Chemistry of gem-Dihalocyclopropanes. XXI. An Example of Competition between 1,3-Insertion and the Vinylcyclopropylidene/Cyclopentenylidene Rearrangement.

Brun, R.; Grace, D. S. B.; Holm, Kjetil H.; Skattebøl, Lars; Krogsgaard‐Larsen, Povl; Ryhage, Ragnar; Isaksson, Roland

doi:10.3891/acta.chem.scand.40b-0021

Cited by 8 publications

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“…Toluene- d 8 was purchased from Isotec and was freshly vacuum-transferred from Na/K. Dimethylcyclopentadiene was synthesized by the method of Skattebøl and converted to the corresponding lithium salt by treatment with n -BuLi in hexanes.…”

Section: Methodsmentioning

confidence: 99%

Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts

1998

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Reaction enthalpies of group 4 metallocenes having the general formula L2M(CH3)2 (L = Cp, 1,2-Me2Cp, Me5Cp; L2 = Me2Si(Me4Cp)( t BuN); M = Ti, Zr, and Hf) with the strong organo-Lewis acid B(C6F5)3 were measured using batch titration calorimetry in toluene. Methide abstraction to form the corresponding L2MCH3 +CH3B(C6F5)3 - contact ion pairs is highly exothermic in all cases. Exothermicity increases with increasing Cp methyl substitution: for M = Zr, ΔH = −23.1(3), −24.3(4), and −36.7(5) kcal mol-1 for L = Cp, Me2Cp, and Me5Cp, respectively. For M = Hf and L = 1,2-Me2Cp, ΔH = −20.8(5) kcal mol-1. “Constrained geometry” complexes (L2 = Me2Si(Me4Cp)( t BuN)) exhibit similar exothermicities, with ΔH = −22.6(2), −23.9(4), and −19.3(6) kcal mol-1 for M = Ti, Zr, and Hf, respectively. In contrast, analogous reactions with methylalumoxane (M:Al = 1:50) are less exothermic, with ΔH = −10.9(3) and −8.9(4) kcal mol-1 for L = 1,2-Me2Cp and M = Zr and Hf, respectively. Under identical conditions, (1,2-Me2Cp)2M(CH3)2 (M = Zr, Hf) complexes also undergo methide abstraction with the less Lewis-acidic triarylboranes (C6F5)2BAr (Ar = 3,5-C6H3F2, Ph, and 3,5-C6H3Me2); however, conversions to the corresponding (Me2Cp)2MCH3 + CH3B(C6F5)2Ar- ion pairs are incomplete. Variable-temperature NMR measurements yield thermodynamic parameters for partial methide abstraction by these less Lewis-acidic boranes. For Ar = 3,5-C6H3F2, ΔH = −18.7(7) and −15.2(8) kcal mol-1 with ΔS = −42(2) and −35(3) e.u.; for Ar = Ph, ΔH = −14.8(8) and −13.3(6) kcal mol-1 with ΔS = −31(2) and −39(2) e.u.; for Ar = 3,5-C6H3Me2, ΔH = −10.8(6) and −12.7(5) with ΔS = −19(2) and −36(4) e.u., in each case for M = Zr and Hf, respectively. Dynamic NMR analyses reveal that the activation barriers for methide abstraction from the neutral metallocene dialkyls are small and relatively insensitive to the borane identity (ΔH ⧧ = 2−6 kcal mol-1) while ion-pair separation/recombination processes are greatly facilitated by polar solvents. Ethylene polymerization activities for eight (Me2Cp)2MCH3 + CH3B(C6F5)2Ar- complexes measured in toluene solution (25 °C, 1 atm) follow a trend in metal (Zr > Hf) as well as a substantial trend in triarylborane (Ar = C6F5 > 3,5-C6H3F2 > Ph ∼ 3,5-C6H3Me2). Polymerization activities correlate roughly with MCH3 + 13C NMR chemical shifts and enthalpies of methide abstraction.

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Section: Methodsmentioning

confidence: 99%

Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts

1998

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“…As stated before, the dimerization of 3 leading to 2 is a formal dimerization. There are examples in the literature where at temperatures of about −80 °C two geminal bromolithiocyclopropanes form a double bond between the cyclopropane rings by undergoing two consecutive Wurtz-type LiBr eliminations. , The first elimination leads to a single bond, the second to the double bond. No real cyclopropylidenes seem to be involved in these cases.…”

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On the Existence of Uncharged Molecules with a Pyramidally Coordinated Carbon: The Cases of Pentacyclo[4.3.0.0^2,9.0^3,8.0^7,9]non-4-ene and Heptacyclo- [7.6.0.0^1,5.0^5,15.0^6,14.0^10,14.0^10,15]pentadecane

Mieusset

Brinker

2005

J. Org. Chem.

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[reaction: see text] B3LYP/6-31G(d) and MP2 calculations predict interactions between the divalent carbon and one double bond in tricyclo[3.2.2.0(2,4)]nona-6,8-dien-3-ylidene (3). Carbene 3 easily forms the more stable 4, a species with a pyramidal geometry. Moreover, the kinetic stability of 4 has been investigated, and some of its decay products are described. Interestingly, 3,3-dibromotricyclo[3.2.2.0(2,4)]nona-6,8-diene (1), the precursor of carbenoid 3, has already been reported and shown to undergo a formal dimerization to give 2. In addition, 15, a compound structurally related to 4, is expected to have a substantially greater stability toward further rearrangement.

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Carbene Rearrangements, XXII Labelling Studies of the Reaction of 8,8‐Dibromobicyclo[5.1.0]octa‐2,4‐diene with Methyllithium

Fleischhauer

Brinker

1987

Chem. Ber.

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In the reaction of 8,8-dibromobicyclo[5.1 .O]octa-2,4-diene (3) with methyllithium four dihydropentalenes are formed. In addition to the already described 1,6a-, 1,4-, and 1,SdihydropentaJenes (7,8, 9), the 1,6-isomer 15 is detected. The dihydropentalenes were characterized by means of their perlluoro-2-butyne adducts. The mechanism of their formation has been elucidated by I2C labelling.Cleavage of the lateral bond a in 4 induces a carbene-carbene rearrangement with 1,3-C migration (Skattebsl rearrangement) to give carbene 13. This stabilizes by a 1,2-vinyl shift to afford 1,6a-dihydropentalene (7). 1,4-,1,5-, and 1,6-dihydropentalene mit Methyllithium werden vier Dihydropentalene gebildet. Zusltzlich zu den bereits beschriebenen 1,6a-, 1,4-und 1,5-Dihydropentalenen (7, 8, 9) wurde das l,6-Isomere 15 gefunden. Die Dihydropentalene wurden anhand ihrer Pertluor-2-butin-Addukte charakterisiert. Der Mechanismus ihrer Bildung wurde durch "CMarkierung aufgekllrt. Die Spaltung der lateralen Bindung a in 4 induzjert eine Carben-Carben-Umlagerung mit 1,3-C-Wanderung (Skattebsl-Umlagerung) zum Carben 13. Dieses stabilisiert sich durch eine 1,2-VinyIverschiebung zu I ,dDihydropentalen (7). Die l , 4 , 1,5-und l,&Dihydropentalene (8, 9, 15) werden durch nachfolgende 1,5-H-Verschiebung gebildet.Although the formation of cyclopentadienes from the reaction of l,ldibromo-2-vinylcyclopropanes with methyllithium has been known since 1962*), the mechanism of the carbene-carbene rearScheme 2 subject rangement'lof of intensive the type studies'! I +2 (Skattebel rearrangement) is still the $--(j"&J"rn Scheme 1When investigating the reactions of gem-dibromovinylcyclopropanes with various substituentq special interest has been paid to the electronic and steric prerequisites of the rearrangement'). Systems in which the gemdibromovinylcyclopropane unit is incorporated into a bicyclic structure have been studied thoroughly@.In 1970. van Vuuren treated 8,8dibromobicyclo[5.l.O]octa-2,4-dime (3) with methyllithiurn" and isolated 1,6a-, 1.4-. and 1,Sdihydropentalene (7.8.9) by means of the corresponding pcdluoro-2-butyne (PFB) adducts 10, 11. and 12, respectively.As a mechanism for the formation of the bicyclo[3.3.0] structure a carbene-carbene rearrangement of 4 to 5 was suggested. Opening of the distal bond b in 4 and 1.34 and subsequent 1.2-H migration led primarily to 1.3adihydropentalene (6) which, due to its trisallylic hydrogen atom, isomerized readily to 7, 8, and 9 by 1.5-H shifts.

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Chemistry of gem-Dihalocyclopropanes. XXI. An Example of Competition between 1,3-Insertion and the Vinylcyclopropylidene/Cyclopentenylidene Rearrangement.

Cited by 8 publications

References 0 publications

Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts

Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts

On the Existence of Uncharged Molecules with a Pyramidally Coordinated Carbon: The Cases of Pentacyclo[4.3.0.0^2,9.0^3,8.0^7,9]non-4-ene and Heptacyclo- [7.6.0.0^1,5.0^5,15.0^6,14.0^10,14.0^10,15]pentadecane

Carbene Rearrangements, XXII Labelling Studies of the Reaction of 8,8‐Dibromobicyclo[5.1.0]octa‐2,4‐diene with Methyllithium

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Chemistry of gem-Dihalocyclopropanes. XXI. An Example of Competition between 1,3-Insertion and the Vinylcyclopropylidene/Cyclopentenylidene Rearrangement.

Cited by 8 publications

References 0 publications

Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts

Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts

On the Existence of Uncharged Molecules with a Pyramidally Coordinated Carbon: The Cases of Pentacyclo[4.3.0.02,9.03,8.07,9]non-4-ene and Heptacyclo- [7.6.0.01,5.05,15.06,14.010,14.010,15]pentadecane

Carbene Rearrangements, XXII Labelling Studies of the Reaction of 8,8‐Dibromobicyclo[5.1.0]octa‐2,4‐diene with Methyllithium

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On the Existence of Uncharged Molecules with a Pyramidally Coordinated Carbon: The Cases of Pentacyclo[4.3.0.0^2,9.0^3,8.0^7,9]non-4-ene and Heptacyclo- [7.6.0.0^1,5.0^5,15.0^6,14.0^10,14.0^10,15]pentadecane