Methine (CH) transfer via a chlorine atom abstraction/benzene-elimination strategy: molybdenum methylidyne synthesis and elaboration to a phosphaisocyanide complex.
20 Mar 2002-Journal of the American Chemical Society (American Chemical Society)-Vol. 124, Iss: 11, pp 2412-2413
TL;DR: This efficient Mo methylidyne synthesis permitted elaboration to an anionic phosphaisocyanide derivative upon deprotonation, functionalization with dichlorophenylphosphine, and ultimate reduction.
Abstract: Methine (CH) transfer to an open coordination site was achieved in one pot by titanium(III) abstraction of Cl from 7-chloronorbornadiene, radical capture by Mo, and benzene extrusion. This efficient Mo methylidyne synthesis permitted elaboration to an anionic phosphaisocyanide derivative upon deprotonation, functionalization with dichlorophenylphosphine, and ultimate reduction.
Citations
More filters
TL;DR: The early years of alkyne metathesis were marked by a somewhat ironic state of affairs: the proposed mechanism was swiftly validated and more than one effective catalyst became available shortly after the discovery of this transformation; surprisingly, however, the impact on synthesis remained very limited for a long period of time.
Abstract: The early years of alkyne metathesis were marked by a somewhat ironic state of affairs: the proposed mechanism was swiftly validated and more than one effective catalyst became available shortly after the discovery of this transformation; surprisingly, however, the impact on synthesis remained very limited for a long period of time. Recent advances, however, suggest that this situation is about to change: the remarkable activity, functional-group tolerance, and reliability of the latest generation of catalysts open the door for highly advanced applications. The resulting (cyclo)alkynes are amenable to numerous postmetathetic transformations, which diversify the product portfolio and bring many different structural motifs into reach. Since the catalysts have also evolved from the glovebox to the benchtop, there should be little barrier left for a wider use of this reaction in organic synthesis.
334 citations
TL;DR: In this paper, the authors survey the rapidly growing field comprising the chemistry of transition metal complexes containing ligands which are made up only of carbon atoms within their coordination spheres, and describe metal complexes which contain linear or cyclic ligands of composition C n (n n n ligands, in order of increasing carbon content of the ligand have been discussed.
Abstract: Publisher Summary This chapter surveys the rapidly growing field comprising the chemistry of transition metal complexes containing ligands which are made up only of carbon atoms within their coordination spheres. The chapter describes metal complexes which contain linear or cyclic ligands of composition C n (n n ligands, in order of increasing carbon content of the ligand have been discussed. This is followed by a discussion on complexes of cyclic all-carbon ligands, such as [C 3 {Fe(CO) 2 Cp} 3 ] + . Complexes containing C n ligands associated with binuclear metal–metal bonded systems are followed by an account of metal cluster complexes containing C n ligands. It also includes hybrid complexes where a cluster supports a C n ligand also attached to a mononuclear metal–ligand fragment. The study is broadly based on a group-by-group approach and includes salient details of synthesis, properties, chemistry and electronic structure.
261 citations
TL;DR: Alkyne metathesis has been studied extensively in the literature as mentioned in this paper, with an emphasis on comparing strengths and weaknesses of different types of catalysts, including two heterogeneous ones.
Abstract: There has been rapid progress and growing interest in alkyne metathesis within the past decade. The availability of highly active catalysts as well as their applications in both organic synthesis and polymer chemistry has served to motivate the advancement of this field. In this article, the development of several different metathesis catalysts, including two heterogeneous ones, are reviewed with an emphasis on comparing strengths and weaknesses. In Section 4, the applications of alkyne metathesis to synthesis of natural products, conjugated polymers as well as shape-persistent macrocycles are discussed. In the last section, a comparison of alkyne metathesis to the well established alkene metathesis is given. Developing an alkyne metathesis catalyst with both high reactivity and robustness to air and moisture remains an unsolved problem of this important and useful reaction.
237 citations
TL;DR: In this article, a new generation of simple methylidene complexes has been prepared by reactions of excited group 4−6 transition metal atoms with methyl halides and methane in solid argon.
194 citations
TL;DR: A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups.
Abstract: A systematic study of alkyne metathesis catalyzed by trialkoxymolybdenum(VI) alkylidyne complexes is reported, in which substrate functional groups, alkynyl substituents, and catalyst ligands are varied. Sterically hindered trisamidomolybdenum(VI) propylidyne complex 5 was prepared conveniently through a previously communicated reductive recycle strategy. Alcoholysis of 5 with various phenols/alcohols provides a set of active catalysts for alkyne metathesis at room temperature, among which the catalyst with p-nitrophenol as ligand shows the highest catalytic activity and is compatible with a variety of functional groups and solvents. A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups. Under reduced pressure using 1,2,4-trichlorobenzene as an involatile solvent, the alkyne metathesis of butynyl substituted compounds proceeds well at 30 °C providing high yields (83%−97%) ...
124 citations
References
More filters
TL;DR: The carbide anion [CMo{N(R)Ar}3] was obtained by deprotonation of the corresponding methylidyne compound, [HCMo{ N(R}3], and was characterized by X-ray diffraction as its {K(benzo-15crown-5)2}+ salt, thereby providing precedent for the carbon atom as a terminal substituent in transition-metal chemistry as discussed by the authors.
129 citations
TL;DR: Besides being a strong reducing agent, carbide [CMo(N[R]Ar)(3)](-) reacts as a nucleophile with elemental chalcogens to form carbon-chalcogen bonds and likewise reacts with PCl(3) to furnish a carbon-phosphorus bond.
Abstract: Anion [CMo(N[R]Ar)_3]- (R = C(CD3)_2CH_3 or tBu, Ar = 3,5-C_6H_3Me_2) containing one-coordinate carbon as a terminal substituent and related molecules have been studied by single-crystal X-ray crystallography, solution and solid-state ^(13)C NMR spectroscopy, and density functional theory (DFT) calculations. Chemical reactivity patterns for [CMo(N[R]Ar)_3]- have been investigated, including the kinetics of proton-transfer self-exchange involving HCMo(N[R]Ar)_3, the carbidomolybdenum anion's conjugate acid. While the Mo⋮C bond lengths in [K(benzo-15-crown-5)_2][CMo(N[R]Ar)_3] and the parent methylidyne, HCMo(N[R]Ar)_3, are statistically identical, the carbide chemical shift of δ 501 ppm is much larger than the δ 282 ppm shift for the methylidyne. Solid-state ^(13)C NMR studies show the carbide to have a much larger chemical shift anisotropy (CSA, 806 ppm) and smaller 95Mo−13C coupling constant (60 Hz) than the methylidyne (CSA = 447 ppm, 1J_MoC = 130 Hz). DFT calculations on model compounds indicate also that there is an increasing MoC overlap population on going from the methylidyne to the terminal carbide. The pKa of methylidyne HCMo(N[R]Ar)_3 is approximately 30 in THF solution. Methylidyne HCMo(N[R]Ar)3 and carbide [CMo(N[R]Ar)3]- undergo extremely rapid proton-transfer self-exchange reactions in THF, with k = 7 × 10^6 M^(-1) s^(-1). Besides being a strong reducing agent, carbide [CMo(N[R]Ar)_3]- reacts as a nucleophile with elemental chalcogens to form carbon−chalcogen bonds and likewise reacts with PCl_3 to furnish a carbon−phosphorus bond.
116 citations
88 citations
TL;DR: In this article, three-coordinate Ti(NRAr)3 [R = C(CD3)2(CH3), Ar = C6H3Me2] was prepared in 73% yield by sodium amalgam reduction of ClTi(NRAR)3 and in 83% yield upon treatment of TiCl3(THF)3 with 3 equiv of Li (NRAr)(OEt2) in the presence of TMEDA.
Abstract: Three-coordinate Ti(NRAr)3 [R = C(CD3)2(CH3), Ar = C6H3Me2] was prepared in 73% yield by sodium amalgam reduction of ClTi(NRAr)3 and in 83% yield upon treatment of TiCl3(THF)3 with 3 equiv of Li(NRAr)(OEt2) in the presence of TMEDA. Ti(tBuNPh)3 was prepared similarly in 75% yield by treatment of TiCl3(THF)3 with 3 equiv of Li(tBuNPh)(OEt2) in the presence of TMEDA. Reaction of Ti(NRAr)3 with NMo(OtBu)3 in hydrocarbon solvents at −35 °C generates a thermally unstable intermediate formulated as (tBuO)3Mo[μ-N]Ti(NRAr)3, which readily loses a tert-butyl radical and isomerizes at 25 °C. Kinetics of the latter process were obtained over the temperature range 20−60 °C; the process exhibits clean first-order behavior. The following activation parameters were obtained: ΔH⧧ = 21.4 ± 0.2 kcal mol-1 and ΔS⧧ = −3.7 ± 0.6 cal mol-1 K-1. The oxo-bridged product (tBuO)2(N)Mo[μ-O]Ti(NRAr)3 was isolated in 83% yield from this reaction. Full characterization of the latter diamagnetic complex included an X-ray crystal struc...
56 citations