[3+2] Cycloadditions of Molybdenum(II) Azide Complexes with

(c) Nelson , J. H.; Schmitt , D. L.; Henty , R. A.; Moore , D. W.; Jonassen , H. B. Inorg. Chem. 1970, 9 ..... James E. Heckler , Bryce L. Anderson , ...
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Organometallics 2010, 29, 4282–4290 DOI: 10.1021/om1007083

[3þ2] Cycloadditions of Molybdenum(II) Azide Complexes with Nitriles and an Alkyne Fu-Chen Liu,* Yu-Liang Lin, and Pei-Shan Yang Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan, Republic of China

Gene-Hsian Lee and Shie-Ming Peng Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Republic of China Received July 20, 2010

A series of products of [3þ2] cycloaddition reactions of molybdenum azide complexes with nitriles and an alkyne were prepared and characterized. These include the tetrazolate complexes Mo(η3C3H5)(CO)2(en)(N4CR) (R = CH3 (1), C6H5 (2), C(CH3)3 (3), CHdCHCN (4)) and the triazolate complexes Mo(η3-C3H5)(CO)2(L2){N3C2(CO2CH3)2} (L2 = en (6), dppe (7)). They are the first examples of a complex with a heterocyclic ligand prepared via a reaction of a group VIB metal azide with an unsaturated dipolarophile. All these complexes are fluxional in solution, with those containing en ligands displaying broad unresolved proton NMR signals at room temperature. With the exception of 1, their solution behavior was studied by low-temperature NMR spectroscopy. In contrast, the dppe complexes display average NMR signals at room temperature due to a fast exchange. The solid-state structures of these cycloaddition products were also determined by singlecrystal X-ray diffraction analysis. The tetrazolate complexes 1, 2, and 4 adopt an asymmetric endoconformation, while complex 3 adopts a symmetric endo-conformation. The tetrazolate ligand is N(1)-bonded in 1 and N(2)-bonded in complexes 2-4. The steric effect is the main reason for the N(2)-bonding mode found in 3. Complex 4 is the first structurally characterized product of a [3þ2] cycloaddition reaction involving the CtN bond of fumaronitrile. The triazolate complexes 6 and 7 adopt an asymmetric endo-conformation, with their heterocyclic ligands being bonded to the metal via N(2).

Introduction 1,3-Dipolar cycloaddition, a common process in organic chemistry,1 involves a reaction of 1,3-dipoles with unsaturated dipolarophiles. Among various types of 1,3-dipoles, the organic azides are particularly important, as they provide an entry into the synthesis of triazoles and tetrazoles.2 These heterocycles and their metal complex derivatives have found *Corresponding authors. E-mail: [email protected]. Fax: 8863-8633570. (1) (a) Kauffmann, T. Angew. Chem., Int. Ed. Engl. 1974, 13, 627. (b) Padwa, A. Angew. Chem., Int. Ed. Engl. 1976, 15, 123. (c) Huisgen, R. Angew. Chem., Int. Ed. Engl. 1963, 2, 565. (2) (a) L’abbe, G. Chem. Rev. 1969, 69, 345. (b) Bleiholder, R. F.; Shechter, H. J. Am. Chem. Soc. 1968, 90, 2131. (c) Huisgen, R. Proc. Chem. Soc. 1961, 357. (d) Lieber, E.; Minnis, R. L.; Rao, C. N. R. Chem. Rev. 1965, 65, 377. (e) Huisgen, R.; Knorr, R.; M€obius, L. L.; Szeimies, G. Chem. Ber. 1964, 98, 4014. (f) Huisgen, R.; Szeimies, G.; M€obius, L. Chem. Ber. 1967, 100, 2494. (g) Patai, S. The Chemistry of Azido Group; Interscience: New York, 1971. (3) (a) Nomiya, K.; Noguchi, R.; Oda, M. Inorg. Chim. Acta 2000, 298, 24. (b) Singh, H.; Chawla, A. S.; Kapoor, V. K.; Paul, D.; Malhotra, R. Prog. Med. Chem. 1980, 17, 151. (c) Fan, W. Q.; Katritzky, A. R. In Comprehensive Heterocyclic Chemistry II; Katritzky, A. R.; Rees, C. W.; Scriven, E. F. V., Eds.; Pergamon Press: Oxford, U.K., 1996; Vol. 4, pp 1-126. (d) Herr, R. J. Bioorg. Med. Chem. 2002, 10, 3379. (e) Truica-Marasescu, F.; Wertheimer, M. R. Plasma Process. Polym. 2008, 5, 44. (f) Katritzky, A. R.; Rees, C. W. Comprehensive Heterocyclic Chemistry; Pergamon Press: Elmsford, NY, 1984; Vol. 5, Part 4A, pp 791-838. pubs.acs.org/Organometallics

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a range of important applications in pharmaceutical and biomedical applications,3 corrosion inhibitors,4 and energetic materials.5 The [3þ2] dipolar cycloaddition of metal azide complexes with unsaturated organic compounds has also been a subject of interest for many decades.6 These azide complexes have been reported to react with nitriles7 and (4) Szocs, E.; bako, I.; Kosztolanyi, T.; Bertoti, I.; Kalman, E. Electrochim. Acta 2004, 49, 1371. (5) (a) Klap€ otke, T. M.; Mayer, P.; Sabate, C. M.; Welch, J. M.; Wiegand, N. Inorg. Chem. 2008, 47, 6014. (b) Klap€otke, T. M.; Stierstorfer, J. J. Am. Chem. Soc. 2009, 131, 1122. (c) Klap€otke, T. M.; Sabate, C. M.; Welch, J. M. Eur. J. Inorg. Chem. 2009, 769. (d) Tao, G.-H.; Twamley, B.; Shreeve, J. M. Inorg. Chem. 2009, 48, 9918. (e) Singh, R. P.; Verma, R. D.; Meshri, D. T.; Shreeve, J. M. Angew. Chem., Int. Ed. 2006, 45, 3584. (f) Tappan, B. C.; Huynh, M. H.; Hiskey, M. A.; Chavez, D. E.; Luther, E. P.; Mang, J. T.; Son, S. F. J. Am. Chem. Soc. 2006, 128, 6589. (g) Poturovic, S.; Lu, D.; Heeg, M. J.; Winter, C. H. Polyhedron 2008, 27, 3280. (6) (a) Beck, W.; Fehlhammer, W. P.; Bauder, M. Chem. Ber. 1969, 102, 3637. (b) Dori, Z.; Ziolo, R. F. Chem. Rev. 1973, 73, 247. (c) Fruhauf, H. W. Chem. Rev. 1997, 97, 523. (7) (a) Bhandari, S.; Frost, C. G; Hague, C. E.; Mahon, M. F.; Molloy, K. J. Chem. Soc., Dalton Trans. 2000, 663. (b) Becker, T. M.; Krause-Bauer, J. A.; Homrighausen, C. L.; Orchin, M. Polyhedron 1999, 18, 2563. (c) Guilard, R.; Perrot, I.; Tabard, A.; Richard, P.; Lecomte, C.; Liu, Y. H.; Kadish, K. M. Inorg. Chem. 1991, 30, 27. (d) Guilard, R.; Perrot, I.; Tabard, A.; Richard, P.; Lecomte, C.; Liu, Y.-H.; Kadish, K. M. Inorg. Chem. 1991, 30, 16. (e) Blunden, S. J.; Mahon, M. F.; Molloy, K. C.; Waterfield, P. J. Chem. Soc., Dalton Trans. 1994, 2135. (f) Bhandari, S.; Mahon, M. F.; Molloy, K.; Palmer, J. S.; Sayers, S. J. Chem. Soc., Dalton Trans. 2000, 1053. r 2010 American Chemical Society

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isonitriles8 to produce metal-nitrogen- and metal-carbonbonded tetrazolate complexes, respectively, and with alkynes9 to furnish triazolate metal complexes. In addition, reactions of metal azide complexes with other unsaturated substrates such as carbon monoxide, carbon disulfide, thiocyanates, and isothiocyanates have also been reported.8b,c,10 In general, these reactions involve electron-rich azide complexes. During the past decades many main group metal11 as well as late transition metal azide complexes of groups VIIB to IIB have been examined in their reactions with unsaturated substrates.7b,c,8a-8c,12 However, [3þ2] dipolar cycloaddition has never been extended to the less electron-rich group VIB metal azide complexes.13 Here we would like to report our recent findings with respect to the reactivity of the molybdenum azides toward nitriles and an alkyne.

Results and Discussion Preparations and Properties of Mo(η3-C3H5)(CO)2(en)(N4CR) (R = CH3 (1); C6H5 (2); C(CH3)3 (3); CHdCHCN (4)). Tetrazolate molybdenum complexes Mo(η3-C3H5)(CO)2(en){N4C(CH3)}, 1, Mo(η3-C3H5)(CO)2(en){N4C(C6H5)}, 2, and Mo(η3-C3H5)(CO)2(en){N4CC(CH3)3}, 3, were isolated from reactions of Mo(η3-C3H5)(CO)2(en)(N3)14 with acetonitrile, benzonitrile, and trimethylacetonitrile, respectively, at elevated temperatures. In contrast, the reaction of Mo(η3C3H5)(CO)2(en)(N3) with fumaronitrile produced Mo(η3C3H5)(CO)2(en){N4C(CHdCHCN)}, 4, at room temperature. The more electron-withdrawing nature of fumaronitrile (8) (a) Huh, H. S.; Lee, Y. K.; Lee, S. W. J. Mol. Struct. 2006, 789, 209. (b) Kim, Y.-J.; Chang, X.; Han, J.-T.; Lim, M. S.; Lee, S.-W. J. Chem. Soc., Dalton Trans. 2004, 2699. (c) Kim, Y.-J.; Kwak, Y.-S.; Lee, S.-W. J. Organomet. Chem. 2000, 603, 152. (d) Fehlhammer, W.; Kemmerich, T.; Beck, W. Chem. Ber. 1972, 112, 468. (e) Kim, Y.-J.; Lee, S.-H.; Lee, S.-H.; Jeon, S., II; Lim, M. S.; Lee, S.-W. Inorg. Chim. Acta 2005, 358, 650. (f) Kim, Y.-J.; Kwak, Y.-S.; Joo, Y.-S.; Lee, S.-W. J. Chem. Soc., Dalton Trans. 2002, 144. (g) Han, W. S.; Lee, H. K.; Kim, Y.-J.; Lee, S.-W. Acta Crystallogr. 2004, E60, m1813. (h) Wehlan, M.; Thiel, R.; Fuchs, J.; Beck, W.; Fehlhammer, W. P. J. Organomet. Chem. 2000, 613, 159. (i) Kim, Y.-J.; Joo, Y.-S.; Han, J.-T.; Han, W. S.; Lee, S.-W. J. Chem. Soc., Dalton Trans. 2002, 3611. (9) (a) Partyka, D. V.; Updegraff, J. B., III; Zeller, M.; Hunter, A. D.; Gray, T. G. Organometallics 2007, 26, 183. (b) Chen, C.-K.; Tong, H.-C.; Hsu, C.-Y. C.; Lee, C.-Y.; Fong, Y. H.; Chuang, Y.-S.; Lo, Y.-H.; Lin, Y.-C.; Wang, Y. Organometallics 2009, 28, 3358. (c) Chang, C. W.; Lee, G. H. Organometallics 2003, 22, 3107. (d) Singh, K. S.; Th€one, C.; Kollipara, M. R. J. Organomet. Chem. 2005, 690, 4222. (10) (a) Busetto, L.; Palazzi, A. Inorg. Chim. Acta 1975, 13, 233. (b) Bhandari, S.; Mahon, M. F.; McGinley, J. G.; Molloy, K. C.; Roper, C. E. E. J. Chem. Soc., Dalton Trans. 1998, 3425. (c) Hsu, S.-C.; Lin, Y.-C.; Huang, S.-L.; Liu, Y.-H.; Wang, Y.; Liu, H. Eur. J. Inorg. Chem. 2004, 459. (d) Beck, W.; Fehlhamnzer, W. P.; Pollrnann, P.; Schachl, H. Chem. Ber. 1969, 102, 1976. (11) (a) Fehlhammer, W. P.; Dahl, L. F. J. Am. Chem. Soc. 1972, 94, 3370. (b) Sisido, K.; Nabika, K.; Isida, T. J. Organomet. Chem. 1971, 33, 337. (c) Kozima, S. J. Organomet. Chem. 1972, 44, 117. (d) Jagerovic, N.; Barbe, J.-M.; Farnier, M.; Guilard, R. J. Chem. Soc., Dalton Trans. 1988, 2569. (e) Guilard, R.; Gerges, S. S.; Tabard, A.; Richard, P.; El Borai, M. A.; Lecomte, C. J. Am. Chem. Soc. 1987, 109, 7228. (12) (a) Gaughan, P.; Bowman, K. S.; Dori, Z. Inorg. Chem. 1972, 11, 601. (b) Beck, W.; Fehlhammer, W. P. Angew. Chem., Int. Ed. Engl. 1967, 6, 169. (c) Treichel, P. M.; Knebel, W. J.; Hess, R. W. J. Am. Chem. Soc. 1971, 93, 5424. (d) Kemmerich, T.; Nelson, J. H.; Takach, N. E.; Boehme, H.; Jablonski, B.; Beck, W. Inorg. Chem. 1982, 21, 1226. (e) Li, G. Q.; Orchin, M. J. Organomet. Chem. 1997, 535, 43. (f) Singh, K. S.; Kreisel, K. A.; Yap, G. P. A.; Kollipara, M. R. J. Coord. Chem. 2007, 60, 505. (g) Wee, S.; Grannas, M. J.; McFadyen, W. D.; O'Hair, R. A. J. Aust. J. Chem. 2001, 54, 245. (h) Kotera, M.; Sekioka, Y.; Suzuki, T. Inorg. Chem. 2008, 47, 3498. (i) Pachhunga, K.; Carroll, P. J.; Rao, K. M. Inorg. Chim. Acta 2008, 361, 2025. (13) Schollhammer, P.; Cabon, N.; Kervella, A.-C.; Petillon, F. Y.; Rumin, R.; Talarmin, J.; Muir, K. W. Inorg. Chim. Acta 2003, 350, 495. (14) Liu, F.-C.; Tsai, T.-C.; Lin, Y.-L.; Lee, C.-S.; Yang, P.-S.; Wang, J.-C. J. Organomet. Chem. 2010, 695, 423.

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could be a reason for such a difference in reaction temperatures. These reactions, shown in eq 1, were monitored for completeness by observing the disappearance of the asymmetric N3 stretching band of azide complex Mo(η3-C3H5)(CO)2(en)(N3) in the IR spectrum.14 The tetrazolate complexes prepared display different degrees of solubility in commonly used polar organic solvents. Thus, complex 4 has a good solubility, while only DMSO and methanol (sparingly) can dissolve complex 1, with complexes 2 and 3 being moderately soluble. Two carbonyl absorption bands of about equal intensity consistent with the presence of a cisM(CO)2 unit15 were observed in the IR spectrum of each complex. The CtN (2219 cm-1) and CdC (1637 cm-1) stretching bands in 4 are consistent with those found in the tetrazole complexes In(tpp)[N4C(CHdCHCN)] (tpp = dianionic tetraphenylporphyrin)16 and Mn(tpp)[N4C(CHdCHCN)].17

Due to the Bailar pseudorotation, fluxional behavior is a general phenomenon observed in a M(η3-C3H5)(CO)2(L2)(X) (M=Mo, W; L2=nonrigid bidentate ligand; X=anionic monodentate ligand) type of complex in solution.18 Complexes 1-4 displayed broad unresolved proton NMR signals at room temperature. Further characterization of the solution behavior of 1 was performed at elevated temperature. As the temperature was raised, the broad signals sharpened gradually, with average NMR signals being observed at 115 °C. At this temperature the proton spectrum displayed only three signals for the allyl group hydrogens (a symmetric pattern). The spectrum averaging resulted from a fast rotation of the triangular face formed by the tetrazole ligand and the chelating en ligand with respect to the face formed by the allyl and two carbonyl ligands.19 In the 13C NMR spectrum the tetrazolate N4C carbon appeared at 159.04 ppm. Complexes 2-4 were characterized by 1H-1H COSY and 1 H-13C HMQC 2D NMR analyses at low temperature (-40 °C for 2; -60 °C for 3 and 4). For each complex a proton spectrum with five allyl, four NH2, and four CH2 proton resonances was observed, suggesting the existence of an asymmetric conformation at low temperature. Two vinyl hydrogens on the substituted tetrazolate ligand of 4 appeared at 7.64 and 6.50 ppm (d, JH-H = 16.4 Hz), consistent with their anti-arrangement. In the 13C NMR spectra, two carbonyl resonances were observed for each complex, and (15) (a) Morales, D.; Clemente, M. E. N.; Perez, J.; Riera, L.; Riera, V.; Miguel, D. Organometallics 2003, 22, 4124. (b) Ascenso, J. R.; de Azevedo, C. G.; Calhorda, M. J.; Carrondo, M. A. A. F.; de, C. T.; Costa, P.; Dias, A. R.; Drew, M. G. B.; Felix, V.; Galv~ao, A. M.; Rom~ao, C. C. J. Organomet. Chem. 2001, 632, 197. (16) Guilard, R.; Jagerovic, N.; Tabard, A.; Naillon, C.; Kadish, K. M. J. Chem. Soc., Dalton Trans. 1992, 1957. (17) Cuilard, R.; Jagerovic, N.; Barbe, J.-M.; Liu, Y. H.; Perrot, I.; Naillon, C.; Caemelbeck, E. V.; Kadish, K. M. Polyhedron 1995, 14, 3041. (18) (a) Faller, J. W.; Haitko, D. A.; Adams, R. D.; Chodosh, D. F. J. Am. Chem. Soc. 1979, 101, 865. (b) Hsieh, A. T. T.; West, B. O. J. Organomet. Chem. 1976, 112, 285. (c) Hsieh, A. T. T.; West, B. O. J. Organomet. Chem. 1974, 78, C40. (19) (a) Brown, R. A.; Endud, S.; Friend, J.; Hill, J. M.; Whiteley, M. W. J. Organomet. Chem. 1988, 339, 283. (b) Chisholm, M. H.; Reichert, W. W.; Cotton, F. A.; Murillo, C. A. J. Am. Chem. Soc. 1977, 99, 1654.

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Figure 1. Molecular structure of Mo(η3-C3H5)(CO)2(en){N4C(CH3)}, 1, with 30% probability thermal ellipsoids.

Figure 3. Molecular structure of Mo(η3-C3H5)(CO)2(en){N4CC(CH3)3}, 3, with 50% probability thermal ellipsoids.

Figure 2. Molecular structure of Mo(η3-C3H5)(CO)2(en){N4C(C6H5)}, 2, with 50% probability thermal ellipsoids.

the tetrazolate ligand carbon atom appeared at 162.38, 170.8, and 159.0 ppm for 2, 3, and 4, respectively. The molecular structures of 1-4 were analyzed by singlecrystal X-ray crystallography. The molecular structures of 1-4 are shown in Figures 1-4. Although the unit cell of 4 contains two crystallographically different molecules, only one molecule is displayed due to the difference being insignificant. The crystallographic data and selected bond distances and bond angles are given in Tables 1-5. The molecular structure of each complex can be described as a distorted octahedral, with the central atom being surrounded by allyl, tetrazolate, en, and two carbonyl ligands. The two carbonyls are cis to each other and occupy the equatorial positions. The allyl occupies an axial position with its open face eclipsing the two carbonyl ligands. Complexes 1, 2, and 4 adopt an asymmetric endo-conformation, with two nitrogen atoms of the en ligand occupying an equatorial and an axial positions and the tetrazolate ligand occupying another equatorial position trans to a carbonyl ligand. Complex 3 adopts a symmetric endo-conformation, in which two nitrogen atoms of the en ligand occupy the equatorial positions, each of them trans to a carbonyl ligand, and the tetrazolate ligand occupies the axial position trans to the allyl ligand. According to our previous study, the solid-state structures of Mo(η3-C3H5)(CO)2(en)(X)14 appear to be dependent on the anionic ligand X-. The asymmetric endo-forms were found for compounds containing a weak field ligand, while the symmetric endo-forms were found in the case of a strong field

Figure 4. Molecular structure of Mo(η3-C3H5)(CO)2(en){N4C(CHdCHCN)}, 4, with 50% probability thermal ellipsoids.

ligand. A strong donor ability of the tert-butyl group may have induced a strong interaction between the metal and the tetrazolate ligand, resulting in the symmetric endoconformation in the solid state. The tetrazolate ligand in 1 is bonded to the Mo via its N(1) atom. The Mo-N(1) bond distance (2.247(12) A˚) is slightly longer than that of the azide complex Mo(η3-C3H5)(CO)2(en)(N3) (2.233(3) A˚).14 The five-membered tetrazolate ring exhibits an irregular pentagonal structure. The NdN bond distances are in the range 1.33(2)-1.40(2) A˚, and the CdN bond distances are 1.29(2) and 1.31(3) A˚, respectively, suggesting a localization of π-electrons on the CdN bond. The short CdN distance has also been found in the tetrazolate complex (2,3,7,8,12,13,17,18-octaethylprophinato)In(N4CMe) (1.28(1) A˚).2d The tetrazolate ligands in 2-4 are N(2)-bonded to the metal. The Mo-N(2) bond distances are 2.2663(17) A˚ in 2, 2.2120(16) A˚ in 3, and 2.2454(17) and 2.2688(18) A˚ in 4. The short Mo-N(2) bond distance in 3 confirmed a strong interaction between Mo and the tetrazolate ligand. The tetrazolate ligand could be coordinated to a metal through either its N(1) or N(2) nitrogen. The theoretic calculation has suggested both types of bonding modes to be essentially energetically equivalent.20 It has been observed that electronegative substituents in the 5-position give predominantly

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Table 1. Crystallographic Data for Mo(η3-C3H5)(CO)2(en){N4C(CH3)}, 1, Mo(η3-C3H5)(CO)2(en){N4C(C6H5)}, 2, Mo(η3-C3H5)(CO)2(en){N4CC(CH3)3}, 3, and Mo(η3-C3H5)(CO)2(en){N4C(CHdCHCN)}, 4 empirical formula fw T (K) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z Fcalcd (g/cm3) cryst size (mm3) radiation (λ, A˚) θ limits (deg) index ranges

C9H16MoN6O2 C14H18MoN6O2 336.22 398.28 150(2) 150(2) orthorhombic triclinic Pnnm P1 15.1003(5) 7.6295(7) 11.6868(4) 9.8074(9) 7.3957(2) 11.8453(11) 110.416(2) 94.424(1) 90 102.060(2) 91.906(2) 118.888(1) 1305.15(7) 806.86(13) 4 2 1.711 1.639 0.15  0.12  0.05 0.25  0.25  0.12 Mo KR (0.71073) Mo KR (0.71073) 2.20-27.49 1.89-27.50 -17 e h e 19 -9 e h e 9 -15 e k e 12 -12 e k e 12 -9 e l e 9 -15 e l e 15 reflns collected 6670 10 455 unique reflns 1611 3689 unique reflns [I > 2.0σ(I )] 680 404 completeness to θ (%) 99.6 99.9 1.010 0.832 μ (mm-1) data/restraints/params 1611/0/137 3689/0/208 a 0.0857 0.0273 R1 [I > 2.0σ(I )] 0.2084 0.0676 wR2b (all data) 0.0507 0.0307 Rint 2 1.220 1.021 GOF on F P P P a b 2 2 2 P 2 2 1/2 R1 = ||Fo|| - |Fc||/ ||Fo|. wR2 = { w(Fo - Fc ) / w(Fo ) } .

C12H22MoN6O2 378.30 150(2) monoclinic P2(1)/c 11.1095(5) 12.4776(5) 12.1090(5)

C11H15MoN7O2 373.24 150(2) triclinic P1 10.6504(7) 10.7583(7) 14.8762(9)

101.432(1)

90.975(1)

1645.25(12) 4 1.527 0.30  0.30  0.10 Mo KR (0.71073) 2.37-27.50 -14 e h e 14 -16 e k e 15 -15 e l e 15 12 313 3762 776 99.8 0.811 3762/0/193 0.0259 0.0622 0.0325 1.059

1485.09(16) 4 1.669 0.40  0.35  0.10 Mo KR (0.71073) 1.38-27.50 -13 e h e 13 -13 e k e 13 -19 e l e 19 19 210 6790 752 99.7 0.899 6790/0/379 0.0263 0.0626 0.0186 1.119

Table 2. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(en){N4C(CH3)}, 1

Table 3. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(en){N4C(C6H5)}, 2

Mo-C(1) Mo-N(1) C(1)-O(1) C(8)-N(1) N(2)-N(3) N(4)-C(8)

1.957(17) 2.254(9) 1.147(19) 1.40(2) 1.38(3)

Mo-C(1) Mo-N(2) Mo-N(6) C(2)-O(2) N(2)-N(1) N(3)-N(4)

112.1(7) 94.8(5) 77.6(4) 86.6(4) 168.0(6) 103.7(14) 108.4(17) 174.3(14)

C(1)-Mo-C(2) C(2)-Mo-N(2) N(5)-Mo-N(6) N(5)-Mo-N(2) C(1)-Mo-N(6) C(8)-N(1)-N(2) N(2)-N(3)-N(4) Mo-C(2)-O(2)

C(1)-Mo-C(2) C(1)-Mo-N(5A) C(2)-Mo-N(5A) N(5)-Mo-N(5A) C(4)-Mo-N(5) C(2)-Mo-N(1) N(3)-N(2)-N(1) Mo-C(1)-O(1) C(3)-C(4)-C(5)

1.85(2) 2.247(12) 1.21(2) 1.29(2) 1.33(2) 1.31(3) 75.8(7) 97.5(7) 94.8(5) 75.5(5) 86.7(6) 171.7(4) 108.0(14) 174.7(17) 115.3(19)

Mo-C(2) Mo-N(5) C(2)-O(2) N(2)-N(1) N(3)-N(4)

C(1)-Mo-N(1) C(2)-Mo-N(5) N(5)-Mo-N(1) N(1)-Mo-N(5A) C(1)-Mo-N(5) C(8)-N(1)-N(2) N(2)-N(3)-N(4) Mo-C(2)-O(2)

N(2)-bonded isomers, while those with electropositive groups in the 5-position lead predominantly to the N(1)-bonding mode.6c,20b,21 Thus, the steric hindrance of the bulky tert-butyl substituent is the main driving force in determining the N(2)bonding mode for complex 3. The interatomic distances within the five-membered tetrazolate ring are more typical than those found in 1, consistent with the delocalization of the π-electrons within the heterocycle. They are in the range 1.317(2)-1.345(2) A˚ in 2, 1.309(2)-1.343(2) A˚ in 3, and 1.324(2)-1.338(3) or 1.321(2)-1.342(2) A˚ in 4 (two independent molecules in the unit cell). In complex 2, the tetrazolate and the phenyl rings are not coplanar. The C(tetrazolate)-C(phenyl) inter-ring distance is (20) (a) Kieft, R. L.; Peterson, W. M.; Blundell, G. L.; Horton, S.; Hendry, R. A.; Jonasson, H. B. Inorg. Chem. 1976, 15, 1721. (b) Redfield, D. A.; Nelson, J. H.; Henry, R. A.; Moore, D. W.; Jonassen, H. B. J. Am. Chem. Soc. 1974, 96, 6298. (c) Nelson, J. H.; Schmitt, D. L.; Henty, R. A.; Moore, D. W.; Jonassen, H. B. Inorg. Chem. 1970, 9, 2678. (21) Paul, P.; Chakladar, S.; Nag, K. Inorg. Chim. Acta 1990, 170, 27.

1.952(2) 2.2663(17) 2.2762(18) 1.158(3) 1.345(2) 1.339(2) 80.08(9) 167.79(8) 75.19(7) 77.69(7) 166.86(8) 103.7(14) 108.18(18) 176.0(2)

Mo-C(2) Mo-N(5) C(1)-O(1) C(8)-N(1) N(2)-N(3) N(4)-C(8) C(1)-Mo-N(2) C(2)-Mo-N(5) N(2)-Mo-N(6) C(1)-Mo-N(5) C(2)-Mo-N(6) N(3)-N(2)-N(1) Mo-C(1)-O(1) C(3)-C(4)-C(5)

1.950(2) 2.2333(18) 1.154(3) 1.328(3) 1.317(2) 1.334(3) 94.59(8) 91.45(8) 86.23(6) 92.15(8) 96.49(8) 110.55(17) 177.20(19) 114.3(2)

Table 4. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(en){N4CC(CH3)3}, 3 Mo-C(1) Mo-N(2) Mo-N(6) C(2)-O(2) N(2)-N(1) N(3)-N(4) C(1)-Mo-C(2) C(2)-Mo-N(2) N(5)-Mo-N(6) N(5)-Mo-N(2) C(1)-Mo-N(6) C(8)-N(1)-N(2) N(2)-N(3)-N(4) Mo-C(2)-O(2)

1.942(2) 2.2120(16) 2.2916(16) 1.152(3) 1.343(2) 1.342(2) 79.64(9) 87.49(7) 75.25(6) 99.46(7) 169.88(7) 104.10(15) 108.22(15) 177.69(18)

Mo-C(2) Mo-N(5) C(1)-O(1) C(8)-N(1) N(2)-N(3) N(4)-C(8) C(1)-Mo-N(2) C(2)-Mo-N(5) N(2)-Mo-N(6) C(1)-Mo-N(5) C(2)-Mo-N(6) N(3)-N(2)-N(1) Mo-C(1)-O(1) C(3)-C(4)-C(5)

1.973(2) 2.2571(17) 1.164(2) 1.329(3) 1.309(2) 1.337(3) 88.36(7) 79.17(6) 81.52(6) 103.28(7) 99.46(7) 110.72(15) 177.10(19) 115.4(2)

1.477 A˚, and the dihedral angle between the rings is 16.74°, suggesting no interannular conjugation between them. The intermolecular hydrogen bonds were found in 2 and 3.

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Table 5. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(en){N4C(CHdCHCN)}, 4

Mo-C(1) Mo-N(2) Mo-N(6) C(2)-O(2) N(2)-N(1) N(3)-N(4) C(9)-C(10) C(1)-Mo-C(2) C(2)-Mo-N(2) N(5)-Mo-N(6) N(5)-Mo-N(2) C(1)-Mo-N(6) C(8)-N(1)-N(2) N(2)-N(3)-N(4) Mo-C(2)-O(2)

molecule 1

molecule 2

1.949(2) 2.2454(17) 2.2794(17) 1.156(3) 1.338(2) 1.327(3) 1.326(3)

1.959(2) 2.2688(18) 2.2768(18) 1.159(3) 1.342(2) 1.332(3) 1.326(4)

79.30(9) 168.95(8) 75.59(7) 79.64(7) 170.39(8) 103.66(17) 108.80(17) 175.0(2)

81.35(9) 169.95(8) 75.59(6) 78.37(7) 165.87(8) 103.44(18) 109.22(18) 178.4(2)

In compound 2, two kinds of intermolecular hydrogen bonds between N(6)H 3 3 3 N(4) (N(4)-N(6) = 3.009 A˚) and CO(1) 3 3 3 HN(5) (N(5)-O(1)=3.017 A˚) result in a bilayered onedimensional polymer. In compound 3, two pairs of intermolecular hydrogen bonds between N(6)H 3 3 3 N(3) (N(3)-N(6) = 3.023 A˚) lead to a dimeric structure. In principle, the cycloaddition of fumaronitrile with a metal azide can take place via either the CdC or CtN bond. If the CdC bond is involved, a triazolate complex is formed accompanied by removal of one HCN molecule. In contrast, if the CtN bond is involved, a tetrazolate complex is formed. Among the literature reports, most of these cycloadditions involve the CdC bond of fumaronitrile.9b,c,12f,12i,22 To our knowledge, there are only two reports16,17 in which the CtN bonds were involved, and complex 4 is the first structurally characterized product of such a reaction. Preparations and Properties of Mo(η3-C3H5)(CO)2(dppe)(N3), 5. Treatment of the molybdenum complex Mo(η3C3H5)(CO)2(CH3CN)2(Br)23 with 1,2-bis(diphenylphosphino)ethane (dppe) and excess NaN3 affords red azide compound Mo(η3-C3H5)(CO)2(dppe)(N3), 5 (eq 2). It is airstable and soluble in CH2Cl2, CHCl3, and acetone.

In general, the energy barrier of the fluxional behavior of the dppe complexes is lower than that of their en analogues. Complex 5 displays average NMR signals at room temperature. Its 31P resonance appears at 44.7 ppm as a singlet. As the temperature was lowered, the signal broadened and eventually split into two signals at 45.19 and 41.72 ppm at -90 °C, due to the nonequivalence of the two phosphorus atoms. In the 13C NMR spectrum, the methylene carbon of the dppe ligand appears at 24.87 ppm as a triplet (Jc-p=19.2 Hz), due to a virtual coupling with two phosphorus atoms.20 This phenomenon also occurs in complex 7 and has been previously observed in other dppe complexes.9c,d,12f In the IR spectrum, the asymmetric N3 stretching band appears at 2057 cm-1, consistent with the generally observed range of 2050-2070 cm-1.10a The molecular structure of 5 is shown in Figure 5, and the crystallographic data and the selected bond distances and (22) Singh, K. S.; Kreisel, K. A.; Yap, G. P. A.; Kollipara, M. R. J. Organomet. Chem. 2006, 691, 3509. (23) Dieck, H. T.; Friedel, H. J. Organomet. Chem. 1968, 14, 375.

Mo-C(2) Mo-N(5) C(1)-O(1) C(8)-N(1) N(2)-N(3) N(4)-C(8) N(7)-C(11) C(1)-Mo-N(2) C(2)-Mo-N(5) N(2)-Mo-N(6) C(1)-Mo-N(5) C(2)-Mo-N(6) N(3)-N(2)-N(1) Mo-C(1)-O(1) C(3)-C(4)-C(5)

molecule 1

molecule 2

1.950(2) 2.2371(18) 1.158(3) 1.335(3) 1.324(2) 1.338(3) 1.149(3)

1.939(2) 2.2384(18) 1.157(3) 1.341(3) 1.321(2) 1.333(3) 1.148(3)

96.42(8) 90.51(8) 82.44(6) 94.82(8) 100.07(8) 110.39(17) 177.2(2) 114.3(2)

98.35(8) 91.58(8) 82.06(6) 90.62(8) 95.78(8) 110.16(17) 177.3(2) 115.9(2)

bond angles are given in Tables 6 and 7. Complex 5 adopts an asymmetric endo-conformation. The Mo-N3 bond distance is 2.253(2) A˚. The N-N bond distances are 1.153(4) and 1.190(3) A˚, the shorter one being between the middle nitrogen and the nitrogen bonded to the metal. These bond distances are similar to those found in the azide complex W(CO)2(η3-C3H5)(en)(N3) (1.152(6) and 1.191(6) A˚).14 The azide moiety exhibits a nearly linear arrangement. The N-N-N bond angle of the azide ligand is 177.4(3)°, which is consistent with the range observed for coordinated azide ligands (173-180°).14,24 Preparations and Properties of Mo(η3-C3H5)(CO)2(en){N3C2(CO2CH3)2}, 6, and Mo(η3-C3H5)(CO)2(dppe){N3C2(CO2CH3)2}, 7. Dppe complex 5 did not react with fumaronitrile. In its reactions with acetonitrile, benzonitrile, and trimethylacetonitrile under reflux conditions it decomposed, with no cycloaddition products being detected. However, it did react with an activated alkyne, dimethyl acetylenedicarboxylate. The triazolate complexes Mo(η3C3H5)(CO)2(en){N3C2(CO2CH3)2}, 6, and Mo η3-C3H5)(CO)2(dppe){N3C2(CO2CH3)2}, 7, were prepared from the reactions of Mo(η3-C3H5)(CO)2(L2)(N3) (L2 = en, dppe) with dimethyl acetylenedicarboxylate at room temperature (eq 3). The reaction completeness was confirmed by the disappearance of the asymmetric N3 stretching band of the starting azide complex. Both complexes are air-stable and have better solubility in generally used polar organic solvent compared with the tetrazolate complexes prepared in this work. In the IR spectrum, two carbonyl absorption bands of about equal intensity were observed for 6 (1928 and 1828 cm-1) and 7 (1940 and 1849 cm-1). The higher carbonyl absorption energy of 7 is due to the π back-bonding ability of the dppe ligand competing for the electron density with the carbonyl ligands. The NdN absorption of the triazolate ring and that of CdO are at 1450 and 1700 cm-1 in 6 and 1434 and 1716 cm-1 in 7.

Complex 6 adopts an asymmetric conformation in solution at low temperature (-100 °C). In the 1H NMR spectrum (24) Palenik, G. H. Acta Crystallogr. 1964, 17, 360.

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Figure 5. Molecular structure of Mo(η3-C3H5)(CO)2(dppe)(N3), 5, with 50% probability thermal ellipsoids. Table 6. Crystallographic Data for Mo(η3-C3H5)(CO)2(dppe)(N3), 5, Mo(η3-C3H5)(CO)2(en){N3C2(CO2CH3)2}, 6, and Mo(η3-C3H5)(CO)2(dppe){N3C2(CO2CH3)2}, 7 empirical formula fw T (K) cryst syst space group a (A˚) b (A˚) c (A˚) β (deg) V (A˚3) Z Fcalcd (g/cm3) cryst size (mm3) radiation (λ, A˚) θ limits (deg) index ranges

C31H29MoN3O2P2 633.45 150(2) orthorhombic P2(1)2(1)2(1) 9.2366(6) 11.6243(7) 26.1056(17) 90 2802.9(3) 4 1.501 0.25  0.18  0.15 Mo KR (0.71073) 1.56-27.50 -12 e h e 12 -14 e k e 15 -33 e l e 33 reflns collected 21 657 unique reflns 6424 unique reflns [I > 2.0σ(I )] 1296 completeness to θ (%) 100.0 0.616 μ (mm-1) data/restraints/params 6424/0/352 a 0.0319 R1 [I > 2.0σ(I )] 0.0708 wR2b (all data) 0.0427 Rint 2 1.108 GOF on F P P P P a b R1 = ||Fo|| - |Fc||/ ||Fo|. wR2 = { w(Fo2 - Fc2)2/ w(Fo2)2}1/2.

asymmetric patterns were observed for both allyl and en hydrogens. In the 13C NMR spectrum the triazolate carbons appeared at 137.3 and 126.2 ppm. Similar to the dppe complex 5, complex 7 also displays average NMR signals at room temperature. Its 31P resonance appears at 51.10 ppm at room temperature and splits into two broad signals at 47.07 and 46.10 ppm at -90 °C, due to the nonequivalence of the two phosphorus atoms at low temperature. In the 13C NMR spectrum, the triazolate carbon signal appears at 138.47 ppm and the methylene

C13H19MoN5O6 437.27 298(2) monoclinic P2(1)/c 7.9487(2) 11.2699(4) 19.7532(6) 91.5180(10) 1768.89(9) 4 1.646 0.47  0.14  0.12 Mo KR (0.71073) 2.06-28.32 -10 e h e 10 -15 e k e 15 -26 e l e 26 19 804 4407 888 100.0 0.781 4407/0/228 0.0216 0.0618 0.0249 1.050

C37H35MoN3O6P2 775.56 298(2) monoclinic P2(1)/n 14.3865(6) 12.1193(5) 21.6669(9) 108.286(1) 3586.9(3) 4 1.436 0.40  0.40  0.25 Mo KR (0.71073) 1.51-27.50 -18 e h e 18 -15 e k e 15 -27 e l e 28 27 248 8248 1592 99.9 0.504 8248/0/444 0.0366 0.0943 0.0360 1.034

carbon of the dppe ligand appears at 26.19 ppm (t, Jc-p = 20.3 Hz). The molecular structures of 6 and 7 are shown in Figures 6 and 7, and the crystallographic data and selected bond distances and bond angles are given in Tables 6, 8, and 9. These two molecules have similar structures. Both complexes adopt asymmetric endo-conformations, with the triazolate being N(2)-bonded to the metal. The Mo-N(2) bond distance is 2.2636(13) A˚ in 6 and 2.2228(18) A˚ in 7. Compared with the en ligand, the dppe ligand is more sterically

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Table 7. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(dppe)(N3), 5 Mo-C(1) Mo-N(1) Mo-P(2) C(2)-O(2) N(2)-N(3) C(1)-Mo-C(2) C(1)-Mo-P(2) C(2)-Mo-P(1) N(1)-Mo-P(1) C(2)-Mo-N(1) N(3)-N(2)-N(1) Mo-C(1)-O(1) C(3)-C(4)-C(5)

1.948(3) 2.253(2) 2.5978(7) 1.145(3) 1.153(4) 79.26(12) 158.75(9) 93.57(9) 77.40(7) 169.53(10) 177.4(3) 174.6(3) 117.3(3)

Mo-C(2) Mo-P(1) C(1)-O(1) N(1)-N(2)

C(1)-Mo-P(1) C(1)-Mo-N(1) C(2)-Mo-P(2) N(1)-Mo-P(2) N(2)-N(1)-Mo P(1)-Mo-P(2) Mo-C(2)-O(2)

1.956(3) 2.4919(7) 1.159(4) 1.190(3)

82.76(8) 104.50(10) 94.79(9) 78.18(6) 130.6(2) 77.23(2) 177.6(3)

Figure 7. Molecular structure of Mo(η3-C3H5)(CO)2(dppe){N3C2(CO2CH3)2}, 7, with 30% probability thermal ellipsoids. Table 8. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(en){N3C2(CO2CH3)2}, 6 Figure 6. Molecular structure of Mo(η3-C3H5)(CO)2(en){N3C2(CO2CH3)2}, 6, with 50% probability thermal ellipsoids.

demanding; therefore, the shorter Mo-N(2) bond distance in 7 may suggest a stronger bonding interaction between the triazolate ligand and the metal. The interatomic distances of the five-membered triazolate ring are similar in both molecules. They are in the range 1.3282(18)-1.391(2) A˚ in 6 and 1.327(3)-1.387(3) A˚ in 7. Compound 6 also contains intermolecular hydrogen bond CO(4) 3 3 3 HN(4) (N(4)-O(4) = 2.957 A˚), resulting in a one-dimensional polymer. It has been reported that the N(1)-bonded triazolate ligand (N3C2(CO2CH3)2) complex is a kinetic product, while its N(2)-bonded isomer is a thermodynamic product.7d,12d The transformation of the N(1) mode to the N(2) mode has been observed during the formation of ruthenium triazolate complexes,9b,c and in several cases both the N(1)- and N(2)bonded isomers have been found to coexist in the reaction.25 In our case, the time-elapsed 31P NMR study of the formation of 7 did not provide any evidence for the existence of the N(1)-bonded isomer during the reaction.

Conclusion This study describes the first examples of [3þ2] cycloaddition reactions of a group VIB metal azide complex Mo(η3C3H5)(CO)2(L2)(N3) (L2 = en, dppe) with nitriles and an alkyne, respectively, to generate tetrazolate complexes 1-4 and triazolate complexes 6 and 7. The heterocyclic ligand is N(1)-bonded in 1 and N(2)-bonded in other tetrazolate and triazolate complexes. The steric effect is the predominant factor in determining the N(2)-bonding mode in 3; however, the electronic effect could account for its symmetric endoconformation. In general, the [3þ2] cycloaddition of fumaronitrile involves the addition of a CdC bond, and the examples involving the CtN bond to form a tetrazolate (25) Parimal, P.; Kamalaksha, N. Inorg. Chem. 1987, 26, 2969.

Mo-C(1) Mo-N(2) Mo-N(5) C(2)-O(2) N(2)-N(3) N(1)-C(8) C(1)-Mo-C(2) C(2)-Mo-N(2) Mo-C(1)-O(1) C(3)-C(4)-C(5)

1.9444(17) 2.2636(13) 2.2781(14) 1.149(2) 1.3434(19) 1.3472(19) 79.66(8) 171.69(6) 176.40(18) 114.82(18)

Mo-C(2) Mo-N(4) C(1)-O(1) N(1)-N(2) N(3)-C(9) C(8)-C(9) C(1)-Mo-N(2) N(4)-Mo-N(5) Mo-C(2)-O(2)

1.9556(17) 2.2404(13) 1.161(2) 1.3282(18) 1.342(2) 1.391(2) 99.47(7) 75.10(5) 176.88(17)

Table 9. Selected Bond Distances (A˚) and Bond Angles (deg) for Mo(η3-C3H5)(CO)2(dppe){N3C2(CO2CH3)2}, 7 Mo-C(1) Mo-N(2) Mo-P(2) C(2)-O(2) N(1)-N(2) N(3)-C(7) C(1)-Mo-C(2) C(2)-Mo-N(2) C(1)-Mo-P(2) C(2)-Mo-P(2) N(2)-Mo-P(1) N(2)-N(1)-C(6) N(1)-C(6)-C(7) P(1)-Mo-P(2) Mo-C(2)-O(2)

1.950(3) 2.2228(18) 2.6059(6) 1.151(3) 1.327(3) 1.333(3) 79.63(11) 165.21(10) 168.90(9) 102.06(8) 83.89(5) 106.16(18) 107.7(2) 76.62(2) 174.3(2)

Mo-C(2) Mo-P(1) C(1)-O(1) N(1)-C(6) N(2)-N(3) C(6)-C(7)

1.977(3) 2.5526(6) 1.147(3) 1.338(3) 1.345(3) 1.387(3)

C(1)-Mo-N(2) C(1)-Mo-P(1) C(2)-Mo-P(1) N(2)-Mo-P(2) N(3)-N(2)-N(1) C(7)-N(3)-N(2) N(3)-C(7)-C(6) Mo-C(1)-O(1) C(3)-C(4)-C(5)

90.46(10) 92.65(9) 85.62(8) 85.62(5) 112.22(18) 105.37(19) 108.5(2) 176.1(3) 116.4(3)

complex are rare. Complex 4 represents the first structurally characterized product of the latter addition mode. The dppe complex 5 reacted with an activated alkyne, dimethyl acetylenedicarboxylate, but failed to react with nitriles. Poor reactivity of 5 toward nitriles can be explained by a lower electron density on the metal in the case of dppe, a good π-acceptor ligand, compared with en.

Experimental Section General Procedures. All manipulations were carried out on a standard high-vacuum line or in a drybox under nitrogen.

Article Reagents were used as obtained from the commercial suppliers, and solvents were dried and freshly distilled prior to use. Mo(CO)2(η3-C3H5)(en)(N3)11 and Mo(CO)2(η3-C3H5)(CH3CN)2(Br)23 were prepared according to the literature procedures. Elemental analyses were obtained on a Hitachi 270-30 instrument. Proton spectra (internally referenced to TMS, δ 0.00 ppm) were recorded on either a Bruker Avance DPX300 or a Bruker Avance II 400 spectrometer operating at 300.130 and 400.132 MHz, respectively. 31P spectra (externally referenced to 85% H3PO4, δ 0.00 ppm) were recorded on a Bruker Avance II 400 spectrometer operating at 161.976 MHz. Infrared spectra were recorded on a JASCO FT-IR 401 spectrometer with 4 cm-1 resolution. X-ray Crystal Structure Determination. Suitable crystals of 1-7 were mounted and sealed inside glass capillaries under nitrogen. Crystallographic data collections were carried out on a Nonius KappaCCD diffractometer with graphite-monochromated Mo KR radiation (λ = 0.71073 A˚) at 150(2) or 298(2) K. Unit cell parameters were retrieved and refined using DENZOSMN26 software on all reflections. Data reduction was performed with the DENZO-SMN26 software. An empirical absorption was based on the symmetry-equivalent reflections and was applied to the data using the SORTAV27,28 program. The structure was solved using the SHELXS-9729 program and refined using SHELXL-9730 by full-matrix least-squares on F2 values. All non-hydrogen atoms in each structure were located and refined anisotropically. All hydrogen atoms were fixed at calculated positions and refined using a riding mode. Crystallographic data of 1-7 are summarized in Tables 1-9. CAUTION: Owing to their potentially explosive nature, reactions with azide salts and their complexes should be performed with extreme care. Preparation of Mo(η3-C3H5)(CO)2(en){N4C(CH3)}, 1. Mo(η3-C3H5)(CO)2(en)(N3) (295.1 mg, 1.0 mmol) and about 20 mL of acetonitrile were placed in a 50 mL flask. After degassing, the solution was refluxed for three days, resulting in a yellow, cloudy solution. The solvent was removed under a dynamic vacuum, leaving behind a yellow solid. Crystallization from methanol furnished 216.2 mg (64.3% yield) of the title compound as yellow crystals. 1H NMR (d6-DMSO, 115 °C): δ 4.72 (br s, 2H, NH2), 3.87 (m, 1H, Hc), 3.40 (br s, 2H, NH2), 3.10 (d, J = 5.9 Hz, 2H, Hs), 2.50 (br s, 2H, CH2), 2.32 (s, 3H, CH3), 2.10 (br s, 2H, CH2), 1.04 (d, J=9.9 Hz, 2H, Ha). 13C NMR (d-DMSO, 115 °C): δ 227.54 (CO), 159.04 (N4C), 71.07(Cc), 56.83 (Ct), 42.82 (en), 10.98 (CH3). IR (KBr): 3309(m), 3279(vw), 3230(w), 3127(w), 2980(w), 2961(vw), 2892(vw), 1914(vs), 1820(vs), 1610(vw), 1587(vw), 1483(vw), 1457(vw), 1370(w), 1327(vw), 1288(vw), 1262(vw), 1232(vw), 1187(vw), 1132(vw), 1116(w), 1056(m), 1017(vw), 998(vw), 954(vw), 931(vw), 913(vw), 883(vw), 869(vw), 803(vw), 690(vw), 651(vw), 625(vw), 607(vw), 576(vw), 555(vw), 533(vw), 507(w), 469(w), 448(vw) cm-1. Anal. Calcd for C9H16MoN6O2: N, 24.99; C, 32.15; H, 4.80. Found: N, 24.87; C, 32.07; H, 4.82. Preparation of Mo(η3-C3H5)(CO)2(en){N4C(C6H5)}, 2. In a drybox, 295.1 mg (1.0 mmol) of Mo(η3-C3H5)(CO)2(en)(N3), 210.0 mg (2.0 mmol) of C6H5CN, and about 20 mL of THF were added into a 50 mL flask. The flask was evacuated, and the mixture was refluxed for 4 days. The resulting orange solution was concentrated, furnishing a viscous, yellow solution, which was washed with hexane several times and dried under vacuum. (26) DENZO-SMN: Otwinowsky, Z.; Minor, W. Processing of X-ray Diffraction Data Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276: Macromolecular Crystllography, Part A; Carter, C. W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; pp 307-326. (27) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33. (28) Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421. (29) SHELXS-97: Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467. (30) Sheldrick, G. M. SHELXL-97; University of G€ottingen: G€ottingen, Germany, 1997.

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Crystallization of the resulting yellow solid from a CH3OH/ ether/hexane mixture led to the isolation of 294.4 mg (73.6% yield) of the title product as yellow crystals. 1H NMR (CD3OD, -40 °C): δ 8.05-7.43 (m, 5H, C6H5), 6.46 (br s, 1H, NH2), 4.29 (br s, 1H, NH2), 4.13 (m, 1H, Hc), 3.96 (br s, 1H, NH2), 3.48 (br s, 1H, NH2), 3.32 (br s, 1H, Hs), 2.92 (br s, 1H, Hs), 2.66 (br s, 1H, CH2), 2.51(br s, 1H, CH2), 2.36 (br s, 1H, CH2), 2.04 (br s, 1H, CH2), 1.29 (d, J = 7.2 Hz, 1H, Ha), 1.02 (d, J = 7.2 Hz, 1H, Ha). 13C NMR (CD3OD, -40 °C): δ 226.19, 225.11 (CO), 162.38 (N4C), 128.98, 128.86, 128.60, 126.12 (C6H5), 69.58 (Cc), 55.79, 55.16 (Ct), 43.44, 41.49 (CH2). IR (KBr): 3318(w), 3308(w), 3208(vw), 3125(w), 3065(vw), 2989(vw), 2964(vw), 2939(vw), 2884(vw), 2862(vw), 1930(vs), 1825(vs), 1607(w), 1456(w), 1443(w), 1384(vw), 1364(vw), 1352(vw), 1333(vw), 1302(vw), 1281(vw), 1263(vw), 1224(vw), 1185(vw), 1176(vw), 1154(vw), 1138(w), 1106(w), 1071(vw), 1053(w), 1038(vw), 1021(vw), 1011(vw), 997(vw), 963(vw), 948(vw), 919(vw), 900(vw), 874(vw), 834(vw), 800(vw), 788(vw), 731(w), 693(w), 670(vw), 666(vw), 626(vw), 604(vw), 577(vw), 566(vw), 537(vw), 508(vw), 497(vw), 472(vw), 465(vw) cm-1. Anal. Calcd for C14H18MoN6O2: N, 21.10; C, 42.22; H, 4.56. Found: N, 21.00; C, 42.29; H, 4.60. Preparation of Mo(η3-C3H5)(CO)2(en){N4CC(CH3)3}, 3. Mo(η3-C3H5)(CO)2(en)(N3) (147.5 mg, 0.5 mmol) and 3.0 mL (37 mmol) of trimethylacetonitrile were placed in a 50 mL flask. After degassing, the mixture was refluxed at 110 °C for three days, giving rise to a yellow, cloudy solution. The solvent was removed under a dynamic vacuum followed by the extraction of the resulting yellow solid with dichloromethane. After removal of dichloromethane the yellow solid was dissolved in a dichloromethane/acetonitrile mixture and layered with hexane for crystallization, furnishing 136.5 mg (72.2% yield) of 3 as yellow crystals. 1H NMR (CD3OD, -60 °C): δ 6.35 (br s, 1H, NH2), 4.19 (br s, 1H, NH2), 3.99 (m, 1H, Hc), 3.93 (br s, 1H, NH2), 3.38 (br s, 1H, NH2), 3.24 (br s, 1H, Hs), 2.80 (br s, 1H, Hs), 2.61 (br s, 1H, CH2), 2.44 (br s, 1H, CH2), 2.18 (br s, 1H, CH2), 1.96 (br s, 1H, CH2), 1.37(s, 9H, CH3), 1.22 (d, J = 9.5 Hz, 1H, Ha), 0.99 (d, J = 8.5 Hz, 1H, Ha). 13C NMR (MeOD, -60 °C): δ 226.1, 225.1 (CO), 170.8 (N4C), 69.4 (Cc), 55.6, 55.1 (Ct), 43.3, 43.1 (en), 30.7 (C(CH3)3), 29.0 (CH3). IR (KBr): 3324(m), 3302(m), 3247(m), 3219(m), 3148(w), 3034(w), 2961(m), 2958(w), 2930(w), 2895(w), 2868(w), 1945(vs), 1832(vs), 1596(m), 1574(m), 1492(m), 1476(m), 1426(w), 1459(m), 1426(w), 1385(w), 1377(w), 1358(m), 1330(vw), 1286(w), 1262(vw), 1234(w), 1190(w), 1160(w), 1146(w), 1119(m), 1094(m), 1045(s), 1034(s), 1017(m), 987(m), 954(w), 921(vw), 902(vw), 872(vw), 861(w), 828(vw), 781(vw), 732(vw), 688(vw), 636(vw), 603(vw), 576(w), 554(w), 529(w), 491(m) cm-1. Anal. Calcd for C12H22MoN6O2: N, 22.50; C, 37.80; H, 6.10. Found: N, 22.48; C, 37.69; H, 6.06. Preparation of Mo(η3-C3H5)(CO)2(en){N4C(CHdCHCN)}, 4. Mo(η3-C3H5)(CO)2(en)(N3) (295.1 mg, 1.0 mmol) and fumaronitrile (85.54 mg, 1.1 mmol) were placed in a 50 mL flask. After degassing, about 25 mL of THF was transferred into the flask. The solution was warmed to room temperature and stirred at room temperature for 24 h, leading to a yellow-orange solution. The solvent removal gave rise to a yellow solid, which was washed with ether several times to remove the unreacted fumaronitrile followed by extraction with dichloromethane. The dichloromethane was removed, and the yellow solid was dissolved in a dichloromethane/acetonitrile mixture and layered with hexane for crystallization, affording 150.13 mg (40.2% yield) of 4 as yellow crystals. 1H NMR (CD3OD, -60 °C): δ 7.64 (d, 1H, J = 16.4 Hz, CH), 6.50 (d, 2H, J = 16.4 Hz, CH and NH2), 4.29 (br s, 1H, NH2), 4.09 (m, 1H, Hc), 3.91 (br s, 1H, NH2), 3.52 (br s, 1H, NH2), 3.28 (br s, 1H, Hs), 2.83 (br s, 1H, Hs), 2.63 (br s, 1H, CH2), 2.50 (br s, 1H, CH2), 2.39 (br s, 1H, CH2), 1.94 (br s, 1H, CH2) 1.30 (d, 1H, J = 9.6 Hz, Ha), 0.99 (d, 1H, J = 8.8 Hz Ha). 13C NMR (CD3OD, -60 °C): δ 226.1, 225.0 (CO), 159.0 (N4C), 137.0 (Cm), 117.2 (CN), 100.1 (Cp),

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69.4 (Cc), 55.4, 54.8 (Ct), 43.3, 41.2 (en). IR (KBr): 3335(m), 3291(m), 3247(m), 3219(m), 3159(w), 3034(w), 2989(m), 2956(w), 2939(w), 2890(w), 2879(w), 2219(m), 1917(vs), 1816(vs), 1637(m), 1604(m), 1588(m), 1456(m), 1403(vw), 1385(m), 1369(vw), 1319(w), 1286(w), 1262(vw), 1229(w), 1171(w), 1160(w), 1122(m), 1089(m), 1078(w), 1053(s), 1039(s), 1012(m), 982(m), 954(w), 927(vw), 902(vw), 880(vw), 869(w), 834(vw), 803(vw), 738(vw), 705(w), 677(vw), 666(vw), 644(vw), 611(vw), 576(w), 556(w), 529(w), 493(m), 471(w) cm-1. Anal. Calcd for C11H15MoN7O2: N, 26.27; C, 35.39; H, 4.05. Found: N, 26.19; C, 35.32; H, 4.10. Preparation of Mo(η3-C3H5)(CO)2(dppe)(N3), 5. In a drybox, 362.1 mg (1.0 mmol) of Mo(η3-C3H5)(CO)2(CH3CN)2(Br) and 420.5 mg (1.0 mmol) of 1, 2-bis(diphenylphosphino)ethane were placed in a 50 mL flask. The flask was evacuated, and about 25 mL of CH2Cl2 was transferred into the flask at -78 °C. The flask was warmed to room temperature, and the stirring was continued for an additional 6 h, giving rise to a red solution of Mo(η3-C3H5)(CO)2(dppe)Br. A NaN3 solution (131.0 mg, 2.0 mmol of NaN3 in 10 mL of CH3OH) was added dropwise into this red solution within a 5 min period. The mixture was kept stirring at room temperature for an additional 24 h, leading to a clear red solution. Following the solvent removal the resulting red solid was extracted with CH2Cl2 several times. The red-orange solid obtained from the extract after dichloromethane removal was dissolved in CH2Cl2 and layered with CH3OH for crystallization, giving rise to 410.9 mg (64.1% yield) of 5 as red crystals. 31P NMR (d6-acetone): δ 44.7. 31P NMR (d6acetone, -90 °C): δ 44.31, 41.09. 1H NMR (d6-acetone): δ 7.46-7.75 (m, 20H, C6H5), 3.57 (m, 1H, Hc), 3.42 (m, 2H, Hs), 2.86 (m, 2H, Hb), 2.32 (m, 2H, Hd), 1.74 ppm (d, J = 10.0 Hz, 2H, Ha). 13C NMR (d6-acetone): δ 224.14 (CO), 133.20, 133.15, 133.10, 132.19, 132.15, 132.10, 130.87, 130.12, 129.02, 128.98, 128.66, 128.62, 128.57 (C6H5), 79.48 (Cc), 57.65 (Ct), 24.87 (t, JC-P = 19.2 Hz, CH2). IR (KBr): 3380(vw), 3332(vw), 3139(vw), 3079(vw), 3052(vw), 3023(vw), 2994(vw), 2960(vw), 2925(vw), 2672(vw), 2057(vs), 1984(vw), 1930(vs), 1851(vs), 1583(vw), 1569(vw), 1542(vw), 1482(w), 1465(vw), 1432(m), 1405(vw), 1384(vw), 1338(vw), 1307(vw), 1278(vw), 1263(vw), 1245(vw), 1230(vw), 1186(w), 1159(vw), 1095(vw), 1068(vw), 1025(vw), 995(vw), 970(vw), 948(vw), 919(vw), 871(w), 808(vw), 816(vw), 744(m), 696(s), 667(w), 646(w), 615(vw), 592(vw), 561(vw), 526(m), 476(w), 462(vw), 422(w) cm-1. Anal. Calcd for C31H29MoN3O2P2: N, 6.63; C, 58.78; H, 4.61. Found: N, 6.63; C, 58.74; H, 4.62. Preparation of Mo(η3-C3H5)(CO)2(en){(N3C2)(CO2CH3)2}, 6. Mo(η3-C3H5)(CO)2(en)(N3) (295.1 mg, 1.0 mmol) and dimethyl acetylenedicarboxylate (156.53 mg, 1.1 mmol) were placed in a 50 mL flask. After degassing, about 25 mL of CH3CN was transferred into the flask. The flask was warmed to room temperature, and the stirring was continued for an additional 12 h when the mixture turned red-brown. The solution was concentrated, and the solvent was allowed to evaporate slowly at room temperature. Crystallization afforded 200.2 mg (46.0% yield) of 6 as yellow crystals. 1H NMR (d8-THF,

Liu et al. -100 °C): δ 6.40 (br s, 1H, NH2), 4.39 (br s, 1H, NH2), 4.22 (m, 1H, Hc), 4.04 (br s, 1H, NH2), 3.74 (s, 6H, CH3), 3.42 (br s, 1H, NH2), 3.12 (br s, 1H, Hs), 2.95 (br s, 1H, Hs), 2.52 (br s, 2H, CH2), 2.40 (br s, 1H, CH2) 1.64 (br s, 1H, CH2) 1.21 (d, J = 9.5 Hz, 1H, Ha), 0.92 (d, J = 8.9 Hz, 1H, Ha). 13C NMR (d8-THF, -100 °C): δ 225.3, 223.8 (CtO), 160.5 (CdO), 137.3, 126.2 (N3C2), 68.5 (Cc), 54.0 (Ct), 49.3 (CH3), 42.1, 39.5 (en). IR (KBr): 3440(m), 3394(w), 3309(m), 3293(m), 3266(m), 3220(m), 3127(w), 3070(vw), 3031(vw), 3008(w), 2973(w), 2950(w), 2911(w), 2896(w), 2842(w), 1928(vs), 1828(vs), 1700(s), 1650(m), 1577(m), 1554(w), 1515(m), 1450(m), 1411(w), 1369(w), 1334(m), 1288(w), 1241(m), 1207(m), 1176(m), 1145(m), 1099(m), 1049(m), 1018(w), 998(w), 968(w), 937(w), 921(vw), 887(w), 871(w), 829(w), 806(m), 775(w), 732(w) cm-1. Anal. Calcd for C13H19MoN5O6: N, 16.01; C, 35.71; H, 4.38. Found: N, 16.00; C, 35.62; H, 4.42. Preparation of Mo(η3-C3H5)(CO)2(dppe){N3C2(CO2CH3)2}, 7. Mo(η3-C3H5)(CO)2(dppe)(N3) (637.1 mg, 1.0 mmol) and dimethyl acetylenedicarboxylate (142.3 mg, 1.0 mmol) were placed in a 50 mL flask. After degassing, about 20 mL of CH2Cl2 was transferred into the flask at -78 °C. The flask was warmed to room temperature, and the stirring was continued for one day. This deep-red solution was concentrated and evaporated at room temperature for crystallization, giving rise to 608.0 mg (78.2% yield) of 7 as orange crystals. 31P NMR (CD2Cl2): δ 51.10. 31P NMR (CD2Cl2, -90 °C): δ 47.07, 46.10. 1 H NMR (CDCl3): δ 7.65-7.13 (m, 20H, C6H5), 4.19 (m, 1H, Hc), 4.13 (br s, 2H, Hs), 3.73 (s, 6H, CH3), 3.41 (m, 2H, Hb), 2.45 (m, 2H, Hd), 2.23 (d, J = 9.2 Hz, 2H, Ha). 13C NMR (CDCl3): δ 224.86 (CtO), 162.38 (CdO), 138.47 (N3C2), 135.49, 135.12, 132.69, 132.64, 132.59, 131.98, 131.94, 131.89, 131.70, 131.50, 131.32, 130.37, 129.79, 128.87, 128.83, 128.78, 128.13, 128.09, 128.04 (C6H5), 86.61 (Cc), 61.19 (Ct), 51.46 (CH3), 26.19 (t, JC-P = 20.3 Hz, CH2). IR (KBr): 3424(vw), 3139(vw), 3073(vw), 3058(vw), 3021(vw), 3000(vw), 2948(w), 2931(vw), 2906(vw), 2861(vw), 2832(vw), 2088(vw), 2073(vw), 2042(vw), 2015(vw), 1940(vs), 1849(vs), 1716(s), 1655(vw), 1637(vw), 1585(vw), 1571(vw), 1542(vw), 1502(vw), 1484(w), 1446(w), 1434(m), 1386(vw), 1336(vw), 1315(vw), 1272(w), 1230(s), 1197(s), 1172(s), 1128(vw), 1091(s), 1025(w), 998(w), 989(w), 968(vw), 954(w), 921(vw), 879(w), 833(w), 821(w), 800(w), 775(w), 754(m), 742(w), 734(w), 713(w), 700(s), 659(w), 615(w), 595(w), 586(w), 563(w), 536(w), 524(s), 482(m), 455(w), 412(w) cm-1. Anal. Calcd for C37H35MoN3O6P2: N, 5.42; C, 57.30; H, 4.55. Found: N, 5.38; C, 57.17; H, 4.56.

Acknowledgment. This work was supported by the National Science Council of the ROC through Grant NSC 99-2113-M-259-001-MY3. Supporting Information Available: Tables of crystallographic data, positional and thermal parameters, and interatomic distances and angles for 1-7. This material is available free of charge via the Internet at http://pubs.acs.org.