Tolman studies

However, in 1924, [Richard C.] Tolman, a theoretical physicist who studied thermodynamics and light interacting with molecules, described how... 

A tetracoordinated complex (20)4 was actually isolated. Complex 20 in the presence of ethylene forms the coordinated complex 21, as can be seen from H NMR. Complex 21 is a model of the intermediate for the additional reaction to form C6 dienes. The model catalyst had been shown to be a codimerization catalyst under more severe conditions (high temperature), although the rate of reaction was very slow compared to the practical systems. These studies are extremely useful in demonstrating the basic steps of the codimerization reactions taking place on the Ni atom. The catalytic cycle based on these model complexes as visualized by Tolman is summarized in Scheme 7. A more complete scheme taking into consideration by-product formation can be found in Tolman (40). 

In the model study by Tolman discussed earlier, the half-life of syn-to-anti isomerization measured by H NMR was found to be 0.36 hours at 30°C. This rate of isomerization is far too slow to affect the stereoselectivity of the hexadiene formed with the catalyst considered here. With the bimetallic catalyst, reaction rates frequently approach 4000 molecules of hexadiene/Ni atom/hour at 25°C (or ca. 1 hexadiene/Ni/second). The rate of insertion reaction d must be at least as fast as this, and the isomerization reaction would have to be even faster to affect the trans/ cis ratio of the product. 

The transition metal catalysed addition of HCN to alkenes is potentially a very useful reaction in organic synthesis and it certainly would have been more widely applied in the laboratory if its attraction were not largely offset by the toxicity of HCN. Industrially the difficulties can be minimised to an acceptable level and we are not aware of major accidents. DuPont has commercialised the addition of HCN to butadiene for the production of adiponitrile [ADN, NC(CH2)4CN], a precursor to 1,6-hexanediamine, one of the components of 6,6-nylon and polyurethanes (after reaction with diisocyanates). The details of the hydrocyanation process have not been released, but a substantial amount of related basic chemistry has been published. The development of the ligand parameters % and 0 by Tolman formed part of the basic studies carried out in the Du Pont labs related to the ADN process [1],... 

The preparation of carbonyl-lr—NHC complexes (Scheme 3.1) and the study of their average CO-stretching frequencies [7], have provided some of the earliest experimental information on the electron-donor power of NHCs, quantified in terms of Tolman s electronic parameter [8]. The same method was later used to assess the electronic effects in a family of sterically demanding and rigid N-heterocyclic carbenes derived from bis-oxazolines [9]. The high electron-donor power of NHCs should favor oxidative addition involving the C—H bonds of their N-substituents, particularly because these substituents project towards the metal rather than away, as in phosphines. Indeed, NHCs have produced a number of unusual cyclometallation processes, some of which have led to electron-deficient... 

Chadwick A. Tolman received his Ph.D. in physical chemistry from the University of California at Berkeley and until recently was a program officer in organic and macromolecular chemistry in the Division of Chemistry of the National Science Foundation. He is now a staff officer at the National Research Council Board on Environmental Studies and Toxicology. He has extensive experience and expertise in chemistry and chemical process development. Dr. Tolman spent 31 years in Central Research at the DuPont Experimental Station. His work has spanned a broad range of subjects, including hydrocarbon oxidation, organometallic chemistry, and the destruction of toxic organic compounds in wastewater. 

Ve see in Figure 7 that Tolman s representation of the radially dependent surface tension also leads to a vanishing thermodynamic barrier, at high but metastable supersaturations, when a value of 6 computed from solutions of the YBG equation on the planar interface is used. This value of the Tolman parameter is consistent with values obtained from simulation studies of the planar Lennard-Jones surface (28,29). It is apparent that the physical picture of nucleation is highly dependent upon the assumed radial dependence of the surface tension. 

Tolman s study of the equilibrium [Eq. (10)] showed that none of the simple fluorinated olefins C2HnF4 were as good as C2H4 in coordinating to the nickel phosphite complex Ni[P(0-o-tolyl)3]3. 

The observation that dissociation of ligand is required to induce reactivity, in this and many of the cases described below, led to Tolman s proposal that most catalytic processes occur through discreet 16- and 18-electron intermediates (24). This proposal has remained a cornerstone for the study of homogeneous catalysis. 

A correlation of the effect of structure on the Ni(0) association constants and reductions by diimide is displayed in Fig. 1. Unfortunately, none of the negatively substituted ethylenes in Tolman s series are included in Garbisch et al. s study. 

P-31 NMR was a powerful tool in studies correlating the structure of tertiary-phosphine-rhodium chloride complexes with their behavior as olefin hydrogenation catalysts. Triphenylphosphine-rhodium complex hydrogenation catalyst species (1) were studied by Tolman et al. at du Pont and Company (2). They found that tris(triphenylphosphine)rhodium(I) chloride (A) dissociates to tri-phenylphosphine and a highly reactive intermediate (B). The latter is dimerized to tetrakis(triphenylphosphine)dirhodium(I) dichloride (C). 

Sarangi R. Aboelella N. Fujisawa K. Tolman W. B. Hedman B. Hodgson K. O. Solomon E. I. X-ray absorption edge spectroscopy and computational studies on LCu02 species superoxide-Cu11 versus peroxide-Cum bonding. J. Am. Chem. Soc. 2006, 128, 8286-8296. 

Tolman, Druliner, and McKinney [5] were pioneers in nickel-catalyzed hydrocyanation they used monodentate phosphites mainly to understand and improve the adiponitrile process. Although bidentate ligands give better results in the adiponi-trile process [21], mechanistic studies with these systems are rare bidentate phos-phinites have been studied in the asymmetric hydrocyanation of MVN [19]. 

Tolman EC (1959) Principles of purposive behavior. In Koch S (Ed.), Psychology a Study of a Science. McGraw-Hill, New York. 

Brunt EM. Nonalcoholic steatohepatitis. Semin Liver Dis 2004 24 3-20. Marchesini G, Bugianesi E, Forlani G, et al. Nonalcoholic fatty liver, steatohepatitis, and the metabolic syndrome. Hepatology 2003 37 917-923. Wanless IR, Lentz JS. Eatty liver hepatitis (steatohepatitis) and obesity an autopsy study with analysis of risk factors. Hepatology 1990 12 1106-1110. Zimmerman HJ. Hepatotoxicity. The adverse effects of drugs and other chemicals in the liver, 2nd edn. Philadelphia Lippincott Williams Wilkins, 1999. Mason P. Cystic fibrosis - the disease. Hosptal Pharmacist 2005 12 201-207. Tolman KG, Eonseca V, Tan MH, et al. Narrative review hepatobiliary disease in type 2 diabetes mellitus. Ann Intern Med 2004 141 946-956. 

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