Electrophilic fluorination of organoplatinum(II) iodides: iodine and platinum atoms as competing fluorination sites

Fluorination Reactions at a Platinum Carbene Complex: Reaction Routes to SF3 , S(=O)F and Fluorido Complexes

The electron-rich Pt complex [Pt(IMes)2 ] (IMes: [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidine]) can be used as precursor for the syntheses of a variety of fluorido ligand containing compounds. The sulfur fluoride SF4 undergoes a rapid oxidative addition at Pt0 to yield trans-[Pt(F)(SF3 )(IMes)2 ]. A photolytic reaction of SF6 at [Pt(IMes)2 ] in the presence of IMes gave the fluorido complexes trans-[Pt(F)2 (IMes)2 ] and trans-[Pt(F)(SF3 )(IMes)2 ] along with trans-[Pt(F)(SOF)(IMes)2 ] and trans-[Pt(F)(IMes')(IMes)] (IMes': cyclometalated IMes ligand), the latter being products produced by reaction with adventitious water. trans-[Pt(F)(SOF)(IMes)2 ] and trans-[Pt(F)2 (IMes)2 ] were synthesized independently by treatment of [Pt(IMes)2 ] with SOF2 or XeF2 . A reaction of [Pt(IMes)2 ] with a HF source gave trans-[Pt(H)(F)(IMes)2 ], and an intermediate bifluorido complex trans-[Pt(H)(FHF)(IMes)2 ] was identified. Compound trans-[Pt(H)(F)(IMes)2 ] converts in the presence of CsF into trans-[Pt(F)(IMes')(IMes)].

The Versatile Behavior of Platinum Alkyne Complexes towards XeF2 : Formation of Fluorovinyl and Fluorido Complexes

Reactions of platinum(0) tolane complexes, bearing a chelating ligand with P and N donor atoms, with the electrophilic fluorinating agent XeF₂ give facile access to platinum(II) β-fluorovinyl fluorido complexes. A series of new platinum(II) β-fluorovinyl complexes have been synthesized and were structurally characterized. Further oxidation with XeF₂ led to ortho-metalated platinum(IV) fluorido compounds. Additional reactions of platinum(0) tolane complexes, bearing a chelating P,P donor ligand, with XeF₂ led to a variety of fluorido and fluorovinyl complexes.

Electrophilic halogenation-reductive elimination chemistry of organopalladium and -platinum complexes

CONSPECTUS: Transition metal-catalyzed organic transformations often reveal competing reaction pathways. Determining the factors that control the selectivity of such reactions is of extreme importance for the design of reliable synthetic protocols. Herein, we present the account of our studies over the past decade aimed at understanding the selectivity of reductive elimination chemistry of organotransition metal complexes under electrophilic halogenation conditions. Much of our effort has focused on finding the conditions for selective formation of carbon (aryl)-halogen bonds in the presence of competing C-C reductive elimination alternatives. In most cases, the latter was the thermodynamically preferred pathway; however, we found that the reactions could be diverted toward the formation of aryl-iodine and aryl-bromine bonds under kinetic conditions. Of particular importance was to maintain the complex geometry that prohibits C-C elimination while allowing for the elimination of carbon-halogen bonds. This was achieved by employing sterically rigid diphosphine ligands which prevented isomerization within a series of Pt(IV) complexes. It was also important to understand that the neutral M(IV) products often observed or isolated in the oxidative addition reactions are not necessarily the intermediates in the reductive elimination chemistry as it generally takes place from unsaturated species formed en route to relatively stable M(IV) complexes. While aryl-halide reductive elimination for heavier halogens can be competitive with aryl-aryl coupling in diaryl M(IV) complexes, the latter reaction always prevails over aryl-fluoride bond formation. Even when one of the aryl groups is a part of a rigid cyclometalated ligand C-C coupling is still the dominant reaction pathway. However, when one of the aryl groups is replaced with a phenolate donor aryl-F bond formation becomes preferred over C-O bond elimination. During our studies, other interesting reactions have been discovered. For example, the fluorination of the C(sp(3))-H bond can be very selective and compete favorably with C-C coupling. Also, in electron-poor complexes, metal oxidation can have higher energy than oxidation of the coordinated iodo ligand resulting in I-F elimination instead of the formation of aryl-I bond. Overall, electrophilic fluorination can lead to often very selective elimination reactions giving new C-C, C-I, C-F, or I-F bonds, with this selectivity dependent on the metal center, supporting ligands, complex geometry, and electrophilic fluorine source. Together with the many reports on the halogenation of organometallic compounds that appeared in recent years, our results contribute to understanding the requirements for selective transformations under electrophilic conditions and design of new synthetic methods for making organohalogen compounds.

Late-stage fluorination: fancy novelty or useful tool?

Charming fluorine: This Essay examines the recent surge in late-stage fluorination reactions and outlines challenges that need to be overcome to increase the impact of modern fluorination methods on the synthesis of complex organofluorine compounds. It is outlined how an improved understanding of the bonding interactions of fluoride could lead to a new class of mild fluorinating reagents and a range of functional-group-tolerant reactions.

Anion-Dependent Switch in C-X Reductive Elimination Diastereoselectivity

Reaction of a complex Pt organometallic species with electrophilic halogen sources in the presence of X- ligands changes the mechanism of reductive elimination from a concerted reductive coupling type to an SN2 type reductive elimination. In the absence of the added X- ligand the reductive elimination is stereoretentive; in its presence, the process is stereoinvertive. This selectivity hinges on the reactivity of a key five-coordinate Pt(IV) intermediate with the X- ligand.

Unprecedented 1,3-migration of the aryl ligand in metallacyclic aryl α-naphthyl Pt(IV) difluorides to produce β-arylnaphthyl Pt(II) complexes

Electrophilic fluorination of aryl α-naphthyl Pt(II) complexes leads to an unprecedented 1,3-migration of the aryl ligand to the β-position of the naphthyl group. The reaction proceeds via the initial oxidative addition of two fluoro ligands to the Pt center followed by C(sp(2))-C(sp(2)) coupling and aryl migration.

Copper-catalyzed, directing group-assisted fluorination of arene and heteroarene C-H bonds

We have developed a method for direct, copper-catalyzed, auxiliary-assisted fluorination of β-sp(2) C-H bonds of benzoic acid derivatives and γ-sp(2) C-H bonds of α,α-disubstituted benzylamine derivatives. The reaction employs a CuI catalyst, a AgF fluoride source, and DMF, pyridine, or DMPU solvent at moderately elevated temperatures. Selective mono- or difluorination can be achieved by simply changing reaction conditions. The method shows excellent functional group tolerance and provides a straightforward way for the preparation of ortho-fluorinated benzoic acids.

Catalytic enantioselective cyclization and C3-fluorination of polyenes

(Xylyl-phanephos)Pt(2+) in combination with XeF(2) mediates the consecutive diastereoselective cation-olefin cyclization/fluorination of polyene substrates. Isolated yields were typically in the 60-69% range while enantioselectivities reached as high as 87%. The data are consistent with a stereoretentive fluorination of a P(2)Pt-alkyl cation intermediate.