Reversible cleavage of chromium-chromium quadruple bond of [Me8Cr2][Li(THF)]4 via modification of the coordination sphere of the alkali cation. Preparation and crystal structure of monomeric [Me4Cr][Li(TMEDA)]2

Hao, Shoukang; Gambarotta, Sandro; Bensimon, Corinne

doi:10.1021/ja00035a061

Cited by 50 publications

(45 citation statements)

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“…Fore xample,a mong the tetragonal dinuclear species M 2 X 4 (M = Cr, Mo,W ;Xis am onoanionic bidentate ligand), aw ide range of Cr-Cr bond lengths between 1.83 and 2.00 have been documented, [1] while the variation of MÀMd istances in the other two heavier congeners is relatively small. [2][3][4][5][6] For instance,t he [Cr 2 Me 8 ] 4À in [Li(THF)] 4 [Cr 2 Me 8 ], where the CrÀCr separation is 1.980(5) ,r eadily fell apart to two mononuclear species [CrMe 4 ] 2À upon treatment with Me 2 NCH 2 CH 2 NMe 2 . [2][3][4][5][6] For instance,t he [Cr 2 Me 8 ] 4À in [Li(THF)] 4 [Cr 2 Me 8 ], where the CrÀCr separation is 1.980(5) ,r eadily fell apart to two mononuclear species [CrMe 4 ] 2À upon treatment with Me 2 NCH 2 CH 2 NMe 2 .…”

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confidence: 99%

“…[1] TheC r ÀCr quadruple bond is typically considered to be strong, but some examples showed short but weak Cr À Cr quadruple bonds. [5] Another example is the dichromium amidinate cis-[Cr(m-k 2 -t BuNC(Me)NEt)(k 2 -t BuNC-(Me)NEt)] 2 ,w hich has aCr À Cr bond length of 1.9601 (12) in the solid state,b ut readily decomposed in benzene and cyclohexane solutions to give am ononuclear compound Cr(k 2 -t BuNC(Me)NEt) 2 . [5] Another example is the dichromium amidinate cis-[Cr(m-k 2 -t BuNC(Me)NEt)(k 2 -t BuNC-(Me)NEt)] 2 ,w hich has aCr À Cr bond length of 1.9601 (12) in the solid state,b ut readily decomposed in benzene and cyclohexane solutions to give am ononuclear compound Cr(k 2 -t BuNC(Me)NEt) 2 .…”

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confidence: 99%

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Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Huang

Liu

et al. 2017

Angew Chem Int Ed

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Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ -HC(N-2,6- Pr C H )(N-2,6-R C H )}] (R=iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes. During the catalysis, the ultrashort Cr-Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ-η :η -1,3,5-(Me Si) C H )[Cr{κ -HC(N-2,6- Pr C H )(N-2,6-R C H )}] (R= Pr (5), Me (8)). In the presence of σ donors, such as THF and 2,4,6-Me C H CN, the bridging arene 1,3,5-(Me Si) C H in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathways of these highly regioselective [2+2+2] cylcotrimerization reactions of terminal alkynes.

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confidence: 99%

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Huang

Liu

et al. 2017

Angew Chem Int Ed

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“…40 The magnetic moment of (9) at 4.98 n B is typical for such a square planar chromium(II) complex. The bridging methyl groups show slightly distorted sp 3 geometries at the hinges of the double butterfly structure.…”

Section: Structure and Propertiesmentioning

confidence: 99%

“…40 However, its reaction with two equivalents tetramethyldibenzotetraaza [14]annulene (tmtaaH 2 ) affords methane and the Cr=Cr system [Cr(tmtaa)] 2 . 400 …”

Section: Scheme 14 [Mobr(pme 3 ) 4 (0(tms))]mentioning

confidence: 99%

Organometallic Compounds of Chromium, Molybdenum and Tungsten without Carbonyl Ligands

Winter

1995

Comprehensive Organometallic Chemistry II

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“…[1] TheC r ÀCr quadruple bond is typically considered to be strong, but some examples showed short but weak Cr À Cr quadruple bonds. [2][3][4][5][6] For instance,t he [Cr 2 Me 8 ] 4À in [Li(THF)] 4 [Cr 2 Me 8 ], where the CrÀCr separation is 1.980 (5) ,r eadily fell apart to two mononuclear species [CrMe 4 ] 2À upon treatment with Me 2 NCH 2 CH 2 NMe 2 . [5] Another example is the dichromium amidinate cis-[Cr(m-k 2 -t BuNC(Me)NEt)(k 2 -t BuNC-(Me)NEt)] 2 ,w hich has aCr À Cr bond length of 1.9601 (12) in the solid state,b ut readily decomposed in benzene and cyclohexane solutions to give am ononuclear compound Cr(k 2 -t BuNC(Me)NEt) 2 .…”

mentioning

confidence: 99%

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Huang

Liu

et al. 2017

Angewandte Chemie

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Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{k 2 -HC(N-2,6i Pr 2 C 6 H 3 )(N-2,6-R 2 C 6 H 3 )}] 2 (R = iPr (1), Me (7)) as catalysts to mediate the [2+ +2+ +2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes.D uring the catalysis,t he ultrashort Cr À Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (m-h 6 :h 6 -1,3,5-(Me 3 Si) 3 C 6 H 3 )[Cr{k 2 -HC(N-2,6-i Pr 2 C 6 H 3 )(N-2,6-R 2 C 6 H 3 )}] 2 (R = i Pr (5), Me (8)). In the presence of s donors,such as THF and 2,4,6-Me 3 C 6 H 2 CN,t he bridging arene 1,3,5-(Me 3 Si) 3 C 6 H 3 in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathwayso ft hese highly regioselective [2+ +2+ +2] cylcotrimerization reactions of terminal alkynes. Scheme 2. Reversible cleavage/formation of the CrÀCr quintuple bond in the cyclotrimerization of Me 3 SiCCH. Scheme 3. No cross reactions between 5 and 8 in THF.

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Reversible cleavage of chromium-chromium quadruple bond of [Me8Cr2][Li(THF)]4 via modification of the coordination sphere of the alkali cation. Preparation and crystal structure of monomeric [Me4Cr][Li(TMEDA)]2

Cited by 50 publications

References 2 publications

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

Organometallic Compounds of Chromium, Molybdenum and Tungsten without Carbonyl Ligands

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

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