Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization
<p>Whereas stoichiometric activation of C-H bonds by complexes of transition metals is becoming increasingly common, selective functionalization of alkanes remains a formidable challenge in organometallic chemistry. The recent advances in catalytic alkane functionalization by transition-met...
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ndltd-CALTECH-oai-thesis.library.caltech.edu-81522021-04-20T05:01:40Z https://thesis.library.caltech.edu/8152/ Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization Rostovtsev, Vsevolod Vladimirovich <p>Whereas stoichiometric activation of C-H bonds by complexes of transition metals is becoming increasingly common, selective functionalization of alkanes remains a formidable challenge in organometallic chemistry. The recent advances in catalytic alkane functionalization by transition-metal complexes are summarized in Chapter I. </p> <p>The studies of the displacement of pentafluoropyridine in [(tmeda)Pt(CH_3)(NC_5F_5)][BAr^f_4] (1) with γ- tetrafluoropicoline, a very poor nucleophile, are reported in Chapter II. The ligand substitution occurs by a dissociative interchange mechanism. This result implies that dissociative loss of pentafluoropyridine is the rate-limiting step in the C-H activation reactions of 1. </p> <p>Oxidation of dimethylplatinum(II) complexes (N-N)Pt(CH_3)_2 (N-N = tmeda(1), α-diimines) by dioxygen is described in Chapter III. Mechanistic studies suggest a two-step mechanism. First, a hydroperoxoplatinum(IV) complex is formed in a reaction between (N-N)Pt(CH_3)_2 and dioxygen. Next, the hydroperoxy complex reacts with a second equivalent of (N-N)Pt(CH_3)_2 to afford the final product, (N-N)Pt(OH)(OCH_3)(CH_3)_2. The hydroperoxy intermediate, (tmeda)Pt(OOH)(OCH_3)(CH_3)_2 (2), was isolated and characterized. The reactivity of 2 with several dime thylplatinum(II) complexes is reported. </p> <p>The studies described in Chapter IV are directed toward the development of a platinum(II)-catalyzed oxidative alkane dehydrogenation. Stoichiometric conversion of alkanes (cyclohexane, ethane) to olefins (cyclohexene, ethylene) is achieved by C-H activation with [(N-N)Pt(CH_3)(CF_3CH_2OH)]BF_4 (1, N-N is N,N'-bis(3,5-di-t- butylphenyl)-1,4-diazabutadiene) which results in the formation of olefin hydride complexes. The first step in the C-H activation reaction is formation of a platinum(II) alkyl which undergoes β-hydrogen elimination to afford the olefin hydride complex. The cationic ethylplatinum(II) intermediate can be generated in situ by treating diethylplatinum(II) compounds with acids. Treatment of (phen)PtEt_2 with [H(OEt_2)_2]Bar^f_4 at low temperatures resulted in the formation of a mixture of [(phen)PtEt(OEt_2)]Bar^f_4 (8) and [(phen)Pt(C_2H_4)H] Bar^f_4 (7). The cationic olefin complexes are unreactive toward dioxygen or hydrogen peroxide. Since the success of the overall catalytic cycle depends on our ability to oxidize the olefin hydride complexes, a series of neutral olefin complexes of platinum(II) with monoanionic ligands (derivatives of pyrrole-2-carboxyaldehyde N-aryl imines) was prepared. Unfortunately, these are also stable to oxidation. </p> 2001 Thesis NonPeerReviewed application/pdf en other https://thesis.library.caltech.edu/8152/1/Rostovtsev%202001.pdf Rostovtsev, Vsevolod Vladimirovich (2001) Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jevj-7928. https://resolver.caltech.edu/CaltechTHESIS:03202014-115036901 <https://resolver.caltech.edu/CaltechTHESIS:03202014-115036901> https://resolver.caltech.edu/CaltechTHESIS:03202014-115036901 CaltechTHESIS:03202014-115036901 10.7907/jevj-7928 |
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<p>Whereas stoichiometric activation of C-H bonds by complexes of transition metals is
becoming increasingly common, selective functionalization of alkanes remains a
formidable challenge in organometallic chemistry. The recent advances in catalytic
alkane functionalization by transition-metal complexes are summarized in Chapter I. </p>
<p>The studies of the displacement of pentafluoropyridine in
[(tmeda)Pt(CH_3)(NC_5F_5)][BAr^f_4] (1) with γ- tetrafluoropicoline, a very poor nucleophile,
are reported in Chapter II. The ligand substitution occurs by a dissociative interchange
mechanism. This result implies that dissociative loss of pentafluoropyridine is the rate-limiting
step in the C-H activation reactions of 1. </p>
<p>Oxidation of dimethylplatinum(II) complexes (N-N)Pt(CH_3)_2 (N-N = tmeda(1), α-diimines)
by dioxygen is described in Chapter III. Mechanistic studies suggest a two-step mechanism. First, a hydroperoxoplatinum(IV) complex is formed in a reaction
between (N-N)Pt(CH_3)_2 and dioxygen. Next, the hydroperoxy complex reacts with a
second equivalent of (N-N)Pt(CH_3)_2 to afford the final product,
(N-N)Pt(OH)(OCH_3)(CH_3)_2. The hydroperoxy intermediate,
(tmeda)Pt(OOH)(OCH_3)(CH_3)_2 (2), was isolated and characterized. The reactivity of 2
with several dime thylplatinum(II) complexes is reported. </p>
<p>The studies described in Chapter IV are directed toward the development of a
platinum(II)-catalyzed oxidative alkane dehydrogenation. Stoichiometric conversion of
alkanes (cyclohexane, ethane) to olefins (cyclohexene, ethylene) is achieved by C-H
activation with [(N-N)Pt(CH_3)(CF_3CH_2OH)]BF_4 (1, N-N is N,N'-bis(3,5-di-t-
butylphenyl)-1,4-diazabutadiene) which results in the formation of olefin hydride
complexes. The first step in the C-H activation reaction is formation of a platinum(II)
alkyl which undergoes β-hydrogen elimination to afford the olefin hydride complex.
The cationic ethylplatinum(II) intermediate can be generated in situ by treating
diethylplatinum(II) compounds with acids. Treatment of (phen)PtEt_2 with
[H(OEt_2)_2]Bar^f_4 at low temperatures resulted in the formation of a mixture of
[(phen)PtEt(OEt_2)]Bar^f_4 (8) and [(phen)Pt(C_2H_4)H] Bar^f_4 (7). The cationic olefin
complexes are unreactive toward dioxygen or hydrogen peroxide. Since the success of
the overall catalytic cycle depends on our ability to oxidize the olefin hydride
complexes, a series of neutral olefin complexes of platinum(II) with monoanionic ligands
(derivatives of pyrrole-2-carboxyaldehyde N-aryl imines) was prepared. Unfortunately,
these are also stable to oxidation. </p>
|
author |
Rostovtsev, Vsevolod Vladimirovich |
spellingShingle |
Rostovtsev, Vsevolod Vladimirovich Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization |
author_facet |
Rostovtsev, Vsevolod Vladimirovich |
author_sort |
Rostovtsev, Vsevolod Vladimirovich |
title |
Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization |
title_short |
Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization |
title_full |
Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization |
title_fullStr |
Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization |
title_full_unstemmed |
Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization |
title_sort |
reactions of platinum(ii) complexes with dioxygen: progress toward alkane functionalization |
publishDate |
2001 |
url |
https://thesis.library.caltech.edu/8152/1/Rostovtsev%202001.pdf Rostovtsev, Vsevolod Vladimirovich (2001) Reactions of platinum(II) complexes with dioxygen: progress toward alkane functionalization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jevj-7928. https://resolver.caltech.edu/CaltechTHESIS:03202014-115036901 <https://resolver.caltech.edu/CaltechTHESIS:03202014-115036901> |
work_keys_str_mv |
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