Andreas Mayr

CrossNets: High-Performance Neuromorphic Architectures for CMOL Circuits

Abstract: The exponential, Moores Law, progress of electronics may be continued beyond the 10‐nm frontier if the currently dominant CMOS technology is replaced by hybrid CMOL circuits combining a silicon MOSFET stack and a few layers of parallel nanowires connected by self‐assembled molecular electronic devices. Such hybrids promise unparalleled performance for advanced information processing, but require special architectures to compensate for specific features of the molecular devices, including low voltage gain and possible high fraction of faulty components. Neuromorphic networks with their defect tolerance seem the most natural way to address these problems. Such circuits may be trained to perform advanced information processing including (at least) effective pattern recognition and classification. We are developing a family of distributed crossbar network (CrossNet) architectures that permit the combination of high connectivity neuromorphic circuits with high component density. Preliminary estimates show that this approach may eventually allow us to place a cortex‐scale circuit with about 1010 neurons and about 1014 synapses on an approximately 10 × 10 cm2 silicon wafer. Such systems may provide an average cell‐to‐cell latency of about 20 nsec and, thus, perform information processing and system training (possibly including self‐evolution after initial training) at a speed that is approximately six orders of magnitude higher than in its biological prototype and at acceptable power dissipation.

Recent Advances in the Chemistry of Metal-Carbon Triple Bonds

Publisher Summary This chapter discusses the recent advances in the chemistry of metal–carbon triple bonds. The chemistry of metal–carbon triple bonds has developed at an increasing pace since the discovery of the first carbine–metal complexes. The metal atoms in the alkylidyne complexes were found to be less shielded than those in nitrido complexes but more shielded than those in compounds containing metal–metal multiple bonds. Aristov and Armentrout and Freiser derived the bond energies of metal– carbon triple bonds from gas-phase experiments. Metal–carbon triple bonds are generally described as consisting of one σ or two π bonds. The first transition-metal– carbyne complexes were synthesized in Fischers laboratory by the treatment of alkoxycarbene pentacarbonylmetal complexes of chromium, molybdenum, and tungsten with boron trihalides. Oxalyl halides react directly with the pentacarbonylmetal acyl complexes of chromium, molybdenum, and tungsten to form the trans-alkylidyne (halo) tetracarbonyl complexes. The rearrangement of the silyl-substituted vinyl complexes has been proposed to occur by 1,2-silyl migration steps. Metal alkylidyne complexes undergo a variety of oxidation and reduction reactions as well as redox-induced transformations of the alkylidyne ligands. Addition of electrophiles to electron-rich isocyanide complexes is a proven synthetic method for the synthesis of aminocarbyne complexes. The chemistry of metal–carbon triple bonds has developed considerably during the late 1980s. The discovery of novel indium alkylidyne complexes indicates that the full range of metal–carbon triple bonds is not yet known.

Synthesis and protonation reactions of trimethylphosphine-substituted carbyne complexes of molybdenum and tungsten. The tungsten alkylidene complexes [(W=CHR)Cl2(CO)(PMe3)2] as precursors for carbyne complexes containing weakly coordinated ligands

Synthese des complexes [(W≡CR)Cl(CO)(PMe 3 ) 3 ] et [M≡CPh)Br(PMe 3 ) 4 ]. Reactions avec HBr. Structure cristalline de [(W=CHPh)Cl 2 (CO)(PMe 3 ) 2 ]

Synthesis, structure, and dynamic behavior of dichloro alkylidene alkyne bis(trimethylphosphine)tungsten complexes.

The mechanism of alkyne polymerization by molybdenumand tungsten-based catalysts has been proposed to propagate via metal alkylidene intermediates (Scheme I).I For mononuclear systems each mechanistic cycle involves coordination of an alkyne to the transition-metal center, formation of a metallacyclobutene, and regeneration of the metal carbene by ring opening. Fischer-type carbyne complexes are among the best catalyst precursors and transformation of the carbyne ligand into a carbene ligand for catalytic activity has been post~lated.~ We have developed simple methods for the synthesis of group 6 transition-metal carbyne complexes3 and we have begun to investigate the reactions of these compounds with unsaturated hydrocarbons. Reactions of pyridine-substituted tungsten carbyne complexes [(W=CR)CI( c O ) , ( p ~ ) ~ ] with activated olefins leading to stable tungsten alkene carbyne complexes have already been d e ~ c r i b e d . ~ Analogous reactions of [(W=LR)CI(CO),(py),] with alkynes did not afford isolable tungsten alkyne carbyne complexes; rather, polymerization of alkynes was observed. More recently, we have developed routes to trimethylphosphine-stabilized metal carbyne complexes and we have shown that deprotonation of the tungsten alkylidene complex [(W==CHPh)(Cl),(CO)(PMe3)2] (1) provides an anionic tungsten carbyne complex, [ ( WSCP~)(CI)~(CO)( PMeJ2]-, containing a labile chloride ligand.5 Dehydrochlorination of 1 in the presence of ligands L thus provides good access to substituted tungsten carbyne complexes [(W=tPh)Cl(CO)L(PMe,),], and we hoped this method might allow the synthesis of stable tungsten carbyne complexes containing alkyne ligands. Here we report about reactions of 1 with acetylenes in the presence of base which afford stable transition-metal alkyne alkylidene complexes,6 possibly via labile tungsten alkyne carbyne complexes. The products exhibit the elements of the first intermediate in Masudas mechanism for acetylene polymerization and they serve as precursors for moderately active alkyne polymerization catalysts. An equimolar mixture of 1, diphenylacetylene, and 1,8-bis(dimethy1amino)naphthalene is allowed to react for 30 min at 0

Development of a T-joint for covalent molecular construction based on 2,2′-bipyridine and phenanthroline isocyanide metal complexes

Abstract Tetracarbonylmolybdenum and halotricarbonylrhenium complexes of laterally extendable or laterally extended bipyridines such as 5,5′-dibromo-2,2′-bipyridine, 5,5′-bis(trimethylsilylethynyl)-2,2′-bipyridine, or 3,8-dibromophenanthroline have been prepared. These complexes are potential precursors for covalent T-joints by substitution of carbon monoxide in the molybdenum complexes or halide in the rhenium complexes by linear terminal ligands. The formation of a covalent T-joint has been demonstrated by attachment of Mo(CO)3(5,5′-bis(trimethylsilylethynyl)-2,2′-bipyridine) units to the free isocyanide groups of ReCl(CO)3(CNC6H10CN)2.

Synthesis of several functionalized cis-diisocyanide and fac-triisocyanide metal complexes

Abstract cis-Diisocyanide metal complexes of the types cis-W(CNR)2(CO)4, cis-ReCl(CNR)2(CO)3, and Fe(η5-C5H5)Cl(CNR)2 and fac-triisocyanide metal complexes of the types fac-W(CNR)3(CO)3 and [Fe(η5-C5H5)(CNR)3]Cl have been prepared. The isocyanides are of the type 4-CNC6H2-3,5-i-Pr2-f, whereby the functionalities f are capable of forming strong coordinative bonds to transition metals (f=CCH, CC-4-C5H4N, or CC-4,4′-biphenyl-C6H2-3,5-i-Pr2-4-NC) or capable of being interconnected with each other by covalent bond formation (f=Br, I, CCSiMe3, CCH). The molecular structures of cis-W(4-CN-3,5-i-Pr2-C6H2CC-4-C5H4N)2(CO)4, cis-ReCl(4-CN-3,5-i-Pr2-C6H2CCH)2(CO)3, and Fe(η5-C5H5)Cl(4-CN-3,5-i-Pr2-C6H2CC-4-C5H4N)2 have been determined by X-ray crystallography.

Fabrication and characterization of novel cross point structures for molecular electronic integrated circuits

Molecular electronic devices have the potential to dramatically increase the density and performance of integrated circuits. In order to realize this potential, reliable and scalable fabrication of nanoscale molecular electronic devices is essential. The authors have developed a new type of cross point structure in which the molecules are self-assembled between two metallic electrodes separated by an aluminum oxide layer. The gap between the electrodes is only a few nanometers wide and is defined by the aluminum oxide layer thickness, so it can be adjusted to match the length of the molecules with high (subnanometer) precision. This fabrication method applies to the study of transport properties of single molecules and at the same time is compatible with processes used in electronic industry, so that it may be used in the future to integrate molecular devices with silicon-based integrated circuits. Since the molecular self-assembly is the last step of the process, damage to molecules can be minimized. The...

Comments on the chemistry of low-valent alkylidyne complexes of the group 6 transition metals

Abstract The chemistry of metal-carbon multiple bonds has grown into a major branch of organometallic chemistry since its beginning in 1963.1 Metal alkylidene and alkylidyne2 complexes, which originated from purely fundamental research efforts, are now used as building blocks for organometallic synthesis, and as catalytic and stoichiometric reagents for organic synthesis. The chemistry of metal alkylidenes has developed much further than the chemistry of metal alkylidynes. However, interest in alkylidyne complex chemistry has been rising in recent years as documented by several review article.3

Protonation of Fischer-type alkylidyne carbonyltungsten complexes. Structural comparison of alkylidyne and alkylidene metal complexes, including a neutron diffraction study of [W(CHCH3)Cl2(CO)(PMe3)2]

Abstract Protonation of alkylidyne tungsten complexes of the types [W(CR)Cl(CO)(PMe3)3] or [W(CR)Cl(CO)(py)(PMe3)2] with HCl affords the η2-alkylidene tungsten complexes [W(CHR)Cl2(CO)(PMe3)2] (7) (R = Me, Et, Ph, p-Tol). Protonation of the complexes [W(CR)X(CO)(CNR′)(PMe3)2] with HOSO2CF3 or HBF4 gives the alkylidene complexes [W(CHR)X(CO)(CNR′)(PMe3)2][Y] (8) (R = Me, R′ = CMe3, X = Cl, Y = CF3SO3, R = Ph, X = Cl; R′ = CMe3, Y = CF3SO3, BF4; R′ = C6H11, Y = BF4; R′ = C6H3Me2-2,6, Y = CF3SO3, R = Ph, R′ = CMe3, X = I, Y = CF3SO3, BF4). The CH bonds of the alkylidene ligands are easily deprotonated with bases such as pyrrolidinocyclopentene or triethylamine. The solid state structures of [W(CPh)Cl(CO)(CNCMe3)(PMe3)2] (5b), [W(CHMe)Cl2(CO)(PMe3)2] (7a). [W(CHPh)Cl2(CO)(PMe3)2] (7c), and [W(CHPh)Cl(CO)(CNCMe3)(PMe3)2][BF4] (8c) were determined by X-ray crystallography. The structure of 7a was also determined by neutron diffraction. Based on the neutron diffraction data of 7a, and closely matching results from the X-ray diffraction studies, it is found that the η2-coordination mode of the alkylidene ligands gives rise to almost equal WC(R) and WH bond distances, 1.857(4) and 1.922(6) A, respectively, in the case of 7a. The length of the alkylidene CH bond in 7a is 1.185(7) A. The structural comparison of 5b and 8c reveals that the protonation of the alkylidyne ligand causes the WCPh bond to lengthen by less than 0.1 A and the WCPh angle to bend by about 15°. The major induced structural change, however, may be described as a lateral shift of the CPh group by about 0.6 A away from the coordination axis defined by the extension of the ClW vector.

TRANSITION METAL COMPLEXES OF ISOCYANOPYRIDINES, ISOCYANOQUINOLINES AND ISOCYANOISOQUINOLINES

Abstract The complexes trans-[FeI2(CN-3-pyridyl)4], trans-[PdI2(CNR)2] (CNR=2-, 3- and 4-isocyanopyridine, 3-isocyanoquinoline, 4-isocyanoquinaldine, 5-isocyanoquinoline, 5-isocyanoisoquinoline) and trans-[PtI2(CNR)2] (CNR=3-isocyanopyridine, 5-isocyanoquinoline) were prepared. The new complexes are thermally stable up to 150°C or higher. The molecular structure of trans-[PdI2(CN-3-quinolyl)2] was determined by X-ray crystallography: monoclinic space group P2 1 c , a=5.8381(5), b=23.685(2), c=7.2122(6), A, β=97.628(8)°, Z=2, 1170 unique reflections, R=0.035, Rw=0.035. In the crystal, the molecular units are packed to form two-dimensional sheets which are held together by π stacking of the 3-quinolyl groups.