Emergence in Chemistry: Chemistry as the Embodiment of Emergence

The main aim of the paper is to reinforce the notion that emergence is a basic characteristic of the molecular sciences in general and chemistry in particular. Although this point is well accepted, even in the primary reference on emergence, the keyword emergence is rarely utilized by chemists and molecular biologists and chemistry textbooks for undergraduates. The possible reasons for this situation are discussed. The paper first re-introduces the concept of emergence based on very simple geometrical forms; and considers some simple chemical examples among low and high molecular weight compounds. On the basis of these chemical examples, a few interesting philosophical issues inherent to the field of emergence are discussed – again making the point that such examples, given their clarity and simplicity, permit one to better understand the complex philosophical issues. Thus, the question of predictability is discussed, namely whether and to what extent can emergent properties be predicted on the basis of the component’s properties; or the question of the explicability (a top down process). The relation between reductionism and emergentism is also discussed as well as the notion of downward causality and double causality (macrodeterminism); namely the question whether and to what extent the emergent properties of the higher hierarchic level affect the properties of the lower level components. Finally, the question is analyzed, whether life can be considered as an emergent property. More generally, the final point is made, that the re-introduction of the notion of emergence in chemistry, and in particular in the teaching, may bring about a deeper understanding of the meaning of chemical complexity and may bring chemistry closer to the humanistic areas of philosophy and epistemology. This revised version was published online in July 2006 with corrections to the Cover Date.     

Asymmetric synthesis of cyclopropanes from lithiated aryloxiranes and alpha,beta-unsaturated Fischer carbene complexes

A diastereo- and enantiospecific formation of tetrasubstituted cyclopropane carbene complexes and cyclopropanecarboxylates from lithiated aryloxiranes and alpha,beta-unsaturated Fischer carbene complexes is described.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.     

Tri-metal Secondary Building Units: Toward the Design of Thermally Robust Crystalline Coordination Polymers

Abstract Three new crystalline coordination polymers [Mn₃(TDC)₄(H₂O)₄](2,6-lutidine)₂(H₂O)₃ 1, P-1, a = 11.351(3), b = 11.391(3), c = 11.480(3), α = 112.838(4), β = 90.696(4), γ = 99.328(4); [Zn₃(1,4-BDC)₃(EtOH)₂] 2, C2/c, a = 19.1308(9), b = 10.6088(5), c = 16.2221(7), β = 108.79(1); and [Zn₃(1,3-BDC)₃(py)₂](MeOH) 3, P2(1)/c, a = 17.142(3), b = 21.544(4), c = 11.805(2), β = 106.441(3); TDC = 2,5-thiophenedicarboxylate, BDC = benzedicarboxylate, have been synthesized by linking tri-metal nodes with poly-carboxylate ligands. Single crystal x-ray analysis shows that 1 is composed of (4,4) 2-D grids with A–A stacking while 2 is comprised of (6,3) triangular networks in an A–B–C stacking pattern and 3 has formed a distorted cubic diamondoid topology. Tri-metal nodes are located at the vertexes of each network. Thermal gravimetric analysis demonstrates that 1 and 2 are thermally robust structures with network decomposition temperatures of 375 °C and 460 °C respectively. Graphical abstract Tri-metal Secondary Building Units: Toward the Design of Thermally Robust Crystalline Coordination Polymers Brian S. Luisi, Zhenbo Ma and Brian Moulton* Tri-metal nodes are shown to be an advantageous target in the synthesis of 2-D crystalline coordination polymers with high thermal stability.      

Dynamic Phenomena and Complexation Effects in the α-Lithiation and Asymmetric Functionalization of Azetidines

In this work it is demonstrated that enantiomerically enriched N-alkyl 2-oxazolinylazetidines undergo exclusive α-lithiation, and that the resulting lithiated intermediate is chemically stable but configurationally labile under the given experimental conditions that afford enantioenriched N-alkyl-2,2-disubstituted azetidines. Although this study reveals the configurational instability of the diastereomeric lithiated azetidines, it points out an interesting stereoconvergence of such lithiated intermediates towards the thermodynamically stable species, making the overall process highly stereoselective (er > 95:5, dr > 85:15) after trapping with electrophiles. This peculiar behavior has been rationalized by considering the dynamics at the azetidine nitrogen atom, the inversion at the C-Li center supported by in situ FT-IR experiments, and DFT calculations that suggested the presence of η³-coordinated species for diastereomeric lithiated azetidines. The described situation contrasted with the demonstrated stability of the smaller lithiated aziridine analogue. The capability of oxazolinylazetidines to undergo different reaction patterns with organolithium bases supports the model termed “dynamic control of reactivity” of relevance in organolithium chemistry. It has been demonstrated that only 2,2-substituted oxazolinylazetidines with suitable stereochemical requirements could undergo C=N addition of organolithiums in non-coordinating solvents, leading to useful precursors of chiral (er > 95:5) ketoazetidines.     

Employment of 2,6-diacetylpyridine dioxime as a new route to high nuclearity metal clusters: Mn6 and Mn8 complexes

The employment of the anion of 2,6-diacetylpyridine dioxime (dapdoH2) as a pentadentate chelate in transition metal cluster chemistry is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn6O2(OMe)2(dapdo)2(dapdoH)4](ClO4)2 (1), [Mn6O2(OMe)2(dapdo)2(dapdoH)4][Ca(NO3)4] (2), and [Mn8O4(OH)4(OMe)2(N3)2(dapdo)2(dapdoH)2(H2O)2] (3). The reaction of [Mn3O(O2CMe)6(py)3](ClO4) with 3 equiv of dapdoH2 (with or without 2 equiv of NEt3) in MeOH gave 1. The same cation, but with a [Ca(NO3)4]2- anion, was found in complex 2, which was obtained from the reaction in MeOH between Mn(NO3)2, Ca(NO3)2, and dapdoH2 in the presence of NEt3. In contrast, addition of NaN3 to several reactions comprising MnCl2, dapdoH2, and NEt3 in MeOH gave the octanuclear complex 3. Complexes 1-3 all possess rare topologies and are mixed-valence: 2MnII, 4MnIII for 1 and 2, and 2MnII, 6MnIII for 3. The core of the cation of 1 and 2 consists of two edge-sharing Mn4 tetrahedra at the center of each of which is a micro4-O2- ion. Peripheral ligation is provided by two micro-OMe-, four micro-dapdoH-, and two micro3-dapdo2- groups. The core of 3 consists of two [MnIIMnIII3(micro3-O)2]7+ "butterfly" units linked together by one of the micro3-O2- ions, which thus becomes micro4. Peripheral ligation is provided by four micro-OMe-, two micro-OH-, two micro-dapdoH-, and two micro4-dapdo2- groups. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1-3 in the 5.0-300 K range; the data for 1 and 2 are identical. Fitting of the obtained magnetization versus field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting, D) established that 1 possesses an S=5 ground state with D=-0.24 cm(-1). For 3, low-lying excited states precluded obtaining a good fit from the magnetization data, and the ground state was instead determined from the ac data, which indicated an S=1 ground state for 3. The combined work demonstrates the ligating flexibility of pyridyl-dioxime chelates and their usefulness in the synthesis of new polynuclear Mnx clusters without requiring the co-presence of carboxylate ligands.     

Transfer of Electrophilic NH Using Convenient Sources of Ammonia: Direct Synthesis of NH Sulfoximines from Sulfoxides

A new system for NH transfer is developed for the preparation of sulfoximines, which are emerging as valuable motifs for drug discovery. The protocol employs readily available sources of nitrogen without the requirement for either preactivation or for metal catalysts. Mixing ammonium salts with diacetoxyiodobenzene directly converts sulfoxides into sulfoximines. This report describes the first example of using of ammonia sources with diacetoxyiodobenzene to generate an electrophilic nitrogen center. Control and mechanistic studies suggest a short‐lived electrophilic intermediate, which is likely to be PhINH or PhIN⁺.     

Regio- and stereoselective lithiation of terminal oxazolinylaziridines: the aziridine N-substituent and the oxazolinyl group effect

The regioselective lithiation of terminal oxazolinylaziridines has been investigated. The steric hindrance of the nitrogen substituent in 1-trityl-2-oxazolinylaziridine 3a, combined with the coordinating ability of the oxazolinyl group, causes beta-lithiation, whereas a completely regioselective alpha-lithiation is observed with the much less sterically demanding 1-benzyl-2-oxazolinylaziridine 3c and a competition between alpha- and beta-lithiation occurs with 1-cumyl-2-oxazolinylaziridine 3b in which the N-substituent has a steric hindrance in between the trityl and the benzyl groups. The application of the lithiation-trapping sequence for the preparation of enantioenriched 2,3-cis-disubstituted oxazolinylaziridines and aziridino-gamma-lactones is also reported.