J. Phys. Chem. A 2010, 114, 5997–6006
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Infrared Spectra of CH2dM(H)NC, CH3-MNC, and η2-M(NC)-CH3 Produced by Reactions of Laser-Ablated Group 5 Metal Atoms with Acetonitrile Han-Gook Cho and Lester Andrews* Department of Chemistry, UniVersity of Incheon, 12-1 Songdo-dong, Yonsu-ku, Incheon, 406-840, South Korea, and Department of Chemistry, UniVersity of Virginia, P.O. Box 400319, CharlottesVille, Virginia 22904-4319 ReceiVed: February 9, 2010; ReVised Manuscript ReceiVed: March 24, 2010
Methylidene isocyanides, methyl isocyanides, and η2-nitrile-π-complexes are observed in the matrix IR spectra from reactions of Group 5 metals with acetonitrile isotopomers. The primary isocyanide products with no trace of cyanide complexes are consistent with the reaction path proposed in the analogous Zr study. The major products (CH2dTa(H)NC, CH3-NbNC, η2-Nb(NC)-CH3, and η2-V(NC)-CH3) after codeposition and reaction of metal with CH3CN clearly show the increasing preference for the higher oxidation-state complex on going down the group column, and the subsequent photochemistry provides further information for molecular rearrangements. The Group 5 metal methylidene isocyanides exhibit more agostic distortion than the Zr counterparts and are comparable to the previously studied Group 5 metal methylidene hydrides and halides. The computed structures and observed frequencies indicate that the effects of metal conjugation (CdTa-NdC:) are minor. Introduction Coordination of metal atoms to electron-rich organic species plays a pivotal role for further rearrangements to more sophisticated end products.1-3 Metal interactions with lone electron pairs and π-electron systems provide driving forces for the formation of new metal bonds, leading to catalytic activities and further reactions such as C-H and C-C bond insertions.2-6 Metal-participating molecular rearrangements often consist of multistep configurational changes involving distinct stationary points and transition states.6 Therefore, investigation of the process for electrophilic coordination of metal atoms and their subsequent molecular rearrangements is essential to understanding the details of the reaction path and eventually to synthesize more precious chemical reagents. Recent studies have shown that reactions of laser-ablated metal atoms with small hydrocarbons and haloalkanes are efficient routes to produce characteristic complexes including carbenes, carbynes, π-complexes, and cyclic products.1-3,7-13 Although they are cousins of the much larger complexes, their small sizes also allow opportunities to closely examine molecular processes involved in metal coordination, bond insertion, H(X) migration, and photochemical reactions. Electronic structure calculations also offer helpful information for spectral assignments and understanding the reaction mechanism.6,11,14 Studies show that Groups 3-10 metals, lanthanides, and actinides undergo C-H(X) bond insertion in reaction with small organic compounds and also produce high oxidation-state complexes15 either during reactions or upon photolysis afterward.7-13 A more recent study shows that reactions of Zr with CH3CN, a well-known electron donor, yields methylidene isocyanide (CH2dZrHNC), methylisocyanide (CH3-ZrNC), and η2-nitrileπ-complex, with no trace of the corresponding cyanide products, and their energies are comparable.16 The primary products suggest a reaction path that includes electrophilic coordination of metal atom to the N-end of CH3CN, formation of the more * Author to whom correspondence should be addressed. E-mail: lsa@ virginia.edu.
stable nitrile-π-complex, C-C bond insertion, and H migration. The observed products are the most stable computed species along the reaction path, and the transition states between the products are examined. The extent of agostic distortion14 and the observed frequencies indicate that the effects of the metal containing conjugation are minor. In this investigation, reactions of Group 5 metal atoms with acetonitrile isotopomers are carried out in an effort to substantiate the previous Zr results. The primary products are identified through isotopic substitution and with helpful information from DFT computations. The increasing preference for the higher oxidation-state product on going down the family column is clear, and the results are in line with the previously proposed reaction path for the Zr system. Experimental and Computational Methods Laser ablated Ta, Nb, and V atoms (Johnson-Matthey) were reacted with acetonitrile isotopomers (CH3CN, CD3CN, and 13 CH313CN) in excess argon during condensation at 10 K using a closed-cycle refrigerator (Air Products Displex). These methods have been described in detail in previous publications.17 Reagent gas mixtures are typically 0.5% in argon. The Nd:YAG laser fundamental (1064 nm, 10 Hz repetition rate, 10 ns pulse width) was focused onto a rotating metal target using 5-10 mJ/pulse. After initial reaction, infrared spectra were recorded at 0.5 cm-1 resolution using a Nicolet 550 spectrometer with a Hg-Cd-Te range B detector. Then samples were irradiated for 20 min periods by a mercury arc street lamp (175 W) with the globe removed using a combination of optical filters or annealed to allow further reagent diffusion. To provide support for the assignment of new experimental frequencies and to correlate with related works,7-13 density functional theory (DFT) calculations were performed using the Gaussian 03 program system,18 the B3LYP density functional,19 the 6-311++G(3df,3pd) basis sets for H, C, N, and V20 and using the SDD pseudopotential and basis sets21 for Nb and Ta to provide vibrational frequencies for the reaction products.
10.1021/jp1012686 2010 American Chemical Society Published on Web 04/28/2010
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Figure 1. Infrared spectra in the 2200-1600 and 900-600 cm-1 regions for the reaction products of the laser-ablated tantalum atom with CH3CN in excess argon at 10 K. (a) Ta and CH3CN (0.50% in argon) codeposited for 1 h, (b) as (a) after visible (λ > 420 nm) irradiation, (c) as (b) after UV (240-380 nm) irradiation, (d) as (c) after visible irradiation, (e) as (d) after UV irradiation, and (f) as (e) after annealing to 28 K. m designates the product absorption, and P and c stand for the precursor and common in the CH3CN matrix spectra. CH2CNH, CH2NCH, and CH3NC absorptions are also indicated.
Figure 2. Infrared spectra in the 2150-1850 and 1300-450 cm-1 regions for the reaction products of the laser-ablated tantalum atom with CD3CN in excess argon at 10 K. (a) Ta and CD3CN (0.50% in argon) codeposited for 1 h and (b-f) as (a) after visible, UV, visible, and UV irradiations and annealing to 28 K following the same sequence in Figure 1. m stands for the product absorption, and P and c designate the precursor and common absorptions in the CH3CN matrix spectra. CD2CND and CD2NCD absorptions are also indicated.
Geometries were fully relaxed during optimization, and the optimized geometry and transition-state structure were confirmed by vibrational analysis. The BPW9122 functional was also employed to support the B3LYP results. The vibrational frequencies were calculated analytically, and zero-point energy is included in the calculation of binding and reaction energies. Previous investigations have shown that DFT calculated harmonic frequencies are usually slightly higher than observed frequencies,7-13,23 and they provide useful predictions for the infrared spectra of new molecules. Results and Discussion Reactions of Group 5 metal atoms with acetonitrile were investigated and infrared spectra (Figures 1-6), and density functional frequency calculations of the products and their relative energies (Figures 7-9) and structures (Figures 10-12) will be presented in turn. Ta + Acetonitrile. Figures 1-3 show the product spectra from reactions of laser-ablated Ta atoms with acetonitrile isotopomers and their variation with subsequent photolysis and
Cho and Andrews
Figure 3. Infrared spectra in the 2200-1700, 1350-1250, and 850-450 cm-1 regions for the reaction products of the laser-ablated tantalum atom with 13CH313CN in excess argon at 10 K. (a) Ta and 13 CH313CN (0.50% in argon) codeposited for 1 h and (b-f) as (a) after visible, UV, visible, and UV irradiations and annealing to 28 K following the same sequence in Figure 1. m stands for product absorption, and P and c designate the product and common absorptions. 13CH2CNH, 13 CH2N13CH, and H13C13CNH2 absorptions are also indicated.
annealing. Isomerization of acetonitrile due to the laser-plume irradiation during ablation produces CH2CNH, CH2NCH, and CH3NC absorptions in the matrix IR spectra.24 The product absorptions are all marked with “m” (m for methylidene), which show photoreversible intensity variations upon visible (λ > 420 nm) and UV (240 < λ < 380 nm) irradiations. They are observed mostly in pairs 1.1-14.0 cm-1 apart as listed in Table 1, and the intensity variations of the components for a pair are opposite each other. The ones shown with boldface letters in Table 1 increase and decrease on UV and visible irradiations, and the other ones with plain letters show intensity changes in the opposite directions. This suggests that at least two competing sites for the Ta product exist in the matrix, and photolysis switches from one to the other depending on the photon energy, leading to the considerable intensity alterations as shown in Figures 1-3. Similar photoreversible intensity variations due to different matrix sites are also observed from Group 4 metal reactions with small alkanes and halomethanes.7 Excellent agreement between the observed and DFT computed frequencies shown in Table 1 substantiates generation of the small Ta methylidene isocyanide, CH2dTa(H)NC. The corresponding cyanide complex (CH2dTa(H)CN) would have similar frequencies except for the C-N stretching band expected at about 2150 cm-1, which is not observed in this study as shown in Figures 1-3. The strongest m absorption at 2027.5 cm-1 (with a weak site absorption at 2024.2 cm-1) is assigned to the N-C stretching mode on the basis of the frequency and the negligible D and substantial 13C (39.4 cm-1) shifts. On the other hand, the m absorption observed at 1782.5 cm-1 (with a site absorption at 1788.7 cm-1) in the Ta-H stretching region shows a large D shift of 505.5 cm-1 (H/D ratio of 1.396) and a negligible 13C shift, leading to an assignment to the Ta-H stretching mode. The observed Ta-H stretching frequency is also compared with 1758.9 and 1732.9 cm-1 for TaH225 and those for the previously studied Ta methylidenes (1753.8 and 1731.9 cm-1 for CH2dTaH2, 1765.0 and 1759.3 cm-1 for CH2dTaHF, 1762.9 and 1759.6 cm-1 for CH2dTaHCl, and 1760.3 cm-1 for CH2dTaHBr).7 A weak m absorption at 1012.9 cm-1 (with a site absorption at 1005.3 cm-1) in the CD3CN spectra (Figure 2) has its 13C counterpart at 1297.3 cm-1, and it is assigned to the CD2 scissoring mode while its H counterpart is probably covered by the common CH4 absorption center at ∼1305 cm-1. Another m absorption is observed at 819.6 cm-1 (with a site absorption at 823.6 cm-1), has its D counterpart at 744.6 cm-1, and has 13 C counterparts at 798.2 cm-1 (with a site absorption at 800.7
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TABLE 1: Observed and Calculated Fundamental Frequencies of CH2dTa(H)NC Isotopomers in the Ground 2A′ Statea approximate description A′ CH2 as. str. A′ CH2 s. str. A′ NC str. A′ Ta-H str. A′ CH2 scis. A′ C-Ta str. A′ Ta-H ip bend A′′ CH2 wag A′ CH2 rock A′ Ta-NC str. A′′ CH2 twist A′ TaNC ip bend A′′ TaNC oop bend A′ Ta-H oop bend A′′ CTaN bend
CH2dTa(H)NC obsb
2027.5, 2024.2 1788.7, 1782.5 823.6, 819.6 698.7, 697.6 657.9, 643.9
13
CD2dTa(D)NC
B3LYPc
intc
BPW91d
intd
3226.3 2789.1 2096.4 1822.3 1344.1 824.2 716.8 703.6 474.7 429.9 415.1 210.0 120.5 107.0 89.0
7 5 518 253 21 55 19 76 25 61 7 1 14 12 3
3170.0 2706.1 2016.2 1791.8 1307.0 815.6 712.4 668.2 488.2 427.0 426.4 215.5 116.4 87.3 55.6
6 4 462 215 20 51 12 68 11 65 8 2 6 4 15
obsb
2027.4 1282.2, 1277.0 1012.9, 1005.3 744.6 508.7
B3LYPc
intc
BPW91d
intd
2389.4 2030.8 2095.1 1293.2 1048.1 724.8 541.4 549.6 344.7 449.6 299.2 195.4 112.8 83.7 82.6
7 9 472 102 18 33 30 51 8 62 3 1 1 4 15
2348.2 1696.9 2015.9 1271.6 1016.8 717.8 540.0 521.5 348.5 449.8 307.9 201.8 108.5 82.3 41.7
7 9 473 102 18 34 19 46 11 54 3 2 2 4 11
CH2dTa(H)N13C
obsb
1988.1, covered 1788.5, 1782.4 1297.3 800.7, 798.2 694.0 652.6, 638.9 464.9
B3LYPc
intc
BPW91d
intd
3215.2 2782.6 2054.1 1822.2 1335.6 802.1 713.7 697.7 468.7 424.8 415.0 208.6 119.5 106.5 86.4
6 5 510 257 20 54 16 74 20 63 7 1 14 11 3
3159.1 2699.8 1976.6 1791.6 1299.2 793.5 708.9 662.7 483.3 421.2 426.3 214.0 115.1 84.8 55.5
5 4 453 219 20 50 11 66 8 65 8 1 6 3 15
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. The absorption that increases and decreases on UV and visible irradiations is bold. c Frequencies and intensities computed with B3LYP/6-311++G(3df, 3pd). d Frequencies and intensities computed with BPW91/6-311++G(3df,3pd). CH2dTa(H)NC has a planar Cs structure.
cm-1). Due to the modest H/D and relatively large 12/13 ratios of 1.101 and 1.027, it is designated to be the C-Ta stretching mode, and its relatively high carbon-metal stretching frequency indicates that it is a carbon-tantalum double bond. In the low frequency region, the weak product absorption at 698.7 cm-1 and its 13C counterpart at 694.0 cm-1 are assigned to the Ta-H in-plane bending mode without observation of the D counterpart. Another m absorption is observed at 657.9 cm-1 (with site absorption at 643.9 cm-1) along with its D counterpart at 508.7 cm-1 and 13C counterpart at 652.6 cm-1 (with a site absorption at 638.9 cm-1) (H/D and 12/13 ratios of 1.293 and 1.008). The large D and small 13C shifts leads to an assignment to the CH2 wagging mode. The m absorption at 464.9 cm-1 in the 13CH313CN spectra is tentatively designated to the CH2 rocking mode without observation of its 12C and D counterparts. Observation of the Ta methylidene isocyanide is parallel to the previously studied CH2dZr(H)NC,16 reconfirming that the small conjugated high oxidation-state complexes can be provided in reactions of transition-metal atoms with a nitrile compound. However, unlike the previous Zr + acetonitrile study, the Ta insertion and π-complexes are not identified in the product spectra. The Ta methylidene isocyanide is the most stable among the plausible products. CH2dTa(H)NC, CH3-TaNC, η2Ta(NC)-CH3, and CH3CNfTa in the doublet, quartet, doublet, and quartet ground states are 56, 48, 37, and 21 kcal/mol more stable than the reactants (Ta(4F) + CH3CN), respectively, and the possible cyanide complexes, CH2dTa(H)CN(D) and CH3-TaCN(Q), are 52 and 47 kcal/mol more stable than the reactants. Although the stability of CH2dTa(H)NC over other plausible products is consistent with its exclusive generation,26 the absence of CH2dTa(H)CN despite the comparable energy supports the previously proposed reaction path for the Zr system.
M + CH3CN f CH3CNfM f η2-Μ(ΝC)-CH3 f CH3-MNC f CH2dM(H)NC
(1)
Initial coordination of the metal atom to the electron-rich N-end of acetonitrile is expected to form CH3CNfTa.27 Subsequent rearrangement will lead to the observed more stable nitrile π-complexes28 in the Nb and V systems (described below) and the previous Zr study. The observed isocyanide insertion products from the Nb, V, and Zr reactions with no trace of the cyanide counterparts, which are energetically comparable, indicates that during C-C bond insertion by the metal atom,
Figure 4. Infrared spectra in the 2150-1650 and 1300-500 cm-1 regions for the reaction products of the laser-ablated niobium atom with CH3CN in excess argon at 10 K. (a) Nb and CH3CN (0.50% in argon) codeposited for 1 h, (b) as (a) after visible irradiation, (c) as (b) after UV irradiation, (d) as (c) after full arc (λ > 220 nm) irradiation, and (e) as (d) after annealing to 28 K. m, i, and π designate the product absorption groups depending the intensity variation in the process of photolysis and annealing, and P and c stand for the precursor and common in the CH3CN matrix spectra. CH2CNH and CH2NCH absorptions are also indicated.
the N-Ta bond is preserved, leading to the C-Ta-N-C backbone. The most stable CH2dTa(H)NC is produced in the end via H migration. Nb + Acetonitrile. The product absorptions from Nb reactions with CH3CN isotopomers are shown in Figures 4 and 5. In contrast to the Ta system, three groups of product absorptions are observed depending on their intensity variation upon photolysis and annealing, which are marked m, i, and π (for methylidene, insertion, and π-complexes). The m absorptions are almost invisible in the original spectrum after codeposition, remain as weak on visible irradiation. They emerge on UV photolysis and almost double on full arc (λ > 220 nm) irradiation. The i absorptions decrease ∼30% and disappear on visible and UV irradiations. The π absorptions slightly increase, halve, and further decrease on visible, UV, and full arc irradiations, respectively. The observed intensity variations of the product absorption groups suggest that the products responsible for the i and π absorptions convert to another product responsible for the m absorptions in the process of photolysis. The m absorption at 2039.9 cm-1 (with site absorptions at 2035.2 and 2031.0 cm-1) in the CD3CN spectra in Figure 5 has its 13C counterpart at 1999.4 cm-1 (with site absorptions at 1994.8 and 1990.8 cm-1). On the basis of the frequency and significant 13C shift, it is assigned to the NC stretching mode.24d The H counterpart expected at the same frequency as that in
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Cho and Andrews the CD3CN spectra is covered by CH2CNH absorption24 except for a site absorption at 2031.0 cm-1. The possible nitrile (CN) stretching absorption expected at ∼2150 cm-1 is again not observed. The m absorption at 1708.3 cm-1 (with site absorptions at 1714.2 and 1693.0 cm-1) in the Nb-H stretching region carries its D counterpart at 1228.0 cm-1 (with site absorptions at 1238.2 and 1217.9 cm-1) and 13C counterpart at 1708.3 cm-1 (with site absorptions at 1714.2 and 1692.6 cm-1). The large D (H/D ratio of 1.391) and negligible 13C shifts lead to an assignment to the Nb-H stretching mode. The Nb-H stretching absorption is indicative of formation of a Nb high oxidationstate product, CH2dNb(H)NC, and its frequency is compared with 1611 and 1569 cm-1 for NbH2;25 1680.7 and 1652.5 cm-1 for CH2dNbH2; and 1698.7, 1697.8, and 1698.7 cm-1 for CH2dNbHF, CH2dNbHCl, and CH2dNbHBr.7 An m absorption is observed at 788.8 cm-1, and its D and 13 C counterparts at 691.8 and 770.5 cm-1 (H/D and 12/13 ratios of 1.140 and 1.024 cm-1), and it is designated to the C-Nb double bond stretching mode on the basis of its frequency and the modest D and relatively large 13C shifts. In the further low frequency region, the m absorption at 528.1 cm-1 in the CD3CN spectra is assigned to the CH2 wagging mode, and the H and 13 C counterparts are covered by precursor absorption. Another m absorption is observed at 587.4 cm-1, where 13C substitution shifts it to 581.9 cm-1 and its D counterpart is too low in frequency to be observed, leading to an assignment to the CH2
Figure 5. Infrared spectra in the 2150-1650 and 1300-500 cm-1 regions for the reaction products of the laser-ablated niobium atom with CD3CN and 13CH313CN in excess argon at 10 K. (a) Nb and CD3CN (0.50% in argon) codeposited for 1 h, (b) as (a) after full arc irradiation, and (c) as (b) after annealing to 28 K. (d) Nb and 13CH313CN (0.50% in argon) codeposited for 1 h, (e) as (d) after visible irradiation, (f) as (e) after UV irradiation, (g) as (f) after full arc irradiation, and (h) as (g) after annealing to 28 K. m, i, and π designate the product absorption groups depending the intensity variation in the process of photolysis and annealing, and P and c designate the precursor and common absorptions in the CD3CN and 13CH313CN matrix spectra. CD2CND, CD2NCD, 13CH213CNH, 13CH2NCH, and 13CH3N13C absorptions are also indicated.
TABLE 2: Observed and Calculated Fundamental Frequencies of CH2dNb(H)NC Isotopomers in the Ground 2A′ Statea approximate description A′ A′ A′ A′
CH2dNb(H)NC obs
b
c
13
CD2dNb(D)NC
c
d
B3LYP int BPW91 int
d
obs
b
CH2 as. str. CH2 s. str. NC str. Nb-H str.
c
c
d
B3LYP int BPW91 int
3207.2 5 3149.3 4 2822.8 3 2724.5 3 covered, 2031.0 2090.8 394 2002.8 308 2039.9, 2035.2, 2031.0 1714.2, 1708.3, 1761.2 290 1741.5 229 1238.2,1228.0, 1217.9 1693.0 A′ CH2 scis. 1342.8 22 1309.1 22 A′ C-Nb str. 788.8 798.9 74 802.0 79 691.8 A′ Nb-H ip bend 723.3 35 730.0 20 A′′ CH2 wag covered 709.7 143 678.0 122 528.1 A′′ CH2 twist 587.4 576.2 41 558.3 43 A′ Nb-NC str. 449.3 45 465.1 15 A′ CH2 rock 428.6 37 427.3 53 A′′ NbNC oop bend 220.0 60 218.4 31 A′ NbNC ip bend 201.3 1 207.5 1 A′′ Nb-H oop bend 133.0 58 78.6 76 A′ CNbN bend 95.9 5 94.0 5
d
obs
CH2dNb(H)N13C
b
B3LYPc intc BPW91d intd
2375.2 6 2332.6 6 2054.1 6 1982.3 10 2090.7 397 2002.6 308 1999.4, 1994.8, 1990.8 1253.3 148 1239.4 116 1714.2, 1708.3, 1692.6
3196.2 4 3138.5 4 2816.4 3 2718.2 2 2049.0 390 1962.7 305 1761.1 291 1741.4 231
1051.2 703.2 553.6 554.7 411.7 433.9 340.1 201.6 185.7 106.8 89.6
1333.6 22 1300.8 22 779.9 77 783.2 82 719.6 30 725.3 15 703.7 139 672.3 118 576.1 41 558.3 44 443.0 37 460.3 11 424.6 42 422.2 54 218.9 63 216.8 33 200.1 1 206.2 1 131.9 55 77.4 75 93.3 4 91.4 4
24 1021.4 47 706.2 46 560.4 99 529.4 17 399.9 60 434.3 4 347.3 21 207.7 1 192.5 49 67.1 5 88.2
22 50 770.5 29 88 covered 17 581.9 50 6 14 1 50 5
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. The strongest matrix site split absorption is bold. Frequencies and intensities computed with B3LYP/6-311++G(3df, 3pd). d Frequencies and intensities computed with BPW91/ 6-311++G(3df,3pd). CH2dNb(H)NC has a planar Cs structure. c
TABLE 3: Observed and Calculated Fundamental Frequencies of CH3-NbNC Isotopomers in the Ground 4A′′ Statea approximate description A′′ CH3 as. str. A′ CH3 as. str. A′ CH3 s. str. A′ NC str. A′ CH3 bend A′′ CH3 bend A′ CH3 deform A′ C-Nb str. A′ Nb-NC str. A′ CH3 rock A′′ CH3 rock A′ NbNC ip bend A′′ NbNC oop bend A′ CNbN bend A′′ CH3 tort
CH3-NbNC b
obs
2045.8
c
CD3-NbNC
B3LYP
int
c
d
d
BPW91
int
3082.0 3053.5 2963.3 2073.3 1409.6 1402.5 1157.5 534.1 485.8 431.4 362.5 188.1 147.4 82.1 46.6
0 5 7 349 5 5 4 23 133 9 8 0 0 4 2
3086.8 2942.9 2881.7 1976.7 1355.7 1346.0 1101.4 579.9 473.9 374.2 300.3 191.2 112.9 83.0 70.1
0 3 5 269 8 4 5 30 89 12 3 1 0 3 0
b
obs
2045.8
B3LYP 2277.5 2251.1 2128.6 2073.2 1022.6 1018.3 913.9 460.9 470.4 361.2 181.7 268.7 146.0 76.1 34.5
c
13
int
c
BPW91
0 3 3 349 2 4 16 41 102 4 1 5 0 4 2
2279.6 2171.2 2069.2 1976.7 984.4 979.1 873.7 495.8 470.5 312.0 181.9 229.5 105.8 76.6 52.9
d
int
d
0 1 3 268 5 4 13 24 79 8 2 2 1 3 0
b
obs
1996.5
CH3-NbN13C
B3LYPc
intc
BPW91d
intd
3071.3 3044.3 2959.2 2031.4 1406.5 1399.2 1147.6 525.7 478.3 424.4 361.0 186.5 145.5 79.9 46.4
0 4 7 347 5 5 3 21 130 9 8 1 0 4 2
3076.6 2933.1 2878.1 1936.8 1352.6 1342.9 1091.6 569.2 467.7 368.0 298.7 189.9 111.3 80.9 70.0
0 3 5 266 8 4 4 28 86 12 3 1 0 2 0
Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP/ 6-311++G(3df, 3pd). d Frequencies and intensities computed with BPW91/6-311++G(3df,3pd). CH3-NbNC has a Cs structure. a
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TABLE 4: Observed and Calculated Fundamental Frequencies of the η2-π-Complex Nb(NC)-CH3 Isotopomers in the Ground 4 A′′ Statea approximate description A′ CH3 as. str. A′′ CH3 as. str. A′ CH3 s. str. A′ CCN as. str. A′′ CH3 bend A′ CH3 bend A′ CH3 deform A′ CH3 rock A′′ CH3 rock A′ C-C str. A′ N-Nb str. A′ C-Nb str. A′′ CCNNb deform A′ CCNb bend A′′ CH3 tort
η2-Nb(NC)-CH3 b
obs
B3LYP
1101.6
3094.7 3089.9 3020.2 1635.8 1468.3 1467.4 1386.2 1122.6 1001.1 942.0 640.8 496.4 311.7 244.5 48.6
606.4
c
Nb(N13C)-13CH3
Nb(NC)-CD3
c
d
d
int
BPW91
int
20 1 34 36 16 15 7 120 17 26 76 4 17 14 1
3042.0 3036.9 2962.0 1561.6 1420.5 1420.4 1335.2 1101.0 964.5 917.0 630.5 505.7 308.0 243.4 26.9
19 2 30 14 14 17 8 92 4 15 58 5 10 13 0
b
obs
1000.1 973.1
572.5
c
B3LYP
int
c
d
d
BPW91
int
2293.9 2285.5 2168.1 1632.1 1058.8 1055.4 1131.8 993.9 807.4 792.7 617.8 467.0 282.6 224.1 35.4
10 2 13 39 6 11 62 93 21 5 65 2 13 13 1
2254.4 2245.2 2126.2 1556.7 1023.9 1022.7 1103.2 973.2 780.8 765.9 610.9 473.3 278.5 222.6 17.2
10 1 11 17 6 14 59 51 7 4 54 2 7 12 1
b
obs
B3LYPc
intc
BPW91d
intd
1069.0
3083.5 3079.1 3017.0 1595.9 1466.0 1464.9 1375.6 1097.8 988.9 925.5 637.4 485.3 302.7 240.0 48.6
19 1 35 38 16 16 6 107 15 30 76 4 16 14 1
3031.0 3026.3 2958.9 1523.0 1418.4 1417.6 1324.9 1075.1 952.5 902.8 627.3 494.3 299.2 239.0 26.9
18 2 31 14 14 18 7 84 3 18 58 4 9 13 0
600.2
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP/ 6-311++G(3df, 3pd). d Frequencies and intensities computed with BPW91/6-311++G(3df,3pd). The Nb nitrile-π-complex has a Cs structure.
twisting mode. Therefore, the primary product responsible for the m absorptions carries Nb-H, CdNb, CH2, and NC moieties, most probably CH2dNb(H)NC. The observed frequencies are well reproduced as shown in Table 2, within the limits of DFT,7-13,23 which substantiate formation of the small Nb methylidene isocyanide. Only one i absorption is observed at 2045 cm-1, which disappears on UV irradiation, and deuteration does not change its frequency, but 13C substitution shifts it to 1996.5 cm-1. We assign the NC stretching absorption to the insertion complex, CH3-NbNC. Table 3 shows that the NC stretching band is the strongest one, and the predicted D and 13C shifts of 0.1 and 41.9 cm-1 correlate excellently with the observed values. Unfortunately, the second strong Nb-N stretching band with about a third the NC stretching absorption intensity expected at ∼470 cm-1 is not observed in the noisier low frequency region. The strongest π absorption is observed at 1101.6 cm-1, and its D and 13C counterparts at 973.1 and 1069.0 cm-1 (H/D and 12/13 ratios of 1.132 and 1.031). It is assigned to the A′ CH3 rocking mode, which is the strongest for the nitrile π-complex, η2-Nb(NC)-CH3, on the basis of the frequency and good correlation with the DFT values (Table 4). For example, the observed frequencies for the isotopomers are compared with the B3LYP frequencies of 1122.6, 993.9, and 1097.8 cm-1. In the low frequency region, another π absorption is observed at 606.4 cm-1, and the D and 13C counterparts are at 572.5 and 600.2 cm-1. The frequency, relatively small isotopic shifts, and reasonable correlation with the DFT values lead to an assignment to the N-Nb stretching mode. The weak π absorption observed at 1000.1 cm-1 in the CD3CN spectra is tentatively designated to the A′ CH3 bending mode. Unfortunately, other absorptions from the Nb nitrile π-complex (η2-Nb(NC)-CH3) are expected to be too weak to be observed or to be covered by precursor absorption in the congested areas. CH2dNb(H)NC, CH3-NbNC, η2-Nb(NC)-CH3, and CH3CNfNb in the doublet, quartet, quartet, and sextet ground states are 42, 48, 35, and 27 kcal/mol more stable than the reactants (Nb(6D) + CH3CN), respectively, and CH2dNb(H)CN and CH3-NbCN in the ground doublet and quartet states are 43 and 48 kcal/mol more stable. The observed CH3-NbNC and η2-Nb(NC)-CH3Nb in the original spectra and CH2dNb(H)CN upon photolysis are the most stable products in the proposed reaction path 1 whereas the cyanide counterparts have essentially the same energy.
Figure 6. Infrared spectra in the 2200-2000, 1620-1520, and 1100-450 cm-1 regions for the reaction products of the laser-ablated vanadium atom with CH3CN and CD3CN in excess argon at 10 K. (a) V and CH3CN (0.5% in argon) codeposited for 1 h, (b) as (a) after visible irradiation, (c) as (b) after UV irradiation, (d) as (c) after annealing to 28 K. (e) V and CD3CN (0.50% in argon) codeposited for 1 h, (f) as (e) after visible irradiation, (g) as (f) after UV irradiation, and (h) as (g) after annealing to 28 K. i and π designate the product absorption groups depending the intensity variation in the process of photolysis and annealing, and P and c designate the precursor and common absorptions in the CD3CN and 13CH313CN matrix spectra. CH2CNH, CH2NCH, CH3NC, CD2CND, and CD2NCD absorptions are also indicated.
V + CH3CN. Figure 6 shows the product absorptions form reactions of V with acetonitrile isotopomers and their variation upon photolysis and annealing. Two groups of product absorptions marked i and π are observed depending on the intensity variation upon photolysis and annealing. The i absorptions are almost invisible in the original spectra, emerge on visible irradiation, and dramatically increase (∼400%) on UV irradiation. They sharpen up in the early stage of annealing and later gradually decrease. The π absorptions, in contrast, are strongest in the original spectra, slightly decrease on visible irradiation, and almost disappear on UV irradiation. The intensity variations of the i and π absorptions suggest that the primary product responsible for the π absorptions from V reaction with acetonitrile converts to a different product responsible for the i absorptions in the process of photolysis. The i absorption at 2058.8 cm-1 shows a negligible D shift; and following the Zr, Ta, and Nb cases, it is assigned to the
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TABLE 5: Observed and Calculated Fundamental Frequencies of CH3-VNC Isotopomers in the Ground 4A′′ Statea approximate description A′ CH3 as. str. A′′ CH3 as. str. A′ CH3 s. str. A′ NC str. A′′ CH3 bend A′ CH3 bend A′ CH3 deform A′ C-V str. A′′ CH3 rock A′ V-NC str. A′ CH3 rock A′ VNC ip bend A′′ VNC oop bend A′ CVN bend A′′ CH3 tort
CH3-VNC obs
b
B3LYP
2058.8
530.9 515.2
c
BPW91
2 3 6 363 4 3 0 44 39 162 7 2 1 8 1
3079.2 2991.4 2898.2 2001.2 1375.6 1340.3 1075.4 559.5 613.1 504.2 381.3 148.1 181.2 81.1 84.8
int
3109.3 3053.7 2981.1 2099.2 1426.9 1410.7 1142.4 556.9 545.1 509.7 413.5 179.9 174.3 79.8 52.6
CD3-VNC
c
d
int
d
obs
3 2 60 287 7 35 10 42 19 95 20 8 1 5 0
b
B3LYP
c
2298.0 2258.0 2137.5 2099.2 1037.0 1024.2 896.1 507.9 408.6 471.9 341.1 175.3 168.0 75.0 41.1
2058.7
483.1 455.6
intc
BPW91d
intd
0 0 1 364 4 3 6 124 24 54 12 1 2 8 2
2275.1 2215.1 2078.6 2001.2 1002.2 972.4 851.5 503.0 465.3 482.7 309.2 143.4 168.1 75.9 66.8
1 0 31 282 5 26 4 65 11 48 22 6 2 5 1
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP/ 6-311++G(3df, 3pd). d Frequencies and intensities computed with BPW91/6-311++G(3df,3pd). CH3VNC has a Cs structure.
TABLE 6: Observed and Calculated Fundamental Frequencies of the η2-π-Complex V(NC)-CH3 Isotopomers in the Ground 3 A′′ Statea approximate description A′ CH3 as. str. A′′ CH3 as. str. A′ CH3 s. str. A′ CCN as. str. A′′ CH3 bend A′ CH3 bend A′ CH3 deform A′ CH3 rock A′′ CH3 rock A′ CCN s. str. A′ N-V str. A′ C-V str. A′′ CCNV deform A′ CCV bend A′′ CH3 tort
η2-V(NC)-CH3 obs
b
covered covered 1080.0, 1066.5 923.4 622.5
B3LYP 3087.9 3087.8 3014.1 1652.5 1468.3 1466.9 1382.3 1082.4 1013.3 928.7 635.3 471.7 323.8 247.2 75.7
c
V(NC)-CD3
c
BPW91
29 6 57 252 10 16 5 226 0 95 48 23 2 31 0
3037.7 3035.8 2957.9 1586.8 1420.5 1419.7 1331.1 1072.6 983.6 910.3 636.6 506.9 326.7 248.7 50.3
int
d
int
d
22 6 41 51 8 18 6 126 6 24 62 3 0 23 0
obs
b
1573.4 1097 957.8, 948.6 607.0
B3LYPc
intc
BPW91d
intd
2288.1 2284.0 2163.9 1649.6 1058.8 1116.3 1054.2 951.8 821.9 791.4 614.1 446.6 292.1 227.9 57.4
15 3 20 253 5 91 11 245 0 8 28 19 2 28 1
2250.8 2244.3 2123.2 1583.0 1023.8 1088.5 1020.3 950.9 803.8 764.8 622.2 473.4 292.8 228.7 38.6
54 6 61 14 93 3 6 53 1 0 21 0
Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. The strongest matrix site split absorption is bold. Frequencies and intensities computed with B3LYP/6-311++G(3df, 3pd). d Frequencies and intensities computed with BPW91/ 6-311++G(3df,3pd). The V nitrile-π-complex has a Cs structure. a
c
NC stretching mode. In the low frequency region, the i absorptions at 530.9 and 515.2 cm-1 along with its D counterpart at 483.1 and 455.6 cm-1 (H/D ratios of 1.099 and 1.131) are assigned to the C-V and V-N stretching modes on the basis of the frequencies and modest D shifts. Table 5 shows that they are the strongest bands for CH3-VNC, and the observed frequencies are 0.981, 0.953, and 1.011 of the B3LYP values. Mode analysis shows substantial coupling between the C-V and V-N stretching modes, which might be the source of the slight under- and overestimation of the C-V and V-N stretching frequencies. The other bands of the insertion complex are too weak to be observed, as shown in Table 5. A strong and relatively broad π absorption is observed at 1080.0 cm-1 (with a site absorption at 1066.5 cm-1), and its D counterpart is at 957.8 cm-1 (with a site absorption at 948.6 cm-1). The only plausible product from reaction of V with CH3CN that shows a strong absorption in the frequency region is the nitrile η2-π-complex, η2-(NC)-CH3. It is assigned to the A′ CH3 rocking mode (Table 6), and the relatively small D shift (H/D ratio of 1.128) for a rocking mode originates from coupling with the C-C and C-V stretching modes. The weak A′ CCN symmetric stretching absorption is observed at 923.4 cm-1, and
the even weaker D counterpart is not observed. The uniquely strong π absorption in the low frequency region at 622.5 cm-1 has its D counterpart at 607.0 cm-1 (H/D ratio of 1.026) and is assigned to the N-V stretching mode (Table 6). The π absorption at 1573.4 and 1097 cm-1 in the CD3CN spectra are designated to the CCN antisymmetric stretching and A′ CH3 bending modes, but their H counterpart expected at ∼1577 and ∼1445 cm-1 are believed to be covered in the congested areas. Table 6 shows very good agreement with the observed and predicted values, where the observed frequencies are 0.954-1.006 of the B3LYP values. Generation of CH3-VNC and η2-V(NC)-CH3 is also consistent with their relative stabilities. CH2dV(H)NC, CH3-VNC, η2-V(NC)-CH3, and CH3CNfV in their doublet, quartet, quartet, and quartet ground states are 7, 41, 21, 17 kcal/mol more stable than the reactants (V(4F) + CH3CN), respectively, whereas CH2dV(H)CN and CH3-VCN in the doublet and quartet ground states are 3 and 40 kcal/mol more stable. Although CH3-VNC is more stable than η2-V(NC)-CH3, the primary product in the original spectra after codeposition of V and CH3CN is the nitrile π-complex. The present results are indicative of a low barrier between η2-V(NC)-CH3 and
Laser-Ablated Group 5 Metals Reacting with Acetonitrile
Figure 7. Energies of the plausible Ta products in the proposed reaction path 1 relative to the reactants (Ta(4F) + CH3CN). Only CH2dTa(H)NC is observed in the matrix IR spectra (see text). CH3-TaNC, η2Ta(NC)-CH3, and CH3CNfTa are believed to form in the course of reaction, but they are not trapped in the matrix with an observable amount.
Figure 8. Energies of the plausible Nb products in the proposed reaction path 1 relative to the reactants (Nb(6D) + CH3CN). CH3-NbNC and η2-Nb(NC)-CH3 are observed in the original matrix IR spectra after deposition, whereas CH2dNb(H)NC is produced during photolysis from the insertion and π-complex (see text). CH3CNfNb is believed to form in the course of reaction, but not trapped in the matrix with an observable amount. CH2dNb(H)NC in the sextet state (not shown) is 36 kcal/mol higher than the reactants.
CH3CNfV, which allows the swift conversion to the π complex during codeposition and much higher barrier between CH3-VNC and η2-(NC)-CH3. Formation of CH3-VNC from the nitrile π-complex requires photolysis (particularly with UV) following codeposition as shown in Figures 6. Reaction Mechanism. Figures 7-9 shows the energies of the products in the proposed reaction path 1 (CH2dM(H)NC, CH3-MNC, η2-M(NC)-CH3, and CH3CNfM). As described above, the primary products of the Group 5 metal systems are CH2dTa(H)NC from Ta reactions, CH3-NbNC and η2Nb(NC)-CH3 from Nb reactions and CH2dNb(H)NC later during photolysis, and η2-V(NC)-CH3 from V reactions and CH3-VNC in subsequent photolysis. They also show the general trend that the higher oxidation-state product becomes more favored with going down the group column.7-13 DFT
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Figure 9. Energies of the plausible V products in the proposed reaction path 1 relative to the reactants (V(4F) + CH3CN). η2-V(NC)-CH3 is the primary product observed in the original matrix IR spectra after deposition, whereas CH3-VNC is produced during photolysis from the π-complex (see text). CH3CNfV is believed to form in the course of reaction, but not trapped in the matrix with an observable amount, and CH2dV(H)NC is not identified.
computations show that the higher oxidation-state complex is relatively more stable with heavier metal as shown in Figures 7-9. The reaction path 1 is originally proposed on the basis of the identified nitrile η2-π-complex and isocyanide products (CH3-ZrNC and CH2dZr(H)NC) from reactions of Zr with acetonitrile isotopomers without formation of the cyanide counterparts. The electron-rich N-end of acetonitrile most probably attracts the electron-deficient metal atom in a similar way of solvation or forming acetonitrile adducts.27 However, the coordination complex (CH3CNfM) is not identified in the matrix spectra probably because of the low yield due to its higher energy relative to the observed primary products. It is, therefore, believed that CH3CNfM swiftly converts to the nitrile η2-π-complex with M moving out of the molecular axis to above the nitrile triple bond. The π-complex is the single primary product in the V original spectra and one of the primary products in the Nb system. In the Ta system, it proceeds further to the much more stable methylidene complexes, not leaving a measurable amount of the π-complex in the matrix. The increasing i absorptions with the decreasing π absorptions upon photolysis in the V system (Figure 6) and observation of the both products in the original Nb spectra (Figures 5 and 6) involve rearrangement from η2-M(NC)-CH3 to CH3-MNC. The rearrangement is in essence C-C bond insertion by the metal atom, which includes moving of the metal atom toward the C-C bond, eventually breaking it, and thereby forming a carbon-metal bond while retaining the nitrogen-metal bond. This rearrangement is a challenging subject in terms of molecular dynamics and theoretical approaches. In the previous Zr study,16 while it was possible to obtain the geometry of the transition state for the rearrangement, the IRC trials failed to show the entire course of rearrangement. Lastly, generation of CH2dNb(H)NC during photolysis with consumption of the insertion and π-complex in the Nb system and exclusive formation of CH2dTa(H)NC are incorporated with H migration from C to M in the isocyanide complex. Excitation to a higher quartet state probably leads to a conversion to the more stable methylidene via H migration, and subsequent system crossing occurs to the doublet ground state. Molecular Structures. The structures of CH2dM(H)NC, CH3-MNC, η2-M(NC)-CH3, and CH3CNfM (M ) Ta, Nb,
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Figure 10. The B3LYP structures of the plausible Ta products in the proposed reaction path 1 with the 6-311++G(3df,3pd) basis sets for H, C, and N, and SDD pseudopotential and basis for Ta. Bond distances and angles are in Å and degrees, respectively. The Ta methylidene isocyanide has a doublet ground state, and the other ones have quartet ground states. The molecular symmetry is denoted under the structure. Notice the agostic distortion of the methylidene isocyanide complex. The C-Ta and N-Ta bonds in the nitrile π-complex (2.045 and 1.986 Å) are shorter than those in CH3-TaNC and CH3CNfTa but are much longer than the C-Ta bond in the Ta methylidene isocyanide (1.896 Å).
Figure 11. The B3LYP structures of the plausible Nb products in the proposed reaction path 1 with the 6-311++G(3df,3pd) basis sets for H, C, and N, and SDD pseudopotential and basis for Nb. Bond distances and angles are in Å and degrees, respectively. The Nb methylidene isocyanide has a doublet ground state, and the other ones have quartet ground states. The molecular symmetry is denoted under the structure. Notice the agostic distortion of the methylidene isocyanide complex. The C-Nb and N-Nb bonds in the nitrile π-complex (2.042 and 1.997 Å) are shorter than those in CH3-NbNC and CH3NCfNb but are much longer than the C-Nb bond in the Nb methylidene isocyanide (1.892 Å).
and V), the plausible products along the reaction path 1, are illustrated in Figures 10-12. Unlike previously studied nonplanar CH2dZr(H)NC,16 the Group 5 metal-conjugated methylidene complexes all have planar Cs structures. Their CH2 moieties are more agostically distorted than the Zr methylidene isocyanide.16 The H-C-M angles of 88.8, 90.0, and 85.3° for CH2dTa(H)NC, CH2dNb(H)NC, and CH2dV(H)NC are smaller than that of 91.3° for CH2dZr(H)NC. They are also compared with those of 92.7, 92.4, and 88.2° for CH2dTaHF, CH2dNbHF, and CH2dVHF and those of 88.7, 88.9, 88.2, and
Cho and Andrews
Figure 12. The B3LYP structures of the plausible V products in the proposed reaction path 1 with the 6-311++G(3df,3pd) basis sets for H, C, N, and V. Bond distances and angles are in Å and degrees, respectively. The V methylidene isocyanide has a doublet ground state, and the other ones have quartet ground states. The molecular symmetry is denoted under the structure. Notice the agostic distortion of the methylidene isocyanide complex. The C-V and N-V bonds in the nitrile π-complex (1.967 and 1.889 Å) are shorter than those in CH3-VNC and CH3CNfV but are longer than the C-V bond in the V methylidene isocyanide (1.757 Å).
87.9° for CH2dTaHCl, CH2dNbHCl, CH2dTaHBr, and CH2dNbHBr, respectively.7 It is reasonable that more-electrondeficient (higher electronegativity) Group 5 metals lead to stronger agostic interactions, but the conjugation effects on the magnitude of the distortion are apparently not noticeable. The observed C-Ta and C-Nb stretching frequencies of 819.6 and 788.8 cm-1 are also compared with those of 809.8, 816.7, 816.6, 777.7, 794.3, and 796.4 cm-1 for CH2dTaHF, CH2dTaHCl, CH2dTaHBr, CH2dNbHF, CH2dNbHCl, and CH2dNbHBr, respectively. The CH2 wagging frequencies of 657.9 cm-1 for CH2dTa(H)NC are also comparable with those of 672.9, 656.3, and 653.6 cm-1 for CH2dTaHF, CH2dTaHCl, and CH2dTaHBr, respectively.7 Evidently, weakening of the C-M bond by conjugation is not observable in the Group 5 metal methylidene cyanides, reconfirming the previous result that the conjugation effects of CdM-N′C: is minor.16 The insertion complex, on the other hand, has a Cs structure and the M-N′C moiety is slightly bent (167.6, 169.4, and 167.7° for the Ta, Nb, and V insertion products). The π-complex also has a Cs structure, and the C-M and N-M bonds are shorter than those in CH3-MNC and CH3CNfM but are longer than the C-M bond in the methylidene complex as shown in Figures 10-12. This indicates that binding of the Group 5 metal atoms to the nitrile group is weaker than in the Zr system, where the C-Zr and N-Zr bonds of η2-Zr(NC)-CH3 are the shortest among those of the Zr products including CH2dZr(H)NC. The back-donation from the Group 5 metal center to the π*orbitals of the CN triple bond is evidently less effective than the exceptionally strong interaction in the corresponding Zr system.16 The binding energy for the Ta, Nb, and V nitrile π-complexes of 48, 48, and 21 kcal/mol are compared with that for the Zr π-complex of 69 kcal/mol. The present results are also in line with the previously reported exceptionally strong back-donation from the Group 4 metals to the π*-orbital of the CC triple bond in η2-M-C2H2.29 The shorter CN bonds for the Ta, Nb, and V η2-π-complexes (1.278, 1.269, and 1.256 Å) than that of η2-Zr(NC)-CH3 (1.280 Å) are also consistent with the weaker back-donations, resulting in the stronger CN bonds.
Laser-Ablated Group 5 Metals Reacting with Acetonitrile On the other hand, the coordination complexes with the N-end of CH3CN (CH3CNfM), which is believed to form first in reactions of the metal atoms with acetonitrile although not observed in the matrix spectra, largely retain the structure of free acetonitrile. They all have C3V structures computed with the DFT methods used in this study. Conclusions Laser-ablated Group 5 metal atoms react with acetonitrile, and the products are identified on the basis of isotopic shifts and correlation with the DFT results. Ta exclusively produces CH2dTa(H)NC in the process of both codeposition and subsequent photolysis, whereas Nb generates CH3-NbNC and η2-Nb(NC)-CH3 in reaction with CH3CN and they transform to CH2dNb(H)NC upon subsequent photolysis. Codeposition of V with acetonitrile leads to almost exclusive production of η2-V(NC)-CH3, and following photolysis transforms the nitrile π-complex to CH3-VNC. Production of the Group 5 metal isocyanide and π-complexes during codeposition and subsequent photolysis and absence of the energetically comparable cyanide counterparts are another evidence for the proposed reaction path 1. The Group 5 metal methylidene isocyanides are more agostic than the Zr methylidene, but the extents of distortion are comparable to those for the previously studied Group 5 metal methylidene halides. The observed C-M stretching and CH2 wagging frequencies of the methylidene isocyanides are also similar to those of the halide analogues, indicating that the effects of the metal containing conjugation system are minor, parallel to the recent results for the Zr methylidene cyanide. The C-M and N-M bonds are shorter than those of CH3CNfM and CH3-MNC but are longer than the C-M bond of CH2dM(H)NC, indicating that binding of the Group 5 metal atoms to the nitrile triple bond is considerably weaker than in the previously studied Zr system,16 where the C-M and N-M bonds are the shortest. It is also consistent with the recent report that the Group 4 metals form exceptionally strong bonds with acetylene due to the unusually strong back-donation from the metal center to the π*-orbitals.29 Acknowledgment. We gratefully acknowledge financial support from National Science Foundation (U.S.) Grant CHE 03-52487 to L.A., and support from the Korea Research Foundation (KRF) grant funded by the Korean government (MEST) (No. 2009-0075428). References and Notes (1) (a) Chang, S.-C.; Hauge, R. H.; Kafafi, Z. H.; Margrave, J. L.; Billups, W. E. J. Am. Chem. Soc. 1988, 110, 7975. (b) de Almeida, K. J.; Cesar, A. Organometallics 2006, 25, 3407. (c) Bihlmeier, A.; Greene, T. M.; Himmel, H.-J. Organometallics 2004, 23, 2350. (2) (a) Kline, E. S.; Kafafi, Z. H.; Hauge, R. H.; Margrave, J. L. J. Am. Chem. Soc. 1987, 109, 2402. (b) Hora´cˇek, M. H.; Hiller, J.; Thewalt, U.; Sˇteˇpnicˇka, P.; Mach, K. J. Oranomet. Chem. 1998, 571, 77. Michelini, M. D. C.; Russo, N.; Alikhani, M. E.; Silvi, B. J. Comput. Chem. 2004, 25, 1647; M + C2H2. (3) (a) Siegbahn, P. E. M.; Blomberg, M. R. A.; Svensson, M. J. Am. Chem. Soc. 1993, 115, 1952. (b) Alikhani, M. E.; Hannachi, Y.; Manceron, L.; Bouteiller, Y. Chem. Phys. 1995, 103, 10128. (c) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2008, 112, 12071; M + C2H4. (4) (a) Pru¨sse, T.; Drewello, T.; Lebrilla, C. B.; Schwarz, H. J. Am. Chem. Soc. 1989, 111, 2857. (b) Legon, A. C.; Lister, D. G.; Warner, H. E. Angew. Chem., Int. Ed. Engl. 1992, 31, 202. (c) Purcell, K. F.; Drago, R. S. J. Am. Chem. Soc. 1966, 88, 919. (5) (a) Wells, N. P.; Phillips, J. A. J. Phys. Chem. A 2002, 106, 1518. (b) Hattori, R.; Suzuki, E.; Shimizu, K. J. Mol. Struct. 2005, 750, 123. (6) (a) Porembski, M.; Weisshaar, J. C. J. Phys. Chem. A 2000, 104, 1524. (b) Willis, P. A.; Stauffer, H. U.; Hinrichs, R. Z.; Davis, H. F. J. Phys. Chem. A 1999, 103, 3706.
J. Phys. Chem. A, Vol. 114, No. 19, 2010 6005 (7) (a) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040, and references therein (Review article, Groups 4-6. (b) Lyon, J. T.; Cho, H.G.; Andrews, L. Organometallics 2007, 26, 2519; Ti, Zr, Hf + CHX3, CX4(c) Lyon, J. T.; Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 6373; Cr, Mo, W + CHX3, CX4(d) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2006, 110, 10063; Group 5 + CH3X. (8) (a) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 2480. (b) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 633; Group 3. (9) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 4096. (b) Cho, H.-G.; Andrews, L. Inorg. Chem. 2008, 47, 1653; Re. (10) (a) Cho, H.-G.; Lyon, J. T.; Andrews, L. Organometallics 2008, 27, 5241. (b) Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 2537. (c) Cho, H.-G.; Andrews, L. Organometallics 2008, 27, 1786; Group 8. (11) Cho, H.-G.; Andrews, L. Reactions of Group 9 Metals with Halomethanes, unpublished data. (12) (a) Cho, H.-G.; Andrews, L. J. Am. Chem. Soc. 2008, 130, 15836. (b) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2008, 112, 12293. (c) Cho, H.-G.; Andrews, L. Organometallics 2009, 28, 1358. (d) Cho, H.-G.; Andrews, L.; Vlaisavljevich, B.; Gagliardi, L. Organometallics 2009, 28, 5623; Group 10. (13) (a) Andrews, L.; Cho, H.-G. J. Phys. Chem. A 2005, 109, 6796. (b) Cho, H.-G.; Lyon, J. T.; Andrews, L. J. Phys. Chem. A 2008, 112, 6902. (c) Lyon, J. T.; Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 1047; Actinides. (d) Cho, H.-G.; Andrews, L. Reactions of Lanthanides with Methane and Halomethanes, unpublished data. (14) (a) von Frantzius, G.; Streubel, R.; Brandhorst, K.; Grunenberg, J. Organometallics 2006, 25, 118, and references therein. (b) Berkaine, N.; Reinhardt, P.; Alikhani, M. E. Chem. Phys. 2008, 343, 241. (c) Roos, B. O.; Lindh, R.; Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 6420. Clot, E. ; Eisenstein in O. Computational Inorganic Chemistry; Kaltzoyannis, N.; McGrady, J. E. Eds.; Structure and Bonding; Springer: Heidelberg, 2004; pp 1-36. Aubert, C.; Buisine, O.; Malacria, M. Chem. ReV 2002, 102, 813, and references therein. (agostic structures). (15) (a) Crabtree, R. H. Chem. ReV. 1995, 95, 987, and references therein. (b) Wada, K.; Craig, B.; Pamplin, C. B.; Legzdins, P.; Patrick, B. O.; Tsyba, I.; Bau, R. J. Am. Chem. Soc. 2003, 125, 7035. (c) Ujaque, G.; Cooper, A. C.; Maseras, F.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1998, 120, 361. (16) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2010, 114, 891. (17) (a) Andrews, L.; Citra, A. Chem. ReV 2002, 102, 885, and references therein. (b) Andrews, L. Chem. Soc. ReV. 2004, 33, 123, and references therein. . (18) 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.; 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, vB.; Chen, vW.; Wong, M. W.; Gonzalez, vC.; Pople, J. A. Gaussian 03, ReVision C.02; Gaussian, Inc.: Wallingford, CT, 2004. (19) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, Y.; Parr, R. G. Phys. ReV. B 1988, 37, 785. (20) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062. (21) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123. (22) (a) Becke, A. D. Phys. ReV. A 1988, 38, 3098. (b) Burke, K.; Perdew, J. P.; Wang, Y. In Electronic Density Functional Theory. Recent Progress and New Directions; Dobson, J. F., Vignale, G., Das, M. P., Ed.s; Plenum: 1998. (23) (a) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502. (b) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937. (24) (a) Maier, G.; Schmidt, C.; Reisenauer, H. P.; Endlein, E.; Becker, D.; Eckwert, J.; Hess, B. A.; Schaad, L. J. Chem. Ber. 1993, 126, 2337. (b) Jacox, M. E. Chem. Phys. 1979, 43, 157. (c) Yang, X.; Maeda, S.; Ohno, K. J. Phys. Chem. A 2005, 109, 7319; Photolysis of CH3CN. (d) Hattori, R.; Suzuki, E.; Shimizu, K. J. Mol. Struct. 2005, 738, 165; CH3NC. (e) Deng, R.; Trenary, M. J. Phys. Chem. C 2007, 111, 17088; HCCNH2. (25) (a) Van Zee, R. J.; Weltner, W., Jr. J. Chem. Phys. 1995, 102, 4367. (b) Wang, X.; Andrews, L. unpublished data. (Nb and Ta + H2).
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J. Phys. Chem. A, Vol. 114, No. 19, 2010
(26) (a) Petrie, S. Phys. Chem. Chem. Phys. 1999, 1, 2897. (b) Rayo´n, V. M.; Redondo, P.; Valde´s, H.; Barrientos, C.; Largo, A. J. Phys. Chem. A 2007, 111, 6334. (c) Kafafi, Z. A.; Hauge, R. H.; Margrave, J. L. Polyhedron 1983, 2, 167; M(CN) isomerism. (27) (a) Balasubrahmanyam, K.; Janz, G. J. J. Am. Chem. Soc. 1970, 92, 4189. (b) Jamro´s, D.; Wo´jcik, M.; Lindgren, J.; Stangret, J. J. Phys. Chem. B 1997, 101, 6758. (c) Cha, J.-N.; Cheong, B.-S.; Cho, H.-G. J. Phys. Chem. A 2001, 105, 1789; solvation in CH3CN.
Cho and Andrews (28) (a) Garcia, J. J.; Brunkan, N. M.; Jones, W. D. J. Am. Chem. Soc. 2002, 124, 9547. (b) Favero, G.; Morvillo, A.; Turco, A. J. Organomet. Chem. 1983, 241, 251; CN π-complex. (29) Cho, H.-G.; Kushto, G. P.; Andrews, L.; Bauschlicher, C. W., Jr J. Phys. Chem. A 2008, 112, 6295.
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