“…Formation of η 2 -Vinyl Complexes. Although metal-mediated couplings of perfluoroalkenes and -alkynes are well precedented, simple insertion reactions in which the migrating group is highly fluorinated are quite rare, presumably due to the increased strength and reduced nucleophilicity of the metal−carbon bond compared to those of hydrocarbon analogues . The slightly shorter metal−C Aryl bond in 2 (2.207(4) Å) 36 compared to 10 (2.226(5) Å) 37 is consistent with this trend. 3 …”
This report describes a novel migratory insertion reaction which leads to the formation of highly fluorinated η 2 -vinyl complexes at a tungsten(II) metal center. Insight into the nature of this transformation was obtained by isolation and crystallographic characterization of a kinetic intermediate in the insertion process. Ambient-temperature photolysis of a toluene solution of the tungsten(II) tetrafluoroaryl metallacycle 2 and perfluoro-2-butyne accesses the kinetic η 2 -vinyl complex 3 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. The solid-state structure of 3 has been determined. Upon heating, 3 is converted to the thermodynamic η 2 -vinyl product 4 in which the fluoride ligands is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand. Detailed kinetic studies are reported for this isomerization reaction using both infrared spectroscopy and UV-visible spectroscopy. In the absence of added ligand, this transformation displays first-order disappearance of 3 with ∆H q) 124((2) kJ/mol, ∆S q ) +48((5) J/(mol‚K) and ∆V q ) +15.6((0.4) cm 3 /mol. This is in accord with a limiting dissociative mechanism. Carbon monoxide enhances the rate of isomerization and shows first-order dependence in p(CO) with ∆H q) 98((3) kJ/mol, ∆S q ) -5((9) J/(mol‚K), and ∆V q ) +3.9-((0.2) cm 3 /mol. The P(OMe) 3 -promoted isomerization displays saturation behavior with ∆H q ) 77((2) kJ/mol, ∆S q ) -46((6) J/(mol‚K), and ∆V q ) +5.5((0.4) cm 3 /mol at 2.2 M P(OMe) 3 . The negative entropy and positive volume of activation indicate that congestion is developed in the transition state. The kinetic data for the ligand-promoted transformations are in agreement with a mechanism involving a rapid pre-equilibrium (K) during which the adduct species [3‚P(OMe) 3 ] is formed, followed by a rate-determining step (k) to produce 5. For this process, k obs ) Kk[P(OMe) 3 ]/(1 + k[P(OMe) 3 ]). Visible spectroscopic evidence for the adduct species [3‚P(OMe) 3 ] has been obtained. Nonlinear least-squares analysis of the k obs versus [P(OMe) 3 ] plot determined a K ) 1.4 ( 0.1 M -1 and a k ) (89 ( 13) × 10 -5 s -1 , such that kK ) 1.2 × 10 -3 M -1 s -1 for the adduct formation. It is unlikely that an actual 20electron species is generated since the η 2 -vinyl ligand can conceivably change its hapticity and function in an η 1 mode.
“…Formation of η 2 -Vinyl Complexes. Although metal-mediated couplings of perfluoroalkenes and -alkynes are well precedented, simple insertion reactions in which the migrating group is highly fluorinated are quite rare, presumably due to the increased strength and reduced nucleophilicity of the metal−carbon bond compared to those of hydrocarbon analogues . The slightly shorter metal−C Aryl bond in 2 (2.207(4) Å) 36 compared to 10 (2.226(5) Å) 37 is consistent with this trend. 3 …”
This report describes a novel migratory insertion reaction which leads to the formation of highly fluorinated η 2 -vinyl complexes at a tungsten(II) metal center. Insight into the nature of this transformation was obtained by isolation and crystallographic characterization of a kinetic intermediate in the insertion process. Ambient-temperature photolysis of a toluene solution of the tungsten(II) tetrafluoroaryl metallacycle 2 and perfluoro-2-butyne accesses the kinetic η 2 -vinyl complex 3 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. The solid-state structure of 3 has been determined. Upon heating, 3 is converted to the thermodynamic η 2 -vinyl product 4 in which the fluoride ligands is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand. Detailed kinetic studies are reported for this isomerization reaction using both infrared spectroscopy and UV-visible spectroscopy. In the absence of added ligand, this transformation displays first-order disappearance of 3 with ∆H q) 124((2) kJ/mol, ∆S q ) +48((5) J/(mol‚K) and ∆V q ) +15.6((0.4) cm 3 /mol. This is in accord with a limiting dissociative mechanism. Carbon monoxide enhances the rate of isomerization and shows first-order dependence in p(CO) with ∆H q) 98((3) kJ/mol, ∆S q ) -5((9) J/(mol‚K), and ∆V q ) +3.9-((0.2) cm 3 /mol. The P(OMe) 3 -promoted isomerization displays saturation behavior with ∆H q ) 77((2) kJ/mol, ∆S q ) -46((6) J/(mol‚K), and ∆V q ) +5.5((0.4) cm 3 /mol at 2.2 M P(OMe) 3 . The negative entropy and positive volume of activation indicate that congestion is developed in the transition state. The kinetic data for the ligand-promoted transformations are in agreement with a mechanism involving a rapid pre-equilibrium (K) during which the adduct species [3‚P(OMe) 3 ] is formed, followed by a rate-determining step (k) to produce 5. For this process, k obs ) Kk[P(OMe) 3 ]/(1 + k[P(OMe) 3 ]). Visible spectroscopic evidence for the adduct species [3‚P(OMe) 3 ] has been obtained. Nonlinear least-squares analysis of the k obs versus [P(OMe) 3 ] plot determined a K ) 1.4 ( 0.1 M -1 and a k ) (89 ( 13) × 10 -5 s -1 , such that kK ) 1.2 × 10 -3 M -1 s -1 for the adduct formation. It is unlikely that an actual 20electron species is generated since the η 2 -vinyl ligand can conceivably change its hapticity and function in an η 1 mode.
“…50% yield of C6F5CO2-Me and C6F5H. 176 The compound 215 can be reduced either chemically or electrochemically by one electron CEpc = -2.07 V vs Fc+/Fc) forming the bicycloheptatrienyl dianion 216. 177 In the presence of P(OMe)3, no significant effect on the electrochemistry of 215 has been observed, but precipitation with hexane gives 217, of which the structure has been determined.…”
Section: Lewis Base Addition and Ring Slippage Reactionsmentioning
“…The weighting scheme was M' = l/[a'(F) + 9.7 x lo-, F2]. After applying a secondary extinction correction [ g = 2.9 (9) x final reliability values were obtained, R = 0.040 and R' = 0.056. Final atomic coordinates are summarized in Table 2.…”
The complex [Mo(C,F,) (CO)2(q-C7H,)] can be reduced either chemically or electrochemically by one electron. Electrochemical studies suggest that the reduction is followed by a rapid but reversible structural change. The orange intermediate reduction product has not yet been isolated in pure form. Chemical reduction with sodium amalgam in tetrahydrofuran in the presence of trimethyl phosphite initially forms this orange product, but precipitation with hexane yields the pale yellow zerovalent o-aryl molybdenum complex Na[cis-mer-Mo(C,F,) (CO),{P(OMe),},],in which the cycloheptatrienyl ligand has been displaced by three trimethyl phosphite groups. This complex has been fully characterized by IR, 'H and 31 P N M R spectroscopy and X-ray crystallography.No stable molybdenum(0) a-alkyl or -aryl complexes have been reported. Whereas the other Group 6 transition metals form a variety of anionic [MR(CO),L]-complexes [M = Cr or W; L = CO, PPh,, PMe,, or P(OMe),; R = Me, Et, Ph, CH,Ph, etc.], lP3 the corresponding molybdenum complexes are apparently not stable. The only reported molybdenum(o) complexes containing organic o-carbon-bound ligands are the anionic heptafluoro-1 -methylpropenyl complex, [Mo(CO),-(C,F,)] -,, and the alkynyl complexes [Mo(C=CR)(CO),L] -(L = C O or PPh,, R = Me or Ph).' The only reported X-ray crystal structure of a zerovalent Group 6 o-alkyl or -aryl complex is that of [N(PPh3)2][cis-WMe(CO),(PMe3)].3 We report here the synthesis, characterization and X-ray crystal structure determination of the zerovalent molybdenum 0-perfluoroaryl complex, Na[c~s-rner-Mo(C,F,)(~o),-{P(OMe),),] 2. This compound was synthesised as part of an investigation of the redox chemistry of the cycloheptatrienylmolybdenum complex [ M o ( C , F , ) ( C ~) ~( ~-C ~H 7)] 1. Isoelectronic cylopentadienyliron complexes are known to undergo both oxidatively-and reductively-induced migratory C O inser-tions.6-s An investigation of the oxidative electrochemistry of compound 1 revealed a reversible one-electron oxidation.' However, chemical oxidation in methanol produced an approximately 50% yield of methylpentafluorobenzoate, indicating that some C O insertion did occur after oxidation. This paper presents the results of the reductive electrochemistry of compound 1 and the characterization and X-ray structural analysis of the product resulting from the reaction of the reduced species 1 -with trimethyl phosphite.
Results and DiscussionElectrochemical Reduction of [ Mo( C,F,)( CO),( -C7H,)] 1.-In a previous investigation it was found that complex 1 displayed a chemically and electrochemically reversible oneelectron oxidation at + 0.49 V us. ferrocenium-ferrocene in CH,CI,.' The reductive electrochemistry of this compound is substantially more complicated. In tetrahydrofuran (thf), cyclic voltammetry of compound 1 at a platinum electrode at a scan t Sodium cis-dicarbonyl-mu-(pentafluorophenyl)tris( trimethyl phosphi te)molybdate(o).
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