Cyclopentadienylmolybdenum(II) and -(III) complexes containing diene and allyl ligands. Part 4. Reactivity studies of the bisallyl complex CpMo(supine-η-C3H5)2 and the allyl-butadiene complex [CpMo(supine-η-C3H5)(supine-η-C4H 6)] [PF6]

Article abstract of DOI:10.1016/S0277-5387(98)00164-8

Compound CpMo(η³-C₃H₅)₂, 3, has been synthesized from CpMoCl₄ and four equivalents of allylmagnesium bromide. While the compound is stable in donor solvents at room temperature, warming in refluxing MeCN induces the formation of 1,5-hexadiene by a metal-mediated allyl-allyl coupling process. Treatment of 3 with Bu^tNC at room temperature affords CpMo(η³-C₃H₅)(Bu^tNC) ₂, 4. A similar reduction with presumed allyl radical loss occurs for [CpMo(η³-C₃H₅)(η⁴-C ₄H₆)]⁺, [1c]⁺, to afford [CpMo(η⁴-C₄H₆)(Bu^tNC) ₂]⁺, 5. Treatment of [1c]⁺ with methyllithium affords two products, the major one (1c) corresponding to the one-electron reduction pathway and the minor one (CpMo(η³-C₃H₅)(η³-C ₃H₄-1-Et), 6, ca. 4%) corresponding to nucleophilic addition. Protonation of the 1c:6 mixture affords a 2:1 mixture of cis and trans 2-pentene, in addition to propene. The room temperature Cp₂Fe⁺PF₆^- oxidation of 3 in MeCN induces the immediate release of 1,5-hexadiene. The oxidation of 3 in Bu^tNC gives complexes [CpMo(CNBu^t)₃ (η²-CH₂CHCH₂CH₂CH=CH ₂)]⁺PF₆^- (7, major) and [CpMo(CNBu^t)₄]⁺PF₆^- (8, minor). Finally, the oxidation of 3 in the presence of butadiene, followed by treatment with CD₃CN, affords a mixture of [CpMo(η³:η³-C₃H₄CH ₂CH₂C₃H₄)(CD₃CN)] ⁺PF₆^-, 9, and [CpMo(η⁴-C₄H₆)(CD₃CN) ₂]⁺PF₆^-, 10. Thermal decomposition of this mixture affords butadiene and 1,5-cyclooctadiene.

Full text of DOI:10.1016/S0277-5387(98)00164-8

Polyhedron Vol[ 06\ No[ 10\ pp[ 2578Ð2699\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166Ð4276"87#99053Ð7
Cyclopentadienylmolybdenum"II# and !"III#
complexes containing diene and allyl ligands[ Part
3[ Reactivity studies of the bisallyl complex
CpMo"supine!h!C2H4#1 and the allyl!
butadiene complex ðCpMo"supine!h!
C2H4#"supine!h!C3H5#ŁðPF5Ł ð0Ł[
Rinaldo Poli\aꢀ and Li!Sheng Wangb
aLaboratoire de Synthese et d|Electrosynthese Organometalliques\ Faculte des Sciences {{Gabriel||\
Á
Á
ꢁ
ꢁ
Universite de Bourgogne\ 5 Boulevard Gabriel\ 10099 Dijon\ France
ꢁ
bDepartment of Chemistry and Biochemistry\ University of Maryland\ College Park\ Maryland 19631\
U[S[A[
"Received 15 February 0887^ accepted 6 April 0887#
Abstract*Compound CpMo"h2!C2H4#1\ 2\ has been synthesized from CpMoCl3 and four equivalents of
allylmagnesium bromide[ While the compound is stable in donor solvents at room temperature\ warming in
re~uxing MeCN induces the formation of 0\4!hexadiene by a metal!mediated allyl!allyl coupling process[
Treatment of 2 with ButNC at room temperature a}ords CpMo"h2!C2H4#"ButNC#1\ 3[ A similar reduction with
presumed allyl radical loss occurs for ðCpMo"h2!C2H4#"h3!C3H5#Ł¦\ ð0cŁ¦\ to a}ord ðCpMo"h3!C3H5#"ButNC#1Ł¦\
4[ Treatment of ð0cŁ¦ with methyllithium a}ords two products\ the major one "0c# corresponding to the one!
electron reduction pathway and the minor one "CpMo"h2!C2H4#"h2!C2H3!0!Et#\ 5\ ca[ 3)# corresponding to
nucleophilic addition[ Protonation of the 0c]5 mixture a}ords a 1]0 mixture of cis and trans 1!pentene\ in
−
addition to propene[ The room temperature Cp1Fe¦PF5 oxidation of 2 in MeCN induces the immediate
release of 0\4!hexadiene[ The oxidation of
2
in ButNC gives complexes ðCpMo"CNBut#2
−
−
"h1−CH11CHCH1CH1CHꢂCH1#Ł¦PF5 "6\ major# and ðCpMo"CNBut#3Ł¦PF5 "7\ minor#[ Finally\ the
oxidation of 2 in the presence of butadiene\ followed by treatment with CD2CN\ a}ords a mixture of
ðCpMo"h2]h2−C2H3CH1CH1C2H3#"CD2CN#Ł¦PF5−\ 8\ and ðCpMo"h3−C3H5#"CD2CN#1Ł¦PF5−\ 09[ Thermal
decomposition of this mixture a}ords butadiene and 0\4!cyclooctadiene[ Þ 0887 Elsevier Science Ltd[ All
rights reserved
———————————————————————————————————————————————
INTRODUCTION
"nꢂ9\ 0aÐc^ 0\ ð0aÐdŁ¦#\ see Scheme 0 ð1Ł[ In these
isomers\ the allyl ligand can adopt either a prone "a or
d# or a supine "b or c# con_guration\ while the buta!
diene ligand adopts either a supine "s!cis# "a or b# or an
s!trans "c or d# con_guration[ While the isomerization
rates are slow in the Mo"II# manifold\ allowing the
isolation of each of the three isomers\ they are rapid
in the Mo"III# manifold\ thus only the most stable
isomer ð0bŁ¦ has been isolated in crystalline form as
a PF5− salt[
We have recently reported the preparation and
properties of a molybdenum complex that contains a
cyclopentadienyl\ a butadiene\ and an allyl ligand in
four di}erent isomeric forms and in two redox!related
oxidation states\ namely ðCpMo"h!C2H4#"h!C3H5#Łn¦
ꢀAuthor to whom correspondence should be addressed]
Tel ¦22!92[79[28[57[70^ fax ¦22!92[79[28[59[87^ E!mail
poliÝu!bourgogne[fr[
We have subsequently reported on the reactivity of
the coordinated ligands in the isomers 0aÐc and in the
2578

2589
R[ Poli and Li!Sheng Wang
Scheme 0[
bis"diene# derivative ðCpMo"h!supine!C3H5#"h!s!trans! athesis and metal reduction\ to provide a single!step
C3H5#Ł¦\ 1\ which is obtained by protonation of 0a in synthesis of CpMo"h!C2H4#1 "see eq[ "0#[ The un!
the presence of butadiene[ While the s!cis!coordinated optimized yield is moderate "33)#[ Nevertheless\ con!
butadiene ligand is resistant to any kind of attack\ sidering that CpMoCl3 can be easily prepared in a
the s!trans!coordinated butadiene can be attacked by single\ nearly quantitative step from commercially
either electrophilic or nucleophilic reagents depending available ðCpMo"CO#2Ł1 ð00Ł\ this procedure rep!
on the electron richness of the system] electrophilic resents an improvement over the previously reported
attack by protons has been observed for the neutral 2!step synthesis from MoCl3"THF#1 via Mo"h2!C2H3#3
compound 0c ð2Ł\ while nucleophilic attack occurs for and MoCl"h2!C2H3#2 ð5\ 6Ł[ The precursor
the cationic complex 1 ð3Ł[ The allyl ligand has only MoCl3"THF#1 must also be prepared in two steps from
been found to engage in electrophilic addition for any commercially available MoCl4 ð01Ł[
of the three isomers of 0 ð2Ł[
The reactivity of organic ligands coordinated to
CpMoCl3¦3CH11CHCH1MgBr
Mo"III# has not been the subject of extensive inves!
tigations[ Compounds with either diene of allyl
ligands on Mo"III# are known\ e[g[ CpMoCl1"h!C3H5#
ð4Ł and CpMo"h!C2H4#1 ð5\ 6Ł\ in addition to the com!
plexes ð0aÐdŁ¦ recently reported by us[ However\ there
is apparently no report on the reactivity of the coor!
dinated p ligands in these or other related compounds[
In fact\ compound CpMo"h!C2H4#1\ 2\ has been
described as {{depressively unreactive|| ð7Ł[ A study of
the reactivity of the allyl and diene ligands on Mo"III#
is of interest for several reasons[ First\ it is interesting
to examine the e}ect of the metal oxidation state on
the reactivity of the ligands[ Second\ it is conceivable
that a stoichiometric or electron!transfer!catalytic
"ETC# ð8\ 09Ł oxidation of the more accessible Mo"II#
precursors could allow the development of new stoi!
chiometric or catalytic transformations that involve
the coordinated ligands[ In this report\ we describe
our exploratory investigations of the reactivity of the
isoelectronic Mo"III# compounds 2 and ð0bŁ¦ under a
variety of conditions[ We show that these complexes\
under suitable conditions\ are attacked by nucleo!
philes and electrophiles\ undergo MoÐC bond break!
ing and CÐC bond forming reactions\ and engage in
oxidative and reductive redox processes[ A new and
improved synthesis of compound 2 is also presented[
: CpMo"h−C2H4#1 "0#
2
Compound 2 has previously been characterized by
X!ray crystallography\ magnetic susceptibility\ and
cryoscopic molecular weight determination ð5Ł[ An
EPR spectrum was not reported[ We have recently
observed that allyldiene complexes such as ð0Ł¦\ iso!
electronic with 2\ exhibit sharp EPR absorptions with
observable coupling to the diene and allyl protons ð1Ł[
Comparative studies have shown that the supine allyl
ligand in ð0bŁ¦ gives measurable coupling to the syn
H atoms but not to the anti H atoms or to the central
H atom\ whereas no coupling can be observed with
either type of H atom for the prone allyl ligand in
ð0aŁ¦ ð1\ 3Ł[ The spectrum of compound 2\ shown
in Fig[ 0\ consists of a pentet of pentets\ indicating
coupling with all the H atoms of the terminal allyl
positions[ This suggests that the con_guration of 2 in
solution is identical with that previously determined
in the solid state\ with both allyl ligands adopting a
supine con_guration[ By comparison with our pre!
vious EPR studies\ the stronger coupling of 5[5 G is
assigned to the syn H atoms and the weaker one of
2[2 G to the anti H atoms[
"b# Reaction of CpMo"h!C2H4#1 with nucleophiles
RESULTS
Compound 2 is stable in donor solvents\ including
MeCN at room temperature[ Warming a MeCN solu!
tion to the re~ux temperature caused the complete
decomposition of the complex and the formation of
"a# New synthesis of CpMo"C2H3#1
The reaction of CpMoCl3 with 3 equivalents of 0\4!hexadiene and propene in a ca] 1]0 ratio as the
allylmagnesium bromide involves chloride:allyl met! major products "×79) by 0H NMR integration#[

Cyclopentadienylmolybdenum"II# and !"III# complexes containing diene and allyl ligands
2580
are consistent with a supine coordination mode[ In
particular\ the indiscernible geminal coupling between
syn and anti protons is a clear indication of the supine
conformation of the allyl ligand ð1\ 02Ð04Ł[
"c# Reaction of ðCpMo"h!C2H4#"h!C3H5#Ł¦ with nucleo!
philes
The reaction between complex ð0bŁ¦ and ButNC
follows the same path observed for compound 2\
namely reduction with formal expulsion of an allyl
radical\ see eq[ "2#[ Compound 4 has previously been
obtained by HBF3 protonation of 0a in the presence
of ButNC and fully characterized ð2Ł[ As established
above for compound 2\ no reaction is observed
between ð0bŁ¦ and MeCN or butadiene under mild
conditions[
ðCpMo"h−C2H4#"h−C3H5#Ł¦¦ButNC"excess#:
ðCpMo"h−C3H5#"CNBut#1Ł¦ "2#
4
The existence of bisallyl Mo"III# complexes such as
2\ and the established nucleophilic attack by car!
banions on Mo"II#!coordinated diene ligands to
a}ord allyl complexes\ made us wonder whether the
same reactivity could be observed for the Mo"III#!
coordinated diene ligand[ Indeed\ reaction of ð0bŁ¦
with methyllithium in THF generates a new EPR!
active complex which is formulated as CpMo"h!
C2H4#"h!C2H3Et#\ 5[ This nucleophilic addition
process\ however\ corresponds to a minor reaction
pathway "3) according to the intensity of the double!
integrated EPR signal#[ The main product of the reac!
tion\ compound 0 ð1Ł\ derives from a single electron
transfer process "see eq[ "3##[ As expected from the
previously reported investigation of the reduction of
ð0bŁ¦ ð1Ł\ the kinetically controlled reduction product
is CpMo"supine!h!C2H4#"supine!h!C3H5#\ 0b\ followed
by the slow isomerization to the thermodynamically
favored CpMo"prone!h!C2H4#"supine!h!C3H5#\ 0a[
Fig[ 0[ Experimental "top# and simulated "bottom# EPR spec!
trum for compound 0 "solvent ꢂ THF\ Tꢂ −099>C#[
Neither does 2 react with a large excess of butadiene
at room temperature[ However\ treatment in neat
ButNC leads to the smooth formation of the dia!
magnetic compound CpMo"h!C2H4#"CNBut#1\ 3\ see
eq[ "1#[
CpMo"h−C2H4#1¦ButNC"excess#
: CpMo"h−C2H4#"CNBut#1 "1#
ðCpMo"h−C2H4#"h−C3H5#Ł¦¦MeLi
3
: CpMo"h−C2H4#"h−C3H5#
The reaction is relatively slow\ starting material
being still present after several hours at room tem!
perature[ NMR spectroscopy shows the initial selec!
tive formation of 3[ Prolonged exposure to the ButNC
solvent\ however\ results in the formation of a new
diamagnetic material that shows only resonances for
0
¦CpMo"h−C2H4#"h−C2H3Et# "3#
5
The nature of the paramagnetic product as 5 is
the Cp ligand and for the tert!Bu group\ thus indi! supported by the results of a protonation study of the
0
cating decomposition of 3 with loss of the residual 0:5 mixture in C D with HBF Et O[ The H!NMR
¾
3
5
5
1
allyl ligand[ This by!product is di}erent from of the organic phase shows the formation of cis! and
ðCpMo"CNBut#3Ł¦ "vide infra# and was not further trans!1!pentene in a relative 1]0 ratio\ in addition to
characterized[ Its formation did not permit the iso! propene\ see eq[ "4#[ There is no observable formation
lation of compound 3 in an analytically pure form[ of 0!pentene from this reaction[ The formation of
The identity of 3\ however\ is established by 0H NMR[ propene by protonation of 0 has previously been stud!
The allyl proton chemical shifts and coupling pattern ied in detail ð2Ł[

2581
R[ Poli and Li!Sheng Wang
"d# Oxidation of CpMo"h!C2H4#1
assignments have been con_rmed by selective homo!
nuclear decoupling experiments\ which also assisted
While compound 2 is stable in acetone and MeCN in the determination of the coupling constants[ The
at room temperature\ oxidation with Cp1Fe¦ in either proton resonances of the dangling vinyl group show
solvent induces an immediate allyl!allyl coupling and typical chemical shifts and coupling pattern[ The coor!
release of free 0\4!hexadiene "see eq[ "5#[ The fate of dinated vinyl group\ on the other hand\ exhibits res!
the ðCpMo¦Ł fragment is unknown but probably leads onances at higher _eld[ The methylene protons
to paramagnetic products\ since no resonances adjacent to the coordinated vinyl group "Hd and He#
0
attributable to the Cp ligand are observed in the H show distinct resonances\ while the other methylene
NMR spectrum[
protons "Hf# are chemically equivalent "1[29 ppm#[
Echoing the proton NMR data\ the 02C NMR spec!
trum also shows the inequivalence of the three iso!
cyanide ligands[ While the coordinated carbon
resonances are signi_cantly di}erent\ both the methyl
and the tertiary carbon atoms of the three tert!butyl
groups give common resonances\ indicating the insen!
sitivity of these nuclei to the immediate chemical
environment of the metal center[
CpMo"h−C2H4#1¦Cp1Fe¦PF5−
: CH11CHCH1CH1CH1CH1 "5#
When the oxidation reaction is carried out in the
presence of ButNC as a trapping agent\ two products
are observed in a ca[ 1]0 ratio "eq[ "6#[ The pre!
dominant product is ðCpMo"CNBut#2"h1−CH11
CHCH1CH1CH1CH1#Ł¦PF−5 \ 6[ This compound
could not be obtained as a pure crystalline material
because
the
minor
product\
compound
ðCpMo"CNBut#3Ł¦PF−5 \ 7\ crystallizes preferentially[
The latter compound has previously been obtained by
a di}erent synthetic method ð05Ł[ The NMR properties
show the equivalence of the four ButNC ligands as
expected for the ubiquitous four!legged piano stool
geometry\ while the three IR bands observed in the
CN stretching region are consistent with the expected
C
3v local symmetry "A0¦B0¦E#[
CpMo"h−C2H4#1¦Cp1Fe¦PF5−¦ButNC"excess#:
ðCpMo"CNBut#2
"h1−CH11CHCH1CH1CH1CH1#Ł¦PF−5
The oxidation of 0 has also been carried out in the
presence of butadiene[ In this case\ a 1[4]0 mixture of
the bisallyl Mo"IV# complex ðCpMo"h2]h2!C2H3CH1
CH1C2H3#"CD2CN#Ł¦PF5−Ł\ 8\ and the butadiene
Mo"II# complex ðCpMo"supine!h!C3H5#"CD2CN#1Ł¦
6
−
¦ðCpMo"CNBut#3Ł¦PF5
"6#
7
The identi_cation of compound 6 rests on the H PF5−Ł\ 09\ forms after treating the reaction residue in
and 02C NMR properties[ Unlike 7\ which has four CD2CN\ see eq[ "7#[ Both complexes have previously
equivalent tert!butyl isocyanide ligands\ complex 6 been obtained by protonation of 0c in the presence of
has three inequivalent isocyanide ligands because of butadiene ð2Ł[ As reported previously\ compound 8 is
the low symmetry[ All 09 protons of the coordinated inde_nitely stable in CD2CN at room temperature[ A
0\4!hexadiene ligand are visible in the 0H NMR spec! thermal study at 099>C in CD2CN in a sealed NMR
trum[ The proton nomenclature is as shown in I[ All tube\ however\ revealed its decomposition to yield
0

Cyclopentadienylmolybdenum"II# and !"III# complexes containing diene and allyl ligands
2582
cyclooctadiene in 69) spectroscopic yield[ Free buta! diene ligand but never at the s!cis butadiene or at
diene is also observed\ presumably deriving from the the allyl ligands[ For the Mo"III# cationic complex
thermal decomposition of 09[
reported here\ we have seen for the _rst time a nucleo!
philic addition to the s!cis butadiene ligand[
DISCUSSION
The nature of the products obtained by protonating
5 "see section "c# below# indicate that this compound
is a mixture of isomers with syn and anti ethylallyl
ligand "1]0 in favor of the anti isomer#[ This mixture
is probably formed by direct nucleophilic addition
to the s!cis butadiene ligand to a}ord the anti allyl
product\ followed by partial isomerization[ An alter!
native pathway to the syn product involving an initial
isomerization to ð0cŁ¦\ followed by nucleophilic attack
at the s!trans diene ligand can be excluded because\
according to our previous studies ð1Ł\ the ther!
modynamics and kinetics for the isomer inter!
conversion reaction would not allow the formation of
a signi_cant amount of the s!trans isomer during the
short time scale of the methylation process[
"a# Nucleophilic attack to Mo"III# vs[ Mo"II#
From our previous studies\ we have established that
the neutral Mo"II# system CpMo"h!C2H3#"h!C3H5#\ in
either of its three stable isomeric forms "0aÐc#\ is not
susceptible to nucleophilic attack ð2Ł[ However\ the
cationic Mo"II# complex ðCpMo"supine!h!C3H5#"s!
trans!h!C3H5#Ł¦\ 1\ can be attacked by nucleophiles
either at the metal "with substitution of the s!trans!
butadiene ligand# or at the s!trans!butadiene endo ter!
minal carbon atom "with formation of an allyl deriva!
tive# ð3Ł[ For these reasons\ we reasoned that a
nucleophilic attack to either the metal\ the butadiene
ligand or the allyl ligand in the Mo"III# complexes 2
and ð0bŁ¦ might occur under the in~uence of the higher
formal oxidation state\ especially for the cationic "b# Allyl!allyl couplin` in Mo"III# and Mo"IV#
system[ As mentioned in the Introduction\ no studies
of the reactivity of Mo"III#!coordinated allyl and
butadiene ligands appear to have been reported[
Processes of allyl!allyl coupling in transition metal
complexes are relevant as elementary steps of catalytic
The results obtained show that the dominant path! dimerization and oligometization of diene ligands ð06Ł[
way is metal reduction[ The tendency of the metal to The metal!assisted coupling of allyl ligands to a}ord
reach an 07!electron con_guration\ especially in the 0\4!hexadiene products is a widely known reaction
presence of p!acidic ligands\ is su.ciently high to force ð06Ð08Ł[ Previous reports for molybdenum complexes
the elimination of allyl radicals[ This pathway is include the interaction of a {{violet solution||\ pre!
observed for both 2 and ð0bŁ¦ in their reaction with sumably containing "h5!C5H5#Mo"h2!C2H4#"m!Cl#1Al!
ButNC[ It is remarkable that\ for complex ð0bŁ¦\ the ClEt\ with propene to ultimately a}ord a 1\3!
observed reaction pathway is more favorable than hexadiene complex via formation of an intermediate
either substitution of the neutral diene ligand or inser! containing coordinated 0\4!hexadiene ð19Ł[ The pro!
tion of the diene into the Mo"III#!allyl bond[ Weaker posed bis"allyl# Mo"IV# intermediate\ i[e[ð"h5!C5H5#
neutral 1!electron donor such as MeCN do not react[ Mo"h2!C2H4#1"C2H6#Ł¦\ however\ was not directly
The reaction of the cationic substrate with methyl! observed[ More recently\ the reaction of the metal!
lithium does indeed lead to the addition product 5 "eq[ metal bonded Mo1"m!h!C2H4#1"h!C2H4#1 complex with
"3##\ but the main product is the neutral derivative 0b CO was shown to produce Mo"CO#5 and 0\4!hexa!
obtained from the single electron transfer pathway[ diene\ via an isolable Mo"CO#3"h3!0\4!hexadiene#
This result\ nevertheless\ indicates an increased re! intermediate ð10Ł[ The corresponding reaction of
activity of the coordinated ligands on going from Mo"h2!C2H4#1"PMe2#2 with CO yields Mo"CO#1
Mo"II# to Mo"III#[ For the Mo"II# complexes of the "PMe2#3 and 0\4!hexadiene ð11Ł[
types investigated by us\ a nucleophilic attack takes
No allyl!allyl coupling process has been described
place "only in the cationic systems# at the s!trans buta! for Mo"III# complexes[ A spontaneous coupling has

2583
R[ Poli and Li!Sheng Wang
been reported to occur upon ligand addition to the however\ may be competing and be responsible for
Cr"III# complex CpCr"h2!C2H4#1 ð12Ł\ while the cor! the formation of propene[
responding Mo complex 2 does not undergo a similar
Even more rapid "instantaneous at room tem!
process under mild conditions ð5Ð7Ł\ in accord with perature# is the elimination of 0\4!hexadiene upon oxi!
the expected greater stability of the heavier metal in dation of 2[ No formation of propene is observed
the higher oxidation state[ In fact\ while s!donor under these conditions[ A hypothetical ðCpMo"h!
ligands do not react with 2\ p acidic ligands induce a C2H4#1"S#Ł¦ intermediate probably forms _rst\ but its
reductive process with loss of an allyl radical\ rather lifetime must be very short because it was not spec!
than an allyl!allyl coupling\ as discussed in the pre! troscopically observed neither in acetone nor in
vious section[ When compound 2 is heated in the s! MeCN[ It is interesting to compare this rapid CÐC
donor solvent MeCN\ however\ the allyl!allyl coup! coupling process with our previous _ndings in bisallyl
ling becomes possible\ paralleling the reactivity of the Mo"IV# chemistry "Scheme 1#[ Complex ðCpMo"h!
chromium analogue[
C2H4#"h!C2H3Me#"MeCN#Ł¦\ which is generated by
It may be questioned whether the formation of 0\4! HBF3 protonation of 0c in MeCN\ is su.ciently stable
hexadiene during the thermal decomposition of 2 in to be observed in solution at room temperature but
MeCN derives from a truly metal!assisted allyl!allyl slowly decomposes by the same CÐC coupling process
coupling or from the coupling of free allyl radicals in a regioselective manner to a}ord 2!methyl!0\4!hex!
in solution after elimination of the latter from the adiene ð2Ł[ Complex 8\ on the other hand\ is perfectly
coordination sphere[ We have not been able to _nd stable in MeCN at room temperature\ whereas it elim!
previous studies of the allyl radical reactivity in the inates cyclooctadiene upon warming to 099>C[ This
presence of MeCN[ We note\ however\ that the H! elimination is also regioselective] no signi_cant
allyl bond is stronger than the HÐCH1CN bond "7820 amount of the possible alternative coupling products
and 71[2 kcal:mol\ respectively# ð13Ł[ This suggests "0\1!divinylcyclobutane and 3!vinylcyclohexene# is
that the allyl radical should preferentially abstract a spectroscopically observed[
H atom from the large excess of MeCN and generate
It is to be emphasized that we have no detailed
0
propene[ The H NMR monitoring of the decompo! information on the structure of the Mo"IV# bis!allyl
sition reaction shows the predominant formation of materials\ thus the mechanism of regiocontrol is open
the coupling product "0\4!hexadiene]propene ꢂ ca[ to speculation[ Mo"IV# half!sandwich derivatives
1]0#\ in agreement with the proposed direct allyl!allyl adopt pseudo!octahedral geometries with one "axial#
coupling[
A thermal allyl radical elimination\ ligand trans to the Cp and four "pseudo!equatorial#
Scheme 1[

Cyclopentadienylmolybdenum"II# and !"III# complexes containing diene and allyl ligands
2584
ligands slightly deviating from the perpendicular reaction products shows that the proton attacks
plane away from the bulkier Cp ligand ð14Ð18Ł[ The regioselectively the unsubstituted terminal allyl
X!ray structure of an isoelectronic CpMo"CO#Br1"h2! position\ in agreement with the electron!releasing
C2H3!1!Me# has pseudo!equatorial Br and CO e}ect of the alkyl substituent[ This result is identical
ligands\ whereas the allyl ligand formally occupies one to what we have observed for the protonation of syn!
pseudo!equatorial and the pseudo!axial positions ð29Ł[ 0!ethylallyl in the Mo"II# complex CpMo"h3!C3H5#"h2!
On the basis of the above information\ we presume syn!C2H3!0!Et# ð3Ł[ In that case\ only trans!1!pentene
that the structures of the bisally Mo"IV# derivatives was obtained from the syn!ethylallyl ligand[ There!
are as drawn in Scheme 1[
fore\ the results of the protonation of 5 indicates that
A product of allyl!allyl coupling containing a coor! this is a mixture of syn! and anti!ethylallyl isomers\
dinated 0\4!hexadiene is su.ciently stable and can be with a prevalence for the anti isomer[ This\ in turn\
observed spectroscopically when the oxidation of 2 is indicates that the alkylation of the s!cis!supine buta!
carried out in ButNC "compound 6#[ Interestingly\ diene ligand is followed by partial "either for thermo!
the 0\4!hexadiene ligand remains coordinated in a h1 dynamic or kinetic reasons# isomerization of the
"monodentate# fashion to the metal center\ rather than resulting anti!allyl ligand to the syn isomer "see
as a h1]h1 "chelating# ligand or being eliminated from Scheme 4#[
the coordination sphere under the large excess of
ButNC which is present[ No spectroscopic evidence
CONCLUSIONS
was obtained for the intermediacy of a chelating hex!
adiene complex\ which is presumed to form as shown
in Scheme 2[ The coordination mode is probably dic!
tated by the electronic requirements of the metal and
the balance between s!donation and p back!donation\
a situation which is commonplace in the chemistry of
carbonyl complexes[ Strain in the chelated inter!
mediate may also be responsible for the observed out!
come of the reaction[
When the oxidation of 2 is carried out in the pres!
ence of excess butadiene\ a similar coupling mech!
anism presumably takes place "Scheme 3#\ leading to
the formation of a mixture of 8 and 09 after treatment
with CD2CN[ The formation of these two products
can be understood on the basis of our previous studies]
coordination of two butadiene ligands in the s!trans
mode leads to CÐC coupling^ coordination of one s!
trans and one s!cis ligands leads to the stable 1^ _nally\
coordination of two s!cis ligands does not occur ð2Ł[
Complex 1 is known to exchange the s!trans butadiene
ligand upon dissolution in acetonitrile ð2Ł[
The reactivity of allyl and diene ligands coordinated
to paramagnetic Mo"III# centers has been explored
for the _rst time[ A variety of transformations have
been established\ including electrophilic addition to
the allyl ligand\ nucleophilic addition to the butadiene
ligand\ allyl!allyl coupling\ metal reduction by single!
electron transfer or via allyl radical elimination\ and
metal oxidation[ A few pathways have been compared
with those in analogous complexes of Cr"III#\ Mo"II#
and Mo"IV#[ The observed patterns can be sum!
marized as follows]
0[ While allyl!allyl coupling occurs spontaneously at
room temperature in CpCr"h2!C2H4#1 ð12Ł\ it takes
place only at higher temperatures for the Mo"III#
compound 2[
1[ The s!donor:p!acceptor ButNC ligand induces
reduction of both 2 and ð0bŁ¦ at room temperature\
with loss of an allyl radical and formation of 07!
electron Mo"II# products[
2[ The stronger s!donor ligand LiMe induces a one!
electron reduction process on ð0bŁ¦\ to produce the
parent complex 0b[
"c# Electrophilic reactivity of Mo"III#!bonded allyl
li`ands
3[ While nucleophilic addition of Me! to a s!cis!coor!
dinated butadiene ligand is not observed for the
Mo"II# complexes 0a\ 0b and 1\ it does occur for
the Mo"III# complex ð0bŁ¦\ although it does not
compete e}ectively with the preferred reduction
pathway[
The protonation of the allyl ligands in compound 5
to generate 1!pentene isomers "eq[ "4## demonstrates
that Mo"III#!coordinated allyl ligands are su.ciently
electron!rich to be subjected to electrophilic attack by
protons[ The absence of any 0!pentene among the
Scheme 2[

2585
R[ Poli and Li!Sheng Wang
Scheme 3[
4[ Protonation of the Mo"III#!bonded allyl ligands
EXPERIMENTAL PROCEDURE
in 5 by strong acids parallels the protonation of
allylmolybdenum"II# complexes\ with the gen! General Procedures
eration of ole_ns[ The protonation of 0!ethylallyl
occurs regioselectively to generate 1!pentenes[
All operations were carried out by standard Sch!
5[ The allyl!allyl coupling reaction is greatly accel! lenk!line techniques under a dinitrogen atmosphere[
erated by oxidation to Mo"IV#[ The rate of this Solvents were dried by conventional methods "THF
coupling process is greatly a}ected by the sub! and Et1O on Na:benzophenone\ toluene and heptane
stitution at the allyl carbons[ Regioselectivity is on Na\ CH1Cl1 on P3O09# and distilled directly from
observed for substituted allyl ligands\ with the the drying agent under dinitrogen[ All routine NMR
h2]h2!0\0?!C2H3CH1CH1C2H3 ligand giving rise to experiments were carried out on a Bruker AM399 or
cyclooctadiene as the sole coupling product[
WF 199 spectrometers[ The 0H and 02C NMR data of

Cyclopentadienylmolybdenum"II# and !"III# complexes containing diene and allyl ligands
2586
Scheme 4[
all compounds are given in Table 0[ Other spec! at −67>C[ Solid CpMoCl3 "3[4 g\ 03[8 mmol# was
trometers used were as follows] EPR\ Bruker ER199^ added to the solution over 04 min\ causing the pre!
IR\ Perkin!Elmer FTIR 0599^ MS\ VG 6969E[ cipitation of a yellow solid[ The suspension was stirred
Elemental analyses were performed by Atlantic Mic! for 0 h at −67>C and then an additional hour at 9>C[
rolab\ Inc[ or the analytical service at the LSEO\ All solvent was evacuated and the solid was dried
Dijon[ Compounds CpMoCl3 ð00Ł and ð0bŁðPF5Ł ð1Ł overnight under vacuum[ The product was extracted
were prepared according to the literature[
with heptane "1×099 mL#\ each washing being stirred
for 0 h to ensure maximum extraction[ The combined
_ltered extracts were evaporated to dryness under
reduced pressure[ The residue was redissolved in
049 mL of heptane\ leaving a small amount of undis!
Preparation of CpMo"h!C2H4#1\ 2
To a diethyl ether solution of allylmagnesium chlor! solved grey solid which was _ltered o}[ The solvent
ide "55 mL\ 0 M\ 55 mmol# was added 59 mL of THF was removed again by evaporation and the residue
Table 0[ 0H!NMR data
Compd
0H!NMR "d#
02C!NMR "d#
CpMo"supine!h!C2H4#"CNBut#1
"3#a
3[84 "4H\ Cp\ s#^ 2[50 "0Hd\ tt\
2JHHe ꢂ 4Hz\ 2JHHf ꢂ 6Hz#^ 1[26 "1He\ d\
2JHHd ꢂ 4Hz#^ 0[46 "0Hf\ d\ 2JHHd ꢂ 6Hz#^
0[02 "07H\ 1CNBut#
ðCpMo"h1!CH1
1
CHCH1Ð
4[78 "0Hg\ ddt\ 2JHHi ꢂ 05Hz\ 2JHHh ꢂ 8Hz\ 057[0 "0C\ s\ CNC"CH2#2#\ 053[2 "0C\ s\
CH1CH
1
CH1#"CNBut#2ŁðPF5Ł
2JHHf ꢂ 2JHHf ꢂ 02Hz#\ 4[99 "0Hi\ ddt\
2JHHg ꢂ 05Hz\ 1JHHh ꢂ 1Hz\
CNC"CH2#2#\ 051[3 "0C\ s\ CNC"CH2#2#\
039[9 "0Cg\ d\ 0JCH ꢂ 044 Hz#\ 003[5 "0Chi\
t\ 0JCH ꢂ 044 Hz#\ 77[8 "4C\ d\
"6#b
3JHHf ꢂ 0[4Hz#\ 3[83 "4H\ s\ Cp#\ 3[82
"0Hh\ ddt\ 2JHHg ꢂ 8Hz\ 1JHHi ꢂ 1Hz\
3JHHf ꢂ 0Hz#\ 1[81 "0Hc\ dddd\
0JCH ꢂ 070 Hz#\ 57[7 "0Cc\ d\
0JCH ꢂ 065 Hz#\ 48[1 "2C\ b\
2JHHb ꢂ 8Hz\ 2JHHa ꢂ 01Hz\ 2JHHd ꢂ 09Hz\ CNC"CH2#2#\ 30[3 "0C} or 0Cde\ t\
2JHHe ꢂ 3Hz#\ 1[29 "1Hf\ m#\ 0[88 "0Hb\
0JCH ꢂ 019 Hz#\ 39[3 "0Cde or 0C}\ t\
2
0
dd\ JHHc ꢂ 8Hz\ 2JHHa ꢂ 2Hz#\ 0[88 "0Hd\ JCH ꢂ 019 Hz#\ 29[3 "8C\ quartet\
m# 0[62 "0Ha\ dd\ 2JHHc ꢂ 01Hz\
2JHHb ꢂ 2Hz#\ 0[49 "8H\ CNBut#\ ½0[3
"0He\ overlapping with CNBut#\ 0[39 "8H\
CNBut#\ 0[26 "8H\ CNBut#
0JCH ꢂ 017 Hz\ CNC"CH2#2#\ ½29 "0Cab\
overlapping with CNC"CH2#2#
ðCpMo"CNBut#3ŁðPF5Ł "7#b
4[09 "4H\ s\ Cp#\ 0[35 "25H\ s\ CNC"CH2#2# 063[9 "3C\ s\ CNC"CH2#2#\ 89[0 "4C\ d\
0J ꢂ 066 Hz\ Cp#\ 48[2 "3C\ s\
CNC"CH2#2#\ 20[0 "01C\ quartet\
0J ꢂ 017 Hz\ CNC"CH2#2#
"a# C5D5^ "b# acetonitrile!d2[

2587
R[ Poli and Li!Sheng Wang
was recrystallized from heptane at −79>C\ yielding a Et1O\ 9[04 mmol# was added by syringe\ causing the
violet microcrystalline solid which was dried under formation of a red solution[ After stirring at room
vacuum for 1 h "yield 0[5 g\ 33)#[ Anal[ Calcd for temperature for 0 h\ all solvent was removed by evap!
C00H04Mo] C\ 43[21^ H\ 5[06[ Found] C\ 43[94^ H\ oration under reduced pressure and the residue was
5[93[ The solid has a dichroic behavior[ Powder and extracted with 19 mL of heptane[ After _ltration\ the
small crystals appear violet to re~ected light but solution was evaporated to dryness under reduced
orange to transmitted light[ Larger crystals are orange pressure\ giving a red solid "yield 14 mg#[ The 0H
as previously reported ð5Ł[ The solid is extremely air NMR spectrum in C5D5 showed resonances of Cp at
sensitive\ turning immediately black upon exposure d 3[09 and 3[16 in a ca[ 3]0 ratio\ which are attributed
to the laboratory atmosphere[ EPR "THF\ −099>C#] to CpMo"supine!h!C2H4#"supine!h!C3H5# "0b# and
` ꢂ 1[921\ aMo ꢂ 22 G\ a3H ꢂ 5[5 G\ a3H ꢂ 2[2 G[ EPR CpMo"prone!h!C2H4#"supine!h!C3H5# "0a#\ respec!
"THF or benzene\ room temperature#] broad singlet tively\ by comparison with the literature ð1Ł[ Con!
at `ꢂ1[917 with Mo satellites\ aMo ꢂ 22 G[
tinued monitoring of this solution showed the slow
conversion of 0b to 0a according to the previous report
ð1Ł[ An EPR study of the C5D5 solution showed an
unresolved multiplet resonance at ` ꢂ 1[922\
aMo ꢂ 22 G\ which is assigned to compound 5[ Double
integration of the EPR resonance against that of the
starting material gives a 3) yield of the paramagnetic
species[
Reaction of 2 with tert!butyl isocyanide[ Formation of
CpMo"supine!h!C2H4#"CNBut#1\ 3
Compound 0 "09 mg\ 30 mmol# was placed in a
NMR tube together with 149 mL of ButNC[ Standing
at room temperature overnight yielded a maroon solu!
tion[ The excess of tert!butyl isocyanide was removed
under reduced pressure and 9[4 mL of C5D5 was
added[ The 0H NMR spectrum showed the formation
of compound 3\ while the EPR spectrum indicated the
presence of the unreacted starting complex 2[ The
separation of these two complexes was not successful[
When the experiment was repeated with longer stand!
ing in ButNC\ decomposition of 3 occurred to generate
another species with the Cp resonance at d 4[25 in
C5D5 and another resonance at d 0[29\ assigned to
But groups[ No allyl resonances are observed for this
species[
Protonation of the mixture of CpMo"h!C2H4#"h!C3H5#
"0a and 0b# and CpMo"h!C2H4#"h!C2H3Et#\ 5
The mixture of complex 0 and 5 obtained by the
procedure described in the previous section "09 mg#
was dissolved in 9[4 mL of C5D5 in an NMR tube[
HBF3 = Et1O "09 mL\ excess# was added\ causing the
immediate formation of a grey precipitate[ The super!
natant was transferred into another NMR tube by
vacuum condensation[ The 0H NMR spectrum
showed the formation of both cis!1!pentene and trans!
1!pentene with a ratio of ca[ 1]0\ in addition to the
signals of propene[ The products were identi_ed by
analysis of the ole_nic proton resonances\ in com!
parison with those reported in the literature ð20Ł[ The
other aliphatic resonances overlap extensively[ 0H
NMR of cis!1!pentene "d\ C5D5#] 4[26 "m#\ 0[84 "m#\
0[44 "m#\ 0[97 "overlap with large Et1O resonance#[ 0H
NMR of trans!1!pentene "d\ C5D5#] 4[36 "m\ 1H#\ 0[84
"m#\ 0[44 "m#\ 0[97 "overlap with large Et1O reson!
Reaction of ð0bŁðPF5Ł with tert!butyl isocyanide[ For!
mation of ðCpMo"supine!h!C3H5#"CNBut#1ŁðPF5Ł\ 4
Compound ð0bŁðPF5Ł "09 mg\ 14 mmol# was mixed
with ButNC "099 mL\ 9[774 mmol# in a NMR tube[
Upon heating to 59>C for 09 min\ a yellow solution
was formed\ accompanied by a black precipitate[ The
solution was centrifuged and the supernatant was
transferred into another NMR tube via cannula[ After
removal of excess tert!butylisocyanide under reduced
pressure\ a yellow oil was obtained[ A 0H NMR spec!
trum in CDCl2 showed resonances at d 4[45 "m\ 1H#\
4[09 "s\ 4H#\ 1[21 "d\ 1H#\ 0[34 "s\ 07H#\ 0[99 "d\ 1H#\
which are attributed to the cation of 4 by comparison
with the literature ð2Ł\ in addition to two unidenti_ed
species with the Cp resonances at d 4[92 and 3[85[
Integration showed a 50]05]12 ratio of the three prod!
ucts[ No EPR active species were detected[
0
ance#[ H NMR of propene "d\ C5D5#] 4[69 "m\ 0H#\
3[88 "dm\ 0H#\ 3[82 "dm\ 0H#\ 0[42 "overlap#[ No other
resonances that could be attributed to a vinyl group
"e[g[ of 0!pentene# could be observed[
Reactions of 2 with ferrocenium hexa~uorophosphate
0[ In acetone!d5[ Compound 2 "09 mg^ 31 mmol# and
Cp1Fe¦PF− "03 mg^ 31 mmol# were mixed in an
5
NMR tube\ to which 9[4 mL of CD2COCD2 was
added[ The formation of 0\4!hexadiene "d 4[68\ m\
1H^ 3[84\ m\ 3H^ 1[96\ m\ 3H# and ferrocene "d
0
Reaction of ð0bŁðPF5Ł with MeLi[ Formation of
CpMo"h!C2H4#"h!C3H5#\ 0\ and CpMo"h!C2H4#"h!
C2H3Et#\ 5
3[04\ s# were detected by H NMR[ No signi_cant
amount of other species was found by 0H NMR[
1[ In acetonitrile!d2[ CpMo"supine!h!C2H4#1 "4 mg\
10 mmol# and Cp1Fe¦PF−5 "6 mg\ 10 mmol# were
placed in an NMR tube\ to which 9[4 mL of
CD2CN was added[ The 0H NMR spectrum of the
Compound ð0bŁðPF5Ł "59 mg\ 9[04 mmol# was sus!
pended in 19 mL of THF[ MeLi "096 mL\ 0[3 M in

Cyclopentadienylmolybdenum"II# and !"III# complexes containing diene and allyl ligands
2588
resulting solution showed the formation of 0\4! parison with the NMR spectra reported in the
hexadiene "d 4[72\ m\ 1H^ 3[86\ m\ 3H^ 1[02\ m\ 3H# literature ð2Ł[ These two main products are
and ferrocene "d 3[04\ s# in a ca[ 0]0 ratio[ No accompanied by several additional Cp containing by!
signi_cant amount of other species was detected by products\ whose overall integrated intensity is ³29)
0H NMR\ while the EPR spectrum showed several of the total[
resonances with no discernible coupling pattern[
Thermal treatment of compound 8 in CD2CN
Reaction of 2 with ferrocenium hexa~uorophosphate in
tert!butyl isocyanide[ Formation of ðCpMo"CNBut#2
The NMR tube containing the CD2CN solution of
"h1!CH11CHCH1CH1CH1CH1#ŁðPF5Ł\
ðCpMo"CNBut#3ŁðPF5Ł\ 7
6\
and
8 and 09 obtained as described in the previous section
was ~ame!sealed[ The solution was heated to 099>C
for 0 h and monitored by 0H NMR spectroscopy[ The
formation of octa!0\4!diene ðd 4[42 "br\ 3H#\ 1[22 "br\
7H#Ł was observed in 64) spectroscopic yield relative
to the initial amount of 8[ Resonances attributable
to free butadiene were also observed[ No resonances
attributable to Cp containing Mo products were
observed[
0[ NMR tube reaction[ Compound 2 "01 mg^ 38 mmol#
−
and Cp1Fe¦PF5 "06 mg^ 40 mmol# were placed in
an NMR tube\ to which 099 mL of ButNC was
added by syringe[ The mixture was vigorously
shaken for 04 min[ C5D5 "9[4 mL# was then added\
yielding a yellow solution[ Two species with Cp
signals at d 3[74 "complex 6# and 4[92 "complex 7#
in a ca[ 1]0 ratio were observed by 0H NMR[
1[ Isolation of compound 7[ Compound 2 "199 mg^
9[71 mmol# and Cp1Fe¦PF5− "161 mg^ 9[71 mmol#
were mixed in a Schlenk tube\ to which 1 mL of
ButNC was added[ The mixture was stirred at room
temperature for 9[4 h\ giving a yellow suspension[
The excess ButNC was completely removed by
evaporation under reduced[ Benzene "09 mL# was
added to the yellow residue\ and the resulting sus!
pension was stirred for 0 h[ The supernatant was
decanted and the yellow solid was recrystallized
from THF "4 mL# at −79>C\ to yield a bright yel!
low crystalline solid which was recovered by _l!
tration and dried under vacuum for 9[4 h "yield
74 mg\ 04)#[ Anal[ Calcd for C14H30N3!
MoPF5 = 9[64C3H7O] C\ 37[45^ H\ 5[73[ Found] C\
37[20^ H\ 5[79[ The THF of solvation was observed
in the 0H NMR spectrum in the correct integrated
intensity[ IR "Nujol\ cm−0#] 1051 m\ 1985 s\ 1949
s\ 730 s "PF5#[ Low resolution mass spectrum
"FAB¦#] m:z 384 ðCpMo"CNBut#3Ł¦\ 099)[
Thermal treatment of complex 2 in CD2CN
Complex 2 "04 mg# was placed in an NMR tube
with 9[4 mL of CD2CN[ The tube was ~ame!sealed
and heated to 099>C in an oil bath for 0 h[ A 0H NMR
spectrum showed the formation of hexa!0\4!diene
"CH11CHÐCH1CH1ÐCH1CH1 resonance at d 1[03#
and propene "CH11CHÐCH2 resonance at d 0[69\
doublet with J ꢂ 5[0 Hz# in a ca[ 1]0 ratio\ plus small
amounts "³19)# of other unidenti_ed species\ the
major component of which shows a CH2 resonance at
d 0[35 "d\ J ꢂ 4[0 Hz#[
Acknowled`ements*We are grateful to the National Science
Foundation "CHE!8497410# for support of this work[
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CH1C2H3#"CD2CN#PF5Ł\
8
and ðCpMo"supine!h!
C3H5#"CD2CN#1ŁðPF5Ł\ 09
−
Complex 2 "ca[ 09 mg# and 03 mg of Cp1Fe¦PF5
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