Richard Waack

A nuclear magnetic resonance study of carbon-lithium bonding in arylmethyllithiums benzyllithium and 1,1-diphenyl-n-hexyllithium

Abstract The nature of carbon-lithium bonding in benzyllithium and 1,1-diphenyl-n-hexyllithium and its variation with solvent is evaluated from carbon, lithium, and proton nuclear magnetic resonance measurements. The solvent dependency of the NMR data is interpreted as evidence that the α-carbons of these arylmethyllithiums have appreciable sp 3 character which increases with decreasing solvent polarity. Anion-cation interaction accordingly increases with decreasing solvent polarity. Solvent induced changes in ligand (anion-cation) interactions are considered to be the predominant factor influencing the nature of the carbon-lithium bonding. The larger π-system of 1,1-diphenyl-n-hexyllithium is suggested to moderate the dependence of anion-cation interaction on solvent and to result in greater (than in benzyllithium) sp 2 character to the α-carbon.

Addition of organolithium reagents to 1,1-diphenyl-ethylene in diethyl ether, kinetics and structure reactivity behaviors

Abstract Kinetic studies of the addition of benzyllithium, allyllithium, phenyllithium, methyllithium and n-butyllithium to 1,1-diphenylethylene in diethyl ether solution show the reactions are first order in DPE and variable order in organolithium reagent. A consequence of the differences in effective reaction orders is that the relative reactivity of these reagents is concentration dependent. Vinyllithium does not give the normal 1 1 adduct with DPE in Et2O. In the concentration range investigated, i.e. between 10−3 and 1 M organolithium, methyllithium is the least reactive and n-butyllithium is the most reactive, by a factor of ∼ 1 4000 . The effective organolithium reaction orders and relative reactivity order in Et2O are similar to those reported in tetrahydrofuran. The rate increase between Et2O and THF reaction media is smallest for phenyllithium (i.e., 90) and largest for benzyllithium, (i.e., 1700).

Dependence of the kinetic isotope effect on the structure of the organolithium metalating reagent in the metalation of triphenylmethane

Abstract Measurements have been made of k H / k D kinetic isotope effects associated with the metalation of a series of triarylmethanes (α-H and α-D) by six organolithium reagents (RLi) in tetrahydrofuran at 22°. The substantial variation in k H / k D value observed with benzyllithium, allyllithium, phenyllithium, vinyllithium, n-butyl-lithium and methyllithium, is attributed to different transition state geometries, dependent on the structures of the organolithium compounds. Hammet σ ϱ plots for each RLi metalating reagent yield ϱ values within the range 2.2 to 3.0, suggesting appreciable negative charge occurs on the triarylmethyl voiety in the transition states. It is inferred from k H / k D values measured with ( p -methylphenyl)diphenylmethane, ( p -methoxyphenyl)diphenylmethane, and triphenylmethane, that the effective basicity of organolithiums towards these substrates increases in the seriesn-butyllithium 〈vinyllithium〈methyllithium〈benzyllithium〈phenyllithium.

ELECTROLYTIC FORMATION OF ORGANOMETALLIC COMPOUNDS

A PROCESS FOR THE PREPARATION OF ORGANOMETALLIC COMPOUNDS COMPRISING CONTACTING AN ACTIVATED OLEFIN OR DIARYL-CONTAINING HYDROCARBON WITH AN ELECTRIC CURRENT IN THE PRESENCE OF AN ALKALI OR ALKALINE EARTH METAL SALT ELECTROLYTE, AND A TETRAALKYL SUBSTITUTED UREA, TETRAALKYL SUBSTITUTED THISOUREA, TETRAALKYL SUBSTITUTED SULFONAMIDE OR A HEXAALKYL OR ARYL SUBSTITUTED PHOSPHORAMIDE POLAR SOLVENT.

Kinetic study of addition of p-t-amylbenzyllithium to 1,1,-diphenylethylene in toluene

p-t-Amylbenzyllithium (I) is found to be appreciably soluble in toluene, in contrast to the very limited solubility of benzyllithium in this solvent. The reaction order in organolithium, for addition of I to 1,1-diphenylethylene, is 0.5. This kinetic behavior and reaction rate are compared to the behavior of benzyllithium in ether solutions and to the behavior of other organolithium reagents in hydrocarbon solution.