Abstract:Irradiation of Tp‘(CO)3WH in the presence of
alkynes or unconjugated dienes generates
η3-allyl complexes,
Tp‘(CO)2W(η3-CHRCHCHR‘). A
kinetic preference for anti-alkyl substitution due to η2-vinyl intermediates exists for the
reactions with terminal alkyne substrates.
The monoalkyl-substituted allyl complexes are configurationally
stable on the NMR time
scale but show a thermodynamic preference for
syn-substitution upon heating in solution.
Separate crystal structures of the syn and anti
isomers of the 1-methyl… Show more
“…The interdependence between the OC-M-CO angle and the orientation of the allyl ligand in tris(pyrazolyl)borate tungsten allyl dicarbonyl species has been studied by Templeton and coworkers by using extended Hückel molecular orbital (EHMO) calculations on a model complex. [10] The adoption of the allyl-rotated configuration in 1·BAr' 4 can be attributed to the steric hindrance between the methyl group of the h 3 -methallyl group and the C À H groups of [9]aneS 3 , which would occur in a normal, nonrotated structure such as in 2·BAr' 4 . Steric interactions have been deemed responsible of the observed allyl orientations in complexes with substituted allyl groups.…”
The labile complex [MoCl(η3‐methallyl)(CO)2(NCMe)2] reacts with the ligand 1,4,7‐trithiacyclononane ([9]aneS3) and the salt NaBAr′4 to afford [Mo(η3‐methallyl)(CO)2([9]aneS3)][BAr′4] (1⋅BAr′4). An analogous reaction of [MoBr(η3‐allyl)(CO)2(NCMe)2] yields [Mo(η3‐allyl)(CO)2([9]aneS3)][BAr′4] (2⋅BAr′4). The new compounds 1⋅BAr′4 and 2⋅BAr′4 were characterized by IR and NMR spectroscopic analysis and X‐ray diffraction studies. Both compounds feature the cyclic thioether [9]aneS3 coordinated as a tridentate ligand to the molybdenum center. The allyl ligand in 2⋅BAr′4 is aligned with the middle of the OC‐Mo‐CO angle, which is acute. Both of these features are typical of most pseudo‐octahedral allyl dicarbonyl molybdenum complexes. In contrast, the allyl group is rotated in 1⋅BAr′4, which is attributed to steric hindrance between the methyl substituent and the ligated thioether, and the OC‐Mo‐CO angle is obtuse. Compound 1⋅BAr′4 undergoes rapid substitution of [9]aneS3 by either chloride and fluoride ions in dichloromethane, and the products include the known species [{Mo(η3‐methallyl)(CO)2}2(μ‐Cl)3]− and a structurally similar new anionic complex with two fluoro and one hydroxo bridging ligands, respectively. Stable supramolecular adducts were formed in the reactions of 1⋅BAr′4 and 2⋅BAr4 with bromide, iodide, hydrogensulfate, and methanesulfonate compounds. The binding constants of these adducts in dichloromethane were calculated from 1H NMR spectroscopic titration data, and the solid‐state structures of the 1⋅Br, 1⋅HSO4, 1⋅I, and 2⋅I adducts were determined by X‐ray diffraction studies. The surprising slightly higher stability of the iodide adduct relative to that of bromide was investigated theoretically, with the results pointing to an effect of the differential solvation of the halide ions.
“…The interdependence between the OC-M-CO angle and the orientation of the allyl ligand in tris(pyrazolyl)borate tungsten allyl dicarbonyl species has been studied by Templeton and coworkers by using extended Hückel molecular orbital (EHMO) calculations on a model complex. [10] The adoption of the allyl-rotated configuration in 1·BAr' 4 can be attributed to the steric hindrance between the methyl group of the h 3 -methallyl group and the C À H groups of [9]aneS 3 , which would occur in a normal, nonrotated structure such as in 2·BAr' 4 . Steric interactions have been deemed responsible of the observed allyl orientations in complexes with substituted allyl groups.…”
The labile complex [MoCl(η3‐methallyl)(CO)2(NCMe)2] reacts with the ligand 1,4,7‐trithiacyclononane ([9]aneS3) and the salt NaBAr′4 to afford [Mo(η3‐methallyl)(CO)2([9]aneS3)][BAr′4] (1⋅BAr′4). An analogous reaction of [MoBr(η3‐allyl)(CO)2(NCMe)2] yields [Mo(η3‐allyl)(CO)2([9]aneS3)][BAr′4] (2⋅BAr′4). The new compounds 1⋅BAr′4 and 2⋅BAr′4 were characterized by IR and NMR spectroscopic analysis and X‐ray diffraction studies. Both compounds feature the cyclic thioether [9]aneS3 coordinated as a tridentate ligand to the molybdenum center. The allyl ligand in 2⋅BAr′4 is aligned with the middle of the OC‐Mo‐CO angle, which is acute. Both of these features are typical of most pseudo‐octahedral allyl dicarbonyl molybdenum complexes. In contrast, the allyl group is rotated in 1⋅BAr′4, which is attributed to steric hindrance between the methyl substituent and the ligated thioether, and the OC‐Mo‐CO angle is obtuse. Compound 1⋅BAr′4 undergoes rapid substitution of [9]aneS3 by either chloride and fluoride ions in dichloromethane, and the products include the known species [{Mo(η3‐methallyl)(CO)2}2(μ‐Cl)3]− and a structurally similar new anionic complex with two fluoro and one hydroxo bridging ligands, respectively. Stable supramolecular adducts were formed in the reactions of 1⋅BAr′4 and 2⋅BAr4 with bromide, iodide, hydrogensulfate, and methanesulfonate compounds. The binding constants of these adducts in dichloromethane were calculated from 1H NMR spectroscopic titration data, and the solid‐state structures of the 1⋅Br, 1⋅HSO4, 1⋅I, and 2⋅I adducts were determined by X‐ray diffraction studies. The surprising slightly higher stability of the iodide adduct relative to that of bromide was investigated theoretically, with the results pointing to an effect of the differential solvation of the halide ions.
“…Similar behavior was seen for the molybdenum analogue. The η 2 -vinyl complexes slowly rearrange to stable η 3 -allyl products in nonaromatic solvents 1
Chloride displacement from
Tp‘(CO)2M⋮CCl (M = Mo, W (1); Tp‘ =
hydridotris(3,5-dimethylpyrazolyl)borate) with LiMe2Cu affords the
methylcarbyne complex
Tp‘(CO)2M⋮CCH3
(M = Mo (2), W (3)). Deprotonation of this
methylcarbyne forms
[Tp‘(CO)2M=CCH2]-
(M
= Mo, W (4)), a nucleophilic vinylidene anion which reacts
with a variety of substrates.
Reaction of 4 with CH3I yields
Tp‘(CO)2W⋮CCH2CH3
(5), while PhC(O)H yields
Tp‘(CO)2W⋮CCH2CH(OH)(Ph) (8) and
PhC(O)CH3 yields
Tp‘(CO)2W⋮CCH2C(OH)(CH3)(Ph)
(10). In
the presence of base complex 8 undergoes elimination to form
a conjugated vinyl carbyne
complex Tp‘(CO)2W⋮CCHCH(Ph) (11).
Reaction of 4 with PhC(O)Cl and then base
forms
Tp‘(CO)2W⋮CCH2C(O)Ph
(14), which rearranges in solution to a metallafuran
complex,
(15).
Spectroscopic data suggests that a dinuclear intermediate,
Tp‘(CO)2W⋮CCH2CPh(OH)CH2C⋮W(CO)2Tp‘
(13), is first formed from 4 and
PhC(O)Cl before
the addition of base produces the expected monomeric product,
Tp‘(CO)2W⋮CCH2C(O)Ph
(14).
“…The terminal proton in the opposite rotamer ( 3a ‘) was located at 12.87 (Chart ). The preferential location of ligand aryl substituents near the aromatic pyrazole rings is a well-documented feature of tris(pyrazolyl)borate W(II) and Mo(II) complexes. ,− 1 Nomenclature for Alkyne Termini 2 Representative Chemical Shifts for Terminal Alkyne Protons…”
Section: Resultsmentioning
confidence: 99%
“…Group VI transition-metal complexes with four-electron-donor (4e - ) alkyne ligands possess a rich and varied chemistry . Nucleophilic addition to cationic 4e - -donor alkyne complexes is known to produce η 2 -vinyl, η 3 -allyl, and carbyne complexes. − The propargyl site of 4e - -donor alkynes in neutral Tp‘(CO)(I)W(RC⋮CR‘) complexes can be regioselectively deprotonated and alkylated to form new alkyne derivatives . The production of cycloalkynes from intramolecular alkylation has recently been realized using this route .…”
Extended reflux of Tp′(CO)(I)W(RCtCR′) (Tp′ ) hydridotris(3,5-dimethylpyrazolyl)borate) complexes in ethyl acetate in the presence of silver cyanide produces Tp′(CO)(CN)W(RCt CR′) complexes in moderate to high yields. A single-crystal X-ray structure of Tp′(CO)-(CN)W(PhCtCMe) shows that the alkyne is aligned parallel to the M-CO axis. Electrophilic attack at the nitrogen of the cyanide ligand with methyl triflate or triflic acid yields cationic isocyanide complexes, whereas attack with HBF 4 results in neutral BF 3 adduct complexes. Coordination of the Tp′(CO)(PhCtCMe)W + fragment to the cyanide nitrogen of Tp′(CO)-(CN)W(HCtCBu n ) to form a CN-bridged dinuclear complex has been achieved. Variabletemperature 1 H NMR measurements reflect acetylene rotation barriers in the Tp′(CO)(L)W-(HCtCH) n+ series (L ) CO, CNH, CNMe {n ) 1}; CN -, CNBF 3 -{n ) 0}) and, thus, quantify π-effects for the cyanide and isocyanide ligands with respect to steric considerations. Extended Hu ¨ckel molecular orbital calculations were carried out on a series of model complexes, [H 3 (CO)(L)W(HCtCH)] n-(L ) CO, CNH {n ) 1}; CN -, H -{n ) 2}) to augment the experimental data.
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