Infrared Spectra of Manganese Insertion, Vinyl, and Cyclic Complexes

Article pubs.acs.org/Organometallics

Infrared Spectra of Manganese Insertion, Vinyl, and Cyclic Complexes Prepared in Reactions of Laser-Ablated Mn Atoms with Methane, Ethane, Ethyl Chloride, and 1,2-Dichloroethane Han-Gook Cho and Lester Andrews* Department of Chemistry, University of Incheon, 119 Academy-ro, Songdo-dong, Yeonsu-gu, Incheon, 460-772, South Korea, and Department of Chemistry, University of Virginia, P.O. Box 400319, Charlottesville, Virginia 22904-4319, United States S Supporting Information *

ABSTRACT: Manganese insertion, vinyl, and cyclic complexes are prepared in direct reactions of excited Mn atoms with CH4, C2H6, C2H5Cl, and CH2ClCH2Cl, all with sextet ground states. The only organometallic product observed in the reaction with methane is CH3−MnH. The analogous insertion product C2H5−MnH is observed with ethane, but hydrogen elimination is accompanied by generation of the vinyl product (CH2CH− MnH). The unusual stabilities of metallacyclic over carbene products in the haloethane systems are in line with the previously observed group 4 metallacyclopropanes. NBO analyses reveal that the distinctively low metal dorbital contribution to the C−M and M−H bonds is responsible for the linear backbones of CH3−MnH and the group 12 metal analogues, which are similar to those of the Grignard reagents. Systematic NBO calculations for the first-row transition-metal CH3−MH complexes show that a low metal d-contribution to the C−M and M−H bonds gives a linear molecular backbone and that increasing d-character in these bonds decreases the C−M−H angle. The stabilities of the half-filled and filled d-orbitals evidently make the group 7 and 12 metals similar to the group 2 metals. The tendency of increasing preference for higher oxidation state complexes with heavier members of the group is most dramatic for the group 7 metals Mn and Re.

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INTRODUCTION Organomanganese reagents are known to be generally more stable than most organometallics from other transition metals.1 The reactivity of organomanganese compounds is often compared to the reactivities of organomagnesium and organozinc compounds.2 Reactions of manganese halides with orgnanolithium or organomagnesium compounds (transmetalation) are considered to be a primary route to provide the firstrow transition-metal compounds.3 A few small manganese complexes have also been studied. Billups et al. reported the photochemical formation of CH3−MnH in pure solid methane and later produced CH2Mn from the spontaneous reaction of Mn and CH2N2 during co-deposition in excess argon, and Ozin et al. made MnH2 in hydrogen-doped solid xenon using selective photoexcitation of Mn atoms.4 Dimethyl manganese, methyl manganese chloride, and other alkyl manganese species were provided by metathesis of Grignard reagents with manganese chloride, but they decompose rapidly.5 Recent examples of small Mn insertion and methylidene complexes with high multiplicities (quartet or sextet) are provided in direct reactions of laser-ablated Mn with halomethanes.6 Only the C−X insertion complex (CH3−MnX, X = halogen) was observed with methyl halides, but both the insertion and methylidene (CX2MnX2) products from reactions with di-, tri-, and tetrahalomethanes, in contrast to the exclusive production of the methylidynes (XCMnX3) from Re reactions.7 These Mn and Re products are a most dramatic example of increasing preference for the higher © XXXX American Chemical Society

oxidation state complexes on going down a transition-metal group column. It is also interesting to note that these Mn insertion complexes contain linear or nearly linear C−Mn−X moieties, which are rare among the transition-metal analogues.4,8−10 The HCC−MnH species recently observed in the reaction with acetylene also possesses a linear structure.11 Similar linear molecular backbones were previously observed only in the Fe products from reactions with halomethanes.12 NBO analyses13 have shown a large s-contribution from Mn to the C−Mn bond, while the Mn−F bond was treated as ionic.6 In this paper, we report small Mn insertion, vinyl, and cyclic products from reactions with CH4, C2H6, C2H5Cl, and CH2ClCH2Cl in excess argon. They are identified in the matrix infrared spectra through isotopic substitution and with helpful predictions from DFT frequency calculations for likely reaction products. These Mn complexes all bear sextet ground states, and the insertion products contain linear molecular backbones. NBO analyses for the Mn, Re, group 12 metal, and Mg insertion complexes reveal the origin of the linear structures and similarities in the chemistry of these metals.2,3

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EXPERIMENTAL AND COMPUTATIONAL METHODS

Laser-ablated manganese atoms were reacted with CH4 (Matheson, UHP grade), 13CH4, CD4, CH2D2 (Cambridge Isotopic Laboratories), Received: March 14, 2013

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dx.doi.org/10.1021/om400217w | Organometallics XXXX, XXX, XXX−XXX

Organometallics

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Figure 1. Infrared spectra in the product absorption regions from reactions of the laser-ablated manganese atoms with methane isotopomers (1.0% in argon) at 10 K. (a) Mn and CH4 co-deposited for 1 h. (b) Like (a) after irradiation (λ > 290 nm), (c) as (b) after UV (240−380 nm) irradiation, and (d) as (c) after annealing to 28 K. (e) Mn and CD4 co-deposited for 1 h, (f−h) as (e) spectra taken after visible (λ > 420 nm) and UV irradiations and annealing to 36 K. (i) Mn and 13CH4 co-deposited for 1 h, (j and k) as (i) after UV irradiation and annealing to 36 K. (l) Mn and CH2D2 co-deposited for 1 h, (m and n) as (l) after UV irradiation and annealing to 28 K. i stands for the product absorption. P and w designate the precursor and water residue absorptions, respectively. C2H6 (Matheson), C2 D6 (MSD Isotopes), C 2 H5 Cl, C2D5Cl, CH2ClCH2Cl, and CD2ClCD2Cl 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.6,8,14 Reagent gas mixtures range from 0.25% to 2.0% in argon. The Nd:YAG laser fundamental (1064 nm, 10 Hz repetition rate, 10 ns pulse width) was focused on a rotating Mn target (Johnson-Matthey) 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 liquid nitrogen cooled 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 and annealed into the 20−40 K range to allow further reagent diffusion and reaction. In order to provide support for the assignment of new experimental frequencies and to correlate with related works,8−12 density functional theory (DFT) calculations were performed using the Gaussian 09 program system,15 the B3LYP density functional,16 and the 6-311+ +G(3df,3pd) basis sets for H, C, F, Cl, and Mn17 to provide vibrational frequencies for the reaction products. Geometries were fully relaxed during optimization, and the optimized geometry was confirmed by vibrational analysis. The BPW91 functional,18 MP2,19 and CCSD20 methods were also employed to complement 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 a few percent higher than observed frequencies,8−12,21,22 and they provide useful predictions for infrared spectra of new molecules.

Figure 2. Infrared spectra in the product absorption regions from reactions of the laser-ablated manganese atoms with C2H6 and C2D6 (1.0% in argon) at 10 K. (a) Mn and C2H6 co-deposited for 1 h, (b−f) as (a) after visible (λ > 420 nm), UV (240−380 nm), visible, and full arc (λ > 220 nm) irradiations and annealing to 28 K. (g) Mn and C2D6 co-deposited for 1 h, (h−k) as (g) after visible, UV, and full arc irradiation and annealing to 28 K. i and v stand for the product absorption groups, while p, w, and c designate the precursor, water residue, and common absorptions.

RESULTS AND DISCUSSION The matrix infrared spectra (Figures 1−4) from reaction products of laser-ablated manganese atoms with methane, ethane, ethyl chloride, 1,2-dichloroethane are investigated, and the observed and calculated frequencies (Tables 1−8) and computed structures (Figures 5−8) will be presented in turn. The DFT frequencies of unobserved higher energy isomers of the products (Tables S1−S5) and the parameters from NBO

analyses for the C−Mn and Mn−X (X = H, Cl, Br) bonds of insertion products (Table S6) are also accessible as Supporting Information. Mn + CH4. The organometallic product absorptions from reactions of Mn with CH4 isotopomers are marked “i” (for the insertion product) as shown in Figure 1. They remain almost unchanged on visible irradiation (λ > 420 nm), but increase in concert more than 50% on UV (λ = 240−380 nm or >290 nm)

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B


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Figure 3. Infrared spectra in the product absorption regions from reactions of the laser-ablated manganese atoms with C2H5Cl and C2D5Cl (0.50% in argon) at 10 K. (a) Mn and C2H5Cl co-deposited for 1 h, (b−e) as (a) after visible (λ > 420 nm), UV (240−380 nm), and full arc (λ > 220 nm) irradiations and annealing to 28 K. (f) Mn and C2D5Cl co-deposited for 1 h, (g−j) as (f) after visible, UV, and full arc irradiation and annealing to 28 K. i and cy stand for the product absorption groups while p, w, and c designate the precursor, water residue, and common absorptions.

irradiation and decrease on stepwise annealing to higher temperatures. The frequencies of the observed product absorptions are listed in Table 1 and are compared with the calculated frequencies for CH3−MnH in Table 2 using several theoretical methods. The strong absorption at 1616.6 cm−1 (with matrix site splitting absorptions at 1623.6 and 1608.2 cm−1) shifts on deuteration to 1162.9 cm−1 (H/D ratio of 1.390) (with similar matrix site absorptions at 1167.1 and 1157.4 cm−1), but shows no 13C shift. These Mn−H and Mn−D stretching frequencies can be compared with the previously reported frequencies of 1592.3 and 1155.1 cm−1 for MnH2 and MnD2.23 The former is very close to the 1616.5 cm−1 value assigned to CH3−MnH from the UV-initiated Mn reaction with methane impurity in the diazomethane system in solid argon.4b The Mn−H stretching band for CH3−MnH produced in solid methane is 34 cm−1 lower due to stronger interaction with the solid methane host,4a and the other assignments to bands for this species in solid methane exhibit 5−9 cm−1 shifts from our solid argon values. In our work the CH2D2 reaction product spectra show both Mn−H and Mn−D stretching absorptions. The MnH2 absorption at 1592.3 cm−1 is observed to be weak over the water residue absorption in the product spectra (too weak to be visible in Figure 1), and the D counterpart is not detected. Other product absorptions also support formation of the insertion product, CH3−MnH. The i absorption observed at 1148.6 cm−1 carries its D and 13C counterparts at 892.1 and 1140.4 cm−1 (H/D and 12/13 ratios of 1.288 and 1.007) and is assigned to the CH3 deformation mode on the basis of its frequency and large D shift. The i absorptions at 540.9 and 505.9 cm−1 are observed with their 13C counterparts at 537.8 and 493.5 cm−1 and assigned to the CH3 rocking and C−Mn stretching modes on the basis of the good agreement with the DFT values (Table S1), while the D counterparts are not observed due to their low frequencies. The four observed

Figure 4. Infrared spectra in the product absorption regions from reactions of the laser-ablated manganese atoms with CH2ClCH2Cl and CD2ClCD2Cl (0.50% in argon) at 10 K. (a) Mn and CH2ClCH2Cl codeposited for 1 h, (b−e) as (a) after visible (λ > 420 nm), UV (240− 380 nm), and full arc (λ > 220 nm) irradiations and annealing to 28 K. (f) Mn and CD2ClCD2Cl co-deposited for 1 h, (g−j) as (f) after visible, UV, and full arc irradiation and annealing to 28 K. cy stands for the product absorption, while p designates the precursor absorption.

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Table 1. Frequencies of Product Absorptions Observed from Reactions of Mn with Methane Isotopomers in Excess Argona

a

13

group

CH4

CD4

i

1623.6, 1616.6, 1608.2

1167.1, 1162.9, 1157.4,

1623.7, 1616.5, 1608.3,

CH4

1148.6 545.0, 542.8, 540.9 505.9

892.1

1140.4 541.7, 539.5. 537.8 493.5

CH2D2 1623.7, 1616.0, 1608.1 1168.3, 1164.2, 1158.4 509.6

description CH3-MH, A1 Mn−H str. CH3−MH, A1 CH3 deform CH3−MH, E CH3 rock CH3−MH, A1 C−M str.

All frequencies are in cm−1. Stronger absorptions in a set are bold. Description gives major coordinate.

(MnH 2 −CH 2 CH 2 , CH 3 CHMnH 2 , CH 3 −Mn−CH 3 , CH2CH−MnH, HCC−MnH, and CH2MnH2), and it turned out that only the CH2 wagging band of vinyl manganese hydride (CH2CH−MnH) was consistent with the observed frequency, H/D isotopic frequency ratio, and strong absorption intensity. The strong MnH2 and MnD2 absorptions observed at 1592.3 and 1155.1 cm−1 indicate that H2- and D2-elimination occur extensively in reactions of Mn with C2H6 and C2D6, unlike in the Mn + CH4 reactions, where only a weak MnH2 absorption (but no MnD2 absorption) is detected. In contrast, the previously studied transition-metal (group 4 and 8 metals,24,25 Re,7 Rh,26 and Pt27) reactions with ethane also show only weak binary metal hydride absorptions. The broad, strong v absorption at 1607.8 cm−1 (with a matrix site absorption at 1635.0 cm−1) shifts to 1156.5 cm−1 (with a site absorption at 1171.1 cm−1) and is assigned to the Mn−H stretching mode. Another v absorption at 468.2 cm−1 in the low-frequency region is assigned to the H3C−Mn stretching mode with its D counterpart at 427 cm−1. The observed v absorptions are in fact the three observable strong bands of the vinyl manganese hydride as shown in Table 5, and their frequencies and D shifts are in good agreement with the B3LYP frequencies of 1643.8, 989.4, and 488.0 cm−1 and the D shifts of 471.0, 224.3, and 35.0 cm−1, respectively, as summarized in Table 5. The v and strong MnH2 absorptions support production of CH2CH−MnH via elimination of H2 during the reaction of excited Mn with C2H6. Both MnH2−CH2CH2 and CH3CHMnH2, other possible products, would show strong MnH2 stretching absorptions higher than 1650 cm−1 (Tables S2 and S3), but they are not observed in this study. These cyclic and carbene complexes are 103 and 172 kJ/mol higher than C2H5−MnH, and CH2CH− MnH + H2 is 100 kJ/mol higher. The energy difference between the insertion and carbene products is much smaller than that in the methane case, probably due to stabilization by the methyl group. Mn + C2H5Cl. Figure 3 shows infrared spectra from reactions of excited Mn atoms with C2H5Cl and its deuterated isotopomer. Two groups of product absorptions marked “i” and “cy” (for cyclic product) are observed on the basis of their behavior in the process of photolysis and correlation with DFT values. The i absorptions increase ∼20 and ∼60% on irradiation with λ > 420 nm and 380 > λ > 240 nm, respectively, and slightly decrease on full arc (λ > 220 nm) photolysis, whereas the cy absorptions increase ∼30%, ∼70%, and ∼50% (150% in total) on irradiation with λ > 420 nm, 380 > λ > 240 nm, and λ > 220 nm, respectively. A trace of MnO2 is observed at 948.0 cm−1 from the reaction with an oxygen impurity.14a The strongest i absorption is observed in the low-frequency region at 499.4 cm−1 with its D counterpart at 468.8 cm−1, and we assign it to the C−Mn stretching mode of C2H5−MnCl on the basis of good correlation with the B3LYP-computed frequency of 493.3 cm−1 and D shift of 30.4 cm−1. Table 6

product bands along with the previous results6 substantiate generation of CH3−MnH. On the other hand, the Mn methylidene complex (CH2 MnH2) is not identified in the product spectra, which would show its strong MnH2 stretching absorptions at ∼1700 and ∼1600 cm−1 and MnH2 scissoring band at ∼640 cm−1 (Table S1). CH3−MnH and CH2MnH2 in the ground sextet and quartet states are 16 and 226 kJ/mol higher in energy than Mn(6S) + CH4. The previous and current studies reveal that excited first-row transition-metal atoms all readily undergo methane activation to form the insertion products, but only the Sc and Ti reactions proceed further to generate the methylidenes as well via H-migration from C to M during co-deposition of the excited atoms produced by laser ablation or subsequent photolysis.4,8−10 Mn + C2H6. Product absorptions from reactions of Mn with ethane isotopomers are shown Figure 2, where unlike the methane case, two sets of organometallic product absorptions are observed and marked “i” and “v” (for insertion and vinyl products) and listed in Table 3. The i absorptions increase ∼10%, ∼50%, and ∼20% (∼80% in total) on irradiation with λ > 420 nm, 240 < λ < 380 nm, and λ > 220 nm, whereas the v absorptions increase ∼5%, ∼30%, and ∼5% (∼40% in total). It is also noticeable that the antisymmetric stretching absorptions of MnH2 and MnD2 at 1592.3 and 1155.1 cm−1 23 are very strong, as shown in Figure 2, in contrast to the Mn + CH4 case. The strongest i absorption is observed at 1556.3 cm−1 (with a matrix site absorption at 1563.8 cm−1), and deuteration shifts it to 1128.6 cm−1 (H/D ratio of 1.379) (with a similar site absorption at 1133.3 cm−1). These Mn−H and Mn−D stretching bands are indicative of a C−H bond insertion product, most probably C2H5−MnH. This product is at 29 kJ/ mol higher energy than the reactants. The other i absorptions are also consistent with generation of the Mn insertion complex. The i absorptions observed at 931.2 and 896.7 cm−1 are accompanied with their D counterparts at 896.7 and 683.5 cm−1, and they are assigned to the C−C stretching and CH2 wagging modes. The product absorptions at 522.3 and 421 cm−1 are designated to the CH2 rocking and C−Mn stretching modes, while their D counterparts are too low in frequency to observe. The product absorption at 2931.0 and 2869.5 cm−1 in the high-frequency region are tentatively assigned to the A″ and A′ CH3 stretching modes. These product absorptions substantiate formation of the insertion complex (C2H5−MnH), parallel to the methane case. The observed and calculated frequencies are given in Table 4. The strong v absorption observed at 975.3 cm−1, above the CH2 wagging absorption of C2H4 at 949 cm−1, which is commonly produced in C2H6 experiments by hydrogen elimination due to metal plume irradiation in the ablation process, shifts to 740.5 cm−1 on deuteration (H/D ratio of 1.317, which is similar to that of ethylene, 1.318). A series of computations was carried out for the plausible products D


464.4

892.1

1148.6 540.9 505.9

Frequencies and intensities are computed with 6-311++G(3df, 3pd) for harmonic calculations, and the all-electron basis set is used for Mn. Frequencies and intensities are in cm−1 and km/mol. Observed in an argon matrix. cComputed with B3LYP. dComputed with MP2. eComputed with CCSD. CH3−MnH has a C3v structure.

1140.4 537.8 493.5

1616.5 1162.9 1616.6

Table 3. Frequencies of Product Absorptions Observed from Reactions of Mn with Ethane Isotopomers in Excess Argona group i

v

MH2

C2H6 2931.0b 2869.5b 1563.8, 1556.3 931.2, 926.7 896.7 522.3, 517.5 421 1635.0, 1607.8 975.3 468.2 1592.3

C2D6 2060.2b 1133.3, 1128.6 833.3, 816.6 683.5

1171.1, 1156.5 740.5 427 1155.1

description C2H5−MnH, A″ CH3 str. C2H5−MnH, A′ CH3 str. C2H5−MnH, A′ Mn−H str. C2H5−MnH, A′ C−C str. C2H5−MnH, A′ CH2 wag C2H5−MnH, A″ CH2 rock C2H5−MnH, A′ C−Mn str. CH2CH−MnH, Mn−H str. CH2CH−MnH, CH2 wag CH2CH−MnH, C−Mn str. MnH2 as. str.

All frequencies are in cm−1. Stronger absorptions in a set are bold. Description gives major coordinate. bTentatively assigned.

a

compares the observed and calculated frequencies. Another strong i absorption at 538.0 cm−1 is designated to the CH2 rocking mode, while its D counterpart is too low in frequency to observe. A weaker i absorption at 937.1 cm−1 is assigned to the C−C stretching mode with its D counterpart at 823.7 cm−1, and another i absorption at 1419.4 cm−1 to the CH3 bending mode. Observation of the C−Cl insertion complex suggests that the Mn atom is first attracted by the electron-rich Cl atom and undergoes C−Cl bond insertion, generating the stable product (C2H5−MnCl). This is analogous to previous reactions with CH3Cl, which gave the CH3−MnCl insertion product exclusively.6 The strongest cy absorption is observed at 1628.0 cm−1 (with a site absorption at 1641.4 cm−1), and deuteration shifts it to 1172.0 cm−1 (H/D ratio of 1.389) (with a matrix site absorption at 1181.2 cm−1). This new Mn−H stretching absorption reveals that another product with a Mn−H bond also forms during co-deposition of excited Mn with C2H5Cl and photolysis afterward. The Mn−H stretching frequency is close to the 1616.6 cm−1 value for CH3−MnH, and we assign it to cyclic HMnCl−CH2CH2. The observed frequency and D shift are in good agreement with the B3LYP and BPW values of 1684.1 and 1687.2 cm−1 and 482.9 and 483.6 cm−1 calculated for the cyclic complex, respectively. Table 7 compares the observed and calculated frequencies. Another strong cy absorption at 992.4 cm−1 shifts to 751.7 cm−1 on deuteration and is assigned to the CH2 wagging mode. DFT computations indicate that the Mn−H stretching and CH2 wagging bands are the strongest ones for the cyclic product, and other bands are too weak to observe, as shown in Table 7. This band has a low 1.320 H/D frequency ratio, owing to anharmonicity, which is typical for a CH2 deformation mode, as may be compared with the above ratios for the vinyl complex and ethylene itself. The observed cy absorptions substantiate generation of the cyclic product. Production of HMnCl−CH2CH2 reveals that not only C−Cl bond insertion but also subsequent H-migration from β-C to Mn readily occur during co-deposition and photolysis afterward. The C2H5−MnCl and HMnCl−CH2CH2 products in their sextet ground states (both 6A′) are 219 and 156 kJ/mol more stable than the reactants (Mn(6S5/2) + C2H5Cl). Other plausible products are the C−H insertion and carbene complexes (ClCH2CH2−MnH and CH3CHMnHCl), and they are, respectively, 13 kJ/mol higher and 46 kJ/mol lower energy than the reactants. Moreover, the C−H insertion

b

3120.0 3037.7 1679.6 1457.3 1183.1 561.3 495.6 286.7 18 × 2 13 432 0×2 3 51 × 2 50 163 × 2 3044.9 2987.5 1629.8 1439.2 1175.7 525.1 482.9 154.4 2278.6 2160.1 1171.4 1063.3 933.0 424.0 461.3 192.4 2313.2 2182.8 1198.8 1057.0 922.2 429.5 466.3 207.0 5×2 3 232 1×2 12 35 × 2 40 85 × 2 2257.1 2145.0 1162.5 1045.1 917.1 398.5 454.6 111.9 3084.6 3010.1 1641.4 1468.6 1206.8 558.2 501.9 266.3 3130.8 3041.0 1679.6 1460.2 1191.4 564.8 508.2 286.8 17 × 2 13 432 1×2 4 52 × 2 52 163 × 2 3055.4 2990.6 1629.8 1442.2 1184.0 528.1 495.1 154.5

obs CCSD MP2 int B3LYP obs CCSD MP2 int B3LYP obs approximate description

E CH3 str. A1 CH3 str. A1 Mn−H str. E deform A1 deform E CH3 rock A1 C−M str. E CMnH bend

B3LYP

c b e d c

CD3−MnD

c b e d

CH3−MnH

c c b

Table 2. Observed and Calculated Fundamental Frequencies of CH3−MnH Isotopomers in the 6A1 Ground Statea

a

MP2d intc

3074.0 3006.9 1641.4 1462.6 1198.5 554.8 487.5 266.3

Article

13

CH3−MnH

CCSDe

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Table 4. Observed and Calculated Fundamental Frequencies of CH3CH2−MnH Isotopomers in the 6A′ Ground Statea CH3CH2−MnH

CD3CD2−MnD

approximate description

obsb

B3LYPc

intc

BPW91d

MP2e

A″ CH3 str. A′ CH3 str. A″ CH2 str. A′ CH3 str. A′ CH2 str. A′ Mn−H str. A′ C−C str. A′ CH2 wag A″ CH2 rock A′ C−Mn str.

2931.0

3057.6 3038.9 3002.8 2993.8 2974.2 1616.5 973.0 936.4 511.0 458.2

46 39 15 59 31 456 12 10 36 45

3012.9 2988.1 2969.9 2936.8 2930.2 1610.8 961.7 891.5 497.3 470.3

3127.4 3111.7 3080.6 3039.7 3034.9 1672.7 1011.7 954.6 539.9 477.4

2869.5 1556.3 931.2 896.7 517.5 421

obsb

2060.2 1128.6 816.6 683.5

B3LYPc

intc

BPW91d

MP2e

2263.7 2249.0 2220.2 2149.6 2160.4 1153.5 864.7 686.3 387.2 417.7

21 18 6 35 6 239 9 8 25 36

2230.0 2209.4 2197.1 2109.0 2128.6 1149.8 848.8 654.4 376.0 426.2

2315.5 2304.8 2277.8 2206.5 2183.0 1194.0 885.3 699.5 412.2 434.8

a

Frequencies and intensities are computed with 6-311++G(3df, 3pd) for harmonic calculations, and the all-electron basis set is used for Mn. Frequencies and intensities are in cm−1 and km/mol. bObserved in an argon matrix. cComputed with B3LYP. dComputed with BPW91. eComputed with MP2. CH3CH2−MnH has a Cs structure.

Table 5. Observed and Calculated Fundamental Frequencies of CH2CH−MnH Isotopomers in the 6A′ Ground Statea CH2CH−MnH approximate description A′ CH2 as. str. A′ CH2 s. str. A′ C−H str. A′ Mn−H str. A′ CH2 scis. A′ C−C str. A′ C−H bend A″ C−H bend A′ CH2 rock A″ CH2 wag A′ C−Mn str. A″ CCMn bend A′ CMnH bend A″ Mn−H bend A′ Mn−H bend

b

obs

1607.8

975.3 468.2

B3LYP

c

BPW91

31 34 25 409 8 11 5 8 8 38 60 52 125 149 57

3069.7 3010.7 2995.4 1635.6 1555.0 1384.6 1228.1 1006.9 946.5 945.7 497.3 347.6 336.3 42.7 117.0

int

3131.9 3070.7 3047.4 1643.8 1607.4 1432.2 1287.1 1063.8 995.8 989.4 488.0 359.2 208.2 156.6 122.9

CD2=CD−MnD

c

d

int

d

29 18 31 337 8 10 10 13 6 31 50 34 110 111 2

obs

b

1156.5

740.5 427

B3LYP

c

2331.0 2258.6 2223.0 1172.8 1521.8 1083.0 1018.3 809.2 728.1 765.1 453.0 286.6 176.7 113.8 94.6

intc

BPW91d

intd

14 12 21 218 16 4 1 1 5 26 53 37 56 76 44

2283.9 2221.3 2179.1 1167.2 1475.6 1041.4 980.8 769.1 691.7 730.0 460.0 275.0 259.7 40.7 99.1

12 7 18 180 7 6 2 2 4 24 50 25 57 56 2

a

Frequencies and intensities are computed with 6-311++G(3df, 3pd) for harmonic calculations, and the all-electron basis set is used for Mn. Frequencies and intensities are in cm−1 and km/mol. bObserved in an argon matrix. cComputed with B3LYP. dComputed with BPW91. CH2CH− MnH has a planar Cs structure.

Table 6. Observed and Calculated Fundamental Frequencies of CH3CH2−MnCl Isotopomers in the 6A′ Ground Statea CH3CH2−MnCl approximate description A″ CaH3 as str. A′ CaH3 as str. A″ CbH2 as str. A′ CaH3 s str. A′ CbH2 s str. A″ CaH3 bend A′ CaH3 deform A′ CbH2 scis. A′ Ca-Cb str. A″ CbH2 rock A′ Cb−Mn str.

b

obs

1419.4 937.1 538.0 499.4

B3LYP

c

3068.6 3049.7 3017.0 3001.6 2986.1 1509.8 1414.9 1196.2 980.0 538.7 493.3

CD3CD2−MnCl

c

BPW91

39 32 10 52 23 7 5 5 13 28 109

3022.0 2998.4 2966.8 2943.6 2929.1 1460.8 1364.9 1142.9 966.1 514.4 499.5

int

d

int

d

32 25 9 45 23 7 5 12 6 21 117

obs

b

823.7 468.8

B3LYP

c

2272.2 2257.1 2168.8 2231.6 2155.9 1087.9 1119.5 1060.9 868.2 409.9 462.9

intc

BPW91d

intd

17 15 5 4 30 4 3 2 8 20 117

2237.2 2217.4 2194.2 2127.0 2114.7 1051.3 1085.4 1045.7 849.4 390.3 465.3

14 11 3 4 27 5 2 5 6 15 125

a

Frequencies and intensities are computed with 6-311++G(3df, 3pd) for harmonic calculations, and the all-electron basis set is used for Mn. Frequencies and intensities are in cm−1 and km/mol. bObserved in an argon matrix. cComputed with B3LYP. dComputed with BPW91. Calculation results only for observable bands (frequency >400 cm−1 and intensity >5 km/mol) are shown. CH3CH2−MnCl has a Cs structure.

respectively, none of which were observed in this study (Tables S4 and S5). Reaction energy favors C−Cl insertion over C−H insertion by 232 kJ/mol, and reaction rate surely favors

complex would show not only the strong Mn−H stretching absorption but also strong CH2 bending, C−C stretching, and C−Cl stretching absorptions at ∼1240, ∼970, and ∼590 cm−1, F


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Table 7. Observed and Calculated Fundamental Frequencies of MnHCl−CH2CH2 Isotopomers in the 6A′ Ground Statea MnHCl−CH2CH2

MnDCl−CD2CD2

approximate description

obsb

B3LYPc

intc

BPW91d

int

obsb

B3LYPc

intc

BPW91d

int

A′ Mn−H str. A′ C−C str. A″ CH2 scis. A′ CH2 scis. A′ CH2 wag

1628.0

1684.1 1665.3 1475.5 1376.3 1025.7

294 14 13 4 128

1687.2 1613.7 1426.3 1338.4 987.9

291 3 12 2 113

1172.0

1201.2 1546.3 1093.4 1004.6 776.4

164 5 6 1 79

1203.6 1501.9 1057.0 975.4 747.5

156 3 6 1 69

992.4

751.7

a

Frequencies and intensities are computed with 6-311++G(3df, 3pd) for harmonic calculations, and the all-electron basis set is used for Mn. Frequencies and intensities are in cm−1 and km/mol. bObserved in an argon matrix. cComputed with B3LYP. dComputed with BPW91. Calculation results only for observable bands (frequency >400 cm−1 and intensity >3 km/mol) are shown. MnHCl−CH2CH2 has a Cs structure.

Table 8. Observed and Calculated Fundamental Frequencies of MnCl2−CH2CH2 Isotopomers in the 6A1 Ground Statea MnCl2−CH2CH2 approximate sescription A1 B1 A1 A1 B2

C−C str. CH2 scis. CH2 scis. CH2 wag MnCl2 str.

obsb covered 1002.3 438

MnCl2−CD2CD2

B3LYPc

intc

BPW91d

intd

1660.5 1475.1 1374.4 1032.7 441.7

3 13 4 126 131

1608.6 1425.5 1336.6 992.2 441.8

2 13 3 109 126

obsb

B3LYPc

intc

BPW91d

intd

761.8 438

1540.0 1093.2 1004.7 782.1 441.3

5 6 2 76 132

1496.0 1056.5 975.3 750.8 441.4

3 6 1 66 127

a

Frequencies and intensities are computed with 6-311++G(3df, 3pd) for harmonic calculations, and the all-electron basis set is used for Mn. Frequencies and intensities are in cm−1 and km/mol. bObserved in an argon matrix. cComputed with B3LYP. dComputed with BPW91. Calculation results only for observable bands (frequency >400 cm−1 and intensity >3 km/mol) are shown. MnCl2−CH2CH2 has a C2v structure.

Figure 5. B3LYP structures of the Mn insertion and methylidene complexes from reaction with methane. The 6-311++G(3df,3pd) basis sets are used for H, C, and Mn. Bond distances and angles are in Å and deg. CH3−MnH and CH2MnH2 have C3v and C2v structures. Only the insertion complex is observed in the matrix IR spectra.

insertion at the electron-rich chlorine center. The carbene product would show a strong Mn−H stretching band near ∼1725 cm−1, which is also not observed in this study: although the carbene is 46 kJ/mol lower in energy than the reactants, the cyclic product is substantially more stable (156 kJ/mol) than the reactants. Mn + CH2ClCH2Cl. Figure 4 shows the product spectra from reactions of excited Mn with CH2ClCH2Cl and its deuterated isotopomer. Only one group of product absorptions is observed (all marked “cy” for cyclic product). They are barely visible in the original deposition spectra, but they triple on visible irradiation and increase ∼400% on UV irradiation (∼7 times in total). No other significant product absorptions are observed. The strong product band observed at 1002.3 cm−1 with its D counterpart at 761.8 cm−1 is assigned to the CH2 wagging mode of the MnCl2−CH2CH2 product on the basis of the excellent correlation with the B3LYP frequency of 1032.7 cm−1 and D shift of 250.6 cm−1. Table 8 compares the observed and calculated frequencies. The low H/D frequency ratio, 1.316, is again characteristic of this vibrational mode. Another cy absorption at 438 cm−1 in the low-frequency region shows a negligible D shift and is assigned to the MnCl2 antisymmetric stretching mode. The observed values are again in good correlation with the DFT frequency of 441.7 cm−1 and D shift

Figure 6. B3LYP structures of the Mn insertion, vinyl hydride, cyclic, and carbene complexes from reactions with ethane. The 6-311+ +G(3df,3pd) basis sets are used for H, C, and Mn. Bond distances and angles are in Å and deg. C2H5−MnH, CH2CH−MnH, MnH2− CH2CH2, and CH3CHMnH2 possess Cs, Cs, C2v, and Cs structures, respectively, and C2H5−MnH and CH2CH−MnH are identified in the product spectra.

of 0.4 cm−1. This is reasonably lower than the 476.8 cm−1 measurement for MnCl2 isolated in solid argon.28 Our B3LYP calculation for MnCl2 predicts a linear sextet state with a strong 473 cm−1 antisymmetric stretching mode and 2.192 Å bond length. Other bands of this cyclic complex are too weak to observe, as shown by the calculated intensities in Table 8. ClCH2CH2−MnCl and ClCH2CHMnHCl, other plausible products, both would show strong C−Cl stretching absorptions near ∼600 cm−1 and the carbene a strong Mn−H stretching absorption as well, which are not observed in this study. G


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with halomethanes and acetylene.6,11 These small Mn complexes in fact exhibit the highest multiplicities among the transition-metal analogues. In comparison, the previously studied Cr and Fe carbene and insertion products possess triplet and quintet ground states,9 the Re carbynes doublet ground states,7 and others lower multiplicity ground states. Parallel to the previously studied Mn insertion complexes, the insertion complexes investigated in this study contain linear or near linear C−M−H subunits, similar to the Grignard reagent.29 The linear C−M−H moiety is rare among the transition-metal analogues (CH3−MH); the group 12 metal insertion complexes also have linear backbones, but the other previously studied transition-metal analogues (groups 3−6, 8− 12, lanthanides, and actinides) do not.8−10 The previous NBO analyses for small Mn insertion complexes from reactions with halomethanes have shown exceptionally high s character contributions from Mn to the C−Mn bonds (∼60%), while the halogen atom is treated as a separate unit (X−).6 Parameters from NBO analyses of the observed insertion products in this study and those from reactions of the other first-row transition metals with CH4 are listed in Table S13. This comparison reveals that a low metal d-contribution to the C−M and M−H bonds corresponds to a linear molecular backbone for the small transition-metal insertion complex. Landis et al. have shown that a higher d-orbital contribution generally leads to a smaller bond angle, explaining the structures of transition-metal hydrides.30 It is noticeable that the Mn and Zn insertion complexes as well as Cd and Hg analogues, which contain linear C−M−H moieties, have very low d-contributions to the C−M and M−H bonds. Due to the stability of the half-filled and filled d-orbitals, the dcontributions to the C−M and M−H bonds are minimal, making them similar to group 2 metals.2,3 However, unlike the Mn and group 12 metal insertion complexes, CH3−ReH has a quartet ground state and a bent structure.7 Evidently the stability of the half-filled d-orbitals is lower than that of the filled d-orbitals. It is interesting to note that the Mn−H bonds (1.775 Å) of MnH2−CH2CH2 in its sextet state are substantially longer than those (1.588−1.692 Å) in the other products with Mn−H bonds in Figures 5−8, whereas the H−H distance is exceptionally short (only 0.867 Å and the B3LYP interatomic distance of H2 is 0.743 Å). Therefore, dissociation of the Mn−

Figure 7. B3LYP structures of the Mn C−Cl insertion, cyclic, C−H insertion, and carbene complexes from reactions with ethane. The 6311++G(3df,3pd) basis sets are used for H, C, Cl, and Mn. Bond distances and angles are in Å and deg. C2H5−MnCl, CH2ClCH2− MnH, MnHCl−CH2CH2, and MHCl−CHCH3 possess Cs, Cs, Cs, and C1 structures, respectively, and C2H5−MnCl and MnHCl−CH2CH2 are identified in the product spectra.

Moreover, the observed cyclic product is much more stable than the C−Cl insertion and carbene complexes: MnCl2− CH2CH2, ClCH2CH2−MnCl, and ClCH2CHMnHCl in their sextet, sextet, and quartet ground states are 400, 237, and 42 kJ/mol more stable than the reactants (Mn(6S5/2) + CH2ClCH2Cl). The sole product indicates that excited Mn atoms are attracted by one chlorine atom and undergo C−Cl bond insertion, and the other Cl atom migrates from C to Mn immediately while the complex is still energized from the reaction exothermicity, thus generating the predominantly most stable cyclic product. This greater stability may be due in part to stronger Mn−Cl as opposed to C−Cl bonds. Structures of Small Mn Complexes. The structures of the small Mn complexes investigated in this study are illustrated in Figures 5−8. The observed insertion, vinyl, and cyclic Mn complexes in this study all bear sextet ground states. The high multiplicities of the products are in line with the previously studied Mn insertion and carbene complexes from reactions

Figure 8. B3LYP structures of the Mn insertion, cyclic, and carbene complexes from reactions with 1,2-dichloroethane. The 6-311++G(3df,3pd) basis sets are used for H, C, Cl, and Mn. Bond distances and angles are in Å and deg. CH2ClCH2−MnCl, MnCl2−CH2CH2, and MHClCHCH2Cl have Cs, C2v, and C1 structures, respectively, and only the cyclic complex is identified in the product spectra. H


Organometallics

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complex does not occur (eq 1) even with UV irradiation. Evidently formation of a C−Mn double bond requires

H bonds (H2-release) is likely from this cyclic product in its sextet state, if produced, which is in fact consistent with the observation of strong MnH2, CH2CH2, and vinyl product (CH2CH−MnH) absorptions in the reaction of Mn with ethane. The cyclic products from reactions of the haloethanes, on the other hand, contain unusually long C−Mn bonds (3.178 and 2.693 Å for MnHCl−CH2CH2 and MnCl2−CH2CH2). Finally, it is interesting to compare the effect of binding the linear sextet ClMnCl molecule with computed 473 cm−1 antisymmetric stretching mode and 2.192 Å bond length to the ethylene molecule to form the cyclic MnCl2−CH2CH2 product observed here with 438 cm−1 Mn−Cl stretching mode and 1002 cm−1 CH2 wagging mode. In the latter the MnCl2 subunit is bent to a 155.8° angle and the Mn−Cl bond lengthened to 2.222 Å (Figure 8), and the ethylene subunit is changed little, although the CH2 wagging mode is increased 53 cm−1 in the complex. The ethylene π orbital is overlapped nicely by the Mn dx2−y2 atomic orbital to form the long Mn−C bonds. These p−d π-bonding orbitals are illustrated in Figure 9.

stabilization such as employing di-, tri-, or tetrahalomethanes6 or CH2N2 reactions.4 The previous studies show that only Sc and Ti among the first-row transition metals generate methylidenene complexes in reactions with methane or photolysis afterward.8−10 Ethane activation takes place similarly with excited Mn to produce C2H5−MnH, and the generation of MnH2 and CH2CH2 as well as CH2CH−MnH reveals that H2-release also occurs in the course of the Mn reaction with ethane. After the formation of C2H5−MnH, the excess reaction energy probably allows H-migration from β-C to Mn to provide MnH2−CH2CH2, which is energetically more stable than CH3CHMnH2. However, the short distance between the two H atoms bonded to Mn in the cyclic product (only 0.867 Å as shown in Figure 6) indicates that H2-elimination from the cyclic complex can occur readily. After the loss of H2, Mn− CH2CH2 rearranges to the vinyl complex (CH2CH−MnH) (eq 2).

Our previous studies have shown that halogen substitution increases methane reactivity toward metals.8 The electron-rich halogen atom attracts the metal atom, and the strong Mn−X bond stabilizes the insertion product. Therefore, it is believed that C2H5−MnCl is first formed in the reaction of Mn and C2H5Cl via C−Cl bond insertion, and the excess reaction energy allows one of the methyl H’s to migrate to Mn, forming the Mn−H, Mn−Cl, and two C−Mn bonds. Due to the strong Mn−Cl bond, cyclic MnHCl−CH2CH2 is relatively stable, and HCl-release does not occur, unlike H2-release from MnH2− CH2CH2. Absence of the carbene product indicates that subsequent dissociation of one of the C−Mn bonds to form the much higher energy carbene complex (CH3CHMnHCl) (eq 3) does not proceed. Similarly conversion from CH3CH2− MnCl to CH3CHMnHCl via H-migration from α-C to Mn (eq 4) does not occur.

Figure 9. C−C π-orbitals for α and β electrons computed with the UB3LYP density functional for MnCl2−CH2CH2 in its sextet ground state and plotted with an isodensity of 0.04 e/Å. Notice the weak bonding with the dx2−y2-orbtial of Mn.

The higher Mulliken charge on Mn [0.61] in MnCl2−C2H4, as compared to [0.46] for MnHCl−C2H4, helps to concentrate the d-orbitals and form a shorter C−Mn bond in these π complexes. The considerably shorter carbene C−Mn bonds in Figures 5−8 are consistent with the previous results showing that the carbene C−Mn bond contains significant π character.6 The vinyl species CH2CH−MnH has a planar structure and a near linear C−Mn−H moiety. The methylidene complexes in Figures 5−8 show no agostic distortion8,31 and possess allene-type structures in contrast to the planar structures of the previously investigated Mn di-, tri-, and tetrahalo methylidenes from halomethanes.6 Reactions. The present results clearly show that Mn, like other transition metals, is an effective methane activation reagent via oxidative C−H bond insertion, although the metal reagent requires excitation through ultraviolet radiation or laser ablation. Previous work with Mn has shown that laser ablation excites Mn to the long-lived metastable 8P state, which can survive to reach the condensing matrix sample and react with precursor molecules before energy relaxation by the matrix.14a Sample annealing does not increase the product yields, which indicates that the cold metal atoms do not react. However, after CH3−MnH formation, subsequent H-migration from C to Mn to form the unstable higher oxidation state methylidene

As mentioned above, cyclic MnCl2−CH2CH2, which is the most stable among the plausible products, is the sole product identified in the Mn and 1,2-dichloroethane spectra, suggesting that Cl-migration from β-C to Mn takes place immediately after C−Cl bond insertion, much faster than corresponding Hmigration. H-migration from α-C to Mn to form the unstable I


Organometallics

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higher oxidation state complex with a C−Mn double bond does not occur either.

Article

ASSOCIATED CONTENT

S Supporting Information *

Calculated frequencies for higher energy products that are not observed. Cartesian coordinates for the title molecules. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

These metallacyclopropanes observed in reactions of Mn with haloethanes and those previously prepared in reactions of group 4 metals and ethane24 show that they are readily produced via H- or Cl-migration from β-C to Mn and more stable than the corresponding carbene complexes. It is also clear that C−H bond insertion is much slower than C−Cl bond insertion such that no C−H insertion product is observed from reactions of the mono- and dihaloethane. Especially in the Mn + C2H5Cl system, no trace of ClCH2CH2−MnH indicates that Mn collisions with C2H5Cl, including the ones on the methyl side, produce a complex with enough lifetime for the metal atom to reposition close to the chlorine atom, which eventually leads to C−Cl insertion during co-deposition and photolysis afterward.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS 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 20090075428) and the KISTI computing center.

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REFERENCES

(1) Cahiez, G.; Duplais, C.; Buendia, J. Chem. Rev. 2009, 109, 1434− 1476 and references therein. (2) Comprehensive Organometallic Chemistry III; Mingos, M. P., Crabtree, R. H., Eds.; Elservier Ltd.: Oxford, U.K., 2007; Vols. 10 and 11. (3) (a) Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; WileyVCH: Weinheim, Germany, 2003; Vol. 20, p 497. (b) Cronan, D. S. In Encyclopedia of Ocean Sciences; Steele, J.; Turekian, K.; Thorpe, S., Eds.; Academic Press: San Diego, 2001; pp 1526−1533. (4) (a) Billups, W. E.; Konarski, M. M.; Hauge, R. H.; Margrave, J. L. J. Am. Chem. Soc. 1980, 102, 7393−7394 (Mn + CH4). (b) Billups, W. E.; Chang, S.-C.; Margrave, J. L.; Hauge, R. H. Organometallics 1999, 18, 3551−3553 (Mn + CH2N2). (c) Ozin, G. A.; McCaffrey, J. G. J. Am. Chem. Soc. 1984, 106, 807−809. (5) (a) Riemschneider, R.; Kassahn, H. G.; Schneider, W. Z. Naturforsch. B 1960, 15, 547−551. (b) Beermann, C.; Clauss, K. Angew. Chem. 1959, 71, 627. (c) Tamura, M.; Kochi, J. J. Organomet. Chem. 1971, 29, 111−129 (Mn alkyl complexes). (6) Cho, H.-G.; Andrews, L. Organometallics 2011, 30, 477−487. (7) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 4098− 4101. (b) Cho, H.-G.; Andrews, L. Inorg. Chem. 2008, 47, 1653−1662 (Re). (8) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040−4053 and references therein. (Review article, groups 4−6). (9) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 633−643 (group 3). (b) Cho, H.-G.; Lyon, J. T.; Andrews, L. Organometallics 2008, 27, 5241−5251 (group 8). (c) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2010, 114, 8056−8068 (Co + CX4). (d) Cho, H.-G.; Andrews, L. Organometallics 2009, 28, 5623−5632 (Ni + CX4). (e) Cho, H.-G.; Andrews, L. Dalton Trans. 2011, 40, 11115−11124 (group 11). (f) Chen, M.; Dixon, D. A.; Wang, X.; Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2011, 115, 5609−5624 (lanthanides). (g) Andrews, L.; Cho, H.-G. J. Phys. Chem. A 2005, 109, 6796−6798. (h) Cho, H.-G.; Lyon, J. T.; Andrews, L. J. Phys. Chem. A 2008, 112, 6902−6907 (actinides). (10) Greene, T. M.; Andrews, L.; Downs, A. J. J. Am. Chem. Soc. 1995, 117, 8180−8187 (group 12 + CH4). (11) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2011, 115, 4929−4934 (group 7 + C2H2). (12) Cho, H.-G.; Andrews, L. Organometallics 2008, 27, 5241−5251 (Fe + CX4). (13) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899−926 and references therein. (14) (a) Chertihin, G. V.; Andrews, L. J. Phys. Chem. A 1997, 101, 8547−8553 and references therein (Mn + O2). (b) Andrews, L.; Citra,

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CONCLUSIONS Reactions of laser-ablated Mn atoms with CH4, C2H6, C2H5Cl, and CH2ClCH2Cl isotopomers have been investigated, and the products identified from matrix IR spectra on the basis of observed frequencies, isotopic shifts, and correlation with the DFT-calculated frequencies. Only the insertion complex is observed in the CH4 spectra, whereas the insertion and vinyl products are found in the C2H6 spectra, insertion and cyclic products in the C2H5Cl spectra, and only the cyclic complex in the 1,2-dichloroethane spectra. No Mn carbynes are identified in contrast to the Re case.7 The MnH2, C2H4, and CH2CH− MnH product absorptions observed in reaction with ethane are indicative of extensive H2-release. The stabilities of the cyclic products, over the carbene complexes with a CMn double bond, identified in the chloroethane systems are in line with those of the previously observed metallacyclopropanes in reactions of group 4 metals with ethane.29 CH3−MnH and the group 12 metal10 analogues possess linear backbones, similar to the Grignard reagents.26 The other Mn insertion complexes investigated in this study also carry a linear or near linear C−Mn−H(Cl) moiety. NBO analyses show that the low d-contributions in the C−Mn and Mn− H(X) bonds are responsible for the linear C−M−H(X) moiety. The stabilities of the half-filled and filled d-orbitals of Mn and group 12 metals allow small d-characters in the C−Mn and Mn−H bonds, making them similar to the group 2 metals. The quartet ground state and bent backbone of the Re analogue7 show that the half-filled d-orbitals are not as stable as the filled d-orbitals. The products identified in reactions of Mn and Re with methane (CH3−MnH and HCReH3) and ethane (C2H5− MnH, CH2CH−MnH, and CH3CReH3)7 show again that the tendency of the increasing preference for higher oxidation state complexes upon going down a transition-metal group column is most dramatic among the group 7 metals Mn and Re. J


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A. Chem. Rev. 2002, 102, 885−911 and references therein. (c) Andrews, L. Chem. Soc. Rev. 2004, 33, 123−132 and references therein. (15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford, CT, 2009. (16) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5653. (b) Lee, C.; Yang, Y.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789. (17) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062− 1066. (18) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098−3100. (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., Eds.; Plenum: New York, 1998. (19) Head-Gordon, M.; Pople, J. A.; Frisch, M. J. Chem. Phys. Lett. 1988, 153, 503−506. (20) Scuseria, G. E.; Janssen, C. L.; Schaefer, H. F., III. J. Chem. Phys. 1988, 89, 7382−7387. (21) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502−16513. (22) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937−2941. (23) (a) van Zee, R. J.; deVore, T. C.; Wilkerson, J. L.; Weltner, W., Jr. J. Chem. Phys. 1978, 69, 1869−1876. (b) Wang, X.; Andrews, L. J. Phys. Chem. A 2003, 107, 4081−4091 (Mn + H2). (24) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2008, 112, 1519−1525 (group 4 + C2H6). (25) (a) Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 2537− 2549. (b) Cho, H.-G.; Andrews, L. Organometallics 2008, 27, 1786− 1796 (group 8). (26) (a) Wang, G.; Chen, M.; Zhou, M. Chem. Phys. Lett. 2005, 412, 46−49. (b) Cho, H.-G.; Andrews, L. Organometallics 2010, 29, 2211− 2222 (Rh). (27) (a) Cho, H.-G.; Andrews, L. Organometallics 2009, 28, 1358− 1368. (b) Cho, H.-G.; Andrews, L. J. Am. Chem. Soc. 2008, 130, 15836−15841 (Pt). (28) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1969, 51, 4143− 4155. (29) (a) Kauffmann, T.; Bisling, M. Tetrahedron Lett. 1984, 25, 293− 296. (b) Cahiez, G.; Alami, M. Tetrahedron Lett. 1986, 27, 569−572 (Grignard reagent). (30) Landis, C. R.; Cleveland, T.; Firman, T. K. J. Am. Chem. Soc. 1995, 117, 1859−1860. (31) (a) von Frantzius, G.; Streubel, R.; Brandhorst, K.; Grunenberg, J. Organometallics 2006, 25, 118−121 and references therein. (b) Berkaine, N.; Reinhardt, P.; Alikhani, M. E. Chem. Phys. 2008, 343, 241−249. (c) Roos, B. O.; Lindh, R.; Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 6420−6424. (d) Clot, E.; Eisenstein, O. In Computational Inorganic Chemistry; Kaltzoyannis, N.; McGrady, J. E., Eds.; Structure and Bonding, Springer: Heidelberg, 2004; pp 1−36. (e) Aubert, C.; Buisine, O.; Malacria, M. Chem. Rev. 2002, 102, 813− 834 and references therein (agostic structures).

K


Infrared Spectra of Manganese Insertion, Vinyl, and Cyclic Complexes

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