Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination

In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

Palladium-catalyzed cross-coupling reactions in total synthesis.

Sol-gel chemistry of transition metal oxides

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.

Cascade reactions in total synthesis.

The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels-Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

https://www.ch.ic.ac.uk/local/organic/pericyclic/DA.pdf

The Diels--Alder reaction in total synthesis.

The formation, structure, and decarbonylation of (η-C5H5)2 Rh2(CO)2 {μ-η1,η1-C(O)C2(CF3)2}

Chloro[N,N′-ethylenebis(thiosalicylideneiminato)]iron(III), [Fe(tsalen)Cl], has been prepared by reaction of [Tl2(tsalen)] with anhydrous FeCl3. A crystal-structure determination has revealed the existence of three modifications of the complex. The α form predominates (96%) and contains equal numbers of weakly interacting Fe–S bridged dimer units (type 1 molecules) and monomers (type 2 molecules) with the Fe having a square-based pyramidal distribution of bonds. The β form consists of monomer species alone, while the γ form has weakly interacting dimer units. A variable-temperature magnetic study and Mossbauer spectral measurements on a bulk sample of the complex indicate that the Fe atoms have the intermediate S= spin state.

Iron complexes of N-substituted thiosalicylideneimines. Part 3. Structure, magnetism, and Mössbauer spectra of the complex chloro[N,N′-ethylenebis(thiosalicylideneiminato)]iron(III), an intermediate-spin complex which exists in three crystalline forms

Monomere Tris(η2‐pyrazolato)‐Lanthanoidkomplexe mit dem sterisch anspruchsvollen 3,5‐Di(tert‐butyl)pyrazolatoliganden

The complexes Pt[N(p-HC6F4)CH2CH2NMe2]X(L) (L = py , X = Cl or Br; L = 2- methylpyridine or 4-methylpyridine, X = Cl ) have been prepared by decarboxylation reactions between PtX2( dmen ) ( dmen = N,N- dimethylethane - 1,2-diamine) and thallous pentafluorobenzoate in the appropriate hot pyridine. Other organoamidoplatinum (II) complexes, Pt[N(R)CH2CH2NMe2] X( py ) (R = p-HC6F4, X = I; R = C6F5, X = Cl , Br or I; R = p-MeC6F4, X = Cl ; R = p-ClC6F4 or p-BrC6F4, X = I) and Pt[N(R)CH2CH2NMe2] Cl ( dmpy ) (R = p-HC6F4; dmpy = 2,5-dimethylpyridine), have been prepared by analogous decarboxylations between PtX2( dmen ), thallous 2,3,5,6- tetrafluorobenzoate, and the corresponding polyfluorobenzene, RF. The mixed halogen complex Pt[N(C6F5)CH2CH2NMe2]I0.63Cl0.37( py ) has been prepared similarly and the crystal structure determined. This shows square-planar stereochemistry with the halogen and pyridine trans to NC6F5 and NMe2 respectively. Comparison of spectroscopic data suggests the other complexes have similar stereochemistry.

Organoamidometallics. II. Decarboxylation Syntheses and Structures of [N,N-Dimethyl-N'-(Polyfluorophenyl)Ethane-1,2-Diaminato(1-)]Platinum(II) Complexes

Redox transmetallation ofTl(C5H4PPh2)with an excess of Sm in refluxing thf (thf = tetrahydrofuran) or Eu indme (dme = 1,2-dimethoxyethane) at room temperature gave thelanthanoid(II) compounds[Sm(C5H4PPh2)2](1) and[Eu(C5H4PPh2)2(dme)](2). Crystallization of (1) or[Yb(C5H4PPh2)2(dme)]with OPPh3 in dme yielded[Sm(C5H4PPh2)2(OPPh3)2](3) and[Yb(C5H4PPh2)2(OPPh3)2](4). Room-temperature transmetallation ofTl(C5H4PPh2)with Nd gave the lanthanoid(III) compound[Nd(C5H4PPh2)3(thf)](5), but analogous reactions with La, Pr, Er, Gd and Y in refluxing thfgenerally gave intractable oils, although in one instance impure[La(C5H4PPh2)3(thf)]·(thf)0 · 5,namely(6)·(thf)0 · 5, wasisolated. This complex was also obtained at room temperature by usingLaI3-activated La metal. Oxidation of (1) with 1 equiv.ofTl(C5H4PPh2)in toluene yielded solvent-freeSm(C5H4PPh2)3(7). Addition of OPPh3 to these systems allowed theisolation of[Ln(C5H4PPh2)3(OPPh3)]·(thf)x(x = 0-1 · 5; Ln = La (8), Pr (9),Nd (10), Sm (11), Er (12), Y (13)). Single-crystal X-ray structuredetermination of(10)·(thf)1 · 5,(11)·(thf)1 · 5 and(12)·(thf)1 · 5revealed formally 10-coordinate complexes with an O-bondedOPPh3, threeη5-C5H4PPh2ligands and lattice thf. The centroids of the C5 ringsand the oxygen atom surround the central metal in a distorted tetrahedralarray.

Organolanthanoids. XXI Synthesis of Bis- and Tris-(diphenylphosphinocyclopenta- dienyl)lanthanoid Compounds and the X-Ray Crystal Structures of [Ln(C5H4PPh2)3(OPPh3)]·(thf)1

Bryan M. Gatehouse

Papers

The formation, structure, and decarbonylation of (η-C5H5)2 Rh2(CO)2 {μ-η1,η1-C(O)C2(CF3)2}

Iron complexes of N-substituted thiosalicylideneimines. Part 3. Structure, magnetism, and Mössbauer spectra of the complex chloro[N,N′-ethylenebis(thiosalicylideneiminato)]iron(III), an intermediate-spin complex which exists in three crystalline forms

Monomere Tris(η2‐pyrazolato)‐Lanthanoidkomplexe mit dem sterisch anspruchsvollen 3,5‐Di(tert‐butyl)pyrazolatoliganden

Organoamidometallics. II. Decarboxylation Syntheses and Structures of [N,N-Dimethyl-N'-(Polyfluorophenyl)Ethane-1,2-Diaminato(1-)]Platinum(II) Complexes

Organolanthanoids. XXI Synthesis of Bis- and Tris-(diphenylphosphinocyclopenta- dienyl)lanthanoid Compounds and the X-Ray Crystal Structures of [Ln(C5H4PPh2)3(OPPh3)]·(thf)1