Yasuo Musashi

Structures and binding energies of benzene–methane and benzene–benzene complexes. An ab initio SCF/MP2 study

Ab initio SCF/MP2 potentials are calculated on benzene–methane and benzene–benzene complexes. Although no energy stabilization appears at the Hartree–Fock level, a small but non-negligible stabilization in energy is observed at the MP2 level in both complexes, indicating the importance of the dispersion energy. Besides the dispersion energy, the electrostatic interaction plays some role in determining the relative stabilities in several cases. The most stable structure of the benzene–methane complex adopts a C3v symmetry with methane lying on the benzene C6 axis and one hydrogen atom pointing towards benzene. The binding energy of this structure is –1.95 kcal mol–1 from MP2/MIDI-4** calculations and –1.09 kcal mol–1 from MP2/6-31G** calculations, where a p-polarization function is added only on the H atoms of methane. The benzene–methane complex is much less stable than the benzene–benzene complex.

Pt-catalyzed hydrosilylation of ethylene. A theoretical study of the reaction mechanism

Abstract All the elementary steps involved in platinum(0)-catalyzed hydrosilylation of ethylene were theoretically investigated in detail with ab initio MO/MP2-MP4(SDQ) and CCD methods. Several important results are summarized as follows: (1) the Si–H oxidative addition of silane to Pt(PH3)2 occurs with a very low barrier. (2) Ethylene is more easily inserted into Pt–H than into Pt–SiR3 (R=H, Cl, or Me). (3) The Si–C reductive elimination from Pt(CH3)(SiR3)(PH3)(C2H4) and the C–H reductive elimination from PtH(CH3)(PH3)(C2H4) occur more easily than those from Pt(CH3)(SiR3)(PH3)2 and PtH(CH3)(PH3)2, respectively. (4) The transition state of the Si–C reductive elimination is non-planar, while that of the C–H reductive elimination is planar. From those results, the reaction mechanism of Pt(PH3)2-catalyzed hydrosilylation of ethylene was discussed. The rate-determining step of the Chalk–Harrod mechanism is the isomerization of ethylene insertion product whose barrier is estimated to be about 22 kcal mol−1 for R=H and Me, and 26 kcal mol−1 for R=Cl (MP4SDQ values are given here), while that of the modified Chalk–Harrod mechanism is the ethylene insertion into Pt–SiR3 whose barrier is 44 kcal mol−1 for R=H, 41 kcal mol−1 for R=Me, and 60 kcal mol−1 for R=CI. Thus, the Chalk–Harrod mechanism is more favorable than the modified Chalk–Harrod mechanism in the Pt(PH3)2-catalyzed hydrosilylation of ethylene. Though cis-PtH(SiH3)(PH3)2 is directly produced by the SiH4 oxidative addition to Pt(PH3)2, the cis-complex might isomerize to the trans-form through Berry’s pseudo-rotation mechanism. Ethylene is much more easily inserted into Pt–H and Pt–SiH3 in trans-PtH(SiH3)(PH3)(C2H4) than in the cis-form. Even in the trans-form, ethylene is more easily inserted into Pt–H than into Pt–SiH3. In the Chalk–Harrod and modified Chalk–Harrod mechanisms including the cis–trans isomerization, the rate-determining step is the cis–trans isomerization whose barrier is about 22 kcal mol−1 in ethylene-promoted isomerization and 29 kcal mol−1 in the PH3-promoted one. Thus, this Chalk–Harrod mechanism is more favorable than the modified Chalk–Harrod mechanism even if a cis–trans isomerization is involved in the reaction, but the barrier of the rate-determining step in the modified Chalk–Harrod mechanism is significantly lowered by the cis–trans isomerization; part of the Pt(PH3)2-catalyzed hydrosilylation of ethylene might occur through the modified Chalk–Harrod mechanism including the cis–trans isomerization.

Bonding nature and reaction behavior of inter-element linkages with transition metal complexes. A theoretical study

Abstract The B–C bond in (HO)2B–CH3 is stronger than the C–C bond in ethane, because a hyperconjugation interaction is formed between boryl pπ orbital and C–H bonding orbital of CH3. The M–B(OH)2 bond (M=Pd or Pt) is also stronger than the M–CH3 bond, because of the presence of back-donating interaction between M dπ and boryl pπ orbitals and the considerably large orbital overlaps between B(OH)2 sp2 and M valence orbitals. Also, the M–XH3 bond (X=C, Si, Ge, or Sn) becomes weaker in the order M–SiH3>M–GeH3>M–SnH3>M–CH3. This result is easily interpreted in terms of the energy level and the expansion of the XH3 sp3 orbital. In the activation reaction of the (HO)2B–XH3 σ-bond, the empty pπ orbital of the boryl group forms the charge-transfer interaction with the M dπ orbital in the transition state (TS), to stabilize the TS and as a result to facilitate σ-bond activation. The allyl–methyl reductive elimination of Pd(CH3)(η3-C3H5)(PH3) requires a very large activation energy, in spite of the very large exothermicity. On the other hand, allyl–silyl, allyl–germyl, and allyl–stannyl reductive eliminations occur with a moderate activation barrier, while they are moderately exothermic (X=Si or Ge) or moderately endothermic (X=Sn). This difference between methyl and the others is clearly interpreted in terms of the presence of hypervalency of silyl, germyl, and stannyl elements.

A theoretical study of platinum-catalyzed disilylation of alkene

Abstract Model compounds of intermediates and transition states involved in the Pt-catalyzed disilylation of alkene were optimized with the energy gradient method and the energy changes along this catalytic reaction were calculated with the ab initio MO/MP4SDQ method. The rate-determining step is the ethylene insertion into the Pt(II)-SiH 3 bond, of which the activation energy was evaluated to be much too high (45 kcal mol −1 ). This high activation energy arises from the strong trans -influence of the silyl group. This result clearly indicates that the disilylation can take place for the substrate that is easily inserted into the metal-silyl bond.

M2E2 four-member ring structure, M2(μ-EH2)2(P2)2 (M=Pd or Pt; E=Si or Ge; P2=(PH3)2 or H2PCH2CH2PH2) versus μ-disilene and μ-digermene-bridged structures, M2(μ-E2H4)(P2)2. A theoretical study

Abstract M2(EH2)2(P2)2 (M=Pd or Pt; E=Si or Ge; P2=(PH3)2 or diphosphinoethane (H2PCH2CH2PH2; dipe)) was theoretically investigated with the DFT method. Natural bond orbital (nbo) analysis and the laplacian of electron density indicate that Pt2(SiH2)2(P2)2 and Pt2(GeH2)2(P2)2 are characterized to be di(μ-silylene)- and di(μ-germylene)-bridged complexes, respectively, which involve M2Si2 and M2Ge2 four-member ring structures, respectively. In other words, they should be represented as Pt2(μ-SiH2)2(P2)2 and Pt2(μ-GeH2)2(P2)2. On the other hand, the palladium(0) analogs are understood in terms of μ-disilene- and μ-digermene-bridged complexes in which the Siue5f8Si and Geue5f8Ge bonding interactions are maintained. Thus, they should be represented as Pd2(μ-Si2H4)(P2)2 and Pd2(μ-Ge2H4)(P2)2. The difference between platinum(0) and palladium(0) complexes is interpreted in terms of the difference in the strength of π-back donation interaction; in the platinum(0) complex, the π-back donation interaction is so strong that the Siue5f8Si and Geue5f8Ge bonds are almost broken, while in the palladium(0) complex the π-back donation interaction is not so strong and thereby the Siue5f8Si and Geue5f8Ge bonding interactions are still maintained. Also in the mononuclear disilene and digermene complexes, M(E2H4)(P2) (M=Pd or Pt; E=Si or Ge), a similar difference between platinum(0) and palladium(0) complexes is observed; platinum(0) complexes are characterized to be a three-member metallacycle complex which involves an Eue5f8E single bond and two Mue5f8E covalent bonds, whereas the palladium(0) analogs are characterized to be the usual disilene and digermene complexes in which the Siue605Si and Geue605Ge double bonds are maintained. This is because the π-back-donating interaction is stronger in platinum(0) complexes than in palladium(0) complexes. In M(C2H4)(P2) and M2(μ-C2H4)(P2)2, the Cue605C double bond is maintained, since the π-back donation is much weaker than those of Si and Ge analogs even in platinum(0) complexes. Thus, these complexes are characterized to be the ethylene complex in which the Cue605C double bond coordinates with the Pt(0) and Pd(0) centers and not the three-member metallacycle complex.

DNS Based Spam Bots Detection in a University

We carried out an entropy study on the DNS query traffic from the outside of a university campus network to the top domain DNS server when querying about reverse resolution on the PC room terminals through April 1st, 2007 to April 30th, 2008. The following interesting results are given: (1) In January 17th, 2008, the DNS query traffic is mainly dominated by several specific IP addresses as their query keywords. (2) We carried out forensic analysis on the PC room terminals in which IP addresses are found in the several specific keywords and it is concluded that the PCs become spam bots when inserting USB based key disk storage.

Platinum-catalyzed hydrosilylation of ethylene. A theoretical study on the reaction mechanism involving cis-trans isomerization of PtH(SiH3)(PH3)2

Abstract Pt(PH 3 ) 2 -catalyzed hydrosilylation of ethylene involving cis – trans isomerization of PtH(SiH 3 )(PH 3 ) 2 was theoretically investigated with ab initio MO/MP2–MP4SDQ and CCD methods. The cis – trans isomerization via Berrys pseudo-rotation mechanism occurs with an activation barrier ( E a ) of 28 kcal/mol when promoted by PH 3 and with E a of 22.1 kcal/mol when promoted by C 2 H 4 , where E a values calculated with the MP4SDQ method are given since both MP4SDQ and CCD methods yield similar values. Ethylene is easily inserted into Pt–H and Pt–SiH 3 bonds of trans -PtH(SiH 3 )(PH 3 )(C 2 H 4 ) with E a of 3.6 kcal/mol and 15.9 kcal/mol, respectively. The Si–C reductive elimination occurs with E a of 24.3 kcal/mol in Pt(CH 3 )(SiH 3 )(PH 3 ) 2 and 11.1 kcal/mol in Pt(CH 3 )(SiH 3 )(PH 3 )(C 2 H 4 ), and the C–H reductive elimination with E a of 17.7 kcal/mol in PtH(CH 3 )(PH 3 ) 2 and 9.9 kcal/mol in PtH(CH 3 )(PH 3 )(C 2 H 4 ), where CH 3 is adopted as a model of C 2 H 5 and CH 2 CH 2 SiH 3 . The rate-determining step is the cis – trans isomerization in both Chalk–Harrod and modified Chalk–Harrod mechanisms involving the cis – trans isomerization, and its barrier is similar to that of the rate-determining step (isomerization of ethylene insertion product; E a =22.4 kcal/mol) in the usual Chalk–Harrod mechanism without the cis – trans isomerization. These results suggest that the reaction mechanism involving the cis – trans isomerization cannot be ruled out, when the cis – trans isomerization is facilitated by introduction of less donating silyl group and use of electron-withdrawing alkene since they would stabilize the pseudo-trigonal pyramidal transition state of the cis – trans isomerization.

An ab initio molecular-orbital study of insertion of CO2 into a RhI–H bond

The insertion of CO2into the RhI–H bond of [RhH(PH3)3] was investigated theoretically by the ab initiomolecular-orbital method, in which geometries of the reactants, the transition state and products were optimized at the Hartree–Fock level, and MP4SDQ, SDCI and coupled cluster calculations were carried out on those optimized structures. This reaction is calculated to occur with a higher activation energy (16 kcal mol –1) and lower exothermicity (24 kcal mol–1) than the similar insertion into the CuI-H bond of [CuH(PH3)2](Ea= 3.5 kcal mol–1 and Eexo=ca. 40 kcal mol–1), calculated at the SDCl level. The lower exothermicity arises from the fact that the RhI–H bond is much stronger than the CuI-H bond. The higher activation energy is interpreted in terms of the stronger RhI-H bond, the weaker electrostatic stabilizing interaction and the stronger exchange repulsion interaction between CO2and [RhH(PH3)3]in the transition state. Owing to this strong exchange repulsion, the transition state does not contain a four-centra type interaction.

Detection of Kaminsky DNS Cache Poisoning Attack

We statistically investigated the total inbound standard DNS resolution traffic from the Internet to the top domain DNS server in a university campus network through January 1st to December 31st, 2010. The following results are obtained: (1) We found five Kaminsky DNS Cache Poisoning (Kaminsky) attacks in observation of rapid decrease in the unique source IP address based entropy of the DNS query request packet traffic and significant increase in the unique DNS query keyword based one. (2) Also, we found nine Kaminsky attacks in the score changes for detection method using the calculated restricted Damerau-Levenshtein distance (restricted edit distance) between the observed current query keyword and the last one by employing both threshold ranges through 1 to 40. Therefore, it has a possibility that the restricted Damerau-Levenshtein distance based detection technology can detect the Kaminsky attacks.

Trends in Host Search Attack in DNS Query Request Packet Traffic

We statistically investigated the total PTR resource record (RR) based DNS query request packet traffic from the Internet to the top domain DNS server in a university campus network through January 1st to December 31st, 2011. The obtained results are: (1) We found twelve host search (HS) attacks in the scores for detection method using the calculated Euclidean distances between the observed IP address and the last observed IP address in the DNS query keywords by employing both threshold ranges of 1.0-2.0 (consecutive) and 150.2-210.4 (random). However, we found nineteen HS attacks in the scores using the calculated cosine distance between the DNS query IP addresses (threshold ranges of 0.75-0.83 and 0.9-1.0). (3) In the newly found HS attacks, we observed that the source IP addresses of the HS attack DNS query packets are distributed. Therefore, it can be concluded that the cosine distance based detection technology has a possibility to detect the source IP address-distributed host search attack.