21.i
The
Transition
Metal Complexes
of
Stannylenes
Paige
M.
Hanchett
Literature
Seminar
February
17,
1987
Stannylenes
are
units
of
divalent
tin
bound
to
two
organic
or
halide
resi-
dues.
Interest
in
these
compounds
has
grown
in
recent
years
as
researchers
seek
to
expand
their
understanding
of
main
group
elements,
particularly
in
their
less
common
oxidation
state.
While numerous
articles
have
been
published
on
the
chemistry
of
transition
metal
carbenes,
much
less
information
is
available
on
their
tin
analogs.
When
freshly
prepared,
most
stannylenes
exist
in
the
monomeric form
but
unless
the
ligands
on
tin
are
sufficiently
bulky,
they
rapidly
polymerize
[1].
The
methylcyclopentadienyl,
cyclopentadienyl
[2]
and amido
[3]
stannylenes
exist
as
monomers due
to
the
steric
bulk
and
electronic
characteristics
of
the
ligands.
The
bis(trimethylsilyl)methyl
[li]
and
$-ketoenolato
complexes
exist
as
loosely
bound
dimers
in
the
solid
state
and
in
solution
a monomer-dimer
equilib-
rium
is
observed.
The
transition
metal
complexes
of
stannylenes
exist
primarily
in
two
forms--base
stabilized
and
non-base
stabilized.
The
organic
ligands
on
tin
are
small
(Me,
t-Bu)
in
the
base
s.tabilized
compounds
of
group
VI
metals
[5]
but
can
be
larger
(CH(SiMe
3
)
2
,
$-ketoenolates)
for
group
VIII
metals
[6].
These com-
pounds
are
stabilized
by
the
~
donation
of
the
base
electrons
to
the
tin.
These
stannylene
complexes
can
be
synthesized
only
if
a
coordinating
solvent
is
pres-
ent
and
they
decompose
if
the
base
is
removed. The
bis-cyclopentadienyl)
stannylene
forms a dimer
with
enneacarbonyl-diiron
where
the
Cp
rings
have
changed from
penta-
to
mono-hapto
[7].
Group
VI
metal
carbonyls
can
form complexes
with
stannylenes
of
intermedi-
ate
and
large
steric
bulk
that
do
not
require
a
11X>lecule
of
base
to
stabilize.
These compounds
exist
for
the
stannylenes
Cp
2
Sn,
(MeCp)
2
sn
[8],
[CH(SiMe
3
)
2
J
2
sn
[9],
and
($-ketoenolato)
2
sn
[10].
The
stability
of
these
compounds
is
due
to
the
strong
~-bonding
between
the
tin
and
the
metal.
11
9sn Mossbauer
spectroscopy
has
proven
to
be
a
useful
tool
in
probing
the
bonding
in
these
compounds. The monomeric
stannylenes
exhibit
rather
large
isomer
shifts
corresponding
to
divalent
tin
[11].
Upon
complexation,
the
isomer
shifts
decrease
and
the
quadrupolar
splitting
values
increase
markedly
[12].
These
changes
suggest
synergic
metal-tin
back-bonding
from
the
ct-orbitals
on
the
metal
to
the
p
or
d
orbitals
of
tin.
Infrared
and
nuclear
magnetic
resonance
data
for
these
compounds
indicate
that
there
is
a
strong
~-interaction
and
support
such
a bonding scheme.
25
Despite
these
results,
a
conclusive
and
satisfactory
explanation
of
the
bonding
in
these
compounds
is
not
yet
available.
The
lack
of
reactivity
studies
of
transition
metal
stannylene
complexes may,
in
part,
account
for
this
defi-
ciency.
Future
research
comparing
the
reactivity
of
stannylene
complexes
to
carbene
complexes
can
be
useful
in
understanding
the
chemistry
of
group
XIV
compounds.
References
1.
Donaldson,
J.
D.,
"The Chemistry
of
Bivalent
Tin,
11
Progr.
Inorg.
Chem.
1972,
~.
287.
2.
Harrison,
P.
G.;
Healy,
M.
A.,
"Spectroscopic
Investigation
of
Dicyclo-
pentadienyltin(II)
and
its
Methylcyclopentadienyl
Analogue,"
J.
Organomet.
Chem.
1973,
2.!_,
153.
3.
Lappert,
M.
F.;
Power,
P.
P.,
"Transition-metal
Chemistry
of
Metal(
II)
Bis(trimethylsilyl)amides
M'
(NR
2
)
2
(R
=
SiMe
3
;
M'
"'
Ge,
Sn,
or
Pb),"
J.
Chem.
Soc.,
Dalton
Trans.
1985, 51.
4.
Davidson,
P.J.;
Harris,
D.
H.;
Lappert,
M.
F.,
"The
Synthesis
and
Physical
Properties
of
Kinetically
Stable
Bis[bis(trimethylsilyl)methyl]-
germanium(II),
-tin(II),
and
-lead(II),"
J.
Chem.
Soc.,
Dalton
Trans.
1976, 2268.
5.
(a)
Marks, T.
J.,
"Dialkylgermylene-
and
-stannylene-Pentacarbonyl-
chromium Complexes,"
J.
Am.
Chem.
Soc.
1971, 93, 7090.
(b)
Brice,
M.
D.;
Cotton,
F.
A.,
"Crystal
and
Molecular
Structure
of
(Di-tert-butylstannylene)pyridinopentacarbonylchromium,"
J.
Am.
Chem.
Soc.
1973, 95, 4529.
6.
(a)
Cornwell,
A.
B.;
Harrison,
P.
G.,
"The
Interaction
of
Tin(II)
Halides
and
Bis(B-ketoenolates)
with
Di-iron
Enneacarbonyl,"
J.
Chem.
Soc.,
Dalton
Trans.
1975, 2017.
(b)
Marks, T.
J.;
Newman,
A.
R.,
"Facile
and
Reversible
Homolysis
of
Iron-Germanium,
-Tin,
and -Lead Bonds
by
Lewis
Bases,"
J.
Am.
Chem.
Soc.
1973, 95, 769.
7.
Harrison,
P.
G.; King, T.
J.;
Richards,
J.
A.,
"Crystal
and
Molecular
Structure
of
D1-µ-bis(
cyclopentadienyl)
stanny
1-bis(
tetracarbonyliron),"
J.
Chem.
Soc.,
Dalton
Trans.
1975, 108, 47.
8.
Cornwell,
A.
B.;
Harrison,
P.
G.;
Richards,
J.
A.,
11
Some
Reactions
of
Dicyclopentadienyl
and
Bis(methylcyclopentadienyl)tin
with
Metal Carbonyl
Compounds,"
J.
Organomet.
Chem.
1976, 108, 47.
9.
(a)
Cotton,
J.
D.;
Davidson,
P.
J.;
Lappert,
M.
F.,
"The Chemistry and
Properties
of
Bis[bis(trimethylsilyl)methyl]tin(II)
and
Its
Lead
Analogue,"
J.
Am.
Chem.
Soc.,
Dalton
Trans.
1976, 2275.
{b)
Cotton,
J.
D.;
Davidson,
P.
J.;
Lappert,
M.
F.;
Donaldson,
J,
D.;
Silver,
J.,
"Mossbauer
Spectroscopy
Studies
of
Bis[
bis(
trimethyl-
silyl)methyl]tin(II)
and
Its
Derivatives,"
J.
Chem.
Soc.,
Dalton
Trans.
1976, 2286.
26
10.
Cornwell,
A.
B.;
Harrison,
P.
G.,
"Chromium, Molybdenum, and Tungsten
Pentacarbonyl
Complexes
of
Tin(II)
Bis(B-ketoenolates),
11
J.
Chem.
Soc.,
Dalton
Trans.
1975, 1486.
11.
Harrison,
P.
G.;
Zuckerman,
J.
J.,
"The Mossbauer Isomer
Shift
of
Tin(II)
Compounds,"
lnorg.
Chim. Acta 1977,
~,
L3.
12.
Grynkewich,
G.
W.;
Ho,
B.
Y.
K.;
Marks,
T.
J.;
Tomaja,
D.
L.;
Zuckerman,
J.
J.,
"Tin-l19m Mossbauer and
X-ray
Photoelectron
(ESCA)
Studies
of
Tin
Oxidation
State
and Bonding
in
Base-Dialkyltin
Pentacarbonylchromium and
Tetracarbony
liron
Complexes,"
lnor
g.
Chem.
1973,
g,
2522.
··r
