Vinylidene complexes of the molybdenum auxiliary Mo(Ph2PCH2CH2PPh2)(C7H7). Structural and spectroscopic investigations on vinylidene ligand orientation

Beddoes, Roy L.; Bitcon, Caroline; Grime, Richard W.; Ricalton, Allen; Whiteley, Mark W.

doi:10.1039/dt9950002873

Cited by 50 publications

(46 citation statements)

References 22 publications

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“…Two isomeric forms differing in the relative positions of the Fc and the Ph substituents are discernible for the PPh 3 -substituted congener 3a up to 388 K in 1,2-D 2 C 2 Cl 4 , at which point this compound decomposes. The observation of just one singlet resonance for each isomer by 31 P NMR spectroscopy argues for a vertical orientation of the allenylidene ligand. This is in agreement with the crystallographically determined structures for 2a and 2b, the latter presented here.…”

Section: Discussionmentioning

confidence: 94%

“…This is in agreement with the crystallographically determined structures for 2a and 2b, the latter presented here. [13] For the dppf-substituted 3b, however, splitting of the singlet 31 P NMR resonance into a well-resolved AB quadruplet is observed upon cooling in CD 2 Cl 2 , pointing to a horizontal alignment of the allenylidene ligand. The energy barrier for allenylidene rotation is determined as 47 kJ/mol at the coalescence temperature of 238 K.…”

Section: Discussionmentioning

confidence: 94%

“…[31] The highest activation energy for vinylidene rotation of which we are aware has been observed for the rhenium com-…”

Section: Synthesis Molecular Structures and Spectroscopic Propertiesmentioning

confidence: 93%

“…[32] The butyl/methyl-substituted vinylidene complex [(η 7 -C 7 H 7 )(dppe)MoϭCϭC(C 4 H 9 )(CH 3 )] ϩ displays separate resonance signals for the two different rotamers at 348 K. [31] The rotational barriers are usually thought of as being more steric than electronic in origin. Calculations on (vinylidene)-metal complexes indicate that the intrinsic (electronic) energy difference between the vertical and horizontal rotamers amounts to no more than 10Ϫ20 kJ/mol.…”

Section: Synthesis Molecular Structures and Spectroscopic Propertiesmentioning

confidence: 99%

“…In view of the further remoteness of the terminal methylene group from the metalϪligand array it is therefore not surprising that allenylidene complexes present even lower rotational barriers than their vinylidene counterparts, and so the observation of a truly significant rotational barrier in an allenylidene ligand is quite unusual. This prompted us to study the dynamic behavior of 3a in 1,2-D 2 C 2 Cl 4 solution by 31 P NMR spectroscopy. Upon warming there was a very slight shift of the two singlet resonance signals, but no broadening was observed up to 388 K, at which point 3a decomposed.…”

Section: Synthesis Molecular Structures and Spectroscopic Propertiesmentioning

confidence: 99%

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(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

et al. 2003

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, L 2 = 2 PPh 3 or 1,1Ј-bis(diphenylphosphanyl)ferrocene (dppf), R = Ph or ferrocenyl] and their spectroscopic and electrochemical characteristics. Three of these compounds possess redox-active, ferrocenebased substituents or ligands − that are oxidized at lower potentials than the ruthenium center itself − attached either to the terminal carbon atom of the allenylidene ligand or to the ruthenium atom. The Fc/Ph-substituted complexes 3a and 3b provide unique examples of hindered rotation of the allenylidene substituent around the M=C bond. For 3a (L 2 = 2 PPh 3 ), two isomers differing in the orientation of the vertically aligned, unsymmetrically substituted allenylidene ligand are discernible even at 388 K. The dppf-substituted congener 3b has the allenylidene ligand in a horizontal orientation and exhibits a rotational barrier, as determined by dynamic 31 P NMR spectroscopy, of ∆G ϶ = 47 kJ/mol at T C = 238 K. The changes in the spectroscopic and electrochemical properties upon replacement of the PPh 3 by a dppf ligand and the Ph by an Fc moiety can be explained in terms of the bonding within these systems. These effects are attenuated when the ferrocene-based redox tags are oxidized, as shown by IR and

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Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 94%

“…[31] The highest activation energy for vinylidene rotation of which we are aware has been observed for the rhenium com-…”

Section: Synthesis Molecular Structures and Spectroscopic Propertiesmentioning

confidence: 93%

Section: Synthesis Molecular Structures and Spectroscopic Propertiesmentioning

confidence: 99%

Section: Synthesis Molecular Structures and Spectroscopic Propertiesmentioning

confidence: 99%

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(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

et al. 2003

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Preparation and Stoichiometric Reactivity of Mononuclear Metal Vinylidene Complexes

Bruce

2008

Metal Vinylidenes and Allenylidenes in Catalysis

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Generation and Coupling of [Mn(dmpe)₂(CCR)(CC)]^. Radicals Producing Redox‐Active C₄‐Bridged Rigid‐Rod Complexes

Fernández

Venkatesan

Blacque

et al. 2003

Chemistry A European J

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The symmetric d(5) trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (dmpe = 1,2-bis(dimethylphosphino)ethane) have been prepared by the reaction of [Mn(dmpe)(2)Br(2)] with two equivalents of the corresponding acetylide LiC triple bond CSiR(3). The reactions of species 1 with [Cp(2)Fe][PF(6)] yield the corresponding d(4) complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)][PF(6)] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu(4)F (TBAF) at -10 degrees C to give the desilylated parent acetylide compound [Mn(dmpe)(2)(C triple bond CH)(2)][PF(6)] (6), which is stable only in solution at below 0 degrees C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(C triple bond CH)][PF(6)] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)(2)(C triple bond CSiR(3))(C=CH(2))] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp(2)Fe][PF(6)] and one equivalent of quinuclidine. The conversion of [Mn(C(5)H(4)Me)(dmpe)I] with Me(3)SiC triple bond CSnMe(3) and dmpe afforded the trans-iodide-alkynyl d(5) complex [Mn(dmpe)(2)(C triple bond CSiMe(3))I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique Mn(III) product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed-valent species [[Mn(dmpe)(2)(C triple bond CH)](2)(micro-C(4))][PF(6)] (11) by C-C coupling of [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [[Mn(dmpe)(2)(C triple bond CSiMe(3))](2)(micro-C(4))][PF(6)] [12](+) is obtained by the reaction of 7 a with one equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The relatively long-lived radical intermediate [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] could be trapped as the Mn(I) complex [Mn(dmpe)(2)(C triple bond CH)(triple bond C-CO(2))] (14) by addition of an excess of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear Mn(II)/Mn(II) compounds [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))] (R = H, 11; R = SiMe(3), 12) are produced by the reduction of [11](+) and [12](+), respectively, with [FeCp(C(6)Me(6))]. [11](+) and [12](+) can also be oxidized with [Cp(2)Fe][PF(6)] to produce the dicationic Mn(III)/Mn(III) species [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))][PF(6)](2) (R = H, [11](2+); R = SiMe(3), [12](2+)). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X-ray diffraction studies have been performed on complexes 4 b, 7 b, 9, [12](+), [12](2+), and 14.

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Vinylidene complexes of the molybdenum auxiliary Mo(Ph2PCH2CH2PPh2)(C7H7). Structural and spectroscopic investigations on vinylidene ligand orientation

Cited by 50 publications

References 22 publications

(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

Preparation and Stoichiometric Reactivity of Mononuclear Metal Vinylidene Complexes

Generation and Coupling of [Mn(dmpe)₂(CCR)(CC)]^. Radicals Producing Redox‐Active C₄‐Bridged Rigid‐Rod Complexes

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Vinylidene complexes of the molybdenum auxiliary Mo(Ph2PCH2CH2PPh2)(C7H7). Structural and spectroscopic investigations on vinylidene ligand orientation

Cited by 50 publications

References 22 publications

(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

(Allenylidene)ruthenium Complexes with Redox‐Active Substituents and Ligands

Preparation and Stoichiometric Reactivity of Mononuclear Metal Vinylidene Complexes

Generation and Coupling of [Mn(dmpe)2(CCR)(CC)]. Radicals Producing Redox‐Active C4‐Bridged Rigid‐Rod Complexes

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Generation and Coupling of [Mn(dmpe)₂(CCR)(CC)]^. Radicals Producing Redox‐Active C₄‐Bridged Rigid‐Rod Complexes