solid (171 mg, 76%) from N2O (1 equiv) and (C5Me4H)2Y(η3-C3H5) (200 mg, 0.537 mmol) in toluene (10 mL). Colorless crystals of 2 suitable for X-ray diffraction were grown over the course of three days from (18) Yu, H.; Jia, G.; Lin, Z. Organometallics 2009, 28, 1158, and references therein. (19) Vaughan, G. A.; Sofield, C. D.; Hillhouse, G. L.; Rheingold, A. L. J. Am. Chem. Soc. 1989, 111, 5491. (20) Labahn, T.; Mandel, A.; Magull, J. Z. Anorg. Allg. Chem. 1999, 625, 1273. (21) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. Organometallics 1991, 10, 134. (22) Evans, W. J.; Seibel, C. A.; Ziller, J. W. J. Am. Chem. Soc. 1998, 120, 6745. (23) Evans, W. J.; Kozimor, S. A.; Brady, J. C.; Davis, B. L.; Nyce, G. W.; Seibel, C. A.; Ziller, J. W.; Doedens, R. J. Organometallics 2005, 24, 2269. (24) Lorenz, S. E.; Schmiege, B. M.; Lee, D. S.; Ziller, J. W.; Evans, W. J. Inorg. Chem. 2010, 49, 6655.
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toluene at -35 °C. 1H NMR (C6D6): δ 6.17 (m, 2H, CH2CHdCH2), 5.83 (s, 4H, C5Me4H), 5.15 (m, 4H, CH2CHdCH2), 4.23 (d, 4H, 3JH-H = 7.0 Hz, CH2CHdCH2), 2.06 (s, 12H, C5Me4H), 2.00 (s, 12H, C5Me4H), 1.96 (s, 12H, C5Me4H), 1.93 (s, 12H, C5Me4H). 13C NMR (C6D6): δ 133.1 (CH2CHdCH2), 120.2 (CH2CHdCH2), 120.0 (C5Me4H), 119.5 (C5Me4H), 117.9 (C5Me4H), 117.3 (C5Me4H), 110.6 (C5Me4H), 53.5 (CH2CHdCH2), 13.5 (C5Me4H), 13.4 (C5Me4H), 12.4 (C5Me4H), 12.2 (C5Me4H). IR: 3079m, 3018m, 2966s, 2911s, 2861s, 2725m, 2060w, 1875w, 1646m, 1433s, 1403s, 1382s, 1326m, 1310m, 1288w, 1216s, 1196s, 1134s, 1113m, 1023m, 1013m, 990s, 967m, 936s, 907w, 796s, 785s, 764s, 697w, 620m cm-1. Anal. Calcd for C42H62N4O2Y2: C, 60.57; H, 7.50; N, 6.73. Found: C, 60.62; H, 7.46; N, 6.68. [(C5Me5)2Y( μ-η1:η2-ONdNC3H5)]2, 3. As described for 1, 3 was obtained as a colorless crystalline solid (106 mg, 87%) from N2O (1 equiv) and (C5Me5)2Y(η3-C3H5) (110 mg, 0.275 mmol) in toluene (10 mL). Colorless crystals of 3 suitable for X-ray diffraction were grown over the course of 3 days from toluene at -35 °C. 1H NMR (C6D6): δ 6.22 (m, 2H, CH2CHdCH2), 5.19 (m, 4H, CH2CHdCH2), 4.32 (d, 4H, 3JH-H = 6.8 Hz, CH2CHdCH2), 2.01 (s, 60H, C5Me5). 13C NMR (C6D6): δ 133.2 (CH2CHdCH2), 118.1 (C5Me5), 119.8 (CH2CHdCH2), 53.8 (CH2CHdCH2), 12.8 (C5Me5). IR: 3079m, 2966s, 2905s, 2860s, 2723m, 2063m, 1848w, 1646m, 1496m, 1428s, 1402s, 1380s, 1306m, 1286m, 1211m, 1177s, 1129s, 1061m, 1022m, 989s, 963m, 922s, 795s, 760w, 729w, 672m, 621m cm-1. Anal. Calcd for C46H70N4O2Y2: C, 62.16; H, 7.94; N, 6.30. Found: C, 62.31; H, 7.90; N, 6.14. [(C5Me5)2Sm( μ-η1:η2-ONdNC3H5)]2, 4. As described for 1, 4 was obtained as a yellow-orange crystalline solid (141 mg, 82%) from N2O (1 equiv) and (C5Me5)2Sm(η3-C3H5) (157 mg, 0.340 mmol) in toluene (10 mL). 1H NMR (C6D6): δ 3.51 (d, 2H, 3 Jcis = 10.2 Hz, CH2CHdCH2 cis), 2.90 (d, 2H, 3Jtrans = 17.0 Hz, CH2CHdCH2 trans), 1.35 (s, 60H, C5Me5) -0.29 (d, 4H, 3 JH-H = 6.7 Hz, CH2CHdCH2). 13C NMR (C6D6): δ 128.8 (CH2CHdCH2), 117.1 (CH2CHdCH2), 114.0 (C5Me5), 46.1 (CH2CHdCH2), 18.6 (C5Me5). Anal. Calcd for C50H82N4O2Sm2: C, 54.61; H, 6.91; N, 5.54. Found: C, 53.65; H, 7.11; N, 4.85. Although the analytical data give a C:H:N ratio of 12.9:20.4:1, close to the 12.5:20.5:1 ratio expected, the analysis was not as good as that for isomorphous 5. Crystals of 4 were surprisingly less stable than those of 1-3 and 5. The 1H NMR spectrum of 4 is shown in the Supporting Information. [(C5Me5)2La( μ-η1:η2-ONdNC3H5)]2, 5. As described for 1, 5 was obtained as a colorless crystalline solid (121 mg, 73%) from N2O (1 equiv) and (C5Me5)2La(η3-C3H5) (150 mg, 0.333 mmol) in toluene (10 mL). 1H NMR (C6D6): δ 6.19 (m, 2H, CH2CHdCH2), 5.20 (m, 4H, CH2CHdCH2), 4.26 (d, 4H, 3 JH-H = 6.9 Hz, CH2CHdCH2), 2.04 (s, 60H, C5Me5). 13C NMR (C6D6) δ 133.2 (CH2CHdCH2), 120.1 (C5Me5), 119.8 (CH2CHdCH2), 53.4 (CH2CHdCH2), 11.9 (C5Me5). IR: 3078m, 2963s, 2909s, 2859s, 2725m, 2062w, 1875w, 1646m, 1496m, 1439s, 1422s, 1398s, 1380s, 1304m, 1286m, 1207m, 1173s, 1129s, 1061m, 1022m, 1003m, 990m, 961m, 935m, 908m, 803w, 788s, 729w, 694w, 619w cm-1. Anal. Calcd for C46H70N4O2La2: C, 55.87; H, 7.13; N, 5.67. Found: C, 55.85; H, 7.79; N, 5.26. The 1H NMR spectrum of 5 is shown in the Supporting Information. X-ray Data Collection, Structure Determination, and Refinement. Crystallographic information on complexes 1-5 is summarized in the Supporting Information and Table 1.
Results and Discussion Recent efforts to make the first dinitrogen complex of scandium focused on the reduction of [(C5Me4H)2Sc] [( μ-Ph)BPh3] with KC8 under nitrogen. This generated a
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Demir et al.
Table 1. X-ray Data Collection Parameters for [(C5Me4H)2Sc( μ-η1:η2-ONdNC3H5)]2, 1, [(C5Me4H)2Y( μ-η1:η2-ONdNC3H5)]2, 2, [(C5Me5)2Y( μ-η1:η2-ONdNC3H5)], 3, [(C5Me5)2Sm( μ-η1:η2-ONdNC3H5)], 4, and [(C5Me5)2La( μ-η1:η2-ONdNC3H5)]2, 5 1
2
4
5
C46H70N4O2Y2 3 2(C7H8) 183(2) monoclinic P21/n 15.8443(8) 13.9604(7) 25.2595(12) 90 91.3400(6) 90 5585.7(5) 4 1.276 2.112 0.0361 0.0961
C46H70N4O2Sm2 3 2(C7H8) 173(2) monoclinic P21/n 14.8358(6) 14.0396(5) 27.3264(10) 90 93.5110(10) 90 5681.1(4) 4 1.398 2.090 0.0308 0.0847
C46H70La2N4O2 3 2(C7H8) 143(2) monoclinic P21/n 14.6563(9) 14.1978(8) 27.4602(16) 90 93.2795(7) 90 5704.8(6) 4 1.366 1.521 0.0261 0.0641
)
C42H62N4O2C42H62N4O2Sc2 3 2(C7H8) Y2 3 2(C7H8) temperature (K) 143(2) 93(2) cryst syst monoclinic monoclinic space group C2/c C2/c a (A˚) 15.7970(13) 15.5705(7) b (A˚) 12.9336(11) 13.2395(6) c (A˚) 26.217(2) 26.4343(12) R (deg) 90 90 β (deg) 106.2580(10) 105.9252(5) γ (deg) 90 90 5142.2(7) 5240.2(4) volume (A˚3) Z 4 4 1.200 1.289 Fcalcd (Mg/m3) 0.308 2.247 μ (mm-1) a 0.0924 0.0383 R1 (I > 2.0σ(I)) 0.2587 0.0915 wR2b (all data) P P P P a b 2 R1 = Fo| - |Fc / |Fo|. wR2 = [ [w(Fo - Fc2)2/ [w(Fo2)2 ]]1/2. )
empirical formula
3
highly reactive species, [(C5Me4H)2Sc]2( μ-η2:η2-N2), that decomposed in one case to make a single crystal containing both dinitrogen and oxide ligands, i.e., {[(C5Me4H)2Sc]2( μη2:η2-N2)[(C5Me4H)2Sc]2(μ-O)}.8 To be able to identify [(C5Me4H)2Sc]2(μ-O) by NMR spectroscopy, an independent synthesis was pursued. Since N2O is used as a source of oxide1,12-18 and since we had previously found that (C5Me5)2Sm(THF)2 reacts with N2O to make [(C5Me5)2Sm]2(μ-O),1 the reaction of (C5Me4H)2Sc(η3-C3H5) with N2O was examined. The allyl complex was chosen since it is one of the more readily accessible reactive M-C bonded species available with electropositive metallocenes.22 Although this reaction was not analogous to the samarium reaction involving metal-based reduction,1 we assumed that this combination would ultimately form the oxide complex, since metallocene oxides of this type are so readily formed even without any obvious source of oxygen. This reaction did not give an oxide, but instead led to an insertion product, [(C5Me4H)2Sc( μ-η1:η2-ONdNCH2CHd CH2)]2, 1, containing an allyl azoxy ligand as shown in eq 2. The 1H NMR spectrum showed resonances consistent with a localized allyl ligand and a single set of (C5Me4H)- resonances that integrated appropriately for 1. No evidence for any other products containing (C5Me4H)- was observed.
Complex 1 was definitively identified by X-ray crystallography, which showed that it crystallizes as a dimer in the solid state. The (RN2O)- ligands bridge the two metallocenes in a μ-η1:η2-mode analogous to that found in the product of reacting (C5Me5)2Sm(CH2C6H5)(THF)21 with N2O, eq 1.20
Figure 1. Thermal ellipsoid plot of [(C5Me5)2Sm( μ-η1:η2ONdNC3H5)]2, 4, drawn at the 30% probability level with hydrogen atoms omitted for clarity. Yttrium and lanthanum complexes 3 and 5 are isomorphous.
To determine the generality of (RN2O)- ligand formation with metallocene allyl complexes as a function of metal and ancillary ligand, analogous reactions were examined with (C5Me4H)2Y(η3-C3H5) and (C5Me5)2M(η3-C3H5) (M = Y, Sm, La). As shown in eq 2, products analogous to 1 were formed in each case and provided complexes that could be analyzed by X-ray diffraction. Since the [(C5Me5)2Ln]2(μ-O) oxides are known for Ln = La,3 Sm,1 and Y,2 the formation of an oxide byproduct in these reactions could be determined by NMR spectroscopy. No evidence for oxide formation was found in any of the spectra. It should be noted that insertion chemistry has also been observed recently with NO and metallocene allyls of these metals.28 Specifically, the (C5Me5)2M(η3-C3H5) complexes (M=Y, Sm, La) react with NO to form {(C5Me5)2M[ONN(CH2CHdCH2)O]}2 products. Structural Comparisons. Complexes 1 and 2 are isomorphous, as are 3-5. Each complex contains a nine-coordinate metal center ligated by two polyalkylcyclopentadienyl ligands, two nitrogen atoms of one (RN2O)- ligand, and an oxygen of the other (RN2O)- ligand. Figure 1 shows the structure of 4 as a representative example. Selected bond distances and angles for 2-5 are shown in Table 2. The data on 1 established
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Table 2. Selected Bond Distances (A˚) and Angles (deg) in [(C5Me4H)2Y( μ-η1:η2-ONdNC3H5)]2, 2, [(C5Me5)2Y( μ-η1: η2-ONdNC3H5)], 3, [(C5Me5)2Sm( μ-η1:η2-ONdNC3H5)], 4, and [(C5Me5)2La( μ-η1:η2-ONdNC3H5)], 5 a
M(1)-Cnt M(1)-N(1) M(1)-N(2) M(1)-O(1) N(1)-N(2) N(1)-O(2) N(2)-C(41) C(41)-C(42) C(42)-C(43) Cnt1-M(1)-Cnt2 M(1)-O(1)-N(3) O(1)-N(3)-M(2) O(1)-M(1)-N(1) a
2
3
4
5
2.345, 2.366 2.410(2) 2.484(2) 2.324(2) 1.264(3) 1.300(2) 1.474(3) 1.592(6) 1.311(9) 131.1 117.2(1) 161.1(2) 80.62(6)
2.405, 2.389 2.484(2) 2.508(2) 2.354(2) 1.264(2) 1.305(2) 1.468(3) 1.498(3) 1.230(4) 129.9 120.9(1) 163.6(1) 74.93(5)
2.464, 2.486 2.556(3) 2.565(3) 2.419(2) 1.258(3) 1.306(3) 1.477(4) 1.495(5) 1.205(6) 130.9 121.3(2) 163.6(9) 74.72(7)
2.550, 2.559 2.642(2) 2.640(2) 2.490(1) 1.258(2) 1.307(2) 1.476(3) 1.502(3) 1.248(4) 131.8 120.2(1) 163.3(1) 75.82(5)
Cnt = centroid of the (C5Me5)- or (C5Me4H)- ligand.
connectivity, but were not of sufficient quality to discuss metrical parameters. In complexes 2-5, the N-N and N-O bond distances in the (RN2O)- ligand are in the NdN double and N-O single bond regions, respectively.25 This suggests that the ligand is more appropriately considered as an allyl-substituted azoxy ligand coordinating through the NdN bond and oxygen anion, [(allyl)NdN-O]-, rather than an allyl nitroso amide coordinating through a single nitrogen with a oxygen donor interaction, [N(allyl)(NdO)]-. Further support for this view comes from the bond distances to the metal. The structures of 3-5 have two similar M-N distances each, consistent with azo ligation, rather than one short and one longer, as expected for an amide/amine coordination mode. Surprisingly, 2 has two rather different Y-N distances despite N-N and N-O distances like those in 3-5. The C-C bond distances of the allyl substituents in each (RN2O)- ligand are consistent with localized C-C single and CdC double bonds.25 The 2.419(2) A˚ Sm-O and 2.556(3) and 2.565(3) A˚ Sm-N bond distances in the samarium complex 4 are equivalent to the corresponding bond distances in the previously reported benzyl complex [(C5Me5)2Sm(ONdNCH2Ph)]2,20 6 [2.422(2) A˚ Sm-O; 2.557(3) and 2.579(2) A˚ Sm-N]. These Sm-N distances (25) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1. (26) Evans, W. J.; Drummond, D. K.; Chamberlain, L. R.; Doedens, R. J.; Bott, S. G.; Zhang, H.; Atwood, J. L. J. Am. Chem. Soc. 1988, 110, 4983.
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are considerably longer than the 2.39(1)-2.45(1) A˚ distances in the azobenzene complex (C5Me5)2Sm(PhNNPh)(THF),26 which has 1.32(1)-1.39(2) A˚ N-N bond distances (two molecules in the unit cell). The Sm-O distance in 4 is much shorter than the 2.532(8)-2.557(9) A˚ Sm-O(THF) bond lengths in (C5Me 5)2Sm(PhNNPh)(THF).26 The fact that the Sm-O bond in 4 is shorter than these latter typical Sm-O(neutral donor ligand) distances is also consistent with the allyl azoxy coordination mode. Complexes 2 and 3 provide an opportunity to compare (C5Me4H)- vs (C5Me5)- analogues. The Y-(ring centroid), Y-N(2), and Y-O(1) distances are 0.02-0.03 A˚ shorter in the (C5Me4H)- complex. This is consistent with the slightly smaller size of the ligand and its less electron-donating nature that may lead to a stronger metal allyl azoxy interation. The Y-N(1) distance in 2 is also shorter, but the difference, 0.07 A˚, is larger than for the other bonds. As described above, this distance in 2 is unusual.
Conclusion N2O readily reacts with allyl metallocene complexes of Sc, Y, and the lanthanides to make allyl azoxy (RN2O)- ligands that can bridge two metal centers to make bimetallic complexes [(C5Me4R)2M( μ-η1:η2-ONdNC3H5)]2. Hence, insertion rather than delivery of oxygen is the preferred mode of reaction. Interestingly, NO behaves similarly with metallocene allyls of these metals.
Acknowledgment. We thank the National Science Foundation for support of this research and the University of Cologne and the Fonds der Chemischen Industrie for support of S.D. This research was facilitated in part by a National Physical Science Consortium Fellowship and by stipend support from Los Alamos National Laboratory (to E.M.). Supporting Information Available: X-ray diffraction data, atomic coordinates, thermal parameters, and complete bond distances and angles for complexes 2-5. This material is available free of charge via the Internet at http://pubs.acs.org. CIF files have also been deposited with the Cambridge Crystallographic Database as CCDC 793386-793389 and 796140. (27) http://www.glasscontoursolventsystems.com. (28) Casely, I. J.; Suh, Y.; Ziller, J. W.; Evans, W. J. Organometallics 2010, 29, 5209.
