There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Owing to the increasing emissions of carbon dioxide (CO2), human life and the ecological environment have been affected by global warming and climate changes. To mitigate the concentration of CO2 in the atmosphere various strategies have been implemented such as separation, storage, and utilization of CO2. Although it has been explored for many years, hydrogenation reaction, an important representative among chemical conversions of CO2, offers challenging opportunities for sustainable development in energy and the environment. Indeed, the hydrogenation of CO2 not only reduces the increasing CO2 buildup but also produces fuels and chemicals. In this critical review we discuss recent developments in this area, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism. We also provide an overview regarding the challenges and opportunities for future research in the field (319 references).

Recent advances in catalytic hydrogenation of carbon dioxide

B. Anionic Ligands 302 IX. Group 9 Catalysts 302 X. Group 10 Catalysts 303 A. Neutral Ligands 303 1. R-Diimine and Related Ligands 303 2. Other Neutral Nitrogen-Based Ligands 304 3. Chelating Phosphorus-Based Ligands 304 B. Monoanionic Ligands 305 1. [PO] Chelates 305 2. [NO] Chelates 306 3. Other Monoanionic Ligands 306 4. Carbon-Based Ligands 306 XI. Group 11 Catalysts 307 XII. Group 12 Catalysts 307 XIII. Group 13 Catalysts 307 XIV. Summary and Outlook 308 XV. Glossary 308 XVI. References 308

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Advances in non-metallocene olefin polymerization catalysis.

One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

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Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure−Activity Relationships

Staudinger reactions of Cy2BN3 with tri-substituted phosphines (R3P) yielded the boron–nitrogen–phosphorus linked systems Cy2BNPR3 (R = Et, tBu, Cy, Ph) (1a–1d respectively). Similarly, reaction of (C6F5)2BN3 with the phosphines PtBu3, PPh3, Ph2PCCPh and Ph2PCCPPh2 yielded (C6F5)2BNPR3 (2a–d respectively). In contrast, the reaction of (C6F5)2BN3 with Ph2P–CCp-tol in the presence of excess Me3SiN3 afforded the bicyclic product 3 [1-(C6F5)2B-4-(p-tol)-1H-1,2,3-triazole-5-P(NH)Ph2] in which both a Staudinger and a cycloaddition reaction has taken place. However, if the Staudinger reaction is prohibited via phosphine oxidation as in the case of (EtO)2P(O)CCP(O)(OEt)2 then the unusual dimeric product 4 [2-(C6F5)2B-4-(P(O)OEt2)-2H-1,2,3-triazole-5-P(O)(OEt)(OB(C6F5)2)] is generated. The structures of 1b–d, 2b–d, 3 and 4 have been determined by X-ray diffraction.

Boron azides in Staudinger oxidations and cycloadditions

Hydroboration without a B–H bond: reactions of the borinium cation [(iPr2N)2B]+ with alkyne, nitrile, ketone and diazomethane

Metal-mediated synthesis of thiol derivatives : synthesis and reactivity of the thiatitanacyclopropane complex cpti(schch2ch2s)2

The development of novel Lewis acids derived from bipyridinium and phenanthrolinium dications is reported. Calculations of Hydride Ion Affinity (HIA) values indicate high carbon-based Lewis acidity at the ortho and para positions. This arises in part from extensive LUMO delocalization across the aromatic backbones. Species [C10 H6 R2 N2 CH2 CH2 ]2+ (R=H [1 a]2+ , Me [1 f]2+ , tBu [1 g]2+ ), and [C12 H4 R4 N2 CH2 CH2 ]2+ (R=H [2 a]2+ , Me [2 b]2+ ) were prepared and evaluated for use in the initiation of hydrodefluorination (HDF) catalysis. Compound [2 a]2+ proved highly effective towards generating catalytically active silylium cations via Lewis acid-mediated hydride abstraction from silane. This enabled the HDF of a range of aryl- and alkyl- substituted sp3 (C-F) bonds under mild conditions. The protocol was also adapted to effect the deuterodefluorination of cis-2,4,6-(CF3 )3 C6 H9 . The dications are shown to act as hydride acceptors with the isolation of neutral species C16 H14 N2 (3 a) and C16 H10 Me4 N2 (3 b) and monocationic species [C14 H13 N2 ]+ ([4 a]+ ) and [C18 H21 N2 ]+ ([4 b]+ ). Experimental and computational data provide further support that the dications are initiators in the generation of silylium cations.

Bipyridinium and Phenanthrolinium Dications for Metal-Free Hydrodefluorination: Distinctive Carbon-Based Reactivity.

The tripodal phosphines MeC(CH2NMe)3P and N(CH2CH2NMe)3P were converted to the corresponding phosphinimines and the corresponding Ti-complexes MeC(CH2NMe)3PNTiCpCl2 (2) and N(CH2CH2NMe)3PNTiCpCl2 (5) were prepared. These species were also alkylated to give the corresponding dimethyl derivatives. Preliminary attempts to utilize these species in the polymerization of ethylene with MAO as the activator resulted in all but negligible activity. An alternative synthetic approach utilizing the bis-phosphinimine (CH2(Me)NPtBu2)2 was developed to prepare (CH2(Me)NP(tBu2)NSiMe3)2 (8), (CH2(Me)NP(tBu2)NH)2 (9) and subsequently [(CH2(Me)NP(tBu2)N)2]Ti(NMe2)2 (10), [(CH2(Me)NP(tBu2)N)2]TiCl2 (11) and [(CH2(Me)NP(tBu2)N)2]TiMe2 (12). For comparison purposes the related species [tBu2(Me2N)PN]2TiCl2 (14) and [tBu2(Me2N)PN]2TiMe2 (15) were also prepared. Compounds (12) and (15), using 2 equiv. of [Ph3C][B(C6F5)4] as the activator, resulted in moderate to good polymerization activities.

Douglas W. Stephan

Papers

Boron azides in Staudinger oxidations and cycloadditions

Hydroboration without a B–H bond: reactions of the borinium cation [(iPr2N)2B]+ with alkyne, nitrile, ketone and diazomethane

Metal-mediated synthesis of thiol derivatives : synthesis and reactivity of the thiatitanacyclopropane complex cpti(schch2ch2s)2

Bipyridinium and Phenanthrolinium Dications for Metal-Free Hydrodefluorination: Distinctive Carbon-Based Reactivity.

Titanium complexes of amidophosphinimide ligands