Abstract:The protonation of the iridapyrrole complex
allows the isolation of the two possible stereoisomers of the chelating Ir(III) alkylidene
(2; Ar‘ = 3,5-C6H3(CF3)2). They undergo easy
and reversible hydride migration onto the electrophilic
carbene atom.
“…Examples of reversible 1,2-H shifts, although known, are still rare . However, in addition to the F ⇌ 2 equilibrium of Scheme , and eq 2, we have found a number of reversible α-H elimination reactions in our studies on the migratory insertion reactions of iridium carbenes. ,,14c, 3 …”
Benzene solutions of the unsaturated fragment TpMe2Ir(C6H5)2 (1), generated in situ from either TpMe2Ir(C2H4)2 or TpMe2Ir(C6H5)2(N2), react with methyl ethers MeOBut, MeOBun, and MeOCH2CH2OMe to
give the organometallic hydride carbene products TpMe2(H)2(C(H)OR) 4 (R = But, 4a; Bun, 4b; CH2CH2OMe, 4c) along with benzylic ethers C6H5CH2OR 5. The overall reaction is very complex and involves
the participation of two molecules of the ether, MeOR, and one of benzene per molecule of the iridium
precursor. The latter induces multiple C−H bond cleavage along with the formation of a new C−C
bond. Hydride carbenes of composition TpMe2Ir(H)(C6H5)(C(H)OR) (2) are early intermediates of this
reaction. They can be shown to undergo a reversible 1,2-H shift between the metal atom and the carbene
carbon atom, until eventually β-H elimination from the Ir−C6H5 unit allows the C−C coupling through
a nonisolable benzyne intermediate. Me−OR bond cleavage, although somewhat more energetically
demanding than C−H activation, can also occur and has been demonstrated in the reaction of 1 with
Me−OBun, which permits the isolation of the hydride n-propyl carbonyl complex TpMe2Ir(H)(CH2CH2CH3)(CO), 10b.
“…Examples of reversible 1,2-H shifts, although known, are still rare . However, in addition to the F ⇌ 2 equilibrium of Scheme , and eq 2, we have found a number of reversible α-H elimination reactions in our studies on the migratory insertion reactions of iridium carbenes. ,,14c, 3 …”
Benzene solutions of the unsaturated fragment TpMe2Ir(C6H5)2 (1), generated in situ from either TpMe2Ir(C2H4)2 or TpMe2Ir(C6H5)2(N2), react with methyl ethers MeOBut, MeOBun, and MeOCH2CH2OMe to
give the organometallic hydride carbene products TpMe2(H)2(C(H)OR) 4 (R = But, 4a; Bun, 4b; CH2CH2OMe, 4c) along with benzylic ethers C6H5CH2OR 5. The overall reaction is very complex and involves
the participation of two molecules of the ether, MeOR, and one of benzene per molecule of the iridium
precursor. The latter induces multiple C−H bond cleavage along with the formation of a new C−C
bond. Hydride carbenes of composition TpMe2Ir(H)(C6H5)(C(H)OR) (2) are early intermediates of this
reaction. They can be shown to undergo a reversible 1,2-H shift between the metal atom and the carbene
carbon atom, until eventually β-H elimination from the Ir−C6H5 unit allows the C−C coupling through
a nonisolable benzyne intermediate. Me−OR bond cleavage, although somewhat more energetically
demanding than C−H activation, can also occur and has been demonstrated in the reaction of 1 with
Me−OBun, which permits the isolation of the hydride n-propyl carbonyl complex TpMe2Ir(H)(CH2CH2CH3)(CO), 10b.
“…The process is reversible, and deprotonation of 682 can happen in the presence of K 2 CO 3 . 109,494 Such a regioselective protonation has also been described for metallafurans in section 4.3.1.…”
Section: Reactivities Of Metallabenzynesmentioning
confidence: 84%
“…The reaction of 681 with HBAr′ 4 (Ar′ = 3,5-C 6 H 3 (CF 3 ) 2 ) gave 682 , as a result of protonation at the β-position of the iridium center. The process is reversible, and deprotonation of 682 can happen in the presence of K 2 CO 3 . , Such a regioselective protonation has also been described for metallafurans in section .…”
Since the prediction of the existence
of metallabenzenes in 1979,
metallaaromatic chemistry has developed rapidly, due to its importance
in both experimental and theoretical fields. Now six major types of
metallaromatic compounds, metallabenzenes, metallabenzynes, heterometallaaromatics,
dianion metalloles, metallapentalenes and metallapentalynes (also
termed carbolongs), and spiro metalloles, have been reported and extensively
studied. Their parent organic analogues may be aromatic, non-aromatic,
or even anti-aromatic. These unique systems not only enrich the large
family of aromatics, but they also broaden our understanding and extend
the concept of aromaticity. This review provides a comprehensive overview
of metallaaromatic chemistry. We have focused on not only the six
major classes of metallaaromatics, including the main-group-metal-based
metallaaromatics, but also other types, such as metallacyclobutadienes
and metallacyclopropenes. The structures, synthetic methods, and reactivities
are described, their applications are covered, and the challenges
and future prospects of the area are discussed. The criteria commonly
used to judge the aromaticity of metallaaromatics are presented.
“…A preferable alternative mode of decomposition of intermediate 27 would involve an α-H shift to give the Pt(IV) carbene hydride species 28 . Formation of 1e would then simply require reductive elimination of Me 3 N, while 25 would result from elimination of HCl.…”
Reaction, in chloroform solution, of (COD)Pt(CH 2 Cl)Cl (5) with Me 2 NCH 2 NMe 2 in the presence of 1 equiv (vs 5) of a monodentate ligand L (L ) Ph 3 P, (p-MeOC 6 H 4 ) 3 P, (p-FC 6 H 4 ) 3 P, Et 3 P, Ph 3 As) gives the (dimethylamino)carbene complexes cis-[LPt(CHNMe 2 )Cl 2 ] (1a-e) via the cyclic ylide intermediates [LPt(CH 2 NMe 2 CH 2 NMe 2 )Cl]Cl (2a-e). Major byproducts of the reaction are the (trimethylammonio)methyl ylide complexes cis-[LPt(CH 2 NMe 3 )Cl 2 ] (11a-e). With L ) Ph 3 As, carbene product 1e is accompanied by a second carbene complex, trans(As,CH 2 )-[(Ph 3 As)Pt(CHNMe 2 )(CH 2 NHMe 2 )Cl]Cl (25). When the reaction with L ) Ph 3 P is carried out in acetonitrile, the amide chelate [(Ph 3 P)Pt(CH 2 CH 2 CONMe 2 )Cl] (24) is formed in addition to 1a and 11a. A deuterium labeling experiment indicates that formation of 24 involves condensation of a CH 2 Cl (or derived) moiety with a molecule of solvent. The structures of complexes 11a and 24, and of the hexafluorophosphate analogue (26) of complex 25, have been confirmed by X-ray crystallographic analyses. Carbene complex 1a, along with other products, is also obtained upon reaction of 5 and Ph 3 P (1:1) with dimethylamine. Formation of 1a in this case can proceed via two pathways, one involving cyclic ylide species 2a as intermediate and the other the N-protonated (dimethylamino)methyl complex cis-[(Ph 3 P)Pt(CH 2 NHMe 2 )Cl 2 ] (20). The mechanistic pathways involved in formation of carbene complexes 1a-e and 25, ylide complexes 2a-e and 11a-e, and (dimethylamino)methyl complex 20 are discussed. It is suggested that formation of the ylide complexes and 20 proceeds via initial attack of amine at platinum and that carbene formation proceeds via platinum(IV) carbene hydride intermediates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
