Table Of Content1 3 8 Topics ni Current yrtsimehC
muihtilonagrO Compounds/
detavloS snortcelE
With Contributions by
.N .M Alpatova, .L .I Krishtalik, A. Maercker,
L1 .S Mali, .N .S Narasimhan, .V.Y Pleskov, M. Theis
With 41 Figures and 71 Tables
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Organolithium compounds solvated electrons.
(Topics in current chemistry ; )831
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Table of Contents
Some Aspects of the Chemistry of Polylithiated Aliphatic
Hydrocarbons
A. Maercker, M. Theis . . . . . . . . . . . . . . . .
Heteroatom Directed Aromatic Lithiation Reactions for
the Synthesis of Condensed Heteroeyclie Compounds
N. S. Narasimhan, R. S. Mall . . . . . . . . . . . . . . 63
Electrochemistry of Solvated Electrons
N. M. Alpatova, L. I. Krishtalik, Y. V. Pleskov ...... 149
Author Index Volumes 101-138 . . . . . . . . . . . . . 221
Some Aspects of the Chemistry of
detaihtilyloP citahpilA snobracordyH
Adaibert Maercker and Manfred Theis
Institut fiir Organische Chemie der Universit~t Siegen,
Adolf-Reichwein-Strage, Siegen, D-5900 FRG
TaMe of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Theoretical Results . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Lithiated Methanes . . . . . . . . . . . . . . . . . . . . . . . 2
2.2 Lithiated Ethanes . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Lithiated Ethenes . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Dilithioacetylene . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5 1,3-Dilithiopropane . . . . . . . . . . . . . . . . . . . . . . . 11
2.6 Other Lithiated C:Hydrocarbons . . . . . . . . . . . . . . . . . 12
2.7 Lithiated C:Hydrocarbons . . . . . . . . . . . . . . . . . . . . 14
2.8 Hypervalent and Related Species . . . . . . . . . . . . . . . . . 20
3 Syntheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1 Halogen-Metal Exchange Relations . . . . . . . . . . . . . . . . 21
3.2 Pyrolysis Reactions . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 Mercury-Lithium Exchange Reactions . . . . . . . . . . . . . . . 25
3.4 Transmetalation Reactions with other Metals . . . . . . . . . . . . 29
3.5 Reductive Metalations . . . . . . . . . . . . . . . . . . . . . . 13
3.6 Metalation of Acidic Hydrocarbons . . . . . . . . . . . . . . . . 36
3.7 Reactions with Lithium Vapor . . . . . . . . . . . . . . . . . . 39
3.8 Fragmentations . . . . . . . . . . . . . . . . . . . . . . . . . 40
4 Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1 Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2 Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Topics in Current Chemistry, VoL 831
© Springer~Verlag, Berlin Heidelberg 1987
Adalbert Maercker and Manfred Theis
1 Introduction
Certain acidic hydrocarbons are known to undergo polymetalation by alkyllithium
compounds, often with N,N,N',N'-tetramethylethylenediamine (TMEDA) as a
catalyst, to give polylithiated organic compounds. Those propargylic, allylic, and
benzylic polymetalations already have been reviewed by West ~1 and Klein ,2 ,}3 the
leaders of two most active research groups in this field. The present review article is
mainly dealing with polylithiated aliphatic hydrocarbons which cannot be obtained
by simple metalation reactions. Often special techniques have been used in order to
reach this goal, e.g. reactions with lithium vapor, a method developed by Lagoawn d
his coworkers .)5,4 Many interesting polylithium organic compounds still have to be
synthesized, although their remarkable structures -- sometimes with anti-van't Hoff
geometries -- have already been proposed by theoretical calculations especially by
Schleyer, Pople, and coworkers ,6 )7 but also by Streitwieser )s and others.
2 Theoretical Results
For compounds not available by synthetic methods theoretical calculations provide
the only information concerning structural details. Moreover polylithium organic
compounds have attracted the interest of theoretical chemists because the geometries
in general do not follow classical structural considerations, i.e. replacement of
hydrogen in a hydrocarbon by lithium almost always results in some fundamental
change in geometry. As in monolithium compounds lithium prefers bridging posi-
tions and in certain polylithiated hydrocarbons even double bridging within the
molecule is possible. Thereby the lithium atoms by using their free p orbitals reach a
higher coordination number which is favorable energetically. On the other hand,
factors other than those involving lithium p orbitals, e.g. electrostatic interactions,
might also be responsible for bridging and sometimes provide a simpler explanation
than multi center covalent bonding.
2.1 Lithiated Methanes
The lithiated methanes havbee en investigated calculationally already ten years ago by
Schleyer, Pople et al. ,9 .}ol The most exciting result is the decrease of the energy differ-
Table .1 Calculated Planar-Tetrahedral Energy
Differences (kcal/mol) for Lithiated Methanes
(RHF) 79
Molecule a STO-3G 4-31G
1 042 861
2 25 42
3 (trans) 45 74
3 (cis) 71 01
3 (cis, triplet) 01 3
4 01 7
5 22 t6
a Singlet state, if not marked otherwise
emoS stcepsA of the Chemistry of Hydrocarbons Aliphatic Polylithiated
ences between the tetrahedral and the (cis-)planar structures with increasing lithiation
(Table .)1
0 t i 0
la Ib
2a 2b
Li ~ L i
~
3a 3b(cis) 3b(trans)
Li iL
LiO
OLi L
6a b4
X
O
iL
Li Li Li ).,(
5a 5b
The stabilization of the planar carbon by lithium was explained by its simultaneous
cs-donor and rc-acceptor ability which can be shown by the following resonance
structures of the cis-planar dilithiomethane 3b (cis):
H e H H H H
H-C:Li 0 ~--,," H-C-Li ",,--" H-C-Li ~- = ®iLO'.~-H = H-~Li ®
=
,i e i.t e ,'i u
Another consequence of the donor/acceptor properties of the lithium atom is the
dramatic stabilization by 37 kcal/m01 (155 kJ/mol) of the cis-planar dilithiomethane
cis) b ( 3 compared with the trans-planar structure trans). b ( 3 In contrast to trans) b ( 3
the lithium atoms in 3b (cis) can interact electronically to form together with the p
orbital at the carbon atom a (4n + 2)-Hiickel system (n = 0) isoelectronically to
the cyclopropenyl cation 6:
Adalbert Maercker and Manfred Theis
i L (cid:127) O
+
6
3bttrans)
3b(cis)
It is remarkable that the lowest inversion barrier (2.9 kcal/mol, 12.1 kJ/mol) of all
calculated species was found for 3b (cis) in its triplet state. This was confirmed by more
accurate calculations considering large scale configuration interaction and cluster
correction delivering even lower values of 1.7 and 1.8 kcal/mol (7.1 and 7.5 kJ/mol)
respectively ill The original result that the triplet states of dilithiomethane 3 might
be energetically favorable, however, could not be confirmed (Table 2). But anyhow,
the energies were found to lie so close together that in molecular dilithiomethane 3
four nearly degenerate states have to be discussed.
Table 2. Calculated Energy Differences (kcal/mol) and Dipole Moments (Debye) for Dilithio-
methane Conformers of Different Multiplicity
Conformer STO-3G )9 4-31G )9 Large Cluster xI ~H
)yticilpitluM( elacS CI )~1 Correction ~J
a 3 )telgnis( 0 0 0.0 0.0 24.5
(triplet) a 3 - 21 - 61 --0.8 1.2 -0.76
3b (cis, singlet) 71 01 4.7 3.8 58.4
triplet) (c/s, b 3 --2 -- 31 9.0 9.3 -- 22.1
Most interestingly the dipole moments of the triplet states are not only very much
smaller but also show reversed polarization: CeLi e. Hand in hand a dramatic di-
minuation of the angle ~ LiCLi in dilithiomethane 3 is found on going from the singlet
to the triplet state 9,11). This is due to the population of a MO in which some Li--Li
bond is maintained. Therefore at least for the triplet state another three resonance
structures have to be added:
H-C- HeLle " : --- H-~®Li = = H-C, Li
Li / ®Li Li /
emoS stcepsA of eht yrtsimehC of citahpilA detaihtilyloP snobracordyH
The structure and bonding in dilithiomethane 3 was reexamined recently in detail
by Streitwieser ~2~ (electron density analysis) and Harrison ~al (Multi-Configuration
SCF calculations), essentially confirmingt he previous results.
Dimers of dilithiomethane 3 have also been calculated by Jemmis, Schleyer, and
dzD(
Pople ~'~L The head to head dimer 3c symmetry) of planar monomers 3b (cis)
the four lithium atoms bridging two perpendicular CH 2 units was found to be the most
stable.
o.. c c
3c
The dimerization energy relative to the energy of two tetrahedral monomers 3a,
37 kcal/mol (155 kJ/mol) (4-31G/5-21G(Li)), is considerable and should be even larger
with higher association. Possible trimer and polymer structures have also been dis-
cussed )4~
2.2 Lithiated Ethanes
Thep otential energy surface of 1,2-dilithioethane 7 was examined by Schleyer, Gleiter,
Pople, and coworkers ~sl at several levels of ab initio theory. The global energy
minimum was found to be the partially bridged trans conformation 7b(C2h
symmetry), although the symmetrically trans doubly bridged structure 7a (D2h
symmetry) is only 1.9 keal/mol (7.95 kJ/mol) higher in energy.
iL iL
iL L|
7a 7b
Triplet states this time are all lying significantly higher in energy and need not be
considered in this connection. The energy gained by partial bridging in 7b,
16.4 kcal/mol (68.6 kJ/mol) (4-31G), can be assessed by comparing the energy of
fully optimized 7b with that of the standard geometry ° (180 dihedral angle) used by
Radom et al. )6~ in calculations of the rotational potential surface of 1,2-dilithio-
ethane .7
