Photochemical Reaction of Mo (CO) 6 with Et2GeH2: NMR and DFT

Organometallics 2009, 28, 5857–5865 DOI: 10.1021/om900299k

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Photochemical Reaction of Mo(CO)6 with Et2GeH2: NMR and DFT Studies of Reaction Products; Crystal Structure of a Novel Complex [{Mo(μ-η2-H-GeEt2)(CO)4}2] Magdalena Zyder,† Andrzej Kochel,† Jaroszaw Handzlik,‡ and Teresa Szyma nska-Buzar*,† †

‡

Faculty of Chemistry, University of Wroczaw, ul. F. Joliot-Curie 14, 50-383 Wroczaw, Poland, and Institute of Organic Chemistry and Technology, Cracow University of Technology, ul. Warszawska 24, 31-155 Krak ow, Poland Received April 21, 2009

The photochemical reaction of Mo(CO)6 with the diethylgermane Et2GeH2 leads to the formation of several new complexes, which were detected by IR and 1H and 13C NMR spectroscopy. From the mixture of compounds, a binuclear complex, [{Mo(μ-η2-H-GeEt2)(CO)4}2], was isolated in crystalline form, and its molecular structure was established by single-crystal X-ray diffraction studies. The agostic hydride ligand of the Mo( μ-η2-H-GeEt2) group was located in the structure at a chemically reasonable position between the Mo and Ge atoms of the Mo-Ge bond of the bridging germyl ligand, and its presence was confirmed by 1H NMR spectroscopy due to a proton resonance at δ = -7.86. Two dihydride complexes were identified by 1H and 13C NMR spectroscopy, due to their differing thermal behavior. A DFT study of the structural properties of possible reaction products was performed.

Introduction The problem of the activation of σ-bonds such as H-H, H-C, H-Si, and H-Ge is still an important research area.1-10 Interest in the process of activation of the H-Ge bond of germanes by transition metals has been growing over the past decade due to its significance for the catalytic *To whom correspondence should be addressed. Fax: þ48 71 328 23 48. Tel: þ48 71 375 7221. E-mail: [email protected]. (1) Kubas, G. J. Chem. Rev. 2007, 107, 4152. (2) Nakata, N.; Fukuzawa, S.; Ishii, A. Organometallics 2009, 28, 534. (3) Tanabe, M.; Ishikawa, N.; Osakada, K. Organometallics 2006, 25, 796. (4) Matthews, S. L.; Pons, V.; Heinekey, D. M. Inorg. Chem. 2006, 45, 6453. (5) Minato, M.; Zhou, D.-Yang; Zhang, L.-B.; Hirabayashi, R.; Kakeya, M.; Matsumoto, T.; Harakawa, A.; Kikutsuji, G.; Ito, T. Organometallics 2005, 24, 3434. (6) (a) White, C. P.; Braddock-Wilking, J.; Corey, J. Y.; Xu, H.; Redekop, E.; Sedinkin, S.; Rath, N. P. Organometallics 2007, 26, 1996. (b) Braddock-Wilking, J.; Corey, J. Y.; White, C.; Xu, H.; Rath, N. P. Organometallics 2005, 46, 4113. (7) Matthews, S. L.; Pons, V.; Heinekey, D. M. J. Am. Chem. Soc. 2005, 127, 850. (8) Ga-dek, A.; Szyma nska-Buzar, T. Polyhedron 2006, 25, 1441. (9) Ga-dek, A.; Kochel, A.; Szyma nska-Buzar, T. J. Organomet. Chem. 2007, 692, 3765. (10) Vincent, J. L.; Luo, S.; Scott, B. L.; Butcher, R.; Unkefer, C. J.; Burns, C. J.; Kubas, G. J.; Lled os, A.; Maseras, F.; Tomas, J. Organometallics 2003, 22, 5307. (11) Marciniec, B.; yawicka, H. Appl. Organomet. Chem. 2008, 22, 510. (12) Lakhtin, V. G.; Knyazev, S. P.; Pavlov, K. V.; Gusel’nikov, L. E.; Buravtseva, E. N.; Kuyantseva, N. A.; Parshkova, L. A.; Mid’ko, A. A.; Bykovchenko, V. G.; Kisin, A. V.; Chernyshev, E. A. Russ. J. Gen. Chem. 2008, 78, 898. (13) Schumann, H.; Aksu, Y. Organometallics 2007, 26, 397. (14) Miura, K.; Ootsuka, K.; Hosomi, A. J. Organomet. Chem. 2007, 692, 514. r 2009 American Chemical Society

process known as hydrogermylation.10-20 Recently we have found that photochemically activated Mo(CO)6 and the norbornadiene (nbd) complex [Mo(CO)4(η4-nbd)] effectively initiate the hydrogermylation of norbornadiene by Et3GeH, which leads to the formation of triethylgermylnorbornene.20 In this paper, we present studies of the activation of the H-Ge bond of diethylgermane using photochemically activated Mo(CO)6. Several organometallic products of this reaction were observed by NMR and IR spectroscopy. One of them was shown by X-ray diffraction studies to be a binuclear complex containing two Mo(CO)4 moieties bridged by two hydridodiethylgermyl ligands and two molybdenum atoms formally in the þ1 oxidation state. To provide support for the assigned structures of the thermally unstable compounds and to better understand their stability, we used density functional theory.

Results and Discussion Photochemical Reaction of Mo(CO)6 with Et2GeH2. In an attempt to generate a coordinatively unsaturated molybdenum(0) complex capable of activating the Ge-H bond, Mo(CO)6 was irradiated in n-heptane containing Et2GeH2. In experiments monitored by IR spectroscopy, it was found (15) Yorimitsu, H.; Oshima, K. Inorg. Chem. Commun. 2005, 8, 131. (16) Kinoshita, H.; Nakamura, T. Kakiya, H.; Shinokubo, H.; Matsubara, S.; Oshima, K. (17) Furukawa, N.; Kourogi, N.; Seki, Y.; Kakiuchi, F.; Murai, S. Organometallics 1999, 18, 3764. (18) Esteruelas, M. A.; Martn, M.; Oro, L. A. Organometallics 1999, 18, 2267. (19) Kuivila, H. G.; Warner, C. R. J. Org. Chem. 1964, 29, 2845. (20) Zyder, M.; Szyma nska-Buzar, T. J. Organomet. Chem. 2009, doi: 10.1016/j.jorganchem.2009.02.013. Published on Web 09/30/2009

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Figure 2. Partial (hydride region) 1H NMR spectra (500 MHz, CDCl3, -20 °C) showing hydride signals of compounds formed during photochemical reaction of Mo(CO)6 with Et2GeH2 in n-heptane solution at -10 °C (a) and at 25 °C (b). Signals are denoted in the same way as compounds 1-3. Figure 1. Partial (carbonyl carbon region) 13C{1H} NMR spectra (126 MHz, CDCl3, -20 °C) showing carbon signals of Mo-Ge compounds formed during photochemical reaction of Mo(CO)6 with Et2GeH2 in n-heptane solution at -10 °C (a) and at 25 °C (b). Signals are denoted in the same way as the Mo-Ge compounds (1-7), and the one at δ = 200.9 is due to Mo(CO)6.

that the decay of the νCO frequency at 1989 cm-1, characteristic of Mo(CO)6, was accompanied by the appearance of several new νCO bands in the region from 2100 to 1900 cm-1, which indicated the formation of a mixture of carbonyl compounds of molybdenum with a lower symmetry than the Oh of Mo(CO)6. The relative intensities of the new bands depended on the reaction temperature (-10 or þ25 °C) and the time of photolysis (2-3 h) (Figure 1S in the Supporting Information). 13C{1H} NMR spectroscopy revealed several signals in the carbonyl region from δ = 220 ppm to 200 ppm due to new carbonyl compounds of different stability (Figure 1). The formation of Mo-H bonds was evidenced by the detection of several high-field resonances in the 1H NMR spectra, in the range from δ = -7 to δ = -10 ppm. For a sample prepared in n-heptane at -10 °C and then dissolved in chloroform-d1, singlet resonances were observed at δ = -7.38 -7.55, -7.86, -9.12, and -10.20 (Figure 2). Two signals with an intensity ratio of 1:1, at δ = -7.55 and -9.12 ppm, correlate in the 2D 1H-1H COSY spectrum, indicating the presence of two hydride ligands in one molecule of molybdenum complex 1. The latter complex decays in chloroform-d1 solution in a few days and was best characterized in a freshly prepared sample obtained in a lowtemperature reaction (-10 °C). Two other equally intense hydride signals, at δ=-7.38 and -10.20 ppm, also correlate in the 2D 1H-1H COSY spectrum, and they must be due to another dihydride complex (2). The hydride resonance at δ= -7.86 was subsequently assigned to the Mo( μ-η2-H-GeEt2) moiety of the most stable binuclear complex [{Mo( μ-η2H-GeEt2)(CO)4}2] (3), which was isolated in crystalline form and whose molecular structure was resolved by means of X-ray diffraction studies (see below). All five hydride signals that were observed look like broad singlets in the

1

H NMR spectrum. However, the line width exhibited by the signal assigned to the agostic hydride of 3 is about 30% smaller than the line width of signals due to the dihydride complexes 1 and 2. This can result from a small JH-H proton-proton coupling of two hydride ligands in 1 and 2 in addition to JH-H(Et). However, the JH-H coupling constant was observed only on the low-intensity signals, which were detected as poorly resolved doublets of quintets, a coupling pattern arising from the sum of the two protonproton coupling constants, JH-H and JH-H(Et). Very small values of JH-H, ca. 2 and 1 Hz, were found for resonances at δ = -7.55 and -9.12 of 1 and at δ = -7.38 of 2, but a slightly higher value of the two JH-H values (JH-H = 2.7 Hz) was detected for the hydride signals at δ = -10.20 of 2. Variable-temperature 1H NMR spectra revealed no temperature dependence. No change in the shape of hydride resonances in the temperature range from 25 to -55 °C was observed. Analysis of several 13C{1H} NMR spectra of compounds prepared at different temperatures (-10 or þ25 °C) made it possible to detect two distinct complexes, 1 and 2, on the basis of their differing thermal behavior (Figure 1). The thermally unstable compound 1 was characterized by five carbonyl carbon signals, each of approximately the same intensity, at δ = 220.9, 218.1, 213.1, 201.8, and 201.4 ppm, which disappeared with time. The thermally more stable compound 2 was detected due to a similar pattern of five approximately equally intense carbonyl signals at δ = 219.0, 218.0, 213.9, 202.9, and 202.1 ppm. The thermally most stable compound, 3, was characterized by three carbonyl carbon signals with an intensity ratio of ca. 1:1:2, at δ = 219.1, 214.4, and 201.9 ppm, which is in agreement with the presence of four carbonyl ligands at the molybdenum atom in complex 3. The presence of the hydride ligands in the coordination sphere of complexes 1, 2, and 3 leads to the splitting of the carbonyl carbon signals into doublets in fully 1 H-coupled 13C NMR spectra. The detected two-bond coupling constants (2JC-H) in the range from 1 to 10 Hz made it possible to propose the mutual position of the carbonyl and hydride ligands in the latter complexes. The highest values of

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Table 1. Crystal Data and Structure Refinement Parameters for 3 empirical formula fw (g mol-1) cryst size (mm) cryst syst space group a (A˚) b (A˚) c (A˚) β (deg) V (A˚3) Z Fcalcd (g cm-3) diffractometer radiation wavelength (A˚) temp (K) μ, mm-1 F(000) data collected, θ min/max (deg) index ranges no. of reflns collected Rint abs coeff, min./max. refinement method no. of data/restraints/params final residuals: R1, wR2 (I > 2σ(I )) R1, wR2 (all data) GOF largest diff peak and hole (e A˚-3)

C16H22Ge2Mo2O8 679.44 0.12 0.10 0.10 monoclinic P21/c 9.183(2) 10.109(2) 14.233(2) 120.82(2) 1134.7(4) 4 1.989 Kuma KM4CCD Mo KR 0.71073 100(2) 3.74 660 2.99/28.66 -9 e h e 12, 13e k e 13, -18 e l e 18 9687 0.0190 0.645/0.678 full-matrix least-squares on F 2 2769/0/133 0.0185, 0.0426 0.0238, 0.0441 1.063 0.54 and -0.34

the coupling constant 2JC-H observed for one of the three carbonyl signals detected in 13C NMR spectra at δ = 214.4 (2JC-H = 9.9 Hz) for 3 indicate the most acute cis OC-Mo-H angle in the latter compound (73.2(7) o, vide infra). Similarly high values of the coupling constant 2 JC-H were observed for one of the five carbonyl carbon signals detected in the 13C NMR spectra at δ = 213.1 (2JC-H = 8.5 Hz) for 1 and at δ = 213.9 (2JC-H = 8.8 Hz) for 2, indicating the closest position of those carbonyl and hydride ligands and similar acute cis OC-Mo-H angles in 1 and 2 to those in 3. The considerably smaller values of 2JC-H, 4.8-3.2 Hz for 1 and 3.9-2.2 Hz for 2, indicate a greater cis OC-Mo-H angle of the other carbonyl and hydride ligands. Two mutually trans carbonyl carbons are coupled with the cis hydride ligands with 2JC-H = 1.1 Hz for 3 (OC-Mo-H angle of 86.8(8)° and 90.9(8)o, vide infra). Thus, the values of 2JC-H decreased with the increase of the cis OC-Mo-H angle and were not detected only for one carbonyl signal of each of the hydride complexes 1-3, that is, the signal of the carbonyl that is approximately trans to the hydride ligand (δ = 218.1 for 1, 219.0 for 2, and 219.1 for 3; the greatest OC-Mo-H angle for 3 is 152.2(7)o, vide infra). It must be noted that NMR data providing the values of the coupling constant 2JC-H are scarce in the literature. For the silane complex [Cr(CO)5(η2-HSiEt3)] two values of 2JC-H, 2.3 and 2.9 Hz, were detected for one trans and four cis carbonyl carbons, respectively.4 The two compounds, 1 and 2, have very similar structures, accounting for similarity in the chemical shifts of the Mo-H and Mo-CO center resonances and comparable values of 2JC-H. Both compounds contain five magnetically nonequivalent carbonyls and two hydride ligands in the coordination sphere of the molybdenum atom. However, it was difficult to propose the molecular structure of the dihydride compounds 1 and 2 based on the NMR data. It was essential to use theoretical methods and calculate the geometry of related complexes (see below). Behind the 13 carbonyl signals assigned to the

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hydride complexes 1-3, another eight signals were detected in the 13C{1H} NMR spectra (Figure 1). Three pairs of carbonyl carbon signals observed in the 13C{1H} NMR spectra with an intensity ratio of ca. 1:4, at δ = 211.1 (1CO), 207.3 (4CO), δ = 210.1 (1CO), 207.1 (4CO), and δ = 210.0 (1CO), 206.6 (4CO), were tentatively assigned to similar pentacarbonyl compounds, with a C4v local symmetry, of the type [Mo(CO)5L] (4-6), where L is most probably a terminal or bridging diethylgermylene ligand formed after the release of a dihydrogen molecule from diethylgermane. Complexes 4-6 were detected by 13C NMR spectroscopy in the mixture of products obtained in a low-temperature reaction (-10 °C) in the approximate ratio of 6:3:1, respectively. In reactions carried out at room temperature, only one compound (5) was detected. It seems very probable that, just like in reactions of secondary silanes, the liberation of a dihydrogen molecule leads to the formation of a silylene ligand,9,21 and in reactions of secondary germanes a germylene ligand (:GeR2) can be formed and coordinated through the donation of its two electrons to a vacant orbital of a pentacarbonyl moiety of a group 6 metal.22-30 Two approximately equally intense carbonyl carbon signals at δ = 211.6 and 211.1 ppm were assigned to an unknown compound 7. The question arises about the difference in the nature of the two dihydride complexes 1 and 2 and the molecular structures of the three pentacarbonyl compounds (4-6). In order to estimate the possible reaction products, a DFT theoretical study was carried out (see below). X-ray Crystal Structure of [{Mo( μ-η2-H-GeEt2)(CO)4}2] (3). The crystal data for 3 are given in Table 1, and selected bond lengths and bond angles are listed in Table 2. The structure of 3, shown in Figure 3, establishes the unique μ-η2 geometry of the bridging H-GeEt2 ligand. The two symmetry-related hydrogen atoms have been located on a difference map and refined. The hydrogen atom is bound to the molybdenum atom (H-Mo = 1.77(2) A˚) as well as to the germanium atom (H-Ge = 1.67(2) A˚) to bridge one of the Mo-Ge bonds of the bridging germyl ligands. Thus, the bridged Mo-Ge bond is substantially longer (Mo(1)-Ge(1)= 2.747(3) A˚) than the other one (Mo(1)-Ge(1)i = 2.656(3) A˚) and much longer than observed in other molybdenum complexes with nonbridging germyls. The Mo-Ge bond lengths of 2.6668(6) and 2.6536(7) A˚ have been found in the binuclear compound [( μ-GeCl2){MoCp(CO)3}2], which contains two [MoCp(CO)3] moieties linked by a GeCl2 bridge.31 (21) Ga-dek, A.; Kochel, A.; Szyma nska-Buzar, T. Organometallics 2003, 22, 4869. (22) Burschka, C.; Stroppel, K.; Jutzi, P. Acta Crystallogr. 1981, B37, 1397. (23) Petz, W. Chem. Rev. 1986, 86, 1019. (24) Jutzi, P.; Hampel, B.; Hursthouse, M. B.; Howles, A. J. J. Organomet. Chem. 1986, 299, 19. (25) Ueno, K.; Yamaguchi, K.; Ogino, H. Organometallics 1999, 18, 4468. (26) Bibal, C.; Mazieres, S.; Gornitzka, H.; Couret, C. Organometallics 2002, 21, 2940. (27) Saur, I.; Rima, G.; Miqueu, K.; Gornitzka, H.; Barrau, J. J. Organomet. Chem. 2003, 672, 77. (28) Saur, I.; Alonso, S. G.; Gornitzka, H.; Lemierre, V.; Chrostowska, A.; Barrau, J. Organometallics 2005, 24, 2988. (29) G orski, M.; Kochel, A.; Szyma nska-Buzar, T. J. Organomet. Chem. 2006, 691, 3708. (30) (a) Zabula, A. V.; Hahn, F .E.; Pape, T.; Hepp, A. Organometallics 2007, 26, 1972. (b) Hahn, F. E.; Zabula, A. V.; Pape, T.; Hepp, A.; Tonner, R.; Haunschild, R.; Franking, G. Chem.;Eur. J. 2008, 14, 1076. (31) Filippou, A. C.; Winter, J. G.; Kociok-K€ ohn; Hinz, I. J. Chem. Soc., Dalton Trans. 1998, 2029.

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Table 2. Selected Bond Distances (A˚) and Angles (deg) for 3a

In the monomeric trichlorogermyl norbornadiene complex [Mo( μ-Cl)(GeCl3)(CO)3(η4-nbd)], the Mo-Ge bond length is 2.631(1) A˚,32 whereas it is 2.6693(5) A˚ in [MoH(GeH2Ph)(CO)(depe)2].10 For the triphenylgermyl complexes [ModC(OEt)Ph(Cp)(GePh3)(CO)2] and [Mo(η3-C6H11)(Cp)(GePh3)(NO)], the Mo-Ge bond length is 2.658(2) and 2.604(2) A˚, respectively.33,34 The length of the η2-coordinated Ge-H bond, 1.67(2) A˚, is not significantly longer than the typical terminal Ge-H bond distance of ca. 1.5 A˚ in

free germanes or in nonbridging germyl ligands, which suggests only little Mo(dπ)-to-Ge-H (σ*) back-donation. A significantly greater Ge-H bond lengthening was found for η2-coordinated diphenylgermane in [Mo(CO)(η2H-GeHPh2)(depe)2] (η2-Ge-H = 2.08(6) A˚, σ-Ge-H = 1.49(7) A˚).10 The Mo-CO bond lengths fall in the range 2.001(2)2.052(2) A˚. Two shorter Mo-CO bond distances (2.001(2) and 2.003(3) A˚) are observed for CO ligands in the position nearly trans to the germanium atoms. These Mo-CO distances are a little shorter than the other two Mo-CO bonds, 2.052(2) A˚, which are mutually trans (C(1)-Mo(1)-C(4) = 177.64(8)o). The two molybdenum atoms in complex 3 are 3.261(5) A˚ apart, a distance that is consistent with a Mo-Mo bond.35 A slightly shorter Mo-Mo bond length (3.2026(4) A˚) has been detected in dinuclear compounds containing bridging diethylsilyl ligands,36 but a notably shorter Mo-Mo bond length (3.164(5) A˚) has been found for [{Mo( μ-I)(CO)4}2].37 The (Mo-Ge)2 cyclic core is planar, with the angles Mo(1)Ge(1)-Mo(1)i = 74.23(1)o and the angle Ge(1)-Mo(1)Ge(1)i = 105.77(1)o, similar to that in the analogous silicon compound, where the angle Mo-Si-Mo=73.93(1)° and the angle Si-Mo-Si = 106.07(1)o.36 The angle subtended at the germanium atom by the two ethyl groups is close to tetrahedral (C(5)-Ge(1)-C(7) = 105.55(8)°), while the angle Mo(1)-Ge(1)-Mo(1)i is considerably more acute at 74.23(1)o. In summary, the crystal structure of 3 is closely related to that of the analogous silicon complex, [{Mo( μ-η2H-SiEt2)(CO)4}2].36 DFT Calculations. In order to estimate the overall geometry of the compounds formed in photochemical reaction of Mo(CO)6 with the diethylgermane Et2GeH2, a DFT theoretical study was carried out (Table 3). The optimized geometry of the mononuclear σ-complex [Mo(CO)5(η2-HGeHEt2)] (A), containing hydrogermane as an η2 ligand with an agostic Mo-H 3 3 3 Ge bond, is shown in Figure 4. At 3.037 A˚, the bridged Mo-Ge bond length of complex A is substantially longer than that calculated (2.763 A˚) and observed (2.747(3) A˚) for binuclear complex 3 and found earlier for the σ-complex [Mo(η2-H-GeHPh2)(CO)(depe)2] (2.6368(7) A˚).10 The Mo-H bond was found to be slightly longer in A than in 3 (1.892 A˚ vs 1.824 A˚ calcd and 1.77(2) A˚ exptl) and significantly longer than the 1.72(6) A˚ found earlier for [Mo(CO)(η2-H-GeHPh2)(depe)2].10 The HGe bond coordinated to the molybdenum atom is lengthened (1.639 A˚) compared with the uncoordinated H-Ge bond (1.540 A˚) in A. In our experimental NMR investigations, compound A was not detected, although analogous σ-complexes of secondary silanes had been detected previously by NMR methods,4,9 and recently the complex [Mo(CO)5(η2H-GeEt3)] has been observed by 1H NMR spectroscopy (δ = -7.95).20 The 1H NMR chemical shift calculated for σ-complex A is in a similar range (δ = -6.25 for an agostic hydride; see Supporting Information, Table S3). The complete oxidative addition of the H-Ge σ-bond to the molybdenum atom and the formation of the seven-coordinate molybdenum(II) complex [MoH(GeHEt2)(CO)5] (B) need

(32) Handzlik, J.; Stosur, M.; Kochel, A.; Szyma nska-Buzar, T. Inorg. Chim. Acta 2008, 361, 502. (33) Chan, L. Y. Y.; Dean, W. K.; Graham, W. A. G. Inorg. Chem. 1977, 16, 1067. (34) Carre, F.; Colomer, E.; Corriu, R. J. P.; Vioux, A. Organometallics 1984, 3, 970.

(35) Baik, M.-H.; Friesner, R. A.; Parkin, G. Polyhedron 2004, 23, 2879. (36) Stosur, M.; Kochel, A.; Keller, A.; Szyma nska-Buzar, T. Organometallics 2006, 25, 3791. (37) (a) Boese, R.; M€ uller, U. Acta Crystallogr. 1976, B32, 582. (b) Schmid, G.; Boese, R.; Welz, E. Chem. Ber. 1975, 108, 260.

atoms

distance

atoms

angle

Mo(1)-C(3) Mo(1)-C(1) Mo(1)-C(2) Mo(1)-C(4) Mo(1)-Ge(1) Mo(1)-Ge(1)i Mo(1)-Mo(1)i Ge(1)-C(5) Ge(1)-C(7) Ge(1)-Mo(1)i Ge(1)-H(1) Mo(1)-H(1) C(5)-C(6) C(7)-C(8)

2.001(2) 2.052(2) 2.003(3) 2.052(2) 2.747(3) 2.656(3) 3.261(5) 1.969(2) 1.966(2) 2.656(3) 1.67(2) 1.77(2) 1.511(3) 1.513(3)

C(3)-Mo(1)-C(1) C(3)-Mo(1)-C(2) C(1)-Mo(1)-C(2) C(3)-Mo(1)-C(4) C(2)-Mo(1)-C(4) C(1)-Mo(1)-C(4) C(3)-Mo(1)-Ge(1) C(1)-Mo(1)-Ge(1) C(2)-Mo(1)-Ge(1) C(4)-Mo(1)-Ge(1) C(3)-Mo(1)-Ge(1)i C(1)-Mo(1)-Ge(1)i C(2)-Mo(1)-Ge(1)i C(4)-Mo(1)-Ge(1)i Ge(1)-Mo(1)-Ge(1)i C(3)-Mo(1)-H(1) C(1)-Mo(1)-H(1) C(2)-Mo(1)-H(1) C(4)-Mo(1)-H(1) Ge(1)-Mo(1)-H(1) Ge(1)-Mo(1)i-Mo(1) Ge(1)i-Mo(1)-Mo(1)i C(5)-Ge(1)-C(7) C(5)-Ge(1)-Mo(1) C(7)-Ge(1)-Mo(1) Mo(1)-Ge(1)-Mo(1)i

91.77(8) 79.15(7) 89.48(7) 90.52(8) 90.43(8) 177.64(8) 170.01(5) 94.07(6) 108.97(5) 83.73(6) 66.58(5) 85.68(5) 145.18(5) 95.72(5) 105.77(1) 152.2(7) 90.9(8) 73.2(7) 86.8(8) 35.9(7) 54.14(3) 51.69(1) 105.55(8) 123.58(6) 116.34(6) 74.23(1)

a Symmetry transformations used to generate equivalent atoms: i (-xþ1, -y, -z).

Figure 3. Molecular structure of [{Mo(μ-η2-H-GeEt2)(CO)4}2] (3). Symmetry transformations used to generate equivalent atoms: i (-xþ1, -y, -z).

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Table 3. Selected PBE0/def2-TZVP-Optimized Bond Distances (A˚) and Angles (deg) for the Mo-Ge Complexes Formed in Photochemical Reaction of Mo(CO)6 and Et2GeH2a complex

Mo-Ge

Mo-H

H-Ge

[Mo(CO)5(η -H-GeHEt2)] (A)

3.037

1.892

[MoH(GeHEt2)(CO)5] (B) [(μ-η4-H2GeEt2){Mo(CO)5}2] (C-1)

2.767 3.131 3.001 3.267 2.758 3.110

1.737 1.893 1.911 1.939 1.734 1.900

1.639 1.540 1.554 1.639 1.633 1.626

2

[(μ-η2-HGeEt2)HMo2(CO)10] (C-2) [(CO)5Mo-Mo(CO)5(η2-H-GeHEt2)] (C-3) [(μ-η4-H2GeEt2)Mo2(CO)9] (C-1-CO) 2

[{Mo(μ-η -H-GeEt2)(CO)4}2] (3)

[{Mo(μ-η2-H-SiEt2)(CO)4}2] (3-Si)b

[Mo(CO)5(GeEt2)] (D) [{Mo(μ-GeEt2)(CO)5}2] (E)

[(μ-GeEt2){Mo(CO)5}2] (F) a

3.159 2.944 2.763 (2.747(3)) 2.676 (2.656(3)) 2.713 (2.709(1)) 2.617 (2.615(1)) 2.518 2.898 2.901 2.928 2.930 2.675 2.662

1.912 1.900 1.824 (1.77(2))

1.632 1.540 1.636 1.640 1.744 (1.67(2))

1.823 (1.786(5))

1.654 (1.615(3))

H-Mo-Ge 28.3 136.7 25.5 29.4 21.5 136.6 26.0

H-Ge-Mo 33.2 90.1 107.6 29.8 35.1 25.9

24.9 31.0 38.2 (35.9(7))

30.7 88.5 29.5 36.7 40.3 (38.3(8))

36.5 (35.1)

41.0 (39.4)

In parentheses experimental values obtained here from the crystal structure. b A silicon complex analogous to 3.36

Figure 4. Optimized structure (distances in A˚) of [Mo(CO)5(η2-H-GeHEt2)] (A).

additional energy (A f B, ΔH=55 kJ/mol and ΔG=61 kJ/mol), but this process leads to a significant decrease in the Mo-Ge and Mo-H distances, to 2.767 and 1.737 A˚, respectively (Figure 5). We could not obtain evidence for the formation of the mononuclear complex [MoH( μ-H-GeEt2)(CO)5], i.e., an isomer of complexes A and B in which both hydrides, the agostic and the terminal one, interact with the same molybdenum atom, and this may explain the NMR data for the dihydride complex 1 or 2. All searches resulted in the structure of A or B. Another σ-complex that was optimized, [( μ-η4-H2GeEt2){Mo(CO)5}2] (C-1), consists of two Mo(CO)5 moieties bridged by the diethylgermane molecule (Figure 6). It can be formed under photochemical conditions from A and Mo(CO)5 (ΔH = -62 kJ/mol, ΔG = -11 kJ/mol). In the latter complex, both the H-Ge σ-bonds of diethylgermane interact as an η2 ligand with the molybdenum atom of two Mo(CO)5 moieties, i.e., the two Mo-Ge bonds are bridged by an agostic hydride. Although the geometry of each of the molybdenum atoms in complex C-1 is very similar, the Mo-H and Mo-Ge bond distances and angles (H-Mo-Ge, H-Ge-Mo) are slightly different but generally close to those

Figure 5. Optimized structure (distances in A˚) of [MoH(GeHEt2)(CO)5] (B).

found for complex A (Table 3). The calculated H-Mo-CO angles are very close in both pentacarbonyl moieties of C-1: 80.0°, 78.1°; 85.3°, 88.8°; 96.5°, 93.7°; 103.1°, 106.2°; 166.8°, 166.0°). However, the smallest H-Mo-CO angles calculated for complex C-1, 80.0° and 78.1°, are greater than those calculated and experimentally detected for complex 3 (70.1° and 73.2(7)o, respectively). These data agree very well with the greater value of the coupling constant 2JC-H =9.9 Hz observed for 3 than for 1 (2JC-H = 8.8 Hz) and strongly suggest that the structure calculated for C-1 is analogous with that described for complex 1, on the basis of the NMR data. 1H NMR chemical shifts calculated for complex C-1 are in a similar range (δ=-3.95 and -6.91) to those observed for the less stable dihydride complex 1 (Figure 2). The structure of another complex that was optimized, [( μ-η2-HGeEt2)HMo2(CO)10] (C-2), similarly to C-1, consists of two Mo(CO)5 moieties (Figure 7). However, in the latter complex, two Mo(CO)5 moieties are bridged by the hydridodiethylgermyl ligand formed after a complete oxidative addition of the H-Ge σ-bonds of H2GeEt2 to the molybdenum atom of

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Figure 6. Optimized structure (distances in A˚) of [(μ-η4-H2GeEt2){Mo(CO)5}2] (C-1). Figure 8. Optimized structure (distances in A˚) of [(CO)5MoMo(CO)5(η2-H-GeHEt2)] (C-3).

Figure 7. Optimized structure (distances in A˚) of [(μ-η2-HGeEt2)HMo2(CO)10] (C-2).

the Mo(CO)5 moiety and the formation of H-Mo and GeMo σ-bond. The hydrogen atom of the bridging germyl ligand is bound to the molybdenum atom (H-Mo=1.939 A˚) as well as to the germanium atom (H-Ge = 1.626 A˚) to bridge the Mo-Ge bond. Thus, the bridged Mo-Ge bond is substantially longer (Mo-Ge=3.267 A˚) than the other one (Mo-Ge=2.758 A˚). In complex C-2, both hydrides, the agostic and the terminal one, interact with the different molybdenum atoms, but the agostic Mo-H bond is substantially longer than the terminal one. The significant difference between two Mo-H distances in C-2 explains very well the NMR spectra we obtained for the more stable dihydride complex 2, for which two hydride resonances were found in a broad range (Δδ = 2.82 ppm) (Figure 2). 1H NMR chemical shifts calculated for complex C-2 are in a similar range (δ = -3.30 and -6.20) to those observed for 2. The transformation of C-1 into C-2 needs additional energy (ΔH = 50 kJ/mol and ΔG = 53 kJ/mol), and this process leads to a significant decrease in the Mo-Ge and Mo-H distances, to 2.758 and 1.734 A˚, respectively (Table 3). However, in our experimental investigations the transformation of C-1 into C-2 was not observed. We also found the complex [(CO)5Mo-Mo(CO)5(η2-HGeHEt2)] (C-3) (Figure 8), an isomer of C-1 that was less stable by ΔH = 49 kJ/mol and ΔG = 48 kJ/mol. Additionally, the structure of a compound (C-1-CO) analogous to C-1 but containing pentacarbonyl and tetracarbonyl moieties connected by the germane bridge was optimized (Figure 9). The transformation of C-1 into C-1-CO needs high energy (ΔH = 158 kJ/mol and ΔG =

Figure 9. Calculated structure (distances in A˚) of [(μ-η4-H2GeEt2)Mo2(CO)9] (C-1-CO).

116 kJ/mol), which is very close to the calculated first bond dissociation energy for Mo(CO)6 (ΔH = 163 kJ/mol and ΔG=115 kJ/mol). However, under photochemical conditions, C-1-CO is very likely to be formed in the reaction of A and Mo(CO)4, for which ΔH=-62 kJ/mol and ΔG=-10 kJ/mol. The diethylgermylene ligand, formed after the release of a dihydrogen molecule from diethylgermane, coordinates to the molybdenum(0) atom of the pentacarbonyl moiety to give the complex [Mo(CO)5(GeEt2)] (D) (Figure 10). At 2.518 A˚, the Mo-Ge distance in complex D is nearly identical with the experimental value obtained by X-ray analysis for the bisgermylenetetracarbonyl complex of molybdenum(0) (2.5189(6) and 2.5204(6) A˚) and consistent with a formal ModGe double bond.30a Complex D transforms via a clearly exothermic but endoergic reaction (2D f E, ΔH = -70 kJ/mol, ΔG = 21 kJ/mol) to give the binuclear complex [{Mo( μ-GeEt2)(CO)5}2] (E), which contains two bridging germylene ligands (Figure 11). This process leads to a significant increase in the Mo-Ge distance, which can be described as transformation of a ModGe double bond to a single one (Table 3). The simultaneous formation of a Ge-Ge bond in E is suggested by the Ge-Ge distance of 2.458 A˚, typical of the single bond.38 Under photochemical (38) Tanabe, M.; Ishikawa, N.; Hanzawa, M.; Osakada, K. Organometallics 2008, 27, 5152.

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Figure 10. Optimized structure (distances in A˚) of [Mo(CO)5(GeEt2)] (D). Figure 12. Optimized structure (distances in A˚) of [(μ-GeEt2){Mo(CO)5}2] (F).

Figure 11. Optimized geometry (distances in A˚) of [{Mo(μ-GeEt2)(CO)5}2] (E).

conditions, the mononuclear complex D can interact with photochemically generated Mo(CO)5 to give a binuclear complex containing one bridging germylene ligand [( μ-GeEt2){Mo(CO)5}2] (F) (Figure 12). This transformation of D is clearly exothermic (D þ Mo(CO)5 f F, ΔH = -119 kJ/mol, ΔG = -53 kJ/mol). The Mo-Ge distances in complex F are significantly longer than in the mononuclear germylene complex D, but shorter than in complex E, which contains two bridging germylene ligands. Dinuclear complexes of the type [( μ-SiR2){W(CO)5}2] (R = Et, Ph) analogous to F had been detected before,9,21 and the molecular structures of two germylene compounds of tungsten, [( μ-GeBr2){W(CO)5}2] and [( μ-GeCl2){W(CO)5}2], were established by single-crystal X-ray diffraction studies.22,29 This suggests that complex F is that identified here by 13C NMR spectroscopy due to two carbonyl signals at δ 210.1 (1CO) and 207.1 (4CO) ppm, as the most stable pentacarbonyl complex, 5 (Figure 1). 13C NMR chemical shifts calculated for complexes D-F are not in satisfactory agreement with experimental results, and compounds D-F are not recognizable with this methodology. However, 13C NMR chemical shifts calculated for complex 3 and an analogue to 3, the silicon complex [{Mo( μ-η2-H-SiEt2)(CO)4}2] (3-Si),36 are in a better agreement with experimental results (all calculated values are shifted to lower field by ca. 14 ppm) (see Supporting Information, Table S3).

Summary and Conclusions The photochemical reaction of Mo(CO)6 with diethylgermane leads to the formation of a mixture of molybdenum

germane complexes of varying stability that were observed by 1H and 13C NMR spectroscopy. From the mixture of compounds only the binuclear complex [{Mo( μ-η2-HGeEt2)(CO)4}2] was isolated in crystalline form, and its molecular structure was established by single-crystal X-ray diffraction studies. To obtain further insight into the reaction products, the geometry of several complexes containing the Mo-Ge bond was estimated by means of DFT calculations ([Mo(CO)5(η2-H-GeHEt2)] (A), [MoH(GeHEt2)(CO)5] (B), [( μ-η4-H2GeEt2{Mo(CO)5}2] (C-1), [( μ-η2-HGeEt2)HMo2(CO)10] (C-2), [(CO)5Mo-Mo(CO)5(η2-HGeHEt2)] (C-3), [( μ-η4-H2GeEt2)Mo2(CO)9] (C-1-CO), [Mo(CO)5(GeEt2)] (D), [{Mo( μ-GeEt2)(CO)5}2] (E), and [( μ-GeEt2){Mo(CO)5}2] (F)). To our knowledge, the optimized compound C-1 is the first example of a σ-complex in which two Ge-H bonds originating from the same molecule of Et2GeH2 coordinate as an η4 ligand to two molybdenum atoms. The formation of such a complex provides a good explanation of the 1H NMR spectra, in which two hydride signals of equal intensity were detected in a very close range (Δδ = 1.57 ppm). In the other optimized dihydride complex, C-2, two hydrides, the agostic and the terminal one, were found. The significant difference between two Mo-H distances in C-2 explains very well the NMR spectra we obtained for the more stable dihydride complex, 2, for which two hydride resonances were found in a broad range (Δδ = 2.82 ppm). The geometry of three complexes (D-F) containing diethylgermylene ligands connected with the molybdenum atom of the pentacarbonyl moiety was optimized by means of DFT calculations, providing a very good explanation for the experimental 13C NMR spectra of the reaction products, in which three pairs of carbonyl carbon signals with an intensity ratio of ca. 1:4 were detected.

Experimental Section General Considerations. The synthesis and all operations were conducted using standard Schlenk techniques under an atmosphere of nitrogen. Solvents and liquid reagents were dried with CaH2 and vacuum transferred into small storage flasks prior to use. IR spectra were measured with a Nicolet-400 FT-IR instrument in solution, as Nujol mulls or KBr pellets. Analyses of the reaction products were performed on a Hewlett-Packard GC-MS system. 1H NMR spectra were recorded with a Bruker AMX 300 or 500 MHz instrument and were referenced to the residual proton peak of the solvent (δ 7.24 CDCl3). 13C, 95Mo,

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and two-dimensional 1H-1H COSY and 1H-13C HMQC NMR spectra were obtained using a Bruker AMX 500 MHz spectrometer at 500 MHz for 1H, 126 MHz for 13C, and 32 MHz for 95 Mo. 95Mo NMR chemical shifts were calibrated relative to Mo(CO)6 (δ -1856). The photolysis source was an HBO 200 W high-pressure Hg lamp. Mo(CO)6 and Et2GeH2 (Aldrich) were used as received. Photochemical Generation of Molybdenum-Diethylgermane Compounds (1-7). A solution of Mo(CO)6 (0.05 g, 0.19 mmol) and Et2GeH2 (0.1 mL, 0.78 mmol) in freshly distilled n-heptane (20 mL) was irradiated through quartz at -10 °C or at room temperature. The course of the reaction was monitored by IR measurements in solution, and photolysis was stopped when the IR band of Mo(CO)6 at ca. 1989 cm-1 reached its minimum intensity (2-3 h) and a new νCO frequency at 2096, 2082, 2058, 2044, 1983, 1971, 1965, and 1945 cm-1 increased. All volatile materials were then evaporated under reduced pressure at room temperature. The resulting brown solid was analyzed by IR and NMR spectroscopy. A sample prepared at -10 °C and freshly analyzed by the 1H NMR method at -20 °C in CDCl3 solution showed the presence of hydride compounds characterized by signals at δ = -7.38 -7.55, -7.86, -9.12, and -10.20. The intensity ratio of these signals depended upon the aging time of the sample with the preferred decrease of the equal intensity signals at δ = -7.55 and 9.12 ppm, while the intensity of the signal at δ=-7.38 was stable. The sample was next analyzed by 13 C and 2D 1H-1H COSY and 1H-13C HMQC NMR spectroscopic methods, making it possible to observe at least seven compounds (1-7). Yellow crystals of the compound [{Mo( μ-η2H-GeEt2)(CO)4}2] (3) were obtained by cooling a saturated nheptane solution to ca. -10 °C. IR and NMR Data (δ, CDCl3, -20 °C) for Compounds 1-7. 1: 1 H NMR: -7.55 (dq, JH-H =2 and 1 Hz, 1H), -9.12 (dq, JH-H = 2 and 1 Hz, 1H). 13C NMR: 220.9 (d, 2JC-H = 4.8 Hz, 1CO), 218.1 (1CO), 213.1 (d, 2JC-H =8.5 Hz, 1CO), 201.8 (d, 2JC-H = 3.2 Hz, 1CO), 201.4 (d, 2JC-H = 3.2 Hz, 1CO). 2: 1H NMR: -7.38 (dq, JH-H =2 and 1 Hz, 1H), -10.20 (dq, JH-H =2.7 and 1 Hz, 1H). 13C NMR: 219.0 (1CO), 218.0 (d, 2JC-H = 3.9 Hz, 1CO), 213.9 (d, 2JC-H =8.8 Hz, 1CO), 202.9 (d, 2JC-H =2.2 Hz, 1CO), 202.1 (d, 2JC-H = 3.3 Hz, 1CO). 3: IR (νCO, cm-1; n-heptane): 2044 (s), 1981 (vs), 1943 (s). 1H NMR: 1.12 (t, 3 JH-H = 8.0 Hz; 6H, Me), 1.07 (q, 3JH-H = 8.0 Hz; 4H, CH2), -7.86 (s, 1H). 13C NMR: 219.1 (1CO), 214.4 (d, 2JC-H =9.9 Hz, 1CO), 201.9 (d, 2JC-H =1.1 Hz, 2CO), 15.4 (tq, 1JC-H =126 Hz, 2 JC-H =4 Hz, 2C, CH2), 7.3 (q, 1JC-H =128 Hz, 2C, Me). 95Mo NMR: -3787. 4: 13C NMR: 211.0 (1CO), 207.3 (4CO). 5: 13C NMR: 210.1 (1CO), 207.1 (4CO). 6: 13C NMR: 210.0 (1CO), 206.6 (4CO). 7: 13C NMR: 211.6 (1CO), 211.1 (1CO). X-ray Crystallography. General Considerations. Crystal data were collected at -173 °C on a Kuma KM4-CCD diffractometer with graphite-monochromated Mo KR radiation, generated from an X-ray tube operated at 50 kV and 25 mA. The images were indexed, integrated, and scaled using the Oxford Diffraction data reduction package.39 A yellow crystal with the approximate dimensions of 0.10 0.10 0.12 mm was used for data collection. The experimental details together with the crystal data are given in Table 1. The structure was solved by the heavy atom method using SHELXS-9740 and refined by the full-matrix least-squares method on all F2 data using SHELXL97.41 The non-hydrogen atoms were included in the refinement with anisotropic displacement parameters, and the hydrogen atoms bonded to carbon atoms were included from ideal geometry of molecules and were not refined. The positions of the hydrogen atom bonded to Ge and Mo atoms were located (39) CCD data collection and reduction GUI, Version 1.173.13 beta (release 14.11.2003); Oxford Diffraction Poland Sp., 1995-2003. (40) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution; University of G€ottingen: Germany, 1997. (41) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of G€ottingen: Germany, 1997.

Zyder et al. in the difference Fourier electron-density map and refined isotropically. The data were corrected for absorption (min./max. absorption coefficients of 0.645 and 0.678).39 Crystallographic data for compound 3 have been deposited at the Cambridge Crystallographic Data Centre (No. CCDC-687644). These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/ retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1123-336-033; e-mail: [email protected]). Computational Details. In an effort to select the most adequate density functional theory method for the systems studied, the following GGA (generalized gradient approximation), meta-GGA, hybrid GGA, and hybrid meta-GGA functionals were tested for predicting the geometry of complex 3: BLYP,42,43 BP86,42,44 PBE,45,46 PW91,47 TPSS,48 VSXC,49 B3LYP,42,43,50,51 B3P86,42,44,50 B97-2,52 PBE0,45,53 M05,54 TPSSh,48,55 and TPSS1KCIS.48,56-58 The experimental structural data were taken as the reference values. Although all the DFT methods employed provided satisfactory structural parameters for complex 3, taking into account the mean unsigned errors in the Mo-Mo, Mo-Ge, Mo-H, Ge-H, Mo-C, and Ge-C distances, the hybrid PBE0 functional appeared to be the most accurate. Therefore, the PBE0 method was used in all subsequent calculations. The triple-ζ valence def2-TZVP basis set,59 recommended for quantitative DFT calculations,59 was applied for all elements. The 28 innermost electrons of Mo were replaced by the Stuttgart effective core potential.60 All structures were fully optimized with the Berny algorithm with redundant internal coordinates.61 Harmonic vibrational frequencies were calculated for each structure to confirm the potential energy minimum. Thermochemical quantities were estimated by treating the systems studied as ideal gas molecules (T = 298.15 K, p = 1 atm). Absolute 1H and 13C shielding values were calculated with the GIAO method62,63 for the PBE0/def2-TZVP geometries. (42) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (43) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (44) Perdew, J. P. Phys. Rev. 1986, B 33, 8822. (45) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865. (46) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 78, 1396. (47) Perdew, J. P.; Chevary, J. A.; Vosko, S. H.; Jackson, K. A.; Pederson, M. R.; Singh, D. J.; Fiolhais, C. Phys. Rev. 1992, B 46, 6671. (48) Tao, J.; Perdew, J. P.; Staroverov, V. N.; Scuseria, G. E. Phys. Rev. Lett. 2003, 91, 146401. (49) Van Voorhis, T.; Scuseria, G. E. J. Chem. Phys. 1998, 109, 400. (50) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (51) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623. (52) Wilson, P. J.; Bradley, T. J.; Tozer, D. J. J. Chem. Phys. 2001, 115, 9233. (53) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158. (54) Zhao, Y.; Schultz, N. E.; Truhlar, D. G. J. Chem. Phys. 2005, 123, 161103. (55) Staroverov, V. N.; Scuseria, G. E.; Tao, J.; Perdew, J. P. J. Chem. Phys. 2003, 119, 12129. (56) Krieger, J. B.; Chen, J.; Iafrate, G. J.; Savin, A. In Electron Correlations and Materials Properties; Gonis, A.; Kioussis, N., Eds.; Plenum: New York, 1999; p 463. (57) Toulouse, J.; Savin, A.; Adamo, C. J. Chem. Phys. 2002, 117, 10465. (58) Zhao, Y.; Lynch, B. J.; Truhlar, D. G. Phys. Chem. Chem. Phys. 2005, 7, 43. (59) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297. (60) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123. (61) Peng, C.; Ayala, P. Y.; Schlegel, H. B.; Frisch, M. J. J. Comput. Chem. 1996, 17, 49. (62) Ditchfield, R. Mol. Phys. 1974, 27, 789. (63) Wolinski, K.; Hilton, J. F.; Pulay, P. J. Am. Chem. Soc. 1990, 112, 8251.

Article The chemical shift values were subsequently obtained using corresponding tetramethylsilane (TMS) shielding calculated at the same theoretical levels as the reference. In the case of compound 3, the following basis sets were tested: def2-TZVP, def2-TZVPP,59 IGLO-III64 (plus def2-TZVP for Mo and Ge), and aug-cc-pVTZ-J65,66 (plus def2-TZVP for Mo, Ge, and Si). As the results obtained with different basis sets were of similar accuracy, compared to the experimental NMR data, the 1H and 13 C chemical shifts for other compounds were calculated with the def2-TZVP basis set. All calculations were carried out using the Gaussian 03 suite of programs.67 For the graphic presentation of the structures, the GaussView 4.1 software was used.68

Acknowledgment. This work was generously supported by the Polish Ministry of Science and Higher Education (Grant No. N204 288534). The authors are grateful to Drs. M. Kowalska and S. Baczy nski for measurements of NMR spectra. (64) Kutzelnigg, W.; Fleischer, U.; Schindler, M. In NMR Basic Principles and Progress; Diehl, P.; Fluck, E.; G€unther, H.; Kosfeld, R.; Seelig, J., Eds.; Springer-Verlag: Berlin, 1990; Vol. 23, p 165. (65) Enevoldsen, T.; Oddershede, J.; Sauer, S. P. A. Theor. Chem. Acc. 1998, 100, 275. (66) Provasi, P. F.; Aucar, G. A.; Sauer, S. P. A. J. Chem. Phys. 2001, 115, 1324.


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Supporting Information Available: Crystallographic data for 3 in CIF format, tables giving Cartesian coordinates and energies of all the optimized structures, selected structural parameters for complex 3 calculated with various DFT methods, calculated 1H and 13C chemical shifts, calculated enthalpies and Gibbs free energies for possible reactions involving the molybdenum compounds, and experimental IR spectra of the reaction products. This material is available free of charge via the Internet at http://pubs.acs.org. (67) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision E.01; Gaussian, Inc.: Wallingford, CT, 2004. (68) Dennington , R., II; Keith, T.; Millam, J. GaussView, Version 4.1; Semichem, Inc.: Shawnee Mission, KS, 2007.

Photochemical Reaction of Mo (CO) 6 with Et2GeH2: NMR and DFT

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