Download R–M Addition to Carbonyls

Chapter 15
Organometallic Compounds
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Organometallic Compounds
• Organometallic compounds contain a carbon-metal
bond
• We have previously encountered alkali metal acetylides.
Alkali metal alkoxides, which have an oxygen-metal ionic
bond, are not considered organometallic
• The huge diversity of metals and nucleophilic nature
(usually) of carbon in these compounds makes them
worthy of study
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Section 15.1
ORGANOMETALLIC
NOMENCLATURES
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Naming Organometallic Compounds
• The metal is considered the parent and the organic
portion is named as a substituent of the metal
• Nonmetals more electronegative than C are named as
anions
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Section 15.2
CARBON–METAL BONDS
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Polarization of C–M Bonds
• Metals are less electronegative than carbon; C–M bonds
are polarized towards carbon
• Carbon is nucleophilic in many (but not all)
organometallic compounds
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Electronegativities of the Elements
C–M bonds often have ionic character, but
can also have some covalent character.
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Section 15.3
PREPARATION OF
ORGANOLITHIUM AND
ORGANOMAGNESIUM
COMPOUNDS
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
R–Li and R–MgX Compounds
• Organolithium compounds are highly useful carbon nucleophiles
• Organomagnesium compounds react similarly and are called
Grignard reagents
• Typically prepared from the highly oxidizable metals and
reducible organohalides (sp and sp2 halides work too!)
Lithium essentially donates two electrons to RX.
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
R–Li and R–MgX Compounds
• Organolithium compounds are highly useful carbon nucleophiles
• Organomagnesium compounds react similarly and are called
Grignard reagents
• Typically prepared from the highly oxidizable metals and
reducible organohalides (sp and sp2 halides work too!)
Magnesium essentially inserts into the R–X bond.
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Single-electron Transfer
• These reactions involve single-electron transfer followed
by departure of a halide anion
• The intermediate after single-electron transfer is a
radical anion
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Section 15.4
ORGANOLITHIUM AND
ORGANOMAGNESIUM
COMPOUNDS AS BRØNSTED
BASES
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
RLi and RMgX as Brønsted Bases
• The R–Li and R–Mg bonds are essentially ionic
– Li and Mg are essentially Li+ and Mg2+
– R is essentially R–, a carbanion!
• Carbanions are strongly basic—pKa(R–H) is between 25
(terminal alkynes) and 70 (alkanes)
• Touching water is out of the question unless the goal is
to install H
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Applications of R–M Basicity
• Taking a step back to the organohalide precursor, protonation
can be used to replace X with H (or deuterium!)
• Strongly basic alkyl Grignard reagents or alkyllithiums can be
used to prepare slightly less basic organometallic compounds
n-Butyllithium and tert-butyllithium are commonly used for the latter purpose.
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Section 15.5
SYNTHESIS OF ALCOHOLS
USING GRIGNARD AND
ORGANOLITHIUM REAGENTS
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
R–M Addition to Carbonyls
• The carbonyl group (O=C) is strongly polarized towards
oxygen; carbon is electrophilic
• The nucleophilic carbon of RLi or RMgX adds at the
electrophilic carbonyl carbon, forging a new C–C bond
This nucleophilic addition process is highly general for carbonyls.
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
R–M Addition to Carbonyls
• The carbonyl group (O=C) is strongly polarized towards
oxygen; carbon is electrophilic
• Protonation with acid upon workup establishes an
alcohol
This nucleophilic addition process is highly general for carbonyls.
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Examples of Nuc. Addition to Carbonyls
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
Examples of Nuc. Addition to Carbonyls
Copyright © 2017 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.