Reactivity of a dichlorophosphido complex. Nucleophilic substitution reactions at metal coordinated phosphorus

Article abstract of DOI:10.1016/j.jorganchem.2014.02.025

Reaction of the dichlorophosphido complex [Cp*Mo(CO) ₃(PCl₂)] (1) with AlCl₃ leads to the bimetallic bridging P₂Cl₃ complex [{Cp*Mo(CO) ₃}₂(μ-P₂Cl₃)][AlCl

Full text of DOI:10.1016/j.jorganchem.2014.02.025

Journal of Organometallic Chemistry 761 (2014) 84e92
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Journal of Organometallic Chemistry
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Reactivity of a dichlorophosphido complex. Nucleophilic substitution
reactions at metal coordinated phosphorus
*
Rakesh A. Rajagopalan, Arumugam Jayaraman, Brian T. Sterenberg
Department of Chemistry and Biochemistry, University of Regina, 3737 Wascana Parkway, Regina, Saskatchewan S4S 0A2, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of the dichlorophosphido complex [Cp*Mo(CO)3(PCl2)] (1) with AlCl3 leads to the bimetallic
bridging P2Cl3 complex [{Cp*Mo(CO)3}2(m-P2Cl3)][AlCl4] (2), which is formed via a Lewis-acid assisted
nucleophilic substitution reaction, and not via a chlorophosphinidene intermediate. A similar reaction
with external nucleophile PPh3 leads to [Cp*Mo(CO)3(P(Cl)PPh3)][AlCl4] (3), which can be viewed as a
phosphine coordinated chlorophosphinidene complex. Addition of two equivalents each of PPh3 and
Received 30 January 2014
Received in revised form
18 February 2014
Accepted 26 February 2014
AlCl3 leads
a double chloride displacement, and formation of the known triphosphenium salt
Keywords:
Phosphinidene
Alkoxyphosphinidene
Nucleophilic substitution
Metal-mediated synthesis
[Ph3PPPPh3][AlCl4]. In this reaction the dichlorophosphido complex effectively act as a source of Pþ.
Reaction of 1 with alkoxides leads to alkoxyphosphido complexes [Cp*Mo(CO)3{P(OR)Cl}] (R ¼ p-t-butyl
phenoxy, menthoxy). These complexes serve as precursors to transient alkoxy phosphinidenes
[Cp*Mo(CO)3{POR}]þ, which can be trapped with alkynes. A computational study on the chloro, alkoxy,
and related amino and alkyl phosphinidenes shows that chloro and alkoxy phosphinidenes have minimal
p
-donation to P from Cl or OR, in contrast to stable aminophosphinidenes, which have significant N to P
p
-donation.
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
simple route to PeCl phosphinidenes, because they can directly
provide products, such as P-heterocycles and CeH activation
Chloride abstraction is now a well established route to cationic
terminal phosphinidene complexes, but phosphinidene complexes
formed via this route are thus far limited to stable amino-
phosphinidenes [1e3] and a transient alkyl phosphinidene [4]. In
contrast, transient neutral terminal phosphinidene complexes have
been described with a much wider variety of substituents on
phosphorus, including alkyl and aryl [5], amino [6], alkoxy [7],
chloro [8], and fluoro [9] substituents. Pikies has also made exten-
sive studies of phosphanylphosphinidenes, however, these ligands
most frequently bind in a side-on fashion, and are classified as
nucleophilic [10]. The cationic electrophilic phosphinidene com-
plexes show similar reactivity to transient neutral electrophilic
phosphinidene [4,11], with some exceptions [12]. However, they
have the advantages of shorter synthetic routes and can be gener-
ated at lower temperatures. We were interested in expanding the
range of possible P substituents. Of particular interest to us is a
products, containing a PeCl bond ready for further substitution. This
led us to explore the chemistry of dichlorophosphido complexes,
which are potential precursors to cationic chloroephosphinidene
complexes. Terminal dichlorophosphido complexes are relatively
rare [13e15], however the reactivity of the known complexes has
been well explored, and typical reactions include oxidation of the
lone pair, coordination to Lewis acids, and reductive coupling [16].
Iron PCl2 complexes have also been used to form phospha-alkenes
via nucleophilic substitution-dehydrohalogenation sequences [15].
As far as we know, direct halide abstraction as a route to chlor-
ophosphinidene complexes has not been attempted, although a
neutral transient chlorophosphinidene has been prepared by a
different route [8]. Of known PCl2 complexes, we were drawn to
[Cp*Mo(CO)3(PCl2)], reported by Malisch [13], because the synthesis
is straightforward, and because it is analogous to the well studied
phosphinidene precursor [Cp*Mo(CO)3{P(Cl)N-i-Pr2}]. Here we
describe the reaction chemistry of this complex with respect to
chloride abstraction and substitution, and its utility as a precursor to
phosphinidene complexes.
* Corresponding author. Tel.: þ1 306 585 4106.
E-mail address: brian.sterenberg@uregina.ca (B.T. Sterenberg).
http://dx.doi.org/10.1016/j.jorganchem.2014.02.025
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
85
Scheme 3.
Scheme 1.
dilution. This suggests that 2 does not form via a phosphinidene
intermediate, but by another mechanism. We suggest that 2 forms
via a Lewis acid assisted nucleophilic substitution mechanism
(Scheme 2).
Results
Compound synthesis and characterization
In order to provide support for this mechanism, the reaction was
carried out in the presence of an external nucleophile. Abstraction
of chloride from 1 in the presence of one equivalent of triphenyl-
phosphine leads to the triphenylphosphine coordinated chlor-
ophosphinidene complex [Cp*Mo(CO)3{P(Cl)(PPh3)}][X] (3)
(Scheme 3). Note that PPh3 does not react with 1 in the absence of a
chloride abstractor. The 31P NMR spectrum of 3 shows two doublets
The dichlorophosphido complex [Cp*Mo(CO)3(PCl2)] (1) was
synthesized from Cp*Mo(CO)3ꢀ and PCl3 using a modification of the
published procedure [13]. The IR spectrum of 1 shows carbonyl
stretching bands at 2018, 1951 and 1931 cmꢀ1 and 31P NMR spec-
trum shows a singlet at
d 408, matching reported values.
Abstraction of chloride from 1 was attempted using AlCl3, AgBF4
and NaBPh4. All reagents led to the same metal complex 2 as the
sole phosphorus containing product, with only the counterions
at
d 179 and d 37.9, both of which show a coupling constant of
454 Hz. The large coupling constant indicates a direct PeP bond.
The IR spectrum of 3 shows three carbonyl stretches at 2019, 1972
and 1934 cmꢀ1, which indicate that the molybdenum center has
retained three carbonyl ligands. Compound 3 has been structurally
characterized, and an ORTEP diagram of the cation is shown in
Fig. 1. The structure of the cation consists of a four legged piano
stool, with three legs occupied by carbonyls and the fourth by the
P(Cl)(PPh3) unit. The metal bound P is trigonal pyramidal. The PPh3
is coordinated to the metal bound P, and is directed away from the
Cp* ring, while the chloro group is directed such that the PeCl bond
is nearly parallel to the Cp* ring. In this position, the Cl atom lies
directly between the bulky Cp* and PPh3 groups. The reactivity of 1
towards nucleophiles, but not towards alkynes, supports the pro-
posed Lewis acid assisted nucleophilic substitution mechanism.
Interestingly, the nucleophilic substitution reaction that leads to
3 can be repeated a second time, leading to the displacement of the
second chloride with PPh3 (Scheme 4). However, the formation of
differing. The 31P NMR spectrum of 2 shows doublets at
d 318 and
258, each having a coupling constant of 528 Hz. The large PeP
coupling constant indicates a direct PeP bond between two
chemically inequivalent P atoms. The IR spectrum shows three
carbonyl stretches at 2020, 1932 and 1953 cmꢀ1, in a pattern
consistent with a Cp*Mo(CO)3X unit. The 1H NMR spectrum shows
peaks at
d 1.95 and 1.89 for two chemically different Cp* groups.
The 13C NMR spectrum shows six carbonyls, and two Cp* groups,
confirming that there are two chemically non-equivalent
Cp*Mo(CO)3 units. The electrospray mass spectrum shows an
isotope pattern (m/z ¼ 780e809) that corresponds to the predicted
masses for C26H30O6P2Cl3Moþ2 . Based on these data, the structure of
2 is assigned as a bimetallic complex containing a bridging P2Cl3
ligand and an overall þ1 charge, which results from the displace-
ment of chloride from one molecule of the dichlorophosphido
ligand of 1 by a second equivalent of 1 (Scheme 1).
The observed product could indicate formation of a transient
chlorophosphinidene, followed by its coordination by a second
equivalent of 1. In order to test this possibility, the chloride
abstraction reaction was carried out in the presence of an alkyne
trapping reagent. Reaction with alkynes to form phosphirenes is
considered a characteristic reaction of terminal phosphinidene
complexes [17]. However, in this attempted trapping reaction,
compound 2 was the only observed product, and no phosphirene
complex was detected, even with a large excess of alkyne and high
Fig. 1. ORTEP diagram showing one of two crystallographically non-equivalent cations
of 3. Hydrogen atoms and the counterion have been omitted for clarity. Selected dis-
tances and angles: Mo1eP1 ¼ 2.531(1), P1eP2 ¼ 2.196(1), P1eCl(1) ¼ 2.102(1), Mo1e
P1eP2 ¼ 112.51(5), Mo1eP1eCl1 ¼ 108.94(5), Cl(1)eP(1)eP(2) ¼ 94.41(5).
Scheme 2.

86
R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
Scheme 4.
the second PeP bond is accompanied by dissociation from the
metal complex. Thus, reaction of 1 with two equivalents of PPh3
and two equivalents of NaBPh4 leads to Ph3PPPPhþ3 , which was
previously synthesized by Schmidpeter et al. from PCl3, PPh3, and
AlCl3 [18]. The fate of the metal fragment in this reaction is not
known. However, if the same reaction is carried out with an addi-
tional equivalent of PPh3, the Cp*Mo(CO)þ3 fragment can be trapped,
forming the known complex [Cp*Mo(CO)3PPh3]þ [19].
Although the dichlorophosphido complex 1 does not serve as a
precursor to the chlorophosphinidene, its facile nucleophilic sub-
stitution reactions led us to consider its use as a precursor to other
phosphido complexes. For example, reaction of 1 with an alkyl
nucleophile can be used as a synthetic route to chloro alkyl phos-
phido complexes, which in turn serve as precursors to alkyl phos-
phinidenes [4]. We have applied this methodology to the known
chlorophosphido complex [Cp*Mo(CO)3{P(Cl)(i-Pr)}] (4), previ-
ously formed from i-PrPCl2 and [Cp*Mo(CO)3]ꢀ. Reaction of 1 with
isopropyl magnesium chloride led to a mixture of unreacted
starting material, mono- and di-substitution. Diisopropylzinc,
however, is more selective, and leads to 4 as the major product
(Scheme 5). Abstraction of chloride from 4 leads to the transient
alkyl phosphinidene complex [Cp*Mo(CO)3{P(i-Pr)}][AlCl4]. Some
of the reaction chemistry of this alkyl phosphinidene, formed via a
different route, was described previously [4].
Scheme 6.
with other products that could not be identified or isolated. The
observed product presumably results from nucleophilic attack on
the phosphinidene complex by the O atom of a second equivalent of
the phosphinidene, followed by hydrolysis by adventitious water.
The fate of the second metal complex in this reaction is not known.
Although stable phenoxy and alkoxy phosphinidenes could not
be observed, transient phosphinidenes are readily identified
through trapping reactions. Abstraction of chloride from com-
pounds 5 or 6 with AlCl3 in the presence of diphenylacetylene leads
to the expected phosphirene complexes [Cp*Mo(CO)3{P(p-
OC6H4C(CH3)3)C(Ph)C(Ph)}[AlCl4] (7) and [Cp*Mo(CO)3{P(OC10H19
C(Ph)C(Ph)}][AlCl4] (8) (Scheme 7). The 31P NMR spectra of 7 and 8
show singlets at
ꢀ21.1 and ꢀ32.6 respectively, in the high field
)
d
region expected for phosphirene complexes. Because the P centre
in 8 is no longer stereogenic, a single isomer of 8 is formed from two
diastereomers of 6. These resonances are deshielded compared to
other comparable phosphirene complexes [2,20] as a result of the
alkoxy or aryloxy substituent. Since reaction with alkynes to form
phosphirenes is considered a characteristic reaction of terminal
electrophilic phosphinidene complexes [17], the observed products
are strong supporting evidence for transient cationic alkox-
yphosphinidenes. These are the first known cationic alkoxy and
aryloxy phosphinidene complexes.
Compound 1 is also an effective precursor to phenoxy- and
alkoxyephosphido complexes. Reaction of 1 with para-t-butyl
phenoxide leads to the phenoxy phosphido complex [Cp*Mo(-
CO)3{P(Cl)(p-OC6H4C(CH3)3)}] (5) (Scheme 6). Similarly, reaction of
1 with (ꢀ)-menthoxide anion leads to the alkoxy phosphido com-
plex [Cp*Mo(CO)3{P(Cl)(OC10H19)}] (6a,b). As
a result of the
chirality of the menthoxy group, 6 exists as two diastereomers as
indicated by 31P NMR spectrum, which shows signals at
421 and
406 in a ratio of 27:73. Other alkoxy and phenoxy phosphido
d
d
complexes, including those with the parent phenoxy and naph-
thoxy groups have also been synthesized, but they formed oils that
were difficult to purify. As a result, we focused on 5 and 6, which are
crystalline.
The chloride group on the phosphido complexes 5 and 6 can be
readily abstracted using AlCl3, however attempts to observe stable
alkoxy phosphinidene complexes were not successful. At low
temperatures, the abstraction reaction is suppressed, but at higher
temperatures, decomposition is rapid. In the absence of trapping
reagents, decomposition of alkoxy or aryloxy phosphinidenes led to
[Cp*Mo(CO)3{PH(OR)2}]þ (identified by electrospray MS), along
Attempts to trap the alkoxy and aryloxy phosphinidenes with
ferrocene were not successful, and the products were the same as
those obtained in absence of a trapping reagent. This contrasts with
the alkyl phosphinidene [Cp*Mo(CO)3{P-i-Pr}]þ, which inserts in to
a CeH bond of ferrocene [4].
Computational study
In order to gain further insight into the relative stabilities of the
various cationic phosphinidene compounds, a computational study
Scheme 5.
Scheme 7.

R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
87
ꢀ
Fig. 2. Optimized structures of A-D. Selected bond distances (A) and angles: A, MoeP ¼ 2.397, PeC ¼ 1.873, MoePeC ¼ 115.76. B, MoeP ¼ 2.476, PeN ¼ 1.671, MoePeN ¼ 119.65.
C, MoeP ¼ 2.423, PeO ¼ 1.658, MoePeO ¼ 108.98. D, MoeP ¼ 2.384, PeCl ¼ 2.065, MoePeCl ¼ 114.02.
has been carried out on a series of cationic complexes with various
P substituents. Neutral terminal phosphinidene complexes have
been extensively studied computationally, including studies on
electrophilic versus nucleophilic natures of phosphinidenes [21],
specific studies on transient electrophilic phosphinidenes [22,23],
stable nucleophilic phosphinidenes [24], and stable electrophilic
order, reflecting the strong NeP p overlap. The PCl and POPh
complexes are intermediate between these extremes, showing
evidence for weak XeP overlap. The MoeP bond orders show that
the P-i-Pr and PeCl phosphinidenes are the strongest
p-acceptors,
while PN-i-Pr2 and POPh are weaker -acceptors. A similar trend
p
was observed in calculations on Cr(CO)5PR (R ¼ H, CH3, SiH3, NH2,
phosphinidenes
[25].
Cationic
complexes,
including
PH2, OH, and SH), where PH, PCH3, and PSiH3 were shown to be
[Cp*Mo(CO)3(PCH3)]þ, have been examined by Pandey et al. using
DFT [26]. However, the role of the P substituent in the stability of
cationic phosphinidenes has not been directly addressed.
DFT calculations were carried out on the complexes
[Cp*Mo(CO)3{PX}]þ, where X ¼ i-Pr (A), N-i-Pr2 (B), OPh (C), and Cl
(D), at the B3LYP level of theory [27]. Mayer bond orders [28] and
NBO charges [29] were calculated, and fragment molecular orbital
(FMO) analysis [30,31] was carried out for each of the complexes.
Optimized structures are shown in Fig. 2. The optimized structure
of aminophosphinidene complex B provided a good agreement
with the experimentally determined structure [1] (see Table S1 of
Supporting Information).
significant
much weaker
p
-acceptor ligands, while POH, PNH2, and PSH were
acceptors [23].
p
Computed NBO charges for AeD are shown in Table 2. The
charges listed are the summed charges on the [Cp*Mo(CO)3] frag-
ment, the charge on P, and summed charges on phosphorus sub-
stituent. The NBO charges show a significant positive charge
localized at P in all of the complexes, consistent with the bonding
model. The summed charge on the P substituent gives an indication
of the electron withdrawing/electron donating abilities of the
substituent. It is assumed based on our bonding model that elec-
tron withdrawing is inductive via the sigma bond, and depends on
These cationic electrophilic phosphinidene complexes can be
viewed as neutral singlet phosphinidenes (PX) coordinated via a
dative bond to a cationic metal complex, or as metallaphosphenium
ions. Either formulation places a formal positive charge and an
empty pz orbital at P. The electron deficiency at P is alleviated by
donation from a heteroatom substituent or by metal-to-P -back
donation (Fig. 3). Computed Mayer bond orders (Table 1) give a
measure of X to P donation, while the MeP bond order gives a
measure of M-to-P -back donation. The P-i-Pr complex has
p
p
p
p
no substituent non-bonding pairs, and as expected, has the lowest
Fig. 3. Heteroatom to P
p donation and M-to-P p-back donation in phosphinidene
PeX bond order. The PNR2 complex has the highest PeX bond
complexes.

88
R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
Table 1
the HOFO-1 occupancy show that the
p
interaction is weaker than
interaction varies
Computed Mayer bond orders for compounds AeD.
the interaction, as expected, but also that the
s
p
significantly across the four complexes, being weakest for X ¼ NR2,
Compound
Substituent
MoeP
PeX
and strongest for X ¼ i-Pr and Cl. This further reinforces the con-
A
B
C
i-Pr
1.326
1.016
1.163
1.302
0.908
1.381
1.084
1.070
clusions drawn from bond orders and NBO charges that M to P
p-
N-i-Pr2
OPh
Cl
back donation is strongest in the chloro and alkyl phosphinidenes,
and weakest in the aminophosphinidene. The phenoxy is
intermediate.
D
Finally, the computed reaction energies (kcal/mol) to abstract
chloride using AlCl3 from their precursors to form complexes AeD
show that all reactions are exothermic. Formation of the amino-
phosphinidene is by far the most exothermic at ꢀ33.1 kcal/mol. It is
followed in order by POPh (ꢀ15.4 kcal/mol), P-i-Pr (ꢀ12.3 kcal/mol)
and PCl (ꢀ7.1 kcal/mol).
relative electronegativities, while electron donation occurs via
p
overlap. Based on induction alone, the expected order of increasing
negative charge on X would be R < NR2 < Cl < OR. The calculated
order is NR2 << Cl < R < OR, clearly showing that NR2 is a signif-
icant
p donor to P, while the other substituents have much less p
overlap. It is also noteworthy that the summed charge on the alkyl
group is greater than that on chloro, contrary to expectation based
on electronegativity, and suggesting that there is at least some Cl to
Discussion
P
p
donation.
We have now examined cationic phosphinidene complexes with
four different functional groups on P, formed via chloride abstrac-
tion. Of these four, aminophosphinidenes are stable [1], alkyl [4] and
alkoxy phosphinidenes are transient and can be trapped, while
chlorophosphinidenes could not be formed by this route. Our
inability to observe stable alkoxy or aryloxy phosphinidenes sug-
The summed charge on the metal fragment gives an indication of
the relative donor/acceptor abilities of the different phosphinidene
ligands. The calculated ordering from strongest donor to strongest
acceptor is PNR2 > POR > PR > PCl. The positioning of PNR2 as
strongest donor/weakest acceptor suggests that strong N to P
donationprecludes significant M to P -back donation, resulting in a
ligand that is primarily a donor, consistent with the bond order
results. The PR and PCl complexes have significantly higher positive
charge on the metal fragment, indicating that they act as -accep-
tors. Because the alkyl substituent on PR has no non-bonding pair,
there is no overlap with the substituent, and the phosphorus pz
orbital is fully available to accept -back donation from the metal.
Based on the metal charge, PCl is an even stronger acceptor than
PR. On the other hand, POPh is only a weak acceptor ligand,
inducing a smaller positive charge on the metal than P-i-Pr or PeCl.
Weak -backdonationand weakO-to-P donationmeansthat theP
p
p
gests that the alkoxy and aryloxy groups do not provide sufficient p-
s
overlap to stabilize the electron deficient phosphorus, making them
comparable to the alkyl phosphinidene. However, in contrast to the
analogous alkyl phosphinidene, the alkoxy phosphinidenes do not
activate the CeH bonds of ferrocene [4], suggesting that they may be
less electrophilic than the alkyl phosphinidene. Our inability to
obtainevidenceforevena transient chlorophosphinidenesuggested
p
p
p
p
that CleP
p overlap is weak or non-existent, and that the chloro
p
substituent may further destabilize the phosphinidene.
The computational study clearly shows why the amino-
phosphinidene is the only stable and isolable complex. Its formation
is far more exothermic than the formation of any of the other phos-
p
p
atom in the POPh complex carries the highest positive charge. In the
PCl and P-i-Pr complexes, the positive charge is delocalized onto the
metal by
delocalized onto N by
phinidenes. The key difference is the extent of N to P
p-donation,
p-back donation, while in the PN-i-Pr2 complex, it is
whichisfargreaterthanthe donationinanyoftheothercomplexes,
p
p
donation. As a result, the POPh phosphini-
and we attribute its stability to this
computational studies have shown that in
p
p
-stabilization. Previous
-donor substituted free
dene is expected to be most electrophilic at P.
Fragment molecular orbital (FMO) analysis allows us to further
phosphinidenes, the ground spin state depends on the extent of
overlap of the non-bonding electrons of -donor substituent with an
empty p orbital of phosphorus [32]. In amino phosphinidenes,
effective -overlap favours the singlet state, but in alkoxy and halo
phosphinidenes, less effective -overlap favours the triplet ground
state. The cationic metal complexes described here show the same
trend: strong donation for the aminophosphinidene, and weak
p-
decompose the MeP interaction into
donation components. In all of these complexes, the MeP
s-donation and p-back
p
s
-
interaction occurs from the highest occupied fragment orbital
(HOFO) of the phosphinidene fragment to the lowest unoccupied
fragment orbital (LUFO) of the [Cp*Mo(CO)3]þ fragment (Fig. 4[i]).
The changes in occupancies to the fragment orbitals upon complex
formation allow us to gauge relative bond strength. The HOFO of
the phosphinidene fragment, used to form the
shows a similar drop in occupancy across the four complexes,
indicating that the -bond strength is approximately equal across
p
p
p
p-
donation in phenoxy and chloro phosphinidenes. The same trend is
observed experimentally in related phosphenium ions, which are
generally stable only when at least one substituent is an amino group
[33]. Clearly, the amino group is uniquely effective at stabilizing
electron deficient phosphorus centers.
s bond, (Fig. 4)
s
the four complexes. Similarly, the increase in occupancy for the
LUFO of the metal fragment is nearly the same across all four
complexes.
The extent of M to P
between the different complexes. In the case of the amino-
phosphinidene, strong NeP donation appears to preclude strong
M to P eback donation. In contrast, the chloro and alkyl phos-
phinidenes, which have weak or no XeP overlap, are stronger
acceptors from the metal. Although -back donation effectively
p-back donation also varies considerably
The
p
interaction occurs from the HOFO-1 of [Cp*Mo(CO)3]þ to
p
the LUFO (the empty pz orbital of P) on the phosphinidene fragment
(Fig. 4[ii]). The increase in the LUFO occupancy, and the decrease in
p
p
p
p
Table 2
alleviates positive charge on P in the alkyl and chloro phosphini-
denes (Table 2), it does not appear to have the same stabilizing
effect as NeP overlap.
Interestingly, the phenoxy phosphinidene has neither strong Oe
P overlap nor metal back donation. This suggests that repulsion by
Computed NBO charges of compounds AeD.
Compound
Substituent
Charge
[Cp*Mo(CO)3]
P
X
A
B
C
i-Pr
0.260
0.113
0.197
0.339
0.933
0.968
1.124
0.823
ꢀ0.192
ꢀ0.082
ꢀ0.321
ꢀ0.161
N-i-Pr2
OPh
Cl
the oxygen lone pairs make
OeP overlap is weak. The lack of
positive charge at P, suggesting that the phenoxy phosphinidene
p
-back donation less favourable even if
p
p
donation results in the highest
D

R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
89
Fig. 4. Isosurface plots (isovalue: 0.02) of selected fragment molecular orbitals (FOs) of [Cp*Mo(CO)3]þ and P(N-i-Pr2) involved in
s-donation [i] and
p
back-donation [ii]. Isosurface
plots of FOs of other complexes (X ¼ i-Pr, OPh, Cl) are similar to those of the N-i-Pr2 complex shown. The values in brackets correspond to the percent changes in FO occupancies
upon formation of complexes A-D from their corresponding [Cp*Mo(CO)3]þ and PR fragments.
should be the most electrophilic. Its failure to activate the CeH
bonds of ferrocene is therefore most likely not a result of insuffi-
cient electrophilicity, but rather a result of an alternative, more
facile reaction, namely nucleophilic attack by the oxygen of a sec-
ond equivalent of the phosphinidene complex.
Although the chlorophosphinidene is clearly the least stable
complex in the series, its formation is still exothermic, and the
calculations reveal no inherent reason for instability. In fact, its P
atom carries less positive charge than the alkyl or phenoxy phos-
phinidenes. This suggests that it should have similar stability and
reactivity to the alkyl or alkoxy phosphinidenes, and should thus be
trappable. Our inability to generate it as a transient species and trap
it is therefore likely not a result of inherent instability, but rather a
result of alternate lower energy pathways that lead to substitution
reactions, rather than abstraction. This alternate reaction, unique to
the chlorophosphinidene, likely results from the lack of steric
protection provided by the chloro substituent.
In conclusion, the dichlorophosphido complex does not serve as
a precursor to a chlorophosphinidene, but undergoes Lewis acid
assisted nucleophilic substitutions with weak nucleophiles,
including itself and PPh3. Reactions with stronger nucleophiles
serve as routes to substituted chlorophosphido complexes, pre-
cursors to phosphinidenes. We have used this route to generate
alkyl, aryloxy and alkoxy phosphinidenes. Unlike amino phosphi-
nidenes, alkoxy or aryloxy phosphinidenes are not stable, but can
be readily trapped with alkynes and phosphines.
solution in THF or CH2Cl2. Mass spectra were recorded using a
Finnigan-Matt TSQ-700 mass spectrometer equipped with elec-
trospray ionization and a Harvard syringe pump. Elemental ana-
lyses were carried out by the Analytical and Instrumentation
Laboratory, Department of Chemistry, University of Alberta. Com-
pounds 7 and 8 formed oils that could not be crystallized. As a
result, satisfactory elemental analyses could not be obtained. Their
formulations are supported by ESI mass spectrometry and NMR
spectroscopy (see Supporting Information for spectra).
Compound synthesis
Synthesis of [Cp*Mo(CO)3(PCl2)] (1)
Compound 1 was synthesized using a modification of the
published procedure [13]. To pentamethylcyclopentadiene
(0.52 g, 3.8 mmol, 0.60 mL) in 50 mL THF was added n-butyl-
lithium (2.4 mL of 1.6 M solution in hexane, 3.8 mmol). Molyb-
denum hexacarbonyl (1.00 g, 3.78 mmol) was then added, and
the resulting solution was heated under reflux for 16 h, resulting
in an orange solution of Li[Cp*Mo(CO)3]. This solution was added
in small portions to a solution of phosphorus trichloride (1.03 g,
7.5 mmol, 0.66 mL) in 75 mL of THF at 0 ꢁC. The reaction mixture
was stirred for 30 min and the solvent was removed under
reduced pressure at 0 ꢁC. The orange residue obtained was
extracted into 3 ꢂ 40 mL of pentane and the resulting solution
was filtered. The pentane filtrate was concentrated to 10 mL and
cooled to ꢀ30 ꢁC, resulting in the formation of large orange
crystals. The crystals obtained were collected and stored
Experimental section
at ꢀ35 ꢁC. Yield ¼ 1.15 g, 73%. IR (THF solution,
n
(CO), cmꢀ1):
2018 s, 1952 s, 1932 s 31P{1H} NMR:
d d 1.96 (d,
408.5. 1H NMR:
General comments
JHP ¼ 9.0 Hz, 15H, C5(CH3)5).
All procedures were carried out under a nitrogen atmosphere
using standard Schlenk techniques or in an inert atmosphere glo-
vebox. THF was distilled from Na/benzophenone. Dichloromethane
and hexane were purified using solvent purification columns con-
taining alumina (dichloromethane) or alumina and copper oxide
catalyst (hexane). Deuterated chloroform was distilled from P2O5.
The NMR spectra were recorded in CDCl3 using a Varian Mercury
Synthesis of [{Cp*Mo(CO)3}2(m-P2Cl3)][AlCl4] (2)
The compound [Cp*Mo(CO)3(PCl2)] (1; 20 mg, 0.047 mmol) was
dissolved in CH2Cl2 (5.0 mL). The resulting solution was added to
AlCl3 (3 mg, 0.024 mmol) and stirred for 30 min. A slow colour
change from orange to dark red was observed. The solvent was
removed under reduced pressure and the residue obtained was
extracted into CH2Cl2 (0.5 mL) and crystallized as orange crystals by
slow diffusion of diethyl ether into the CH2Cl2 solution. Yield:
300 spectrometer operating at 300.179 MHz (1H), 75.479 MHz (13
{1H}), and 121.515 MHz (31P{1H}). Infrared spectra were recorded in
C

90
R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
2
19.4 mg, 52.2%. IR (CH2Cl2 solution,
n
(CO), cmꢀ1): 2020 s, 1953 s,
PCH(CH3)2), 21.3 (d, JCP ¼ 3 Hz, PCH(CH3)2), 10.6 (d, JCP ¼ 6 Hz,
1
1933 s. 31P{1H} NMR:
d
318 (d, JPP ¼ 527 Hz, MoPP), 258 (d,
C5(CH3)5). Anal, Calcd for C16H22O3PClMo: C, 45.25; H, 5.22. Found:
1JPP ¼ 528 Hz, MoPP). 1H NMR:
d
5.29 (s, CH2Cl2),
d
2.16 (d,
233.2
C, 45.06; H, 5.34.
JHP ¼ 1.5 Hz,15H, C5(CH3)5). 2.05 (s,15H, C5(CH3)5). 13C NMR:
d
(d, JCP ¼ 8 Hz, MoCO), 227.7 (s, MoCO), 227.3 (d, JCP ¼ 4 Hz, MoCO),
224.8 (s, MoCO), 224.4 (s, MoCO), 221.6 (s, MoCO), 110.9 (s,
C5(CH3)5), 108.4 (s, C5(CH3)5), 11.1 (s, C5(CH3)5), 10.7 (d, JCP ¼ 4 Hz,
C5(CH3)5). MS (electrospray, CH2Cl2 solution): m/z ¼ 789e809 (Mþ)
(Fig. 5). Anal. Calcd for C26H30AlCl7Mo2P2O6$CH2Cl2: C, 30.81; H,
3.06. Found: C, 30.82; H, 3.16. Co-crystallized CH2Cl2 was observed
in the 1H NMR spectrum of the crystals.
Synthesis of [Cp*Mo(CO)3{P(Cl)(OC6H4C(CH3)3)}] (5)
Butyl lithium (0.749 mL of 1.6 M solution in THF, 1.198 mmol)
was added dropwise to a solution of 4-tert-butylphenol (180 mg,
1.198 mmol) in THF (5 mL). The solution was stirred for 30 min.
Compound 1 (500 mg, 1.198 mmol) was dissolved in THF (25 mL).
The 4-tert-butylphenoxide ion solution was then added dropwise,
resulting in gradual colour change from orange to dark red. The
solvent was removed under reduced pressure and the dark residue
obtained was extracted in pentane (10 mL) and filtered. The
pentane was removed under reduced pressure and the residue was
dissolved in minimum amount of hexane. The hexane solution was
then cooled to ꢀ35 ꢁC for 24 h, resulting in the formation of large
Synthesis of [Cp*Mo(CO)3{P(Cl)(PPh3)}][AlCl4] (3)
Compound
1 (20 mg, 0.047 mmol) and PPh3 (12.5 mg,
0.047 mmol) were dissolved in CH2Cl2 (0.5 mL). The resulting so-
lution was added to AlCl3 (6 mg, 0.047 mmol) and stirred for
30 min. An immediate colour change from yellow to dark red was
observed. The solvent was then removed under reduced pressure.
The residue was extracted into CH2Cl2 (0.5 mL) and crystallized as
yellow crystals by slow diffusion of diethyl ether into the CH2Cl2
dark red crystals. Yield: 558 mg, 87.7%. IR (hexane solution,
n
(CO),
7.32
cmꢀ1): 2017 s, 1953 s, 1931 s. 31P{1H} NMR: 403.3. 1H NMR:
d
d
3
3
4
(dm, 2H, JHH ¼ 9 Hz, Ph), 7.10 (ddm, 2H, JHH ¼ 9 Hz, JHP ¼ 3 Hz,
Ph), 1.98 (d, 15H, JHP ¼ 0.6 Hz, C5(CH3)5), 1.29 (s, 9H, C(CH3)3). 13
C
2
solution. Yield: 24.6 mg, 63%. IR (THF solution, n
(CO), cmꢀ1): 2017 s,
NMR:
d
245.0 (s, MoCO), 233.4 (d, JCP ¼ 7 Hz, MoCO), 226.1 (s,
MoCO), 155.6 (d, 2JCP ¼ 3 Hz, ipso-Ph), 145.2 (d, JCP ¼ 1 Hz, ipso-Ph),
1967 s, 1932. s 31P{1H} NMR:
d
177 (d, 1JPP ¼ 453 Hz, MoPP), 35.7 (d,
3
1JPP ¼ 451 Hz, MoPP). 1H NMR:
d 7.71e6.78 (multiplets, Ph), 1.88 (s,
125.2 (s, Ph), 117.5 (d, JPC ¼ 9 Hz, Ph), 104.9 (s, C5(CH3)5), 30.4 (s,
15H, C5(CH3)5). 13C NMR:
d
233.6 (dd, JCP ¼ 10 Hz, JCP ¼ 3 Hz, MoCO),
C(CH3)3), 9.28 (d, JCP
¼
7 Hz, C5(CH3)5). Anal. Calcd for
C
23H28O4ClMoP: C, 52.04; H, 5.32. Found: C, 51.92; H, 5.80.
228.1 (s, MoCO), 221.5 (s, MoCO), 134.7 (d, JCP ¼ 4 Hz, Ph), 133.9 (s,
Ph), 133.8 (s, Ph), 133.5 (dd, JCP ¼ 15 Hz, JCP ¼ 4 Hz, Ph), 130.5 (d,
JCP ¼ 12 Hz, Ph), 120.6 (dd, 1JCP ¼ 58 Hz, 2JCP ¼ 6 Hz, ipso-Ph), 108.5
(s, C5(CH3)5), 10.7 (d, JCP ¼ 6 Hz, C5(CH3)5). MS (electrospray, CH2Cl2
Synthesis of [Cp*Mo(CO)3{P(Cl)(OC10H19)}] (6)
Butyl lithium (74.9 L of 1.6 M solution in THF, 0.119 mmol) was
m
solution): m/z ¼ 639e652 (Mþ). Anal. Calcd. for C31H30MoO3
added dropwise to a solution of (ꢀ)-menthol (18.7 mg, 0.119 mmol)
in THF (5 mL). The solution was stirred for 30 min. Compound 1
(50 mg, 0.119 mmol) was dissolved in THF (10 mL). The menthoxide
solution then added dropwise, resulting in an immediate colour
change from orange to dark red. The reaction solution was stirred
for 30 min and the solvent was removed under reduced pressure.
The dark red residue was extracted into pentane (10 mL) and
filtered. The pentane was removed and the dark oily residue was
redissolved in minimum amount of hexane. The hexane solution
was then cooled to ꢀ35 ꢁC, resulting the formation of dark red
-
Cl5AlP2: C, 45.80; H, 3.72. Found: C, 45.70; H, 3.69.
Synthesis of [Cp*Mo(CO)3{P(Cl)(i-Pr)}] (4)
A solution of Zn(i-Pr)2 was prepared by dropwise addition of i-
PrMgCl (0.734 mL of 2 M solution in THF, 1.460 mmol) to a solution
of ZnCl2 (100 mg, 0.734 mmol) in 5 mL of THF, followed by 30 min of
stirring. Compound 1 (100 mg, 0.239 mmol) was dissolved in THF
(25 mL). A portion of the Zn(i-Pr)2 solution (0.922 mL of 0.13 M
solution in THF, 0.119 mmol) was added dropwise to the solution of
1, resulting in an immediate colour change from orange to dark red.
After the addition was completed, the resulting solution was stirred
for 30 min and the solvent was removed under reduced pressure.
The dark red residue was extracted in pentane (20 mL) and filtered.
The pentane was removed under reduced pressure and the
resulting orange oil was dissolved in minimum amount of hexane.
The hexane solution was then kept at ꢀ35 ꢁC for two days, resulting
in the formation of orange crystals. Yield: 50.9 mg, 50%. IR (hexane
crystals. Yield: 40.2 mg, 62.5%. IR (CH2Cl2 solution, n
(CO), cmꢀ1):
2009 s, 1939 s, 1919s. 31P{1H} NMR:
d
421.4 (27%), 406.3 (73%). 1H
3
NMR (major diastereomer): 3.68 (ddt, 1H, JHP
¼
32.7 Hz,
3JHH ¼ 11.1 Hz, 3JHH ¼ 4.5 Hz, HA menthol), 2.37e2.07 (broad mul-
tiplets, menthol), 1.89 (s, 15H, C5(CH3)5), 1.77e1.24 (broad multi-
3
plets, menthol), 0.91 (d, 3H, JHH ¼ 6.6 Hz, CH(CH3)2(menthol)),
3
3
0.87 (d, 3H, JHH ¼ 7.2 Hz, CH3 (menthol)), 0.77 (d, JHH ¼ 6.9 Hz,
CH(CH3)2 (menthol)). 13C NMR (major diastereomer):
d 246.3 (s,
solution,
n
(CO), cmꢀ1): 2007 s, 1944 s, 1915 s. 31P{1H} NMR:
d
269.7.
MoCO), 235.2 (d, JPC ¼ 7 Hz, MoCO), 227.3 (s, MoCO), 106.0 (s,
2
1H NMR:
d
2.31 (d sept, 1H, 2JHP ¼ 27.9 Hz, 3JHH ¼ 7.0 Hz, CH(CH3)2),
C5(CH3)5), 82.3 (d, JCP ¼ 5 Hz, menthol C1), 49.4 (s, menthol C2),
3
3
42.5 (s, menthol C6), 34.4 (s, menthol C4), 31.9 (s, menthol C5), 24.8
(s, (CH3)2C, menthol), 23.1 (s, menthol C3), 22.3 (s, menthol CH3),
21.3 (s, menthol CH(CH3)2), 16.0 (s, menthol CH(CH3)2), 10.5 (d,
JPC ¼ 6 Hz, C5(CH3)5). Anal. Calcd for C23H34O4PClMo: C, 51.45; H,
6.38. Found: C, 51.06; H, 6.40.
1.96 (s, 15H, C5(CH3)5, 1.37 (dd, 3H, JHP ¼ 23.4 Hz, JHH ¼ 7.2 Hz,
CH(CH3)2), 1.36 (d, 3H, JHH ¼ 6.9 Hz, CH(CH3)2). 13C NMR:
d 236.8
3
2
(d, JCP ¼ 9 Hz, MoCO), 229.1 (s, MoCO), 225.0 (s, MoCO), 106.6 (s,
C5(CH3)5), 36.4 (d, 1JCP ¼ 47 Hz, PCH(CH3)2), 22.7 (d, JCP ¼ 18 Hz,
2
Synthesis of [Cp*Mo(CO)3{P(OC6H4C(CH3)3)C(Ph)C(Ph)}][AlCl4] (7)
[Cp*Mo(CO)3{P(Cl)(OC6H4C(CH3)3)}] (5; 50 mg, 0.0941 mmol)
and diphenylacetylene (16.7 mg, 0.0941 mmol) were dissolved in
CH2Cl2 (5.0 mL). The resulting solution was added to AlCl3 (12.5 mg,
0.0941 mmol) and stirred for 30 min. The solvent volume was
reduced to w2 mL, and pentane (10 mL) was added to the
concentrated reaction solution with rapid stirring, resulting in the
formation of a dark oil. The supernatant was decanted and the oil
was washed with pentane (5.0 mL) and dried under vacuum. Yield:
24 mg, 38.4%. IR (CH2Cl2 solution, n
(CO), cmꢀ1): 2017 s, 1979 s,
Fig. 5. Electrospray MS of
2 showing molecular ion cluster. a. Calculated for
C
26H30Cl3Mo2O6P2. b. Experimental.
1951 s. 31P{1H} NMR: ꢀ21.4, 1H NMR: 7.6e6.8 (multiplets, Ph), 7.12

R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
91
(dm, 2H, 3JHH ¼ 9 Hz, Ph), 6.66 (ddm, 2H, 3JHH ¼ 9 Hz, 4JHP ¼ 3 Hz,
Additionally, single-point computations were performed to print
the one electron integrals of all phosphinidene complexes and their
fragments. The keywords used for this computation are #P rb3lyp
gen 5D NoSymm Pop¼Full IOp(3/33¼1) SCF¼Tight (pseudo¼read is
included only when a transition metal is present). The single-point
output files, generated by Gaussian 09 software package, were used
in the AOMix software package (revision 6.81) [31] to calculate
Mayer bond orders [28] between atoms and to analyse the mo-
lecular orbital compositions in terms of contributions from frag-
ment orbitals that was performed using Mulliken population
analysis [35].
Ph), 2.12 (s, C5(CH3)5), 1.08 (s, 9H, C(CH3)3). 13C NMR:
d 226.3 (s,
MoCO), 225.7 (d, JCP ¼ 40 Hz, MoCO), 149.6 (d, JCP ¼ 2 Hz, ipso-Ph),
148.4 (d, 1JCP ¼ 17, phosphirene ring C), 146.3 (d, JCP ¼ 16, Ph), 132.7
(s, Ph), 130.1 (s, Ph), 129.3 (d, JCP ¼ 6 Hz, Ph), 127.3 (d, JCP ¼ 2 Hz, Ph),
126.6 (s, Ph), 120.8 (d, JCP ¼ 5 Hz, ipso-Ph), 110.1 (s, C5(CH3)5, 31.4 (s,
C(CH3)3), 11.7 (s, C5(CH3)5). MS (electrospray, CH2Cl2 solution): m/z
669e678 (Mþ).
Synthesis of [Cp*Mo(CO)3{P(OC10H19)C(Ph)C(Ph)}][AlCl4] (8)
[Cp*Mo(CO)3{P(Cl)(OC10H19}] (6, 50 mg, 0.0931 mmol) and
diphenylacetylene (16.6 mg, 0.0931 mmol) were dissolved in
CH2Cl2 (5 mL). The resulting solution was added to AlCl3 (12 mg,
0.0931 mmol) and stirred for 30 min. The solvent volume was
reduced under reduced pressure and pentane (10 mL) was added to
the concentrated reaction solution with rapid stirring. The super-
natant was removed and the resulting dark coloured oil was
washed with pentane (5.0 mL) and dried under vacuum. Yield:
Acknowledgements
This work was financially supported by the University of Regina.
We also thank Bob McDonald and Mike Ferguson (University of
Alberta) for X-ray data collection.
62.6 mg, 62.5%. IR (THF solution, n
(CO), cmꢀ1): 2007 s, 1959 s,
Appendix A. Supplementary material
1920 s. 31P{1H} NMR:
3.18 (multiplet, 1H, HA menthol), 1.80e1.77 (multiplets, menthol),
d
ꢀ32.6. 1H NMR:
d 7.48e6.89 (multiplets, Ph),
CCDC 982682 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
1.76 (s, 15H, C5(CH3)5), 1.75e0.53 (broad multiplets, menthol), 0.50
3
(d, 3H, JHH
¼
6.0 Hz, eCH(CH3)2 (menthol)), 0.39 (d, 3H,
3JHH ¼ 6.0 Hz, CH3 (menthol)), 0.01 (d, 3H, JHH ¼ 9 Hz, CH(CH3)2).
3
13C NMR:
d
229.2 (s, MoCO), 226.5 (d, JCP ¼ 8 Hz, MoCO), 225.9 (s,
1
MoCO), 148.0 (d, JPC ¼ 18 Hz, phosphirene ring C), 147.6 (d,
1JCP ¼ 15 Hz, phosphirene ring C),133.0 (s, Ph),132.8 (s, Ph),130.4 (s,
Ph), 130.2 (s, Ph), 129.7 (d, JCP ¼ 6 Hz, o-Ph), 129.3 (d, JCP ¼ 6 Hz, o-
Ph), 129.1 (s, Ph), 128.7 (s, Ph), 127.2 (d, 2JCP ¼ 3 Hz, ipso-Ph), 126.8
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.02.025.
2
2
(d, JCP ¼ 3 Hz, ipso-Ph), 109.7 (s, C5(CH3)3), 79.9 (d, JCP ¼ 15 Hz,
menthol C1), 48.6 (d, JCP ¼ 5 Hz, menthol C2), 42.6 (s, menthol C6),
33.6 (s, menthol C4), 31.8 (s, menthol C5), 25.7 (s, menthol
CH(CH3)2), 22.9 (s, menthol C3), 22.0 (s, menthol CH3), 21.2 (s,
menthol CH(CH3)2), 16.0 (s, menthol C(CH3)2), 11.5 (s, C5(CH3)5). MS
(electrospray, THF solution): m/z ¼ 675e684 (Mþ).
References
[1] B.T. Sterenberg, K.A. Udachin, A.J. Carty, Organometallics 20 (2001) 2657e
2659.
[2] J. Sánchez-Nieves, B.T. Sterenberg, K.A. Udachin, A.J. Carty, J. Am. Chem. Soc.
125 (2003) 2404e2405.
[3] (a) B.T. Sterenberg, K.A. Udachin, A.J. Carty, Organometallics 22 (2003) 3927e
3932;
(b) T.W. Graham, R.P.Y. Cariou, J. Sanchez-Nieves, A.E. Allen, K.A. Udachin,
R. Regragui, A.J. Carty, Organometallics 24 (2005) 2023e2036.
[4] R.A. Rajagopalan, B.T. Sterenberg, Organometallics 30 (2011) 2933e2938.
[5] (a) A. Marinetti, F. Mathey, J. Fischer, A. Mitschler, J. Am. Chem. Soc. 104 (1982)
4484e4485;
X-ray crystallography
A suitable crystal of compound 3 was mounted on a glass fiber.
Programs for diffractometer operation, data collection, cell index-
ing, data reduction and absorption correction were those supplied
by Bruker AXS Inc., Madison, WI. Diffraction measurements were
made on a PLATFORM diffractometer/SMART 1000 CCD using
(b) F. Mathey, Dalt. Trans. (2007) 1861e1868;
(c) M.L.G. Borst, R.E. Bulo, C.W. Winkel, D.J. Gibney, A.W. Ehlers, M. Schakel,
M. Lutz, A.L. Spek, K. Lammertsma, J. Am. Chem. Soc. 127 (2005) 5800e5801.
[6] (a) F. Mercier, B. Deschamps, F. Mathey, J. Am. Chem. Soc. 111 (1989) 9098e
9100;
graphite-monochromated Mo-K
a
radiation at ꢀ80 ꢁC. The unit cell
was determined from randomly selected reflections obtained using
the SMART CCD automatic search, center, index and least-squares
routines. Integration was carried out using the program SAINT
and an absorption correction was performed using SADABS. Struc-
ture solution was carried out using the SHELX97 [36] suite of pro-
grams and the WinGX graphical interface [37]. Initial solutions were
obtained by direct methods and refined by successive least-squares
cycles. All non-hydrogen atoms were refined anisotropically.
(b) J.B.M. Wit, G.T. van Eijkel, F.J.J. de Kanter, M. Schakel, A.W. Ehlers, M. Lutz,
A.L. Spek, K. Lammertsma, Angew. Chem. Int. Ed. 38 (1999) 2596e2599;
(c) J.B.M. Wit, G.T. van Eijkel, M. Schakel, K. Lammertsma, Tetrahedron 56
(2000) 137e141;
(d) M.L.G. Borst, R.E. Bulo, D.J. Gibney, Y. Alem, F.J.J. de Kanter, A.W. Ehlers,
M. Schakel, M. Lutz, A.L. Spek, K. Lammertsma, J. Am. Chem. Soc. 127 (2005)
16985e16999;
(e) M.L.G. Borst, N. van der Riet, R.H. Lemmens, F.J.J. de Kanter, M. Schakel,
A.W. Ehlers, A.M. Mills, M. Lutz, A.L. Spek, K. Lammertsma, Chem. Eur. J. 11
(2005) 3631e3642.
[7] S. Holand, F. Mathey, Organometallics 7 (1988) 1796e1801.
[8] M.P. Duffy, F. Mathey, J. Am. Chem. Soc. 131 (2009) 7534e7535.
[9] C. Compain, B. Donnadieu, F. Mathey, Organometallics 25 (2006) 540e543.
[10] (a) R. Grubba, K. Baranowska, J. Chojnacki, J. Pikies, Eur. J. Inorg. Chem. 2012
(2012) 3263e3265;
Computational methods
Gas phase structures were optimized without any symmetry
constraints using density functional theory (DFT), with a wave
function incorporating the B3LYP exchange-correlation functional
[27], as implemented in Gaussian 09 (revision C. 01) software
package [34]. Basis set LANL2DZ was used for Mo and 6-31G(d,p)
was used for all other atoms (C, H, O, N, P, Cl, and Al). Vibrational
frequency analysis was used to confirm minima. Gaussian 09 was
also used to compute NBO charges and isosurface plots [29]. The
keywords used for optimization, vibrational, and NBO analyses are
(b) W. Domanska-Babul, J. Chojnacki, E. Matern, J. Pikies, Dalt. Trans. (2009)
146e151;
(c) J. Pikies, E. Baum, E. Matern, J. Chojnacki, R. Grubba, A. Robaszkiewicz,
Chem. Commun. (2004) 2478e2479;
(d) J. Olkowska-Oetzel, J. Pikies, Appl. Organomet. Chem. 17 (2003) 28e35.
[11] (a) B.T. Sterenberg, O.S. Senturk, K.A. Udachin, A.J. Carty, Organometallics 26
(2007) 925e937;
(b) K. Vaheesar, T.M. Bolton, A.L.L. East, B.T. Sterenberg, Organometallics 29
(2010) 484e490.
[12] (a) T.W. Graham, K.A. Udachin, A.J. Carty, Chem. Commun. (2005) 5890e5892;
(b) T.W. Graham, K.A. Udachin, M.Z. Zgierski, A.J. Carty, Can. J. Chem. 85 (2007)
885e888.
#
opt freq¼noraman rb3lyp pop¼(npa,full) gen pseudo¼read.

92
R.A. Rajagopalan et al. / Journal of Organometallic Chemistry 761 (2014) 84e92
[13] R. Maisch, M. Barth, W. Malisch, J. Organomet. Chem. 260 (1984) C35eC39.
[14] (a) E.A.V. Ebsworth, R.O. Gould, N.T. McManus, N.J. Pilkington, D.W.H. Rankin,
J. Chem. Soc. Dalt. Trans. (1984) 2561e2567;
(b) L. Weber, H. Misiak, H.G. Stammler, B. Neumann, Z. Anorg. Allg. Chem. 620
(1994) 1730e1735.
[15] L. Weber, L. Pumpenmeier, H.-G. Stammler, B. Neumann, Dalt. Trans. (2004)
659e667.
(d) G. Zhao, F. Basuli, U.J. Kilgore, H. Fan, H. Aneetha, J.C. Huffman, G. Wu,
D.J. Mindiola, J. Am. Chem. Soc. 128 (2006) 13575e13585;
(e) F. Basuli, B.C. Bailey, J.C. Huffman, M.H. Baik, D.J. Mindiola, J. Am. Chem.
Soc. 126 (2004) 1924e1925.
[25] K.K. Pandey, P. Tiwari, P. Patidar, J. Organomet. Chem. 740 (2013) 135e140.
[26] (a) K.K. Pandey, A. Lledós, J. Organomet. Chem. 695 (2010) 206e214;
(b) K.K. Pandey, P. Tiwari, P. Patidar, J. Phys. Chem. A 116 (2012) 11753e
11762;
(c) K.K. Pandey, P. Tiwari, P. Patidar, S.K. Patidar, R. Vishwakarma, P.K. Bariya,
J. Organomet. Chem. 751 (2014) (2013) 781e787.
[27] (a) A.D. Becke, Phys. Rev. A 38 (1988) 3098e3100;
[16] (a) L. Weber, U. Sonnenberg, H.G. Stammler, B. Neumann, Z. Naturforsch. B 46
(1991) 714e718;
(b) L. Weber, U. Sonnenberg, Chem. Ber. 124 (1991) 725e728;
(c) W. Malisch, K. Jörg, E. Gross, M. Schmeusser, A. Meyer, Phosphorus Sulfur
Relat. Elem. 26 (1986) 25e29;
(b) J.P. Perdew, Phys. Rev. B 33 (1986) 8822e8824.
(d) E.A.V. Ebsworth, N.T. McManus, N.J. Pilkington, D.W.H. Rankin, J. Chem.
Soc. Chem. Commun. (1983) 484e485.
[17] K.B. Dillon, F. Mathey, J.F. Nixon, Phosphorus: The Carbon Copy, John Wiley &
Sons, Ltd., Chichester, 1998, p. 30.
[18] A. Schmidpeter, S. Lochschmidt, W.S. Sheldrick, Angew. Chem. Int. Ed. Engl. 24
(1985) 226e227.
[19] P. Leoni, E. Aquilini, M. Pasquali, F. Marchetti, M. Sabat, J. Chem. Soc. Dalt.
Trans. (1988) 329e333.
[20] K. Vaheesar, C.M. Kuntz, B.T. Sterenberg, J. Organomet. Chem. 745e746 (2013)
347e355.
[21] (a) A.W. Ehlers, E.J. Baerends, K. Lammertsma, J. Am. Chem. Soc. 124 (2002)
2831e2838;
(b) G. Frison, F. Mathey, A. Sevin, J. Organomet. Chem. 570 (1998) 225e234.
[22] (a) A.W. Ehlers, K. Lammertsma, E.J. Baerends, Organometallics 17 (1998)
2738e2742;
[28] I. Mayer, Chem. Phys. Lett. 97 (1983) 270e274.
[29] A.E. Reed, R.B. Weinstock, F. Weinhold, J. Chem. Phys. 83 (1985) 735e746.
[30] J. Rusanova, E. Rusanov, S.I. Gorelsky, D. Christendat, R. Popescu, A.A. Farah,
R. Beaulac, C. Reber, A.B.P. Lever, Inorg. Chem. 45 (2006) 6246e6262.
[31] S.I. Gorelsky, AOMix Software, University of Ottawa, Ottawa, ON, 2013.
[32] M.T. Nguyen, A. Van Keer, L.G. Vanquickenborne, J. Org. Chem. 61 (1996)
7077e7084.
[33] (a) C. Hering, A. Schulz, A. Villinger, Inorg. Chem. 52 5214e5225; (b)
A.H. Cowley, R.A. Kemp, Chem. Rev. 85 (1985) 367e382.
[34] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. Montgomery, J. A., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam,
M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski,
R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador,
J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman, J.V. Ortiz,
J. Cioslowski, D.J. Fox, Gaussian 09, Revision C. 01, Gaussian, Inc., Wallingford
CT, 2009.
(b) S. Grigoleit, A. Alijah, A.B. Rozhenko, R. Streubel, W.W. Schoeller,
J. Organomet. Chem. 643e644 (2002) 223e230;
(c) J.-G. Lee, J.E. Boggs, A.H. Cowley, Polyhedron 5 (1986) 1027e1029;
(d) S. Creve, K. Pierloot, M.T. Nguyen, Chem. Phys. Lett. 285 (1998) 429e437.
[23] S. Creve, K. Pierloot, M.T. Nguyen, L.G. Vanquickenborne, Eur. J. Inorg. Chem.
(1999) 107e115.
[24] (a) H. Aktas¸ , J.C. Slootweg, A.W. Ehlers, M. Lutz, A.L. Spek, K. Lammertsma,
Organometallics 28 (2009) 5166e5172;
(b) A.T. Termaten, T. Nijbacker, A.W. Ehlers, M. Schakel, M. Lutz, A.L. Spek,
M.L. McKee, K. Lammertsma, Chem. Eur. J. 10 (2004) 4063e4072;
(c) A.T. Termaten, H. Aktas, M. Schakel, A.W. Ehlers, M. Lutz, A.L. Spek,
K. Lammertsma, Organometallics 22 (2003) 1827e1834;
[35] (a) R.S. Mulliken, J. Chem. Phys. 23 (1955) 1833e1840;
(b) R.S. Mulliken, J. Chem. Phys. 23 (1955) 1841e1846.
[36] G.M. Sheldrick, Release, 97-2 ed., 1998.
[37] L.J. Farrugia, Appl. Cryst. 32 (1999) 837e838.