Manganese(0) radicals and the reduction of cationic carbonyl complexes: selectivity in the ligand dissociation from 19-electron species

Kuchynka, D. J.; Amatore, Christian; Kochi, Jay K.

doi:10.1021/ic00243a009

Cited by 40 publications

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“…Although the observation of a bent 19e CO complex is surprising, the literature contains other reports of bent CO ligands in a variety of contexts. As was mentioned in the Introduction, the bending of a ligand to avoid a 19e configuration at the metal has been reported previously . A number of experimental and computational studies have been carried out on CO-bound myoglobin, and the Fe–C–O angle has been debated and reported to take on a wide range of values from completely bent to completely linear .…”

Section: Resultsmentioning

confidence: 70%

“…In many cases, transiently lived 19e structures are proposed to involve the rearrangement of a ligand to accommodate the excess electron density at the metal center. A two-electron donor ligand might rearrange to become a one-electron donor; an aromatic ring might “slip,” resulting in a lower coordination number; or a phosphine or phosphite ligand might adopt a radical electronic configuration . Examples of such structures are shown in Scheme .…”

Section: Introductionmentioning

confidence: 99%

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Direct Observation of a Bent Carbonyl Ligand in a 19-Electron Transition Metal Complex

2013

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The photochemistry of [CpRu(CO)2]2 in P(OMe)3/CH2Cl2 solution has been studied using picosecond time-resolved infrared (TRIR) spectroscopy. Photolysis at 400 nm leads to the formation of 17-electron CpRu(CO)2(•) radicals, which react on the picosecond time scale to form 19-electron CpRu(CO)2P(OMe)3(•) adducts. The TRIR spectra of this adduct display an unusually low CO stretching frequency for the antisymmetric CO stretching mode, suggesting that one carbonyl ligand adopts a bent configuration to avoid a 19-electron count at the metal center. This spectral assignment is supported by analogous experiments on [CpFe(CO)2]2 in the same solvent, combined with DFT studies on the structures of the 19-electron adducts. The DFT results predict a bent CO ligand in CpRu(CO)2P(OMe)3(•), whereas approximately linear Fe-C-O bond angles are predicted for CpFe(CO)2P(OMe)3(•). The observation of a bent CO ligand in the 19-electron ruthenium adduct is a surprising result, and it provides new insight into the solution-phase behavior of 19-electron complexes. TRIR spectra were also collected for [CpRu(CO)2]2 in neat CH2Cl2, and it is interesting to note that no singly bridged [CpRu(CO)]2(μ-CO) photoproduct was observed to form following 400- or 267-nm excitation, despite previous observations of this species on longer time scales.

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Section: Resultsmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Direct Observation of a Bent Carbonyl Ligand in a 19-Electron Transition Metal Complex

2013

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“…7 does not appear to arise via 6 , since the latter is stable to irradiation: exposing a 4:1 mixture of 6 and 5a to light results in a 4:1 mixture of 6 and 7 . The requirement of light to induce formation of 7 suggests possible involvement of radical pathways, as has been shown for related systems. , …”

Section: Resultsmentioning

confidence: 76%

Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme

et al. 2009

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A variety of C-H and C-C bond forming reactions of group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C 2þ compounds. The metal formyl complexes M(CO) 3 (PPh 3 ) 2 (CHO) (M=Mn, Re) are substantially stabilized by coordination of boranes BX 3 (X = F, C 6 F 5 ) in the form of novel boroxycarbene complexes M(CO) 3 -(PPh 3 ) 2 (CHOBX 3 ), but these boron-stabilized carbenes do not react with hydride sources to undergo further reduction to metal alkyls. The related manganese methoxycarbene cations [Mn(CO) 5-x (PPh 3 ) x (CHOMe)] þ (x=1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atmosphere of CO. The resulting acyls, cis-and trans-Mn(PPh 3 )(CO) 4 (C(O)CH 2 OMe), can be alkylated to form the cationic carbene complex [Mn(PPh 3 )(CO) 4 (C(OR)CH 2 OMe)] þ , which undergoes a 1,2 hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or diethyl ether adducts of [Mn(PPh 3 )(CO) 4 ] þ . The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh 3 )(CO) 4 (CH 2 COOMe) and is protonolyzed to yield methyl acetate and [Mn(PPh 3 )(CO) 4 ] þ ; addition of L (L = PPh 3 , CO) to the manganese cation regenerates [Mn(PPh 3 )(CO) 4 (L)] þ . Since the original formyl complex can be obtained by the reaction of [Mn(PPh 3 )(CO) 5 ] þ with [PtH(dmpe) 2 ] þ , which in turn can be generated from H 2 , this set of transformations amounts to a stoichiometric cycle for selectively converting H 2 and CO into a C 2 compound under mild conditions.

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“…Tyler indicated that the disproportionation mechanism generally involves the intermediacy of 19e complexes:180-184 With Mn2(CO)10, the inefficiency of the disproportionation in the presence of amines N was attributed to the necessity of Mn2(CO)10 to substitute twice and to add a third ligand to form the 19e intermediate Mn(CO)3N3'. Consistently, the use of a tridentate ligand N3 is an efficient means of forming this 19e inter- Mn(COV + N3 -Mn(CO)3N3* + 2CO (131) Mn(CO)3N3* + Mn2(CO)10 -Mn(CO)3N3+ + Mn2(CO)10" (132) Mn2(CO)10--Mn(CO)5-+ Mn(COy (133) With Cp2Fe2(CO)4, the disproportionation also works in this way, but only with (dialkylphosphino)ethane as donor. 222 With other donors, the back ET reaction prevents formation of the disproportionation products.…”

Section: Disproportionationmentioning

confidence: 87%

Nineteen-electron complexes and their role in organometallic mechanisms

Astruc¹

1988

Chem. Rev.

201

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Manganese(0) radicals and the reduction of cationic carbonyl complexes: selectivity in the ligand dissociation from 19-electron species

Cited by 40 publications

References 0 publications

Direct Observation of a Bent Carbonyl Ligand in a 19-Electron Transition Metal Complex

Direct Observation of a Bent Carbonyl Ligand in a 19-Electron Transition Metal Complex

Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme

Nineteen-electron complexes and their role in organometallic mechanisms

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