Characterization of the energy surface for the oxidative addition of silanes to manganese complex CpMn(CO)2(heptane)

Hester, Dennis M.; Sun, Jiemin; Harper, Aaron W.; Yang, Gilbert K.

doi:10.1021/ja00039a040

Cited by 55 publications

(25 citation statements)

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“…The available cone angles of phosphines [18] are reported to be identical to those of analogous silyl ligands. [19] Thus, the cone angles of the SiHPh 2 and SiMe 2 Ph groups are 1288 and 1228, respectively, that is, HSiMe 2 Ph is sterically less demanding than Ph 2 SiH 2 . In addition, since HSiMe 2 Ph and H 2 SiMePh are very similar electronically, major influence of electronic factors on reactivity can be excluded as well.…”

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confidence: 99%

Reactivity of Rhodium–Triflate Complexes with Diphenylsilane: Evidence for Silylene Intermediacy in Stoichiometric and Catalytic Reactions

Goikhman

Milstein

2005

Chemistry A European J

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Addition of Ph2SiH2 to [Rh(iPr3P)2(OTf)] (1) yielded the thermally unstable RhIII adduct [Rh(iPr3P)2(OTf)(H)(SiPh2H)] (2), which decomposed to [Rh(iPr3P)2(H)2(OTf)] (3), liberating (unobserved) silylene. The silylene was trapped by 1, resulting in the RhI-silyl complex [Rh(iPr3P)2(SiPh2OTf)]. Complex 3 was converted to 2 by addition of diphenylsilane, providing a basis for a possible catalytic cycle. The last reaction did not involve a RhI intermediate, as shown by a labeling study. Complex 1 catalyzed the dehydrogenative coupling of Ph2SiH2 to Ph2HSi--SiHPh2. A mechanism involving a silylene intermediate in this catalytic cycle is proposed. The mechanism is supported by complete lack of catalysis in the case of the tertiary silanes Ph2MeSiH and PhMe2SiH, and by a study of individual steps of the catalytic cycle. The outcome of the reaction of Ph2SiH2 with styrene in the presence of 1 depends on the complex/substrate ratio; under stoichiometric conditions olefin hydrogenation prevailed over hydrosilylation, whereas with excess of substrates hydrosilylation prevailed. Catalytic hydrosilylation resulted in double addition giving Ph2Si(CH2CH2Ph)2. Mechanistic aspects of the reported processes are discussed, and a new hydrosilylation mechanism based on silylene intermediacy is proposed.

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confidence: 99%

Reactivity of Rhodium–Triflate Complexes with Diphenylsilane: Evidence for Silylene Intermediacy in Stoichiometric and Catalytic Reactions

Goikhman

Milstein

2005

Chemistry A European J

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“…Metal-alkane binding enthalpies have been determined by photoacoustic calorimetry (PAC) and TRIR spectroscopy for a range of group 6 [M(CO) 5 (heptane)] and group 7 [M(Cp)(CO) 2 (heptane)] complexes in solution, and these are found to range between 40 and 57 kJ⅐mol Ϫ1 (10,(20)(21)(22)(23)(24). Gas-phase TRIR studies have demonstrated that the shorter n-alkane species have progressively lower binding energies to the metal, with CH 4 being the most weakly bound (25).…”

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confidence: 99%

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Cowan

Portius

Kawanami

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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We have used fast time-resolved infrared spectroscopy to characterize a series of organometallic methane and ethane complexes in solution at room temperature: W(CO)5(CH4) and M( 5 OC5R5)(CO)2(L) [where M ‫؍‬ Mn or Re, R ‫؍‬ H or CH3 (Re only); and L ‫؍‬ CH4 or C 2 H 6 ]. In all cases, the methane complexes are found to be short-lived and significantly more reactive than the analogous nheptane complexes. Re(Cp)(CO)2(CH4) and Re(Cp*)(CO)2(L) [Cp* ‫؍‬ 5 OC5(CH3)5 and L ‫؍‬ CH4, C2H6] were found to be in rapid equilibrium with the alkyl hydride complexes. In the presence of CO, both alkane and alkyl hydride complexes decay at the same rate. We have used picosecond time-resolved infrared spectroscopy to directly monitor the photolysis of Re(Cp*)(CO)3 in scCH4 and demonstrated that the initially generated Re(Cp*)(CO)2(CH4) forms an equilibrium mixture of Re(Cp*) ( T here is considerable interest in sigma-bonded organometallic alkane complexes, particularly since they have been identified as key intermediates in the transition metal-mediated COH activation process (1-3). Although such complexes generally are very short-lived intermediates (4), they have been known for over 30 years. Early experiments involved the photolysis of complexes such as Cr(CO) 6 and Fe(CO) 5 to generate the unstable intermediates Cr(CO) 5 or Fe(CO) 4 in low-temperature matrices, where coordination to cocondensed CH 4 results in the formation of Cr(CO) 5 (CH 4 ) and Fe(CO) 5 (CH 4 ) (5, 6).Flash photolysis experiments have demonstrated that the photolysis of Cr(CO) 6 in cyclohexane solution at room temperature forms Cr(CO) 5 (cyclohexane) (7). Subsequently, several examples of alkane complexes in solution have been reported, and studies on the mechanism of the COH activation process have clearly demonstrated the role of these complexes in oxidative addition reactions (1,8,9). Time-resolved infrared (TRIR) spectroscopy has proved to be a powerful tool for the study of metal carbonyl alkane complexes. Their reactivity decreases on going both across and down groups 5, 6, and 7 (10-12), and these observations led to the identification of a very long-lived alkane complex, Re(Cp)(CO) 2 (nheptane) (Cp ϭ 5 OC 5 H 5 ), which has a lifetime of Ϸ25 ms at room temperature (13). The relative stability of Re(Cp)(CO) 2 (alkane) complexes allowed Re(Cp)(CO) 2 (C 5 H 10 ) to be observed at 180 K by NMR spectroscopy (14), and subsequent NMR studies have been carried out to determine the binding modes of a series of related alkanes to the Re(CpЈ)(CO) 2 moiety (15, 16).The activation of methane is of particular interest because of the potential of using this abundant hydrocarbon as both an energy source and chemical feedstock (17). Organometallic methane complexes have been characterized in low-temperature matrix isolation experiments (5,6,18). In solution, the existence of methane complexes has been inferred by examining product ratios and from the rates of COH activation and reductive elimination reactions in isotopic labeling experiments (19).The lifetime of the...

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“…The obtained enthalpy of activation DH -1 should include two contributions: the Co-N bond energy of the chelator and the released solvation energy to form a ring opened reaction intermediate I S . It was reported that a metal-solvent bond in a coordinatively unsaturated cyclopentadienyl metal carbonyl compound is about 8 kJ/mol [52][53][54]. Thus the energy needed to break the chelated bond might be about 54 kJ/mol estimated from the summation of DH -1 (about 46 kJ/mol for 3a and 3b) and the solvation energy from Yang's data.…”

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confidence: 99%

Chelate ring closing and opening behavior in cyclopentadienyl cobalt(III) complexes with pendant nitrogen functional group

Zhou

Zhang

et al. 2010

Journal of Organometallic Chemistry

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Characterization of the energy surface for the oxidative addition of silanes to manganese complex CpMn(CO)2(heptane)

Cited by 55 publications

References 1 publication

Reactivity of Rhodium–Triflate Complexes with Diphenylsilane: Evidence for Silylene Intermediacy in Stoichiometric and Catalytic Reactions

Reactivity of Rhodium–Triflate Complexes with Diphenylsilane: Evidence for Silylene Intermediacy in Stoichiometric and Catalytic Reactions

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Chelate ring closing and opening behavior in cyclopentadienyl cobalt(III) complexes with pendant nitrogen functional group

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