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Volumn 18, Issue 20, 1999, Pages 4156-4164

Detailed mechanistic information on methane elimination from a methyl(hydrido)platinum(IV) complex. Relevance for the mechanism of methane activation

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EID: 0000264395     PISSN: 02767333     EISSN: None     Source Type: Journal    
DOI: 10.1021/om9901426     Document Type: Article
Times cited : (65)

References (47)
  • 10
    • 85034535165 scopus 로고    scopus 로고
    • note
    • 2-methane complex is consistently shown throughout this paper with a symmetrically (via two hydrogen atoms) bonded methane. This is an arbitrarily chosen convention. It may also be unsymmetrically bonded, such that basically one C-H bond functions as a donor. Since rotation of bonded methane is extremely facile and practically activationless (see ref 42), our conclusions concerning H/D exchange (see discussion) do not depend on the exact geometry of η2-bonded methane.
  • 22
    • 85034551629 scopus 로고    scopus 로고
    • note
    • 1 and K.
  • 23
    • 85034548546 scopus 로고    scopus 로고
    • note
    • For the limitations of the temperature range, see the Supporting Information.
  • 24
    • 85034558278 scopus 로고    scopus 로고
    • note
    • The more restricted pressure range for the trans isomer stems from the fact that the glass walls accept protons under high pressure, which leads to isomerization to give the more reactive cis isomer. An enhancement in reactivity was observed under pressures higher than those plotted in Figure 3.
  • 26
    • 0001455787 scopus 로고
    • Although elimination reactions are generally accompanied by a very positive activation entropy, the ΔS* values for alkane elimination cover a wide range (Gould, G. L.; Heinekey, D. M. J. Am. Chem. Soc. 1989, 111, 5502), which is indicative of different rate-determining steps or composite rate laws.
    • (1989) J. Am. Chem. Soc. , vol.111 , pp. 5502
    • Gould, G.L.1    Heinekey, D.M.2
  • 28
    • 85034551421 scopus 로고    scopus 로고
    • note
    • D, since it prevents formation of the Pt-H complex. However, the secondary isotope effect of six deuterium atoms will lead to a systematic error that could be as large as the uncertainty of our determination.
  • 32
    • 85034545345 scopus 로고    scopus 로고
    • note
    • It is important to note that isomerization to give the trans hydride 2b was not observed under these conditions. Although the equilibrium is not too unfavorable for interconversion of 2a into 2b, there is no low-energy path for an intramolecular isomerization. Obviously, the kinetic barrier for placing the methane hydrogen in SS2 trans to amine is higher than for the migration of the hydrogen into the cis position. This may be due to the kinetic trans effect of the amine donor, quite similar to the effect discussed below.
  • 34
    • 0030057443 scopus 로고    scopus 로고
    • D of 5 at room temperature is the maximum kinetic isotope effect calculated from the Pt-H vibration frequency, whereas a value close to 3 was reported experimentally: Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 5961.
    • (1996) J. Am. Chem. Soc. , vol.118 , pp. 5961
    • Stahl, S.S.1    Labinger, J.A.2    Bercaw, J.E.3
  • 39
    • 85034543293 scopus 로고    scopus 로고
    • note
    • A treatment of the complete system is possible, but unfortunately not simple. We treated the complete system shown in Scheme 3 using the computer algebra system MAPLE (Maple V.3, student version, 1981-1994, Waterloo Maple Software and University of Waterloo) The evaluation of [SS1], [SS2], and [SS1′] in terms of the rate constants is possible. The calculation of the rates for formation of intermediate (2a-C-D) and product leads to a system of two linear differential equations that can be solved. However, the solution is so complex (a multiterm expression that fills several pages) that no meaningful conclusion could be drawn.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.