Infrared Spectra of CH3–MH through Methane Activation by Laser

Article pubs.acs.org/JPCA

Infrared Spectra of CH3−MH through Methane Activation by LaserAblated Sn, Pb, Sb, and Bi Atoms Han-Gook Cho and Lester Andrews* Department of Chemistry, University of Incheon, 119 Academy-ro, Yonsu-gu, Incheon, 406-772, South Korea, and Department of Chemistry, University of Virginia, P.O. Box 400319, Charlottesville, Virginia 22904-4319, United States S Supporting Information *

ABSTRACT: Methane activation has been carried out by laser-ablated Sn, Pb, Sb, and Bi atoms. All four metals generate the insertion complex (CH3− MH), but subsequent H-migration from C to M to form CH2−MH2 and CH−MH3 complexes is not observed. Our previous and present experimental and computational results indicate that the higher oxidation state complexes become less favored with increasing atomic mass in groups 14 and 15, which is opposite the general trend found for transition metals. The C−H bond insertion evidently occurs during reaction on sample condensation, and the product dissociates on broad-band photolysis afterward. The insertion complex contains a near right angle C−M−H moiety because of high p contribution from the metal center to the C−M and M−H bonds unlike many transition-metal analogues. The computed methylidene structures for these main group metals are not agostic possibly because of the absence of valence dorbitals.

■

INTRODUCTION Methane activation is a reaction that cleaves a C−H bond, which was traditionally considered unreactive.1−4 Efficient C− H cleavage has been a long-standing chemical subject because of its potential industrial importance of transforming naturally abundant saturated small hydrocarbons to more valuable functionalized organic products. Much effort has been devoted to design new catalysts and to synthesize more effective organometallic C−H insertion reagents.1,2 Thermal and photochemical reaction paths have also been investigated.3,4 A series of recent studies have demonstrated that transitionmetal atoms including the lanthanides and actinides are in fact effective CH4 activation reagents, and in many second- and third-row transition-metal systems, subsequent H migration also occurs to generate high oxidation state complexes (CH2 MH2 and CHMH3).5−7 The increasing preference of the high oxidation state products with increasing atomic mass in a family group is demonstrated in reactions of not only small alkanes but haloalkanes, unsaturated hydrocarbons, and acetonitrile as well.5,8,9 This new breed of small-transitionmetal complexes is amenable to high-level computations,10 which also often shows interesting photochemical reactions and distinctive structural distortions resulting from interactions between the valence d-orbitals of the metal center and the ligand electron pairs.5,11 Previous studies also reveal that methane activation can occur with main group metal atoms.12−14 While the insertion product is mostly produced, CH2SiH2 and CHSiH3 have been identified along with CH3−SiH in reactions of CH4 + Si, and the methylidyne is also generated in reaction of SiH4 + C.13 Similarly, CH3−NH and CH2NH2 are also observed in gasphase reactions.15 On the other hand, only CH3−GeH and © 2012 American Chemical Society

(CH3)2CGeH2 are identified in photolysis and pyrolysis of Ge compounds.14 In this study, direct reactions of heavy groups 14 and 15 metals (Sn, Pb, Sb, and Bi) with CH4 have been performed to examine whether or not these main group metals undergo methane activation and subsequent H migration similar to the transition metals and the lighter members in these family groups.

■

EXPERIMENTAL AND COMPUTATIONAL METHODS Laser-ablated Sn, Pb, Sb, and Bi atoms were reacted with CH4 (Matheson, UHP grade), 13CH4, CD4, and CH2D2 (Cambridge Isotopic Laboratories) in excess argon during condensation at 4 K using a closed-cycle refrigerator (Air Products Displex). Reagent gas mixtures ranged 1.0−4.0% (typically 3%) in argon. The Nd:YAG laser fundamental radiation (1064 nm, 10 Hz repetition rate, 10 ns pulse width) was focused on rotating Sn, Pb, Sb, and Bi targets using 5−10 mJ/pulse, and the ablated material was codeposited with the argon/methane samples.16 After the 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 10 min periods by a mercury arc street lamp (175 W) with the globe removed using a combination of optical filters and were annealed to allow further reagent diffusion. To provide support for the assignment of new experimental frequencies and to correlate with related works,5−7 density functional theory (DFT) calculations were performed using the Received: May 25, 2012 Revised: July 23, 2012 Published: July 23, 2012 8500

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506

The Journal of Physical Chemistry A

8501

a

Bi

Pb Sb

Observed in an argon matrix. Bold absorptions are the strongest. Frequencies are in cm−1. bMetals investigated in this study. cIdentified product and assigned vibrational mode.

426.2 594.5

488.4 1712.8, 1664.0, 1621.8 1144.1

627.7

470.6 1226.9, 1194.1, 1161.6

1713.0, 1664.1, 1621.8 1226.0, 1194.2, 1161.5

1505.2, 1478.4, 1472.2, covered, 1065.6, 1055.5 1885.4, 1846.6, 1842.1, 1839.4 1352.6, 1327.3, 1322.9, 1321.0

1627.3 770.0 1505.1, 1487.7, 1472.4 1885.8, 1846.7, 1842.0, 1839.3 1410.3 1192.9 817.1 1169.4 582.5 1079.6, 1065.5, 1055.5 1352.7, 1326.9, 1323.1, 1320.9

1627.4, 1169.6

CH2D2 CH4

13

1627.3 775.7 1505.0, 1487.7, 1472.5 1885.0, 1846.3, 1842.0, 1839.2 1413.9 1199.4 822.1 555.8 505.2 1712.8, 1664.0, 1621.8 1150.5 796.6 448.7

laser-ablated Sn, Pb, Sb, and Bi atoms with methane isotopomers were investigated, and DFT frequency calculations of the products (Tables S1−S8 of the Supporting Information), Natural Bond Order (NBO)24 results (Table S9 of the Supporting Information), and structures (Figure 6) will be presented in turn. Sn + CH4. Figure 1 shows infrared spectra for the reaction products of laser-ablated Sn atoms codeposited with methane

Sn

Figure 1. Infrared spectra in the product absorption regions from reaction of the laser-ablated tin atoms with methane isotopomers in excess argon at 4 K. (a) Sn and CH4 (3.0% in argon) codeposited for 1 h, (b) as a after annealing to 20 K, (c) as b after UV (240−380 nm) irradiation, and (d) as c after irradiation with λ > 290 nm. (e) Sn and CD4 (3.0% in argon) codeposited for 1 h, (f) as e after annealing to 30 K, (g) as f after irradiation with λ > 290 nm, and (h) as g after full arc (λ > 220 nm) irradiation. (i) Sn and 13CH4 (3.0% in argon) codeposited for 1 h, (j) as i after annealing to 20 K, and (k) as j after full arc irradiation. (l) Sn and CH2D2 (4.0% in argon) codeposited for 1 h, (m) as l after annealing to 20 K, and (n) as m after irradiation with λ > 290 nm. The product absorptions are marked with i while P and w stand for precursor and water residue absorptions.

CD4

RESULTS AND DISCUSSION The matrix infrared spectra (Figures 1−5, Figures S1 and S2 of the Supporting Information, and Table 1) from reactions of

CH4

■

groupb

Table 1. Observed Frequencies and Assignments for the Product Absorptions from Methane Isotopomer Reactions with Sn, Pb, Sb, and Bia

descriptionc

Gaussian 09 program system;17 the B3LYP density functional;18 the 6-311++G(3df,3pd) basis sets for H and C19 and SDD core potential; and the basis sets for Sn, Pb, Sb, and Bi20 to provide vibrational frequencies for the reaction products. Geometries were fully relaxed during optimization, and the optimized geometry was confirmed by vibrational analysis. The BPW9121 functional was also employed to complement the B3LYP results. The vibrational frequencies were calculated analytically, and zero-point energy was 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,5−9,22,23 and they provide useful predictions for infrared spectra of new molecules.

CH3−SnH, Sn−H str. CH3−SnH, CH3 rock CH3−PbH, Pb−H str. CH3−SbH, Sb−H str. CH3−SbH, A′′ CH3 bend CH3−SbH, A′ CH3 deform CH3−SbH, A′ CH3 rock CH3−SbH, A′ CSbH bend CH3−SbH, C−Sb str. CH3−BiH, Bi−H str. CH3−BiH, A′ CH3 deform CH3−BiH, A′ CH3 rock CH3−BiH, C−Bi str.

Article

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506

The Journal of Physical Chemistry A

Article

isotopomers in excess argon during condensation at 4 K and their variation in annealing and broad-band photolysis. Only one group of new product absorptions marked i (for insertion) are observed. They sharpen in the early stage of annealing and increase slightly on UV (240−380 nm) irradiation but decrease on irradiation with λ < 240 nm. A strong i absorption observed at 1627.3 cm−1 shifts to 1169.4 cm−1 on deuteration (H/D ratio of 1.392) but shows no isotopic shift on 13C substitution. They both appear in the CH2D2 spectrum. These Sn−H and Sn−D stretching bands indicate that C−H insertion of methane occurs by Sn atoms forming an insertion complex (CH3−SnH). The observed frequencies are compared with 1657.3 and 1654.8 cm−1 for SnH2, 1190.8 and 1188.2 cm−1 for SnD2, 1630.4 cm−1 for SnH, and 1183.1 cm−1 for SnD,25 which are not observed in this study. A weak product absorption observed at 775.7 cm−1 along with its D and 13C counterparts at 582.5 and 770.0 cm−1 is designated to the A′ CH3 rocking mode. Unlike the insertion product, the methylidene (CH2SnH2) and methylidyne (CH−SnH3) are not identified in the matrix IR spectra as these species would show their strongest SnH2 and SnH3 stretching bands near 1850 and 1800 cm−1. These results are also in line with the higher relative energies of the high oxidation state complexes. Compared to the reactants Sn(3P0) + CH4, the CH3−SnH complex (ground-state singlet) is more stable by −35 kJ/mol, while the CH2SnH2 and CH− SnH3 species (singlet and triplet ground states, respectively) are +101 and +300 kJ/mol higher in energy. The present results are compared with the recent studies on the Si + CH4 reaction by Maier et al., where both the insertion (CH3−SiH) and higher oxidation state (CH2SiH2 and CH− SiH3) products are generated.13a,b More recently, Schreiner et al. reported the formation CH−SiH3 in the reaction of C + SiH4.13c The CH3−SiH, CH2SiH2, and CH−SiH3 products are also predicted to be −153, −171, and +20 kJ/mol in energy relative to Si(3P0) + CH4. In contrast, CH3−GeH, CH2 GeH2, and CH−GeH3 are −102, −46, and +169 kJ/mol relative to Ge(3P0) + CH4. The general tendency of increasing stability for the higher oxidation state product with increasing atomic mass in a family group for transition metals5−9 clearly does not apply to the group 14 metal atoms. Pb + CH4. Figure 2 illustrates the product absorptions again marked i from Pb reactions with CH4 isotopomers. They sharpen in the early stages of annealing but decrease on UV (λ < 420 nm) irradiation. The strong product absorption at 1505.0 cm−1 (with matrix site absorptions at 1487.7 and 1472.5 cm−1) shifts to 1079.6 cm−1 (with matrix site absorptions at 1065.5 and 1055.5 cm−1) (H/D ratio of 1.394) but shows essentially no change on 13C substitution. These Pb−H and Pb−D stretching frequencies are compared with 1541.6, 1534.6, and 1532.7 cm−1 for PbH2 and 1106.4, 1100.6, and 1099.3 cm−1 for PbD2,25 which were not observed in this study. We assign the product absorptions to the lead insertion product (CH3−PbH). No other considerable product absorptions were observed. Table S3 of the Supporting Information reveals that the observed Pb−H and Pb−D stretching frequencies agree well with the predicted values of 1547.4 and 1097.3 cm−1, and other bands are expected to be too weak to observe (the second strong A′ CH3 rocking band is predicted to be 20 times weaker than the Pb−H stretching band). The strong Pb−H stretching absorption indicates that C−H insertion of methane by this heavy main group metal

Figure 2. Infrared spectra in the product absorption regions from reaction of the laser-ablated lead atoms with methane isotopomers in excess argon at 4 K. (a) Pb and CH4 (3.0% in argon) codeposited for 1 h, (b) as a after annealing to 20 K, (c) as b after full arc (λ > 220 nm) irradiation, and (d) as c after annealing to 35 K. (e) Pb and CD4 (3.0% in argon) codeposited for 1 h, (f) as e after annealing to 20 K, (g) as f after visible (240−380 nm) irradiation, and (h) as g after irradiation with 240 < λ < 380 nm. (i) Pb and 13CH4 (3.0% in argon) codeposited for 1 h, (j) as i after annealing to 20 K, and (k) as j after full arc irradiation. (l) Pb and CH2D2 (4.0% in argon) codeposited for 1 h, (m) as l after annealing to 20 K, and (n) as m after irradiation with λ > 290 nm. The product absorptions are marked with i while P and w stand for precursor and water residue absorptions.

readily occurs, but no further reaction to the methylidene or methylidyne via H migration happens. Again, these results are in line with the fact that the high oxidation state complexes are energetically much higher than the insertion product. The possible products CH3−PbH, CH2PbH2, and CH−PbH3 in their singlet, singlet, and triplet ground states are −7, +203, and +419 kJ/mol in energy relative to the reactants (Pb(3P0) + CH4). The previous and present results show that the high oxidation state complexes become less favored with going down in the group 14 column opposite from that of the transition-metal systems.5 Sb + CH4. Figures 3 and 4 and Figures S1 and S2 of the Supporting Information illustrate the reaction product spectra from Sb atoms codeposited with CH4 isotopomers during condensation at 4 K and their variation in subsequent annealing and photolysis. Parallel to the Sn and Pb cases, only one group of product absorptions marked i is observed in the group 15 metal spectra although the absorptions are considerably stronger than in the Sn and Pb cases. They sharpen in the early stages of annealing but decrease on broad-band photolysis. The strong product absorption at 1842.0 cm−1 is accompanied with site absorptions at 1885.0, 1846.3, and 1839.2 cm−1, and deuterium substitution shifts it to 1323.1 cm−1 (H/D ratio of 1.392) and the site absorptions to 1352.7, 1326.9, and 1320.9 cm−1 while 13C substitution brings negligible isotopic shifts. The weak SbH2 and SbD2 absorptions are also observed at 1869.0 and 1863.7 cm−1 and at 1341.8 and 1337.6 cm−1.26 8502

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506

The Journal of Physical Chemistry A

Article

Figure 3. Infrared spectra in the product absorption regions from reaction of the laser-ablated antimony atom with CH4 in excess argon at 4 K. (a) Sb and CH4 (3.0% in argon) codeposited for 1 h, (b) as a after annealing to 30 K, (c) as b after full arc (λ > 220 nm) irradiation, and (d) as c after annealing to 35 K. The product absorptions are marked with i while P designates the precursor absorption in the CH4 matrix spectra. CH3 and C2H2 absorptions are also indicated.

the A′′ CH3 bending, A′ CH3 deformation, and A′ C−Sb−H bending modes, respectively. These six product absorptions substantiate formation of the antimony insertion complex (CH3−SbH). However, the higher oxidation state products (CH2−SbH2 and CH−SbH3) are again not observed most probably because of their higher energies. The molecules CH3−SbH, CH2−SbH2, and CH−SbH3 in their ground doublet states are −27, +109, and +389 kJ/mol in energy relative to Sb(4S3/2) + CH4. Parallel to group 14, the higher oxidation state product becomes less favored on going down in group 15, which is opposite the trend observed from transition-metal groups.5−9 In addition, CH3− NH, CH2−NH2, and CH−NH3 are −239, −267, and +14 kJ/ mol in energy relative to N(4S3/2) + CH4; CH3−PH, CH2− PH2, and CH−PH3 are −148, −82, and +132 kJ/mol relative to P(4S3/2) + CH4; and CH3−AsH, CH2−AsH2, and CH−AsH3 are −85, +19, and +282 kJ/mol relative to As(4S3/2) + CH4. Bi + CH4. The bismuth product absorption regions are illustrated in Figure 5. The stretching absorption at 1664.0 cm−1 (with matrix site absorptions at 1712.8 and 1621.8 cm−1) shows a large D shift to 1194.1 cm−1 (with site absorptions at 1226.9 and 1161.6 cm−1) (H/D ratio of 1.397) but no shift on 13 C substitution. The CH2D2 spectra show both the Bi−H and the Bi−D stretching absorptions. The observed frequencies are compared with 1686.4 and 1693.2 cm−1 for BiH2 and 1209.5 and 1214.4 cm−1 for BiD2,26 which are not observed in this study. The strong product Bi−H and Bi−D stretching absorptions most probably arise from CH3−BiH (Table 1 and Table S7 of the Supporting Information), and the strong bismuth−hydrogen stretching absorptions reveal that the heaviest group 15 metal is also an effective C−H bond insertion agent. Other product absorptions, though much weaker, are also observed. The ones at 1150.5, 796.6, and 448.7 cm−1 are assigned to the A′ CH3 deformation, A′ CH3 rocking, and C− Bi stretching modes on the basis of good correlation with the DFT values (Table S7 of the Supporting Information) with all supporting formation of the insertion complex via C−H bond

Figure 4. Infrared spectra in the product absorption regions from reaction of the laser-ablated antimony atom with CD4 in excess argon at 4 K. (a) Sb and CD4 (3.0% in argon) codeposited for 1 h, (b) as a after annealing to 30 K, (c) as b after full arc (λ > 220 nm) irradiation, and (d) as c after annealing to 35 K. The product absorptions are marked with i. The band labeled c is common for this precursor and different metals; the CD3 absorption is also indicated.

The strong Sb−H and Sb−D stretching absorptions are designated for the insertion product (CH3−SbH) on the basis of the reasonable correlation with the DFT values (Table 1 and Table S5 of the Supporting Information). Another product absorption at 828.2 cm−1 is accompanied by D and 13C counterparts at 627.7 and 817.1 cm−1 (H/D and 12/13 ratios of 1.319 and 1.014) and is assigned to the A′ CH3 rocking mode. Another product absorption at 505.2 cm−1 shows a small D shift to 470.6 cm−1 but a sizable 13C shift to 488.4 cm−1 and is designated as the C−Sb stretching mode. The weak product absorptions at 1413.9, 1199.4, and 555.8 cm−1 are assigned to 8503

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506

The Journal of Physical Chemistry A

Article

Figure 5. Infrared spectra in the product absorption regions from reaction of the laser-ablated bismuth atoms with methane isotopomers in excess argon at 4 K. (a) Bi and CH4 (3.0% in argon) codeposited for 1 h, (b) as a after annealing to 30 K, (c) as b after visible (λ > 420 nm) irradiation, and (d) as c after irradiation with 380 > λ > 240 nm. (e) Bi and CD4 (3.0% in argon) codeposited for 1 h, (f) as e after annealing to 20 K, (g) as f after annealing to 30 K, and (h) as g after full arc (λ > 220 nm) irradiation. (i) Bi and 13CH4 (3.0% in argon) codeposited for 1 h, (j) as i after annealing to 30 K, and (k) as j after full arc irradiation. (l) Bi and CH2D2 (4.0% in argon) codeposited for 1 h, (m) as l after annealing to 30 K, and (n) as m after full arc irradiation. The product absorptions are marked with i while P and w stand for precursor and water residue absorptions.

Figure 6. The B3LYP structures of the Sn, Pb, Sb, and Bi insertion and methylidene complexes with the 6-311++G(3df,3pd) basis sets for H and C and SDD pseudopotential and basis for Sn, Pb, Sb, and Bi. Bond distances and angles are in Å and deg. The insertion products own Cs structures; notice the near right C−M−H angles. The methylidene structures are not agostic unlike many transition-metal analogues. While CH2SnH2 possesses a planar C2v structure, other methylidenes possess nonplanar Cs structures. Only insertion products, which are considerably more stable than the methylidenes, are observed in the matrix IR spectra (see text).

insertion by Bi. Again, the high oxidation state products are not observed in line with their considerably higher energies: CH3− BiH, CH2−BiH2, and CH−BiH3 are 4, 169, and 490 kJ/mol higher in energy relative to Bi(4S3/2) + CH4. These heavy groups 14 and 15 metals exclusively generate the insertion products. Molecular Structures. The structures of groups 14 and 15 metal insertion and methylidene complexes are illustrated in Figure 6. Groups 14 and 15 metal insertion complexes all have staggered Cs structures. The tin methylidene (CH2SnH2) owns a planar C2v structure, whereas the Pb, Sb, and Bi analogues have Cs structures with HCMH dihedral angles of 29.4, 51.2, and 48.8°. The near right angle C−M−H moiety of the insertion complex reflects the high p contributions of the metal atom to the C−M and M−H bonds (Table S9 of the Supporting Information ), for example, 91.7 and 92.0% natural p contribution in CH3−SnH. NBO analysis also shows that the C−M bonds of the group 14 metal methylidenes are double bonds (effective natural bond orders (EBO) of 1.97 and 1.93 for the Sn and Pb complexes), whereas those of the group 15 metal methylidenes are single bonds (EBO of 1.00 and 0.99 for the Sb and Bi analogues). The unpaired electron and high p contributions of the group 15 metal to the C−M and M−H bonds lead to the large HCMH dihedral angle. In addition, these methylidene complexes are not agostic (showing no distortion of the CH2 group).10 Unlike the transition metals,

the metals of groups 14 and 15 do not have easily available empty d-orbitals, which can accommodate interaction with the C−H bonding electrons. In the transition-metal systems, conversion from the insertion complex (CH3−MH) to a higher oxidation state product (CH2MH2 or HCMH3) is accompanied with an increase in the C−M bond order utilizing the valence d-orbitals. The higher C−M bond order helps to compensate or even to exceed the decreasing bond energy in replacing the C−H bonds of CH3−MH with the M−H bonds leading to its stability. For example, CH2WH2 and HCWH3 are 4 and 46 kJ/mol more stable than CH3−WH.7d The higher C−M bond orders of small transition metal high oxidation state complexes have been confirmed by their observed high stretching frequencies, short bond lengths, and NBO and CASSCF results.5−7 In contrast, it is far more difficult for the main group metal to employ d-orbitals to form a multiple C−M bond. While the bond energies of Si−H and N−H (323 and 391 kJ/mol) are lower compared with that of C−H (413 kJ/mol),27 the M−H bond energy decreases with increasing atomic mass in groups 8504

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506

The Journal of Physical Chemistry A

Article

analogues;5−7,10 the absence of empty valence d-orbitals results in the symmetric CH2 group. The heavy main group metal atoms readily undergo methane activation via C−H insertion similar to the transition metals, but their photochemistry, product structures, and relative energies between plausible products are considerably different from those of the transition metals.

14 and 15. The B3LYP average bond energies of Si−H, Ge−H, Sn−H, and Pb−H for MH4 are 318, 288, 256, and 232 kJ/mol, respectively, and those of N−H, P−H, As−H, Sb−H, and Bi− H for MH3 are 390, 321, 292, 264, and 244 kJ/mol, respectively. As a result, the higher oxidation state products become energetically less favored on going down the family column. Reactions. The reactions of groups 14 and 15 metal atoms with methane examined in this study are similar to those of the first row transition metals,7 readily undergoing methane activation via C−H bond insertion, but no further H migration from C to M occurs during condensation and photolysis afterward. These selective C−H insertions are as effective as found in the transition-metal systems, and particularly, Sb is the most reactive. However, unlike the transition-metal systems, which often require separate photolysis,5−7 groups 14 and 15 metal C−H insertion reactions to form CH3−MH primarily occur during condensation (eq 1) dissipating the excess energy to the matrix. M* + CH4 → CH3MH* → CH3MH

■

S Supporting Information *

Tables of calculated frequencies and additional figures for Sb and methane reaction products. This material is available free of charge via the Internet at http://pubs.acs.org.

■

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

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 KISTI supercomputing center. We thank one referee for voluntarily cross checking our DFT calculations with highly correlated coupled cluster simulations. Since dispersion is not of decisive importance (no agnostic interaction), the density functional level of theory is adequate for these main group metal bearing systems.

Moreover, groups 14 and 15 insertion complexes easily dissociate on photolysis as shown in Figures 1−5 and Figures S1−S2 of the Supporting Information. The methyl metal (CH3−M) is not observed while the absorptions from the insertion complex decrease on broad-band photolysis, whereas the CH3 and CD3 radical absorptions at 603 and 453 cm−1 increase as shown in Figures 3 and 4.28 Increase of the methyl radical absorption during photolysis was not observed in the previous transition-metal studies.5−7 The dissociation energy of the C−M bond is also smaller than that of the M−H bond, for example, 293 versus 347 kJ/mol for the Sb system. While further study is needed to investigate the exact photodissociation channel of groups 14 and 15 insertion complexes, the present results suggest that it is the C−M bond that dissociates during photolysis of these heavy main group metal insertion complexes (eq 2).

■

(2)

CH3MH → CH3M + H

(3)

AUTHOR INFORMATION

Corresponding Author

(1)

CH3MH → CH3 + MH

ASSOCIATED CONTENT

■

REFERENCES

(1) (a) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879− 2932. (b) Chen, H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000, 287, 1995−1997. (c) Shinji, M.; Fumitoshi, K.; Shinya, S.; Yasuo, T.; Asayuki, K.; Motohiro, S.; Naoto, C. Nature 1993, 366, 529−531. (d) Podkolzin, S. G.; Stangland, E. E.; Jones, M. E.; Peringer, E.; Lercher, J. A. J. Am. Chem. Soc. 2007, 129, 2569−2576. Díaz-Requejo, M. M.; Pérez, P. J. Chem. Rev. 2008, 108, 3379−3394 (catalytic CH4 activation). (2) (a) Tsang, J. Y. K.; Buschhaus, M. S. A.; Legzdins, P. J. Am. Chem. Soc. 2007, 129, 5372−5373. (b) Crabtree, R. H. J. Organomet. Chem. 2004, 689, 4083−4091. (c) Davis, H. M. L.; Beckwith, R. E. Chem. Rev. 2003, 103, 2861−2903 (C−H insertion agent). (3) (a) Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. Soc. 1982, 104, 3723−3725. (b) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982, 104, 352−354 (photochemical CH4 activation). (4) (a) Butschke, B.; Schwarz, H. Organometallics 2011, 30, 1588− 1598. (b) Schröder, D.; Schwarz, H. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 18114−18119 (thermal CH4 activation). (5) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040−4053 and references therein (review article, groups 4−6). (6) (a) Andrews, L.; Cho, H.-G. J. Phys. Chem. A 2005, 109, 6796− 6798. (b) Lyon, J. T.; Andrews, L.; Malmqvist, P.-A.; Roos, B. O.; Yang, T.; Bursten, B. E. Inorg. Chem. 2007, 46, 4917−4925. (c) Cho, H.-G.; Lyon, J. T.; Andrews, L. J. Phys. Chem. A 2008, 112, 6902− 6907. (d) Cho, H.-G.; Andrews, L. Lanthanides + CH4, unpublished data. (Actinides and Lanthanides + Alkanes), 2008. (7) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 633−643. (b) Andrews, L.; Cho, H.-G.; Wang, X. Inorg. Chem. 2005, 44, 4834− 4842. (c) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2006, 110, 3886− 3902. (d) Cho, H.-G.; Andrews, L.; Marsden, C. Inorg. Chem. 2005, 44, 7634−7643. (e) Billups, W. E.; Konarski, M. M.; Hauge, R. H.; Margrave, J. L. J. Am. Chem. Soc. 1980, 102, 7393−7394. (f) Chang, S.-

CONCLUSIONS Reactions of laser-ablated Sn, Pb, Sb, and Bi atoms with methane isotopomers generate the insertion products (CH3− MH) revealing that these heavy groups 14 and 15 metals also readily undergo C−H bond insertion. However, subsequent H migration to form high oxidation state products is evidently prohibited during codeposition and photolysis afterward probably because of their considerably higher energies. The previous observation of the Si and N methylidenes (CH2 SiH2 and CH2NH2)13,15 and the DFT results reveal that the higher oxidation state complexes become less favored with going down in these family groups, which is opposite the general trend recently discovered from transition-metal systems. Unlike the transition-metal cases,5−7 these main group metal reactions evidently occur during codeposition, and the product dissociates on broad-band photolysis afterward. The mostly p contributions from the metal atom to the C−M and M−H bonds lead to a near right angle C−M−H moiety in the insertion complex. The unobserved methylidenes of these main group metals are not agostic unlike many transition-metal 8505

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506

The Journal of Physical Chemistry A

Article

C.; Hauge, R. H.; Billups, W. E.; Margrave, J. L.; Kafafi, Z. H. Inorg. Chem. 1988, 27, 205−206. (g) Cho, H.-G.; Andrews, L. Dalton Trans. 2011, 40, 11115−11124. (h) Greene, T. M.; Andrews, L.; Downs, A. J. J. Am. Chem. Soc. 1995, 117, 8180−87. (8) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2008, 112, 12071− 12080. (9) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2010, 114, 5997−6006. (10) (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) Chung, G.; Gordon, M. S. Organometallics 2003, 22, 42. (d) de Jong, G. T.; Bickelhaupt, F. M. J. Chem. Theory Comput. 2007, 3, 514. (e) Roos, B. O.; Lindh, R.; Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 6420−6424. (11) (a) Lyon, J. T.; Cho, H.-G.; Andrews, L.; Hu, H.-S.; Li, J. Inorg. Chem. 2007, 46, 8728−8738. (b) Cho, H.-G.; Lyon, J. T.; Andrews, L. Organometallics 2008, 27, 5241−5251. (12) (a) Hassanzadeh, P.; Hannachi, Y.; Andrews, L. J. Phys. Chem. 1993, 97, 6418. (b) Greene, T. M.; Lanzisera, D. V.; Andrews, L.; Downs, A. J. J. Am. Chem. Soc. 1998, 120, 6097. (c) Lafleur, R. D.; Parnis, J. M. J. Phys. Chem. 1992, 96, 2429. (d) Himmel, H.-J.; Downs, A. J.; Greene, T. M.; Andrews, L. Organometallics 2000, 19, 1060 (main group metals + CH4). (13) (a) Maier, G.; Reisenauer, H. P.; Glatthaar, J. Chem.Eur. J. 2002, 8, 4383−4931. (b) Reisenauer, H. P.; Mihm, G.; Maier, G. Angew. Chem. 1982, 94, 864. (c) Schreiner, P. R.; Reisenauer, H. P.; Sattelmeyer, K. W.; Allen, W. D. J. Am. Chem. Soc. 2005, 127, 12156− 12157 (Si + CH4 and C + SiH4). (14) (a) Khabashesku, V. N.; Kudin, K. N.; Tamas, J.; Boganov, S. E.; Margrave, J. L.; Nefedov, O. M. J. Am. Chem. Soc. 1998, 120, 5005. (b) Becerra, R.; Harrington, C. R.; Leigh, W. J.; Kefala, L. A.; Walsh, R. Organometallics 2006, 25, 4439−4443. (c) Trinquier, G.; Barthelat, J.C.; Satge, J. J. Am. Chem. Soc. 1982, 104, 5931−5936 (CH3−GeH). (15) (a) Radisic, D.; Xu, S.; Bowen, K. H., Jr. Chem. Phys. Lett. 2002, 354, 9−13. (b) la Cour Jansen, T.; Trabjerg, I.; Rettrup, S.; Pagsberg, P.; Sillesen, A. Acta Chem. Scand. 1999, 53, 1054 (CH3−NH and CH2NH2). (16) (a) Andrews, L.; Citra, A. Chem. Rev. 2002, 102, 885−912 and references therein. (b) Andrews, L. Chem. Soc. Rev. 2004, 33, 123−132 and references therein. (17) 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. (18) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (b) Lee, C.; Yang, Y.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789. (19) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062− 1065. (20) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (21) (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, 1998. (22) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502−16513. (23) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937−2941. (24) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899−926 and references therein. (25) (a) Wang, X; Andrews, L.; Chertihin, G. V.; Souter, P. F. J. Phys. Chem. A 2002, 106, 6302−6308. (b) Wang, X.; Andrews, L. J. Am. Chem. Soc. 2003, 125, 6581−6587 (Sn and Pb + H2). (26) Wang, X.; Souter, P. F.; Andrews, L. J. Phys. Chem. A 2003, 107, 4244−4249 (Sb and Bi + H2). (27) Wall, F. T. Chemical Thermodynamics, 3rd ed.; W. H. Freeman: San Francisco, CA, 1974; p 63. (28) (a) Milligan, D. E.; Jacox, M. J. Chem. Phys. 1967, 47, 5146− 5156. (b) Jacox, M. E. J. Mol. Spectrosc. 1977, 66, 272−287 (CH3).

8506

dx.doi.org/10.1021/jp305117d | J. Phys. Chem. A 2012, 116, 8500−8506