organometallic
bond between a metal and carbon
-changes polarity of carbon (slightly + becomes slightly -)
Grignard reagents
an organomagnesium compound, prepared by addition of an alkyl, aryl, or alkenyl halide to Mg metal in diethyl ether or THF
-dissolve as coordination compounds solvated by ether
what is an alternative to Grignard reagents?
Alkyl lithiums
carbon-metal bonds in RMgX and RLi are best described as….
polar covalent
carbanion
an anion in which carbon has an unshared pair of e- and bears a - charge
-great nucleophiles
limitations to carbanion
- can’t make grignards w/ acidic or electrophilic functional groups
- can’t do simple SN2 using alkyl halides; E2 dominates
Grignard reagent reacts with formaldehyde to give
primary alcohol
Grignard reagent reacts with aldehydes to give
secondary alcohols
Grignard reagents react with esters to give
tertiary alcohols
Grignard reagents react with ketones to give
tertiary alcohols
Grignard reagents react with epoxides to give
primary alchols
epoxides
illustrate how many common organic functional groups contain electophile carbons
matchmaker-homewrecker steps
- find the +, find the -, then hook them together (arrows from - to +)
- look for alternative negative or positive partners
- we are considering RMgX and RLi as our partial - (neg = nucleophile) the search is for the partial pos
addition of a nucleophile to carbonyl group
- racemic mixture produced
- often tetrahedral product with a new chiral center
- if none of the starting materials is chiral and the rxn takes place in an achiral environment, the enantiomers will be formed as a racemic mixture
- new C-C bond formed
Gilman reagents
- lithium diorganocopper reagents
- prepared by treating an alkyl, aryl, or alkyl, or alkenyl Lithium compound with Cu(I) Iodide
- use less electrophilic metal = less reactive
- rules of SN2 mechanism no longer hold
- add Cu(I) salt to RLi
coupling Gilman with a vinyl halide
is stereospecific, configuration of c-c double bond is restrained
Gilman reagent + epoxide
ring opening is stereoselective
carbene
- (R2C); a neutral molecule in which a carbon atom is surrounded by only 6 valence electrons
- in its lowest energy state, carbon is sp2 hybridized w the unshared pair of electrons occupying the 3rd sp2 orbital
simmon-smith reaction
- way to add methylene to an alkene to form a cyclopropane
- generation of Simmons-smith reagent
- CH2i ICH2ZnI
- concerted mechanism (happens all at once)
