Anders Lennartson

A Different Approach to Enantioselective Organic Synthesis: Absolute Asymmetric Synthesis of Organometallic Reagents†

Voilà, optical activity: Both enantiomers of 1-chloroindene have been synthesized in high selectivity from solely achiral starting materials, and without using optically active catalysts (see scheme). These symmetry-breaking syntheses provide a proof-of-concept for a new approach to asymmetric synthesis. NCS=N-chlorosuccinimide.

An Iron(III) Iodosylbenzene Complex: A Masked Non‐Heme FeVO

Iodosylarenes are an important class of oxygen atom transfer reagents in organic synthesis, and they are often used in conjunction with transition-metal-based catalysts. These are most commonly iron and manganese porphyrin, Mn-corrole, Mn-corrolazinato, 14] and Mn-salen complexes, and even cytochrome P450. Hypervalent metal– oxo complexes that relay the oxygen atom from the iodosylarene donor to the substrate acceptor are most commonly invoked as the active oxidants in these catalytic mechanisms. Accordingly iodsosylarenes have been used in the preparation of hypervalent metal–oxo complexes. No metal-complexed iodosylarene has been structurally characterized in the solid state; however, the isolation of a reactive iodosylbenzene complex of Mn-porphyrin was reported nearly 30 years ago. Oxygen atom transfer from iodosylarenes to LM complexes give the corresponding LMO species (or LCMO if the ligand is non-innocent, for example when L = porphyrin) [Equation (1), steps i + ii]. Occasionally, intervening transient species assigned to metal–iodosylarene adducts have been spectroscopically identified in these types of reactions. More or less unstable MnO porphyrin and salen 18,19] systems, CrO, [(porphC)FeO] systems, and [FeO(tmc)] (tmc = tetramethylcyclam) have been accessed by oxygen atom transfer from iodosylbenzene to the appropriate Mn, Cr, Fe, and Fe precursors respectively. Recently, a novel CoO solution species was generated at 60 8C by the reaction of 2-(tert-butylsulfonyl)iodosylbenzene with [Co(TMG3tren)(OTf)] . Nam et al. have demonstrated the back-reaction of the equilibrium ii in Equation (1) by formation of a spectrosopically detected species assigned to [(porph)Fe(OIPh)] from the reaction of [(porphC)FeO] with iodobenzene.

Four-site cooperative spin crossover in a mononuclear Fe(II) complex.

Round and round: A mononuclear Fe(II)  complex (see picture) with an N(4)S(2) coordination set has been characterized in four polymorphic forms. Two of the polymorphs display four-site cooperative spin crossover (SCO), shown conclusively by the crystal structure of a fully ordered 1:3 high-spin/low-spin state. The presence of S donor atoms in SCO-active compounds is unusual, and further investigation of Fe(II)  complexes for SCO activity is warranted.

Total Spontaneous Resolution of Five‐Coordinate Complexes

Talking about a resolution: Bulk quantities of five-coordinate complexes have been resolved for the first time using zinc and cadmium diethyldithiocarbamate species. The stereochemical outcome can be controlled by seeding with the desired isomer, giving access to either enantiomer in high enantiomeric excess and yield.

cis- and trans-Bis(benzoylacetonato)pyridinecopper(II): co-crystallisation of isomers and reversible pyridine loss with retention of crystallinity

The pyridine adduct of bis(benzoylacetonato-O,O′)copper(II) crystallises in both its cis- and trans-isomers within the same crystal. Copper(II) exhibits square pyramidal coordination geometry in both isomers with weak coordination of pyridine. The square planes of the isomers are mutually orthogonal, forming a square grid, in the channels of which the pyridine molecules are stacked, approximately perpendicular to the c-axis. Pyridine is readily lost from crystals unprotected by pyridine solvent, forming a crystalline powder. This powder absorbs pyridine vapour to reform microcrystalline bis(benzoylacetonato)pyridinecopper(II).

Low Molecular Weight Norbornadiene Derivatives for Molecular Solar-Thermal Energy Storage

Abstract Molecular solar‐thermal energy storage systems are based on molecular switches that reversibly convert solar energy into chemical energy. Herein, we report the synthesis, characterization, and computational evaluation of a series of low molecular weight (193–260 g mol−1) norbornadiene–quadricyclane systems. The molecules feature cyano acceptor and ethynyl‐substituted aromatic donor groups, leading to a good match with solar irradiation, quantitative photo‐thermal conversion between the norbornadiene and quadricyclane, as well as high energy storage densities (396–629 kJ kg−1). The spectroscopic properties and energy storage capability have been further evaluated through density functional theory calculations, which indicate that the ethynyl moiety plays a critical role in obtaining the high oscillator strengths seen for these molecules.

Absolute Asymmetric Synthesis: Protected Substrate Oxidation

Three new conglomerates incorporating bidentate sulfide ligands coordinated by Ru(II) centers have been prepared. Total spontaneous resolution by slow crystallization gives highly enantioenriched crystal batches, which are used in enantioselective oxidation of the sulfide ligands to give chiral sulfoxide complexes with >98 % ee. All relevant stereoisomers have been characterized by single-crystal X-ray diffraction, CD spectroscopy, and chiral HPLC. If the ligand range can be extended to monodentate sulfides, a large-scale and recyclable process for enantioselective oxidation of sulfides can be designed.

Reversible Guest Binding in a Non‐Porous FeII Coordination Polymer Host Toggles Spin Crossover

Formation of either a dimetallic compound or a 1 D coordination polymer of adiponitrile adducts of [Fe(bpte)](2+) (bpte=[1,2-bis(pyridin-2-ylmethyl)thio]ethane) can be controlled by the choice of counteranion. The iron(II) atoms of the bis(adiponitrile)-bridged dimeric complex [Fe2 (bpte)2 (μ2 -(NC(CH2 )4 CN)2 ](SbF6 )4 (2) are low spin at room temperature, as are those in the polymeric adiponitrile-linked acetone solvate polymer {[Fe(bpte)(μ2 -NC(CH2 )4 CN)](BPh4 )2 ⋅Me2 CO} (3⋅Me2 CO). On heating 3⋅Me2 CO to 80 °C, the acetone is abruptly removed with an accompanying purple to dull lavender colour change corresponding to a conversion to a high-spin compound. Cooling reveals that the desolvate 3 shows hysteretic and abrupt spin crossover (SCO) S=0↔S=2 behaviour centred at 205 K. Non-porous 3 can reversibly absorb one equivalent of acetone per iron centre to regenerate the same crystalline phase of 3⋅Me2 CO concurrently reinstating a low-spin state.

Total spontaneous resolution of nine-coordinate complexes

Because Na5[Dy(oda)3](H2O)6(BF4)2 (oda = oxodiacetate) (1a), Na5[Er(oda)3](H2O)6(BF4)2 (1b) and Na5[Pr(oda)3](H2O)6(BF4)2 (1c) all crystallise in a Sohncke space group (R32), absolute asymmetric synthesis has been possible; we have obtained an optically active crystal batch of eg1b without using chiral starting materials. Nine-coordinate enantiomers have thus been resolved (without the use of chiral ligands). The crystal structures have been analysed in order to identify factors favouring spontaneous resolution, and two racemic phases of Na3[Gd(oda)3](H2O)6 (2) and Na3NH4[Pr(oda)3](SCN)(H2O)4 (3) were prepared for comparison. The Na+, BF4−, and H2O building blocks in 1a–c result in a chiral network that can transfer stereochemical information between the chiral nine-coordinate [Ln(oda)3]3− anions, ultimately leading to the formation of enantiopure crystals. In the absence of NaBF4 (as in 2), or by the replacement of NaBF4 with NH4SCN (as in 3), neither stereochemical transfer nor spontaneous resolution occurred.

An aqueous non-heme Fe(IV)oxo complex with a basic group in the second coordination sphere

The Fe(IV)oxo complex of a coordinatively flexible multidentate mono-carboxylato ligand is obtained by the one electron oxidation of a low spin Fe(III) precursor in water.