Abstract:UV irradiation of the cycloheptadienyl complexes [(η 5 -C 7 H 8 R)Cr(CO) 3 SnPh 3 ] (1a, R ) H; 1b, R ) C(Me)S(CH 2 ) 3 S; 1c, R ) CHPh 2 ) or cyclohexadienyl complexes [(η 5 -C 6 H 6 R)Cr(CO) 2 -(NO)] (7, R ) C(Me)S(CH 2 ) 3 S) and 2 equiv of 2-butyne or 3-hexyne in toluene or n-hexane gave new tricyclic complexes 2, 5, and 8. These complexes arise from sequential [5 + 2] and homo[5 + 2] cycloadditions of two alkyne molecules to the η 5 -dienyl manifold forming 11-alkylidenetricyclo[5.3.1.0 4,10 ]undeca-2,5-d… Show more
“…General experimental details are described elsewhere and complexes 3k and 3l 19 were prepared using the literature procedures.…”
Section: Methodsmentioning
confidence: 99%
“…In an earlier study, Ernst and co-workers reported the reaction of PhC⋮CSiMe 3 with a dienyl titanium complex that also appears to proceed via an initial metal-promoted [5 + 2] cycloaddition . Very recently, we reported the [5 + 2], homo [5 + 2] double addition of alkynes to both cycloheptadienyl(triarylstannyl)- and cyclohexadienyl(nitrosyl) chromium manifolds (Scheme ) 1 [6 + 2] Additions of Alkynes to Trienes Mediated by Chromium Complexes 2 Chromium Mediated Cycloheptadienyl−Alkyne Coupling …”
UV irradiation of the cyclohexadienyl complex
[(η5-C6H7)Mn(CO)3]
(1) and 1 or 2 equiv of
the alkynes PhC⋮CR (R = H, Me, Ph) in toluene gave both the [5 +
2] adducts
[{η2: 3-C8H7Ph(R)}Mn(CO)3] (2) and the
tricyclic [5 + 2],homo[5 + 2] double adducts
[(η1:2:2-C10H7Ph2R2)Mn(CO)3] 3a−d. The
reactions involve sequential metal-mediated alkyne
cycloadditions,
first across the η5-dienyl ligand and then across the
resulting olefin−allyl manifolds. Reaction
of the monoadducts 2 with an additional equivalent of
2-butyne or 1-phenyl-1-propyne gave
the mixed double adducts 3e−j. The THF
complex
[(η5-C6H7)Mn(CO)2(THF)]
(4) reacted
thermally with 1-phenyl-1-propyne to form both types of adducts
2 and 3, indicating the
role of UV light is to generate a coordinatively unsaturated metal
center by CO ejection.
Photolysis of 1 and dimethyl acetylenedicarboxylate
gave the organic double adduct 1,2,3,10-tetrakis(methoxycarbonyl)tricyclo[5.2.1.04,9]deca-2,5-diene
(5a), whereas protonation of
3a,c using
HBF4·Et2O gave the analogous organic
tricyclodienes 5b,c. Reaction of
the
adducts
[(η1:2:2-C10H7R4)Mn(CO)3]
(3a, 3k R = Me; 3l R = Et) with
carbon monoxide (200
psi; 100 °C) gave new CO insertion products
6a−c. The single addition product
2c, the
double adducts 3a and 3j, and the CO insertion
products 6b,c have been characterized
by
X-ray diffraction studies.
“…General experimental details are described elsewhere and complexes 3k and 3l 19 were prepared using the literature procedures.…”
Section: Methodsmentioning
confidence: 99%
“…In an earlier study, Ernst and co-workers reported the reaction of PhC⋮CSiMe 3 with a dienyl titanium complex that also appears to proceed via an initial metal-promoted [5 + 2] cycloaddition . Very recently, we reported the [5 + 2], homo [5 + 2] double addition of alkynes to both cycloheptadienyl(triarylstannyl)- and cyclohexadienyl(nitrosyl) chromium manifolds (Scheme ) 1 [6 + 2] Additions of Alkynes to Trienes Mediated by Chromium Complexes 2 Chromium Mediated Cycloheptadienyl−Alkyne Coupling …”
UV irradiation of the cyclohexadienyl complex
[(η5-C6H7)Mn(CO)3]
(1) and 1 or 2 equiv of
the alkynes PhC⋮CR (R = H, Me, Ph) in toluene gave both the [5 +
2] adducts
[{η2: 3-C8H7Ph(R)}Mn(CO)3] (2) and the
tricyclic [5 + 2],homo[5 + 2] double adducts
[(η1:2:2-C10H7Ph2R2)Mn(CO)3] 3a−d. The
reactions involve sequential metal-mediated alkyne
cycloadditions,
first across the η5-dienyl ligand and then across the
resulting olefin−allyl manifolds. Reaction
of the monoadducts 2 with an additional equivalent of
2-butyne or 1-phenyl-1-propyne gave
the mixed double adducts 3e−j. The THF
complex
[(η5-C6H7)Mn(CO)2(THF)]
(4) reacted
thermally with 1-phenyl-1-propyne to form both types of adducts
2 and 3, indicating the
role of UV light is to generate a coordinatively unsaturated metal
center by CO ejection.
Photolysis of 1 and dimethyl acetylenedicarboxylate
gave the organic double adduct 1,2,3,10-tetrakis(methoxycarbonyl)tricyclo[5.2.1.04,9]deca-2,5-diene
(5a), whereas protonation of
3a,c using
HBF4·Et2O gave the analogous organic
tricyclodienes 5b,c. Reaction of
the
adducts
[(η1:2:2-C10H7R4)Mn(CO)3]
(3a, 3k R = Me; 3l R = Et) with
carbon monoxide (200
psi; 100 °C) gave new CO insertion products
6a−c. The single addition product
2c, the
double adducts 3a and 3j, and the CO insertion
products 6b,c have been characterized
by
X-ray diffraction studies.
“…[1] Despite the potential utility of this reaction, a substantial number of unresolved mechanistic issues remain. The [5+2] cycloaddition of alkynes with h 5 -pentadienyl complexes [2] has not been examined computationally; in this class of cycloadditions, only the rhodium-catalyzed coupling of vinylcyclopropanes with p-systems has so far been studied by computational methods. [3] Early pentadienyl/alkyne coupling processes were hampered by poor yields and/or selectivities, mostly due to uncontrolled insertion of multiple alkyne units.…”
Alkyl-substituted η(5)-pentadienyl half-sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η(2),η(3)-cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η(5)-cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, C-C bond formation, olefin arm capture, and a second C-C bond formation; the initial decoordination/capture step is rate-limiting. Once the η(2),η(3)-cycloheptadienyl complex has been formed, isomerization to η(5)-cycloheptadienyl again involves several steps: olefin decoordination, β-hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1- and 5-positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3-position have a strongly retarding effect on the same step. Substituents at the alkyne (2-butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive.
“…[20Ϫ23] Also, photo-assisted cycloadditions of alkynes to η 5 -dienyl ligands have been reported by us [24Ϫ28] and others. [29,30] In this respect, the role of cumulenes and heterocumulenes as partners in transition-metal-promoted cycloadditions has so far been described only in a few papers. [31,32] In the following we will discuss our studies upon the reactions of photochemically generated dicarbonyl(η 5 -2,4-cyclohexadienyl)(tetrahydrofuran)manganese (2) with selected 1,1-disubstituted cumulenes.…”
[Mn(η5‐C6H7)(CO)3] (1) forms highly reactive [Mn(η5‐C6H7)(CO)2(THF)] (2) upon UV irradiation in THF at 208 K. Solvent complex 2 reacts between 208 and 293 K with 1,1‐disubstituted allenes C3H2RR′ [R, R′ = CH3, CH3 (A); CH3, C6H5 (B); C2H5, C6H5 (C); C6H5, C6H5 (D); OCH3, Si(CH3)3 (E)] to four different types of complexes: The [5+2] cycloadduct [Mn(η3:2‐C9H9RR′)(CO)3] (3E), rearranged [5+2] cycloadducts [Mn(η3:2‐C9H9RR′)(CO)3] (4B, 4C, 4D), 1:2 adducts [Mn(η3:2‐C12H11R2R′2)(CO)3] (5A–5E), and the 1:3 adduct [Mn{η3:2:2‐C15H13(CH3)6}(CO)2] (6A). The constitutions of the products were established by IR and NMR spectroscopy, as well as by C,H elemental analysis and mass spectrometry. The crystal and molecular structure of 6A was determined by X‐ray structure analysis. A formation mechanism for the complexes is proposed.
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