Tridentate phosphine ligands bearing aza-crown ether lariats

Article abstract of DOI:10.1016/j.poly.2017.11.012

Crown ethers are useful macrocycles that act as size-selective binding sites for alkali metals. These frameworks have been incorporated into a number of macromolecular assemblies that use simple cations as reporters and/or activity triggers. Incorporating crown ethers into secondary coordination sphere ligand frameworks for transition metal chemistry will lead to new potential methods for controlling bond formation steps, and routes that couple traditional ligand frameworks with these moieties are highly desirable. Herein we report the syntheses of a family of tridentate phosphine complexes bearing tethered aza-crown ethers (lariats) designed to modularize the variation of aza-crown size, lariat length, and distal phosphine substituents, followed by the synthesis and solid-state structures of Mo(III) complexes bearing cations in the pendent crown ethers.

Full text of DOI:10.1016/j.poly.2017.11.012

Polyhedron xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Tridentate phosphine ligands bearing aza-crown ether lariats
⇑
Levente G. Pap, Navamoney Arulsamy, Elliott B. Hulley
Department of Chemistry, University of Wyoming, Dept. 3838, 1000 E. University Avenue, Laramie, WY 82071, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Crown ethers are useful macrocycles that act as size-selective binding sites for alkali metals. These frame-
works have been incorporated into a number of macromolecular assemblies that use simple cations as
reporters and/or activity triggers. Incorporating crown ethers into secondary coordination sphere ligand
frameworks for transition metal chemistry will lead to new potential methods for controlling bond for-
mation steps, and routes that couple traditional ligand frameworks with these moieties are highly desir-
able. Herein we report the syntheses of a family of tridentate phosphine complexes bearing tethered aza-
crown ethers (lariats) designed to modularize the variation of aza-crown size, lariat length, and distal
phosphine substituents, followed by the synthesis and solid-state structures of Mo(III) complexes bearing
cations in the pendent crown ethers.
Received 7 October 2017
Accepted 8 November 2017
Available online xxxx
Keywords:
Phosphine
Crown ether
Molybdenum
Alkali metal
Heterobimetallic
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
of the ligand framework could be tuned, such as the size of the
crown ether, lariat length, and distal phosphine substituents. A
Since their discovery by Pedersen [1], crown ethers have proved
to be extremely useful binding sites for alkali metals cations. One
of the most important properties of crown ether chemistry is the
size-dependence of cation binding, largely dictated by the inner
size of the macrocycle. In addition to alkali metals, these host
molecules are able to bind a wide range of ionic and neutral species
[2–5], and have been utilized as chemical modulators in a wide
range of ion-selective applications [2,4,6–10]. In transition metal
(TM) chemistry, secondary coordination sphere modifications have
become an important way of modulating stoichiometric and cat-
alytic activity [11–14]. Secondary coordination sphere modifica-
tions of TMs involving control of simple cations and their
interactions with TM-bound substrates are a relatively under-
explored area. McLain was among the first to investigate such sys-
tems, reporting studies of alkyl insertion promoted by tethered
alkali metals [15,16], and systematic studies of cation-substrate
interactions have had renewed interest [17,18]. Our laboratory
has been developing multidentate lariat-ether phosphine ligands
in order to further investigate the secondary coordination effects
of tethered cations on catalytic and stoichiometric reactions of
both polar and non-polar substrates. Herein we report the modular
synthesis of a family of such phosphines bearing aza-crown ethers.
Our overall goal was to develop a modular synthetic pathway to
tridentate phosphine ligands tethered to aza-crown ethers (lari-
ats). A critical aspect of our synthetic strategy was that key features
key intermediate in this approach is an aza-crown tethered phos-
phonate, wherein the –(CH2)n– tether is established directly
between aza-crown ether and phosphonate precursors. Several
examples of such compounds have been prepared, most notably
by Keglevich (n = 2–5) [19–21]; the chemistry we present here
has focused on just two lariat lengths (–CH2– and –CH2CH2–),
but can be readily extended to these longer-lariat precursors.
2. Results and discussion
2.1. Synthesis of lariat primary phosphines
Entry into the target framework (Scheme 1) began with aza-
macrocycles 1-aza-15-crown-5 (1a) and 1-aza-18-crown-6 (1b)
[22], where control of the linker length between N and P atoms
is readily accomplished via various nucleophilic addition
strategies.
Routes toward amine-tethered phosphonates and phosphonate
esters have been previously reported [16,20–26], however reduc-
tion to the primary phosphines and further homologation has (to
our knowledge) not been reported.
A single CH2 linker can be installed by the Kabachnick-Fields
reaction as outlined by the Keglevich group [27–29]. The aza-
crown ether 1a condenses with formaldehyde and diethylphos-
phonate under microwave conditions to form 2a. At this stage,
the pure phosphonate can be isolated after extraction with triethy-
lamine, which can be reduced to the primary phosphine 3a with
LiAlH4 in Et2O. The primary phosphine is highly reactive; the N–
⇑
Corresponding author.
E-mail address: ehulley@uwyo.edu (E.B. Hulley).
https://doi.org/10.1016/j.poly.2017.11.012
0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.
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2
L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
15
(CH2O)n
conc. HCl
HP(O)(OEt)2
O
O
15
1,2
N
15,18
LiAlH4
N
O
O
O
N
H
H
N
P
THF
80°C
(5W wave)
Et2O
0°C
PH2
OEt
EtO
2a
1 a,b
15= 1-Aza-15-Crown-5
18= 1-Aza-18-Crown-6
3a
O
P
H2O
reflux
O
O
15, 18
15,18
15,18
N
( )n
P
N
N
LiAlH4
R2P
PR2
Et2O
0°C
6 a (n=1, R = Ph)
7 a,b (n=2, R = Ph)
8 a,b (n=2, R = iPr)
9 a,b (n=2, R = Et)
PH2
5 a,b
P
OEt
OEt
O
4 a,b
Scheme 1. Synthesis of primary phosphines synthons 3 and 5 used for the synthesis of tridentate lariat phosphines 6–9.
CH2–P linkage is prone to hydrolytic and/or radical cleavage (see
below), severely limiting the possible purification/derivatization
steps.
15
15
N
N
Ligands and ligand precursors based on the ethylene spacer are
far more robust and offer a wider variety of synthetic approaches.
The ethylene-linked aza-crown phosphonates 4a and 4b were pre-
pared via Michael addition to diethylvinylphosphonate in refluxing
water using a modification of published procedures [20,21], Reduc-
tion to the primary phosphine proceeded in the same manner as
with 2a, by the action of LiAlH4 in Et2O. Although the reduction
ultimately produces good yields of these aza-crown tethered pri-
mary phosphines, the work-up is somewhat cumbersome. Follow-
ing a published LiAlH4 quenching procedure [30], a prescribed
portion of water, LiOH solution, and a second portion of water
are slowly added to the cooled reaction solution. No matter how
slowly the quenching steps are performed, quenching is very
uneven and prone to rapid heating and boiling of the ether solvent.
Intramolecular binding of intermediate Li+- or AlXn+-phosphides to
the crown is possible [31], leading to precipitation and subsequent
irregular hydrolysis kinetics.
PH2
PH2
3a
5a
– 146
– 147
– 148
– 171
– 172
– 173
ppm
ppm
Fig. 1. 31P NMR spectra of 3a and 5a, highlighting the primary, secondary and
tertiary P–H couplings.
The single-carbon spacing between the phosphine and nitrogen
in 3a leads to a significant upfield shift of the 31P resonance relative
to the longer 5a and 5b (Fig. 1). Moreover, in contrast to the
expected trends, the JPH and JPH couplings between the primary
phosphine and methylene protons in 5a and 5b are essentially
the same magnitude (5 Hz), leading to a triplet of pentets in the
proton-coupled 31P NMR spectrum.
2.2. Assembling the tridentate TM-binding environment
2
3
The overall objective is to design a scalable and modular syn-
thesis of these frameworks so that we could systematically inves-
tigate the impacts of substituents and linker length on alkali metal-
substrate interactions in TM complexes. To that end, we initially
focused on using primary phosphine synthons and rely on addition
of the P-H bonds across the C@C bonds in vinylphosphines and
vinylphosphonates [32,33]. We investigated both radical-initiated
and anion-catalyzed variations of these reactions.
Although the radical-initiated approach works well for the more
robust 5a and 5b (see below), the single-methylene linked 3a did
not survive radical coupling conditions without significant byprod-
ucts. Instead we have found that 3a is readily amenable to anionic
We have exclusively used Li+ salts when it has been necessary to
expose intermediates to cationic reagents. Crown ethers are
designed to carry cations into organic solutions, an obvious potential
problem for our future studies if the preparation of non-metalated
crown intermediates were impossible. Li+ usually has lower binding
affinity in the larger unsubstituted macrocycles (e.g. aza-15-crown-
5 and aza-18-crown-6) when compared to other cations [20,21], and
thus the complications from cation binding are minimized.
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L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
3
coupling conditions with diphenylvinylphosphine to synthesize 6a
in 87% yield.
our products and residual vinylphosphine are observable in crude
reaction mixtures by 31P NMR spectroscopy if the reaction is run
for the prescribed time. In the case of R = iPr (8a and 8b) reactions
that ran for more than a day led to significant amounts (24%) of a
side product that was consistent with a compound consisting of
multiple P–P bonds (Fig. S24). After coupling and removal of excess
vinylphosphine in vacuo, 8a and 8b are sufficiently free of impuri-
ties to be isolated as-is, whereas crude 9a and 9b require purifica-
tion steps similar to those for 7a/7b. The viscous and oily crude
products are layered on a silica pad and washed with hexane, fol-
lowed by a 1:1 mixture of dichloromethane and hexane (these
washings contain byproducts and are discarded). The silica is then
washed with dichloromethane and the clean products 9a and 9b
are isolated as light yellow oils (in 90% and 89% yields,
respectively).
P
2
Ph
Ph
15
15
tBuOLi
N
N
THF
65 °C
Ph2P
PPh2
P
PH2
3a
6a
The product 6a can be prepared very cleanly; excess
diphenylvinylphosphine can be removed via hexane extraction of
a methanolic solution of 6a. Attempts to purify 6a via silica gel
chromatography led to hydrolysis of the methylene spacer and
isolation of only the deformylated secondary phosphine.
2.3. Attempted alternative strategies and side products
15
We had initially hoped that we would be able to access a wider
range of R-group substitutions on the distal phosphines via the
route highlighted in Scheme 3.
Primary phosphine 5b reacted with diethylvinylphosphonate
under anionic conditions (a solution was cooled to À78 °C and a
LiOtBu in THF was added dropwise over 5 min) to yield diphospho-
nate 10b, which was reduced to the triphosphine 11b with LiAlH4
in 77% yield.
N
H
15
silica gel
– "CH2O"
Ph2P
PPh2
+
P
N
H
Ph2P
PPh2
P
6a
Due to these difficulties in purification, 6a was the only methy-
lene-separated derivative that we could isolate in analytically pure
form. Other derivatives of this ligand framework can nonetheless
be prepared via this method and used (unpurified) for the forma-
tion of metal complexes; work in this area is still ongoing.
Although assembly of the tridentate framework from ethylene-
linked 5a and 5b worked rather well under anionic conditions, we
found it synthetically expedient to rely instead on radical-initiated
couplings (Scheme 2).
The initial (perhaps overly optimistic) hope was to chlorinate
the distal phosphine arms of 11b so that we might be able to alky-
late or arylate with a variety of nucleophilic reagents [34], however
we were unable to find chlorination conditions that reliably made
isolable amounts of the proposed tetrachloride 12b. We were
unable to cleanly synthesize 12b despite thirty-five distinct chlori-
nation conditions with different chlorine sources (PCl5, PCl3, phos-
gene, and C2Cl6). On one occasion we were able to observe
conversion to a new compound consistent with the proposed 12b
in roughly quantitative yield on NMR scale (30 mg) with PCl5
(Figs. S37–S39), but due to irreproducibility and its high reactivity
we were unable to optimize this reaction nor isolate the product.
The 31P NMR resonance associated with the central phosphine of
12b is quite broad, implying chemical exchange, and sharpens
somewhat upon application of broadband 1H-decoupling. We
hypothesize this species is protonated at the aza-crown nitrogen
and engages in reversible binding with the central phosphine.
i
All six derivatives of this framework (R = Ph, Pr, Et for the aza-
15-crown-5 and aza-18-crown-6 macrocycles) can be synthesized
in consistently good yields. The phenyl-derivatives 7a/7b were
prepared from radical-initiated coupling of primary phosphines
5a/5b with diphenylvinylphosphine for 18 h in refluxing THF.
Depending on the cleanliness of the radical reaction, the resulting
viscous, pale yellow oils can sometimes be used without purifica-
tion, otherwise they are purified by distributing over a silica pad
and washing with hexane to remove excess diphenylvinylphos-
phine. The silica was then washed with THF and the solvent was
removed from the filtrate under reduced pressure to yield the
products as viscous oils in yields of 89–94% (over a dozen synthetic
trials). Similarly, the isopropyl derivatives 8a/8b and ethyl deriva-
tives 9a/9b could be synthesized by radical coupling with their
respective vinylphosphine precursors for 6 h. In all cases, only
O
P
2
OEt
OEt
LiOtBu
18
18
N
N
O
O
THF (–78 ºC to 22 ºC)
(EtO)2P
P(OEt)2
PH2
5 b
P
10 b
15,18
N
Et2O
0°C
LiAlH4
5a,b
AIBN
THF (reflux)
AIBN
THF (reflux)
Cl–
PH2
2
PPh2
2
PEt2
31P NMR:
19.0, t (broad)
184.9, d
18
+
NH
18
AIBN
THF (reflux)
PiPr2
2
N
J
P-P = 20 Hz
4 PCl5
15,18
15,18
15,18
CH2Cl2
Cl2P
PCl2
H2P
PH2
N
P
P
N
N
12 b
11 b
proposed
Et2P
iPr2P
PEt2
PPh2
PiPr2
Ph2P
P
not yet isolated
P
P
9 a,b
7 a,b
8 a,b
Scheme 3. Synthesis of triphosphine 11b from 5b (via 10b) and its proposed
Scheme 2. Assembly of the tridentate scaffold from primary phosphines 5a and 5b.
chlorination.
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L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
iPr
Cl
Indeed, it seems likely the amine moiety of the aza-crown is
responsible for complicating chlorination reactions.
15,18
iPr
P
N
P
Mo
Cl
15,18
+ MoCl3(THF)3
PiPr2
Cl
We have also noticed that the ethylene-bridged primary phos-
phine 5b and/or its alkylation products may not be sufficiently
stable to radical coupling conditions when using electron-poor
alkenes. During the course of our studies we discovered that
although 10b formed under radical coupling conditions with
diethylvinylphosphonate, it formed in a roughly 1:1 ratio with a
new 31P-containing species consistent with tetraphosphine 13
(with concomitant formation of aza-crown 1b).
P
iPr
N
iPr2
P
iPr
P
8a, 8b
Na(NTf2
)
Ca(OTf)2
–
NTf2
iPr
iPr
Cl
Cl
iPr
iPr
P
P
18
P
P
P
Na+
Mo
Cl
Mo
Cl
OTf
N
O
Cl
P
Cl
TfO
iPr
N
iPr
Ca2+
15
iPr
iPr
(8a[Ca(THF)(OTf)2])MoCl3
[(8b[Na])MoCl3][NTf2]
O
P
2
OEt
OEt
18
18
Scheme 4. Metallation of 8a and 8b with MoCl3(THF)3 and complexation with Ca
(OTf)2 and Na(NTf2), respectively.
18
O
N
AIBN
P
N
N
H
+
+
P(OEt)2
3
O
O
75°C
(EtO)2P
P(OEt)2
13
1b
P
PH2
5 b
6 b
crystalline materials, we were able to crystallize two ‘salted’
derivatives.
Treatment of solutions of intermediates (8a)MoCl3 or (8b)
MoCl3 with a variety of simple salts led to significant changes in
the 1H NMR spectra, but the latent paramagnetism and high spec-
tral complexity prevented determining binding metal coefficients.
We were able to crystallize new products in two cases, (8a)MoCl3
with Ca(OTf)2 and (8b)MoCl3 with Na(NTf2), by addition of 1.2
equivalents of metal salt to solutions of the Mo(III) precursors (in
ether/THF/toluene 1:1:1). (Figs. 3 and 4). The (P3)MoCl3 cores in
(8a[Ca(OTf)2(THF)])MoCl3 and [(8b[Na])MoCl3][NTf2] are nearly
isostructural and are similar to other (mer-triphosphine)MoCl3
complexes [36–39], where the Mo–Cl distances are all between
2.38 and 2.44 Å and the Mo–P distances are between 2.46 and
2.47 Å for the central phosphine and 2.55–2.57 Å for the distal
phosphine arms (see Table 1). The calcium complex (8a[Ca(OTf)2(-
THF)])MoCl3 bears an eight-coordinate calcium atom (best
described as a square-faced bicapped trigonal prism) that binds
both triflate anions and a THF molecule, a coordination geometry
that appears to be common for Ca2+ complexes of 15-crown-5
derivatives [3,40–42]. The cation/crown size mismatch of the
Ca2+ complex is notable, as engineering such ‘‘destabilized” sys-
tems may prove critical for the type of secondary coordination
sphere interactions we are investigating. In contrast to the overall
neutral [Ca2+]/Mo complex, the sodium complex [(8b[Na])MoCl3]
[NTf2] manifests as a salt in the solid state, with the distorted pen-
tagonal bipyramidal Na+ ion preferring to interact with the chlo-
ride of an adjacent complex and forming a 1D-chain coordination
polymer (d(Mo–ClÁ Á ÁNa) = 2.8478(8) Å). The Mo–Cl bond trans to
the trialkylphosphine in [(8b[Na])MoCl3]+ is marginally longer
than that in (8a[Ca(OTf)2(THF)])MoCl3 (2.4478(5) Å versus 2.439
(2) Å, respectively), thus there is a slight perturbation from the
Mo–ClÁÁÁNa interaction on the ground state structure of the Mo
(III) core. Unlike triflate, interactions between the triflimide anion
with other alkali and alkaline earth metals are relatively rare out-
side of the parent salts [43–46]. The sodium is thus rendered suf-
ficiently electrophilic to distort the crown (moving the nitrogen
of the aza-crown to a pseudoaxial position) and interact with the
Mo-bound chloride.
Since it is a relatively electron-poor alkene, it is plausible that
diethylvinylphosphonate reacts with phosphinyl radicals rather
slowly and P–C bond cleavage (and subsequent fragmentation) of
intermediate radicals is competitive with alkene addition. Although
we have not independently synthesized 13, the 31P NMR spectrum
of 13 is nearly identical to that observed for the previously reported
isopropyl variant P(CH2CH2(PO(OiPr)2)3 (Fig. 2) [35].
2.4. Molybdenum phosphine complexes bearing tethered cations
We have begun to explore the coordination chemistry of these
lariat phosphine ligands in Mo systems, giving particular attention
to the nature of the binding of simple alkali metal cations in the
crown ether moieties. Of the lariat phosphines prepared above,
only two of the ligands (8a and 8b) have thus far resulted in the
eventual formation of crystalline Mo-based products. The lack of
crystallinity might be expected for compounds with large confor-
mational flexibility (the pure ligands themselves all manifest as
liquids under ambient conditions), but we anticipated that locking
the crown ether via cation binding would assist in the isolation of
crystalline products.
As with related Mo(III) phosphine complexes, substitution of
the THF ligands of MoCl3(THF)3 is facile and rapid (Scheme 4),
and substitution is evident by the conversion of the pale orange
suspension of MoCl3(THF)3 to dark brown solutions of (8a/8b)
MoCl3 complexes within 2–3 min. These complexes, highly soluble
in halogenated solvents, are isolable as pale orange powders upon
precipitation with ether. We screened a variety of alkali and alka-
line earth salts (Li+, Na+, K+, Mg2+, Ca2+) of non-coordinating anions
(OTfÀ, NTf2À, B(C6F5)4À) in an effort to see evidence of cation capture
and potential interactions with metal-bound ligands. Thus
although the parent compounds (8a/8b)MoCl3 do not manifest as
We found the use of ethereal solvents to be necessary for ade-
quate solvation of the alkali and alkaline earth metal salts, but
crown ether capture of Ca2+ (by 8a) and Na+ (by 8b) is sufficiently
reversible under these conditions that bulk products contained co-
crystallized Ca(OTf)2 or Na(NTf2). Thus although crystals of highly-
soluble (8a[Ca(OTf)2(THF)])MoCl3 and (8b[Na])MoCl3 were isolable
(in low yields, 5–10%), they were both found to be mixed with
crystals of Ca(OTf)2 or Na(NTf2) [47], respectively, and as a result
could not be isolated in bulk crystalline form.
O
O
P
P
P(OiPr)2
P(OEt)2 3
3
–19.1, q (JP-P = 49.6 Hz), 1P
29.4, d (JP-P = 49.6 Hz), 3P
ref 34
–18.8, q (JP-P = 51 Hz), 1P
30.4, d (JP-P = 51 Hz), 3P
this work
Fig. 2. Comparison of 31P NMR spectral data of proposed 13 and known compound
P(CH2CH2(PO(OiPr)2)3.
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L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
5
Fig. 3. Solid-state structure of (8a[Ca(OTf)2(THF)])MoCl3. Crystallization solvent (THF) and hydrogen atoms have been omitted for clarity.
Fig. 4. Solid-state structure of (8b[Na])MoCl3 with two adjacent asymmetric units shown to highlight intermolecular Mo–ClÁ Á ÁNa interactions. Hydrogen atoms and the
triflimide anions ((CF3SO2)2NÀ, one per Na) have been omitted for clarity.
Table 1
3. Conclusion
Comparison of selected solid-state structure metrics of (8a[Ca(OTf)2(THF)])MoCl3 and
of [(8b[Na])MoCl3[NTf2].The data for [(8b[Na])MoCl3[NTf2] refer to the majority
disorder component (85%).
A general method for the preparation of tridentate phosphine
ligands bearing lariat crown-ethers has been developed. In addi-
tion to the systems outlined here, the overall approach is likely
to be general for polydentate phosphine aza-crown lariats of essen-
tially any lariat length. Such variations could help to tune the inter-
actions between encapsulated alkali metals and TM-bound
substrates, which is our particular interest, but may also find use
in a host of other applications. We have begun to develop a family
of Mo-based systems based on this ligand architecture and pre-
sented two examples of crystallographically-characterized Mo(III)
complexes bearing pendent cations. The reduction chemistry of
complexes of this type are currently under exploration and will
be the subject of a future publication.
(8a[Ca(OTf)2(THF)])MoCl3
[(8b[Na])MoCl3][NTf2]
d(Mo–Cl1), Å
d(Mo–Cl2), Å
d(Mo–Cl3), Å
d(Mo–P1), Å
d(Mo–P2), Å
d(Mo–P3), Å
\(Cl1–Mo–Cl2), °
\(Cl1–Mo–Cl3), °
\(Cl2–Mo–Cl3), °
\(P1–Mo–P2), °
\(P1–Mo–P3), °
\(P2–Mo–P3), °
2.439(2)
2.444(2)
2.390(2)
2.461(2)
2.553(1)
2.572(2)
92.96(5)
92.88(5)
173.72(5)
78.84(5)
77.54(5)
156.21(5)
2.4478(5)
2.3814(8)
2.4416(8)
2.4689(5)
2.5741(7)
2.5613(8)
90.59(3)
93.73(2)
174.05(3)
78.07(2)
78.59(2)
156.03(3)
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6
L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
PH2CH2N), d 53.9 ppm (s, 2C, NCH2CH2O), d 69.7 ppm (s, 2C, OCH2-
4. Experimental section
CH2N), d 70.2 ppm (s, 2C, OCH2CH2O), d 70.5 ppm (s, 2C, OCH2CH2-
O), d 71.0 ppm (s, 2C, OCH2CH2O). 31P NMR (CDCl3): d À172.2 ppm
All manipulations were conducted under N2, Ar or using high-
vacuum line and glovebox techniques unless otherwise noted. All
ambient-pressure chemistry was carried out under a pressure of
approximately 590 torr (elevation ꢀ7220 ft) and a temperature of
22 3 °C unless otherwise stated; a table of pressure-corrected
boiling points for the solvents used in this manuscript are reported
in the Supplementary Material. All solvents were dried using an
Innovative Technologies PureSolv Solvent Purification System.
Deuterated solvents used in NMR studies were dried over activated
3 Å molecular sieves. NMR spectra were obtained with a Bruker
DRX-400 or Bruker DRX-600 instruments using 5 mm NMR tubes
fitted with re-sealable Teflon valves; reported spectral data were
acquired at 400 MHz unless otherwise noted. 1H and 13C NMR
spectra were referenced internally to either tetramethylsilane or
residual protic solvent peaks. 31P NMR spectra were referenced
to an 85% H3PO4 external standard. Reagents were purchased from
Sigma–Aldrich and used without further purification. High-resolu-
tion mass spectroscopy (HRMS) data were obtained on an AB Sciex
5800 MALDI-TOF mass spectrometer. Calibration were performed
internally by Poly(ethylene glycol) 600 and 2,5-dihydroxybenzoic
acid was used as a matrix. Air sensitive samples were prepared
in a glove box and were carried to the mass spectrometer in a
sealed container. The same loading procedure was used for all sam-
ples and the exposure to O2 while loading was limited to 10–15 s
followed by a 25 s pump down time. Diethylvinylphosphonate,
diethylphosphonyl chloride, diphenylphosphonyl chloride, diiso-
propyl phosphonyl chloride, and MoCl5 were purchased and used
as received. The phosphine starting materials 2a [20], 4a [20],
diethylvinyl phosphine [48], diphenylvinyl phosphine [49], and
diisopropylvinyl phosphine [50] were synthesized according to a
modification of literature procedures (details in Supporting Infor-
mation). Representative syntheses for 3a, 5a and 8a are presented
here; synthetic and analytical details for the other compounds dis-
cussed in this report are available in the Supplementary Material.
1
3
(tt, 1P, JP-H = 196.2 Hz, JP-H = 8.4 Hz, PH2); HRMS (MALDI-TOF):
MLi+, found 272.16585. C11H24NO4PLi+ requires 272.15975.
4.2. 13-(2-Phosphanylethyl)-1,4,7,10-tetraoxa-13-
azacyclopentadecane) (5a)
A 100 mL Schlenk flask was charged with 4a (3.92 g, 10.2
mmol), a stir bar and 10 mL Et2O under N2 atmosphere. The system
was sealed with a rubber septum and taken out of the glovebox,
placed under Ar atmosphere, and cooled down to 0 °C. A suspen-
sion of LiAlH4 (1.4 g, 37 mmol) in 10 mL Et2O was prepared and
loaded into a syringe with a large-gauge needle (all in the glove-
box) and was added slowly, over the course of 10 min to the solu-
tion of 4a. Note: Gas generation upon addition of LiAlH4 is
substantial and requires sufficient ventilation to prevent over pres-
surizing. After addition, the reaction was allowed warm up to room
temperature. Solvent was evaporated and 15 mL deoxygenated DI
H2O was added, followed by 15 mL 10% aqueous LiOH, and then
another 10 mL DI H2O were slowly added to the solid material
(all dropwise) over the course of 1 h to quench the excess LiAlH4.
Note: It is crucial to perform the quenching slowly! Fast addition
of water can result in dark/black side products. After quenching,
the water was evaporated under high-vacuum at 50 °C. The result-
ing solid white powder was taken into the glovebox, extracted with
THF (5 Â 10 mL) and filtered through a Celite pad. Solvent was
removed in vacuo and the resulting colorless, pale yellow oil was
used without any further purification (2.29 g, 80%). 1H NMR
1
(CDCl3): d 1.65 ppm (m, 2H, PCH2CH2N), d 2.61 ppm (dtt, 2H, JH-
2
4
P = 195.70 Hz, JH-H = 7.26 Hz, JH-H = 6.00 Hz, NCH2CH2PH2),
d
3
2.71 ppm (m, 2H, PCH2CH2N), d 2.77 ppm (t, 4H, JH-H = 6.0 Hz,
OCH2CH2N), d 3.59 ppm (m, 16H, OCH2CH2O and OCH2CH2N). 13C
{1H} NMR (CDCl3): d 11.8 ppm (d, JC-P = 9.5 Hz, PCH2CH2N), d
1
1
27.5 ppm (d, JC-P = 4.3 Hz, NCH2CH2P), d 53.7 ppm (s, NCH2CH2O),
d 70.1 ppm (s, NCH2CH2O), d 70.5 ppm (s, OCH2CH2N), d 70.8 ppm
(s, OCH2CH2O), d 70.9 ppm (s, OCH2CH2O). 31P NMR (CDCl3): d
1
2
3
4.1. 13-(2-Phosphanylmethyl)-1,4,7,10-tetraoxa-13-
azacyclopentadecane) (3a)
À147.2 ppm (ttt, JP-H = 195.7 Hz, JP-H = 5.0 Hz, JP-H = 4.1 Hz);
HRMS (MALDI-TOF): MH+, found 280.17163. C12H26NO4PH+
requires 280.16722.
A 100 mL Schlenk flask was charged with 1-aza-15-crown-5-
methyl-phosphonate (1.00 g, 2.707 mmol), a magnetic stir bar
and Et2O (10 mL) under N2 atmosphere. The system was sealed
with a rubber septum and taken out of the glovebox, placed under
Ar atmosphere, and cooled down to 0 °C. A suspension of LiAlH4
(463 mg, 12.1 mmol) in 10 mL Et2O was prepared and loaded into
a syringe with a large-gauge needle (all in the glovebox) and was
added slowly, over the course of 10 min to the solution of 2a. Note:
Gas generation upon addition of LiAlH4 is substantial and requires
sufficient ventilation to prevent over pressurizing. After addition,
the reaction was allowed warm up to room temperature. Solvent
was evaporated and 15 mL deoxygenated DI H2O was added to
the solid material, followed by 15 mL 10% aqueous LiOH, and then
another 10 mL DI H2O (all dropwise) over the course of 1 h to
quench the excess LiAlH4. Note: It is crucial to perform the quench-
ing slowly! Fast addition of water can result in dark/black side
products. After quenching, the water was evaporated under high-
vacuum at 50 °C. The resulting solid white powder was taken into
the glovebox, extracted with THF (5 Â 15 mL) and filtered through
a Celite pad. Solvent was removed in vacuo and the resulting color-
less, pale yellow oil was used without any further purification
(521 mg, 72%). 1H NMR (CDCl3): d 2.48 ppm (m, 2H, H2PCH2N), d
4.3. 13-(2-(Bis(2-(diphenylphosphanyl)ethyl)phosphanyl) ethyl)-
1,4,7,10-tetraoxa-13-azacyclopentadecane) (7a)
A 50 mL Schlenk flask was charged with 5a (2.285 g, 8.179
mmol), a magnetic stir bar, diphenylvinylphosphine (3.476 g,
16.38 mmol), AIBN (88 mg, 0.5359 mmol) and 15 mL THF under
N2 atmosphere. The sealed system was taken out of the glovebox
and heated to reflux for 18 h under Ar atmosphere. Upon cooling
the solvent was removed in vacuo yielding a light-yellow oil which
was used without any further purification (5.431 g, 94%). 1H NMR
(CDCl3): d 1.46 ppm (m, 4H, Ph2PCH2CH2P), d 1.55 ppm (m, 2H,
PCH2CH2N), d 2.02 ppm (m, 4H, Ph2PCH2CH2P), d 2.58 ppm (m, 2H,
PCH2CH2N), d 2.72 ppm (m, 4H, 3JH-H = 6.29 Hz, NCH2CH2O), d 3.66
m,
ppm (m, 16H, OCH2CH2O and OCH2CH2N), d 7.32 ppm (m, 12H,
pPh), d 7.39 ppm (m, 8H, oPh). 13C{1H} NMR (CDCl3): d 22.0 ppm (t,
1
1
2C, JC-P = 15.5 Hz, (PCH2CH2PPh2), d 23.7 ppm (t, 2C, JC-P = 13.4
1
Hz, Ph2PCH2CH2P), d 24.1 ppm (d, 1C, JC-P = 16.95 Hz, PCH2CH2N),
d 53.4 ppm (d, 1C, JC-P = 17.1 Hz, NCH2CH2P), d 54.1 ppm (s, 2C,
2
NCH2CH2O), d 70.0 ppm (s, 2C, NCH2CH2O), d 70.2 ppm (s, 2C,
OCH2CH2O), d 70.4 ppm (s, 2C, OCH2CH2O), d 71.0 ppm (s, 2C, OCH2
CH2O), d 128.5 ppm (d, 4C, 3JC-P = 6.5 Hz, mPhA
+
mPhB), d 128.6 ppm
3
2.77 ppm (t, 4H, JH-H = 5.95 Hz, OCH2CH2N); d 3.63 ppm (m, 16H,
(s, 2C, 4JC-P = 2.8 Hz, pPhA), d 128.7 ppm (s, 2C, 4JC-P = 2.8 Hz, pPhB), d
1
3
2
OCH2CH2O); d 3.71 ppm (dt, 2H, JH-P = 196.2 Hz, JH-H = 8.4 Hz,
132.6 ppm (d, 4C, JC-P = 18.2 Hz, JC-P = 4.4 Hz, oPhA), d 132.8 ppm
NCH2PH2). 13C{1H} NMR (CDCl3): d 27.5 ppm (d, 1C, JC-P = 5.7 Hz,
(d, 4C, 2JC-P = 18.2 Hz, JC-P = 4.4 Hz, PhB), d 138.2 ppm (d, 2C, PhA),
1
o
i
Please cite this article in press as: L.G. Pap et al., Polyhedron (2017), https://doi.org/10.1016/j.poly.2017.11.012

L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
7
d 138.4 ppm (d, 2C, iPhB). 31P{1H} NMR (CDCl3): d À12.7 ppm
authors thank Kasey Trotter (funded by the Wyoming Research
Scholars Program) for experimental assistance, Profs. Dean Roddick
and Robert Corcoran for helpful discussions, and Prof. Ed Clennan
for the use of his microwave reactor. We also are grateful to Prof.
Franco Basile for the use of an AB Sciex 5800 MALDI-TOF mass
spectrometer, the acquisition of which was made possible by the
National Science Foundation (NSF-MRI CHE-1429615).
3
3
(d, JP-P = 26.7 Hz), d À23.7 ppm (t, JP-P = 26.7 Hz). HRMS (MALDI-
TOF): MH+, found 704.32629. C40H52NO4P3H+ requires 704.31820.
4.4. X-ray crystallography
The X-ray diffraction data for (8a[Ca(OTf)2(THF)])MoCl3 and
[(8b[Na])MoCl3][NTf2] were measured at 100 K on a Bruker SMART
APEX II CCD area detector system equipped with a graphite
Appendix A. Supplementary data
monochromator and a Mo K
a fine-focus sealed tube operated at
1.5 kW power (50 kV, 30 mA). The crystals were mounted on MiTe-
Gen micromounts using Paratone N oil and the detector was placed
at a distance of 5.13 cm from the crystal during the data collection.
A series of narrow frames of data were collected for each of the
CCDC 1578149 and 1578148 contains the supplementary crys-
tallographic data for 8a[Ca(OTf)2(THF)]MoCl3 and [(8b[Na])MoCl3]
[NTf2]. These data can be obtained free of charge via http://www.
ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Sup-
plementary data associated with this article can be found, in the
online version, at https://doi.org/10.1016/j.poly.2017.11.012.
crystals with a scan width of 0.5° in
x or / and an exposure time
of 10 s per frame. The frames were integrated with the Bruker
SAINT Software package using a narrow-frame integration algo-
rithm [51]. The data were corrected for absorption effects by the
multi-scan method (SADABS) [52]. Crystallographic data collection
parameters and refinement data are collected below in Table 1.
The structure was solved by the direct methods using SHELXTL as
implemented in the Bruker APEX2 (V. 6.14) Software Package
[53,54]. All non-hydrogen atoms were located in successive Fourier
maps and refined anisotropically. Complete crystallographic
details are available in the Supplementary Material (Table S2).
Compound (8a[Ca(OTf)2(THF)])MoCl3 crystallizes in the mono-
clinic system belonging to the P21/n space group. The yellow rect-
angular plates were grown from THF solutions. The crystals are air
sensitive and diffracted poorly (R1 = 7.31%; Rint = 23.5%) – we sus-
pect the Ca2+ in renders the complex highly hygroscopic. The
asymmetric unit contains one complex molecule and one solvated
THF molecule. All non-hydrogen atoms except those of the THF sol-
vate are located in successive Fourier maps and refined anisotrop-
ically. All H atoms were placed in calculated positions and refined
isotropically adopting a riding model with fixed positional param-
eters. One of the ethylene linkages in the clathrate is disordered
and the disorder is modeled by assigning two sets of positions
for the associated C and H atoms. The Ca2+ cation is coordinated
to the clathrate oxygen atoms, two triflate anions and a THF mole-
cule. Although the calcium-bound THF is well ordered, the solvated
THF is highly disordered and refinements did not satisfactorily
converge on a reasonable solution. The data were therefore cor-
References
[1] C.J. Pedersen, J. Am. Chem. Soc. 89 (1967) 2495.
[2] G.W. Gokel, J.F. Stoddart, Crown Ethers and Cryptands, Royal Society of
Chemistry, Cambridge, 2016.
[3] J.W. Steed, Coord. Chem. Rev. 215 (2001) 171.
[4] L. Yang, D.-J. Liao, A. Wu, H. Yan, Tetrahedron Lett. 58 (2017) 889.
[5] G.W. Gokel, D.M. Goli, C. Minganti, L. Echegoyen, J. Am. Chem. Soc. 105 (1983)
6786.
[6] R. Cacciapaglia, L. Mandolini, Chem. Soc. Rev. 22 (1993) 221.
[7] G.G. Talanova, Ind. Eng. Chem. Res. 39 (2000) 3550.
[8] M.R. Kita, A.J.M. Miller, J. Am. Chem. Soc. 136 (2014) 14519.
[9] J. Grajeda, M.R. Kita, L.C. Gregor, P.S. White, A.J.M. Miller, Organometallics 35
(2016) 306.
[10] M.R. Kita, A.J.M. Miller, Angew. Chem. Int. Ed. 56 (2017) 5498.
[11] R.L. Lucas, M.K. Zart, J. Murkerjee, T.N. Sorrell, D.R. Powell, A.S. Borovik, J. Am.
Chem. Soc. 128 (2006) 15476.
[12] M. Rakowski DuBois, D.L. DuBois, Acc. Chem. Res. 42 (2009) 1974.
[13] S. Raugei, S. Chen, M.-H. Ho, B. Ginovska-Pangovska, R.J. Rousseau, M. Dupuis,
D.L. DuBois, R.M. Bullock, Chem. - A Eur. J. 18 (2012) 6493.
[14] D.L. Miller, B.J. Boro, K. Grubel, M.L. Helm, A.M. Appel, Eur. J. Inorg. Chem. 2015
(2015) 5781.
[15] S.J. McLain, J. Am. Chem. Soc. 105 (1983) 6355.
[16] V. Berdini, M. Bassetti, G. Mancini, L. Mandolini, D. Monti, J. Organomet. Chem.
551 (1998) 331.
[17] A. Hazari, J.A. Labinger, J.E. Bercaw, Angew. Chem., Int. Ed. 51 (2012) 8268.
[18] J.B. Geri, J.P. Shanahan, N.K. Szymczak, J. Am. Chem. Soc. 139 (2017) 5952.
}
[19] G. Keglevich, T. Novák, T. Imre, P. Bakó, L. Toke, K. Újszászy, K. Ludányi,
Heteroat. Chem. 10 (1999) 573.
[20] G. Keglevich, T. Novák, P. Bakó, K. Újszászy, K. Ludányi, K. Tóth, L. Tõke, J. Incl.
Phenom. Macrocycl. Chem. 34 (1999) 299.
[21] T. Novák, P. Bakó, T. Imre, G. Keglevich, A. Dobó, L. Tõke, J. Incl. Phenom.
Macrocycl. Chem. 38 (2000) 435.
[22] F. Fallouh, D. Bernier, D. Virieux, H.J. Cristau, J.L. Pirat, Phosphorus. Sulfur.
Silicon Relat. Elem. 181 (2006) 219.
[23] M. Tazaki, K. Nita, M. Takagi, K. Ueno, Chem. Lett. 11 (1982) 571.
[24] M.P. Lowe, J.C. Lockhart, W. Clegg, K.A. Fraser, Angew. Chem., Int. Ed. English
33 (1994) 451.
[25] B. Zhang, A. Clearfield, J. Am. Chem. Soc. 119 (1997) 2751.
[26] C.V. Krishnamohan Sharma, A.J. Hessheimer, A. Clearfield, Polyhedron 20
(2001) 2095.
[27] M.I. Kabachnik, T.Y. Medved, Dokl. Akad. Nauk. SSSR (1952) 689.
[28] E.K. Fields, J. Am. Chem. Soc. 74 (1952) 1528.
[29] I. Prauda, I. Greiner, K. Ludányi, G. Keglevich, Synth. Commun. 37 (2007) 317.
[30] P.G. Edwards, B.M. Kariuki, P.D. Newman, H.A. Tallis, C. Williams, Dalt. Trans.
43 (2014) 15532.
[31] H.-F. Wu, L.-W. Chen, J. Chinese Chem. Soc. 45 (1998) 689.
[32] R.B. King, R.N. Kapoor, J. Am. Chem. Soc. 91 (1969) 5191.
[33] R.B. King, J.C. Cloyd, P.N. Kapoor, J. Chem. Soc., Perkin Trans., 1 (1973) 2226.
[34] J.J. Adams, A. Lau, N. Arulsamy, D.M. Roddick, Inorg. Chem. 46 (2007) 11328.
[35] P.A.T. Hoye, J.W. Ellis, Process for Preparing Organophosphines, U.S. Patent
5,284,555, 1994.
[36] B. Pietsch, L. Dahlenburg, Inorg. Chim. Acta 145 (1988) 195.
[37] P.J. Desrochers, K.W. Nebesny, M.J. LaBarre, S.E. Lincoln, T.M. Loehr, J.H.
Enemark, J. Am. Chem. Soc. 113 (1991) 9193.
[38] K. Yoon, G. Parkin, A.L. Rheingold, J. Am. Chem. Soc. 113 (1991) 1437.
[39] Q. Liao, N. Saffon-Merceron, N. Mézailles, Angew. Chem., Int. Ed. 53 (2014)
14206.
[40] T. Akutagawa, N. Takamatsu, K. Shitagami, T. Hasegawa, T. Nakamura, T. Inabe,
W. Fujita, K. Awaga, J. Mater. Chem. 11 (2001) 2118.
rected by the SQUEEZE/PLATON program considering the solvate as a
diffused contribution [55].
Compound [(8b[Na])MoCl3][NTf2] crystallizes in the cen-
trosymmetric monoclinic space group C2/c. The asymmetric unit
contains a complex cation and a bistriflimide anion. Both ions are
well separated and reasonably well ordered except for one of the
mono-hapto chloride ligands. The disordered Cl atom is refined
by assigning two site occupancies of 0.85 and 0.15. All H atoms
were placed in calculated positions and refined isotropically adopt-
ing a riding model with fixed positional parameters. All atoms of
the two ions are located on general positions, but one of the chlo-
ride ligands which interacts with a neighboring complex cation
with the associated ClÁ Á ÁNa distance of 2.8477(9) Å, leading to a
chain of polymeric cation units.
Acknowledgements
The authors gratefully acknowledge financial support from the
Institutional Development Award (IDeA) from the National Insti-
tute of General Medical Sciences of the National Institutes of
Health (Grant # 2P20GM103432) and the National Science Foun-
dation (CHE 0619920). The project described was also supported
by the UW Office of Vice President of Research, UW School of
Energy Resources, and the UW Department of Chemistry. The
Please cite this article in press as: L.G. Pap et al., Polyhedron (2017), https://doi.org/10.1016/j.poly.2017.11.012

8
L.G. Pap et al. / Polyhedron xxx (2017) xxx–xxx
[41] J. Hu, L.J. Barbour, R. Ferdani, G.W. Gokel, Chem. Commun. (2002) 1806.
[42] P.C. Junk, J.W. Steed, J. Coord. Chem. 60 (2007) 1017.
[43] M. Schmeisser, F.W. Heinemann, P. Illner, R. Puchta, A. Zahl, R. Van Eldik, Inorg.
Chem. 50 (2011) 6685.
[44] K. Matsumoto, R. Hagiwara, O. Tamada, Solid State Sci. 8 (2006) 1103.
[45] M.G. Davidson, P.R. Raithby, A.L. Johnson, P.D. Bolton, Eur. J. Inorg. Chem. 2003
(2003) 3445.
[48] F.R. Askham, G.G. Stanley, E.C. Marques, J. Am. Chem. Soc. 107 (1985) 7423.
[49] C.E. Anderson, D.C. Apperley, A.S. Batsanov, P.W. Dyer, J. a K. Howard, Dalt.
Trans. (2006) 4134.
[50] S. Chakraborty, O. Blacque, T. Fox, H. Berke, Chem. - A Eur. J. 20 (2014) 12641.
[51] Bruker, Apex II (2009) Bruker AXS Inc., Madison, Wisconsin, USA.
[52] G.M. Sheldrick, SADABS, Programs Scaling Absorpt. Correct. Area Detect. Data
(1997) University of Göttingen: Göttingen, Germany.
[46] S.M. Peterson, M.L. Helm, A.M. Appel, Dalt. Trans. 44 (2015) 747.
[47] R. Dinnebier, N. Sofina, L. Hildebrandt, M. Jansen, Acta Crystallogr. Sect. B
Struct. Sci. 62 (2006) 467.
[53] G.M. Sheldrick, Acta Crystallogr. Sect. A Found. Crystallogr. 64 (2008) 112.
[54] Bruker AXS Inc., 2008.
[55] A.L. Spek, Acta Crystallogr. Sect. C, Struct. Chem. 71 (2015) 9.
Please cite this article in press as: L.G. Pap et al., Polyhedron (2017), https://doi.org/10.1016/j.poly.2017.11.012