CC BY
28
UDC 66.065.5
L. I. Matienko, L. A. Mosolova, V. I. Binyukov, E. M. Mil, Kh. S. Abzaldinov, G. E. Zaikov
CATALYSIS WITH TWO- AND THREE-COMPONENTS SYSTEMS BASED ON REDOX INACTIVE
METAL COMPOUND, LIST, IN SELECTIVE ETHYL BENZENE OXIDATION BY DIOXYGEN
Keywords: nanostructures, binary and triple catalytic .systems based on redox inactive metal (lithium) compound, H-bonds, catalysis,
ethyl benzene, oxidation, dioxygen, a-phenyl ethyl hydroperoxide.
Mechanism of catalysis with binary and triple catalytic systems based on redox inactive metal (lithium) compound {LiSt+L2} and {LiSt+L2+PhOH} (L2=DMF or HMPA), in the selective ethyl benzene oxidation by dioxygen into a-phenyl ethyl hydroperoxide is researched. The possibility of the stable supramolecular nanostructures formation on the basis of triple systems, {LiSt+L2+PhOH}, due to intermolecular H-bonds, is researched with the AFM method.
Ключевые слова: наноструктуры, двойные и тройные каталитические системы на основе соединения металла постоянной валентности (литий), H-связи, катализ, этилбензол, окисление, молекулярный кислород, a-фенил этил гидропероксид.
Изучен механизм катализа двойными и тройными каталитическими системами, основанными на соединении металла постоянной валентности (литий) {LiSt+L2} и {LiSt+L2+PhOH} (L2=DMF or HMPA), в селективном окислении этилбензола молекулярным кислородом. Методом АСМ (Атомно-Силовой Микроскопии) исследована возможность формирования стабильных супрамолекулярных наноструктур на основе тройных систем {LiSt+L2+PhOH} за счёт межмолекулярных H-связей.
1 Introduction
The problem of selective oxidation of alkylarens to hydro peroxides is economically sound. Hydro peroxides are used as intermediates in the large-scale production of important monomers. For instance, propylene oxide and styrene are synthesized from a-phenyl ethyl hydroperoxide, and cumyl hydroperoxide is the precursor in the synthesis of phenol and acetone [1, 2]. The method of modifying the Ni11 and Fe11,111 complexes with mono- or multidentate ligands used in the selective oxidation of alkylarens (ethylbenzene and cumene) with molecular oxygen to afford the corresponding hydro peroxides aimed at increasing their selectivity has been first proposed by L.I. Matienko [3,4].
The phenomenon of a substantial increase in the selectivity (S) and conversion (C) of the ethylbenzene oxidation to the a-phenyl ethyl hydroperoxide upon addition of PhOH together with N-metyl-2-pyrrolidone (MP),
hexamethylphosphorotriamide (HMPA) or alkali metal stearate MSt (M = Li, Na) as modifying ligands to metal complex NiII(acac)2 was discovered in our works [3,4]. In case of triple systems with additives of MSt the observed values of C [C >35% at SPEHmax = 90%, [ROOH]max (1.6-1.8 mol/l) far exceeded those obtained with the other ternary catalytic systems {NiII(acac)2+ L2 + PhOH} (L2 = MP, HMPA) and the majority of active binary systems. These results by L.I. Matienko and L.A. Mosolova are protected by the Russian Federation patent (2004).
The high efficiency of three-component systems {NiII(acac)2+MSt+PhOH} (M = Na, Li) that introduced compound of redox inactive metal seems to be due formation of extremely stable supramolecular structure due to intermolecular H-bonds [4,5]. We have proposed a new approach for research the possibility of supramolecular structures formation based on catalytic active triple complexes NiII(acac)2 MSt PhOH (M=
Na, Li) [6] with use of method of AFM-microscopy, and at first we have received the evidence in favor supramolecular structures formation [6, 7]. In present work we examine catalytic activity of triple system {LiSt+L2+PhOH} (L2=DMF), based on compound of redox inactive metal only, in ethyl benzene oxidation to PEH. With AFM method we researched a possibility of supramolecular structures formation based on triple system based on Li-contained compound [4, 5].
Often compounds of metals of constant valency are used in combination with redox-active transition-metal complexes to promote a variety of reactions involving the transfer of electrons. It was reported that rates of O2 reduction by Mn11 complex are accelerated in the presence of group 2 metal ions [8]. This effect is typified in metalloproteins such as the copper zinc superoxide dismutase, in which both metal ions have been proposed to be functionally active [8].
It is known also [9] that compounds of redox inactive metals are used in many cases as catalysts for oxidation of hydrocarbons. Earlier we have researched the possibility of activating alkali metals compounds with additions of modifying ligands [10]. We established the positive effects of monodentate electron donating ligands HMPA and DMF on the rate, selectivity, max concentration PEH, and conversion of ethyl benzene oxidation to PEH, catalyzed with LiSt [10]. In the present article we will examine our new data on catalysis with triple systems {LiSt+L2+PhOH} (L2 = DMF) and will generalize these data with results, received by us earlier and in present article, on mechanism of catalysis with binary systems {LiSt+L2} (L2 = DMF, HMPA), and also triple system, based on nickel complex {NiII(acac)2+LiSt+PhOH}, in reactions of selective ethyl benzene oxidation to PEH.
2 Experimental
Ethylbenzene (RH) was oxidized with dioxygen at 120°C in glass bubbling-type reactor [5] in the presence of LiSt and also binary {LiSt+DMF} or
triple {LiSt+DMF+PhOH} systems.
HMPA and DMF were cleared with vacuum distillation above the CaO.
LiSt was got by adding of hot water solution of LiOH (brands of Ch.Cl.) to the heated spirit solution of HSt (brands of Ch.Cl.). The got LiSt solution was filtered, washed with hot water and dried in a vacuum at 20oC to permanent weight.
Analysis of oxidation products. a-Phenylethylhydroperoxide (PEH) was analyzed by iodometry. By-products, including
methylphenylcarbinol (MPC), acetophenone (AP), and phenol (PhOH) as well as the RH content in the oxidation process were examined by GLC [5].
An order in which PEH, AP, and MPC formed was determined from the time dependence of product accumulation rate ratios at t ^ 0. The variation of these ratios with time was evaluated by graphic differentiation ([4], see Fig.2, 3). Experimental data processing was done using special computer programs Mathcad and Graph2Digit.
AFM SOLVER P47/SMENA/ with Silicon Cantilevers NSG11S (NT MDT) with curvature radius 10 nm, tip height: 10 - 15 ^m and cone angle < 22° in taping mode on resonant frequency 150 KHz was used [6].
As substrate the polished Silicone surface special chemically modified was used.
Waterproof modified Silicone surface was exploit for the self-assembly-driven growth due to H-bonding of complexes LiStHMPAPhOH with Silicone surface. The saturated chloroform (CHCl3) solution of complex LiSt HMPA PhOH was put on a surface, maintained some time, and then solvent was deleted from a surface by means of special method - spin-coating process.
In the course of scanning of investigated samples it has been found, that the structures are fixed on a surface strongly enough due to H-bonding. The self-assembly-driven growth of the supramolecular structures on modified Silicone surface on the basis of complexes LiSt HMPA PhOH, and also LiStHMPA, or LiStPhOH, due to H-bonds and perhaps the other non-covalent interactions, was researched.
3 Results and discussion
3.1 Catalysis with LiSt and with binary system {LiSt+L2} (L2 = DMF, HMPA) in ethyl benzene oxidation by dioxygen
Here we go back to the experiment got before, and complemented by interpretation of mechanism with bringing in of literary data.
Earlier we have researched the effect of DMF and HMPA on the kinetics of ethyl benzene oxidation with dioxygen in the presence of LiSt at 1200C [10]. The concentration of LiSt has varied within the interval (0.1-1.0)10-2 mol/l. To raise the concentration of LiSt above 1.0 -10-2 mol/l was not be able due to difficult solubility of LiSt in ethyl benzene.
First of all in the presence of the LiSt catalyst increasing in initial rate of accumulation of PEH was observed similar the influence of compounds of other
metals of constant valency [11]. The rates of the accumulation of other oxidation products of AP and MPC were falling compared with no catalyzed ethyl benzene oxidation. This is possibly due to the decreasing in the chain decomposition of PEH in the presence of constant valence metal salts. Unlike the no catalyzed ethyl benzene oxidation, in reactions ethyl benzene oxidation in the presence of the LiSt the phenol was formed in relatively small concentrations = 1.0-10-2 mol/l at deep stages of ethyl benzene oxidation. The other oxidation products in concentrations compared with PEH, AP, MPC and PhOH, were not found. I [P] = A [RH] (I[P] = [PEH] + [AP] + [MPC] + [PhOH]).
The initial rate of oxidation of ethyl benzene w0 in the presence of the LiSt is increased slightly from (2.0±0.2)^0-6 moll-1s-1 (without Cat) to (3,5+0,3)-10-6 moll-1s-1 ([LiSt]=1,0T0-3 mol/l) and to (6,8+0,3)-10-6 moll-1s-1 ([LiSt]=1,0^10-2 mol/l). Selectivity of oxidation of ethyl benzene into PEH takes about SPEH«90-92% at the conversion of oxidation C«5%, which is substantially higher than in no catalyzed oxidation (Speh«80-75%) at the same conversion.
This is the first time we have shown that the use of additives of electron donating ligands L allows under certain conditions to considerably improve the properties LiSt (and also NaSt, and KSt) as a catalysts for the ethyl benzene oxidation into PEH [10]. So, for example, in the presence additions of HMPA or DMF we observed the synergetic increasing in initial rate w0 (Table 1) and growth of conversion of ethyl benzene oxidation into PEH (C~16-20% at the conservation of selectivity not less than SPEH~90-93%, catalyzed with LiSt [10].
Later activities of the donor additives were confirmed in [12] on example of ethyl benzene oxidations in the presence of the other catalytic systems (cadmium or zinc compounds with o-phenantroline).
Dependence of initial rates w0 on [L2] ([LiSt] = const) at catalysis with system {LiSt + L2} has extreme character (Table 1 [10]).
Table 1 - The initial rates of ethyl benzene oxidation in the presence of LiSt (1.0^10-2 mol/l), and LiSt and various additives of HMPA and DMF [10].
L2, mole/l •103 HMPA, w</105, moll-1s-1 DMF, Wcf105, moll-1s-1
— 0.68+0.3
0.5 2.8+0.3
1.0 4.9+0.2 1.9+0.1
2.0 5.4+0.1
3.0 2.4+0.2
4/0 9.4+0.7
5.0 3.3+0.1
10.0 4.4+0.2 2.6+0.1
One can see on Table 1, that the maximum rate of ethyl benzene oxidation, w0, in the presence of catalytic system {LiSt + HMPA} far surpasses in ~ 14 times and, in the case of {LiSt + DMF} - in ~ 5 times the rate of oxidation catalyzed by the LiSt.
Additives of HMPA increase the activity (w0) of LiSt to a greater extent than additives of DMF, and
that is consistent with the values of the donor numbers of these ligands HMPA (DN = 155.2 kJ/mol) > DMF (DN = 106.4 kJ/mol) [4].
Increase in activity LiSt (growth of w0) in ethyl benzene oxidation in the presence of additives of HMPA or DMF can be associated with the destruction of the associates [13, 14], for example, (LiSt)n (n>2). Associates are able to be less active in the oxidation reactions compared with the monomer form of catalyst [13]. However, the synergetic growth of w0 in 14 times in presence of HMPA or ~5 times in the case of additives DMF suggest that the role of these ligands at initial stages of catalytic oxidation is not only in the destruction of the associates [15]. In all probability, the primary function of donor ligands HMPA or DMF is, possible, to control activity of formed complexes LiSt L2 in reactions of the chain initiation (O2 activation), the homolytic decomposition of PEH and, perhaps, the chain propagation Cat + RO2^.
3.2 Catalysis with triple system {LiSt +L2+PhOH} (L2 = DMF) in ethyl benzene oxidation by dioxygen. Consequence of oxidation products formation
As mentioned before, the phenomenon of a substantial increase in the selectivity (S) and conversion (C) of the ethyl benzene oxidation to the to a-phenyl ethyl hydro peroxide upon addition of PhOH together with monodentate ligands N-metylpirrolidon-2, HMPA, or alkali metal stearates MSt (M=Li, Na) as metalloligands to metal complexes Ni''(acac)2 was discovered in our works [3,4].
There are characteristic features for triple systems including metalloligand-modifiers L2=NaSt, LiSt (and N-metylpirrolidon-2 (MP), HMPA also) as compared with the most active binary systems. The advantage of these triple systems is the long-term activity of the in situ formed complexes NiII(acac)2,L2,PhOH. Unlike binary systems, the acac-ligand in nickel complex does not undergo transformations in the course of ethyl benzene oxidation in this case. (The formation of triple complexes NiII(acac)2,L2,PhOH at vary early stages of oxidation was established with kinetic methods [3,4,5]). So the reaction rate remains practically the same during the oxidation process. In the course of the oxidation the rates of products accumulation unchanged during the long period t < 30 - 40 hours.
The additives of PhOH to binary system {LiSt+DМF} change kinetics of products formation in ethyl benzene oxidation, catalyzed with {LiSt+DMF}, by analogy with catalysis by {NiII(acac)2+ MSt + PhOH}. That is, in the presence of {LiSt+DMF+PhOH} (Fig. 1b) the rates of accommodation of oxidation products PEH, AP, MPC remain practically the same during the oxidation process (< 20-30(40) hours) unlike the catalysis with binary system {LiSt+DMF} (Fig.1a). Interesting, that at catalysis with {LiSt+DMF+PhOH} (and {LiSt+DMF (HMPA)}) the oxidation products PEH, AP, MPC are formed with maximum initial rate without the auto acceleration period by analogy with the catalysis with the triple system {NiII(acac)2+LiSt(NaSt)+PhOH} [5,7]. While the products PEH, AP, MPC and PhOH formed with auto
acceleration periods in the case of ethyl benzene oxidation, catalyzed with LiSt, or {Ni"(acac)2+MP+PhOH}.
1
2 3
* * 1 * --
a
b
Fig. 1 - Kinetics of accumulation of PEH (1), AP (2), MPC (3) in ethyl benzene oxidation, catalyzed by binary {LiSt+DMF} (a) and triple system {LiSt+DMF+PhOH} (b). [LiSt] = 110-2 mol/l, [DMF] = 110-2 mol/l, [PhOH] = 1.210-2 mol/l, 1200C
At catalysis with triple system {LiSt+DMF+PhOH} the parallel formation of a-phenyl ethyl hydroperoxide (PEH), acetophenone (AP) and methylphenylcarbinol (MPC) was observed (Wap(mpc)/Wpeh * 0at t ^ 0, Wap/Wmpc * 0at t ^ 0) throughout the reaction of ethyl benzene oxidation at t < 20-30(40) hours ).
The analogical kinetics we observed earlier in the case of the catalysis with triple complexes Ni(acac)2«L2»PhOH (L2 = NaSt, LiSt) [5,7].
The received data point to the next mechanism of acetophenone and methylphenylcarbinol formation in ethyl benzene oxidation in the presence {LiSt+DMF+PhOH} system: AP and MPC form in parallel with PEH rather than as a result of PEH decomposition by analogy with the catalysis by triple system NiII(acac)2«L2»PhOH (L2 = LiSt (NaSt)) [5] and (LiSt+DMF(HMPA)}, - in the chain propagation at participation of Cat (Cat+RO2*^) and quadratic chain termination (2RO2*^). This is unlike non-catalytic oxidation and catalysis of ethyl benzene oxidation by LiSt (see, for example, Fig.2a) and binary system {NiII(acac)2+MSt} at the absence PhOH [4]. In these ethyl benzene oxidation reactions AP and MPC - result of PEH decomposition and quadratic chain termination (2RO2*^) (catalysis by LiSt), and also the chain propagation at participation of Cat (Cat+RO2*^) (catalysis by {NiII(acac)2+MSt}) [4].
[c]
The interesting result was received in the case of ethyl benzene oxidation, catalyzed with LiSt without additives. Acetophenone AP and hydro peroxide PEH are formed parallel (wAP/wPEH * 0 at t^-0), but MPC is product of PEH decomposition (wMPC/wPEH^-0) at t^0) during all reaction of oxidation (Fig.2a). At that AP and MPC are formed parallel each other (wAP/wMPC * 0 at t^-0). Analogous kinetics of oxidation products: AP formed parallel with ROOH, but dimethylphenylcarbinol (DMPC) - from ROOH,-we observed in the cumene oxidation, catalyzed with
II II
Ni(acac)2 and system {Ni(acac)2 + MP} [4].
0,12 0,1 A AA a A
-s 0,08 « H p^ <1 0,06 -S-5-A-A- A A A A A
57
-a 0,04
0,02
0 -1-1-1-1-1-1-1-
0 2 4 6 8 10 12 14
j h
b
Fig. 2 - Dependences A[MPC]ij/A[PEH]ij (a) and A[AP]ij/A[PEH]ij (b) on time tj in the course of ethyl benzene oxidation, catalyzed with LiSt (a), and system {LiSt+DMF} (b) [LiSt] = 110-2 mol/l, [DMF] =310-3 mol/l 120°C
Additions of ligand-modifier of DMF ([DMF] = (3-10) 10-3 mol/l) in the reaction of ethylbenzene oxidation, catalyzed with LiSt, change the mechanism of formation of MPC. In this case at catalysis with complex LiSt DMF both products, AP and MPC, appear in parallel with PEH (see, for example, Fig.2b). At this parallelism of formation of AP and MPC also takes place. The analogous mechanism we established for catalysis with the system {LiSt+HMPA}:
wAP(MPC)/wPEH * 0at t ^ 0, wAP/wMPC * 0at t ^ 0).
Earlier we have established that concentration of PhOH at catalysis with system {NiII(acac)2 (3.010-3 mol/l) + LiSt (NaSt) (3.0-10-3 mol/l) + PhOH (3.0-10-3 mol/l)}, as well as at catalysis with similar system {NiII(acac)2 (3.0-10-3 mol/l) + MP (7.0-10-2 mol/l) + PhOH (3.0-10-3 mol/l)} including MP as donor exo ligand L2, decreases during the first hours of oxidation (see, for example, Fig. 3a) [4,5,7]. Analogous results we received in the case of ethyl benzene oxidation with molecular oxygen, catalyzed with triple system {LiSt+DMF+PhOH} (Fig.3b). These changes in PhOH concentrations seem to be due to the triple complexes NiII(acac)2-L2 PhOH formation [4,5,7] and point to triple complexes LiSt DMF PhOH formation also.
[c]
2[kl[f 5-
U.'llf
j0>:10~ i [c]
37 5-10"3-
25*10 3-
12 5-10"3-
0 l[l 20 30 40 50
t, h
b
Fig. 3 - PhOH kinetics in reactions of ethyl benzene oxidation catalyzed by triple systems: (a) -{Ni"(acac)2 (3.0-10-3 mol/l) + LiSt (3.0-10-3 mol/l) + PhOH (310-3 mol/l)} [29], (b) - {LiSt(1.010-2 mol/l) +DMF(1.010-2 mol/l) +PhOH(0.810-2 mol/l). Data on the catalysis with {LiSt+DMF+PhOH} system are presented for the first time
Dependences SPEH on C in ethyl benzene oxidation in PEH, catalyzed with triple systems {LiSt+DMF+PhOH} at [LiSt] = 110-2 mol/l = const and different concentrations [PhOH] and [DMF] (Fig.
21 30 tJ, 40
a
4), also show in favor of triple complexes LiSt DMF PhOH formation.
100 90 80 70 60
I
50 40 30 20 10 0¿ 0
t-
10
15
20
25
30
C, %
Fig. 4 - Dependences Speh on C in ethyl benzene oxidation in PEH, catalyzed with triple systems {LiSt+DMF+PhOH}: □ - [LiSt] = 110-2 mol/l, [DMF] = 110-2 mol/l, [PhOH] = 1.210-2 mol/l; A - [LiSt] = 110-2 mol/l, [DMF] = 110-2 mol/l, [PhOH] = 0.810-2 mol/l; 0 - [LiSt] = 110-2 mol/l, [DMF] = 310-3 mol/l, [PhOH] = 110-3 mol/l. 1200C
3.3 Mechanism of catalysis with Li-compound catalytic systems in the hydrocarbons oxidations by dioxygen
3.3.1 Role of chain initial (O2 activation) and chain propagation (Cat + RO2^) stages
The mechanism of action of compounds of redox inactive metals in liquid-phase reactions of hydrocarbons oxidation is researched insufficiently because of their relatively small activity and poor solubility in hydrocarbon media. The limited data suggest that lithium salts accelerate the hydrocarbons oxidation by increasing the chain initial rates (activation of molecular O2) [16, 17] and chain branching [17, 18]. The accelerating the decomposition of the PEH to the free radicals at the catalysis with the LiSt may be due to the lower energy barrier in consequence of complex LiSt-ROOH formation by analogy with [19].
Based on quantum chemical calculations [16] prominent activity of lithium salts in comparison with other alkaline metals (Na, K, Rb) is connected with partial filling in of vacant Li+ s-orbital with electrons from opposite charged anion, and this can explain the weak covalent character of Li-X bond and greater solubility of lithium salts in organic solvents. It was shown that the interaction of Li+ with O2 is the most strong in the case of bent end-on configuration (2s)Li-O2(1^g). The assessing catalytic activity of Li+ ion in the "radical" reactions [20-22], including those featuring 3O2 and radical OOH was filled with quantum-chemical methods of calculation. In complex Li+-O-O with enhanced electronic density on distance atom of oxygen, O-O bond is less stable compared to O-O bond in the complexes of transition metal with dioxygen [22].
As we had shown, the systems based on lithium ion - the triple- {LiSt +DMF +PhOH} and binary {LiSt +DMF (HMPA)} systems, obviously was
inactive in the reaction of hydro peroxide decomposition. However the ability of redox-inactive lithium ions to facilitate free radical formation in chain initiation (activation of O2), possibly, takes place in the case of the catalysis with Li-systems, {LiSt +DMF +PhOH} and {LiSt +DMF (HMPA)}.
In these systems dioxygen activation may be promoted through the formation of intramolecular H-bonds [4]. The role of intramolecular H-bonds in catalysis was established by us in the case of formation of triple catalytic complexes {Ni''(acac)2-L2PhOH} (L2 = N-methylpirrolidon-2 (MP)) in the ethyl benzene oxidation with molecular oxygen [4].
The schemes of radical chain hydrocarbons oxidation including intermediate formation peroxo complexes [LMOOR] with further their homolytic decomposition at the O-O bond [4] may explain parallel formation of alcohol and ketone under catalytic ethylbenzene oxidation in the presence LiSt DMF(HMPA) or LiSt DMF PhOH.
Presumably, the additional coordination of DMF or HMPA (L2) (and PhOH (L3)) with LiSt favors the stabilization of oxo-species [L2 (L3) LiO"] formed in the homolytic decomposition of peroxo complexes [L2 (L3) LiOOR] at the O-O bond, and AP and MPC formation in the stage of chain propagation
[L2 (L3) LiO'- OR]
[L2 (L3) LiO] + [OR]
^R'R"C=O (or ROH) + R
So catalysis with {LiSt +DMF +PhOH} and {LiSt +DMF(HMPA)} is largely associated with involvement of these systems in the steps of chain initiation (activation of O2) and also chain propagation (Cat + RO2^).
As one can see in Fig. 4, in the case of catalysis with triple system on the basis of Li compound the degree of conversion C and selectivity SPEH of ethyl benzene oxidation in PEH are reduced compared with nickel-containing triple systems [4]. As the triple system {LiSt +DMF +PhOH} is not active in PEH decomposition, falling SPEH seems to be due to the increasing role of chain propagation stage (Cat + RO2^) in mechanism of catalysis with triple systems {LiSt +DMF +PhOH}. The reduction in conversion of ethyl benzene oxidation (Fig.4) compared with catalysis by complexes {Ni''(acac)2NaSt(LiSt)PhOH} can be associated with less stability of triple complexes {LiSt DMF PhOH} in the course of ethyl benzene oxidation.
3.3.2 Role of intermolecular H-bonding in stabilization of triple catalytic complexes {LiStL2PhOH}
Nanostructure science and supramolecular chemistry are fast evolving fields that are concerned with manipulation of materials that have important structural features of nanometer size (1 nm to 1 ^m) [23]. Nature has been exploiting no covalent interactions for the construction of various cell components. For instance, microtubules, ribosomes, mitochondria, and chromosomes use mostly hydrogen bonding in conjunction with covalently formed peptide bonds to form specific structures.
H-bonds are commonly used for the fabrication of supramolecular assemblies because they are
5
—>
directional and have a wide range of interactions energies that are tunable by adjusting the number of H-bonds, their relative orientation, and their position in the overall structure. H-bonds in the center of protein helices can be 20 kcal/mol due to cooperative dipolar interactions [24, 25].
The porphyrin linkage through H-bonds is the binding type generally observed in nature. One of the simplest artificial self-assembling supramolecular porphyrin systems is the formation of a dimer based on carboxylic acid functionality [26].
The high efficiency of three-component systems {NiII(acac)2 +L2 +PhOH} (L2 =MSt (M = Na, Li), HMPA) in the reaction of selective oxidation of ethyl benzene to a-phenyl ethyl hydroperoxide on parameters S, C, w=const is associated with the formation of extremely stable heterobimetallic heteroligand complexes Ni(acac)2^ L2 •PhOH. We assumed that the stability of complexes Ni(acac)2 • L2 •PhOH during ethyl benzene oxidation can be associated as one of reasons, with the supramolecular structures formation due to intermolecular H-bonds (phenol-carboxylate) [26-28] and, possible, the other non-covalent interactions:
{NiII(acac)2+NaSt(or LiSt)+PhOH}^ Ni(acac)^ L2^PhOH ^{Ni(acac)^ L^PhOH}n
In favor of formation of supramolecular macrostructures due to intermolecular (phenol-carboxylate) H-bonds and, possible, the other non-covalent interactions [27-29], based on the triple complexes {Ni(acac)2L2PhOH} in the real catalytic ethyl benzene oxidation, show data of AFM-microscopy, which we received at first (L2=NaSt, LiSt, HMPA) [7,30]. Spontaneous organization process, i.e., self-organization, of triple complexes on surfaces of modified silicon are driven by the balance between intermolecular and molecule-surface interactions, which may be the consequence of hydrogen bonds and the other non-covalent interactions [31].
As mentioned above, complexes of lithium with DMF or HMPA as catalysts practically does not differ on the parameters of Speh ~ 90-93% and C=20%, on mechanism of oxidation products formation. Therefore, possibility of forming stable self-organized supramolecular nanostructures in the course of ethyl benzene oxidation due to hydrogen bonding, as one of possible reasons of stabilizing the three-component systems LiSt L2 PhOH (on parameters Speh, C , w=const), we researched on the example of complexes of LiSt with HMPA and PhOH.
The association of triple complexes LiSt L2 PhOH (L2 =HMPA) in supramolecular structures due to intermolecular H-bonding may be followed from analysis of data, which we received with AFM-microscopy. Data of structures on the basis of complexes LiSt HMPA PhOH, which self-organized on the surface of the modified silicon at the apartment of a uterine solution on a surface, were got first.
As one can see (Fig. 5), nanoparticles on the basis of triple complexes LiSt HMPA PhOH (image on 4.0x4.0 (^m)) have clear cell-type structure and are
characterized in height from 2 to 3.5 nm (Fig.5a,b) and have a width of ~100 -120 nm (Profile on Fig.5c).
Unlike nanostructures, based on triple complexes LiSt HMPA PhOH, self-organized structures, based on binary complexes LiSt HMPA differ in heterogeneity on form and on the height changing from <2 to 35-40 nm as compared with clearer cell-type nanostructures on the basis of triple complexes LiSt HMPA PhOH (Fig. 5). The greater number of particles based on binary complexes {LiSt HMPA has a height less than 2 nm and a width of -50-60 nm. Nanostructures, based on binary complexes LiSt PhOH, have height <1-2 mn.
1,0
0 0 0,5
1,0 W
a
20.4 Height Crop
0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0
ytn
b
Fig. 5 - The AFM three- (a) and two-dimensional image (b) (4.0x4.0 (^m)) of the structures received on a surface of modified silicone on the basis of triple complexes LiSt HMPA PhOH and profile of one of these structures (c)
The received AFM data (Fig. 5) point to the very probable stable supramolecular nanostructures appearance on the basis of heteroligand triple complexes {LiSt L2 • PhOH} n at expense of intermolecular (phenol-carboxylate) H-bonds [27-31] and, possible, the other non-covalent interactions (van Der Waals-attractions and tc-bonding) [27-31], also in the real catalytic ethyl benzene oxidation with dioxygen, catalyzed by triple systems {LiSt + L2 +PhOH}.
4 Conclusions
1. So inclusion of phenol in coordination sphere of a complex LiSt L2 (L2=DMF) leads to formation of a triple complex LiSt L2 PhOH with different catalytic activity. In the presence of {LiSt +DMF +PhOH} system the rates of accommodation of oxidation products PEH, AP, MPC remain practically the same during the oxidation process (< 20-30 hours) unlike the catalysis with binary system {LiSt +DMF}. At catalysis with {LiSt +DMF +PhOH} (and {LiSt +DMF}) systems the oxidation products PEH, AP, MPC are formed with maximum initial rate without the auto acceleration period by analogy with the catalysis by the triple nickel-lithium (sodium) catalytic systems, {Ni''(acac)2+LiSt(NaSt)+PhOH}.
The mechanism of acetophenone and methylphenylcarbinol formation in ethyl benzene oxidation in the presence of triple {LiSt+DMF+PhOH} and binary {LiSt+DMF} systems was identical: unlike non-catalytic oxidation and catalysis by LiSt, AP and MPC form in parallel with PEH rather than as a result of PEH decomposition. The increase in selectivity SPEHmax ~ 90% at catalysis with LiSt HMPA PhOH in comparison with no catalyzed oxidation (SPEHmax < 80%) is due to change in an order, in which products PEH, AP, and MPC form. Catalysis with {LiSt+DMF+PhOH} and {LiSt+DMF} is largely associated with involvement of these systems in the stages of chain initiation (activation of O2) and also chain propagation (Cat + RO2'^).
2. We applied at first AFM method in the analytical purposes to research the possibility of the supramolecular macro structures formation based on heteroligand triple complexes LiSt L2 PhOH (L2=HMPA) with the assistance of intermolecular H-bonds.
We have shown that the self-assembly-driven growth of structures based on LiSt L2 PhOH (L2=HMPA) complexes seems to be due to the connection of complexes with a surface of modified silicone, and further formation of supramolecular nanostructures {LiSt L2 PhOH} n at expense of directional intermolecular (phenol-carboxylate) H-bonds, and, possibly, other non-covalent interactions (van Der Waals-attractions and ^-bonding). The nanostructures, based on triple complexes LiSt L2 PhOH, are characterized with clear cell-type structure.
It is possible to suppose formation of stable supramolecular structures in the course of the ethyl benzene oxidation with dioxygen, catalyzed by catalytic system {LiSt+L2+PhOH} and this can be one of the explanations of the stability triple systems (w s const)
during the selective oxidation process of the ethyl
benzene oxidation into a-phenyl ethyl hydroperoxide.
Abbreviations:
AFM method - Atomic-Force Microscopy method;
(Acac)~ - Acetylacetonate ion; PhOH - phenol;
DMF - dimethylformamide;
HMPA - hexamethylphosphrotriamide;
MP - N-methylpirrolidon-2;
MSt - stearates of alkaline metals (M= Li);
DN - donor number.
5 References
1. A.K. Suresh, M.M. Sharma, T. Sridhar, Industrial Hydrocarbon Oxidation, Ind. Eng. Chem. Res. 39, 39583969 (2000).
2. K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, 3nd ed., transl. by Lindley C.R. New York: VCH, 1997.
3. L.I. Matienko, Solution of the problem of selective oxidation of alkylarenes by molecular oxygen to corresponding hydroperoxides. Catalysis initiated by Ni(II), Co(II), and Fe(III) complexes activated by additives of electron-donor mono- or multidentate extra-ligands, In: Reactions and Properties of Monomers and Polymers, A. D'Amore and G. Zaikov (Eds.), Chapter 2, New York: Nova Sience Publ. Inc., 2007, p.21-41.
4. L.I. Matienko, L.A. Mosolova, G.E. Zaikov, Selective Catalytic Hydrocarbons Oxidation. New Perspectives, New York: Nova Science Publ. Inc., USA, 2010, 150 P.
5. L.I. Matienko, V.I. Binyukov, L.A. Mosolova, Mechanism of selective catalysis with triple system {bis(acetylacetonate)Ni(II)+metalloligand+phenol} in ethylbenzene oxidation with dioxygen. Role of H-bonding interactions. Oxid. Commun., 37, 20-31 (2014).
6. L.I. Matienko, L.A. Mosolova, V.I. Binyukov, E.M. Mil, G.E. Zaikov "The new approach to research of mechanism catalysis with nickel complexes in alkylarens oxidation" "Polymer Yearbook" 2011. N.-Y.: Nova Science Publishers, 2012, pp 221-230.
7. Ludmila Matienko, Vladimir Binyukov, Larisa Mosolova and Gennady Zaikov, The selective ethylbenzene oxidation by dioxygen into a-phenyl ethyl hydroperoxide, catalyzed with triple catalytic system {Nin(acac)2+NaSt(LiSt)+PhOH}. Formation of nanostructures {Nin(acac)2-NaSt-(PhOH)}n with assistance of intermolecular H-bonds. Polymers Research Journal, 5, 423-431, (2011).
8. Y.J. Park, J.W. Ziller, A.S. Borovik, The effect of Redox-Inactive Metal Ions on the Activation of Dioxygen: Isolation and Characterization of Heterobimetallic Complex Containing a Mnm-(|-OH)-Can Core, J. Am. Chem. Soc., 133, 9258-9261 (2011).
9. A.M. Siroegko Liquid-phase oxidation of alkanes, cycloalkanes and their oxygen-containing derivatives by oxygen and ozone in presence of compounds of s - and 3d -elements, Abstract of thesis of dissertation on the competition of graduate degree of doctor of chemical sciences. Leningrad: LTI the name of LenSovet, 1985. 53 P.
10. L.A. Mosolova, L.I. Matienko, Influence of additions of elektrondonating complex forming compounds on catalytic activity of lithium stearate in the reaction of ethyl benzene oxidation, Kinetics and catalysis, 25, 1262-1264 (1984).
11. V.K. Ciskovski, Yu.L. Moskovich, Features of reaction of oxidization of hydrocarbons oxidation in the hydro peroxides catalyzed by salts of metals of constant valency, Kinetics and catalysis, 15, 1466-1469 (1974).
12. S.K. Kozlov, Ph. I. Tovstokhatko, V.M. Potekhin, Catalysts, activated with attended N-heterocyclic ligand - 1,
10-phenantroline, for the cumene oxidation, J. Appl. Chemistry, 59, 217-219 (1986). (in russian)
13. M.N. Monakov, V.A. Kudryashov, N.K. Kastalskaya-Borozdinskaya, Catalytic activity of transition metals at oxidation of n.-alkanes, Kinetics and catalysis, 22, 183-(1981).
14. D.E. Fenton, C. Nave, Anionic Hexafluoroacetylacetonate Complexes of Alkali Metals, J. Chem. Soc. Chem. Comm., №13, 662- 668 (1971).
15. H.J. Reich, Role of Organolithium Aggregates and Mixed Aggregates in Organolithium Mechanisms, Chem. Rev., 113, 7130-7178 (2013).
16. K. Ohkubo, H. Shimata, Y. Shiotani, M. A. Okada, Theoretical Study of Catalytic Activity of Group I Metal Salts in Homogeneous Liquid-Phase Oxidation, Bull. Chem. Soc. Jap., 44, 1188-1197 (1971).
17. S.K. Ivanov, M.I. Boneva, Oxidation of ethyl benzene in the presence of lead naphthenate, Oxid. Commun, 7, 305319 (1984).
18. Ch.E. Ckarlampidi, N.M. Batyirshin, V.G. Ivanov, Salts of metals of constant valency are catalysts of chain-radical oxidation of hydrocarbons, Petrochemistry, 20, 708-710 (1980).
19. L.V. Petrov, V.M. Solyanikov, Z.Ya. Petrova, Catalysis of homolytic decomposition of hydroperoxides by the ions of metals of constant valency, DAS, 230, 366-370 (1976).
20. A. Von Onciul, T. Crark, Enhanced Hyperconjugation and Facile 1,2-Halogen Shifts in Metal Cation Complexes of 2-Halogenoalkyl Radicals: An ab Initio Study, J. Chem. Soc. Chem. Comm. №15, 1082-1084 (1989).
21. H. Hofman, T. Crark, Electrostatic Catalysis of Oxidation Reactions by Metal Cations. An ab Initio Study, J. Am. Chem. Soc., 113, 2422-2425 (1991).
22. H. Hofman, T. Crark, Lithium - Ion - Catalyzed Epoxidation by Triplet Dioxygen: An ab Initio Study, Angew. Chem. Int. Ed. Engl., 29, 648-650 (1990).
23. St. Leninger, B. Olenyuk, P.J. Stang, Self-Assembly of Discrete Cyclic Nanostructures Mediated by Transition Metals, Chem. Rev.,100, 853-908 (2000).
24. P.J. Stang, B. Olenyuk, Self-Assembly, Symmetry, and Molecular Architecture: Coordination as the Motif in the Rational Design of Supramolecular Metallacyclic Polygons and Polyhedra, Acc. Chem. Res., 30, 502-518 (1997).
25. C.M. Drain, A.I. Varotto Radivojevic, Self-Organized Porphyrinic Materials, Chem. Rev., 109, 1630-1658 (2009).
26. I. Beletskaya, V.S. Tyurin, A.Yu. Tsivadze, R. Guilard, Ch. Stem, Supramolecular Chemistry of Metalloporphyrins, Chem. Rev., 109, 1659-1713 (2009).
27. M. Dubey, R.R. Koner, M. Ray, Sodium and Potassium Ion Directed Self-assembled Multinuclear Assembly of Divalent Nickel or Copper and L-Leucine Derived Ligand, Inorg. Chem., 48, 9294-9302 (2009).
28. E.V. Basiuk, V.V. Basiuk, J. Gomez-Lara, R.A. Toscano, A bridged high-spin complex bis-[Ni(II)(rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)]-2,5-pyridinedicaboxylate diperchlorate monohydrate, J. Incl. Phenom. Macrocycl. Chem. 38, 45-56 (2000).
29. P.Mukherjee, M.G.B. Drew, C.J. Gomez-Garcia, A. Ghosh, (Ni2), (Ni3), and (Ni2 + Ni3): A Unique Example of Isolated and Cocrystallized Ni2 and Ni3 Complexes, Inorg. Chem., 48, 4817-4825 (2009).
30. L.I. Matienko, V.I. Binyukov, L.A. Mosolova, E.M. Mil, G.E. Zaikov, The Supramolecular Nanostructures as Effective Catalysts for the Oxidation of Hydrocarbons and Functional Models of Dioxygenases, Polymers Research Journal, 8, 91-116 (2014).
31. D. Gentili, F. Valle, C.Albonetti, F. Liscio, M. Cavallini, Self-Organization of Functional Materials in Confinement, Acc. Chem. Res., 47, 2692-2699 (2014).
© L. 1 Matienko - Doctor of Chemistry, Head of Laboratory, N. M. Emanuel Institute of Biochemical Physics RAS, Moscow, Russia, matienko@sky.chph.ras.ru, L. A. Mosolova - Ph.D., Senior researcher, N. M. Emanuel Institute of Biochemical Physics RAS, Moscow, Russia, V. I. Binyukov - Ph.D., Leading researcher, N. M. Emanuel Institute of Biochemical Physics RAS, Moscow, Russia, bin707@mail.ru, E. M Mil - Doctor of Biology, Leading researcher, N. M. Emanuel Institute of Biochemical Physics RAS, Moscow, Russia, Kh. S. Abzaldinov - Ph.D., Associate Professor, Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia, G. E. Zaikov - Doctor of Chemistry, Full Professor, Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia.
© Л. И. Матиенко - доктор химических наук, заведующий лабораторией, Институт биохимической физики им. Н.М. Эмануэля РАН, Москва, Россия, matienko@sky.chph.ras.ru, Л. А. Мосолова - кандидат химических наук, старший научный сотрудник, Институт биохимической физики им. Н.М. Эмануэля РАН, Москва, Россия, В. И. Бинюков - кандидат биологических наук, ведущий научный сотрудник, Институт биохимической физики им. Н.М. Эмануэля РАН, Москва, Россия, bin707@mail.ru, Е. М Миль - доктор биологических наук, ведущий научный сотрудник, Институт биохимической физики им. Н.М. Эмануэля РАН, Москва, Россия, Х. С. Абзальдинов - кандидат химических наук, доцент, кафедра технологии пластических масс, Казанский национальный исследовательский технологический университет, Казань, Россия, Г. Е. Заиков - доктор химических наук, профессор, кафедра технологии пластических масс, Казанский национальный исследовательский технологический университет, Казань, Россия.
