When Sterics Overcome Electronics: An Unusual Haptotropic P→N

84

Organometallics 2011, 30, 84–91 DOI: 10.1021/om1007709

When Sterics Overcome Electronics: An Unusual Haptotropic PfN Pentacarbonyltungsten Shift Holger Helten,† Gregor Schnakenburg,† J€ org Daniels,† Anthony J. Arduengo III,*,‡ and Rainer Streubel*,† †

Institut f€ ur Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universit€ at Bonn, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany, and ‡Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States Received August 8, 2010

Acid-induced ring expansion of 2H-azaphosphirene complexes 1a-c with HCN is described. These reactions yielded 2H-1,4,2-diazaphosphole complexes 2a-c as a mixture with their κN-coordination isomers 3a-c in different ratios, depending upon the steric demand of the C3-substituent on the diazaphosphole ring. DFT calculations revealed that the isomerization can proceed in one step via a haptotropic PfN W(CO)5 shift. When a mixture of 2b and 3b was heated in acetonitrile, complete decomplexation with formation of 2H-1,4,2-diazaphosphole 5 was observed. Reaction of 2b and 3b with tetra-n-butylammonium fluoride in the presence of [Et3NH][OTf] led to complete desilylation of the P-CH(SiMe3)2 substituent and formation of complex 6, showing only κP-coordination. In addition to NMR, IR, and UV/vis spectra, the single-crystal X-ray diffraction structures of 2a,b and 6 are discussed. The synthesis of five-membered N-heterocycles such as triazoles using click reactions1 has received increasing interest in recent years because it usually follows a facile and reliable protocol, i.e., [3þ2] cycloaddition of azides and alkynes, and thus can be applied to various fields of research.2 Nonetheless, this chemistry has yet to be extended to heavier main group element heterocycles. Recently, a novel and facile methodology for ring expansion was developed for 2H-azaphosphirene complexes (I),3 leading to 2H-1,4,2-diazaphosphole complexes (II) (Scheme 1). This process employs formal insertion of a nitrile into the P-N bond of I using triflic acid (CF3SO3H or TfOH) and, subsequently, a nitrogen base such as triethylamine or pyridine.4 Detailed experimental and computational studies on a plausible pathway of this ring expansion reaction were presented,4a which revealed that complexes II are most probably formed via the intermediates III and IV. In the first step the 2H-azaphosphirene complex (I) is protonated at nitrogen by *To whom correspondence should be addressed. E-mail: aj@ ajarduengo.net; [email protected]. (1) (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem. 2001, 113, 2056. Angew. Chem., Int. Ed. 2001, 40, 2004; (b) Wu, P.; Feldman, A. K.; Nugent, A. K.; Hawker, C. J.; Scheel, A.; Voit, B.; Pyun, J.; Frechet, J. M. J.; Sharpless, K. B.; Fokin, V. V. Angew. Chem. 2004, 116, 4018. Angew. Chem., Int. Ed. 2004, 43, 3928. (c) Yoo, E. J.; Ahlquist, M.; Kim, S. H.; Bae, I.; Fokin, V. V.; Sharpless, K. B.; Chang, S. Angew. Chem. 2007, 119, 1760. Angew. Chem., Int. Ed. 2007, 46, 1730; (d) Hein, J. E.; Tripp, J. C.; Krasnova, L. B.; Sharpless, K. B.; Fokin, V. V. Angew. Chem. 2009, 121, 8162. Angew. Chem., Int. Ed. 2009, 48, 8018. (2) (a) Cronin, S.; Chandrasekar, P. H. J. Antimicrob. Chemother. 2010, 65, 410. (b) Holub, J. M.; Kirshenbaum, K. Chem. Soc. Rev. 2010, 39, 1325. (3) (a) Streubel, R. Coord. Chem. Rev. 2002, 227, 175. (b) Streubel, R. Top. Curr. Chem. 2003, 223, 92. (4) (a) Helten, H.; Engeser, M.; Gudat, D.; Schilling, R.; Schnakenburg, G.; Nieger, M.; Streubel, R. Chem.;Eur. J. 2009, 15, 2602. (b) Helten, H.; Daniels, J.; Nieger, M.; Streubel, R. New J. Chem. 2010, 34, 1593. pubs.acs.org/Organometallics

Published on Web 12/08/2010

Scheme 1. 2H-Azaphosphirene Complexes (I), 2H-1,4,2-Diazaphosphole Complexes (II), and Intermediates III and IV of the Formation of IIa

a [M] denotes a M(CO)5 moiety (M = Cr, Mo, W); R, R0 , and R00 denote common organic substituents.

the acid to give the phosphenium complex III. The latter is easily attacked by a nitrile at its highly electrophilic phosphorus center, resulting in the formation of IV, which then undergoes cyclization to yield an N-protonated 2H-1,4,2-diazaphosphole complex. Upon deprotonation the 2H-1,4,2-diazaphosphole complexes II are finally obtained. This new concept could also be applied to the synthesis of a 2,3-dihydro-1,3-azaphosphete and a 3H-1,3-azaphosphole complex via insertion of an isonitrile or an alkyne, respectively.5 Furthermore, this chemistry could easily be extended to oxaphosphirane6 and azaphosphiridine7 complexes, thus firmly establishing a click chemistry concept to the field of phosphorus heterocyclic chemistry. Acid-induced reactions of differently substituted 2H-azaphosphirene complexes with hydrogen cyanide, each affording (5) Helten, H.; von Frantzius, G.; Schnakenburg, G.; Daniels, J.; Streubel, R. Eur. J. Inorg. Chem. 2009, 2062. (6) (a) Helten, H.; Marinas Perez, J.; Daniels, J.; Streubel, R. Organometallics 2009, 28, 1221. (b) Marinas Perez, J.; Helten, H.; Donnadieu, B.; Reed, C. A.; Streubel, R. Angew. Chem. 2010, 122, 2670. Angew. Chem., Int. Ed. 2010, 49, 2615. (7) Fankel, S.; Helten, H.; von Frantzius, G.; Schnakenburg, G.; Daniels, J.; Chu, V.; M€ uller, C.; Streubel, R. Dalton Trans. 2010, 39, 3472. r 2010 American Chemical Society

Article

Organometallics, Vol. 30, No. 1, 2011

Table 1. Selected 31P{1H} and 13C{1H} NMR Spectroscopic Data for 2a-c, 3a-c,a 5,b and 6b

Scheme 2. Reactions of 2H-Azaphosphirene Complexes 1a-c with HCN and TfOH and Subsequently with Pyridine

2a δP |JWP|/Hz δC(Cexo) |1JPC|/Hz δC(C3) |1þ4JPC|/Hz δC(C5) |2þ3JPC|/Hz c

mixtures of κP- and κN-bound coordination isomers of II of various ratios depending on the substitution pattern, are presented herein. Variable-temperature NMR measurements evidence a chemical equilibrium between these haptomers. When such complexes are heated in acetonitrile, decomplexation occurs. Additionally, desilylation, associated with a haptotropic NfP pentacarbonyltungsten shift, is observed.

Results and Discussion Reactions of 2H-azaphosphirene complexes 1a-c with HCN in CH2Cl2 were achieved using the TfOH/base protocol, i.e., the addition of a TfOH solution at -78 °C and, after warming to ambient temperature, addition of pyridine (Scheme 2). Interestingly, these reactions afforded not only the expected products, the 2H-1,4,2-diazaphosphole complexes 2a-c, but, in each case, mixtures of two coordination isomers thereof: 2a and 3a (ratio 5: 1), 2b and 3b (ratio 24: 1), and 2c and 3c (ratio 1: 2). Complexes 3a-c constitute the first examples of κN-bonded 2H-1,4,2-diazaphosphole complexes. The isomeric complexes could not be separated, and the NMR spectra of the mixtures of 2a8 and 3a and of 2b and 3b revealed the signals of both complexes with unchanged ratios after several purification steps, even after recrystallizing and redissolving. Nevertheless, elemental analyses of the purified mixtures yielded satisfactory results, and the products were characterized by various analytical methods (multinuclear NMR experiments, mass spectrometry, IR and UV/vis spectroscopy); the structures of 2a,b were confirmed by single-crystal X-ray diffraction studies (Figure 2; for the structure of 2a see Supporting Information, Figure S.1). Complexes 2c and 3c decomposed during column chromatography. Repetition of the reaction, removing all volatiles in vacuo, dissolving the residue in diethyl ether, and separation of the pyridinium triflate by filtration, yielded a crude product that provided consistent NMR spectroscopic information. The 1H, 13C{1H}, 31P{1H}, and 29Si{1H} NMR spectra of each mixture showed two sets of resonance signals according to the isomeric compounds, and the data for each complex could unambiguously be assigned by means of various shift-correlated 2D NMR experiments (Table 1). The data for 2a-c were easily assigned. Their 31P NMR chemical shifts are generally observed at 105-108 ppm with (8) It is noteworthy that complex 2a could not be synthesized via our previously developed SET protocol using ferricenium salts; see: Helten, H.; Neumann, C.; Espinosa, A.; Jones, P. G.; Nieger, M.; Streubel, R. Eur. J. Inorg. Chem. 2007, 4669.

85

105.6 227.6 17.3 3.9 203.0 22.0 163.7 7.8

3a

2b

121.2 105.4 232.3 17.9 18.1 55.0 3.4 208.5 195.7 35.5 21.1 170.3 162.9 14.2 9.2

c

3b

2c

118.6 107.6 226.3 17.9 17.9 56.6 9.4 199.5 210.1 35.9 22.3 171.0 161.7 12.0 8.1

c

3c

5

116.3 96.1 16.9 18.8 56.3 45.9 215.4 199.3 38.5 44.6 171.4 162.2 12.0 3.6

c

6 95.7 240.3 17.7 24.9 195.0 8.7 165.5 10.3

a See Scheme 2 for atom numbering; all data in C6D6. b See Scheme 4. Not resolved.

tungsten-phosphorus coupling constant magnitudes of ca. 230 Hz. The 13C resonances of the C3 centers appear at very low field (>195 ppm) and exhibit |2þ3JPC| values of about 21-22 Hz. The C5 centers resonate at considerably higher field (162-163 ppm) and have very small phosphorus-carbon coupling constant magnitudes (8-9 Hz), thus indicating that at least two scalar couplings contribute to these values. The proton at C5 resonates at 7.9-8.3 ppm, showing a common magnitude about 34 Hz of the phosphorusproton coupling constant for 2a-c. In the cases of the κN-coordinated heterocycles 3a-c the C5H proton resonates at slightly lower field (8.3-8.7 ppm), and the corresponding phosphorus-proton coupling constant magnitudes are only about 7 Hz. The 31P resonances appear downfield from those of 2a-c. These phosphorus resonances are slightly broadened with no resolved 183W, 31 P, and 31P,1H couplings. The ring carbon atoms show 13C resonances downfield from those of complexes 2a-c with significantly larger phosphorus-carbon coupling constant magnitudes. Also the CO carbon centers resonate at slightly lower field than the P-metalated analogues. Both signals appear as doublets, and the magnitudes of the phosphoruscarbon coupling constants of cis- and trans-CO carbons are virtually identical (2-3 Hz). These coupling constants differ from the typical pattern observed for κP-complexes such as 2a-c, where the trans-CO carbons exhibit |2JPC| values of 22-23 Hz. The P-bound CH carbon resonates in the same range as that of complexes 2a-c (17-18 ppm), but the magnitude of its phosphorus-carbon coupling constant is considerably larger (55-57 Hz). An increase of |1JPC| values is generally observed upon removal of a κP-bonded W(CO)5 fragment as a consequence of the formation of a lone pair of electrons at phosphorus.9 An interesting aspect of the spectra of 3a-c is that for the two trimethylsilyl groups only one 1H signal was observed; the same phenomenon was found also in the 13C{1H} and 29Si{1H} NMR spectra. This observation suggests an inversion of the phosphorus center that is fast on the NMR time scale. The identification of which of the two nitrogen centers donates to the transition metal in complexes 3a-c could be made on the basis of 2D 1H,15N HMBC NMR experiments (see Supporting Information, Figures S.2-S.4). The spectrum of a mixture of 2a and 3a displayed two sets of correlation signals, which allow the assignment of the 15N NMR data to the N1 and N4 centers of both complexes. (9) Berger, S., Braun, S., Kalinowski, H.-O. NMR-Spektroskopie von Nichtmetallen, 31P-NMR-Spektroskopie, Vol. 3; Georg Thieme: Stuttgart, 1993. (10) Berger, S.; Braun, S.; Kalinowski, H.-O. NMR-Spektroskopie von Nichtmetallen, 15N-NMR-Spektroskopie, Vol. 2; Georg Thieme: Stuttgart, 1992; p 25ff.

86

Organometallics, Vol. 30, No. 1, 2011

Scheme 3. N-Donor Complexes 3a and 411b and Their 15N NMR Coordination Shiftsa

a 3a: ΔδN = δN(κN-complex) - δN(κP-complex), in CDCl3; 4: ΔδN = δN(complex) - δN(ligand), in H2O.

Both nitrogen atoms of 2a show correlations with the C5H proton, and only one nitrogen (at δN = -86) shows a second correlation signal with the CH proton of the CH(SiMe3)2 group. This nitrogen, which features a large phosphorusnitrogen coupling constant magnitude (54 Hz), is unambiguously assigned to the N1 center. The N4 center resonates at δN = -64 and displays a phosphorus-nitrogen coupling constant of 9 Hz. These data are in the same range as those for other κP-bound 2H-1,4,2-diazaphosphole complexes reported previously.4a Also the nitrogen centers of complex 3a show correlations with its C5H proton. While the N4 resonance (δN = -53, |2þ3JPN| = 24 Hz) is only marginally downfield shifted with respect to 2a (ΔδN = þ11), the N1 center (which also shows a correlation with the CH(SiMe3)2 group) resonates at significantly higher field (δN = -165, |1þ4JPN| = 68 Hz). That the 2H1,4,2-diazaphosphole ligand of 3a donates to the pentacarbonyltungsten fragment via N1 follows from these observations (a PfN1 metal shift causes a shielding of this nitrogen atom by ΔδN = -79). Negative 15N NMR coordination shifts are generally observed for transition metal-coordinated N-donors.10-12 For instance, in the platinum complex 4 (Scheme 3) the 15N resonance of ammonia experiences a high-field shift by ΔδN = -46.4 relative to free ammonia, and the resonance of the imine center of the 1-methylimidazole ligand is highfield shifted by an even larger value of ΔδN = -91.9, consistent with the higher s-orbital character in the coordinating N lone pair.11b On the other hand, the signal of the nonligated N-methyl center is slightly low-field shifted with respect to the uncomplexed heterocycle (ΔδN = þ4.7).11b (11) (a) Nee, M.; Roberts, J. D. Biochemistry 1982, 21, 4920. (b) Alei, M., Jr.; Vergamini, P. J.; Wageman, W. E. J. Am. Chem. Soc. 1979, 101, 5415. (c) Appleton, T. G.; Hall, J. R.; Ralph, S. F.; Thompson, C. S. M. Aust. J. Chem. 1988, 41, 1425. (d) Appleton, T. G.; Hall, J. R.; Ralph, S. F. Inorg. Chem. 1988, 27, 4435. (e) Pazderski, L.; Szzyk, E.; Sitkowski, J.; Kamienski, B.; Kozerski, L.; Tousek, J.; Marek, R. Magn. Reson. Chem. 2006, 44, 163. (f) Schurko, R. W.; Wasylishen, R. E. J. Phys. Chem. A 2000, 104, 3410. (g) van Stein, G. C.; van Koten, G.; Vrieze, K.; Brevard, C.; Spek, A. L. J. Am. Chem. Soc. 1984, 106, 4486. (h) Wrackmeyer, B.; Schamel, K.; Herberhold, M. Z. Naturforsch. B 1989, 44, 55. (12) (a) Hagen, R.; Warren, J. P.; Hunter, D. H.; Roberts, J. D. J. Am. Chem. Soc. 1973, 95, 5712. (b) Motschi, H.; Pregosin, P. S.; Venanzi, L. M. Helv. Chim. Acta 1979, 62, 667. (c) van der Poel, H.; van Koten, G.; Grove, D. M.; Pregosin, P. S.; Ostoja Starzewski, K. A. Helv. Chim. Acta 1981, 64, 1174. (d) Boreham, C. J.; Broomhead, J. A.; Fairlie, D. P. Aust. J. Chem. 1981, 34, 659. (e) Watabe, M.; Takahashi, M.; Yamasaki, A. Inorg. Chem. 1983, 22, 2650. (f) van Stein, G. C.; van Koten, G.; Vrieze, K.; Spek, A. L.; Klop, E. A.; Brevard, C. Inorg. Chem. 1985, 24, 1367. (g) Bissinger, H.; Beck, W. Z. Naturforsch. B 1985, 40, 507. (h) Pregosin, P. S.; R€uedi, R.; Anklin, C. Magn. Reson. Chem. 1986, 24, 255. (i) Isobe, K.; Nanjo, K.; Nakamura, Y.; Kawaguchi, S. Bull. Soc. Chem. Jpn. 1986, 59, 2141. (j) Nakashima, Y.; Muto, M.; Kawano, K.; Kyogoku, Y.; Yoshikawa, Y. Bull. Soc. Chem. Jpn. 1989, 62, 2455.

Helten et al.

The 2D 1H,15N HMBC NMR spectrum of the mixture of 2b and 3b revealed only the 15N NMR spectroscopic data for κP-complex 2b, as it is present in large excess here. The data are almost identical to those for complex 2a; the differences in their chemical shifts are below 2 ppm (δN(N1) = -88, |1þ4JPN| = 60 Hz; δN(N4) = -66, |2þ3JPN| = 8 Hz). For the haptomeric complex 3b a signal was detected arising only from the correlation of N4 at δN = -56 with the C5H proton. Complementary to this result, in the case of the mixture of 2c and 3c correlation signals of both nitrogen centers were detected for the κN-coordinated derivative 3c, which in this case is the major isomer. The 15N data thus obtained (δN(N1) = -170, |1þ4JPN| = 65 Hz; δN(N4) = -60 |2þ3JPN| = 6 Hz) are very similar to those for complex 3a. The mass spectra of the mixtures of the isomeric complexes 2a and 3a and of 2b and 3b revealed successive losses of CO ligands and even loss of the entire W(CO)5 moiety. The IR spectra (KBr) showed one set of CtO stretch vibration bands for each mixture, most likely assigned to the major haptomers 2a,b. They both show a single, well-separated band at approximately 2070 cm-1 and another band with low intensity at ca. 1985 cm-1, which can be assigned to normal modes of local A1 and B1 symmetry, respectively. In the range 1900-1950 cm-1 three very intense and partially overlapping bands appear, which are attributable to vibrations of local A1 and E symmetry. The bands of κN-complexes 3a,b presumably are overlapped by the former and/or have intensities too low to be observed. The UV/vis absorption spectrum of the mixture of 2b and 3b (see Supporting Information, Figure S.7) shows a lowenergy transition at λmax = 438 nm, which is assigned, on the basis of recently published results on related systems,4b to a metal-diazaphopshole-ligand charge transfer (MLCT) process. A more intense π-π* absorption appears with λmax = 347 nm. Presumably both bands are assigned to the major isomer, 2b. In the spectrum of 2a and 3a (see Supporting Information, Figure S.6) two partially overlapping lowenergy bands are visible (λmax = 433 and 398 nm) as well as two partially overlapping bands in the range of π-π* transitions (λmax = 312 and 296 nm). In this case they may be assigned to the κP- and the κN-isomer, 2a and 3a, respectively. Noteworthy are the extremely long-wave optical end absorptions observed in both spectra: λonset = 619 (2a, 3a) and 601 nm (2b, 3b). According to time-dependent (TD) DFT calculations (see Supporting Information), this observation is a result of the presence of the κN-coordinated isomers, which exhibit energetically very low-lying MLCT transitions with considerable oscillator strengths. Variable-temperature 31P{1H} NMR measurements were carried out on a toluene solution of the mixture of the two haptomeric complexes 2a and 3a (see Supporting Information, Figure S.5). This study revealed that the relative amount of κN-complex 3a (as estimated by signal integration) slightly increased with temperature. Complex 3a constituted only 8% at -10 °C, ca. 16% at þ30 °C, and about 21% at þ60 °C. This observation evidences an interconversion of both species and, thus, the existence of a chemical equilibrium between the two haptomeric 2H1,4,2-diazaphosphole complexes in solution. Since the introduction of the concept of hemilability in ligand design by Jeffrey and Rauchfuss,13 there has been an increasing interest in synthesis and use of hemilabile ligands, (13) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658.

Article

as the different features associated with each donor atom confer unique reactivity to their metal complexes.14 Stalke and co-workers have established so-called Janus Head ligands, which combine both hard and soft coordination sites. Such ligands are able to donate via either nitrogen, phosphorus, carbon, or more than one center to one metal,15,16 or they form heterobimetallic complexes with different metal fragments.16,17 Equilibria between N and P as well as N,P coordination modes of chelating ligands have also been reported.18 However, the observations made for complexes 2a, 3a, 2b, 3b, 2c, and 3c are, apparently, unprecedented examples where equilibria were evidenced between coordination isomers involving both nitrogen and phosphorus donor centers that belong to one ring system and donate to the same metal fragment. A reasonable explanation for the observed haptotropic PfN metal shift is the steric congestion at phosphorus in the κP-complexes due to repulsion between the W(CO)5 fragment and the aryl substituent at C3, being most pronounced with the bulky ferrocenyl group in 2c. This interpretation is in agreement with the thermal behavior of the state of the equilibrium, since an increase of internal movement should cause further destabilization of the κP-complexes with increasing temperature. The reason that a haptotropic PfN metal shift was not observed in the cases of C5-substituted 2H-1,4,2-diazaphosphole tungsten complexes4 presumably is that the presence of a substituent at C5 makes the formation of a κN-complex less favorable for steric reasons. The rearrangement reaction was modeled by means of DFT methods (B3LYP/def2-TZVP/ECP-60-MWB (W), COSMO (ε = 8.93; CH2Cl2)//RI-BP86/def2-SV(P)/ECP60-MWB (W), COSMO) on the most sterically demanding system, the 3-ferrocenyl-substituted system (2c f 3c), as a good case in point. This revealed that the haptotropic PfN W(CO)5 shift can proceed in one step via the transition structure depicted in Figure 1 and that the barrier is remarkably low (ΔGq298 = 47.0 kJ 3 mol-1). When a mixture of complexes 2b and 3b was heated in acetonitrile at 75 °C (Scheme 4, i), after 5 min the resonance of 3b was no longer detected by 31P NMR reaction monitoring. Instead, a signal at δ = 96.1 (|3þ4JPH| = 19.1 Hz) showing no 183W,31P coupling, assigned to the free ligand (14) (a) Davies, J. A.; Hartley, F. R. Chem. Rev. 1981, 81, 79. (b) Braunstein, P.; Naud, F. Angew. Chem. 2001, 113, 702. Angew. Chem., Int. Ed. 2001, 40, 680. (c) Braunstein, P.; Boag, N. M. Angew. Chem. 2001, 113, 2493. Angew. Chem., Int. Ed. 2001, 40, 2427. (d) Gade, L. H. J. Organomet. Chem. 2002, 661, 85. (e) Piers, W. E.; Emslie, D. J. H. Coord. Chem. Rev. 2002, 233-234, 131. (f) Elsevier, C. J.; Reedijk, J.; Walton, P. H.; Ward, M. D. Dalton Trans. 2003, 1869. (15) (a) Pfeiffer, M.; Stey, T.; Jehle, H.; Kl€ upfel, B.; Malisch, W.; Chandrasekhar, V.; Stalke, D. Chem. Commun. 2001, 337. (b) Murso, A.; Stalke, D. Eur. J. Inorg. Chem. 2004, 4272. (c) Murso, A.; Stalke, D. Dalton Trans. 2004, 2563. (d) Stey, T.; Stalke, D. Z. Anorg. Allg. Chem. 2005, 631, 2931. (e) Stey, T.; Pfeiffer, M.; Henn, J.; Pandey, S. K.; Stalke, D. Chem.; Eur. J. 2007, 13, 3636. (16) Baier, F.; Fei, Z.; Gornitzka, H.; Murso, A.; Neufeld, S.; Pfeiffer, M.; R€ udenauer, I.; Steiner, A.; Stey, T.; Stalke, D. J. Organomet. Chem. 2002, 661, 111. (17) Stey, T.; Henn, J.; Stalke, D. Chem. Commun. 2007, 413. (18) (a) Arena, C. G.; Bruno, G.; De Munno, G.; Rotondo, E.; Drommi, D.; Faraone, F. Inorg. Chem. 1993, 32, 1601. (b) Amatore, C.; Fuxa, A.; Jutand, A. Chem.;Eur. J. 2000, 6, 1474. (19) In reactions of 2H-1,4,2-diazaphosphole complexes under different conditions, 31P NMR resonances 2σ(I)) = 0.0274, wR2 (for all data) = 0.0584, S = 0.967, max./min. residual electron density = 0.977/-1.342 e 3 A˚-3. Crystal structure data for complex 2b (C18H23N2O5PSSi2W): crystal size 0.33  0.17  0.09 mm, monoclinic, C2/c, a = 27.6553(6) A˚ , b = 8.3362(2) A˚, c = 22.5825(5) A˚ , β = 110.8330(10)°, V=4865.80(19) A˚3, Z=8, Fcalc = 1.776 Mg 3 m-3, 2θmax=55°, collected (independent) reflections=23 882 (5469), Rint = 0.0639, μ = 5.029 mm-1, 330 refined parameters, 0 restraints, R1 (for I > 2σ(I)) = 0.0245, wR2 (for all data) = 0.0556, S = 1.034, max./min. residual electron density=1.250/ -1.755 e 3 A˚-3. Crystal structure data for complex 6 (C12H7N2O5PSW): crystal size 0.43  0.17  0.04 mm, triclinic, P1, a = 6.7855(2) A˚, b = 10.4987(4) A˚, c = 11.5844(4) A˚, R = 95.964(2)°, β = 100.540(2)°, γ = 107.410(2)°, V = 763.02(5) A˚3, Z = 2, Fcalc = 2.203 Mg 3 m-3, 2θmax = 51°, collected (independent) reflections = 14 278 (2824), Rint = 0.0522, μ = 7.834 mm-1, 224 refined parameters, 0 restraints, R1 (for I > 2σ(I)) = 0.0209, wR2 (for all data) = 0.0429, S = 1.016, max./min. residual electron density = 0.753/-1.858 e 3 A˚-3. Crystallographic data of 2a,b and 6 have been deposited at the Cambridge Crystallographic Data Centre under the numbers CCDC-785536 (2a), CCDC-786051 (2b), and CCDC-786052 (6). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Theoretical Methods. DFT calculations were carried out with the Turbomole V5.9.1 program package.26a Optimizations26b were done with the local Slater-Dirac exchange27 and the correlation energy density functional (No.V) by Vosko, Wilk, and Nusair (VWN (V))28 together with Becke’s gradient-corrected exchange functional B8829 in combination with the gradient-corrected correlation functional by Perdew (P86)30 within the RI approximation31 and the valence-double-ζ basis set def2-SV(P).32 For tungsten the effective core potential ECP60-MWB33 was employed. During the optimizations the influence of the polar solvent was taken into account by employing the COSMO approach34 with ε = 8.93. For cavity construction the atomic radii of Bondi,35 obtained from cystallographic data, were used; the atomic radius of tungsten was set to 2.2230 A˚. The transition state was located by using a TRIM algorithm.36 An (26) (a) Ahlrichs, R.; B€ar, M.; H€aser, M.; Horn, H.; K€ olmel, C. Chem. Phys. Lett. 1989, 162, 165. (b) v. Arnim, M.; Ahlrichs, R. J. Chem. Phys. 1999, 111, 9183.

Organometallics, Vol. 30, No. 1, 2011

91

excellent initial guess was obtained through relaxed surface scans along the major reaction coordinate. All stationary points were characterized by numerical vibrational frequencies calculations.37 Single-point calculations were carried out using the three-parameter hybrid functional Becke338 (B3) in combination with the gradient-corrected correlation functional by Lee, Yang, and Parr39 (LYP) using the valence-triple-ζ basis set def2-TZVP,40 and ECP-60-MWB for tungsten. The COSMO approach was employed with the same parameters as used for optimizations. Zero-point corrections and thermal corrections to free energies were adopted from frequency calculations on the optimization level (RI-BP86/def2-SV(P)/ECP-60-MWB(W), COSMO). It has been shown that this approach is appropriate for reactions of epoxide, aziridine, and thiirane with methanethiolate.41

Acknowledgment. This work was supported by a “DAAD Doktorandenstipendium”. We also thank the Deutsche Forschungsgemeinschaft (SFB 624, “Template”), The National Science Foundation (CHE-0413521, CHE0342921), the Fonds der Chemischen Industrie (Kekule grant for H.H.), and the COST action CM0802 “PhoSciNet” for financial support and the John von Neumann Institute for Computing (HBN12) for computing time. Supporting Information Available: Depiction of the structure of 2a, 2D 1H,15N HMBC NMR spectra of the mixtures of 2a and 3a, 2b and 3b, and 2c and 3c, variable-temperature 31P{1H} NMR spectra of the mixture of 2a and 3a, and the results of TDDFT calculations. This material is available free of charge via the Internet at http://pubs.acs.org. (27) (a) Dirac, P. A. M. Proc. R. Soc. (London) A 1929, 123, 714. (b) Slater, J. C. Phys. Rev. 1951, 81, 385. (28) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200. (29) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (30) Perdew, J. P. Phys. Rev. B 1986, 33, 8822. € (31) (a) Eichkorn, K.; Treutler, O.; Ohm, H.; H€aser, M.; Ahlrichs, R. € Chem. Phys. Lett. 1995, 240, 283. (b) Eichkorn, K.; Treutler, O.; Ohm, H.; H€aser, M.; Ahlrichs, R. Chem. Phys. Lett. 1995, 242, 652. (c) Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor. Chem. Acc. 1997, 97, 119. (32) Sch€afer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571. (33) Andrae, D.; H€aussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123. €rmann, G. J. Chem. Soc., Perkin Trans. 2 1993, (34) Klamt, A.; Sch€ uu 799. (35) Bondi, A. J. Phys. Chem. 1964, 68, 441. (36) Helgaker, T. Chem. Phys. Lett. 1991, 182, 503. (37) (a) Deglmann, P.; Furche., F.; Ahlrichs, R. Chem. Phys. Lett. 2002, 362, 511. (b) Deglmann, P.; Furche, F. J. Chem. Phys. 2002, 117, 9535. (c) Deglmann, P.; May, K.; Furche, F.; Ahlrichs, R. Chem. Phys. Lett. 2004, 384, 103. (38) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (39) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (40) (a) Weigend, F.; H€aser, M.; Patzelt, H.; Ahlrichs, R. Chem. Phys. Lett. 1998, 294, 143. (b) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297. (41) (a) Helten, H.; Schirmeister, T.; Engels, B. J. Phys. Chem. A 2004, 108, 7691. (b) Helten, H.; Schirmeister, T.; Engels, B. J. Org. Chem. 2005, 70, 233. (c) Vicik, R.; Helten, H.; Schirmeister, T.; Engels, B. Chem. Med. Chem. 2006, 1, 1021.