“…A thorough and detailed examination of the reactivity of mono- and binuclear allenyl (−C(H)CCH 2 ) and propargyl (−CH 2 C⋮CH) complexes has revealed a varied and exciting organometallic chemistry for this C 3 fragment . A number of these transformation are particularly relevant to organic synthesis such as the Lewis acid-mediated [3+2] cycloaddition reactions of tungsten propargyl derivatives with aldehydes to give η 1 -2,5-dihydro-3-furyl-based products, the formation of five-, six-, and seven-membered lactone rings via tungsten-promoted cyclocarbonylation reactions, the synthesis of α-methylene butyrolactones via the alkoxycarbonylation of molybdenum and tungsten compounds, the synthesis of indanones and unsaturated carbonyl compounds via oxidative carbonylation of tungsten propargyl derivatives, and the titanium-mediated synthesis of allenyl and homopropargyl alcohols . In addition, the fundamental reactivity of mononuclear η 3 - and binuclear σ−η 2 -coordinated propargyl and allenyl ligands has attracted considerable academic interest, and numerous examples of unusual reactivity patterns have been reported .…”
Nucleophilic addition of tris(dialkylamino) phosphines, P(NR2)3 (R = Me or Et, nPr), to
[Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] (1) affords the dimetallacyclopentene derivatives
[Fe2(CO)6(μ-PPh2)(μ-η1:η1-HCC{P(NR2)3}CH2)] (R = Me, 2a; R = Et, 2b; R = nPr, 2c) or a
mixture of the vinylidene- and dimetallacyclobutene-bridged complexes [Fe2(CO)6(μ-PPh2)(μ-η1-CC(CH3){P(NMe2)3})] (3a) and [Fe2(CO)6(μ-PPh2)(μ-η1:η1-(CH3)CC{P(NMe2)3})] (4a),
respectively, depending upon the reaction conditions. For instance, addition of P(NR2)3 to
an ether solution of [Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] gave the dimetallacyclopentenes 2a−c, whereas pretreatment of a solution of the allenyl starting material with
HBF4 prior to the addition of P(NR2)3 gave the vinylidene- and dimetallacyclobutene-bridged
products, which co-crystallized as a 67:33 mixture, as determined by single-crystal X-ray
crystallography and 1H NMR spectroscopy. We have subsequently shown that the σ−η-allenyl
complex [Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] undergoes a clean and quantitative
acid-promoted rearrangement to the σ−η-acetylide-bridged isomer [Fe2(CO)6(μ-PPh2){μ-η1:η2-C⋮CH3}] (5). 1H NMR and deuterium labeling studies suggest that this isomerization
occurs via initial protonation at Cγ to afford a kinetic intermediate which rapidly rearranges
to its thermodynamically more stable propyne-bridged counterpart followed by deprotonation.
Clearly, the vinylidene and dimetallacyclobutene products isolated from the reaction between
1 and tris(dialkylamino) phosphine in the presence of acid arise from nucleophilic addition
to the α- and β-carbon atoms of the acetylide bridge in [Fe2(CO)6(μ-PPh2){μ-η1:η2-C⋮CCH3}],
and not from nucleophilic addition followed by hydrogen migration. In refluxing toluene,
the dimetallacyclopentenes [Fe2(CO)6(μ-PPh2)(μ-η1:η1-HCC{P(NR2)3}CH2)] slowly decarbonylate to give [Fe2(CO)5(μ-PPh2)(μ-η1:η3-C(H)C{P(NR2)3}CH2)] (R = Me, 6a; R = Et, 6b; R
= nPr, 6c) bridged by a σ−η3-coordinated vinyl carbene. In the case of R = Et and nPr a
competing isomerization also affords the highly unusual zwitterionic α-phosphonium-alkoxide-functionalized σ−σ-alkenyl complex [Fe2(CO)5(μ-PPh2){μ-η1:η2-{P(NR2)3}C(O)CHCCH2}] (R = Et, 7b; R = nPr, 7c), via a P(NR2)3−carbonyl−allenyl coupling sequence. In
contrast, isomerization of dimetallacyclopentene [Fe2(CO)6(μ-PPh2)(μ-η1:η1-HCC{PPh3}CH2)] (8) to its σ−η-alkenyl counterpart [Fe2(CO)5(μ-PPh2){μ-η1:η2-PPh3C(O)CHCCH2}] (9)
is essentially complete within 1 h at room temperature with no evidence for the formation
of the corresponding vinyl carbene. Thermolysis of a toluene solution of 8 in the presence of
excess P(NEt2)3 results in exclusive formation of 7b, whereas at room temperature phosphine
substitution affords 2b, via PPh3−P(NEt2)3 exchange. The isomerization of 8 to 9 and 2b,c
to 7b,c appears to involve a dissociative equilibrium between the kinetic regioisomeric
intermediate dimetallacyclopentene and 1, nucleophilic attack of phosphine at a carbonyl
ligand of 1 to give a zwitterionic acylat...
“…A thorough and detailed examination of the reactivity of mono- and binuclear allenyl (−C(H)CCH 2 ) and propargyl (−CH 2 C⋮CH) complexes has revealed a varied and exciting organometallic chemistry for this C 3 fragment . A number of these transformation are particularly relevant to organic synthesis such as the Lewis acid-mediated [3+2] cycloaddition reactions of tungsten propargyl derivatives with aldehydes to give η 1 -2,5-dihydro-3-furyl-based products, the formation of five-, six-, and seven-membered lactone rings via tungsten-promoted cyclocarbonylation reactions, the synthesis of α-methylene butyrolactones via the alkoxycarbonylation of molybdenum and tungsten compounds, the synthesis of indanones and unsaturated carbonyl compounds via oxidative carbonylation of tungsten propargyl derivatives, and the titanium-mediated synthesis of allenyl and homopropargyl alcohols . In addition, the fundamental reactivity of mononuclear η 3 - and binuclear σ−η 2 -coordinated propargyl and allenyl ligands has attracted considerable academic interest, and numerous examples of unusual reactivity patterns have been reported .…”
Nucleophilic addition of tris(dialkylamino) phosphines, P(NR2)3 (R = Me or Et, nPr), to
[Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] (1) affords the dimetallacyclopentene derivatives
[Fe2(CO)6(μ-PPh2)(μ-η1:η1-HCC{P(NR2)3}CH2)] (R = Me, 2a; R = Et, 2b; R = nPr, 2c) or a
mixture of the vinylidene- and dimetallacyclobutene-bridged complexes [Fe2(CO)6(μ-PPh2)(μ-η1-CC(CH3){P(NMe2)3})] (3a) and [Fe2(CO)6(μ-PPh2)(μ-η1:η1-(CH3)CC{P(NMe2)3})] (4a),
respectively, depending upon the reaction conditions. For instance, addition of P(NR2)3 to
an ether solution of [Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] gave the dimetallacyclopentenes 2a−c, whereas pretreatment of a solution of the allenyl starting material with
HBF4 prior to the addition of P(NR2)3 gave the vinylidene- and dimetallacyclobutene-bridged
products, which co-crystallized as a 67:33 mixture, as determined by single-crystal X-ray
crystallography and 1H NMR spectroscopy. We have subsequently shown that the σ−η-allenyl
complex [Fe2(CO)6(μ-PPh2){μ-η1:η2-(H)CαCβCγH2}] undergoes a clean and quantitative
acid-promoted rearrangement to the σ−η-acetylide-bridged isomer [Fe2(CO)6(μ-PPh2){μ-η1:η2-C⋮CH3}] (5). 1H NMR and deuterium labeling studies suggest that this isomerization
occurs via initial protonation at Cγ to afford a kinetic intermediate which rapidly rearranges
to its thermodynamically more stable propyne-bridged counterpart followed by deprotonation.
Clearly, the vinylidene and dimetallacyclobutene products isolated from the reaction between
1 and tris(dialkylamino) phosphine in the presence of acid arise from nucleophilic addition
to the α- and β-carbon atoms of the acetylide bridge in [Fe2(CO)6(μ-PPh2){μ-η1:η2-C⋮CCH3}],
and not from nucleophilic addition followed by hydrogen migration. In refluxing toluene,
the dimetallacyclopentenes [Fe2(CO)6(μ-PPh2)(μ-η1:η1-HCC{P(NR2)3}CH2)] slowly decarbonylate to give [Fe2(CO)5(μ-PPh2)(μ-η1:η3-C(H)C{P(NR2)3}CH2)] (R = Me, 6a; R = Et, 6b; R
= nPr, 6c) bridged by a σ−η3-coordinated vinyl carbene. In the case of R = Et and nPr a
competing isomerization also affords the highly unusual zwitterionic α-phosphonium-alkoxide-functionalized σ−σ-alkenyl complex [Fe2(CO)5(μ-PPh2){μ-η1:η2-{P(NR2)3}C(O)CHCCH2}] (R = Et, 7b; R = nPr, 7c), via a P(NR2)3−carbonyl−allenyl coupling sequence. In
contrast, isomerization of dimetallacyclopentene [Fe2(CO)6(μ-PPh2)(μ-η1:η1-HCC{PPh3}CH2)] (8) to its σ−η-alkenyl counterpart [Fe2(CO)5(μ-PPh2){μ-η1:η2-PPh3C(O)CHCCH2}] (9)
is essentially complete within 1 h at room temperature with no evidence for the formation
of the corresponding vinyl carbene. Thermolysis of a toluene solution of 8 in the presence of
excess P(NEt2)3 results in exclusive formation of 7b, whereas at room temperature phosphine
substitution affords 2b, via PPh3−P(NEt2)3 exchange. The isomerization of 8 to 9 and 2b,c
to 7b,c appears to involve a dissociative equilibrium between the kinetic regioisomeric
intermediate dimetallacyclopentene and 1, nucleophilic attack of phosphine at a carbonyl
ligand of 1 to give a zwitterionic acylat...
“…A little water (1.0−2.0 equiv) is a prerequisite for this syn stereoselection. The syn isomer of 9 was characterized by an X-ray diffraction study. , The effect of the α-( tert -butyl)dimethylsilyl group on syn stereoselectivity deserves attention. As depicted in Scheme , we monitored the CF 3 SO 3 H/H 2 O acidification of an α-silyloxy η 1 -propargyl complex in proton NMR experiments (−40 °C, CDCl 3 ).…”
Section: Resultsmentioning
confidence: 99%
“…X - ray Diffraction Studies of 14 , 50, and 53. Crystal data and data collection of 9 , 18 , 19 , 24 , and 27 have appeared in the communication of this article; they will not be reported here. Single crystals of 14 , 50 , and 53 were sealed in glass capillaries under an inert atmosphere.…”
Section: Methodsmentioning
confidence: 99%
“…Crystal data, ORTEP drawing, and structure factors of compounds 9 , 18 , 19 , 24, and 27 have appeared in the communication of this work; these repetitive data will not be reported in this article.…”
Intramolecular alkoxycarbonylation of tungsten-propargyl compounds proceeds with excellent diastereoselectivities to form η 3 -δ-and --lactones but for γ-lactones. With OSi(t-Bu)Me 2 substituted for an R-hydroxy group , η 3 -γ-lactones are stereoselectively formed with syn stereoselection . An optically active tungsten η 3 -γ-lactone is prepared from D-(+)-xylose to illustrate the stereochemical effect of OSi(t-Bu)Me 2 . All these η 3 -γ-, -δ-, and --lactones are converted to allyl anions that react in situ with aldehydes and ketones to produce various β-(hydroxylalkyl)-R-methylene-γ-lactones with good diastereoselectivity. This reaction is also applied to the synthesis of chiral R-methylene butyrolactones. Organic carbonyls add to the π-allyl groups of η 3 -γ-and -δ-lactones opposite the tungsten fragment, whereas additions occur from the metal side for η 3 --lactones. The stereochemical courses of these reactions are discussed in detail. These two tungsten-promoted reactions efficiently effect stereoselective transformation of chloroalkynols to complex R-methylene-γ-lactones, which are useful materials for syntheses of trisubstituted 1,3-, 1,4-, and 1-5-diols.
“…Acid-promoted intramolecular alkoxycarbonylations of tungsten−η 1 -propargyl complexes 1 − 3 led to formation of η 3 -γ, η 3 -δ-, and η 3 -ε-lactones 4 − 6 in good yields; , the reaction involved the tungsten−η 2 -allene cationic intermediates A . − Among these cyclizations, δ- and ε-lactones 5 and 6 followed anti and syn stereoselections 1,2 respectively, whereas the η 3 -γ-lactone 4 was formed in 1:1 diastereomeric mixtures. , The selectivity problem of 4 can be circumvented by introduction of a dimethyl- tert -butylsiloxy group on these η 1 -propargyl species such as 7 (Scheme , path 2), leading to syn stereoselection of η 3 -γ-lactone 4 ; , the reaction requires small amounts of H 2 O and CF 3 SO 3 H (optimum conditions: H 2 O, 0.8−1.0 equiv; CF 3 SO 3 H, 0.30 equiv). The overall reaction is shown in path 2 of Scheme ; the proposed formation mechanism of syn η 3 -γ-lactones 4 is supported by results obtained from isotopic H 2 O* (O* = 18 O) labeling as well as by isolation of the key η 3 -2-carboxyallyl intermediate. , To study thoroughly the drastic impact of the siloxy group, we report here a new cyclization of these propargyl complexes with alteration of their tethered siloxy groups. 1 …”
Treatment of tungsten-η 1 -4-(triethylsiloxy)propargyl and η 1 -4-(tripropylsiloxy)propargyl compounds 8a-d and 9a-d with CF 3 CO 2 H in cold CH 2 Cl 2 yielded a mixture of tungsten η 1 -2,5-dihydrofurans 10a-d and η 3 -syn-γ-lactones 4a-d. The product ratios depend on the types of alkyl and siloxy substituents of the propargyl ligand; η 1 -2,5-dihydrofurans 10a-d were formed in significant amount when the substituent is a secondary alkyl group. This cyclization pathway is in sharp contrast to our previous report that the dimethyl-tertbutylsiloxy group yielded only η 3 -syn-γ-lactones 4a-d. To validate this reaction on a complex system, we prepared the chiral tungsten-η 1 -4-(triethylsiloxy)propargyl species 12b, which ultimately gave optically active tungsten η 1 -2,5-dihydrofuran 13 in 68% yields. In connection with our previous report, we elaborated three types of cyclization reactions on chiral tungsten η 1 -propargylic triols 12a-c, to afford chiral η 1 -2,5-dihydrofurans and unsaturated γ-and δ-lactones in reasonable yields.
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