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Nature of the transient intermediate involved in the reactions between tricarbonyl(tropylium)tungsten(0) and molybdenum(0) fluoroborate and iodide ion
Cl
Joktkl of Or&no~metallic ChemiatJy, 149 (1978) Cl-C6 _ OHsevierSequoiaS~,~e-_PrintedinTheNetherIands
Preliminary Communication .Nature of theTransient
htermediate
Tricarbonyl(uopylIum)~~~n(O)
PaulPowell,Leslte
hvolved
In the Reactions between
and molybdenum(O) Fluoroborate
and Iodide Ion
J. Russell and ElizabethStyles
Dept. of Cbemisay,
Royal Holloway College,
Egham, Surrey TW20 OEX
Alan J. Brown, Oliver W. Howarthand Peter Moore* Dept. of Chemisnyand
Molecular
Sciences,
University
of Warwick.
Coventry CV4 7AL
(Received January 9th, 1978)
Summary. -
Thereactions
between iodLde ion and [M(C7H7)(CO)
]BF4 (h%= MO, W; l3 C7H~ = nopylium ion) have been investigated kinetIcally by flow H n .m.r. and by stopped-flow
spectrophotometry,
lntermedlates areformed
and the n.m.r.
in each reaction by transfer of the iodide ion to the
tropylium ring, from an tnttlalrapldly metal-iodide
method shows that two fluxional
formed totermediate probably involving a
bond.
A brown intermediate is reported to form during thecourse of reactIon (1) @I = MO, W;.Crf
=tropylIum
CM(C7H7)C0)3
ion):'
I+ + I- -
CM(C+-f7)C0)211
The structureof the intermediatehas
+ CO
(1)
not been established previously
and could
arlse from attackd Iodide ion atthe tropylium Ion, at the metal or even at one of the carbonylgroups.
Prevbus studleshave shown that nucleophibs such as HS-, MeO2 and phosphlnes and phosphftes are also known to
and H- react at the tropyUum ioa,
be involved in attackat aromatlc rings.3 carbonylgroup~
has beenestablIsh+,
In othercasesnucleophilic
as in the reactions with au&es
and in the reactions of drenyi(atcarbonyl)iron(o) for the formation of an acyl derivative. ’
[M(Iv%GN)~(CO)~]
where dIspkcement
orhydrazines,
where there Is infra-redievidence
NucleophilLc attack atthe metal centre is
alsoknown tooccur during t&e reactioa of [M(C7H.,)(CO)3]+ with aceton&e,
attackatthe
(M = Cr,
MO and W)
of the tropylium ion takes place and
Is eventually formed.6
4
+-
CM(C7H,I)(CO)2
ki2 [M(C~,I)(CO)2(a;etwe)]~
[M(C7H,)(C0)&
F;yhen%%= W, the spectrophotometric
(4)
(acetone11 + CO _-+acetooe
(5)
results show that formation of the browu
%meri&lia&~2
foUows the-rate- law:. da2J/dt = {a/(1 + K[ I-])][r-][ W(C~,)(CO)~~. -1 -1 * 7 dm3mol At*7;2K,-a=k,K=771 f 45 dm3moI s lK=61 -1 2 and htiack t3G I&nItia& vahe of ki at high [I-] ia 12.7 f 0.8 8 . Formation of I was aLso folk&d
between 219.and 258 K by SFFTi%lR
under the limiting condition -1 = of high [I-], aad the activation parameters associated with k, are AH*/kJ mol -1 -1 mol =75*32and -23*10forM=Waod 89-p i 8;; and 60.3 l 2.4, bsf/J K
MO te.spectiveIy: interaiediate _’ I which forms rapIdly upon mixing the compIexes with excess iodide ion could either ti an ioa_p8ir, iodide ion is co-ordinated
or more l3kely a complex in which the We favour
at +e metal centre,
structure gf&
intermediateI
(structures -s
or ij
either structure &or
’, A _ being more IigeIy since conversion to _I2
is facilitati
There are two pieces of
by &e&*eometry.
evidence in favour of initia.1attack at the metal centre rather than toa-&ir ‘f0rmim0a
l
with kl fim
Fir&y,
the st@fkaatI~
eoth&ptes of actlvat&
assoctated
with the -&eat& stre@th of W-I compared witfi MO-I boads, and we
wouM no; ez@ect s&
a dtffe&ze
our SF~N&&~e&eri&& w
dkerent
- ..
ii&t m:@$tii&
ii&
ifr’
was an ton-pair.
the Iegs rea&ve
ex$&S [-‘(aad befdre qy
formed) .&z&G Is a &&ica&
I&&e&g
&t
Secondly, we observe In
tungstea complex at 237 K, that
of the brown Inter&diate~2 : n&l&e ati) of &&ingbt
has
c3
(A)
H (a)
CD)
(Cl
[ca.
93% profrably (s)]
and at 6 = 5.19 p.p.m.
height of the resonance from the majori*
[ca.
7%, probably @)I
specIea (6 = 5.47 p.p.m.,
and the
Av =1.86 3
Hz at 237 K) when compIeteIy formed la nearly twke as large as that observed
f.nitIaIIy forl’.
This fits with struchlres
A_ or Efarl’
which would be
expected to be fhxxional and therefore have a broadened C H resonance. It 77 proved ImpkssIbIe ID freeze out the broad resonance associated witbJ’ owing to &e Iow soIubiIityat p.p.m.
from (c)
greatlyreduced
temperatures,
knt&eresonanceat6
= 5.47
did colIapse upon cooIing, as shown in the figure.
The
spectral assigments shown for (SC, are consistent with some closely related StJXCtUreS. cg-Js. whereas
The unique hydrogen atom
c(c7HpC~)31' in
'and
&e adduct -benveen
C(CgH7)FdCO)31 Twhichhss
baa a resmance
at Iow fIeId.’
(a)hasaresbnanceathighffeIdas
in
[ W(C7H7)(CO)3]s
and I$P,
3
a different srxucture the uniquehydrogen
The complex between [ W(C7H7)(CO)3
]+ and Rx: P Is
reported ts bavea structure the same as that postulated for the brown intermedIate (C) with I-replaced by RI:;, of (C)where
tile chemkai
and tbts la confirmed by the low temperature
spectrum
shifts are very similar to those observed at. room
temperapre for the stable adduct with E$ P (figure 1. Studies of the rateof
loss of thebrown intermediate
12 toglve
the.ffnal product
136 K
(3)
146K
(2)
/L
(1)
186K
_ii 9 ZO
* 5.0
6.0
-Fig.- I,
(1) -.(4)
_ VarhbIe
(5 1. Room tgmperaf+&
4.0
Solvent , 2-o.
~.of $)_.
~_
237 K
b(ppm)
tempixature %
, 3.0
jI-3n.m.r.-spectra
n.m;k. ~spectrum of. the BuiP klduci .:
of-[ (C~j)W(CO),]~~~lelmulatlo_n
Ia- (6)].
= ..
:-
.__ =-
-.:‘~.$?&te
C5
-.
.. :
an in&ialrapid
: .. ‘.
_c++v*forithe
reactI&
The rate constants
approxtmately Inversely wltkthe initial complex -2 s-i from 1.9 x 10 whett[&mplex] = 5 x lOa mol dmm3, -3 -3 when [complex] = 5 x 10 mol dm . Furthermore, Lf solutions
are pre-saturated
with CO befc%rethe addition of iodide ion, the brown lntermedtate for quite a lmgperiod
can be sraMllsed ~reabtIons(4)
-(5):
Initially when [CO]“decreasesuntil
of time. This behaviour is cmsistent with
appllcatlon of the steady-state approxhnattan to the postulated
solvento-complexgives
= k’83/&_2[CO]
k(observed) 8, k(observed)
finallyk(ohserved)
= k;,
htas
+ k3); (k;= k2[acetone]). [CO]
z k*2k3&_2[ CO].
increases Since [CO]
the final rate is inversely dependent on [complex]
(4) - (5)are reversible
step.
s~w.step..vary
myc&c&r&I&+ryk~g .__ to 4-6 ,;&-I .
[complex],
followed by aslower
also ccnslstentwlth
is directly related to
as observed.
.Reacticns
the observation that the final product is not In a , since there is no brown intermediate refcrmed when
equilibrhtm with f
the final product Isreactedwith The possibility
in solution the rate
excess CO.
that the minor intermedlate species observed in these reactlons
(tentatively assignedtheendo-structure,
g) Is, in fact, the solvento-complex
postulated in reactIons (4) - (5) is unlikely since the concentration of _D Is not signtficantly reducedwhen ezess
the reaction (M = W) Is carried out in the presence of an
ch the basis of the reversible
of CO.
reaction (4),
the concentration of
the minor species would be erpected to be reduced tozero under these conditions. The mechantsm postulated here for the formation of the intermediate (L2) is very shnLla.r to thatreportedrecently nucleophiles (e.g. followed by uansfer
Ni,
OEt-,
for the reactions between [ (C,H,)Fe(CO),]+ E$P),
and
attack occurring first at the metal centre 10
of tie nucleophtle to the C,Hy ring.
Acknowledgement We thank the S.R.C.
for financial support. References
1.
R.B. Ktngand M.B.
Bisnette, berg.
A. Franxagllaa. Inorg. Chem., 2.
J.D. Munroand P.L.
3.
G.R. John, L.A.P.
Maguire,
horg.
Kane-Magulre
J. Organometallic
L.A.P.Kane-Maguire,
5 (1966)
3 (1964)
D.A.
and D.A. Swe&art,
Chem.,
J.C.S.
3475, 3479, 3484.
Swelgart, J. Organometallic M. Gower and L.A.P.
108 (1976)
Chem. Comm.,
Chim. Acta,
18 (1976)
J.31; 17 (1976)
Inorg. Chlm. Acta,
12 (1975)
Ll9; J.L.
(Chem. Snc. Specialist PeriodicalReports)
785; R.B. KLng and
1837.
Pauson, J. Chem. !Zoc., (1961)
120 (1976) C45-47;
them.,
Chem.,
Kane-
C15; D.A. SweIgart and (1976)
13;
A. Salxer,
221; P. Hackett and G. Jaauen,
Davidson,
Borg.
5 (1977) 387.
Reaction Mechanisms
4,
R.j.AngeEcr,
Amounts~.
5.
G, fscbiam,
C,mradiaiand
EC,&. Hine,B.P.pahasoaand$. LA,i?_ 6,
&.M.
~ane&fagufre, .AIXBLandEhA,P.
Reseercfi,
S 11972) .%3!5.
CL Boanbif, hoq. Levis,
J~C,S,
cIzilln. Acta, C&em. Comm.,
44 w75)
<197Sl 8f;
pe.rsmalcommun icatml. Kane-NIagufre,
f.C.&
rJaltoa,
D.A.
Coach, .O;W, Hoiaarta and P. &bore, J. Phys. B., 8 (1975)
8,
h$.L.
Mae*-s.I;,.-
(f96SI
99aidfSf
tG.
j;I3;
audW,D.
mesz,
Adv.
83’1.
fhganometallk Qem,,
3
m
Mahkr and R;. l%t+t, I- Amaze*,Chem, !Sec., 1u (1963)
33-A; mnv~,
1683.
Clgn)
7.
9.
3.%!&;
S-K, CitawJELaudWw,K, G&M,
Imqg, Cbim,Acta,
39!55.. 19 0976)
uf-L32.
Joktkl of Or&no~metallic ChemiatJy, 149 (1978) Cl-C6 _ OHsevierSequoiaS~,~e-_PrintedinTheNetherIands
Preliminary Communication .Nature of theTransient
htermediate
Tricarbonyl(uopylIum)~~~n(O)
PaulPowell,Leslte
hvolved
In the Reactions between
and molybdenum(O) Fluoroborate
and Iodide Ion
J. Russell and ElizabethStyles
Dept. of Cbemisay,
Royal Holloway College,
Egham, Surrey TW20 OEX
Alan J. Brown, Oliver W. Howarthand Peter Moore* Dept. of Chemisnyand
Molecular
Sciences,
University
of Warwick.
Coventry CV4 7AL
(Received January 9th, 1978)
Summary. -
Thereactions
between iodLde ion and [M(C7H7)(CO)
]BF4 (h%= MO, W; l3 C7H~ = nopylium ion) have been investigated kinetIcally by flow H n .m.r. and by stopped-flow
spectrophotometry,
lntermedlates areformed
and the n.m.r.
in each reaction by transfer of the iodide ion to the
tropylium ring, from an tnttlalrapldly metal-iodide
method shows that two fluxional
formed totermediate probably involving a
bond.
A brown intermediate is reported to form during thecourse of reactIon (1) @I = MO, W;.Crf
=tropylIum
CM(C7H7)C0)3
ion):'
I+ + I- -
CM(C+-f7)C0)211
The structureof the intermediatehas
+ CO
(1)
not been established previously
and could
arlse from attackd Iodide ion atthe tropylium Ion, at the metal or even at one of the carbonylgroups.
Prevbus studleshave shown that nucleophibs such as HS-, MeO2 and phosphlnes and phosphftes are also known to
and H- react at the tropyUum ioa,
be involved in attackat aromatlc rings.3 carbonylgroup~
has beenestablIsh+,
In othercasesnucleophilic
as in the reactions with au&es
and in the reactions of drenyi(atcarbonyl)iron(o) for the formation of an acyl derivative. ’
[M(Iv%GN)~(CO)~]
where dIspkcement
orhydrazines,
where there Is infra-redievidence
NucleophilLc attack atthe metal centre is
alsoknown tooccur during t&e reactioa of [M(C7H.,)(CO)3]+ with aceton&e,
attackatthe
(M = Cr,
MO and W)
of the tropylium ion takes place and
Is eventually formed.6
4
+-
CM(C7H,I)(CO)2
ki2 [M(C~,I)(CO)2(a;etwe)]~
[M(C7H,)(C0)&
F;yhen%%= W, the spectrophotometric
(4)
(acetone11 + CO _-+acetooe
(5)
results show that formation of the browu
%meri&lia&~2
foUows the-rate- law:. da2J/dt = {a/(1 + K[ I-])][r-][ W(C~,)(CO)~~. -1 -1 * 7 dm3mol At*7;2K,-a=k,K=771 f 45 dm3moI s lK=61 -1 2 and htiack t3G I&nItia& vahe of ki at high [I-] ia 12.7 f 0.8 8 . Formation of I was aLso folk&d
between 219.and 258 K by SFFTi%lR
under the limiting condition -1 = of high [I-], aad the activation parameters associated with k, are AH*/kJ mol -1 -1 mol =75*32and -23*10forM=Waod 89-p i 8;; and 60.3 l 2.4, bsf/J K
MO te.spectiveIy: interaiediate _’ I which forms rapIdly upon mixing the compIexes with excess iodide ion could either ti an ioa_p8ir, iodide ion is co-ordinated
or more l3kely a complex in which the We favour
at +e metal centre,
structure gf&
intermediateI
(structures -s
or ij
either structure &or
’, A _ being more IigeIy since conversion to _I2
is facilitati
There are two pieces of
by &e&*eometry.
evidence in favour of initia.1attack at the metal centre rather than toa-&ir ‘f0rmim0a
l
with kl fim
Fir&y,
the st@fkaatI~
eoth&ptes of actlvat&
assoctated
with the -&eat& stre@th of W-I compared witfi MO-I boads, and we
wouM no; ez@ect s&
a dtffe&ze
our SF~N&&~e&eri&& w
dkerent
- ..
ii&t m:@$tii&
ii&
ifr’
was an ton-pair.
the Iegs rea&ve
ex$&S [-‘(aad befdre qy
formed) .&z&G Is a &&ica&
I&&e&g
&t
Secondly, we observe In
tungstea complex at 237 K, that
of the brown Inter&diate~2 : n&l&e ati) of &&ingbt
has
c3
(A)
H (a)
CD)
(Cl
[ca.
93% profrably (s)]
and at 6 = 5.19 p.p.m.
height of the resonance from the majori*
[ca.
7%, probably @)I
specIea (6 = 5.47 p.p.m.,
and the
Av =1.86 3
Hz at 237 K) when compIeteIy formed la nearly twke as large as that observed
f.nitIaIIy forl’.
This fits with struchlres
A_ or Efarl’
which would be
expected to be fhxxional and therefore have a broadened C H resonance. It 77 proved ImpkssIbIe ID freeze out the broad resonance associated witbJ’ owing to &e Iow soIubiIityat p.p.m.
from (c)
greatlyreduced
temperatures,
knt&eresonanceat6
= 5.47
did colIapse upon cooIing, as shown in the figure.
The
spectral assigments shown for (SC, are consistent with some closely related StJXCtUreS. cg-Js. whereas
The unique hydrogen atom
c(c7HpC~)31' in
'and
&e adduct -benveen
C(CgH7)FdCO)31 Twhichhss
baa a resmance
at Iow fIeId.’
(a)hasaresbnanceathighffeIdas
in
[ W(C7H7)(CO)3]s
and I$P,
3
a different srxucture the uniquehydrogen
The complex between [ W(C7H7)(CO)3
]+ and Rx: P Is
reported ts bavea structure the same as that postulated for the brown intermedIate (C) with I-replaced by RI:;, of (C)where
tile chemkai
and tbts la confirmed by the low temperature
spectrum
shifts are very similar to those observed at. room
temperapre for the stable adduct with E$ P (figure 1. Studies of the rateof
loss of thebrown intermediate
12 toglve
the.ffnal product
136 K
(3)
146K
(2)
/L
(1)
186K
_ii 9 ZO
* 5.0
6.0
-Fig.- I,
(1) -.(4)
_ VarhbIe
(5 1. Room tgmperaf+&
4.0
Solvent , 2-o.
~.of $)_.
~_
237 K
b(ppm)
tempixature %
, 3.0
jI-3n.m.r.-spectra
n.m;k. ~spectrum of. the BuiP klduci .:
of-[ (C~j)W(CO),]~~~lelmulatlo_n
Ia- (6)].
= ..
:-
.__ =-
-.:‘~.$?&te
C5
-.
.. :
an in&ialrapid
: .. ‘.
_c++v*forithe
reactI&
The rate constants
approxtmately Inversely wltkthe initial complex -2 s-i from 1.9 x 10 whett[&mplex] = 5 x lOa mol dmm3, -3 -3 when [complex] = 5 x 10 mol dm . Furthermore, Lf solutions
are pre-saturated
with CO befc%rethe addition of iodide ion, the brown lntermedtate for quite a lmgperiod
can be sraMllsed ~reabtIons(4)
-(5):
Initially when [CO]“decreasesuntil
of time. This behaviour is cmsistent with
appllcatlon of the steady-state approxhnattan to the postulated
solvento-complexgives
= k’83/&_2[CO]
k(observed) 8, k(observed)
finallyk(ohserved)
= k;,
htas
+ k3); (k;= k2[acetone]). [CO]
z k*2k3&_2[ CO].
increases Since [CO]
the final rate is inversely dependent on [complex]
(4) - (5)are reversible
step.
s~w.step..vary
myc&c&r&I&+ryk~g .__ to 4-6 ,;&-I .
[complex],
followed by aslower
also ccnslstentwlth
is directly related to
as observed.
.Reacticns
the observation that the final product is not In a , since there is no brown intermediate refcrmed when
equilibrhtm with f
the final product Isreactedwith The possibility
in solution the rate
excess CO.
that the minor intermedlate species observed in these reactlons
(tentatively assignedtheendo-structure,
g) Is, in fact, the solvento-complex
postulated in reactIons (4) - (5) is unlikely since the concentration of _D Is not signtficantly reducedwhen ezess
the reaction (M = W) Is carried out in the presence of an
ch the basis of the reversible
of CO.
reaction (4),
the concentration of
the minor species would be erpected to be reduced tozero under these conditions. The mechantsm postulated here for the formation of the intermediate (L2) is very shnLla.r to thatreportedrecently nucleophiles (e.g. followed by uansfer
Ni,
OEt-,
for the reactions between [ (C,H,)Fe(CO),]+ E$P),
and
attack occurring first at the metal centre 10
of tie nucleophtle to the C,Hy ring.
Acknowledgement We thank the S.R.C.
for financial support. References
1.
R.B. Ktngand M.B.
Bisnette, berg.
A. Franxagllaa. Inorg. Chem., 2.
J.D. Munroand P.L.
3.
G.R. John, L.A.P.
Maguire,
horg.
Kane-Magulre
J. Organometallic
L.A.P.Kane-Maguire,
5 (1966)
3 (1964)
D.A.
and D.A. Swe&art,
Chem.,
J.C.S.
3475, 3479, 3484.
Swelgart, J. Organometallic M. Gower and L.A.P.
108 (1976)
Chem. Comm.,
Chim. Acta,
18 (1976)
J.31; 17 (1976)
Inorg. Chlm. Acta,
12 (1975)
Ll9; J.L.
(Chem. Snc. Specialist PeriodicalReports)
785; R.B. KLng and
1837.
Pauson, J. Chem. !Zoc., (1961)
120 (1976) C45-47;
them.,
Chem.,
Kane-
C15; D.A. SweIgart and (1976)
13;
A. Salxer,
221; P. Hackett and G. Jaauen,
Davidson,
Borg.
5 (1977) 387.
Reaction Mechanisms
4,
R.j.AngeEcr,
Amounts~.
5.
G, fscbiam,
C,mradiaiand
EC,&. Hine,B.P.pahasoaand$. LA,i?_ 6,
&.M.
~ane&fagufre, .AIXBLandEhA,P.
Reseercfi,
S 11972) .%3!5.
CL Boanbif, hoq. Levis,
J~C,S,
cIzilln. Acta, C&em. Comm.,
44 w75)
<197Sl 8f;
pe.rsmalcommun icatml. Kane-NIagufre,
f.C.&
rJaltoa,
D.A.
Coach, .O;W, Hoiaarta and P. &bore, J. Phys. B., 8 (1975)
8,
h$.L.
Mae*-s.I;,.-
(f96SI
99aidfSf
tG.
j;I3;
audW,D.
mesz,
Adv.
83’1.
fhganometallk Qem,,
3
m
Mahkr and R;. l%t+t, I- Amaze*,Chem, !Sec., 1u (1963)
33-A; mnv~,
1683.
Clgn)
7.
9.
3.%!&;
S-K, CitawJELaudWw,K, G&M,
Imqg, Cbim,Acta,
39!55.. 19 0976)
uf-L32.