Matrix Infrared Spectra and Theoretical Calculations of Fluoroboryl

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Article Cite This: J. Phys. Chem. A XXXX, XXX, XXX−XXX

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Matrix Infrared Spectra and Theoretical Calculations of Fluoroboryl Complexes F2B−MF (M = C, Si, Ge, Sn and Pb) Bing Xu,* Li Li, Wenjie Yu, Tengfei Huang, and Xuefeng Wang*

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School of Chemical Science and Engineering, Shanghai Key Lab of Chemical Assessment and Sustainability, Tongji University, Shanghai, 200092, China ABSTRACT: The reactions of laser-ablated C, Si, Ge, Sn, and Pb atoms with BF3 have been studied using matrix isolation Fourier transform infrared (FTIR) spectroscopy and density functional theoretical (DFT) calculations. All atoms generate the inserted complex F2B−MF, which were trapped in inert gas and identified by the isotopic substitutions and DFT frequency calculations. DFT and CCSD(T) calculations show that triplet F2B−CF is the most stable isomer with two singly occupied molecular orbitals, while singlet F2B−MF (M= Si, Ge, Sn and Pb) molecules possess a near right angle B−M−F moiety with lone pair electrons on the M atom. The bonding difference between C and other group 14 atoms is mainly caused by relativistic effect, which is that, for heavier metal atom valences, s and p orbitals have a lower tendency to form hybrid orbitals.

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INTRODUCTION Boryl complexes play important roles for C−H borylation reactions, in which boryl groups incorporate into organic molecules to form organoboron compounds with a carbon− boron bond.1−3 The organoboron compounds have broad applications in chemical synthesis because the C−B bond can easily be converted into a C−X (X = Br, Cl), C−O, C−N, or C−C bond. The transition metal boryl complexes have been investigated intensively, for example, Taylor and Merola provided the first structural evidence for a transition metal boryl compound,4,5 and from then on many new boryl complexes were reported. The fluorine substituted boryl, fluoroboryl, has been synthesized through boron trifluoride activated by oxidative addition to the transition-metal complex [(Cy3P)2Pt] to form [(Cy3P)2Pt(BF2)(FBF3)].6 Very recently a fluoroboryl radical (NHC-BF2) was generated from 1,3dimethylimidazol-2-ylidene difluoroborane (NHC−BF2H) by laser flash photolysis experiments and characterized by UVspectroscopy and rate constant measurements.7 The bonding between boron and main group elements has been an attractive subject.8−11 For example, laser-ablated boron atoms react with methyl fluoride in an argon stream to form two major products: CH2BF and CHBF, which are produced through boron insertion into the C−F bond, followed by loss of one or two H atoms. The calculations predict that there is no dative bonding in either CH2BF or CHBF, despite the empty p-orbital on B and the filled porbitals on the halogen atom.11 In addition, the reactions of laser-ablated boron atoms with C2H4, C2H6,7 CH3NH2,9 and CH3OH10 in solid noble gas matrices have also produced the BC, BN, or BO bond, respectively. Some boron cation complexes, B3(CO)n+12 and [ArB3O4]+, [ArB3O5]+, [ArB4O6]+, and [ArB5O7]+13 were prepared in gas phase, in which B3(CO)4+12 has a chemical bonding pattern similar to allene, and [ArB3O5]+, [ArB4O6]+, and [ArB5O7]+13 cation complexes have planar structures each involving anaromatic boroxol ring. © XXXX American Chemical Society

The observation of BiB and BiB multiple bonds in BiB2O2− and Bi2B− are generated by laser vaporization of a mixed B/Bi target and are characterized by photoelectron spectroscopy and ab initio calculations,14 which is the first report about the bonding between boron and heavier main group element. The reactions of the laser-ablated metal (M = Ti, Zr, Hf, Th) atoms with BF3 were conducted and the fluoroborylene complexes FBMF2 have been prepared in which B−F bonds were inserted to form F2B−MF boryl complexes.15,16 In this paper, group 14 elements have been performed to react with BF3 to examine whether or not these main group elements undergo similar subsequent F migration as for transition metals. The fluoroboryl complexes, F2B−MF (M = C, Si, Ge, Sn and Pb), have been identified by boron isotopic substitution and theoretical frequency calculations. The bonding formation between boron and main group element has been investigated by the electron localization function (ELF) analysis and the theory of atoms-in-molecules (AIM).

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EXPERIMENTAL AND THEORETICAL METHODS Laser-ablated group 14 (C, Si, Ge, Sn, Pb) atoms were reacted with 11BF3 and 10BF3 in excess argon during condensation at 4 K using a closed-cycle helium refrigerator (Sumitomo Heavy Industries Model SRDK-408D2). The samples of 11BF3 and 10 BF3 were purchased from Jinglin (Shanghai) Chemical Industry Limited Liability Company (Shanghai, China, chemical purity, ≥99.99%). Reagent gas mixtures ranged 0.1%-1% (typically 0.5%) in argon. The Nd:YAG laser fundamental radiation (1064 nm, 10 Hz repetition rate with 10 ns pulse width) was focused on rotating freshly cleaned SiC, Received: May 10, 2018 Revised: August 11, 2018 Published: August 24, 2018 A

DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A Si, Ge, Sn and Pb targets using 5−10 mJ/pulse, and the ablated material was codeposited uniformly onto a cooled 4 K CsI window with the argon/boron trifluoride samples. The laserablated group 14 atoms have been reacted with BF3 in excess argon for 1 h at a deposition rate of 2−4 mmol/h. After initial reaction, infrared spectra were recorded on a Bruker 80 V spectrometer at 0.5 cm−1 resolution between 4000 and 400 cm−1 using a HgCdTe range B detector. Then samples were annealed to different temperatures; they were later irradiated by a mercury arc lamp (Philips, 175 W), and more spectra were recorded. In order to assign these observed frequencies, the complementary density functional theory (DFT) calculations were performed using the Gaussian 09 program.17 The hybrid B3LYP18,19 and BPW9120 density functional were employed for reaction product molecules. The 6-311++G(3df, 3pd) basis sets21 for B, F, C, Si, and Ge atoms and the SDD pseudopotential basis sets22 for Sn, Pb atoms were used to provide vibrational frequencies for reaction products. The single point energy calculations were performed with the correlated molecular orbital theory coupled cluster CCSD(T) theory.23−25 We applied natural bond order (NBO) analysis,17,26 the electron localization function (ELF)27 analysis and the theory of atoms-in-molecules (AIM)28 performed by Multiwfn code29 to investigate bonding characters. In addition, ab initio calculations based on high-level multiconfigurational wave function method were also performed to obtain the accurate electronic structures information on different multiply carbon compounds by ORCA 4.0.1 program.30,31 CASSCF calculations including four active electrons in eight active orbitals, i.e., CAS(4e, 8o), were performed with Def2-TZVP basis set and the effect of dynamic correlation was taken into account by NEVPT2 on top of the wave functions at CAS(4e, 8o)/Def2-TZVP level to get more accurate energies.32−36

Figure 1. Infrared spectra of the laser-ablated Si atom reactions with BF3 in excess solid argon. (a−d) 0.5% 11BF3: (a) codeposition for 60 min and (b) after annealing to 25 K, (c) after λ > 220 nm irradiation for 10 min, and (d) after annealing to 30 K. (e−h) 0.5% 10BF3: (e) codeposition for 60 min and (f) after annealing to 25 K, (g) after λ > 220 nm irradiation for 8 min, and h) after annealing to 30 K.

were also done with 10 BF 3 using the same sample concentration and laser power (Figure 1, top), and this group of bands shifted to 1329.0, 1248.1, and 805.5 cm−1, which has a behavior similar to that of the counterparts produced with 11BF3. The 1284.8 cm−1 band is close to the B−F vibration mode at 1276 cm−1 for the FBThF2 molecule.16 This band shifts to 1329.0 cm−1 with 10BF3 substitution, giving 1.0344 as the 10 B/11B isotopic frequency ratio, which is in good agreement with the boron isotopic frequency ratio 1.0347 for the antisymmetric stretching vibration of the F−B−F radical.35 The 1208.7 cm−1 band shifts to 1248.1 cm−1, giving a 10B/11B isotopic frequency ratio of 1.0326, which fits the calculated ratio of 1.0324, substantiating the assignment of the F−B−F symmetric stretching vibration. The 802.8 cm−1 band is close to 833.7 cm−1 of an Si−F mode in HSiF,38 which shifted to 805.5 cm−1 (Figure 1, top) in 10BF3, suggesting the band is due to the stretching vibration of an Si−F mode. Hence we assign this group of bands to the F2BSiF molecule. The B3LYP/BPW91 calculations predict the F2BSiF molecule to have C1 symmetry with the 1A ground electronic state. As listed in Table 1, our B3LYP calculation predicts that the F−11B(10B)−F antisymmetric stretching mode is at 1294.8 cm−1 (1339.4 cm−1), which is in very good agreement with the experimental value, overestimating by about 0.78% (0.78%) (where the values in parentheses are for 10B counterparts). The F−11B(10B)−F symmetric stretching mode is calculated at 1206.8 cm−1 (1245.9 cm−1), which is only 1.9 cm−1 (2.2 cm−1) or 0.16% (0.18%) lower than the observed value. The Si−F stretching mode is predicted at 798.7 cm−1, which is underestimated by 0.51% (0.84%). The BPW91 frequencies are calculated at 1251.2 cm−1 (1294.2 cm−1), 1165.1 cm−1 (12.2.9 cm−1), and 768.8 cm−1 (768.8 cm−1) for the F−11B(10B)−F antisymmetric, symmetric stretching mode

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RESULTS AND DISCUSSION The experiments have been done with 0.5% 11BF3 or 10BF3 or the mixture of them in excess argon. Typical infrared spectra in the selected regions for the reactions of laser-ablated group 14 atoms with 11BF3 or 10BF3 in excess argon are illustrated in Figures 1−6, and the absorption bands are listed in Tables 1−5. The product absorptions behaviors responding to stepwise annealing and irradiation are also shown in these figures and will be discussed below. Common species, such as BF2, BF, and HBF2 absorptions, which were produced during the experiment owing to precursor fragment, have been reported previously.37 Moreover, weak absorptions for trace impurities such as H2O, CO2, and CO in our experiments were observed. Five targets were ablated in experiments and corresponding products are reported below. In order to prevent producing carbon clusters, the SiC target instead of C target was used to produce carbon atoms. Therefore, we introduce Si product first, which would be convenient to distinguish F2BCF from F2BSiF when using the SiC target. F2BSiF. Infrared spectra for the reaction of Si atom with 11 BF3 and 10BF3 in excess argon and their variation in annealing and photolysis are shown in Figure 1. New product absorptions marked F211BSiF at 1284.8, 1208.7, and 802.8 cm−1 appeared upon codeposition in the reaction of Si with 11 BF3. These bands decreased about 20% on annealing to 25 K, and had no change after λ > 220 nm irradiation, but decreased again about 25% on finally annealing to 30 K. Experiments B

DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A Table 1. Observed and Calculated Fundamental Frequencies of F211BSiF and F210BSiF in the Ground 1A Statea F211BSiF b

F210BSiF b

approximate description

obsd

calcd(int) B3LYP

calcd(int) BPW91

obsd

BF2 antisym str BF2 sym str Si−F str BF2 bend BF2 rock B−Si str F2BSi def F2BSiF def F2BSiF def

1284.8 1208.7 802.8

1294.8(332.4) 1206.8(194.3) 798.7(118.8) 598.0(2.2) 534.3(45.9) 325.8(35.8) 148.8(2.4) 140.3(5.9) 36.8(1.0)

1251.2(308.8) 1165.1(180.8) 768.8(104.7) 579.2(2.3) 514.3(41.8) 314.4(30.8) 140.1(2.0) 132.3(4.7) 40.4(0.9)

1329.0 1248.1 805.5

calcd(int) B3LYP

calcd(int) BPW91

1339.4(357.7) 1245.9(208.4) 798.7(118.2) 606.1(5.7) 551.5(44.1) 326.7(36.8) 149.8(2.4) 140.6(5.9) 36.9(1.0)

1294.2(332.2) 1202.9(193.8) 768.8(104.2) 587.1(5.4) 530.6(40.0) 315.4(31.7) 141.0(2.0) 132.7(4.7) 40.4(0.9)

a The vibrational frequencies (cm−1) and intensities (km/mol, in parentheses) are calculated using B3LYP/6-311++g(3df,3pd) and BPW91/6311++g(3df,3pd). bObserved in an argon matrix.

and Si−F stretching mode, respectively, being 2.62 (2.62), 3.61 (3.62), and 4.24 (4.56)% lower than the observed values. Compared with B3LYP, BPW91 often underestimated the frequencies,39,40 but the results calculated from BPW91 are close to the observed values in our argon matrix experiments, which confirm the assignment of insertion product F2BSiF. The higher oxidation state products (FB−SiF2 and B−SiF3) are not observed in the experiment owing to their higher relative energies. Compared with total energy of Si (3A) + BF3, the F2B−SiF (ground-state singlet) and FB−SiF2 (ground-state singlet) complexes are predicted to be 30.94, 10.79 kcal/mol lower in energy, while the B−SiF3 molecule (ground-state singlet) is 8.79 kcal/mol higher in energy at the CCSD(T) level. F2BCF. The infrared spectra for the reaction of laser-ablated C (SiC target) atom codeposited with 11BF3 or 10BF3 in excess argon and their following behavior on annealing and broad photolysis are shown in Figure 2. Besides the bands at 1284.8, 1208.7, and 802.8 cm−1 for F211BSiF, a new group of product absorptions were observed, which appeared at 1380.3, 1170.3, and 598.8 cm−1 after codeposition of C (SiC) reaction with 11 BF3 (Figure 2, lower set). These new bands had no significant change on annealing to 25 K, and slightly increased after λ > 220 nm irradiation, but decreased about 25% upon annealing to 30 K. The complementary experiments were also done with isotopic sample (10 BF3), having the same concentration and laser power as that for the 11BF3 experiment. As shown in Figure 2, these absorption bands appeared at 1419.5, 1206.0, and 623.0 cm−1, respectively. This group bands are assigned to F2BCF molecule. First, the 1380.3 cm−1 band is assigned to B−F stretching mode, which is very close to 1389.9, and 1387.7 cm−1 for BF2 stretching frequencies.37 The 1380.3 cm−1 band shift to 1419.5 cm−1 with 10 BF3, exhibiting isotopic frequency ratio of 1.0284 that is close to the boron isotopic frequency ratio 1.0280 of B2F4 molecule reported previously,41 which imply that the 1380.3 cm−1 band is due to B−F stretching vibration. The 1170.3 cm−1 band shifts to 1206.0 cm−1, giving a 10B/11B isotopic frequency ratio 1.0305, due to the B−C−F stretching vibration. The B3LYP/BPW91 calculations predict the F2BCF molecule to have C1 symmetry with the 3A ground electronic state. As listed in Table 2, the B−C stretching vibration is calculated at 1475.9 cm−1, which might be masked by the precursor BF3 peak. The F−11B(10B)−F antisymmetric stretching mode is calculated at 1397.1 cm−1 (1447.8 cm−1), which is in very good agreement with the experimental value, overestimating only by 1.22% (1.99%). The 11B(10B)−C−F

Figure 2. Infrared spectra of the laser-ablated SiC (C) atom reactions with BF3 in excess solid argon. (a−d) 0.5% 11BF3: (a) codeposition for 60 min and (b) after annealing to 25 K, (c) after λ > 220 nm irradiation for 10 min, and (d) after annealing to 30 K. (e−h) 0.5% 10 BF3: (e) codeposition for 60 min and (f) after annealing to 25 K, (g) after λ > 220 nm irradiation for 8 min, and (h) after annealing to 30 K.

stretching mode is computed at 1189.0 cm−1 (1212.5 cm−1), which is 1.60% (0.54%) higher than the observed value. The BF2 bending mode is predicted at 600.1 cm−1 (623.5 cm−1), which is overestimated by 0.22% (0.08%). The BPW91 frequencies are all slightly 2.17 (1.42), 1.44 (2.44), and 3.94 (4.08)% lower than the observed values for these two stretching and one bending mode. Consequently, these absorption bands are assigned to the carbon insertion product F2BCF. In our experiment the borylene (FBCF2) and borylidyne (BCF3) are not identified due to the higher relative energies of the high oxidation state complexes. Compared to the total energy of C (3A) + BF3, the BF2−CF (ground-state triplet), BF-CF2 (ground state singlet) and B−CF3 species (singlet ground state) complexes are predicted to be 36.02 and 2.51 kcal/mol lower and 44.74 kcal/mol higher in energy. C

DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A Table 2. Observed and Calculated Fundamental Frequencies of F211BCF and F210BCF in the Ground 3A Statea F211BCF approximate description B−C str BF2 antisym str B−C−F str F2BC def BF2 wag FBCF bend FBCF bend F2BCF def F2BCF def

b

obsd

1380.3 1170.3 598.8

F210BCF

calcd(int) B3LYP

calcd(int) BPW91

1475.9(68.4) 1397.1(330.0) 1189.0(418.9) 789.5(9.5) 600.1(38.1) 537.7(14.1) 409.8(2.7) 208.9(1.5) 179.5(2.5)

1434.7(58.2) 1350.3(304.9) 1153.5(387.6) 765.5(6.8) 575.2(29.2) 520.5(11.9) 396.9(2.5) 204.3(0.98) 172.8(2.1)

obsd

b

1419.5 1206.0 623.0

calcd(int) B3LYP

calcd(int) BPW91

1498.4(82.7) 1447.8(360.5) 1212.5(430.4) 790.4(8.8) 623.5(41.4) 540.6(13.4) 410.7(2.7) 209.4(1.4) 179.9(2.5)

1456.4(69.1) 1399.3(332.0) 1176.6(399.7) 766.4(6.4) 597.6(31.7) 523.3(11.3) 397.7(2.5) 204.7(0.95) 173.2(2.1)

a The vibrational frequencies (cm−1) and intensities (km/mol, in parentheses) are calculated using B3LYP/6-311++g(3df,3pd) and BPW91/6311++g(3df,3pd). bObserved in an argon matrix.

629.0 cm−1 after codeposition in reaction with 11BF3 (Figure 3, bottom). These bands decreased about 20% on annealing to 25 K, and slightly increased on λ > 220 nm photolysis, but decreased about 20% upon annealing to 30 K. These bands shift to 1332.8, 1235.5, and 628.4 cm−1 in the reaction of Ge with 10BF3 in excess solid argon. The 1289.3 and 1196.9 cm−1 bands shift to 1332.8 and 1235.5 cm−1 with 10BF3 substitution, giving 1.0337 and 1.0322 10 B/11B isotopic frequency ratios, which fit the calculated frequency ratios 1.0346 and 1.0319 and are in good agreement with the previously reported values of the B−F vibration mode.16,37 The observed band at 629.0 cm−1 have nearly no shifts at the isotopic substitution (band at 628.4 cm−1 in Figure 3, top), which is close to the two independent experimental values of 665.7 cm−1 42 and 662.4 cm−1 43 obtained from the microwave spectrum of GeF, indicating that this band is possibly due to Ge−F stretching vibration. Therefore, these absorption bands come from one molecule, namely F2BGeF. A mixture of B isotopes has been used to ensure that a single B atom is in the product. The spectrum of reaction of Ge with the mixture of 0.5%11BF3 and 0.5% 10BF3 (1:1) was shown in Figure 5b. The 1289.3, 1196.9, and 629.0 cm−1 for F211BGeF and 1332.8, 1235.5 and 628.4 cm−1 for F210BGeF were found after codeposition. Compared with the spectrum of 0.5%11BF3 (Figure 5a) and 0.5% 10BF3 (Figure 5c), there are no additional peaks appeared between 1289.3 cm−1 (11B−F antisymmetrical stretching mode) and 1332.8 cm−1 (10B−F antisymmetrical stretching mode) or 1196.9 cm−1 (11B−F symmetrical stretching mode) and 1235.5 cm−1 (10B−F

F2BGeF. The spectrum of Ge + BF3 is shown in Figure 3. One new group of bands appeared at 1289.3, 1196.9, and

Figure 3. Infrared spectra of the laser-ablated Ge atom reactions with BF3 in excess solid argon. (a−d) 0.5% 11BF3: (a) codeposition for 60 min and (b) after annealing to 25 K, (c) after λ > 220 nm irradiation for 8 min, and (d) after annealing to 30 K. (e−h) 0.5% 10BF3: (e) codeposition for 60 min and (f) after annealing to 25 K, (g) after λ > 220 nm irradiation for 8 min, and (h) after annealing to 30 K.

Table 3. Observed and Calculated Fundamental Frequencies of F211BCeF and F210BCeF in the Ground 1A Statea F211BGeF b

F210BGeF b

approximate description

obsd

calcd(int) B3LYP

calcd(int) BPW91

obsd

BF2 antisym str BF2 sym str Ge−F str BF2 bend BF2 rock B−Ge str F2BGe def F2BGeF def F2BGeF def

1289.3 1196.9 629.0

1302.3(331.8) 1195.4(220.0) 629.3(101.9) 575.7(4.1) 494.6(23.2) 254.0(28.7) 140.2(1.6) 120.0(5.5) 49.8(1.8)

1257.7(309.1) 1154.7(203.7) 611.2(88.4) 557.4(3.1) 473.5(19.7) 246.8(26.1) 133.7(1.2) 114.7(4.5) 48.0(1.5)

1332.8 1235.5 628.4

calcd(int) B3LYP

calcd(int) BPW91

1347.3(356.6) 1233.5(235.3) 630.5(103.1) 581.8(2.9) 514.5(24.2) 255.6(29.4) 141.3(1.6) 120.3(5.5) 49.8(1.8)

1301.1(332.1) 1191.7(217.6) 612.4(89.3) 563.2(2.2) 492.5(20.5) 248.5(20.5) 134.7(1.2) 114.9(4.5) 48.1(1.5)

The vibrational frequencies (cm−1) and intensities (km/mol, in parentheses) are calculated using B3LYP/6-311++g(3df,3pd) and BPW91/6311++g(3df,3pd). bObserved in an argon matrix. a

D

DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A

The observed 1272.3 and 1175.3 cm−1 bands shift to 1313.6 and 1212.4 cm−1 with 10BF3 substitution, giving 1.0325 and 1.0316 10B/11B isotopic frequency ratios and fitting the calculated ratios of 1.0344 and 1.0313, which are in consistent with the previously reported isotopic frequency ratio of B−F stretching mode.15,37 The Sn−F stretching vibration was observed in our experiments, which is close to the reported values of F2Sn·PhMe (536 cm−1).42 The spectrum of reaction of Sn with the mixture of 0.5%11BF3 and 0.5% 10BF3 (1:1) was shown in Figure 5e. No additional peaks appeared between

symmetrical stretching mode), suggesting that a single B atom instead of two B atoms presents in the product. The DFT computations predict the F2BGeF molecule to have C1 symmetry with the 1A ground electronic state. The B3LYP/BPW91 calculated frequencies are listed in Table 3. The calculated F−11B(10B)−F antisymmetric stretching frequency is at 1302.3 cm−1 (1347.3 cm−1) by B3LYP, which is overestimated by 13.0 cm−1 (14.5 cm−1) or 1.01% (1.09%). The F−11B(10B)−F symmetric stretching mode is calculated at 1195.4 cm−1 (1233.5 cm−1), which is only 1.5 cm−1 (2.0 cm−1) or 0.13% (0.16%) lower than the observed value. The B3LYP predicted stretching vibration of Ge−F is slightly higher than the observed values (0.05% for F211BGeF, 0.33% for F210BGeF respectively). The BPW91 frequencies are all slightly lower than the observed values about 2.45 (2.38), 3.53 (3.55), and 2.83 (2.55)%. So these bands are confirmed to the F2BGeF molecule. However, the higher oxidation state products (FB−GeF2 and B−GeF3) are not observed as well because of their higher energies. F2BSnF. As shown in Figure 4, the absorption bands appeared at 1272.3 cm−1, 1175.3 and 525.4 cm−1 in Sn + 11BF3

Figure 5. Infrared spectra from codeposition of laser evaporated Ge (Sn) atoms with BF3 in excess argon. (a−c) Ge target: (a) 0.5% 11 BF3; (b) 0.5% 11BF + 0.5% 10BF3; (c) 0.5% 10BF3. (d−f) Sn target: (d) 0.5% 11BF3; (e) 0.5% 11BF + 0.5% 10BF3; (f) 0.5% 10BF3.

1272.3 cm−1 (11B−F antisymmetrical stretching mode) and 1313.6 cm−1(10B−F antisymmetrical stretching mode) or 1175.3 cm−1 (11B−F symmetrical stretching mode) and 1212.4 cm−1(10B−F symmetrical stretching mode) compared with the spectrum of Sn in 0.5%11BF3(Figure 5 (d)) and 0.5% 10 BF3 (Figure 5f), suggesting that a single B atom instead of two B atoms is in the product. We assigned these bands to the F2BSnF molecule. The DFT computed frequencies for F2BSnF molecule are listed in Table 4. The F−11B(10B)−F antisymmetric stretching frequency calculated by B3LYP method is at 1285.1 cm−1 (1329.3 cm−1), which is overestimated by 12.8 cm−1 (15.7 cm−1) or 1.01% (1.20%). The calculated F−11B(10B)−F symmetric stretching mode is at 1176.1 cm−1 (1212.9 cm−1), which is only 0.8 cm−1 (0.5 cm−1) or 0.07% (0.04%) higher than the observed value. Moreover, the B3LYP predicted that the stretching vibration of Sn−F is slightly higher than the observed values (2.78% for F211BSnF, 2.25% for F210BSnF respectively). Notice the BPW91 frequencies are all slightly lower than the observed values as expected. Again no further reaction happened to produce the borylene or borylidyne via F migration due to higher energies. F2BPbF. The spectrum of reaction products is shown in Figure 6. New bands appeared at 1268.5 cm−1, 1142.6 and 475.1 cm−1 on codeposition in the experiment of Pb + 11BF3 (Figure 5, bottom). These peaks increased about 80% upon annealing to 25 K, and enhanced about 20% after λ > 220 nm

Figure 4. Infrared spectra of the laser-ablated Sn atom reactions with BF3 in excess solid argon. (a−e) 0.5% 11BF3: (a) codeposition for 60 min and (b) after annealing to 25 K, (c) after λ > 300 nm irradiation for 8 min, (d) after λ > 220 nm irradiation for 8 min, and (e) after annealing to 30 K. (f−j) 0.5% 10BF3: (f) codeposition for 60 min and (g) after annealing to 25 K, (h) after λ > 300 nm irradiation for 8 min, (i) after λ > 220 nm irradiation for 8 min, and (j) after annealing to 30 K.

experiment, which decreased about 30% upon annealing to 25 K, and sequentially decreased about 50% after λ > 300 nm irradiation, but increased 100% on λ > 220 nm photolysis and decreased slightly after annealing to 30 K. The complementary isotopic substitution experiment was also done in the same conditions, and these bands shifted to 1313.6, 1212.4, and 528.0 cm−1, having the consistent change behaviors in the reaction of Sn with 10BF3. E

DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A Table 4. Observed and Calculated Fundamental Frequencies of F211BSnF and F210BSnF in the Ground 1A Statea F211BSnF b

F210BSnF b

approximate description

obsd

calcd(int) B3LYP

calcd(int) BPW91

obsd

BF2 antisym str BF2 sym str BF2 bend Sn−F str BF2 rock B−Sn str F2BSn def F2BSnF def F2BSnF def

1272.3 1175.3

1285.1(313.0) 1176.1(250.4) 563.6(7.6) 540.0(100.7) 446.1(15.5) 217.6(27.6) 123.8(0.8) 99.6(6.5) 28.1(2.3)

1246.7(293.3) 1136.3(238.7) 544.9(7.0) 519.5(84.9) 424.5(12.3) 211.6(24.7) 118.4(0.6) 93.7(5.4) 31.3(2.1)

1313.6 1212.4

525.4

528.0

calcd(int) B3LYP

calcd(int) BPW91

1329.3(335.7) 1212.9(267.3) 569.1(6.4) 539.9(101.5) 464.6(15.7) 218.3(27.9) 124.7(0.8) 99.7(6.5) 28.1(2.3)

1289.6(314.5) 1171.9(254.8) 550.2(5.9) 519.4(85.3) 442.1(12.5) 212.2(25.1) 119.3(0.6) 93.7(5.4) 31.3(2.1)

The vibrational frequencies (cm−1) and intensities (km/mol, in parentheses) are calculated using B3LYP/6-311++g(3df,3pd)/SDD and BPW91/ 6-311++g(3df,3pd)/SDD. bObserved in an argon matrix.

a

response to the photo irradiation and annealing as the product in 11BF3 sample. The band appeared at 1268.5 cm−1 shifted to 1296.8 cm−1, giving 1.0223 for the 10B/11B isotopic frequency ratio, which is near to the boron isotopic frequency ratio of 10B/11B (1.0280) of the B2F4 molecule.41 The counterpart in Pb + 10BF3 for 1142.6 cm−1 was not observed, which might be covered by H10BF2 peaks at 1181.2 and 1177.1 cm−1. The observed 475.1 cm−1Pb−F stretching mode have nearly no shift at the isotopic substitution (band at 475.6 cm−1 in Figure 5, top), which is close to the Pb−F stretching frequency at 496.3 cm−1 for F2Pb· CO.44 As listed in Table 5, the calculated F−11B(10B)−F antisymmetric stretching frequency at B3LYP level is at 1278.8 cm−1 (1322.9 cm−1), which is overestimated by 10.3 cm−1 (26.1 cm−1) or 0.81% (2.01%). The F−11B(10B)−F symmetric stretching mode is calculated at 1167.0 cm−1 (1203.3 cm−1), which is 24.4 cm−1 or 2.14% higher than the observed value. The BPW91 results are all slightly lower than the observed values. According to the DFT calculations, we assign these bands to the F2BPbF molecule. Nevertheless, the higher oxidation state products (FB−PbF2 and B−PbF3) are again not observed in line with their considerably higher energies.

Figure 6. Infrared spectra of the laser-ablated pb atom reactions with BF3 in excess solid argon. (a−d) 0.5% 11BF3: (a) codeposition for 60 min and (b) after annealing to 25 K, (c) after λ > 220 nm irradiation for 8 min, and (d) after annealing to 30 K. (e−h) 0.5% 10BF3: (e) codeposition for 60 min and (f) after annealing to 25 K, (g) after λ > 220 nm irradiation for 8 min, and (h) after annealing to 30 K.

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BONDING DFT calculations suggest that the triplet F2BCF is the global minimum structure in the reaction of the laser-ablated C atom with BF3. The singlet F2B−CF is 7.97 and 6.53 kcal/mol higher in energy than triplet F2BCF at B3LYP and CCSD(T)

irradiation, but decreased about 50% on annealing to 30 K. For the reaction of Pb with 10BF3 (Figure 5, top), these bands shifted to 1296.8 and 475.6 cm−1, which have the same

Table 5. Observed and Calculated Fundamental Frequencies of F211BPbF and F210BPbF in the Ground 1A Statea F211BPbF b

F210BPbF b

approximate description

obsd

calcd(int) B3LYP

calcd(int) BPW91

obsd

BF2 antisym str BF2 sym str BF2 bend Pb−F str BF2 rock B−Pb str F2BPb def F2BPbF def F2BPbF def

1268.5 1142.6

1278.8(308.4) 1167.0(280.4) 559.5(10.9) 469.0(95.0) 423.3(7.5) 198.3(25.6) 121.5(0.4) 89.8(6.5) 28.0(2.9)

1241.0(290.3) 1128.7(267.6) 541.3(10.1) 455.7(79.5) 405.7(5.7) 194.1(22.5) 117.0(0.3) 86.9(5.5) 29.6(2.5)

1296.8

475.1

475.6

calcd(int) B3LYP

calcd(int) BPW91

1322.9(330.3) 1203.3(299.3) 564.9(9.5) 469.1(96.7) 441.0(6.4) 199.4(26.1) 122.5(0.4) 89.9(6.5) 28.0(2.9)

1283.7(310.8) 1163.7(285.7) 546.5(8.8) 455.8(80.4) 422.7(5.2) 195.2(22.9) 117.9(0.3) 87.0(5.5) 29.6(2.5)

The vibrational frequencies (cm−1) and intensities (km/mol, in parentheses) are calculated using B3LYP/6-311++g(3df,3pd)/SDD and BPW91/ 6-311++g(3df,3pd)/SDD. bObserved in an argon matrix.

a

F

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Figure 7. Structures of the inserted F2BMF molecules (M = C, Si, Ge, Sn, Pb) optimized using the B3LYP and BPW91 (italic) functionals. The 6311++G(3df,3pd) basis set was used for B, F, C, Si, and Ge atoms and the SDD pseudopotential basis set for Sn and Pb atoms. Bond lengths were given in Å and angles in deg. The energies were single point energy using CCSD(T) method. The energies are in kcal/mol and relative to corresponding M + BF3.

Figure 8. Selected active molecular orbitals in F2BCF for the triplet (top row) and the singlet states at CAS(4e, 8o)/Def2-TZVP level. The contour line used is 0.04 e au−3. MO occupation numbers are given with each orbital.

π type bond was formed out of the plane and the other one electron seems not forming a really π bond in the plane between B and C atom. A Mayer bond order of 1.14 was computed at the CAS(4e, 8o)/Def2-TZVP level. The NBO

levels, respectively. The natural orbitals with their occupation numbers are shown in Figure 8, and both for the triplet and the singlet states of the carbon were calculated by the CASSCF/ NEVPT2 method. For the triplet state (top row), one-electron G

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Table 6. Compositions of Natural Localized Molecular Orbitals (NLMO) from NBO Analysis of F2BMF (M = C, Si, Ge, Sn, Pb)a molecule F2BCF

bond B−C B−C B−F1 B−F2 C−F

F2BSiF

F2BGeF

BF2SnF

F2BPbF

C(LP) B−Si B−F1 B−F2 Si−F Si(LP) B−Ge B−F1 B−F2 Ge−F Ge(LP) B−Sn (1)B−F1 (2)B−F1 B−F2 Sn−F Sn(LP) B−Pb (1)B−F1 (2)B−F1 B−F2 Pb−F Pb(LP)

NLMO 38% B(s0.40p0.60) + 62% C(s0.37p0.63) 36% B(s0.38p0.62) + 64% C(s0.62p0.37) 18% B(p0.99d0.01) + 82% C(p) 18% B(s0.28p0.71) + 82% F(s0.42p0.58) 18% B(s0.32p0.68) + 82% F(s0.41p0.59) 18% B(s0.31p0.68) + 82% F(s0.42p0.58) 18% B(s0.30p0.70) + 82% F(s0.42p0.57) 25% C(s0.22p0.78) + 75% F(s0.30p0.70) 25% C(s0.34p0.65) + 75% F(s0.31p0.69) 100% C(s0.43p0.57) 62% B(s0.42p0.57) + 38% Si(s0.08p0.91) 17% B(s0.29p0.70) + 83% F(s0.43p0.57) 17% B(s0.29p0.70) + 83% F(s0.43p0.57) 10% Si(s0.12p0.86d0.02) + 90% F(s0.34p0.65) 100% Si(s0.83p0.17) 61% B(s0.42p0.58) + 39% Ge(s0.06p0.93) 17% B(s0.29p0.70) + 83% F(s0.44p0.56) 17% B(s0.29p0.70) + 83% F(s0.44p0.56) 11% Ge(s0.09p0.90) + 89% F(s0.23p0.77) 100% Ge(s0.88p0.12) 67% B(s0.42p0.58) + 33% Sn(s0.05p0.95) 16% B(s0.28p0.71) + 84% F(s0.44p0.56) 7% B(s0.01p0.98) + 93% F(p0.99) 16% B(s0.29p0.70) + 84% F(s0.44p0.56) 8% Sn(s0.06p0.94) + 92% F(s0.20p0.79) 100% Sn(s0.90p0.10) 67% B(s0.42p0.58) + 33% Pb(s0.03p0.96) 16% B(s0.29p0.71) + 84% F(s0.44p0.56) 6% B(p0.98d0.01) + 94% F(p) 16% B(s0.29p0.70) + 84% F(s0.44p0.56) 9% Pb(s0.04p0.95) + 91% F(s0.17p0.83) 100% Pb(s0.93p0.07)

occ α β α α β α β α β α

1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.98 1.97 2.00 2.00 1.99 1.99 1.97 2.00 2.00 1.99 1.99 1.96 2.00 2.00 2.00 1.99 1.99 1.97 2.00 2.00 2.00 2.00 2.00

a

All the data are calculated by B3LYP hybrid density functional. LP denotes lone pair.

analysis (Table 6) also shows a pseudo half π bond formed mostly by donation from single 2p electron of the C atom to the empty 2p orbital of B atom. The low row in Figure 8 gives the orbital for the singlet state of F2B−CF, which shows that the lone pair electrons of C atom has not participated in π bonding between B and C atom and the Mayer bond order of B−C bond is 0.98. Furthermore, the B−C bond length is 1.530 and 1.582 Å for triplet and singlet F2B−CF, respectively, which is in accordance with the bond order and relative energy level of two different multiplicity of F2B−CF. For the remaining group 14 atoms, the DFT computations suggest that the singlet boryl complexes F2B−MF (M = Si, Ge, Sn, Pb) are the most stable products and the energy difference between the singlet and triplet of F2B−MF is 21.0, 27.8, 30.3, and 37.4 kcal·mol−1 for Si, Ge, Sn, and Pb, respectively. As shown in Figure 7, the surface of the B−M−F moiety is nearly perpendicular to that of F−B−F moiety and the angle B−M−F moiety is close to right angle, which reflects the high p contributions of metal atom to the B−M and M−F bonds. With natural bond orbital (NBO) analysis listed in Table 6 the p contributions of B−M and M−F bonds are 91 and 86%, 93 and 90%, 95 and 94%, and 96 and 95% for Si, Ge, Sn, and Pb in F2B−MF molecule, respectively. Moreover, the NBO analysis (Table 6) shows that Si, Ge, Sn, and Pb atoms possess a lone pair electrons, which mainly originates from the

ns orbital and the composition of s orbital is 83, 88, 90, and 93%, respectively, suggesting that these atoms are nearly nonhybridized between s and p orbitals. For group 14 atoms, carbon is special since it has almost equal 2s and 2p orbital radial expectation values.45 However, for the heavier atoms, the considerable value difference between valence s and p atomic orbital increase, and the value differences are 0.39, 0.48, 0.57, and 0.79 Å for Si, Ge, Sn, and Pb, respectively,46−50 which was mainly caused by relativistic effect. Obviously there is a lower tendency to form hybrid orbital between s and p orbital for the heavier atoms. In their compounds these heavier atoms preserve the valence ns electron as core-like electrons and keep valence shell (ns)2(npx)1(npy)1 configuration.48−50 Furthermore, Si, Ge, Sn, and Pb atoms prefer to have nonbonding electrons in atomic orbitals with a higher percentage of s-character than C atom (43% s) and the higher s-character suggests a relatively higher HOMO−LUMO gap in these atoms.49 Therefore, for the stable inserted complexes, the F2B−CF is triplet while the remaining F2B−MF (M = Si, Ge, Sn, Pb) is singlet. In our atoms-in-molecules (AIM) picture (Figure 9) the bond critical point (BCP) between B and C, Si, Ge, Pb locates in the region with negative Laplacian value (∇2ρcp = −0.222 for B−C, −0.137 for B−Si, −0.095 for B−Ge, 0.0097 for B− Sn, and −0.029 for B−Pb). As pointed out in the AIM H

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CONCLUSIONS Reactions of laser-ablated C, Si, Ge, Sn, Pb atoms with BF3 have been studied in excess solid argon at 4 K through matrix isolation infrared spectroscopy and density functional theoretical (DFT) calculations. All atoms generated the insertion fluoroboryl complex F2BMF, which were identified by the 10 BF3 isotopic substitutions and DFT frequency calculations (B3LYP and BPW91). However, subsequent α-F migration to form higher oxidation-state products is evidently prohibited during codeposition and following irradiation due to their relatively higher energies. The F2B−MF molecules possess a near right angle B−M−F moiety except for F2B−CF (121°), which reflects the high valence p proportion from the M center in the B−M and M−F bonds. The difference between C and other heavier atoms in group 14 is mainly caused by relativistic effects.

Figure 9. Contour line diagrams of the Laplacian of the electronic density of F2BMF (M = C, Si, Ge, Sn, Pb) at B3LYP level, the basis sets 6-311++G(3df,3pd) used for B, F, C, Si, and Ge and SDD used for Sn and Pb. Red lines are in regions of the negative charge concentrations (∇2ρ(r) < 0). Green lines are in regions of the positive charge depletion (∇2ρ(r) > 0).

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AUTHOR INFORMATION

Corresponding Authors

methodology,47,51 the classification of the interaction is defined by the sign of ∇2ρcp. Thus, the interactions between B and Si, Ge, and Pb are in the region of the covalent bond. Although the ∇2ρcp for B−Sn is larger than zero, it is close to zero. The negative value of the local energy density H(r) = −0.02899 for B−Sn indicates the covalent bonding character.52 Moreover, the |Vcp|/Gcp value is a good indicator for the bond properties, which when smaller than 1 indicates ionic bond and large than 2 often manifests a covalent bond.47,51 The |Vcp|/Gcp value is 2.35, 2.84, 2.92, 1.72, and 2.76 for the CP of B−M bonds (M = C, Si, Ge, Sn, and Pb, respectively), indicating an increase in covalent character from C to Ge, a decrease from Ge to Sn, and an increase again from Sn to Pb. The population analyzed by electron localization function (ELF) is 2.47, 2.11, 2.20, 2.05, and 1.97 e between B−C, B−Si, B−Ge, B−Sn and B−Pb bonds, respectively, suggesting the bond strength decrease along this group followed by a decrease in the electronegativity. Thereby the bond length of B−E (E C, Si, Ge, Sn, Pb) bond is 1.317, 1.324, 1.322, 1.325, and 1.325 Å, respectively, which reproduced the same change trend. However, the irregularity at Ge atom is due to the fact that the d subshell is filled up for the first time, as known in terms of dblock contraction.48,50 A similar change trend is observed in the natural charge of the B atom (Table 7), namely, from C to Pb, the natural charge on B atom is 1.02, 0.74, 0.77, 0.67, and 0.68, respectively, in accordance with the red shift of the F−B− F antisymmetric stretching mode from C to Pb (except Ge).

*(B.X.) E-mail: [email protected]. *(X.W.) E-mail:[email protected]. ORCID

Bing Xu: 0000-0002-5521-0035 Xuefeng Wang: 0000-0001-6588-997X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (Nos. 21371136 and 21873070).

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REFERENCES

(1) Mkhalid, I. A. I.; Barnard, J. H.; Marder, T. B.; Murphy, J. M.; Hartwig, J. F. C-H Activation for the Construction of C-B Bonds. Chem. Rev. 2010, 110, 890−931. (2) Hartwig, J. F. Borylation and Silylation of C-H Bonds: A Platform for Diverse C-H Bond Functionalizations. Acc. Chem. Res. 2012, 45, 864−873. (3) Yoshida, H. Borylation of Alkynes under Base/Coinage Metal Catalysis: Some Recent Developments. ACS Catal. 2016, 6, 1799− 1811. (4) Baker, R. T.; Ovenall, D. W.; Calabrese, J. C.; Westcott, S. A.; Taylor, N. J.; et al. Boryliridium and Boraethyliridium Complexes fac[IrH2(PMe3)3(BRR′)] and fac-[IrH(PMe3)3(η2-CH2BHRR′). J. Am. Chem. Soc. 1990, 112, 9399−9400.

Table 7. Charge on Each Atom and Bond Order of F2BMF Molecules (M = C, Si, Ge, Sn, Pb)a F2BCF a

B−M a B−F1 a B−F2 a M−F q(B) q(M) q(F1) q(F2) q(F3) μ/De

F2BSiF

F2BGeF

F2BSnF

F2BPbF

B3LYP

BPW91

B3LYP

BPW91

B3LYP

BPW91

B3LYP

BPW91

B3LYP

BPW91

1.02 0.84 0.85 0.95 0.44/1.02 −0.29/0.21 0.03/-0.46 0.02/-0.46 −0.20/-0.31 0.68

1.03 0.86 0.87 0.97 0.47/0.96 −0.35/0.20 0.03/-0.44 0.02/-0.44 −0.17/-0.29 0.71

0.92 0.84 0.84 0.56 −0.005/0.74 0.34/0.92 −0.001/-0.49 −0.004/-0.49 −0.33/-0.68 1.10

0.93 0.86 0.86 0.61 −0.009/0.71 0.28/0.88 0.01/-0.47 0.01/-0.47 −0.29/-0.65 0.88

0.92 0.83 0.83 0.56 −0.14/0.77 0.64/0.90 −0.03/-0.49 −0.02/-0.49 −0.44/-0.68 2.15

0.92 0.86 0.86 0.61 −0.13/0.73 0.58/0.86 −0.02/-0.47 −0.03/-0.47 −0.40/-0.65 1.90

0.85 0.82 0.82 0.41 −0.18/0.67 0.79/1.11 −0.05/-0.50 −0.05/-0.50 −0.51/-0.77 3.25

0.86 0.85 0.85 0.47 −0.19/0.64 0.69/1.06 −0.02/-0.48 −0.02/-0.48 −0.46/-0.73 2.95

0.85 0.81 0.81 0.42 −0.24/0.68 0.73/1.10 0.04/-0.51 0.04/-0.51 −0.56/-0.76 4.20

0.85 0.84 0.84 0.49 −0.26/0.65 0.68/1.05 0.05/-0.48 0.05/-0.48 −0.52/-0.73 3.80

The superscript letter “a” denotes Wiberg bond order (WBI). q denotes Mulliken/Natural Charge.

a

I

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DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.jpca.8b04437 J. Phys. Chem. A XXXX, XXX, XXX−XXX