A new and selective cycle for dehydrogenation of linear and cyclic alkanes under mild conditions using a base metal

Abstract

Selectively converting linear alkanes to α-olefins under mild conditions is a highly desirable transformation given the abundance of alkanes as well as the use of olefins as building blocks in the chemical community. Until now, this reaction has been primarily the remit of noble-metal catalysts, despite extensive work showing that base-metal alkylidenes can mediate the reaction in a stoichiometric fashion. Here, we show how the presence of a hydrogen acceptor, such as the phosphorus ylide, when combined with the alkylidene complex (PNP)Ti=CHBu(CH) (PNP=N[2-P(CHMe)-4-methylphenyl]), catalyses the dehydrogenation of cycloalkanes to cyclic alkenes, and linear alkanes with chain lengths of C to C to terminal olefins under mild conditions. This Article represents the first example of a homogeneous and selective alkane dehydrogenation reaction using a base-metal titanium catalyst. We also propose a unique mechanism for the transfer dehydrogenation of hydrocarbons to olefins and discuss a complete cycle based on a combined experimental and computational study.

Room temperature olefination of methane with titanium–carbon multiple bonds

“…More evidence for B being the more reactive tautomeric form, was derived from an independent synthesis involving “CH 2 ” group transfer from a phosphorus ylide to the titanium olefin complexes of the type (PNP)Ti(CH 2 t Bu)(η 2 -olefin). 13 Upon transfer of “CH 2 ”, B is not observed, but instead tautomerizes quickly to 1 corroborating our claim that B lies 7.8 kcal mol –1 higher in energy to 1 (based on calculated free energies). 10 , 13 …”

“… 13 Upon transfer of “CH 2 ”, B is not observed, but instead tautomerizes quickly to 1 corroborating our claim that B lies 7.8 kcal mol –1 higher in energy to 1 (based on calculated free energies). 10 , 13 …”

Transition-metal complex-catalyzed alkane functionalization

“…最近 Goldberg课题组 [47,48] 、Goldman课题组 [49] 和William课 题组 [50] 报道了双噁唑啉配位的NCN配体, 不同于之 [51] 报 道的PNP配位的铑配合物11, Roddic课题组 [52,53] 和本 课 题 组 [54] 报 道 的 PCP配 位 的 钌 和 锇 配 合 物 12和 13, Vedernikov课题组 [55] 报道的双吡啶配位的两性铂配 合物14. 最近, Mindiloa课题组 [56] [57] . 尽管可利用非均相催化剂实现烷 烃至相应的烷基苯类化合物的转化, 但反应所需的 温度高, 产率以及选择性均较差 [58~60] .…”

Addition of alkynes and osmium carbynes towards functionalized dπ–pπ conjugated systems

“…The reactions of M≡C and C≡C bonds tend to afford cycloaddition intermediates or products on account of their high degree of unsaturation. For example, the alkyne metathesis undergoes metallacyclobutadiene intermediates process 12 – 14 , and [2+2], [2+2+1], and [2+2+2] cycloaddition products have been widely published 26 – 37 . Acyclic products, however, have never been reported.…”

“…The M≡C bonds have been shown rich reactivity with electrophiles and nucleophiles [4][5][6][7][8] . Therefore, metal carbyne complexes are valuable in synthetic chemistry as precursors for interesting organometallic compounds [9][10][11] , and can be used as homogeneous catalysts in the synthesis of organic compounds and polymers [12][13][14][15][16][17][18] . Alkynes containing C≡C bonds are also a class of compounds with triple bonds.…”