ARTICLE pubs.acs.org/JPCA
Computational Studies on Ethylene Addition to Nickel Bis(dithiolene) Li Dang,† Xinzheng Yang,†,§ Jia Zhou,† Edward N. Brothers,*,‡ and Michael B. Hall*,† † ‡
Department of Chemistry, Texas A&M University, College Station, Texas, USA Department of Chemistry, Texas A&M University at Qatar, Doha, Qatar
bS Supporting Information ABSTRACT: The density functionals B3LYP, B3PW91, BMK, HSE06, LCωPBE, M05, M06, O3LYP, TPSS, ω-B97X, and ω-B97XD are used to optimize key transition states and intermediates for ethylene addition to Ni(edt)2 (edt = S2C2H2). The efficacy of the basis sets 6-31G**, 6-31++G**, cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ is also examined. The geometric parameters optimized with different basis sets and density functionals are similar and agree well with experimental values. The ω-B97XD functional gives relative energies closest to those from CCSD, while M06 and HSE06 yield results close to those from CCSD(T). CASSCF and CASSCF-PT2 calculation results are also given. Variation of the relative energies from different density functionals appears to arise, in part, from the multireference character of this system, as confirmed by the T1 diagnostic and CASSCF calculations.
’ INTRODUCTION Metal bis(dithiolene) complexes have been widely studied1,2 because of the unusual chemical, redox, and optical properties, related to the non-innocent nature of the dithiolene ligand.3 This non-innocent character makes it difficult to assign the oxidation state of the metal center.4 For example, Scheme 1 shows three simplest resonance forms that one might assign to a neutral metal bis(dithiolene), Ni(S2C2R2)2 (1R). The formal oxidation state of the central metal atom varies between 0, II, and IV, depending on the resonance form assigned to the ligand. For example, if the ligands assignments are thioketones, the metal has a formal oxidation state of 0, while if the assignments are thiolates, the metal is IV. The formal oxidation state of the metal would be II when the assignment of both ligands is semiquinone (Scheme 1) or when one is thioketone and the other is thiolate (not shown in Scheme 1). In an attempt to resolve which oxidation state is most realistic, the electronic structure,5 diradical character,6 and hyperpolarizabilities7 of metal dithiolene complexes related to the ligand’s non-innocent character have been studied experimentally5ad and theoretically.5f,g,6,7 The broken symmetry unrestricted density functional theory (DFT), multireference post-HartreeFock,6b CASSCF/ CASPT2,6c and CASVB6c calculations have been used to investigate the singlet diradical character of some nickel bis(dithiolene) complexes, and the best description of their oxidation state is NiII.6 In addition to their interesting electronic properties, such as their ability to prevent laser-induced fading of optical data storage media,8 metal bis(dithiolene) complexes show unusual reactivity toward alkenes, where they react to form S,S0 -adducts.9,10 Using this chemistry, Wang and Stiefel developed an electrocatalytic scheme for olefin purification by nickel bis(dithiolene) with electron-withdrawing substituents, where the S,S0 -interligand r 2011 American Chemical Society
adduct that is initially formed releases alkene and the nickel bis(dithiolene) anion upon reduction.9d Although formation of the interligand adduct is symmetry-forbidden, our previous theoretical study11 showed that these symmetry issues can be avoided by a twostep process via a twisted cis-interligand intermediate. More recent experimental studies show that formation of S,S0 -intraligand adduct, whose formation is symmetry-allowed, dominates in pure neutral Ni(S2C2R2)2 (R = CF3, CN), while the interligand adduct is the primary product only in the presence of the anion [Ni(S2C2R2)2] (R = CF3, CN).12 To date, most of the theoretical calculations on this reaction have been carried out by MP2 or with the density functional B3LYP,11,13 while the unusual electronic structures suggest that a more accurate calculation of correlation energy may affect the computed results significantly. Here, we examine the suitability of various density functionals and basis sets for studying the key intermediates and transition states leading to intraligand and interligand adducts when ethylene adds to the simplest nickel bis(dithiolene), Ni(edt)2 (edt = S2C2H2).6c,14 Coupled cluster singles and doubles (CCSD),15 CCSD with perturbative triples corrections (CCSD(T)),16 complete active space self-consistent field (CASSCF),17 and CASSCF with second-order perturbative corrections (CASSCF-PT2)18 calculations are compared to these DFT results as a means of calibration.
’ COMPUTATIONAL DETAILS All species were optimized by using the Gaussian 09 suite of programs19 by using the functionals B3LYP,20 B3PW91,21 Received: June 24, 2011 Revised: November 7, 2011 Published: November 09, 2011 476
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Scheme 1
Scheme 2
BMK, 22 HSE06, 23 LC-ωPBE, 24 M05, 25 M06, 26 O3LYP, 27 TPSS,28 ω-B97X,29 and ω-B97XD.30 All geometry optimizations were done with an all-electron Pople-type 6-31++G** basis set,31 which uses the WachtersHay basis set for Ni.32 Single-point calculations using the geometry optimized by B3LYP and ω-B97XD were performed with CCSD15 and CCSD(T);16 in these calculations, the T1 diagnostic value33 was also examined. Several other basis sets, 6-31G**,34 cc-pVDZ,35 aug-cc-pVDZ,36 cc-pVTZ,37 and aug-cc-pVTZ,36 were used with the TPSS functional to examine basis set effects on this system. The geometric structures of all species were optimized in the gas phase. For the species whose singlet states are not pure according to stability analysis (the reactant with the highest exact-exchange functionals and species with ethylene coordinated on Ni; see Table S4 in Supporting Information, SI), the broken spin symmetry (BS) procedure38 was performed to compute the energy of the spinpurified low-spin (LS) state as LS
E ¼
BS
EðHS ÆS2 æ LS ÆS2 æÞ HS EðBS ÆS2 æ LS ÆS2 æÞ HS 2 ÆS æ BS ÆS2 æ
ð1Þ
where HS refers to the triplet state that is related to the low-spin state by spin flip and ÆS2æ is the expected value of the total spin operator. Calculating the harmonic vibrational frequencies and noting the number of imaginary frequencies confirmed the nature of all equilibrium structures (no imaginary frequency) and transitionstate structures (only one imaginary frequency). The latter were also confirmed to connect appropriate intermediates, reactants, or products by intrinsic reaction coordinate (IRC) calculations.39 The relative electronic energies of the lowest-energy singlet state are used in the Results and Discussion. The 3D molecular structures displayed in this article were drawn by using the JIMP2 molecular visualizing and manipulating program.40 All CASSCF17
and CASSCF-PT218 calculations were carried out with the Molpro program.41
’ RESULTS AND DISCUSSION Scheme 2 shows all possible addition products and transition states from Ni(edt)2 and ethylene examined in this study. When ethylene binds with Ni(edt)2, 1H, there may be a cis-interligand adduct 2H formed from a twisted intermediate, 2yH, via transition state TS2yH or an intraligand adduct 3H via transition state TS3H. 4H and 5H are alternative intermediates that might be involved in this reaction. We did not recalculate the transition state between 2yH and 2H because our previous calculated results indicated that its barrier is low and does not play major role in the mechanism.11 Figure 1 shows some structural details of the geometries of the species involved in Scheme 2. Before describing how the basis sets and functionals affect these geometries, we will present their general features. The reactant 1H is a symmetrical square-planar structure with SC and CC bond distances intermediate between those expected for single and double bonds, as would be expected for its Ni(II) oxidation state and corresponding ligand resonance structures. The transition states for ethylene addition, TS2yH and TS3H, show ethylenic CC bonds close to that calculated for the CC double bond in free ethylene, while the SC (ethylenic) bonds in TS2yH and TS3H are much longer than those in the products 2yH and 3H, confirming that TS2yH and TS3H are early transition states. When ethylene adds to 1H to form 2H via the twisted intermediate 2yH, the dihedral angle S20 S10 S1S2 changes from 0 in 1H to ∼46 in transition state TS2yH and ∼36 in the twisted intermediate 2yH. This angle then relaxes back to ∼7 in the interligand adduct 2H. The ethylenic CC bond has a single-bond character in products 2yH, 2H, and 3H, and the NiS (ethylenic) bond length increases from reactant 1H to products 2H and 3H by about 0.12 Å, showing that there is (1) π-bond loss in ethylene, 477
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Table 1. Relative Energies Calculated from TPSS with Different Basis Sets in kcal/mol TPSS/basis set 1H + C2H4
6-31G** 6-31++G** cc-pvdz aug-cc-pvdz cc-pvtz aug-cc-pvtz 0.0
0.0
0.0
0.0
0.0
0.0
19.7
24.4
25.8
24.1
25.4
25.5
2yH
7.5
11.0
10.7
9.7
9.9
9.8
2H
9.7
9.5
10.0
8.6
9.7
9.6
24.2
25.3
26.2
24.4
26.0
25.8
3H
18.7
18.2
18.5
17.4
18.7
18.3
4H
2.6
9.3
11.4
9.8
14.7
14.9
5H
0.7
9.7
11.0
9.8
13.8
13.9
TS2yH
TS3H
From the structural studies, we can conclude that optimized geometries are relatively insensitive to the basis set and the functional. 3. Basis Set Effects on Relative Energies. Relative energies (1H + C2H4 = 0.0) calculated from TPSS with different basis sets are listed in Table 1 and shown as a bar graph in Figure 2. The energies for the two key adducts, interligand 2H and intraligand, 3H, are relatively independent of the basis sets. The smallest basis set 6-31G** has a rather poor basis set on the metal, and this is reflected in the large difference between 6-31++G** and 6-31G** for TS2yH and 2yH, where the metal bonding is affected by twisting, as well as for 4H and 5H, where the bonding to the metal changes its coordination number. For 4H and 5H, one also observes somewhat smaller but significant differences between the double-ζ cc-pVDZ and triple-ζ cc-pVTZ basis sets, both with and without diffuse (aug-) functions, which is again due to the conjunction of the large change in metal bonding for these species and the difference in the metal basis set. Overall, the results from 6-31++G** and aug-cc-pVDZ are similar in this reaction and not too different from the larger basis sets. One can therefore argue that 6-31++G** is an acceptable compromise between speed and accuracy, while not forgetting the general trends for the larger basis sets. 4. Functional Effects on Relative Energies. Table 2 lists the energies, relative to 1H + C2H4, for the species in Scheme 2 for different density functionals and the CCSD calculations. The data are summarized as a bar graph in Figure 3. Generally, for the same functional, the reaction barrier for the formation of the intraligand adduct (TS3H) is lower than that of the interligand adduct (TS2yH), which is consistent with the experimental results that the intraligand adduct was the major product with pure nickel bis(dithiolene). Differences in these barriers range from a high for LC-ωPBE of 8.5 kcal/mol to a low for TPSS of 0.9 kcal/mol; the latter is the only negative value. The results for the relative energies of the twisted intermediate, 2yH, interligand adduct, 2H, and intraligand adduct, 3H, are even more varied. The relative energies for 2yH and 2H are positive for B3LYP, O3LYP, and TPSS and negative for the other functionals. For 3H, B3LYP, B3PW91, BMK, HSE06, M05, M06, O3LYP, TPSS, and ω-B97X give positive relative energies, while the other functionals give negative ones. For these three products, the relative energy differences between functionals are much larger, ∼40 kcal/mol, than the ∼10 kcal/mol differences calculated for the transition states. Although these initially appear to be wild variations in the energies of 2yH, 2H, and 3H, their energies are systematically related to each other. Thus, the LC-ωPBE functional predicts the highest stability for all of these species, while TPSS predicts the lowest stability for all. Close comparison of the
Figure 1. Optimized geometries for the species involved in Scheme 2. The geometries from different functionals and basis sets look similar; see Tables S1 and S2 (SI) for structural details.
(2) SC (ethylenic) σ-bond formation, and (3) weakening of NiS (ethylenic) bonds. There is no net reaction at the nickel atom in the formation of 2H and 3H, but in 4H and 5H, NiC bond formation is involved. The ethylenic CC bond in 4H is similar to that in free ethylene, confirming the weak coordination of the CC double bond to Ni in 4H. In 5H, the increase of ethylenic CC and NiS (ethylenic) bonds compared to those in free ethylene and reactant 1H suggests that the π-bond is essentially broken in ethylene and that NiC and SC (ethylenic) single σ-bonds are formed. 1. Basis Set Effects on Geometries. Values for the geometric parameters of the structures in Figure 1 from TPSS calculations with different basis sets as well as the experimental parameters for 1H and the average values are shown in Table S1 (SI). The metaGGA functional TPSS has been shown to have good performance in transition-metal chemistry.42 Here, all of the basis sets give similar structural parameters, which are in good agreement with the experimental values. The differences of the bond lengths from different basis sets are less than 0.1 Å, and those of the angles from different basis sets are less than 1. 2. Density Functional Effects on Geometries. Values for the geometric parameters of the structures in Figure 1 for different functionals with the 6-31++G** basis set together with experimental parameters for 1H, as well as average values, are shown in Table S2 (SI). All of the functionals give structural parameters similar to each other and to the experimental values. Like the effects of the basis set on geometries, the differences of the bond lengths for different functionals are less than 0.1 Å, and those of the angles for different functionals are less than 2 478
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Figure 2. Relative energies of TPSS optimized geometries for different basis sets.
Table 2. Relative Energies for the Species in Scheme 2 with Different Density Functionals Based on the 6-31++G** Basis Set and CCSD Single-Point Calculations in kcal/mola methods/6-31++G** B3LYP B3 PW91 BMK HSE06 LC-ωPBE M05 M06 O3LYP TPSS ω-B97X ω-B97XD CCSD-1 CCSD-2 CCSD-3 CCSD(T) 1H + C2H4
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0
29.9
26.3
37.8
24.3
27.6
28.4 25.6
31.6
24.4
46.2
31.1
28.7
25.5
27.2
22.3
2yH 2H
5.2 2.2
1.9 4.2
5.9 7.4 10.2 10.2
28.1 31.7
4.2 6.0 7.2 9.7
8.4 6.9
11.0 9.5
4 8.2
11.2 15.2
12.1 14.6
17.0 20.4
16.5 20.5
4.3 7.4
TS3H
27.7
23.8
29.7
20.4
19.1
26.1 20.5
31.5
25.3
38.3
24.5
21.4
17.7
17.4
17.2
3H
13.0
6.6
1.5
1.0
21.7
17.4
18.2
2.5
3.8
7.1
12.5
12.3
0.9
4H
21.9
17.1
29.7
14.7
23.4
21.6 12.4
24.0
8.9
25.2
21.3
15.8
15.9
15.6
3.9
5H
15.7
9.3
13.9
5.6
7.3
10.5
17.7
9.7
17.5
6.0
4.1
2.3
1.7
0.2
TS2yH
0.0
4.4
1.0 4.9
a
CCSD-1: CCSD/6-31++G**//B3LYP/6-31++G**; CCSD-2: CCSD/aug-cc-pVDZ//B3LYP/6-31++G**; CCSD-3: CCSD/aug-cc-pVDZ//ωB97XD/6-31++G**; CCSD(T): CCSD(T)/aug-cc-pVDZ//ω-B97XD/6-31++G**.
Figure 3. Relative energies from different functionals with fully optimized geometries in basis set 6-31++G**and CCSD and CCSD(T) single-point calculations.
relative reaction energies is shown in Figure 4, where the relative energy of 3H is plotted against that of 2H. Here, one can easily see that these two reaction energies track each other closely. Thus, it would appear that the wild variation in the DFT energies is due to a dramatic change in the electronic structure of
1H + C2H4 compared to the electronically similar adducts 2H and 3H. Consistent with this observation, the two early TSs and the weakly bond adduct 4H track each other with similar variations in their relative energies because these are electronically like 1H + C2H4. These electronic similarities and differences 479
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are rooted in the “non-innocent” nature of the dithiolene ligand, whose valence assignment can range from thiolate, [S2C2R2]2, to thioketone [S2C2R2]0. This range of assignments produces Ni oxidation states that range from Ni0 to NiIV, while it is quite clear that in Ni(S2C2R2)2, the oxidation state is NiII and remains NiII through two reductions (see Introduction). CCSD and CCSD(T) single-point calculations were carried out and are shown in Table 2 and Figure 3 together with the results of the density functionals. CCSD-1 is a CCSD/ 6-31++G(d,p) single-point calculation based on the B3LYP optimized geometries. CCSD-2 is a CCSD/aug-cc-pVDZ single-point
calculation based on the B3LYP optimized geometries. CCSD3 is a CCSD/aug-cc-pVDZ single-point calculation based on the ω-B97XD optimized geometries. CCSD(T) calculation is also single-point calculation with aug-cc-pVDZ based on the ω-B97XD optimized geometries. The ω-B97XD functional gives results closest to the CCSD calculation without triples correction. CCSD(T) single-point calculation gives somewhat different results from the CCSD results, with CCSD(T) values differing by as much as 13 kcal/mol from the CCSD values. Here, the HSE06 and M06 functionals seem to provide a better match. Table 3 gives the T1 diagnostic values, which are all larger than 0.02, showing that there is multireference (near-degeneracy) character in all of these species. However, the multireference character appears to be significantly larger for 1H, TS2yH, and TS3H. This difference in multireference character is likely the origin of the variation in the DFT and CCSD energies. Consistent with the hypothesis, one observes that both CCSD and CCSD(T) predict similar values for the relative stability of 2H over 3H. Again, as for DFT, the large variations are for 1H + C2H4 compared to the adducts (2H, 3H), a reflection of the larger T1 values for 1H. Likewise, the energies relative to 1H + C2H4 for the transitions states TS2yH and TS3H are similar for CCSD and CCSD(T). CASSCF/CASSCF-PT2 calculations with the Ahlrichs VDZ basis set43 were then performed at the ω-B97XD/6-31++G** optimized geometry to examine the nature of the multireference character. The pathway to product 2H was selected to illustrate the orbital interactions between ethylene and Ni(edt)2 (1H). For this reaction, two pπ orbitals of ethylene interact with the two pπ orbitals on sulfur atoms to form product 2H with two new CS σ-bonds. Thus, we choose as the total active space for the reaction the π-system of ethylene (2 electrons and 2 orbitals) and the ligand π-system of Ni(edt)2 (1H) (8 orbitals and 10 electrons).
Figure 4. Linear correlation of the relative reaction energies (kcal/mol) with different density functionals for 3H versus 2H.
Table 3. T1 Diagnostic Values from CCSD(T1diag) Calculations species
1H
TS2yH
2yH
2H
TS3H
3H
4H
5H
T1
0.060
0.065
0.047
0.045
0.058
0.049
0.067
0.054
Figure 5. CASSCF calculated localized molecular orbitals in active space for 1H (a) and 2H (b) with occupations in parentheses. 480
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The Journal of Physical Chemistry A After localization,17 the eight CASSCF orbitals of Ni(edt)2 (1H) are the four C pπ orbitals each with 1 e and the four S pπ orbitals each with 1.5 e, as shown in Figure 5a. Energetically, the S pπ orbitals are lower in energy than the C pπ orbitals; yet more stable are the Ni d orbitals and NiS bonding orbitals, which are not directly involved in the reaction. This CASSCF calculation confirms the semiquinone character of the ligand in 1H. The active space of 2H is 10 orbitals, shown in Figure 5b, occupied by 12 e, a count that includes the two pπ orbitals from ethylene that make the new CS bonds. In making these new bonds, two orbitals from S atoms of Ni(edt)2 interact with two p orbitals from ethylene to form two bonding orbitals and two antibonding orbitals. The two correlated singly occupied orbitals that make up each bond are shown in Figure 5b with occupation numbers of 1.1 (#5 and #6) and 0.9 (#9 and #10). One can see that the new CS σ-bonds are polarized toward the more electronegative element. The orbitals from C atoms of Ni(edt)2 are not engaged directly in the reaction but are split into two sets with slightly different occupation numbers (#3, #4 and #7, #8). The two remaining sulfur orbitals now revert to nearly uninvolved lone pairs, a change that contributes to the reduction in multireference character in the product 2H. The reaction enthalpy at 0 K is 3.3 and 7.7 kcal/mol at the CASSCF-PT2 and CASSCF levels, respectively. The reaction barrier is 49.5 and 46.2 kcal/mol at the CASSCF-PT2 and CASSCF levels, respectively. Although these CASSCF(-PT2) calculations provide a useful description of the electronic structure, the basis set is too small to expect that the energies would be highly accurate.
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’ ASSOCIATED CONTENT
bS
Supporting Information. Complete refs 14 and 19, detailed structural parameters for the examined species at TPSS with different basis sets, stability analysis results, and atomic coordinates of optimized stationary points and transition states. This material is available free of charge via the Internet at http:// pubs.acs.org.
’ AUTHOR INFORMATION Present Address §
College of Chemistry, University of California, Berkeley, CA.
’ ACKNOWLEDGMENT This research was supported by the Qatar National Research Fund (QNRF) under NPRP 08-426-1-074. ’ REFERENCES (1) (a) Sawyer, D. T.; Srivatsa, G. S.; Bodini, M. E.; Schaefer, W. P.; Wing, R. M. J. Am. Chem. Soc. 1986, 108, 936. (b) Zuleta, J. A.; Burberry, M. S.; Eisenberg, R. Coord. Chem. Rev. 1990, 97, 47. (c) Cassoux, P.; Valade, L. Coord. Chem. Rev. 1991, 110, 115. (2) Pilato, R. S.; Stiefel, E. I. In Bioinorganic Catalysis, 2nd ed.; Reedijk, J., Bouwman, E., Eds.; Marcel Dekker: New York, 1999; pp 81152. (3) (a) Szilagyi, R. K.; Lim, B. S.; Glaser, T.; Holm, R. H.; Hedman, B.; Hodgson, K. O.; Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 9158. (b) Deplano, P.; Pilia, L.; Espa, D.; Mercuri, M. L.; Serpe, A. Coord. Chem. Rev. 2010, 254, 1434. (4) Sugimori, A.; Akiyama, T.; Kajitani, M.; Sugiyama, T. Bull. Chem. Soc. Jpn. 1999, 72, 879. (5) (a) Schrauzer, G. N.; Rabinowitz, H. N. J. Am. Chem. Soc. 1968, 90, 4297. (b) Siiman, O.; Fresco, J. J. Am. Chem. Soc. 1970, 92, 2652. (c) Yudanov, V.; Zakharov, I. I.; Startsev, A. N.; Zhidomirov, G. M. React. Kinet. Catal. Lett. 1997, 61, 117. (d) Herman, Z. S.; Kirchner, R. F.; Loew, G. H.; Mueller-Westerhoff, U. T.; Nazzal, A.; Zerner, M. C. Inorg. Chem. 1982, 21, 46. (e) Petrenko, T.; Ray, K.; Wieghardt, K. E.; Neese, F. J. Am. Chem. Soc. 2006, 128, 4422. (f) Kogut, E.; Tang, J. A.; Lough, A. J.; Widdifield, C. M.; Schurko, R. W.; Fekl, U. Inorg. Chem. 2006, 45, 8850. (g) Patra, A. K.; Bill, E.; Bothe, E.; Chlopek, K.; Neese, € ller, T.; Stobie, K.; Ward, M. D.; McCleverty, J. A.; F.; WeyhermU Wieghardt, K. Inorg. Chem. 2006, 45, 7877. (h) Kapre, R. R.; Bothe, E.; Weyherm€uller, T.; George, S. D.; Muresan, N.; Wieghardt, K. Inorg. Chem. 2007, 46, 7827. (i) Begue, D.; Labeguerie, P.; Zhang-Negrerie, D. Y.; Avramopoulos, A.; Serrano-Andres, L.; Papadopoulos, M. G. Phys. Chem. Chem. Phys. 2010, 12, 13746. (6) (a) Bachler, V.; Olbrich, G.; Neese, F.; Wieghardt, K. Inorg. Chem. 2002, 41, 4179. (b) Ray, K.; Weyherm€uller, T.; Neese, F.; Wieghardt, K. Inorg. Chem. 2005, 44, 5345. (c) Serrano-Andres, L.; Avramopoulos, A.; Li, J.; Labequerie, P.; Begue, D.; Kell€o, V.; Papadopoulos, M. G. J. Chem. Phys. 2009, 131, 134312. (7) Papadopoulos, M. G.; Waite, J. Inorg. Chem. 1993, 32, 277. (8) Faulmann, C.; Cassoux, P. Solid-State Properties (Electronic Magnetical, Optical) of Dithiolene Complex-Based Compounds; John Wiley & Sons, Ltd: 2004, p 399. (9) (a) Clark, G. R.; Waters, J. M.; Whittle, K. R. J. Chem. Soc., Dalton Trans. 1973, 821. (b) Kajitani, M.; Kohara, M.; Kitayama, T.; Asano, Y.; Sugimori, A. Chem. Lett. 1986, 2109. (c) Kajitani, M.; Kohara, M.; Kitayama, T.; Akiyama, T.; Sugimori, A. J. Phys. Org. Chem. 1989, 2, 131. (d) Wang, K.; Stiefel, E. I. Science 2001, 291, 106. (e) Kunkely, H.; Vogler, A. Inorg. Chim. Acta 2001, 319, 183. (f) Geiger, W. E. Inorg. Chem. 2002, 41, 136. (10) (a) Schrauzer, G. N.; Mayweg, V. P. J. Am. Chem. Soc. 1965, 87, 1483. (b) Schmitt, R. D.; Wing, R. M.; Maki, A. H. J. Am. Chem.
’ CONCLUSION Important intermediates and transition states involved in ethylene addition to nickel bis(dithiolato), Ni(S2C2H2)2, have been studied with different density functionals and basis sets and compared to CCSD, CCSD(T), CASSCF, and CASSCF-PT2 results. The optimized geometries are relatively insensitive to the choice of the basis set or the functional. However, the relative energies are moderately sensitive to the basis set choice and are very sensitive to the density functional choice. There is a large difference in relative energies between 6-31++G** and 6-31G** due to the rather poor basis set on the metal for the latter one. The relative energies from 6-31++G** and aug-cc-pVDZ are similar in this reaction. The augmentation of either the cc-pVDZ or the cc-pVTZ to aug-cc-pVDZ and aug-cc-pVTZ makes only small differences. However, the change from (aug-)cc-pVDZ to (aug-)cc-pVTZ does seem to affect the relative energies where there is a change in metal coordination. The two early transition states TS2yH and TS3H and the weakly bond adduct 4H track each other with respect to their relative energies from different density functionals because they are electronically similar to 1H + C2H4. There is a large systematic variation in the DFT relative energies for the adducts 2yH, 2H, and 3H because of the dramatic change in the electronic structure of 1H compared to that of the adducts. These electronic similarities and differences are rooted in this “non-innocent” nature of the dithiolene ligand, which leads to substantial multireference character confirmed by T1 values and CASSCF calculations. The ω-B97XD functional gives results comparable to CCSD single-point calculations, while the HSE06 and M06 results are closer to the CCSD(T) single-point calculation. 481
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dx.doi.org/10.1021/jp205971b |J. Phys. Chem. A 2012, 116, 476–482
