Reactivity of the phosphinidene-bridged complexes [Mo2Cp(μ-κ1:κ1,η5-PC5H 4)(η6-1,3,5-C6H3 tBu3)(CO)2] and [Mo2Cp

Article abstract of DOI:10.1021/om201048s

The cyclopentadienylidene-phosphinidene complex [Mo₂Cp(μ- κ¹:κ¹,η⁵-PC₅H ₄)(η⁶-*)(CO)₂] (1) (Cp = η⁵-C₅H₅; Mes* = 2,4,6-C ₆H

Full text of DOI:10.1021/om201048s

Article
pubs.acs.org/Organometallics
Reactivity of the Phosphinidene-Bridged Complexes [Mo2Cp(μ-
κ1:κ1,η5-PC5H4)(η6-1,3,5-C6H3 Bu3)(CO)2] and [Mo2Cp2(μ-PH)(η6-1,3,5-
t
t
C6H3 Bu3)(CO)2] toward Alkynes: Multicomponent Reactions in the
Presence of Ligands
M. Angeles Alvarez, Inmaculada Amor, M. Esther García,* Daniel García-Vivo, Miguel A. Ruiz,*
́
and Jaime Suarez
́
́ ́
Departamento de Química Organica e Inorganica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain
S
* Supporting Information
ABSTRACT: The cyclopentadienylidene-phosphinidene complex [Mo2Cp(μ-κ1:κ1,η5-
t
PC5H4)(η6-HMes*)(CO)2] (1) (Cp = η5-C5H5; Mes* = 2,4,6-C6H2 Bu3) reacted with
RCCR′ in refluxing toluene solutions to give the corresponding phosphide derivatives
[Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCRCR′}(η6-HMes*)(CO)2] (R = R′ = CO2Me; R = H, R′ =
CO2Me, p-tol), displaying a phosphametallacyclobutene ring. In contrast, the phosphinidene
complex [Mo2Cp2(μ-PH)(η6-HMes*)(CO)2] (2) reacted with MeO2CCCCO2Me at room
temperature to give first the monocarbonyl phosphide-acyl complex [Mo2Cp2{μ-κ1:κ1,η3-
PHC(CO2Me)C(CO2Me)C(O)}(η6-HMes*)(CO)], the latter evolving progressively to
the isomeric dicarbonyl [Mo2Cp2(μ-κ1:κ1,η1-PHC(CO2Me)C(CO2Me)}(η6-HMes*)-
(CO)2] (Mo−P ca. 2.57 Å). When different ligands such as CO, PMe3, P(OMe)3, or
CNXyl were added at room temperature to toluene solutions containing compound 1 and
different alkynes, relatively fast multicomponent reactions took place to give with good yields the corresponding phosphide-acyl
complexes [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCRCR′C(O)}(η6-HMes*)(CO)2] (R = R′ = CO2Me; R = H, R′ = CO2Me, p-tol),
and [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C(CO2Me)C(O)}(η6-HMes*)(CO)(L)] (L = PMe3, P(OMe)3) or the related
phosphide-iminoacyl derivatives [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCRCR′C(NXyl)}(η6-HMes*)(CO)2] (Xyl = 2,6-C6H3Me2; R
= R′ = CO2Me; R = H, R′ = CO2Me, C(O)Me), respectively, all of them displaying five-membered phosphametallacyclo-
pentenone or phosphametallacyclopentenimine rings. Separate experiments revealed that the latter complexes (R = R′ = CO2Me)
could be decarbonylated photochemically to yield the corresponding monocarbonyls [Mo2Cp{μ-κ1,η5:κ1,η3-(C5H4)PC-
(CO2Me)C(CO2Me)C(X)}(η6-HMes*)(CO)] (X = O, NXyl), the latter rearranging at room temperature to give the
corresponding phosphametallacyclobutene isomers [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C(CO2Me)}(η6-HMes*)-
(CO)(CX)]. A side product was also formed during the photochemical treatment of the dicarbonyl substrate, it being finally
isolated after chromatographic workup as the alkenylphosphide-chloride complex [Mo2CpCl{μ-κ1,η5:κ1,η2-(C5H4)PC-
6
́
(CO2Me)CH(CO2Me)}(η -HMes*)(CO)] (Mo−P = 2.553(2) and 2.436(2) Å).
Chart 1
INTRODUCTION
■
Phosphinidene ligands (PR) are the phosphorus analogues of
carbenes,1 and their metal complexes are particularly attractive
synthons for the design of phosphaorganic molecules on the
coordination sphere of metal centers.2 As is the case of their
carbene counterparts, mononuclear complexes having bent
phosphinidene ligands can be roughly divided into electrophilic
ones (Fischer type), displaying a reactivity comparable to that
of singlet carbenes, and nucleophilic ones (Schrock type),
displaying a phospha-Wittig reactivity.1,2 This can be
rationalized by considering that, in a simplified way, the
metal−phosphorus bonding in these complexes approaches the
extreme descriptions of single-dative and double bonds,
respectively (A and B in Chart 1), while the high reactivity
of these molecules arises from the presence of both the multiple
M−P bonds and the lone electron pair at phosphorus, coupled
to the availability in both cases of a low-energy, P-centered
LUMO. This chemistry has developed as an exciting area of
Special Issue: F. Gordon A. Stone Commemorative Issue
Received: October 28, 2011
Published: January 23, 2012
© 2012 American Chemical Society
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research since the early observations of [2+1] cycloaddition
reactions of transient electrophilic phosphinidene complexes
with alkenes and alkynes to form coordinated phosphiranes and
phosphirenes.2,3 In contrast with the latter behavior, the
nucleophilic complexes have been shown instead to undergo
[2+2] cycloaddition reactions with alkynes, and even with
alkenes in a few instances, to give phosphametallacycles.2,4
Compared to this state of facts, the chemistry of phosphini-
dene-bridged binuclear complexes has been comparatively little
explored until recently,5−8 in spite of the diverse behavior that
might be anticipated for the different coordination modes of
the PR ligands in binuclear environments (D to F in Chart 1).
In our early studies on the behavior of the metal−metal
bonded complex [Mo2Cp2(μ-PMes*)(CO)4] (Cp = η5-C5H5;
component reaction (MCR), perhaps involving a pyramidal
intermediate of type F, that is largely unprecedented in the
chemistry of isolable phosphinidene complexes, although a few
related MCRs involving transient phosphinidene-derived
mononuclear complexes have been reported,11 and thus
deserved a more detailed analysis. In this paper we report our
full studies on the reactivity of 1 toward different alkynes, both
in the absence and in the presence of two-electron donor
ligands such as CO, isocyanides, or phosphines. For
comparative purposes, we have also studied some of these
reactions using the isoelectronic phosphinidene complex
[Mo2Cp2(μ-PH)(η6-HMes*)(CO)2] (2) as the starting sub-
strate (Chart 2). According to recent density functional theory
(DFT) calculations, the PH complex 2 displays a π(Mo−P)
bonding interaction essentially located at the P−MoCp(CO)2
bond,8d whereas that interaction in 1 is largely delocalized over
the Mo−P−Mo skeleton (not represented in Chart 2), and this
difference should lead to an increased reactivity for 2
(compared to 1) concerning the [2+2] cycloadditions. As it
will be discussed below, our results suggest unexpectedly that,
rather than two different reaction pathways ([2+2] cyclo-
addition vs MCR processes, depending on the presence of
ligands), the reactions of compounds 1 and 2 toward alkynes
might be rationalized through a single reaction pathway
involving initially the formation of intermediates having
pyramidal phosphinidene ligands of type F.
t
Mes* = 2,4,6-C6H2 Bu3; type D), we found that HCC(p-tol)
would insert into the Mo−P bond of the complex under
photochemical activation, to give a rare phosphaallyl derivative
[Mo2Cp2(μ-η1:η2,κ1-C(p-tol)CHPMes*)(CO)4].6a This result
was somewhat reminiscent of the only other related reaction
involving binuclear phosphinidene complexes, that of the
transient complex of type D [Fe2(μ-PtBu)(CO)6] with RC
CR′ to give the corresponding derivatives [Fe2(μ-κ1,η1:κ1,η2-
CRCR′PtBu)(CO)6].9 In the case of our dimolybdenum
substrate, however, a photoexcited state involving a pyramidal
phosphinidene ligand (type F in Chart 1) was proposed to be
involved in this and related reactions.6a,c Interestingly, the
diiron complex [Fe2Cp2(μ-PCy)(μ-CO)(CO)2], having a quite
nucleophilic pyramidal PR ligand of type F, was later shown to
react readily with alkynes, although in a more complex way,
with the incoming molecule being eventually bound not only to
P but also to the Cp or carbonyl ligands, depending on the
particular alkyne used.7b Neither of the above reactions are
strictly comparable to those observed between mononuclear
phosphinidene complexes and alkynes.
RESULTS AND DISCUSSION
■
Reactions of Complexes 1 and 2 with Alkynes. The
cyclopentadienylidene-phosphinidene complex 1 reacts readily
with several alkynes in refluxing toluene to give the
corresponding derivatives [Mo2 Cp{μ-κ1 ,η5 :κ1 ,η1 -
(C5H4)PCRCR′}(η6-HMes*)(CO)2] (3a: R = R′ =
CO2Me; 3b: R = H, R′ = CO2Me; 3c: R = H, R′ = p-tol).
Compounds 3a−c exist in solution as an equilibrium mixture of
syn and anti isomers in each case, with the syn/anti ratio being
dependent on the solvent (Chart 3). These isomers differ in the
In contrast to the above behavior, a preliminary study on the
reactivity of an asymmetric complex of type E as the
cyclopentadienylidene-phosphinidene complex [Mo2Cp(μ-
κ1:κ1,η5-PC5H4)(η6-HMes*)(CO)2] (1) (Chart 2) revealed
Chart 3
Chart 2
relative orientation of the cyclopentadienyl rings with respect to
the average plane of the phosphametallacyclobutene ring of the
molecule, as discussed later on. We also note that the reaction
with methyl propiolate is not selective, since it actually gives a
mixture of 3b and the corresponding phosphide-acyl complex
[Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC(CO2Me)C(O)}(η6-
HMes*)(CO)2] (6b), a product more conveniently prepared in
the presence of CO, as discussed later on (Chart 4).
As predicted on the basis of its better-suited electronic
structure, the phosphinidene complex 2 is more reactive than 1,
and it is able to react with the activated alkynes DMAD
(dimethyl acetylenedicarboxylate) and methyl propiolate at
room temperature. Unfortunately the latter reaction gave a
mixture of products that could not be characterized. In contrast,
the reaction of 2 with DMAD takes place at room temperature
that this compound failed to react with alkenes and alkynes at
room temperature, but reacted with alkynes in refluxing toluene
solutions to give products apparently resulting from a [2+2]
cycloaddition of the alkyne to its multiple Mo−P bond.8b This
is reminiscent of the behavior of nucleophilic mononuclear
phosphinidene complexes2,4 and also of some mononuclear
phosphide complexes.10 Interestingly, however, we found
recently that the reactivity of 1 could be dramatically increased
in the presence of CO or CNXyl ligands (Xyl = 2,6-C6H3Me2),
with 1 then being able to react rapidly at room temperature
with several electron-poor alkynes and alkenes to give novel
five-membered phosphametallacycles resulting from a highly
selective coupling between the alkyne/alkene, the added ligand,
and the Mo−P multiple bond.8e This resulted in a multi-
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= H, R′ = C(O)Me), respectively (Charts 4 and 5). All these
Chart 4
complexes are derived from the regioselective coupling of the
Chart 5
almost instantaneously and with high selectivity, but gives
unexpectedly the monocarbonyl phosphide-acyl complex
[Mo2Cp2{μ-κ1:κ1,η3-PHC(CO2Me)C(CO2Me)C(O)}(η6-
HMes*)(CO)] (4), the latter evolving progressively to the
isomeric dicarbonyl [Mo2Cp2(μ-κ1:κ1,η1-PHC(CO2Me)C-
(CO2Me)}(η6-HMes*)(CO)2] (5). Compound 5 displays a
phosphametallacyclobutene ring comparable to those of
compounds 3a−c, while compound 4 displays a sort of
phosphametallacyclopentenone ring. But more importantly, the
fact that 5 is formed from 4 has critical mechanistic implications
concerning the hypothetical [2+2] cycloadditions supposed
initially to be responsible for the formation of compounds such
as 3 and 5, a matter to be discussed later on. We finally note
that the isomerization 4/5 is completed in ca. 24 h in toluene
solution at room temperature, whereas it becomes faster when
adding some tetrahydrofuran to these toluene solutions, then
entering alkyne with the P atom of the phosphinidene ligand
and either carbonyl or isocyanide ligands bound to
molybdenum. Moreover, as found for compounds 3, most of
these compounds (except for the more congested molecules 7,
8, and 9a) exist in solution as solvent-dependent equilibrium
mixtures of the corresponding syn and anti isomers, these also
differing in the relative orientation of the cyclopentadienyl rings
with respect to the average plane defined by the five-membered
phosphametallacycle (only shown for compounds 6 in Chart
4). We finally note that the reaction with (p-tolyl)acetylene in
the presence of CO gave also significant amounts of the
diphosphanediyl complex [Mo2{μ-κ1,η5:κ1,η5-(C5H4)PP-
(C5H4)}(η6-HMes*)2], a singular molecule derived from the
reaction of 1 with CO, as shown by independent experiments.12
Photochemical Transformations Relating Different
Phosphametallacycles. Since the phosphide-acyl complexes
6 have one more CO group than the corresponding
compounds of type 3, we examined possible interconversion
routes between these two types of compounds using the
DMAD derivatives 3a and 6a. First we noticed that 3a did not
react with CO (3 atm) even in refluxing toluene. This indicates
the presence of a significant kinetic barrier to the insertion of
CO into the Mo−C bonds of compounds of type 3. The same
applies to the reverse reaction, since compound 6a does not
experience any significant transformation in refluxing toluene
after a few hours. However, a CO molecule indeed can be
removed out of 6a upon irradiation with visible−UV light,
although that reaction does not yield 3a, but the monocarbonyl
[Mo2Cp{μ-κ1,η5:κ1,η3-(C5H4)PC(CO2Me)C(CO2Me)C-
(O)}(η6-HMes*)(CO)] (10), an isomer of 3a still retaining a
five-membered phosphametallacyclopentenone ring (Scheme
2), along with small and variable amounts of a second complex
identified by a 31P NMR resonance at 45.8 ppm. Upon
chromatographic workup, this minor product is transformed
into the chloro complex [Mo2CpCl{μ-κ1,η5:κ1,η2-(C5H4)PC-
(CO2Me)CH(CO2Me)}(η6-HMes*)(CO)] (11), with an
alkenylphosphide ligand (Chart 6). Thus, this minor side
product is tentatively formulated as the corresponding hydroxo
complex [Mo2Cp(OH){μ-κ1,η5:κ1,η2-(C5H4)PC(CO2Me)
CH(CO2Me)}(η6-HMes*)(CO)], possibly arising from the
reaction with trace amounts of water present in the photolytic
experiment.
Scheme 1
being completed in ca. 1 h, an observation with no obvious
explanation.
Reactions in the Presence of Other Ligands. When
different ligands such as CO, PMe3, P(OMe)3, or CNXyl are
added at room temperature to toluene solutions containing
compound 1 and different alkynes, relatively fast MCR
reactions take place to give with good yields the corresponding
phosphide-acyl complexes [Mo2 Cp{μ-κ1 ,η5 :κ1,η1-
(C5H4)PCRCR′C(O)}(η6-HMes*)(CO)2] (6a: R = R′ =
CO2Me; 6b: R = H, R′ = CO2Me; 6c: R = H, R′ = p-tol), and
[Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C(CO2Me)C-
(O)}(η6-HMes*)(CO)(L)] (7: L = PMe3; 8: L = P(OMe)3) or
the related phosphide-iminoacyl derivatives [Mo2Cp{μ-
κ1,η5:κ1,η1-(C5H4)PC(R)C(R′)C(NXyl)}(η6-HMes*)-
(CO)2] (9a: R = R′ = CO2Me; 9b: R = H, R′ = CO2Me; 9d: R
Compound 10 is structurally related to 4, but thermally more
robust, and it can be isolated in a conventional way. Yet, the
solutions of 10 also rearrange progressively (rapidly upon
heating) to yield its dicarbonyl isomer 3a, having the four-
membered phosphametallacycle, with the transformation being
completed in ca. 3 d at room temperature. Interestingly, this
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(CO2Me)}(η6-HMes*)(CNXyl)(CO)] (13), an isocyanide
complex structurally related to compounds 3 and 5. Upon
standing at room temperature (more rapidly in the presence of
added tetrahydrofuran), compound 12 transforms progressively
into 13, the latter being the product that could be finally
isolated in the conventional way.
Scheme 2
Solid-State Structure of Compounds 3a and 5. The
structure of the cyclopentadienylidene-phosphinidene complex
3a (Figure 1 and Table 1) was confirmed during our
Chart 6
Figure 1. ORTEP diagram (30% probability) of compound syn-3a,8b
t
with H atoms and Bu and CO2Me groups (except the C1 atoms)
omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
syn-3a8b
parameter
Mo1−P
Mo2−P
3a
2.4810(8)
2.5136(9)
2.198(3)
1.352(4)
1.799(3)
1.779(3)
77.7(1)
transformation can be reversed photochemically. Thus,
irradiation of toluene solutions of 3a with visible−UV light
for 1 h at room temperature cleanly yields its isomer 10, along
with a small amount of the hydroxo complex mentioned above.
As it was the case of 3a, compound 10 does not react with CO
(3 atm) at room temperature so as to give 6a.
Mo1−CC
CC
CC−P
P−CMo
OC−Mo1−CO
Mo1−P−Mo2
Mo1−P−CC
Mo2−P−CC
Similar transformations were also observed for the
phosphide-iminoacyl complex 9a (Scheme 3). Thus, the
144.61(3)
87.0(1)
126.7(1)
Scheme 3
preliminary study on this chemistry,8b and that of the
phosphinidene complex 5 has been now examined also through
an X-ray analysis. Although the poor quality of the diffraction
data prevents a detailed analysis of the metric parameters for 5,
the connectivity and overall conformation of the molecule is
thus firmly established.
The molecule of 3a corresponds to the syn isomer, with the
cyclopentadienylic rings placed on the same side of the average
plane defined by the atoms of the almost flat phosphametalla-
cyclobutene ring (average torsion angle ca. 10°, C(3)−C(6) =
1.352(4) Å). The latter is derived from a formal [2+2]
cycloaddition of an alkyne molecule to the short P−Mo bond
of compound 1, almost perpendicularly to the Mo2P plane, as
expected by considering the orbital interactions involved. As a
result, however, both Mo−P distances are elongated. In
particular, the long Mo−P length of 2.5153(7) Å now
approaches the reference values of single-bond lengths (e.g.,
2.555(3) Å for the corresponding distance in the asymmetri-
cally bridged [W2Cp2(μ-PMes)(CO)4(PH2Mes)], with Mes =
2,4,6-C6H2Me3,13 or 2.608(1) Å in [Mo2{μ-κ1,η5:κ1,η5-(C5H4)-
PP(C5H4)}(η6-HMes*)2]),12 while the Mo(1)−P length of
2.4810(8) Å within the ring has a value closer to those of
single-dative P→Mo bonds (ca. 2.45 Å for MoPR3 complexes).
irradiation of the latter complex with visible−UV light in
toluene solutions gave as the major product the monocarbonyl
derivative [Mo2Cp{μ-κ1,η5:κ1,η3-(C5H4)PC(CO2Me)C-
(CO2Me)C(NXyl)}(η6-HMes*)(CO)] (12), structurally re-
lated to compounds 4 and 10, along with smaller amounts of
the isomer [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C-
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Table 2. Selected IR and 31P NMR Data for New Compounds
a
a
a
b
compound
ν(MoCO)
ν(CO)
ν(MoCX)
δ(P) /ppm
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)}(η6-
1944 (vs), 1864 (s)
1696 (m)
−21.5 (syn)
HMes*)(CO)2] (3a)
−12.7 (anti)
−25.4 (syn)
−12.4 (anti)
−23.9 (syn)
−10.5 (anti)
−6.0 (d, 317)
[Mo2Cp{μ-(C5H4)PCHC(CO2Me)}(η6-HMes*)
(CO)2] (3b)
[Mo2Cp{μ-(C5H4)PCHC(p-tol)}(η6-HMes*)(CO)2]
1933 (vs), 1848 (m)
1923 (vs), 1836 (s)
1728 (s)
(3c)
c
c
c
d
d
[Mo2Cp2{μ-PHC(CO2Me)C(CO2Me)C(O)}(η6-
HMes*)(CO)] (4)
[Mo2Cp2{μ-PHC(CO2Me)C(CO2Me)}(η6-HMes*)
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)C(O)}(η6- 1949 (vs), 1877 (s)
1913 (vs)
1699 (s)
1699 (s)
c
c
1941 (vs), 1860 (s)
1698 (m)
−137.8 (d, 258)
(CO)2] (5)
1730 (m)
1724 (m)
1589 (m, sh),
1566 (m)
82.3 (syn)
83.8 (anti)
79.7 (syn)
76.1 (anti)
HMes*)(CO)2] (6a)
[Mo2Cp{μ-(C5H4)PCHC(CO2Me)C(O)}(η6-HMes*) 1942 (vs), 1866 (s)
(CO)2] (6b)
[Mo2Cp{μ-(C5H4)PCHC(p-tol))C(O)}(η6-HMes*)
1580 (m, sh),
1565 (m)
d
1936 (vs), 1857 (s)
1580 (m)
86.3 (syn)
d
(CO)2] (6c)
84.0 (anti)
d
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)C(O)}(η6- 1807 (s)
HMes*)(CO)(PMe3)] (7)
1735 (s)
1731 (s)
1652 (m)
1632 (m)
102.7 [d, 7, μ-P], 29.7 [d, 7]
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)C(O)}(η6- 1839 (s)
191.9 [d, 11]
93.5 [d, 11, μ-P]
81.5
HMes*)(CO){P(OMe)3}] (8)
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)C(NXyl)} 1942 (vs), 1869 (s)
(η6-HMes*)(CO)2] (9a)
1730 (m)
1718 (m)
1540 (w)
1542 (w)
[Mo2Cp{μ-(C5H4)PCHC(CO2Me)C(NXyl)}(η6-
1939 (vs), 1863 (s)
75.4 (syn)
68.2 (anti)
76.4 (syn)
67.1 (anti)
57.5
HMes*)(CO)2] (9b)
[Mo2Cp{μ-(C5H4)PCHC{C(O)Me}C(NXyl)}(η6-
HMes*)(CO)2] (9d)
1937 (vs), 1860 (s)
1691 (m)
1531 (w)
e
e
e
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)C(O)}(η6- 1946 (vs)
1687 (s, br)
1691 (m)
1683 (vs)
1689 (s)
1687 (s, br)
HMes*)(CO)] (10)
[Mo2CpCl{μ-(C5H4)PC(CO2Me)CH(CO2Me)}(η6-
HMes*)(CO)] (11)
1982 (vs)
45.5
49.8
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)C(NXyl)} 1928 (vs)
1587 (w)
(η6-HMes*)(CO)] (12)
d
[Mo2Cp{μ-(C5H4)PC(CO2Me)C(CO2Me)}(η6-
HMes*)(CNXyl)(CO)] (13)
2047 (vs, CN), 2007 (m,
CN), 1848 (vs)
−8.5 (syn)
d
8.9 (anti)
a
b
Recorded in CH2Cl2 solution, unless otherwise stated; data in cm−1; X = O, NXyl. Recorded in CD2Cl2 solutions at 290 K and 121.50 MHz unless
otherwise stated; δ in ppm relative to external 85% aqueous H3PO4; J(PH) given in brackets, J(PP) given in square brackets, both in hertz. In
c
d
e
petroleum ether solution. In C6D6 solution. ν(CO) 1946 (vs), 1758 (m), 1694 (m) cm−1 in petroleum ether solution.
The coordination environment around the P atom is not
tetrahedral, but rather of a distorted pyramidal-trigonal type,
with the Mo(1), Mo(2), P, and C(6) atoms almost in the same
plane (sum of angles around P ca. 358°) and the cyclo-
pentadienylidene C(14) atom occupying the apical position.
Although initially we considered this perhaps as resulting from
a residual π(Mo−P) interaction in the molecule (cf. the
bonding in [{Cp(CO)2Mo}2PMn(CO)4], a complex displaying
a phosphide ligand with a T-shaped environment),14 our recent
work on the heterometallic derivatives of 1 indicates that this
unusual geometry around P rather emerges from the geo-
metrical constraints imposed by the bifunctional PC5H4 ligand
and steric effects.8d
The molecule of 5 has two significant differences when
compared to that of 3a. First, it corresponds to an anti isomer,
with the cyclopentadienylic rings placed at opposite sides of the
average plane of the phosphametallacyclobutene ring, which is
also quite flat. Second, it displays a relatively normal tetrahedral
environment around phosphorus, in agreement with the
comments made above on the origin of the structural anomalies
displayed by different derivatives of 1.
same basic structural features and are consistent with the solid-
state structures discussed for 3a and 5. In addition, they clearly
indicate that two isomers coexist in solution in each case, as
mentioned before (syn and anti isomers, Chart 3) except for 5,
for which a single isomer is present in solution (presumably the
anti isomer found in the crystal). The syn isomers appear to be
favored in low-polarity solvents such as benzene or toluene,
while more polar solvents such as dichloromethane seem to
favor the anti isomers.
The IR spectrum of all these compounds (except for the
monocarbonyl 13) displays two C−O stretching bands
corresponding to the terminal carbonyls, with relative
intensities (very strong and strong, in order of decreasing
frequency) as anticipated for M(CO)2 oscillators having C−
M−C angles less than 90° (ca. 78° in the crystal of 3a),15 with
their wavenumbers expectedly increasing with the number of
CO2Me groups present in the original alkyne [1904 cm−1 (3a)
> 1891 cm−1 (3b) > 1880 cm−1 (3c)]. At the same time, they
display strongly shielded 31P NMR resonances, in the range
+10 to −20 ppm (ca. −140 ppm for the PH complex 5), which
is consistent with the presence of a ligand of type PR2 bridging
two metal atoms without a metal−metal bond.16 These shifts
are not very different from those measured for the relatively
scarce number of mononuclear complexes reported to have
Solution Structure of Compounds 3a−c, 5, and 13.
The spectroscopic data available for these compounds (Table 2
and Experimental Section) indicate that all of them share the
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comparable phosphametallacyclobutene rings (cf. 85.0 ppm for
[Cp2Zr{P(Mes*)C(H)CPh}].4e
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
anti-6a8e
The major isomer for compound 3a (almost the unique one
in toluene solutions) gives rise to a 31P NMR resonance more
shielded than the minor isomer (Table 2) and thus is
reasonably assigned to the isomer found in the crystal (syn).
We have assumed that the same ordering of 31P shifts between
syn and anti isomers holds for the other compounds of this
type, this being consistent with the NOESY spectra recorded
for 3c. Indeed, for that compound NOE enhancements were
detected for the minor isomer in C6D6 solution between the Cp
Mo1−P
Mo2−P
Mo1−C1
Mo1−C2
Mo1−C3
C3−C4
C4−C5
P−C5
2.474(1)
2.557(1)
1.957(6)
1.954(6)
2.211(5)
1.518(7)
1.343(6)
1.820(5)
2.190(5)
1.787(5)
1.221(6)
Mo−P−Mo2
Mo1−P−C5
Mo2−P−C5
Mo2−P−C155
Mo1−C3−C4
C3−C4−C5
C4−C5−P
C1−Mo1−C2
C1−Mo1−P
C2−Mo1−P
C3−Mo1−P
136.8(1)
105.0(2)
117.0(2)
57.3(2)
119.8(3)
118.7(4)
112.8(4)
77.5(2)
Mo2−C15
P−C15
C3−O3
116.2(2)
78.0(2)
t
and Bu groups, thus allowing its identification as the anti
isomer. At the same time, significant NOE enhancements were
also observed between the ortho protons of the C6H4 group and
the Cp ligand and between the CH protons of the former
73.2(1)
during our preliminary study on the MCR reactions of
compound 1.8e The molecule in the crystal corresponds to an
isomer of type anti, and it can be derived from that of 3a after
formal insertion of a CO molecule into the Mo−C bond of the
phosphametallacyclobutene ring (a reaction not taking place
actually, as noted above). This yields a more relaxed five-
membered phosphametallacyclopentenone MoPC3 ring (CC
= 1.343(6) Å), with the P and C atoms almost in a plane, but
the Mo atom significantly deviated from it (by ca. 0.85 Å). Due
to that unstrained geometry, the Mo−P lengths now approach
better the expected values of single (Mo(2)−P = 2.557(1) Å)
and single-dative (Mo(1)−P = 2.474(1) Å) bonds, as proposed
on the basis of simple electron-count rules. Yet, the
environment around the P atoms is of the unusual trigonal-
pyramidal type characteristic of many derivatives of the
cyclopentadienylidene-phosphinidene complex 1, with the
Mo(1), Mo(2), P, and C(5) atoms almost in the same plane
(sum of angles around P ca. 359°) and the cyclopentadieny-
lidene C(15) atom occupying the apical position.
The five-membered MoPC3 ring in 6a is comparable to that
present in the diiron phosphide-acyl complex [Fe2Cp2{μ-
κ1:κ1,η1-CyPCHC(p-tol)C(O)}(μ-CO)(CO)], a related mole-
cule derived from the reaction of the pyramidal-phosphinidene
complex [Fe2Cp2(μ-PCy)(μ-CO)(CO)2] with HCC(p-
tol).7b The interatomic distances within the phosphametalla-
cycles in these two compounds are comparable to each other,
after allowing for the differences in the covalent radii for Mo
and Fe,19 with the main difference being of a conformational
nature, since the FePC3 ring in the diiron complex is almost
planar, while the corresponding one in 6a is not, as noted
above.
t
alkyne and either the Bu or C5H4 groups, thus confirming the
regioselectivity of the reaction leading to these complexes, with
the CH atom of the alkyne being specifically attached to the P
atom of the starting substrate. This is also indicated by the fact
that the PCH 1H NMR resonances in both isomers of 3b (ca. 7
ppm) display a relatively low 2JPH coupling of 11 Hz, consistent
with a geminal arrangement of P and H atoms around a double
CC bond, a feature also present in the spectra of compounds
3
of types 6 and 9 (see below). In contrast, transoid JPH
couplings through a double CC bond are expected to be
significantly higher (ca. 30 Hz).17
The 13C NMR spectra of compounds 3 and 5 are also
consistent with the regioselective formation (for the terminal
alkynes) of the phosphametallacycle ring, with the Mo-bound C
atom of the alkyne giving rise to a quite deshielded resonance at
ca. 200 ppm and displaying a relatively high P−C coupling
(15−25 Hz), while the P-bound carbon atom gives rise to a
more shielded resonance as expected (ca. 158 ppm in 3a or 5,
ca. 140 ppm for the PCH resonance in 3c) and displays a lower
P−C coupling (<5 Hz), a feature also present in the spectra of
compounds 6 to 9 (see below). We note that these chemical
shifts are comparable to those measured for the mononuclear
zirconium complexes [Cp2Zr{P(Mes*)C(R)CPh}] (R = Ph,
Me, H), the latter displaying Zr−CPh resonances also around
200 ppm.4e We finally note that the carbonyl ligands of the
Mo(CO)2Cp fragments give rise to two distinct resonances in
each case, with PC couplings of ca. 30 and 3 Hz in each case, as
expected from their different positioning (cis and trans,
respectively) relative to the P atom.18
Solid-State Structure of Compound 6a. The structure of
the DMAD derivative 6a (Figure 2 and Table 3) was confirmed
Solution Structure of Compounds 6 to 9. The
spectroscopic data available for these compounds (Table 2
and Experimental Section) indicate that all of them share the
same basic structural features and are consistent with the solid-
state structure discussed for 6a. In addition, as was the case of
compounds 3, they clearly indicate that syn and anti isomers
coexist in solution in most cases, as mentioned above (Chart 4)
except for the DMAD derivatives 7, 8, and 9a, for which a
single isomer is present in solution. There is no clear trend
concerning the influence of the solvent on the equilibrium ratio
between these isomers.
The IR spectra of the dicarbonyl compounds 6 and 9 in the
C−O stretching region display two strong bands at frequencies
slightly higher than those of the corresponding complexes of
type 3, an effect ascribed to the influence of the acyl or
iminoacyl groups now present in these molecules. The latter
groups give rise to characteristic resonances at lower
Figure 2. ORTEP diagram (30% probability) of compound anti-6a,8e
t
with H atoms and Bu and CO2Me groups (except the C1 atoms)
omitted for clarity.
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frequencies, at ca. 1580 and 1540 cm−1, respectively, for
compounds 6 and 9. The monocarbonyl compounds 7 and 8
expectedly give rise to a single carbonyl stretch at lower
frequencies (ca. 1820 cm−1), whereas the C−O stretch of the
corresponding acyl group (ca. 1640 cm−1) now appears at
frequencies higher than in the dicarbonyl compounds (Table
2).
after deinsertion from the MoPC3 ring of 12 (kinetic product).
Finally, the appearance of more than one C−N stretching band
in the IR spectra of 13 cannot be taken as an indication of cis/
trans isomerism around the MoCp(CO)(CNR) center.
Actually, such splitting of C−N bands is a common feature
of complexes having terminal isocyanide ligands and is due to
the presence in solution of variable amounts of conformers with
bent isocyanide ligands.21
All compounds 6 to 9 give rise to a 31P NMR resonance in
the range 65−85 ppm, a relatively low chemical shift still
consistent with the presence of a phosphide-like bridging ligand
in the absence of metal−metal bonds. Yet, these shifts are some
100 ppm higher than the corresponding values in compounds
3, a difference that can be attributed to the higher ring strain in
the four-membered cycles of the latter complexes, compared to
the five-membered rings of complexes 6 to 9. This shielding
effect on P nuclei placed in strained rings is well documented
for complexes having chelate diphosphine ligands.20 We finally
note that the 31P chemical shifts in these compounds are rather
insensitive to the syn/anti isomerism (Table 2).
Structural Characterization of Compounds 4, 10, and
12. Full characterization of these species was precluded because
of their low thermal stability and easy transformation into the
corresponding isomers having a four-membered phosphame-
tallacyclobutene ring (5, 3a, and 13, respectively), although the
available data allow unambiguous definition of the essential
structural features of these molecules (Table 2 and Exper-
imental Section). The IR spectra of these compounds display in
each case two strong bands indicative respectively of the
presence of a single carbonyl ligand (ca. 1930 cm−1) and acyl
(ca. 1690 cm−1 for 4 and 10, masked with the bands from the
CO2Me groups) or iminoacyl ligands (1587 cm−1 for 12). This
could be corroborated through a 13C NMR spectrum of
compound 10, this exhibiting two resonances at 254.0 and
237.0 ppm that can be assigned to the acyl and carbonyl
ligands, respectively. The position of the former resonance
actually is not very different from that in the phosphide-acyl
precursor 6a (ca. 265 ppm). This confirms that, upon
decarbonylation of the precursor 6a (and presumably also in
the case of 9a), the five-membered MoPC3 rings are preserved,
and we propose that they just rearrange to coordinate their
CC double bonds so as to fill the vacancy left by the carbonyl
ligand (Schemes 2 and 3). This should be expectedly
accompanied by a significant shielding of the corresponding
carbon resonances. Unfortunately, these resonances could not
be located in the spectrum of 10, probably due to broadening
effects. Although we are not aware of previous examples for a
coordinated phosphide-acyl ligand analogous to that proposed
here, we note the strong structural relationship with several
alkenyl-acyl or alkenyl-iminoacyl and related ligands bridging
dimetal centers (Chart 7).22−25 Interestingly, some of these acyl
The identification of syn and anti isomers in the solutions of
6 and 9 was made on the basis of standard NOESY
experiments, these allowing the identification of the relevant
Cp/C5H4 (syn) and Cp/tBu (anti) enhancements and also
confirming in the case of 6b the spatial proximity of the former
CH proton of the alkyne to the C5H4 ring. In addition, we note
1
that all derivatives of terminal alkynes give rise to PCH H
NMR resonances at about 7 ppm and displaying low P−H
couplings of ca. 8 Hz, as found for compounds 3b,c, this
indicating the same regioselectivity in the formation of the five-
membered phosphametallacycles, with the terminal carbon of
the alkyne being bound to the P atom. For further comparison,
the mentioned diiron complex [Fe2Cp2{μ-κ1:κ1,η1-CyPCHC(p-
tol)C(O)}(μ-CO)(CO)] displays a comparable 1H NMR
resonance for its PCH atom (δ 7.90 ppm, JHP = 13 Hz).7b
The 13C NMR spectra of compounds 6 to 9 are also
consistent with a regioselectivity (for terminal alkynes) identical
to that of compounds 3. Actually, the P-bound carbon atom of
the former alkyne gives rise to a resonance comparable to the
corresponding ones in compounds 3 (ca. 160 ppm and with
unmeasurably small P−C couplings), while the other C atom of
the alkyne, now bonded to an acyl or iminoacyl group, gives
rise to a resonance at ca. 165−170 ppm displaying a relatively
high P−C coupling (20−25 Hz). Finally, the acyl and iminoacyl
groups give rise to diagnostic resonances much more
deshielded (at ca. 270 and 210 ppm, respectively), as expected.
The monocarbonyl complexes 7 and 8 are obtained as single
isomers in each case. Apart from the syn/anti isomerism, two
possible arrangements of the PMe3/P(OMe)3 ligands (trans or
cis relative to the other P atom) are possible. Fortunately, the
13C spectrum of 8 allows the unambiguous identification of the
complex as having a trans arrangement of its P ligands, since
both the acyl (JPC = 38 and 11 Hz) and the carbonyl resonances
(JPC = 42 and 28 Hz) display large P−C couplings to both P
atoms, which is indicative of acute P−Mo−C angles.18 This
geometrical arrangement is likely to be the most favored on
steric grounds. As for the isocyanide complex 13, there are two
isomers in solution. Since no splitting of the C−O stretching
band of the carbonyl ligand is observed, we conclude that the
observed isomerism must be of the syn/anti type. The
isocyanide ligand is most likely placed trans to the P atom,
since this expectedly leads to minimum steric repulsions, as
found for the phosphine complexes 7 and 8, and also
corresponds to the initial position that this ligand must occupy
Chart 7
complexes undergo decarbonylation and deinsertion reactions
comparable to those relating our complexes, a matter to be
discussed below.
Structural Characterization of Compound 11. The
molecule of the chloro complex 11 (Figure 3 and Table 4) can
be viewed as derived from that of 10 by removing the acyl
group and replacing it with chlorine (at the metal) and
hydrogen (at carbon) atoms, yielding an alkenyl-phosphide
ligand π-bound to the MoCp(CO) fragment (Mo−C lengths
ca. 2.25 Å, C−C = 1.43(1) Å) in an allyl-like fashion. Once
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gives support to an alternative and unified explanation to
account for the formation of all alkyne derivatives of the
phosphinidene complexes 1 and 2 (Scheme 4; only derivatives
of 1 represented).
Scheme 4
Figure 3. ORTEP diagram (30% probability) of compound 11, with H
atoms (except H3) and tBu and CO2Me groups (except the C1 atoms)
omitted for clarity.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 11
Mo1−P
Mo2−P
Mo2−Cl1
Mo2−C1
Mo2−C2
Mo2−C3
P−C13
P−C2
C2−C3
C3−C6
2.553(2)
2.436(2)
2.510(2)
1.993(8)
2.244(7)
2.258(8)
1.789(7)
1.799(7)
1.431(9)
1.468(10)
Mo1−P−Mo2
Mo1−P−C2
Mo2−P−C2
Mo2−P−C135
C6−C3−C2
C3−C2−P
C1−Mo2−C3
C1−Mo2−P
C1−Mo2−Cl1
P−Mo2−Cl1
165.39(9)
132.7(2)
61.8(2)
121.5(2)
125.4(7)
112.8(5)
123.7(3)
82.4(2)
80.6(2)
128.1(1)
more, the geometry around phosphorus is of the trigonal-
pyramidal type, with the Mo(1), Mo(2), and C(2) atoms
defining a plane containing the P atom, and the apical position
being occupied by the cyclopentadienylidene C(13) atom. The
́
́
Mo−P lengths of 2.553(2) Å (Mo1−P) and 2.436(2) Å
(Mo2−P) are now very close to the reference values for single
and single-dative Mo−P bond lengths,8d as proposed on the
basis of simple electron-count formalism.
Spectroscopic data in solution for 11 are consistent with the
structure found in the crystal. We note that the E-conformation
of the alkenyl ligand found in the crystal is fully consistent with
the large P−H coupling of the corresponding 1H NMR
resonance (31 Hz), while its relatively low chemical shift (4.84
ppm) is indicative of the retention of the π-coordination of the
alkenyl group in solution.
All reactions would be initiated by the coordination of a
ligand (L) to the MoCp(CO)2 center of the phosphinidene
complex. This ligand would be the added ligand in each case
(CO, PR3, CNR, ...) or, if no other ligand is added, a molecule
of the alkyne itself, always used in excess. This would yield an
intermediate species [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(η6-HMes*)-
(CO)2L] (A) having a pyramidal phosphinidene ligand. We
have actually performed a DFT calculation of such an
intermediate when L = CO (see the Experimental Section for
details of the calculations). The optimized structure (Figure 4
and Table 5) expectedly features a four-legged piano-stool
Mo(CO)3P fragment and a pyramidal environment around
phosphorus (sum of angles 284.7°). The corresponding Mo−P
length has been greatly increased, as anticipated from the bond
order reduction to unity (2.835 Å, to be compared with 2.272 Å
computed for 1).8d The weakening of this bond is so large that
an analysis of the topology of the electron density of the
molecule, under the AIM theory,26 failed to locate the
corresponding bond critical point (cf. ρ = 0.311 e Å−3 for the
short Mo(2)−P bond in A, while the short bond in 1 has a
value of 0.627 e Å−3).8b All of this actually justifies the fast
homolytic cleavage of that Mo−P bond of 1 occurring under a
CO atmosphere, to give the dimers [Mo2Cp2(CO)6] and
Pathways in the Reactions of the Phosphinidene
Complexes 1 and 2 with Alkynes. According to DFT
calculations on compounds 1 and 2, the π(Mo−P) bonding
interactions in these molecules take place perpendicularly to
the Mo−P−Mo plane, as the corresponding antibonding
interactions do (incidentally, the LUMO in these molecules).8d
Therefore, these orbitals would have the right shape to account
for the formation of the phosphametallacyclobutene derivatives
3 and 5 via a concerted [2+2] cycloaddition pathway between
the phosphinidene complex 1 or 2 and the corresponding
alkyne, thus paralleling the behavior of the mononuclear
nucleophilic phosphinidene complexes. However, there are
several facts in support of an alternative reaction pathway: (a)
the reactivity of 1 toward alkynes is dramatically increased in
the presence of simple ligands (CO, PR3, CNR, ...) to give
derivatives having phosphametallacyclopentenone rings, (b) an
intermediate (4) having the same phosphametallacyclopente-
none ring is detected in the room-temperature reactions of 2
with DMAD, and (c) the latter type of molecules (4, 10, and
12) undergo fast thermal rearrangement into the corresponding
phosphametallacyclobutene isomers 3, 5, and 13. All of this
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discussed in the preceding sections actually are an exact
representation of the sequence C → D → 3 here proposed.
Moreover dimetal complexes having dimetallacyclopentenone
rings also offer independent precedents of related trans-
formations, not only of the coordination of the CC double
bond (analogous to the C → D step),23a but also of deinsertion
of CO to give dimetallacyclobutene rings (analogous to the D
→ 3 step).22,23b Finally, when L = CNXyl, the nucleophilic
attack of the carbanionic atom in the corresponding
intermediate B would preferentially occur at the isocyanide,
rather than at a carbonyl ligand. Although the origin of this
chemoselectivity is not clear to us at the moment, we note that
an analogous selectivity has been reported in the related
reactions of the thiolate complexes [FeCp(SPh)(CNMe)(CX)]
(X = O, S) with DMAD to give the thiametallacyclopenteni-
mine derivatives [FeCp{κ1,η1-SPhCRCRC(NMe)}(CX)],
derived from the specific binding of the alkyne to the
isocyanide, rather than to the carbonyl or thiocarbonyl
ligands.28 We finally note that related phosphametallacyclo-
pentenone rings have been also described as resulting from the
reactions of mononuclear carbonyl complexes having pyramidal
PR2 ligands with activated alkynes.29
Figure 4. DFT-optimized structure of intermediate A (L = CO), with
H atoms omitted for clarity.
Table 5. Selected Bond Lengths (A) and Angles (deg) for the
DFT-Optimized Geometry of Intermediate A (L = CO)
Mo1−P
Mo2−P
P−C20
Mo1−CO(cis)
Mo1−CO(cis)
Mo1−CO(trans)
2.835
2.701
1.793
2.003
1.999
1.994
Mo1−P−Mo2
Mo1−P−C20
Mo2−P−C20
P−Mo1−CO(cis)
P−Mo1−CO(cis)
P−Mo1−CO(trans)
122.9
107.3
54.5
68.7
68.5
125.4
[Mo2{μ-κ1,η5:κ1,η5-(C5H4)PP(C5H4)}(η6-HMes*)2].12 Of in-
terest to the present discussion, however, is the fact that the
electronic structure of this intermediate has been greatly
modified, so that the P atom is now a much better donor site, as
illustrated by the nature of the HOMO−2 orbital, correspond-
ing to a nonbonding electron pair on the phosphorus atom
quite high in energy (see the Supporting Information). As a
result, it is expected that this pyramidal intermediate becomes a
donor much stronger than the starting substrate 1.
The intermediates of type A, therefore, would be
nucleophilic enough to attack a molecule of alkyne to give a
zwitterionic phosphide intermediate B, this resembling the
alkylation and related reactions of stable complexes having
pyramidal phosphinidene bridges.7,27 The attack would occur
specifically at the terminal carbon, in the case of terminal
alkynes, both because of the smaller steric hindrance of that
position and because in this way the negative charge generated
in the resulting intermediate is better delocalized by the vicinal
CO2Me (or p-tol) groups. Incidentally, we note that the same
type of regioselectivity has been found in the concerted [2+2]
cycloadditions of mononuclear nucleophilic phosphinidene
complexes with alkynes,2j,4 or even in related reactions
involving terminal trigonal PR2 ligands.10
The zwitterionic intermediate B would then evolve differ-
ently depending on the nature of L: when L = alkyne, PR3, or
CO, an attack of the internal atom of the alkyne to a carbonyl
in cis position would follow, yielding the phosphametallacyclo-
pentenone derivatives of type 6, 7, and 8. The overall result
from 1 thus is parallel to that observed previously by us in the
reactions of the stable pyramidal phosphinidene complex
[Fe2Cp2(μ-PCy)(μ-CO)(CO)2] toward different alkynes.
When L = alkyne (reactions in the absence of other ligands),
the resulting complex C would not be stable, but would
rearrange by ejection of L and coordination of the double bond
of the MoPC3 ring, to yield monocarbonyl intermediates D
analogous to complexes 10 and 4, which, due to the high
temperature of the experiment (typically refluxing toluene),
would rapidly rearrange into the isomers with the phosphame-
tallacyclobutene ring (3), thus eluding detection. We should
note that the observed transformations 6a → 10 → 3a
CONCLUDING REMARKS
■
Although the reactions of the phosphinidene complexes 1 and
2 with alkynes eventually lead to products containing either
four-membered MoPC2 rings (in the absence of other ligands)
or five-membered MoPC3 rings (in the presence of CO, CNR,
or PR3 ligands), they all seem to follow an analogous
multicomponent reaction pathway involving an intermediate
with a pyramidal phosphinidene ligand that reacts with the
alkyne to give a five-membered MoPC3 ring after cyclization
involving a coordinated CO or CNR group. These reactions are
regioselective, so that the terminal carbon of the alkyne is
attached to the P atom, and chemoselective too, so that the ring
is preferentially formed with the isocyanide (if added) rather
than with the carbonyl ligands. These products can dissociate a
CO (photochemically) or alkyne (thermally) ligand, then
rearranging first through coordination of the double CC
bond of the phosphametallacyclopentenone ring and then
through CO deinsertion from the latter ring, to finally yield the
corresponding phosphametallacyclobutene isomer, with the
latter step being reversed photochemically. The latter
complexes, therefore, would not be formed through a [2+2]
cycloaddition pathway, as might have been supposed on the
basis of the known chemistry of mononuclear phosphinidene
complexes.
EXPERIMENTAL SECTION
■
General Procedures and Starting Materials. All manipulations
were carried out under a nitrogen (99.995%) atmosphere using
standard Schlenk techniques. All reactions were carried out using
Schlenk tubes equipped with J. Young valves. Solvents were purified
according to literature procedures and distilled prior to use.30
Petroleum ether refers to that fraction distilling in the range 338−
343 K. The compounds [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(η6-HMes*)-
(CO)2] (1) and [Mo2Cp(μ-PH)(η5-C5H5)(η6-HMes*)(CO)2] (2)
6c,8d
t
were prepared as described previously (Mes* = 2,4,6-C6H2 Bu3).
Photochemical experiments were performed using jacketed Pyrex
Schlenk tubes cooled by tap water (ca. 288 K) or by a closed 2-
propanol circuit, kept at the desired temperature with a cryostat. A 400
W mercury lamp placed ca. 1 cm away from the Schlenk tube was used
for the experiments with visible−UV light. Chromatographic
separations were carried out using jacketed columns cooled by tap
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exists as an equilibrium mixture of syn and anti isomers, with their ratio
being 8:1 in dichloromethane and 17:1 in toluene, as determined by
1H NMR spectroscopy. Spectroscopic data for syn-3a: 1H NMR: δ 5.36
(m, 1H, C5H4), 5.34 (s, 5H, Cp), 5.31, 5.03 (2 m, 2 × 1H, C5H4), 4.95
(d, JHP = 4, 3H, C6H3), 4.06 (m, 1H, C5H4), 3.71, 3.53 (2s, 2 × 3H,
OCH3), 1.17 (s, 27H, tBu). 1H NMR (400.13 MHz, tol-d8): δ 5.69 (m,
1H, C5H4), 5.16 (s, 5H, Cp), 4.97 (m, 1H, C5H4), 4.90 (d, JHP = 4,
3H, C6H3), 4.65, 4.00 (2 m, 2 × 1H, C5H4), 3.68, 3.33 (2s, 2 × 3H,
OCH3), 1.13 (s, 27H, tBu). 13C{1H} NMR: δ 253.7 (d, JCP = 32, CO),
245.1 (d, JCP = 3, CO), 199.2 (d, JCP = 25, Mo−CC), 176.4, 176.0
(2d, CO2Me), 157.3 (d, JCP = 4, P−CC), 112.1 [s, C(C6H3)], 92.0
(s, Cp), 90.8 [d, JCP = 4, CH(C5H4)], 88.6 [d, JCP = 34, C(C5H4)],
88.0 [s, CH(C5H4)], 87.1 [d, JCP = 8, CH(C5H4)], 80.5 [d, JCP = 17,
CH(C5H4)], 71.7 [s, CH(C6H3)], 51.3, 51.0 (2s, OCH3), 35.1 [s,
Table 6. Crystal Data for Compound 11
parameter
11·C4H8O
mol formula
mol wt
C39H54ClMo2O6P
877.12
cryst syst
monoclinic
P21/c
space group
radiation (λ, Å)
a, Å
0.71073
9.5448(4)
16.4260(9)
25.1954(13)
90
b, Å
c, Å
α, deg
β, deg
88.649(4)
90
1
C(tBu)], 31.3 [s, CH3(tBu)]. Spectroscopic data for anti-3a: H NMR:
γ, deg
V, Å3
δ 5.82 (m, 1H, C5H4), 5.38 (s, 5H, Cp), 4.88 (m, 1H, C5H4), 4.80 (d,
JHP = 5, 3H, C6H3), 4.75, 4.27 (2 m, 2 × 1H, C5H4), 3.70, 3.49 (2s, 2 ×
3H, OCH3), 1.18 (s, 27H, tBu). 13C{1H} NMR: δ 112.1 [s, C(C6H3)],
92.9 (s, Cp), 73.8 [s, CH(C6H3)], 51.2, 51.1 (2s, 2 × OCH3), 34.5 [s,
C(tBu)], 31.5 [s, CH3(tBu)]; other resonances of this isomer were
masked by those of the major isomer and thus could not be identified
in the spectra.
3949.1(3)
4
Z
calcd density, g cm−3
absorpt coeff, mm−1
temperature, K
θ range,deg
index ranges (h, k, l)
reflns collected
indep reflns (Rint)
reflns with I > 2σ(I)
1.475
0.787
100
1.48 to 26.4
−11, 11; 0, 20; 0, 31
32 328
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC(CO2Me)}-
(η6-HMes*)(CO)2] (3b). The procedure is analogous to that described
for 3a, but using HCCCO2Me (8 μL, 0.089 mmol) and a reaction
time of 60 min at 383 K, to give a brown solution containing a mixture
of the compounds 3b and 6b. The solvent was then removed under
vacuum, the residue was extracted with petroleum ether (3 × 5 mL),
and the extracts were filtered using a canula. Removal of the solvent
from the filtrate gave compound 3b as a brown powder (0.012 g,
40%). Unfortunately, no satisfactory elemental analysis could be
obtained for 3b due to its rapid decomposition upon manipulation in
the air. In solution, this complex exists as an equilibrium mixture of syn
and anti isomers, with their ratio being 5:6 in dichloromethane and 2:1
8053 (0.156)
4251
a
R indexes [data with I > 2σ(I)]
R1 = 0.0649
b
wR2 = 0.1242
a
R indexes (all data)
R1 = 0.1488
b
wR2 = 0.1569
GOF
0.984
restraints/params
Δρ(max, min), e Å−3
0/454
0.704, −0.821
1
a
R = ∑||Fo| − |Fc||/∑|Fo|. wR = [∑w(|Fo|2 − |Fc|2)2/∑w|Fo|2]1/2. w =
in toluene, as determined by H NMR spectroscopy. The residue left
b
2
1/[σ2(Fo ) + (aP)2 + bP], where P = (Fo2 + 2Fc2)/3. a = 0.0533, b =
after the extraction with petroleum ether was dissolved in CH2Cl2 and
chromatographed at 288 K. Elution with dichloromethane gave a green
fraction yielding, after removal of solvents, compound [Mo2Cp{μ-
κ1,η5:κ1,η1-(C5H4)PCHC(CO2Me)C(O)}(η6-HMes*)(CO)2] (6b)
as a greenish-brown powder (0.010 g, 32%). A more selective
preparation of 6b is described below. Spectroscopic data for syn-3b: 1H
0.0000.
water or with a cryostat. Commercial aluminum oxide (Aldrich,
activity I, 150 mesh) was degassed under vacuum prior to use. The
latter was mixed under nitrogen with the appropriate amount of water
to reach the activity IV. All other reagents were obtained from the
usual commercial suppliers and used as received. IR stretching
frequencies were measured in solution and are referred to as ν (bond).
Nuclear magnetic resonance (NMR) spectra were routinely recorded
at 300.13 (1H), 121.50 (31P{1H}), or 75.47 MHz (13C{1H}) at 290 K
in CD2Cl2 solutions unless otherwise stated. Chemical shifts (δ) are
given in ppm, relative to internal tetramethylsilane (1H, 13C) or
external 85% aqueous H3PO4 (31P). Coupling constants (J) are given
NMR: δ 7.04 (d, JHP = 11, 1H, PCH), 5.38 (s, 5H, Cp), 4.99 (d, JHP
=
4, 3H, C6H3), 5.22, 5.16, 4.84, 4.78 (4 m, 4 × 1H, C5H4), 3.90 (s, 3H,
t
1
OMe), 1.17 (s, 27H, Bu). Spectroscopic data for anti-3b: H NMR: δ
6.97 (d, JHP = 11, 1H, PCH), 5.32 (s, 5H, Cp), 5.11, 4.22 (2 m, 2 ×
1H, C5H4), 4.90 (m, 2H, C5H4), 4.80 (d, JHP = 4, 3H, C6H3), 3.62 (s,
t
JHP = 1, 3H, OCH3), 1.19 (s, 27H, Bu).
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC(p-tol)}(η6-
HMes*)(CO)2] (3c). The procedure is analogous to that described for
3a, but using HCC(p-tol) (20 μL, 0.158 mmol) and a reaction time
of 3 h at 373 K to give a brown solution. The solvent was then
removed under vacuum, the residue was extracted with CH2Cl2−
petroleum ether (1:1), and the extracts were chromatographed at 288
K. Elution with dichloromethane/petroleum ether (1:2) gave a green
fraction yielding, after removal of solvents, compound 3c as a brown
powder (0.018 g, 58%). In solution, this complex exists as an
equilibrium mixture of syn and anti isomers, with their ratio being 5:6
1
in Hz. H and 13C NMR assignments were usually carried out by
combining the information from standard DEPT, HSQC, and NOESY
experiments as appropriate. Compounds 3a, 6a,b, and 9a,b were
reported in separated communications.8b,e The synthesis and
spectroscopic details of these compounds are reproduced here to
facilitate comparison with the other compounds reported in this full
paper.
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C-
(CO2Me)}(η6-HMes*)(CO)2] (3a). Neat dimethyl acetylenedicarbox-
ylate (DMAD) (9 μL, 0.073 mmol) was added to a solution, prepared
in a glass bulb equipped with a J. Young valve, of compound 1 (0.023
g, 0.035 mmol) in toluene (2 mL). After closing the valve, the mixture
was heated and stirred at 368 K for 2 h to give a brown solution. The
solvent was then removed under vacuum, and the residue was
chromatographed on an alumina column (activity IV) refrigerated with
water. Elution with dichloromethane gave a green fraction, yielding,
after removal of the solvent under vacuum, compound 3a as a green
microcrystalline solid (0.016 g, 57%). Unfortunately, no satisfactory
elemental analysis could be obtained for this product due to its rapid
decomposition upon manipulation in the air. In solution, this complex
1
in dichloromethane and 4:3 in toluene, as determined by H NMR
spectroscopy. Anal. Calcd for C39H47Mo2O2P: C, 60.78; H, 6.15.
Found: C, 60.45; H, 5.98. Spectroscopic data for syn-3c: 1H NMR
(C6D6): δ 7.59, 7.09 (AA′XX′, JHH +JHH′ = 8, 2 × 2H, C6H4), 7.19 (d,
JPH = 11, 1H, PCH), 5.13 (s, 5H, Cp), 4.89, 4.83, 4.57, 4.16 (4 m, 4 ×
1H, C5H4), 4.95 (d, JHP = 4, 3H, C6H3), 2.18 (s, 3H, Me), 1.14 (s,
27H, tBu). 13C{1H} NMR (100.63 MHz, C6D6): δ 259.2 (d, JCP = 30,
MoCO), 247.5 (d, JCP = 3, MoCO), 138.5 (d, JCP = 4, PCH), 129.0 (s,
m-C6H4), 126.7 (s, o-C6H4), 110.2 [s, C(C6H3)], 91.7 (s, Cp), 89.3 [s,
CH(C5H4)], 86.0 [d, JCP = 7, CH(C5H4)], 83.6 [s, CH(C5H4)], 80.1
[d, JCP = 15, CH(C5H4)], 71.2 [s, CH(C6H3)], 34.7 [s, C(tBu)], 31.4
[s, CH3(tBu)], 21.2 [s, CH3(p-tol)]. Other resonances of this isomer
could not be assigned unambiguously. Spectroscopic data for anti-3c:
2758
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Organometallics
Article
73.2 [s, CH(C6H3)], 52.7, 52.2 (2s, OMe), 35.6 [s, C(tBu)], [s,
CH3(tBu)].
1H NMR: δ 7.63, 7.12 (AA′XX′, JHH + JHH′ = 8, 2 × 2H, C6H4), 6.85
(d, JPH = 10, 1H, PCH), 5.19 (s, 5H, Cp), 5.17, 4.94, 4.64, 4.58 (4 m, 4
× 1H, C5H4), 4.57 (d, JHP = 4, 3H, C6H3), 2.19 (s, 3H, Me), 1.05 (s,
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC(CO2Me)C-
(O)}(η6-HMes*)(CO)2] (6b). The procedure is analogous to that
described for 6a, but using methyl propiolate (8 μL, 0.089 mmol) and
a similar workup. This led to compound 6b as a brown microcrystal-
line powder (0.032 g, 91%). In solution, this complex exists as an
equilibrium mixture of syn and anti isomers, with their ratio being 1:2
t
27H, Bu). 13C{1H} NMR (100.63 MHz, C6D6): δ 138.6 (s, PCH),
129.6 (s, m-C6H4), 126.1 (s, o-C6H4), 105.9 [s, C(C6H3)], 92.5 (s,
Cp), 89.6 [s, CH(C5H4)], 87.6 [d, JCP = 8, CH(C5H4)], 83.9 [s,
CH(C5H4)], 81.9 [d, JCP = 11, CH(C5H4)], 74.1 [s, CH(C6H3)], 34.0
[s, C(tBu)], 31.6 [s, CH3(tBu)], 21.1 [s, CH3(p-tol)]. Other
resonances of this isomer could not be assigned unambiguously.
Reaction of 2 with DMAD. Neat DMAD (8 μL, 0.065 mmol) was
added to a solution of compound 2 (0.026 g, 0.040 mmol) in toluene
(1 mL), and the mixture was stirred at room temperature for 20 min to
give an orange-brown solution containing a mixture of compounds
[Mo2Cp2{μ-κ1:κ1,η3-PHC(CO2Me)C(CO2Me)C(O)}(η6-HMes*)-
(CO)] (4) and [Mo2Cp2{μ-κ1:κ1,η1-PHC(CO2Me)C(CO2Me)}-
(η6-HMes*)(CO)2] (5). Then tetrahydrofuran (0.5 mL) was added to
the solution, and the mixture was further stirred for 1 h to yield an
orange-brown solution containing compound 5 as the major species.
The solvents were then removed under vacuum, the residue was
extracted with toluene−petroleum ether (2:1), and the extracts were
filtered using a canula. Removal of the solvents from the filtrate yielded
compound 5 as a brown microcrystalline solid (0.029 g, 92%). The
crystals used in the X-ray study of this complex were grown by slow
diffusion at 253 K of layers of petroleum ether and toluene into a
concentrated solution of the complex in dichloromethane. Anal. Calcd
for C36H47Mo2O6P (5): C, 54.14; H, 5.93. Found: C, 53.89; H, 5.79.
Spectroscopic data for compound 4: 1H NMR (C6D6): δ 5.08 (d, JHP = 1,
5H, Cp), 4.96 (d, JHP = 6, 3H, C6H3), 4.55 (d, JHP = 5, 5H, Cp), 4.05
(d, JHP = 317, 1H, PH), 3.49, 3.28 (2s, 2 × 3H, OMe), 1.16 (s, 27H,
1
in dichloromethane and 1:1 in benzene, as determined by H NMR
spectroscopy. Anal. Calcd for C35H43Mo2O5P: C, 54.84; H, 5.65.
1
Found: C, 54.92; H, 5.66. Spectroscopic data for syn-6b: H NMR: δ
7.53 (d, JHP = 8H, 1H, PCH), 5.25, 5.15, 4.80, 4.47 (4 m, 4 × 1H,
C5H4), 5.12 (s, 5H, Cp), 4.92 (d, JHP = 4, 3H, C6H3), 3.71 (s, 3H,
t
OMe), 1.13 (s, 27H, Bu). 13C{1H} NMR: δ 271.3 [d, JCP = 9,
MoC(O)], 248.5 (d, JCP = 20, MoCO), 239.6 (s, MoCO), 165.4 (s,
CO2Me), 160.3 (d, JCP = 5, PCHC), 112.5 [s, C(C6H3)], 91.6 (s,
Cp), 90.5 [d, JCP = 23, C(C5H4)], 88.6 [d, JCP = 5, CH(C5H4)], 88.5
[d, JCP = 8, CH(C5H4)], 83.9 [s, CH(C5H4)], 83.1 [d, JCP = 16,
CH(C5H4)], 72.0 [s, CH(C6H3)], 52.2 (s, OMe), 35.4 [s, C(tBu)],
31.2 [s, CH3(tBu)].13C NMR: δ 160.3 (dd, JCH = 166, JCP = 5,
1
PCH=C). Spectroscopic data for anti-6b: H NMR: δ 7.65 (d, JHP = 8,
1H, PCH), 5.40, 5.04, 5.01, 4.79 (4 m, 4 × 1H, C5H4), 5.33 (s, 5H,
Cp), 4.89 (d, JHP = 4, 3H, C6H3), 3.67 (s, 3H, OMe), 1.15 (s, 27H,
tBu). 13C{1H} NMR: δ 268.2 [d, JCP = 9, MoC(O)], 248.3 (d, JCP
=
27, MoCO), 239.9 (s, MoCO), 165.7 (s, CO2Me), 162.9 (s, PCH
C), 111.0 [s, C(C6H3)], 94.8 (s, Cp), 90.7 [d, JCP = 23, C(C5H4)],
90.5 [d, JCP = 5, CH(C5H4)], 85.4 [d, JCP = 8, CH(C5H4)], 84.6 [s,
CH(C5H4)], 81.3 [d, JCP = 16, CH(C5H4)], 73.1 [s, CH(C6H3)], 52.1
(s, OMe), 34.9 [s, C(tBu)], 31.3 [s, CH3(tBu)]. 13C NMR: δ 162.9 (d,
JCH = 166, PCHC). The resonances for the internal carbon atoms of
the alkyne in both isomers (PC=C resonances) could not be located in
the spectrum.
1
tBu). Spectroscopic data for compound 5: H NMR (C6D6): δ 5.14 (s,
5H, Cp), 4.54 (d, JHP = 6, 3H, C6H3), 4.52 (d, JHP = 5, 5H, Cp), 3.87
(d, JHP = 258, 1H, PH), 3.75, 3.44 (2s, 2 × 3H, OMe), 1.13 (s, 27H,
tBu). 13C{1H} NMR (100.61 MHz, toluene-d8, 188 K): δ 258.6 (d, JCP
= 25, MoCO), 249.1 (s, MoCO), 200.5 (d, JCP = 16, MoCC), 177.1,
176.8 (2s, CO2Me), 158.3 (d, JCP = 5, PCC), 105.2 [s, C(C6H3)],
92.3, 84.8 (2s, Cp), 74.8 [s, CH(C6H3)], 51.3, 50.9 (2s, OMe), 34.9 [s,
C(tBu)], 31.0 [s, CH3(tBu)].
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC(p-tol)C-
(O)}(η6-HMes*)(CO)2] (6c). The procedure is analogous to that
described for 6a, but using (p-tolyl)acetylene (20 μL, 0.158 mmol)
and a reaction time of 40 min. After removal of the solvent from the
reaction mixture, the residue was extracted with petroleum ether and
the extracts were chromatographed at 288 K. Elution with dichloro-
methane−petroleum ether (1:9) gave a green fraction, yielding, after
removal of the solvents, the known diphosphanediyl complex [Mo2{μ-
κ1,η5:κ1,η5-(C5H4)P−P(C5H4)}(η6-HMes*)2]12 (0.014 g, 69%). The
residue left after petroleum ether extraction was dissolved in
dichloromethane and chromatographed at 253 K. Elution with
dichloromethane gave a red and then a green band, these yielding
respectively the dimer [Mo2Cp2(CO)6] (0.008 g, 72%) and compound
6c as a green microcrystalline solid (0.007 g, 18%). In solution, the
latter complex exists as an equilibrium mixture of syn and anti isomers,
with their ratio being 1:2 in dichloromethane or benzene, as
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C-
(CO2Me)C(O)}(η6-HMes*)(CO)2] (6a). A toluene solution (4 mL)
of compound 1 (0.030 g, 0.046 mmol) and DMAD (8 μL, 0.065
mmol) was placed in a bulb equipped with a Young’s valve. The bulb
was cooled at 77 K, degassed under vacuum, and then refilled with
CO. The solution was allowed to reach room temperature, the valve
was then closed, and the mixture was further stirred at 313 K for 15
min to give a brown solution. The solvent was then removed under
vacuum, and the residue was chromatographed at 253 K. Elution with
dichloromethane gave a gray fraction yielding, after removal of the
solvent under vacuum, compound 6a as a brown microcrystalline solid
(0.035 g, 92%). In solution, this complex exists as an equilibrium
mixture of syn and anti isomers, with their ratio being 1:2 in
dichloromethane and 1:4 in benzene, as determined by 1H NMR
spectroscopy. Anal. Calcd for C37H45O7Mo2P: C, 53.89; H, 5.50.
1
determined by H NMR spectroscopy. Spectroscopic data for syn-6c:
1H NMR (C6D6): δ 7.53, 7.09 (2 m, AA′BB′, JHH = 8, 2 × 2H, C6H4),
7.41 (d, JHP = 10, 1H, PCH), 4.96 (s, 5H, Cp), 4.80, 4.77, 4.73, 4.43 (4
m, 4 × 1H, C5H4), 4.78 (d, JHP = 3, 3H, C6H3), 2.13 (s, 3H, C6H4Me),
t
1
1.04 (s, 27H, Bu). Spectroscopic data for anti-6c: H NMR (C6D6): δ
7.55, 7.02 (2 m, AA′BB′, JHH = 8, 4H, C6H4), 7.07 (d, JHP = 10, 1H,
PCH), 5.31 (s, 5H, Cp), 4.80, 4.75, 4.70, 4.47 (4 m, 4 × CH, C5H4),
4.55 (d, JHP = 4, 3H, C6H3), 2.08 (s, 3H, p-C6H4Me), 0.93 (s, 27H,
tBu).
1
Found: C, 53.94; H, 5.57. Spectroscopic data for syn-6a: H NMR: δ
5.34 (s, 5H, Cp), 5.31, 5.07, 4.87, 4.52 (4 m, 4 × 1H, C5H4), 4.88 (d,
JHP = 3, 3H, C6H3), 3.72, 3.64 (2s, 2 × 3H, OMe), 1.18 (s, 27H, tBu).
13C{1H} NMR: δ 268.0 [d, JCP = 11, MoC(O)], 247.4 (d, JCP = 30,
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C-
(CO2Me)C(O)}(η6-HMes*)(CO)(PMe3)] (7). Neat DMAD (8 μL,
0.065 mmol) and then PMe3 (6 μL, 0.060 mmol) were added to a
solution of compound 1 (0.030 g, 0.046 mmol) in toluene (4 mL),
whereupon the mixture turned into a greenish-brown solution. After
further stirring for 10 min, the solvent was removed under vacuum and
the residue was chromatographed at 258 K. Elution with dichloro-
methane gave a green fraction yielding, after removal of the solvent,
compound 7 as a green microcrystalline solid (0.026 g, 66%). Anal.
Calcd for C39H54Mo2O6P2: C, 53.68; H, 6.24. Found: C, 53.50; H,
6.08. 1H NMR (C6D6): δ 5.11 (s, 5H, Cp), 5.01, 4.93, 4.80, 4.63 (4 m,
4 × 1H, C5H4), 4.73 (s, br, 3H, C6H3), 3.39, 3.35 (2s, 2 × 3H, OMe),
MoCO), 239.8 (s, MoCO), 168.1, 167.0 (2s, CO2Me), 164.2 (d, JCP
=
19, PCC), 157.5 (s, PCC), 114.2 [s, C(C6H3)], 95.6 (s, Cp), 90.9
[d, JCP = 4, C(C5H4)], 89.0 [d, JCP = 4, CH(C5H4)], 86.6 [d, JCP = 10,
CH(C5H4)], 85.3 [s, CH(C5H4)], 82.1 [d, JCP = 18, CH(C5H4)], 73.0
[s, CH(C6H3)], 52.9, 52.5 (2s, OMe), 35.2 [s, C(tBu)], 31.3 [s,
1
CH3(tBu)]. Spectroscopic data for anti-6a: H NMR: δ 5.15 (s, 5H,
Cp), 5.18, 5.14, 5.07, 4.27 (4 m, 4 × 1H, C5H4), 4.95 (d, JHP = 3, 3H,
t
C6H3), 3.74, 3.68 (2s, 2 × 3H, OMe), 1.14 (s, 27H, Bu). 13C{1H}
NMR: δ 263.4 [d, JCP = 11, MoC(O)], 249.6 (d, JCP = 24, MoCO),
239.6 (s, MoCO), 168.7 (s, 2CO2Me), 165.1 (d, JCP = 20, PCC),
157.8 (s, PCC), 114.0 [s, C(C6H3)], 92.1 (s, Cp), 91.2 [d, JCP = 20,
C(C5H4)], 88.9 [d, JCP = 10, CH(C5H4)], 87.9 [d, JCP = 4,
CH(C5H4)], 83.9 [d, JCP = 18, CH(C5H4)], 83.6 [s, CH(C5H4)],
t
1.43 (d, JHP = 9, 9H, PMe), 1.10 (s, 27H, Bu).
2759
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Organometallics
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Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C-
(CO2Me)C(O)}(η6-HMes*)(CO){P(OMe)3}] (8). The procedure is
analogous to that described for 7, but using P(OMe)3 (6 μL, 0.051
mmol) and a reaction time of 20 min. After similar workup, compound
8 was isolated as a green microcrystalline solid (0.030 g, 70%). Anal.
Calcd for C39H54Mo2O9P2: C, 50.88; H, 5.91. Found: C, 50.73; H,
5.81. 1H NMR: δ 5.25, 5.05, 4.86, 4.59 (4 m, 4 × 1H, C5H4), 5.16 (s,
5H, Cp), 4.83 (s, br, 3H, C6H3), 3.69, 3.60 (2s, 2 × 3H, OMe), 3.48
(d, JHP = 11, 9H, POMe), 1.17 (s, 27H, tBu). 1H NMR (C6D6): δ 5.37
(s, 5H, Cp), 5.02, 4.87, 4.79, 4.58 (4 m, 4 × 1H, C5H4), 4.71 (s, br,
3H, C6H3), 3.66 (d, JHP = 11, 9H, POMe), 3.43, 3.42 (2s, 2 × 3H,
OCH3), 1.06 (s, 27H, tBu). 13C{1H} NMR: δ 278.4 [dd, JCP = 38, 11,
MoC(O)], 256.7 (dd, JCP = 42, JCP = 28, MoCO), 169.5, 169.3 (2s, 2
× CO2Me), 165.6 (d, JCP = 26, PCC), 159.2 (s, PCC), 112.2 [s,
br, C(C6H3)], 94.2 (s, Cp), 90.2 [d, JCP = 4, CH(C5H4)], 89.5 [d, JCP
= 12, C(C5H4)], 86.7 [d, JCP = 9, CH(C5H4)], 84.8 [s, CH(C5H4)],
82.7 [d, JCP = 18, CH(C5H4)], 72.0 [s, br, CH(C6H3)], 52.6, 51.8 (2s,
2 × OMe), 52.5 (d, JCP = 6, POMe), 35.1 [s, C(tBu)], 31.3 [s,
CH3(tBu)].
[d, JCP = 15, CH(C5H4)], 71.8 [s, CH(C6H3)], 51.5 (s, OMe), 35.3 [s,
C(tBu)], 31.3 [s, CH3(tBu)], 19.4, 18.9 [2s, CH3(Xyl)]. Spectroscopic
data for anti-9b: H NMR (400.13 MHz): δ 6.90, 6.84 [2d, JHH = 7,
1
2H, m-H(Xyl)], 6.78 [d, JHP = 7, 1H, PCH], 6.71 [t, JHH = 7, 1H, p-
H(Xyl)], 5.34, 5.01, 4.94, 4.78 (4 m, 4 × 1H, C5H4), 5.28 (s, 5H, Cp),
4.89 (d, JHP = 3, 3H, C6H3), 3.05 (s, 3H, OMe), 2.19, 1.94 (2s, 2 ×
3H, Me), 1.20 (s, 27H, tBu). 1H NMR (400.13 MHz, C6D6): δ 7.12−
7.05 [m, 2H, m-H(Xyl)], 6.90 [t, JHH = 7, 1H, p-H(Xyl)], 6.79 (d, JHP
= 7, PCH), 5.23 (s, 5H, Cp), 5.02, 4.70, 4.43, 4.36 (4 m, 4 × 1H,
C5H4), 4.58 (d, JHP = 4, 3H, C6H3), 3.07 (s, 3H, OMe), 2.72, 2.18 (2s,
t
2 × 3H, Me), 0.98 (s, 27H, Bu). 13C{1H} NMR (100.61 MHz): δ
251.7 (d, JCP = 23, MoCO), 242.8 (s, MoCO), 208.1 [s, br,
MoC(NXyl)], 168.6 (d, JCP = 25, PCC), 156.8 [s, br, C1(Xyl)],
154.6 (s, br, PCH), 128.6, 123.9 [2s, br, C2,6(Xyl)], 127.6, 127.3 [2s,
br, C3,5(Xyl)], 121.7 [s, C4(Xyl)], 110.0 [s, C(C6H3)], 93.9 (s, Cp),
91.9 [d, JCP = 8, C(C5H4)], 90.1 [d, JCP = 5, CH(C5H4)], 85.2 [d, JCP
= 9, CH(C5H4)], 84.4 [s, CH(C5H4)], 80.8 [d, JCP = 14, CH(C5H4)],
72.9 [s, CH(C6H3)], 51.3 (s, OMe), 34.8 [s, C(tBu)], 31.4 [s,
CH3(tBu)], 20.4, 19.0 [2s, CH3(Xyl)].
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C-
(CO2Me)C(NXyl)}(η6-HMes*)(CO)2] (9a). Xylylisocyanide (185 μL
of a 0.25 M solution in petroleum ether, 0.046 mmol) was added to a
solution of compound 1 (0.030 g, 0.046 mmol) and DMAD (8 μL,
0.065 mmol) in toluene (2 mL), whereupon the mixture changed
instantaneously from red to brown. The solvent was then removed
under vacuum, and the residue was chromatographed at 253 K.
Elution with dichloromethane gave a gray-purple fraction, yielding,
after removal of the solvent under vacuum, compound 9a as a brown
microcrystalline solid (0.038 g, 89%). Anal. Calcd for
C45H54O6Mo2NP: C, 58.26; H, 5.87; N, 1.51. Found: C, 58.16; H,
5.82; N, 1.34. 1H NMR: δ 6.93, 6.84 [2d, JHH = 7, 2 × 1H, m-H(Xyl)],
6.74 [t, JHH = 7, 1H, p-H(Xyl)], 5.20 (s, 5H, Cp), 5.16, 5.09, 4.73, 4.28
(4 m, 4 × 1H, C5H4), 4.97 (s, br, 3H, C6H3), 3.65 (s, 3H, OMe), 3.30
(s, br, 3H, OMe), 2.13, 1.88 (2s, 2 × 3H, Me), 1.18 (s, 27H, tBu). 1H
NMR (C6D6): δ 7.12−7.05 [m, 2H, m-H(Xyl)], 6.93 [t, JHH = 7, 1H,
p-H(Xyl)], 5.00 (s, 5H, Cp), 4.98 (s, br, 3H, C6H3), 4.89, 4.77, 4.74,
4.25 (4 m, 4 × 1H, C5H4), 3.77 (s, 3H, OMe), 3.20 (s, br, 3H, OMe),
2.36, 2.33 (2s, 2 × 3H, Me), 1.17 (s, 27H, tBu). 13C{1H} NMR (75.47
MHz): δ 253.5 (d, JCP = 26, MoCO), 240.9 (s, MoCO), 206.6 [s, br,
MoC(NXyl)], 168.9 (s, 2CO2Me), 168.4 (d, JCP = 22, PCC), 151.8
(s, PCC), 150.3 [s, br, C1(Xyl)], 127.7, 127.4 [2s, C3,5(Xyl)], 125.7,
125.0 [2s, br, C2,6(Xyl)], 122.1 [s, C4(Xyl)], 113.4 [s, br, C(C6H3)],
92.5 (s, Cp), 91.6 [d, JCP = 20, C(C5H4)], 88.4 [d, JCP = 4,
CH(C5H4)], 88.3, 83.5 [2s, CH(C5H4)], 82.7 [d, JCP = 17,
CH(C5H4)], 72.9 [s, CH(C6H3)], 52.8, 51.8 (2s, OMe), 35.5 [s,
C(tBu)], 31.3 [s, CH3(tBu)], 19.7, 18.6 [2s, CH3(Xyl)].
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC{C(O)Me}-
C(NXyl)}(η6-HMes*)(CO)2] (9d). The preparative and purification
procedures are identical to those described for 9a, but using 3-butyn-2-
one instead (8 μL, 0.110 mmol). Elution with dichloromethane gave a
gray-brown band yielding compound 9d as a greenish-brown
microcrystalline solid (0.037 g, 94%). This compound was shown
(by NMR) to exist in solution as an equilibrium mixture of syn and
anti isomers, with the syn/anti ratio being 9:4 in C6D6 or CD2Cl2.
Anal. Calcd for C43H52O3Mo2NP: C, 60.49; H, 6.14; N, 1.64. Found:
1
C, 60.37; H, 6.01; N, 1.49. Spectroscopic data for syn-9d: H NMR
(400.13 MHz): δ 6.95, 6.88 [2d, JHH = 7, 2H, m-H(Xyl)], 6.79 [t, JHH
= 7, 1H, p-H(Xyl)], 6.50 (d, JHP = 8, 1H, PCH), 5.09 (s, 5H, Cp),
5.22, 5.15, 4.93, 4.45, (4 m, 4 × 1H, C5H4), 4.88 (d, JHP = 3, 3H,
C6H3), 2.09, 2.00 (2s, 2 × 3H, Me), 2.06 [s, br, 3H, C(O)Me], 1.16 (s,
t
1
27H, Bu). H NMR (300.13 MHz, C6D6): δ 7.18, 7.11 [2d, JHH = 7,
2H, m-H(Xyl)], 7.02 [t, JHH = 7, 1H, p-H(Xyl)], 6.59 (d, JHP = 8, 1H,
PCH), 4.86 (s, 5H, Cp), 4.77 (d, JHP = 4, 3H, C6H3), 4.75−4.66 (m, 3
× 1H, C5H4), 4.37 (m, 1H, C5H4), 2.41, 2.21 (2s, 2 × 3H, Me), 2.25
[s, 3H, C(O)Me], 1.06 (s, 27H, tBu). 13C{1H} NMR: δ 252.7 (d, JCP
=
30, MoCO), 241.2 (s, MoCO), 214.4 [s, C(O)Me], 203.4 [s, br,
MoC(NXyl)], 170.9 (d, JCP = 20, PCC), 152.5 [s, C1(Xyl)], 144.5
(s, br, PCH), 127.9, 127.5 [2s, C3,5(Xyl)], 126.0, 124.6 [2s, C2,6(Xyl)],
122.1 [s, C4(Xyl)], 111.8 [s, C(C6H3)], 91.9 (s, Cp), 92.6 [d, JCP = 18,
C(C5H4)], 89.0 [d, JCP = 8, CH(C5H4)], 88.3 [d, JCP = 4, CH(C5H4)],
83.6 [s, CH(C5H4)], 82.6 [d, JCP = 15, CH(C5H4)], 71.6 [s,
CH(C6H3)], 35.3 [s, C(tBu)], 31.3 [s, CH3(tBu)], 29.8 [s, br, C(O)
Me], 20.1, 18.8 [2s, Me(Xyl)]. Spectroscopic data for anti-9d: 1H NMR
(400.13 MHz): δ 6.95, 6.88 [2d, JHH = 7, 2H, m-H(Xyl)], 6.81 [t, JHH
= 7, 1H, p-H(Xyl)], 6.59 (d, JHP = 8, 1H, PCH), 5.10 (s, 5H, Cp),
5.07, 5.02, 4.99, 4.70, (4 m, 4 × 1H, C5H4), 4.86 (d, JHP = 4, 3H,
C6H3), 2.25, 1.96 (2s, 2 × 3H, Me), 2.02 [s, br, 3H, C(O)Me], 1.20 (s,
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η1-(C5H4)PCHC(CO2Me)C-
(NXyl)}(η6-HMes*)(CO)2] (9b). The preparative and purification
procedures are identical to those described for 9a, but using methyl
propiolate instead (8 μL, 0.089 mmol). Elution with dichloromethane
gave a gray-brown band yielding compound 9b as a greenish-brown
microcrystalline solid (0.037 g, 92%). This compound was shown (by
NMR) to exist in solution as an equilibrium mixture of syn and anti
isomers, with the syn/anti ratio being 7:2 in C6D6 and 7:3 in CD2Cl2.
Anal. Calcd for C43H52O4Mo2NP: C, 59.38; H, 6.03; N, 1.61. Found:
t
1
27H, Bu). H NMR (400.13 MHz, C6D6): δ 7.18, 7.11 [2d, JHH = 7,
2H, m-H(Xyl)], 7.00 [t, JHH = 7, 1H, p-H(Xyl)], 6.68 (d, JHP = 8, 1H,
PCH), 5.03 (s, 5H, Cp), 4.75−4.66 (m, 3 × 1H, C5H4), 4.56 (d, JHP
4, 3H, C6H3), 4.45 (m, 1H, C5H4), 2.67, 2.14 (2s, 2 × 3H, Me), 2.25
[s, 3H, C(O)Me], 0.97 (s, 27H, tBu). 13C{1H} NMR: δ 253.8 (d, JCP
=
=
1
C, 59.24; H, 5.95; N, 1.37. Spectroscopic data for syn-9b: H NMR
21, MoCO), 241.6 (s, MoCO), 212.9 [s, C(O)Me], 207.1 [s, br,
MoC(NXyl)], 171.3 (d, JCP = 20, PCC), 152.9 [s, C1(Xyl)], 148.3
(s, br, PCH), 128.1, 127.7 [2s, C3,5(Xyl)], 125.8, 125.2 [2s, C2,6(Xyl)],
122.3 [s, C4(Xyl)], 110.0 [s, C(C6H3)], 92.6 (s, Cp), 90.0 [d, JCP = 4,
CH(C5H4)], 85.7 [d, JCP = 8, CH(C5H4)], 84.3 [s, CH(C5H4)], 80.7
[d, JCP = 15, CH(C5H4)], 72.7 [s, CH(C6H3)], 34.7 [s, C(tBu)], 31.5
[s, CH3(tBu)], 30.3 [s, br, C(O)Me], 20.5, 19.2 [2s, Me(Xyl)]. The
resonance for the C(C5H4) atom could not be identified in the
spectrum of the mixture of isomers.
(400.13 MHz): δ 6.90, 6.84 [2d, JHH = 7, 2H, m-H(Xyl)], 6.72 (d, JHP
= 7, 1H, PCH), 6.71 [t, JHH = 7, 1H, p-H(Xyl)], 5.22, 5.13, 4.89, 4.43
(4 m, 4 × 1H, C5H4), 5.21 (s, 5H, Cp), 4.89 (d, JHP = 3, 3H, C6H3),
3.17 (s, 3H, OMe), 2.13, 1.93 (2s, 2 × 3H, Me), 1.15 (s, 27H, tBu). 1H
NMR (400.13 MHz, C6D6): δ 7.12−7.05 [m, 2H, m-H(Xyl)], 6.90 [t,
JHH = 7, 1H, p-H(Xyl)], 6.86 [d, JHP = 7, PCH], 5.04 (s, 5H, Cp), 4.80
(d, JHP = 3, 3H, C6H3), 4.70 (m, 2H, C5H4), 4.61, 4.35 (2 m, 2 × 1H,
C5H4), 3.16 (s, 3H, OMe), 2.41, 2.37 (2s, 2 × 3H, Me), 1.07 (s, 27H,
tBu). 13C{1H} NMR (100.61 MHz): δ 253.5 (d, JCP = 28, MoCO),
241.1 (s, MoCO), 206.4 [s, br, MoC(NXyl)], 169.8 (d, JCP = 22,
PC=C), 158.4 [s, br, C1(Xyl)], 151.7 (s, br, PCH), 127.7, 127.4 [2s,
C3,5(Xyl)], 126.1, 125.1 [2s, br, C2,6(Xyl)], 121.7 [s, C4(Xyl)], 111.9
[s, br, C(C6H3)], 92.8 [d, JCP = 16, C(C5H4)], 92.1 (s, Cp), 88.5 [s,
CH(C5H4)], 88.4 [d, JCP = 4, CH(C5H4)], 83.4 [s, CH(C5H4)], 82.4
Preparation of [Mo2Cp{μ-κ1,η5:κ1,η3-(C5H4)PC(CO2Me)C-
(CO2Me)C(O)}(η6-HMes*)(CO)] (10). Method A. A solution of
compound 3a (0.032 g, 0.040 mmol) in toluene (5 mL) was irradiated
with visible−UV light at 288 K for 1 h to give a green solution. The
solvent was then removed under vacuum, and the residue was
chromatographed at 253 K. Elution with dichloromethane gave a green
2760
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Organometallics
Article
fraction yielding, after removal of the solvent, compound 10 as a green
powder (0.024 g, 75%). This complex progressively transforms back
into 3a at room temperature. Elution with dichloromethane−
tetrahydrofuran (9:1) gave a second green fraction, yielding
analogously small and variable amounts (<0.005 g) of the chloro
complex [Mo2CpCl{μ-κ1,η5:κ1,η2-(C5H4)PC(CO2Me)CH-
(CO2Me)}(η6-HMes*)(CO)] (11) as a green solid. The crystals
used in the X-ray study of this complex were grown by slow diffusion
at 273 K of a layer of petroleum ether into a concentrated solution of
the complex in dichloromethane−tetrahydrofuran (5:1).
using a riding model. A molecule of tetrahydrofuran was present in the
unit cell. Crystallographic data and structure refinement details are
collected in Table 6.
Computational Details. Computations were carried out using the
GAUSSIAN03 package,36 in which the hybrid method B3LYP was
applied with the Becke three-parameter exchange functional37 and the
Lee−Yang−Parr correlation functional.38 Effective core potentials and
their associated double-ζ LANL2DZ basis set were used for the metal
atoms.39 The light elements (P, O, C, and H) were described with the
6-31G* basis.40 Geometry optimization was performed under no
symmetry restrictions, using initial coordinates derived from the X-ray
data of compound 1, and frequency analyses were performed to ensure
that a minimum structure with no imaginary frequencies was achieved.
For interpretation purposes, Mulliken charges were computed as
usual,41 and natural population analysis charges were derived from the
natural bond order analysis of the data.42 Molecular orbitals and
vibrational modes were visualized using the Molekel program.43 The
topological analysis of ρ was carried out with the Xaim routine.44
Method B. The procedure is analogous to that described in Method
A, but using compound 6a as starting material (0.033 g, 0.040 mmol)
and a reaction time of 1.5 h. After similar workup of the resulting
mixture, compounds 10 (0.022 g, 70%) and 11 (<0.005 g) were
isolated analogously. Spectroscopic data for 10: 1H NMR (400.54 MHz,
233 K): δ 5.52, 5.32, 5.15, 4.26 (4 m, 4 × 1H, C5H4), 5.12 (s, 5H, Cp),
5.06, (s, br, 3H, C6H3), 3.56, 3.47 (2s, 2 × 3H, OMe), 1.21 (s, 27H,
tBu). 13C{1H} NMR (100.61 MHz, 233 K): δ 254.0 [s, MoC(O)],
237.0 (d, JCP = 6, MoCO), 176.3, 175.7 (2s, CO2Me), 107.9 [s,
C(C6H3)], 93.6 (s, Cp), 88.3 [s, CH(C5H4)], 87.9 [d, JCP = 8,
CH(C5H4)], 86.3 [s, CH(C5H4)], 82.7 [d, JCP = 23, C(C5H4)], 79.9
[d, JCP = 18, CH(C5H4)], 78.0 [br, CH(C6H3)], 51.9, 51.6 (2s, OMe),
34.7 [s, C(tBu)], 31.8 [s, CH3(tBu)]; the resonances of the other C
atoms of the MoPC3 ring could not be identified in the spectrum.
Spectroscopic data for 11: 1H NMR (C6D6): δ 5.75, 4.77, 4.73, 4.14 (4
m, 4 × 1H, C5H4), 4.99 (d, JHP = 3, 5H, Cp), 4.91 (d, JHP = 5, 3H,
C6H3), 4.84 (d, JHP = 31, 1H, CH), 3.63, 3.30 (2s, 2 × 3H, OMe), 1.06
ASSOCIATED CONTENT
* Supporting Information
■
S
A pdf file containing tables of data from the DFT calculations
of intermediate A, and a CIF file giving the crystallographic data
for the structural analysis of compound 11. This material is
available free of charge via the Internet at http://pubs.acs.org.
t
AUTHOR INFORMATION
Corresponding Author
*E-mail: garciame@uniovi.es (M.E.G.); mara@uniovi.es
(M.A.R.).
(s, 27H, Bu).
■
Photolysis of Compound 9a. A solution of compound 9a (0.037
g, 0.040 mmol) in toluene (5 mL) was irradiated with visible−UV light
at 288 K for 1.5 h. Tetrahydrofuran (1 mL) was then added to the
resulting solution, and the mixture was further stirred at room
temperature for 1 h to give a brown solution. The solvent was then
removed under vacuum, and the residue was chromatographed at 253
K. Elution with dichloromethane−petroleum ether (9:1) gave a brown
fraction, yielding, after removal of the solvents, compound [Mo2Cp{μ-
κ1,η5:κ1,η1-(C5H4)PC(CO2Me)C(CO2Me)}(η6-HMes*)(CNXyl)-
(CO)] (13) as a brown microcrystalline powder (0.026 g, 72%). This
compound was shown (by NMR) to exist in solution as an equilibrium
mixture of syn and anti isomers, with the syn/anti ratio being 5:1 in
C6D6. If the addition of tetrahydrofuran and room temperature stirring
steps are suppressed, then a mixture of compound 13 and its precursor
[Mo2Cp{μ-κ1,η5:κ1,η3-(C5H4)PC(CO2Me)C(CO2Me)C(NXyl)}-
(η6-HMes*)(CO)] (12) is obtained, the latter being isolated after
chromatographic separation (elution with dichloromethane−tetrahy-
drofuran (4:1) at 253 K) as a greenish-brown powder (ca. 0.015 g,
ACKNOWLEDGMENTS
We thank the DGI of Spain (Project CTQ2009-09444), the
■
́
Consejeria de Educacion
́
of Asturias (Project PB09-027 and
grant to J.S.), the Universidad de Oviedo (grant to I.A.), and
the COST action CM0802 “PhoSciNet” for supporting this
work.
DEDICATION
■
This work is dedicated to Prof. F. G. A. Stone in recognition of
his outstanding contributions to modern inorganic chemistry,
for his personal kindness, and for the good time we all had at
Bristol in the eighties.
1
40%). Spectroscopic data for 12: H NMR (400.13 MHz, CD2Cl2, 233
K): δ 7.07 [d, JHH = 7, 1H, m-H(Xyl)], 6.97 [d, JHH = 7, 1H, m-
H(Xyl)], 6.91 [t, JHH = 7, 1H, p-H(Xyl)], 5.46 (m, 1H, C5H4), 5.18−
5.07 (m, 5H, C6H3 + C5H4), 4.85 (s, 5H, Cp), 4.25 (m, 1H, C5H4),
3.61, 3.51 (2s, 2 × 3H, OMe), 2.37, 2.01 (2s, 2 × 3H, Me), 1.23 (s,
REFERENCES
■
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t
1
27H, Bu). Spectroscopic data for syn-13: H NMR (C6D6): δ 6.90−
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Cp), 5.02 (d, JHP = 4, 4H, C6H3 + C5H4), 3.49, 3.34 (2s, 2 × 3H,
OMe), 2.46 (s, 6H, Me), 1.20 (s, 27H, tBu). Spectroscopic data for anti-
13: 1H NMR (C6D6): δ 6.89−6.78 (m, 3H, Xyl), 6.56, 4.79, 4.49, 4.13
(4 m, 4 × 1H, C5H4), 5.43 (s, 5H, Cp), 4.58 (d, JHP = 5, 3H, C6H3),
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t
3.74, 3.32 (2s, 2 × 3H, OMe), 2.36 (s, 6H, Me), 1.05 (s, 27H, Bu).
X-ray Structure Determination of Compound 11. The X-ray
intensity data were collected on a Kappa-Appex-II Bruker diffrac-
tometer using graphite-monochromated Mo Kα radiation at 100 K.
The software APEX31 was used for collecting frames with the ω/ϕ
scan measurement method. The Bruker SAINT software was used for
the data reduction,32 and a multiscan absorption correction was
applied with SADABS.33 Using the program suite WinGX,34 the
structure was solved by Patterson interpretation and phase expansion
using SHELXL9735 and refined with full-matrix least-squares on F2
using SHELXL97. All the positional parameters and the anisotropic
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́
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2761
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