A density functional study was performed to design a new N‑heterocyclic silyl pincer fullerenes based on the reactions of diaminofullerene with chlorosilanes SiHRCl2. Reaction energies of the formation of pincer fullerene ligands increased through the substitution of flanking arms with CH3 and phenyl groups. However, substituting hydrogen of SiH2 with methyl slightly increased the corresponding reaction energies, replacing of hydrogen with phenyl groups decreased the reaction energies of the considered pincer fullerenes. While the calculated electrophilicity values of the pincer fullerenes are larger than the electrophilicity values obtained for the fullerene derivatives, the substitution of hydrogen atoms of central SiH2 and PH2 did not have a noticeable impact on the electrophilicity values of the pincer fullerenes. The only exception was SiHPh(NCH2PH2)2C60. Natural bonding orbital analysis showed that the delocalization of electrons from the lone pairs of flanking arms phosphorous atoms to the n* orbital of transition metal atoms was a key factor for stabilizing the considered complexes. The strongest interaction was due to the delocalization of electrons from lone pairs of phosphorous atoms in the flanking arms to the LP* of transition metals, which was follow by the delocalization of electrons of the Si-H σ* orbitals to the LP* of transition metals.
Research Article
Computational Design of New N-Heterocyclic Silyl Pincer Fullerenes
https://doi.org/10.21203/rs.3.rs-306811/v1
This work is licensed under a CC BY 4.0 License
You are reading this latest preprint version
Pincer Ligand
Fullerene
Electrophilicity
NBO
DFT.
There has been an extensive growth in the interest in the chemistry of complexes of transition metals of pincer ligands after Moulton and Shaw’s outstanding report in 1976 about a wide range of pincer-ligated metal complexes [1]. Strong binding to the metal center is made by the tridentate coordination of pincer ligands and this outcomes in high stability of the pincer metal unit and decomposition on heating happens only at temperature higher than 100°C [2]. The robustness of pincer-type complexes together with hemilability of donor group positions are of highly significant for designing the catalysts that should be satisfactorily stable to resist the harsh reaction conditions [2–7]. On the other hand, the donor groups don't need to be strongly bonded to make sure that it might reversibly dissociate and form a coordination site needed for activating inert bonds. They can react with external ligands (e.g. isocyanides, H2, CO, CO2, dihalides, water, acids, oxidizing and reducing agents, or even Na metal) with the assistance of the thermal stability and tight binding of pincer complexes [8–10]. Simultaneously, they keep the pincer coordination of the ligand even at raised temperature. This explains how several pincer-type catalysts can be utilized as catalysts for extensively endothermic reactions like the dehydrogenation of organic substrates [7, 8]. There has been a great deal of attention to this among researchers after the main report by Jensen et al. [11] of an example of iridium pincer complex for alkane dehydrogenation. Therefore, the reasonable design and synthesis of pincer-type ligands, of which stereoelectronic properties are controllable using practical modification, have been long an objective in inorganic and organometallic chemistry [12].
In the pincer ligands, a central moiety supplies two electrons from the donor atom (like phosphorus, nitrogen, oxygen, and carbon) to the transition metal. The two atoms are donated through a covalent bond that is also an “anchor.” Two neutral pendant arms are on either side of the central donor atom, which provide a lone pair of electrons from heteroatoms (e.g. nitrogen, oxygen, sulfur, or phosphorus). These aspects play a critical role in stabilizing the metal center and characterizing the “active sector” in the coordination of the complex, see Fig. 1. As seen, there is a straight impact on the steric hindrance about the metal in bulky R groups that can add chirality in the complex through chiral LRn groups. However, the ring size relies upon the size of the linker arms (Y); consequently, it affects the reactivity of the complex and the bite angle. It is feasible to modulate the adjustments in the electronic properties of the pincer ligands utilizing the fine control given by the nature of the substituent on the central aromatic ring (Z). This minimumly affects the steric of the ligand. The nature of the central donor atom (X, typically C, N, O or P) may likewise have a significant electronic effect, particularly through the variety of the trans impact [11–13]. The probability of including other less conventional donor atoms as the equatorial donor is another field of study. Silicon, as a donor, have gotten a unique consideration as electropositive σ-silyl ligands can stabilize higher oxidation states and gratitude to their solid trans impact they can labialize trans ligands, while the both have likely uses in catalysis. Stobart et al. [14] were the first group to introduce the phosphine/silyl-based pincer ligands with flexible alkyl backbones and then extended to the NSiN [15, 16], PSiP [17, 18], and SSiS [19] pincer frameworks. Dixon et al. [20] depicted silicon-based pincer ligands and enforced the meridional geometry by adding an appropriately stiff backbone. They announced the synthesis of the primary instances of N-heterocyclic σ-silyl pincer ligands that is highlighted with a PSiP-LXL donor triad with reactions of 1,2-C6H4(NHCH2PPh2)2 with chlorosilanes SiHRCl2 (R = Ph, Cl) along with trimethylamine, see Fig. 2. Regardless of the relevance between experimental and theoretical efforts about the pincer-ligated metal complexes, we tracked down no theoretical/experimental work about pincer ligands on the fullerene surface. Thinking about a similar procedure, diamino fullerene C60(NH2)2 can be used as precursors and for designing of new pincer fullerene ligands [21–23]. The reactions of 1,2-C6H4(NHCH2PPh2)2 with chlorosilanes SiHRCl2 (R = H, CH3 and ,Ph) were taken into account in the design of SiHR(NCH2PPL2)2C60 R and L = H, CH3 and phenyl, see Fig. 2. Nine pincer fullerene ligands SiHR(NCH2PL2)2C60, R and L = H, CH3 and phenyl were taken into account, see Fig. 3. Then, the pincer-ligated metal complexes were developed by adding a transition metal (Fe, Co, Ni and Cu) to the pincer bites to examine their formation using their electronic properties and stability.
Taking into account the immensity of investigated systems, optimization method is qualified bit by bit. The geometries of the fullerene pincer ligands SiHR(NCH2PPL2)2C60 R and L = H, CH3 and phenyl (1–9, Fig. 3) were optimized at the beginning at the M06-2X/3-21G level of theory. Thereafter, the optimal geometries of the structures determined in past stages were calculated based on standard 6-311G(d, p) and 6-311G+(d, p) basis set. Frequency calculations were performed for the whole systems at the same level of theory, and the actual frequencies were supported as all of them were structures with little energy. The geometries of these pincer fullerene ligands together and the significant geometrical parameters are illustrated by Fig. 3. The pincer-ligated metal complexes were determined by adding transition metals and then optimal geometries for all the structures were obtained at the same level of theory. The M06-2X functional is in a new generation of hybrid meta-generalized gradient approximation exchange-correlation functionals consisting an accurate treatment of the dispersion energy. The M06-2X functional [24] and 6-311G+(d, p) basis sets were utilized for optimization of geometry and single-point energy calculations. The basis set superposition error (BSSE) effects on the energies are also considered via a counterpoise [25] method. All DFT calculations are performed utilizing GAMESS suite of programs [26, 27]. Wave functions determined at the M06-2X/6-311 + G(d, p) level of theory were analyzed by the natural bond orbital (NBO) method [28, 29].
Twelve pentagons in six pyracylene units designed C60 fullerene cage with icosahedral (Ih) symmetry which led to a single type of carbon atom and two types of C-C bonds including the [6, 6] and [5, 6] ring fusion sites. The length of the bond at [6, 6] and [5, 6] ring fusions in the optimized structure of C60 were estimated about 1.392 and 1.455 Å respectively, at the M06-2X/6-311 + G(d, p) level. They are in a perfect agreement with the previously reported values (1.401 and 1.458 Å correspondingly) [48, 49, 50, 51]. Each amination reaction added the elements NRR and H across a [6, 6] π-bond on [60] fullerene. A number of regiochemistry are possible but experimental evidence recommends that aminations prefer either a 1,2- or a 1,4-addition. The addition reaction of C60 with amines is a widely studied topic [21–23]. Moreover, 1,2-addition of amine to the [6, 6]-bond of fullerene C60 led to formation of two newly C-N bonds with 1.469 Å at the M06-2X/6-311 + G(d, p) level of theory. The [6, 6] C-C bond lengths of 1,2-diamino fullerene were equal to 1.628 Å, which are lengthier than normal C-C bond lengths in fullerene (1.401 Å) [30, 31]. To design of nine pincer fullerene ligands in this study, 1,2-diamino fullerene were utilized as precursors. The geometries of these pincer fullerene ligands together and the significant geometrical parameters are illustrated in Fig. 3. Table S1 (supplementary material) shows the geometrical coordination of the considered structures, calculated at the M06-2X/6-311G+(d, p) level of theory. The geometrical characteristics of the optimized structures of the pincer fullerene ligands are discussed shortly to have better pictures of these derivatives. There is a change from 108° in the pristine C60 fullerene and 95.5° in the diamino fullerene to ~ 99.1–99.3° in the pincer fullerenes in the obtained calculated bond angle between each of the attached sites and the two first neighboring atoms of the pentagon changes. In addition, the hexagon-hexagon bond is pulled outward from the fullerene surface with the bond length decreasing from 1.628 Å (in the C60(NH2)2) to 1.603–1.609 Å in pincer fullerenes. The selected bond distances (Å) i.e. Ccage-N 1.465–1.469, N − Si 1.760–1.767, Si − H 1.494–1.499, C − N 1.451–1.456, C − P 1.920–1.930 Å are consistent with the reported values for N-Heterocyclic σ-siliyl pincer ligands [20]. As mentioned above, the IR vibrational frequencies were computed for the systems at the same level of theory. In addition, the actual frequencies showed that they were structures with minimized energy. The distinctive IR spectroscopic fingerprints yielded valuable insight into the future experimental detections. However, it is notable that at the beginning, theoretical frequencies are overestimated universally in comparison with the results even in the case of more accurate methods. Therefore, the preset study is not an attempt to predict the exact frequencies. This study is aimed at finding patterns in the data than can help us determining different forms of pincer fullerenes. Figure 4 shows the simulated IR vibrational spectra of the SiH2-(NCH2PH2)2C60, and the prominent peaks are quite clear. Thus, it is better to discuss the spectra region by region. In the different vibrational frequencies theoretically found for SiH2(NCH2PH2)2C60, two lowest-energy modes of 505.6 and 612.0 cm− 1 correspond to out-of-plane bending of C-C bonds and breathing mode of fullerene cage. On the other hand, the following vibrations frequencies at 830.8 and 1011.6 cm− 1 are due to the out of plane wagging and in-plane scissoring of HSiH angles, respectively. The vibrational frequency at 2285 cm− 1 with highest intensity is assigned to the symmetric stretching of the SiH bonds coupled with the symmetric stretching of the PiH bonds. The SiH2(NCH2PH2)2C60 exhibits symmetric and asymmetric stretching of CH bonds at 3034 and 3113 cm− 1 respectively. Similar data were obtained for the pincer fullerene ligands, which are in agreement with those values obtained for N-Heterocyclic σ-siliyl pincer ligands.
In order to investigate the formation of the pincer fullerene ligands SiHR(NCH2PL2)2C60, R and L = H, CH3 and phenyl, the reactions of C60(NHCH2PPh2)2 with chlorosilanes SiHRCl2 (R = H, CH3 and phenyl) were taken into account (Fig. 2), and the reaction energies, Er were obtained in the standard way as follows:
Er = ESiHR(NCH2PL2)2C60 + E[Cl2] - E[C60(NHCH2PPh2)2] - E[SiHRCl2] (1)
where ESiHR(NCH2PL2)2C60 and E[C60(NHCH2PPh2)2] are total energies of the pincer fullerenes and C60(NHCH2PPh2)2 and E[Cl2] and E[SiHRCl2] refer to energies of Cl2 and chlorosilanes, respectively. As listed in Table 1, the calculated Er values of the formation of the considered pincer fullerenes is in 46.8–61.6 kcal/mol range, which are lower than the Er values obtained for the SiHR(NCH2PPh2)2C6H4 at the same theory level. In comparison between the calculated reaction energies of pincer fullerenes, some important results were found. As noted, to analyze the influence of the nature of the flanking arms and central silicon atom on fullerene pincer ligands, the substitution of flanking arms and central silicon atom with CH3 and phenyl groups was changed. Clearly, substituting flanking arms with CH3 and phenyl groups increased the reaction energies of the pincer fullerene ligands formation. While substituting of hydrogen of SiH2 with methyl led to a slight increase of the reaction energies, replacing of hydrogen with phenyl groups decreased the reaction energies of the considered pincer fullerenes.
|
Et |
Er |
ω |
Q/e(Si) |
Q/e(P) |
||
|---|---|---|---|---|---|---|
|
1 |
SiH2(NCH2PH2)2C60 |
-3430.441947 |
49.8 |
4.12 |
1.367 |
0.234 |
|
2 |
SiH2(NCH2P(CH3)2)2C60 |
-3586.817778 |
60.8 |
4.17 |
1.373 |
0.77 |
|
3 |
SiH2(NCH2(PpH)2)2C60 |
-4349.193209 |
59.9 |
4.11 |
1.375 |
0.806 |
|
4 |
SiHCH3(NCH2PH2)2C60 |
-3469.548665 |
50.6 |
4.14 |
1.65 |
0.229 |
|
5 |
SiHCH3(NCH2P(CH3)2)2C60 |
-3625.924495 |
61.6 |
4.16 |
1.661 |
0.766 |
|
6 |
SiHCH3(NCH2(PpH)2)2C60 |
-4388.2994 |
61.0 |
4.12 |
1.659 |
0.797 |
|
7 |
SiHPh(NCH2PH2)2C60 |
-3660.144867 |
46.8 |
4.13 |
1.654 |
0.236 |
|
8 |
SiHPh(NCH2P(CH3)2)2C60 |
-3816.519828 |
58.4 |
4.22 |
1.653 |
0.779 |
|
9 |
SiHPh(NCH2(PpH)2)2C60 |
-4578.897951 |
55.8 |
4.23 |
1.664 |
0.815 |
To examine the electronic properties of the considered pincer ligands, electrophilicity was calculated, which can be used as a base to examine the electrophilic competency of the system under consideration through using the electronic chemical potential (µ) to measure tendency of the system to obtain an extra electron from next electron-rich species. At the same time, it uses hardness (η) to describe the system resistance to electron exchange with the environment. Parr et al. defined a general index for the electrophilicity strength [32]. The definition is based on the quantitative chemical concepts in DFT such as the electronic chemical potential (µ) and hardness (η) [33, 34]. Employing a quadratic and finite difference approximation, Parr et al. [32] interpreted that µ and η may be equal to µ= -(IP + EA)/2 and η = IP - EA [73]. The values of IP = E(M+) – E(M) and the EA = E(M) – E(M− ) were obtained based on vertical ionization potentials and electron affinities. Finally, the electrophilicity index was defined as ω = µ2/2η [33]. Therefore, electrophilicity ω values were obtained for the pincer ligands based the mentioned formula and listed in Table 1. As listed Table 1, the obtained electrophilicity values of the pincer fullerenes are in 4.11–4.23 eV range, which are larger than the electrophilicity values obtained for the fullerene derivatives with heterocyclic ring systems. It is notable that the substitution of hydrogen atoms of central SiH2 and PH2 do not have noticeable impact on the electrophilicity values of the pincer fullerenes, except for SiHPh(NCH2PH2)2C60 in which substituting flanking arms with CH3 and phenyl increases the electrophilicity of the considered pincer fullerenes.
The pincer-ligated metal complexes were prepared by adding a transition metal (Fe, Co, Ni and Cu) to the pincer bites. Through this, their formation based on structure, electronic properties, stability was predicted. Two five-member metallocyclic rings were formed by the complexation of a metal to three adjacent coplanar sites of pincer fullerene ligands. Figure 5 illustrates the geometries and the important geometrical parameters of these complexes. The criteria of stability of different pincer-ligated metal complexes namely the difference between the total energy of pincer-ligated metal complexes, the constituent, and individual transition metals, and pincer fullerene ligands were used to calculate binding energies (Eb). Using the counterpoise (CP) method [25], the binding energies were corrected for basis set superposition error (BSSE). Clearly, binding energies range from − 84.24 to -88.59 eV. It is notable that the metal-silicon bonds are shorter than expected for single covalent bonds. For example, Co-Si and Co-P bond lengths in Co-SiHPh(NCH2PH2)2C60 (2.271 and 2.201 Å) is smaller than the corresponding single Co-Si and Co-P bond lengths (2.43 and 2.19 Å). When the hybrid orbitals of the ligands and the hybrid orbitals of the metal atoms in the metal complexes are overlapped, delocalization of electrons happens. Therefore, we perform NBO analysis to have a deeper insight into the nature of electronic conjugation among the bonds in the pincer-ligated metal complexes. The NBO analysis is a useful tool to determine these delocalizations of the electrons. The NBOs have close relationship with the picture of localized bonds and lone pairs as basic units of molecular structure. It is possible therefore, to interpret ab initio wave-functions based on the classical Lewis structure concepts through transforming these functions to NBO form [28]. The present study is mostly about the results of second-order perturbation theory analysis of Fock matrix in NBO of the complexes. With regard to each donor NBO(i) and acceptor NBO(j), the stabilization energy E(2) pertinent to delocalization is obtained as follows [28, 29].
where qi represents the donor orbital occupancy, ϵi and ϵj represent the orbital energies, and 
stands for the off-diagonal NBO Fock matrix element. With higher values of the E(2), the interaction between the donors and acceptors is intensified [10]. The strongest interactions of n* orbitals of transition metal atoms with lone pairs of phosphorous atoms and the Si-H σ* orbitals of central silicon atoms are listed Table 2. As seen, the strongest interaction of all happens because of the delocalization of electrons from lone pairs of phosphorous atoms (donor) in the flanking arms to the LP* of transition metals (acceptor) followed by the Si-H σ* orbitals of central silicon atoms (donor) to the LP* of transition metals (acceptor). For example the delocalization of electrons from the lone pairs of flanking arms phosphorous atoms to the n* orbitals of Fe atom resulted in the interaction of LP P with LP* Fe stabilizing the complex by about 48.41 kcal/mol. On the other hand, the delocalization of electrons from the Si-H σ* orbitals of central silicon atoms to the LP* orbitals of Fe atom stabilizes the complex by only 13.37 kcal/mol. Therefore, it seems that the delocalization of electrons from the lone pairs of flanking arms phosphorous atoms to the n* orbitals of Fe atoms is a more important factor for stabilizing the complexes in comparison to the orbitals of central silicon atoms.
|
Eb |
M-Si |
M-P |
E(2)* |
E(2)** |
|
|---|---|---|---|---|---|
|
Fe-SiHPh(NCH2PH2)2C60 |
-85.47 |
2.267 |
2.184 |
12.99 |
48.41 |
|
Co-SiHPh(NCH2PH2)2C60 |
-88.59 |
2.271 |
2.201 |
13.37 |
50.65 |
|
Ni-SiHPh(NCH2PH2)2C60 |
-87.31 |
2.259 |
2.211 |
13.28 |
50.05 |
|
Cu-SiHPh(NCH2PH2)2C60 |
-84.24 |
2.244 |
2.209 |
13.1 |
48.25 |
| * BD SiH (donor)→ LP* Fe (acceptor) in kcal/mol | |||||
| ** LP P (donor)→ LP* Fe (acceptor) in kcal /mol | |||||
A density functional study was carried out to design of new n‑heterocyclic silyl pincer fullerenes. The reactions of C60(NH2)2 with chlorosilanes SiHRCl2 (R = H, CH3, and Ph) were taken into account to design the nine pincer fullerene ligands SiHR(NCH2PL2)2C60, R and L = H, CH3, and Ph and the pincer-ligated metal complexes achieved by adding a transition metal to the pincers. According to the findings, following points are notable. Substituting flanking arms with CH3 and phenyl groups increases the reaction energies of the formation of the pincer fullerene ligands. While substituting the hydrogen of SiH2 with methyl leads to a slight increase of the reaction energies, replacing of hydrogen with phenyl groups decreases the reaction energies of the considered pincer fullerenes. In addition, the calculated electrophilicity values of the pincer fullerenes range are larger than the electrophilicity values obtained for the fullerene derivatives. Therefore, the substitution of hydrogen atoms of central SiH2 and PH2 do not have noticeable impact on the electrophilicity values of the pincer fullerenes, except for SiHPh(NCH2PH2)2C60. Natural bonding orbital analysis (NBO) showed that the interaction of the phosphorous lone pairs in the flanking arms with the n* orbitals of transition metal atoms was stronger than the interaction of Si-H σ* orbitals of central silicon atoms with the LP* of transition metals.
Acknowledgement:
We gratefully acknowledge for the financial support from the Research Council of Alzahra University.
Conflict of Interest Self-Declaration Form for All Authors
|
Criteria |
Applicability |
|
|
Funding |
Not applicable |
|
|
Conflicts of interest/Competing interests |
|
There is no conflict of interest in the manuscript. |
|
Availability of data and material |
|
All data are provided in supplementary material. |
|
Code availability |
Not applicable |
|
|
Authors' contributions |
Not applicable |
|
|
Additional declarations for articles in life science journals that report the results of studies involving humans and/or animals |
Not applicable |
|
|
Ethics approval |
|
All authors approved Ethics. |
|
Consent to participate |
|
All the authors approve consent for participate of this submission. |
|
Consent for publication |
|
All the authors approve consent for publication of this submission.
|
- Moulton CJ, Shaw BL (1976) Transition metal–carbon bonds. Part XLII. Complexes of nickel, palladium, platinum, rhodium and iridium with the tridentate ligand 2,6-bis[(di-t-butylphosphino)methyl]phenyl. J. Chem. Soc. Dalton Trans. 1020–1024
- Asaya M, Morales-Morales D (2015) Non-symmetric pincer ligands: complexes and applications in catalysis. Dalton Trans 44:17432–17447
- Wanniarachchi S, Liddle BJ, Toussaint J, Lindeman SV, Bennett B, Gardinier JR (2010) Chemical switching behaviour of tricarbonylrhenium(i) complexes of a new redox active ‘Pincer’ ligand. Dalton Trans 39:3167–3169
- Prokhorov AM, Hofbeck T, Czerwieniec R, Suleymanova AF, Kozhevnikov DN, Yersin H (2014) Brightly luminescent Pt (II) pincer complexes with a sterically demanding carboranyl-phenylpyridine ligand: a new material class for diverse optoelectronic applications. J Am Chem Soc 136:9637–9642
- Lam ES-H, Lam WH, Yam VW-W (2015) A Study on the Effect of Dianionic Tridentate Ligands on the Radiative and Nonradiative Processes for Gold(III) Alkynyl Systems by a Computational Approach. Inorg Chem 54:3624–3630
- Albrecht M, van Koten G (2001) Platinum Group Organometallics Based on "Pincer" Complexes: Sensors, Switches, and Catalysts In memory of Prof. Dr. Luigi M. Venanzi and his pioneering work in organometallic chemistry, particularly in PCP pincer chemistry. Angew Chem Int Ed 40:3750–3781
- Peris E, Crabtree RH (2018) Key factors in pincer ligand design. Chem Soc Rev 47:1959–1968
- Choi J, MacArthur AHR, Brookhart M, Goldman AS (2011) Dehydrogenation and related reactions catalyzed by iridium pincer complexes. Chem Rev 111:1761–1779
- van Koten G, Milstein D (2013) Organometallic Pincer Chemistry. Springer-Verlag, Berlin-Heidelberg
- Szabo KJ, Wendt OF (2014) Pincer and Pincer-Type Complexes: Applications in Organic Synthesis and Catalysis. Wiley-VCH, Germany
- Gupta M, Hagen C, Flesher RJ, Kaska WC, Jensen CM (1996) A highly active alkane dehydrogenation catalyst: stabilization of dihydrido rhodium and iridium complexes by a P–C–P pincer ligand. Chem. Commun. 2083–2084
- Lawrence MAW, Green K-A, Nelson PN, Lorraine SC (2018) Review: Pincer ligands-Tunable, versatile and applicable. Polyhedron 143:11–27
- van der Vlugt JI, Reek JNH (2009) Neutral tridentate PNP ligands and their hybrid analogues: versatile non-innocent scaffolds for homogeneous catalysis. Angew Chem Int Ed 48:8832–8846
- Stobart SR, Zhou X, Cea-Olivares R, Toscano A (2001) Activation of Water and of Dioxygen by a Bis(diphenylphosphinopropyl)silyl (biPSi) Complex of Ruthenium(II): Formation of Bis(diphenylphosphinopropyl)siloxo Cage Complexes. Concomitant Oxygen Atom Insertion into a Silicon – Carbon Bond. Organometallics 20:4766–4768
- Tilley TD, Sangtrirutnugul P (2008) Alkyl and Hydrido Complexes of Platinum(IV) Supported by the Bis(8-quinolyl)methylsilyl Ligand. Organometallics 27:2223–2230
- Kwok W-H, Lu G-L, Rickard CEF, Roper WR, Wright LJ (2004) Nucleophilic substitution reactions at the Si–Cl bonds of the dichloro(methyl)silyl ligand in five- and six-coordinate complexes of ruthenium(II) and osmium(II). J Organomet Chem 689:2511–2522
- Ruddy AJ, Mitton SJ, McDonald R, Turculet L (2012) ‘Hemilabile’ silyl pincer ligation: platinum group PSiN complexes and triple C–H activation to form a (PSiC)Ru carbene complex. Chem Commun 48:1159–1161
- Korchin EE, Leitus G, Shimon LJW, Konstantinovski L, Milstein D (2008) Silanol-Based Pincer Pt(II) Complexes: Synthesis, Structure, and Unusual Reactivity. Inorg Chem 47:7177–7189
- Hill AF, Neumann H, Wagler J (2010) Bis(methimazolyl)silyl Complexes of Ruthenium. Organometallics 29:1026–1031
- Dixon LSH, Hill AF, Sinha A, Ward JS (2014) N-Heterocyclic Silyl Pincer Ligands. Organometallics 33:653–658
- Hu X, Jiang Z, Jia Z, Huang S, Yang X, Li Y, Gan L, Zhang S, Zhu D (2007) Amination of [60]fullerene by ammonia and by primary and secondary aliphatic amines - Preparation of amino[60]fullerene peroxides. Chem Eur J 13:1129–1141
- Janaki J, Premila M, Gopalan P, Sastry VS, Sundar CS (2000) Thermal stability of a fullerene-amine adduct. Thermochim Acta 356:109–116
- Glen Miller P (2006) Reactions between aliphatic amines and [60]fullerene: a review. C R Chimie 9:952–959
- Zhao Y, Truhlar DG (2008) The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor Chem Account 120:215–241
- Boys SF, Bernardi F (1970) The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol Phys 19:553–566
- Schmidt MW, Baldridge KK, Boatz JA, Elbert ST, Gordon MS, Jensen JH, Koseki S, Matsunaga N, Nguyen KA, Su SJ, Windus TL, Dupuis M, Montgomery JA (1993) General atomic and molecular electronic structure system. J Comput Chem 14:1347–1363
- Gordon MS, Schmidt MW (2005) In: Dykstra CE, Frenking G, Kim KS, Scuseria GE (eds) Advances in Electronic Structure Theory: GAMESS a Decade Later in “Theory and Applications of Computational Chemistry: the First Forty Years”. Elsevier, Amsterdam
- Reed AE, Curtiss LA, Weinhold F (1988) Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint. Chem Rev 88:899–926
- Reed AE, Weinstock RB, Weinhold F (1985) Natural population analysis. J Chem Phys 83:735–746
- Hedberg K, Hedberg L, Bethune DS, Brown CA, Dorn HC, Johnson RD, Vries M (1991) Bond lengths in free molecules of buckminsterfullerene, C60, from gas-phase electron diffraction. Science 254:410–412
- Hawkins JM, Meyer A, Lewis TA, Loren SD, Hollander FJ (1991) Crystal structure of osmylated c60: confirmation of the soccer ball framework. Science 252:312–313
- Parr RG, Szentpály LV, Liu S (1999) Electrophilicity Index. J Am Chem Soc 121:1922–1924
- Parr RG, Donnelly RA, Levy M, Palke WE (1978) Electronegativity: the density functional viewpoint. J Chem Phys 68:3801–3807
- Politzer P, Murry JS (2006) A link between the ionization energy ratios of an atom and its electronegativity and hardness. Chem Phys Lett 431:195–198