Potassium and Yttrium Complexes of a Rigid Bis-Phosphido POP-Donor Ligand

Article abstract of DOI:10.1002/ejic.201700430

Dilithiation of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethyl-xanthene (XBr₂) followed by addition of 2 equiv. of (2,4,6-triisopropylphenyl)dichlorophosphine (TrippPCl₂) afforded 4,5-bis[(2,4,6-triisopropylphenyl)chlorophosphino]-2,7-di-tert-butyl-9,9-dimethylxanthene (XP₂Cl₂), which was reduced to 4,5-bis[(2,4,6-triisopropylphenyl)phosphino]-2,7-di-tert-butyl-9,9-dimethylxanthene (H₂XP₂) using excess LiAlH₄. Deprotonation of H₂XP₂ with excess KH in DME provided the dipotassium salt, [K₂(XP₂)(dme)_n] (1; n = 2.5–4), and stirring 1 in THF followed by recrystallization from hexanes yielded tetrametallic [K₄(XP₂)₂(THF)₄] (2) which features a central K₄P₄ cage. Reaction of [YI₃(THF)_3.5] with [K₂XP₂(dme)_2.5] afforded a mixture of products including [(XP₂)YI(THF)₂] (3) and (PTripp)₃; pure 3 could be isolated in low yield by extraction with a minimum volume of hexanes or O(SiMe₃)₂. In the solid state, 3 adopts a face-capped trigonal bipyramidal coordination geometry with a planar xanthene backbone and an angle of 85° between the P(1)/C(4)/C(5)/P(2) and P(1)/Y/P(2) planes.

Full text of DOI:10.1002/ejic.201700430

DOI: 10.1002/ejic.201700430
Full Paper
Cage Compounds
Potassium and Yttrium Complexes of a Rigid Bis-Phosphido
POP-Donor Ligand
Kelly S. A. Motolko,[a] David J. H. Emslie*[a] Hilary A. Jenkins,[b] and James F. Britten[b]
Abstract: Dilithiation of 4,5-dibromo-2,7-di-tert-butyl-9,9-di- by recrystallization from hexanes yielded tetrametallic
methyl-xanthene (XBr2) followed by addition of 2 equiv. of [K4(XP2)2(THF)4] (2) which features a central K4P4 cage. Reaction
(2,4,6-triisopropylphenyl)dichlorophosphine (TrippPCl2) af- of [YI3(THF)3.5] with [K2XP2(dme)2.5] afforded a mixture of prod-
forded 4,5-bis[(2,4,6-triisopropylphenyl)chlorophosphino]-2,7- ucts including [(XP2)YI(THF)2] (3) and (PTripp)3; pure 3 could be
di-tert-butyl-9,9-dimethylxanthene (XP2Cl2), which was reduced isolated in low yield by extraction with a minimum volume of
to 4,5-bis[(2,4,6-triisopropylphenyl)phosphino]-2,7-di-tert-butyl- hexanes or O(SiMe3)2. In the solid state, 3 adopts a face-capped
9,9-dimethylxanthene (H2XP2) using excess LiAlH4. Deproton- trigonal bipyramidal coordination geometry with a planar
ation of H2XP2 with excess KH in DME provided the dipotassium xanthene backbone and an angle of 85° between the P(1)/C(4)/
salt, [K2(XP2)(dme)n] (1; n = 2.5–4), and stirring 1 in THF followed C(5)/P(2) and P(1)/Y/P(2) planes.
Introduction
Ancillary ligands play a critical role in defining the thermal sta-
bility and reactivity of metal complexes, and we have previously
explored the use of rigid 4,5-bis(anilido)xanthene ligands in
actinide and lanthanide chemistry. For example, the XA2 [4,5-
bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-
xanthene] pincer ligand was employed for the synthesis of
thorium(IV), uranium(IV) and uranium(III) chloro complexes,[1,2]
as well as dialkyl complexes of tetravalent thorium[1,3] and
uranium[4] (Figure 1), thorium(IV) monoalkyl cations, and a
Figure 1. Neutral 4,5-bis(anilido)xanthene alkyl complexes of thorium(IV), ura-
nium(IV), yttrium(III) and lutetium(III).
thorium(IV) dication.[3,5] Furthermore, we recently reported the
synthesis of Y, Lu and La derivatives of the XN2 [4,5-bis(2,4,6-
triisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene]
we became interested to probe the rare earth coordination be-
ligand, including monoalkyl derivatives (Figure 1) which
havior of a 4,5-bis(arylphosphido)xanthene analogue of XN2.
are highly active catalysts for alkene and alkyne hydroamin-
ation.[6,7]
In comparison to amido ligands, phosphido ligands are far
less explored in group 3 and f-element chemistry,[8] especially
multidentate ligands containing phosphido donors. Ligands of
this type which have been employed in rare earth chemistry
are illustrated in Figure 2. The PN-, PO-, PPP-, OPO- and Cp/P-
donor ligands a,[9–11] b,[9,12] c (L = PR2),[13] c (L = OMe),[14] and
f[15,16] were assembled prior to metal coordination. By contrast,
d[11,17] and g[16] resulted from cyclometallation, and dianionic
e[12] formed from monoanionic b (R′ = H), through metal-medi-
ated transfer of a methyl group from oxygen to the phosphorus
donor of a second equivalent of ligand b.
In combination with large rare earth and actinide elements,
the xanthene-backbone XA2 and XN2 ligands present a rigid
meridionally-coordinating pincer array that is capable of stabi-
lizing highly reactive organometallic derivatives. Additionally,
the rigidity of the ligand framework provides an opportunity to
introduce softer donor atoms into the coordination sphere of
rare earth or actinide elements, and we have previously pre-
pared uranium(III) and (IV) complexes of a thioxanthene ana-
logue of the XA2 ligand, TXA2.[2] As an extension of this concept,
Herein we report the synthesis of a direct phosphorus ana-
logue of the H2[XN2] pro-ligand, H2[XP2], and potassium com-
plexes of the XP2 dianion, including the first example of a potas-
sium phosphido compound with a K4P4 cubic cage structure.
The synthesis and structural characterization of an yttrium
iodido XP2 complex is also described, allowing comparison of
the binding preferences of XP2 and XN2 in the coordination
sphere of yttrium.
[a] Department of Chemistry & Chemical Biology, McMaster University,
1280 Main St. West, Hamilton, Ontario, L8S 4M1, Canada
E-mail: emslied@mcmaster.ca
http://www.chemistry.mcmaster.ca/emslie/emslie.html
[b] McMaster University Analytical X-ray Diffraction Facility,
1280 Main St. West, Hamilton, Ontario, L8S 4M1, Canada
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201700430.
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Figure 2. Multidentate phosphido ligands employed in rare earth chemistry.
1
Results and Discussion
analysis (Scheme 1). The H and 31P NMR spectra of H2XP2 re-
1
vealed J1H,31P couplings of 225 Hz and 229 Hz for the P-H sig-
Reaction of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene
(XBr2) with 2 equiv. of nBuLi in THF, followed by addition of
2 equiv. of (2,4,6-triisopropylphenyl)dichlorophosphine (Tripp-
PCl2) afforded a 73 % yield of 4,5-bis[(2,4,6-triisopropylphenyl)-
chlorophosphino]-2,7-di-tert-butyl-9,9-dimethylxanthene (XP2Cl2)
as an approximate 1:1 ratio of diastereomers (Scheme 1; dia-
stereomers were not assigned as rac or meso due to overlap-
ping CMe2 signals in 1H and 13C NMR spectra of the Cs-symmet-
ric meso isomer). Samples enriched in each diastereomer could
be obtained by washing the isolated solid with a small volume
of hexanes; the solid residue contained > 95 % of one diastereo-
mer, while the mother liquor contained > 60 % of the other
diastereomer.
nals of the two diastereomers, similar to those in Ph2PH
(218 Hz),[18] as well as related PCP-,[19] PNP-,[20] and POP-do-
nor[21] pro-ligands (211–227 Hz).
Stirring H2XP2 with excess KH in DME for 72 h produced the
dipotassium salt of the dianion, [K2(XP2)(dme)2.5] (1) as an or-
ange solid in 80 % isolated yield (Scheme 1). The 31P NMR spec-
trum of [K2(XP2)(dme)2.5] comprises of a single peak at δ =
–83.7 ppm, consistent with the removal of chirality at phos-
phorus upon deprotonation, and the 1H NMR spectrum is indic-
ative of C2v symmetry. Crystals of [K2(XP2)(dme)4] were grown
by cooling a concentrated DME solution to –30 °C (Figure 3)
and reveal a K2P2 rhombus-shaped core, with 78–82° angles
between the P(1)/C(4)/C(5)/P(2) and P(1)/K/P(2) planes. Two
DME molecules are coordinated to each potassium atom and
the ligand backbone is essentially planar with a 1° angle be-
tween the planes of the two aryl rings in the backbone.
Figure 3. X-ray crystal structure of compound 1. Ellipsoids are set at 50 %
probability. The tert-butyl groups are rotationally disordered over multiple posi-
tions, and in each case, only one is shown for clarity. Hydrogen atoms are
omitted, and the coordinating DME molecules are depicted in wire-frame. Se-
lected bond lengths [Å] and angles [°]: K(1)–P(1) 3.395(2), K(1)–P(2) 3.332(1),
K(2)–P(1) 3.320(1), K(2)–P(2) 3.277(1), K(1)–O(1) 2.868(3), K(2)–O(1) 2.958(2),
P(1)–K(1)–P(2) 80.12(3), P(1)–K(2)–P(2) 82.03(3), K(1)–P(2)–K(2) 98.06(3), K(1)–
P(1)–K(2) 96.00(3), C(4)–P(1)–C(24) 97.8(2), C(5)–P(2)–C(39) 100.6(2), K(1)–O(1)–
K(2) 117.83(8), C(4)–P(1)–K(1) 84.2(1), C(4)–P(1)–K(2) 88.9(1), C(5)–P(2)–K(1)
85.5(1), C(5)–P(2)–K(2) 87.4(1), C(24)–P(1)–K(1) 134.1(1), C(24)–P(1)–K(2) 129.8(1),
C(39)–P(2)–K(1) 130.2(1), C(39)–P(2)–K(2) 131.3(1).
Scheme 1. Synthesis of XP2Cl2, H2XP2·LiCl and [K2(XP2)(dme)n] (n = 2.5–4).
Tripp = 2,4,6-triisopropylphenyl.
Pure or enriched samples of the diastereomers of XP2Cl2
were used to simplify NMR characterization. However, separa-
tion of diastereomers was not required prior to reaction with
LiAlH4 to form 4,5-bis[(2,4,6-triisopropylphenyl)phosphino]-2,7-
di-tert-butyl-9,9-dimethyl-xanthene (H2XP2), which was isolated
in 87 % yield as an approximate 1:1 mixture of diastereomers,
Related phosphido complexes include polymeric [{K2(POP)}∞]
containing 1.0–1.5 equiv. of occluded LiCl based on elemental [POP = 4,5-bis(tert-butylphosphido)-9,9-dimethyl-xanthene] fea-
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turing K···P and K···Caryl contacts between adjacent K2(POP)
units,[21] [{(PNP)K2(THF)3}2] {PNP = 2,6-bis[2-(phenylphosphido)-
phenyl]pyridine} with a ladder-like K4P4 core,[20] and polymeric
[{(Ph2P)K(pmdeta)}∞], and [{(RPhP)K(pmdeta)}2] [R = CH(SiMe3)2;
pmdeta = N,N,N′,N′′,N′′-pentamethyldiethylene-triamine] with
rhombus-shaped K2P2 cores.[22] The K–Oxant distances of
2.868(3) and 2.958(2) Å in 1 are similar to those in K2(POP)
[2.869(2) Å], and the K–P distances in 1 [3.277(1) to 3.395(2) Å]
fall within the range reported for the aforementioned literature
compounds [3.128(1)–3.538(1) Å]. However, the C–P–C angles
of 97.8(2) and 100.6(2)° are accute, more so than the com-
pounds cited above [102.7(1)–107.5(1)°], presumably to mini-
mize unfavorable steric interactions between ortho-isopropyl
groups and the two dme ligands on each potassium centre.
Stirring [K2(XP2)(dme)2.5] (1) in THF at 24 °C for 5 h, followed
by removal of the solvent in vacuo and recrystallization from
hexanes afforded [K4(XP2)2(THF)4] (2) as orange crystals in 22 %
yield. The 1H NMR spectrum of 2 contains a single complement
of peaks for a top-bottom-symmetric XP2 ligand (distinct from
those of compound 1), and the 31P NMR spectrum features a
single peak at –85.14 ppm, which is slightly shifted compared
to that of 1. The reaction to form 2 is reversible, since stirring
2 in DME at room temperature regenerates compound 1.
Figure 4. X-ray crystal structure of compound 2. Ellipsoids are set at 50 %
probability. Hydrogen atoms are omitted, and the 2,4,6-triisopropylphenyl
groups and coordinated THF molecules are depicted in wire-frame. Interactions
between K(1) and the aryl ring on P(3), and K(4) and the aryl ring on P(2) are
not shown for clarity. The tert-butyl groups are rotationally disordered over
multiple positions, and in each case, only one is shown for clarity. Selected
bond lengths [Å] and angles [°]: K(1)–P(1) 3.203(3), K(1)–P(2) 3.218(3), K(2)–
P(1) 3.201(3), K(2)–P(2) 3.232(3), K(3)–P(3) 3.249(3), K(3)–P(4) 3.217(3), K(4)–P(3)
3.221(3), K(4)–P(4) 3.215(2), K(1)–P(3) 3.328(3), K(2)–P(4) 3.540(3), K(3)–P(1)
3.568(3), K(4)–P(2) 3.335(3), K(1)–O(1) 3.141(6), K(2)–O(1) 3.049(5), K(3)–O(2)
3.033(6), K(4)–O(2) 3.127(5), K(3)–P(4)–K(2) 79.77(6), K(2)–P(1)–K(3) 79.56(6), all
The solid-state structure of 2 consists of two K2(XP2) units
linked to form a K4P4 cube, with K–P–K and P–K–P angles of
80–90° and 89–101°, respectively (Figure 4). The K–P distances
in the square faces bridged by the xanthene backbone lie in a
narrow range [3.201(3)–3.249(3) Å], and are shorter than the
K–P bonds in 1. By contrast, the K–P distances linking these two
faces are longer, at 3.328(3), 3.335(3), 3.540(3), and 3.568(3) Å;
the two shorter K–P bonds are augmented by interactions be-
tween potassium and the ipso- and ortho-carbon atoms of an
aryl group on phosphorus [K–C = 3.32(1)–3.40(1) Å; f in Fig-
ure 5], whereas the longer K–P bonds are not bridged by com-
parable K–Caryl interactions (K–C > 3.8 Å). Nevertheless, a similar
range of K–P distances was reported for polymeric [{K2(POP)}∞]
[3.220(1)–3.518(1) Å][21] and tetrametallic [{(PNP)K2(THF)3}2]
[3.228(1)–3.538(1) Å].[20] The K–OTHF distances of 2.667(5)–
2.712(6) Å in 2 lie within the typical range.[20,23] By contrast, the
K–Oxant distances are significantly longer; at 3.033(6)–3.141(6) Å,
these bonds are longer than the K–Oxant bonds in [K2(XAT)-
(alkane)] [XAT = 4,5-bis(2,6-dimesitylanilido)-2,7-di-tert-butyl-
9,9-dimethylxanthene; 2.534(3)–2.619(2)],[24] K2(POP) [2.869(2) Å],
and 1 [2.868(3)–2.958(2) Å].
other K–P–K
= 85.06(7)–90.37(6), P(1)–K(2)–P(4) 100.62(7), P(4)–K(3)–P(1)
99.71(7), all other P–K–P = 88.98(7)–95.66(7).
Figure 5. The central cores of (a) [{Li4(PH-SitBuAr-PSiPh3)2}2(Li2Cl2)], (b)
[{Na6(NMe2)6}{(Na(tmeda))3(NMe2)3}2], (c) [{Rb(PH(Dmp))}4]·C7H8 (Dmp = 2,6-di-
mesitylphenyl), (d) [Cs4{NH(SiMe3)}4], (e) [{Cs(η6-toluene)}4{P(H)SitBu3}4], and (f)
compound 2. M4Pn4 cores are shown in ball-and-stick format, while key sur-
rounding atoms (not including H atoms) are shown as capped sticks.
While a significant number of Li4(NR2)4 cubic cage structures
have been described,[25] only a handful of cubic M4(PnR2)4 cage
structures incorporating heavier alkali metal and/or pnictogen
elements have been reported. In fact, structurally characterized Cs4P4 core (e in Figure 5).[29] Compound 2 is therefore the first
examples are limited to [{Li4(PH-SitBuAr-PSiPh3)2}2(Li2Cl2)] fea- structurally characterized phosphido complex featuring a cubic
turing two Li4P4 cubes bridged by a Li2Cl2 unit (a in Figure 5);[26]
[{Na4(NMe2)4}{(Na(tmeda))3(NMe2)3}2] presenting central
K4P4 core.
a
Reaction of [K2(XP2)(dme)2.5] with [YI3(THF)3.5] in THF pro-
duced a mixture of products (consistently >10 peaks in the 31P
Na4N4 cube linked through opposite faces to Na3N3 ladder
structures; related [{Na6(NMe2)6}{(Na(tmeda))3(NMe2)3}2] with an
Na6N6 core composed of two face-sharing cubes (b in Figure 5);
[{Rb(PH(Dmp))}4]·C7H8 (Dmp = 2,6-dimesitylphenyl) with a was identified by H, 13C and 31P NMR spectroscopy (compari-
Rb4P4 core (c in Figure 5);[27] [Cs4{NH(SiMe3)}4] with a Cs4N4 core son with an independently prepared sample) and X-ray crystal-
(d in Figure 5);[28] and [{Cs(η6-Toluene)}4{P(H)SitBu3}4] with a lography [Figure 6; the structure is closely analogous to
NMR spectrum) including [(XP2)YI(THF)2] (3) and tris(2,4,6-triiso-
propylphenyl)triphosphirane {(PTripp)3};[30] the latter compound
1
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[31]
those of (PMes)3
and (PAnt)2(PAr);[32] Mes = mesityl, Ant =
9-Anthracenyl; Ar = C6H2{o-CH(SiMe3)2}2{p-C(SiMe3)3}]. Crude 3
was isolated as the major product after extraction into a small
volume of hexanes, and pure 3 was isolated as an orange pow-
der by a second extraction with a small volume of either
O(SiMe3)2 or hexanes in an 18 % overall yield (Scheme 2). X-ray
quality crystals were obtained by cooling a concentrated hex-
anes solution of 3 to –30 °C (Figure 7). It is of note that the
unexpected byproducts formed in the synthesis of 3 do not
arise from thermal decomposition of 3 over the duration of the
reaction, given that the 31P NMR signal for 3 did not decrease
in intensity once the reaction reached completion.
Figure 7. Two views of the X-ray crystal structure of compound 3. Ellipsoids
are set to 50 % probability. Hydrogen atoms are omitted for clarity. The tert-
butyl groups are rotationally disordered over multiple positions, and in each
case, only one is shown for clarity. In view b, the 2,4,6-triisopropylphenyl
groups are depicted in wire-frame. Selected bond lengths [Å] and angles [°]:
Y–P(1) 2.715(2), Y–P(2) 2.762(2), Y–I 2.9639(10), Y–O(1) 2.508(4), Y–O(2) 2.322(5),
Y–O(3) 2.336(5), P(1)–Y–P(2) 110.87(7), P(1)–Y–I 122.43(5), P(2)–Y–I 121.79(5),
O(2)–Y–O(3) 162.0(2), O(2)–Y–I 81.6(1), O(3)–Y–I 81.9(1), O(1)–Y–O(2) 126.6(2),
O(1)–Y–O(3) 70.3(2), O(1)–Y–P(1) 68.6(1), O(1)–Y–P(2) 67.4(1).
Figure 6. X-ray crystal structure of (PTripp)3 with ellipsoids set to 50 %
probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å]
and angles [°]: P(1)–P(2) 2.2367(6), P(1)–P(3) 2.2060(6), P(2)–P(3) 2.2151(6), P(1)–
C(11) 1.864(2), P(2)–C(31) 1.852(2), P(3)–C(51) 1.849(2), P(2)–P(1)–P(3) 59.81(2),
P(1)–P(2)–P(3) 59.41(2), P(1)–P(3)–P(2) 60.78(2), C(11)–P(1)–P(2) 101.01(5),
C(11)–P(1)–P(3) 96.76(5), C(31)–P(2)–P(1) 107.69(6), C(31)–P(2)–P(3) 112.08(6),
C(51)–P(3)–P(1) 115.24(5), C(51)–P(3)–P(2) 116.53(5).
respectively, with an I–Y–[P(1)P(2)centroid] angle of 159.5°. The
O(2)–Y–O(3) angle is 162.0(2)°, and the O(2)–Y–I and O(3)–Y–I
angles are 81.6(1)° and 81.9(1)°, respectively. The O(1) donor of
the xanthene backbone caps the centre of the P(1)/P(2)/O(3)
face with O(1)–Y–P and O(1)–Y–O(3) angles between 67.4(1) and
70.3(2)°.
Scheme 2. Attachment of the XP2 ligand to yttrium by salt metathesis (L =
THF).
The X-ray crystal structure of 3 (Figure 7) revealed that the
xanthene backbone of the XP2 ligand is planar, and the geome-
try at yttrium is approximately face-capped trigonal bipyrami-
dal with the anionic donors in equatorial positions and the THF
ligands in axial positions. Yttrium lies 1.55 Å out of the
P(1)/C(4)/C(5)/P(2) plane, leading to an 85° angle between the
P(1)/C(4)/C(5)/P(2) plane and the PYP plane. By comparison;
yttrium lies 0.50 Å out of the N(1)/C(4)/C(5)/N(2) plane of the
related XN2 ligand in [(XN2)Y(CH2SiMe3)(THF)] (Figure 8), with a
Figure 8. X-ray crystal structure of previously reported [(XN2)Y(CH2SiMe3)(THF)],
highlighting the extent to which yttrium lies within the plane of the ligand.
Reproduced with permission from reference 6. Copyright 2017 American
Chemical Society.
The Y–P distances in 3 are 2.715(2) Å and 2.762(2) Å, falling
31° angle between the N(1)/C(4)/C(5)/N(2) plane and the NYN near the middle of the spectrum observed for the terminal
plane.[6] The P(1)–Y–P(2), P(1)–Y–I, and P(2)–Y–I angles in the phosphido ligands in [(Y{P(SiMe3)2}2{μ-P(SiMe3)2})2] [2.660(2)–
equatorial plane of 3 are 110.87(7), 122.43(5) and 121.79(5)°, 2.693(2) Å],[33] [Y{P(SiMe3)Ar}I2(thf)3] (Ar
=
2,6-C6H3iPr2)
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[2.699(2) Å],[34] [(CpTMS2)2Y(PHR)(THF)] [CpTMS2
C5H3(SiMe3)2;
SitBu3] [2.770(1) Å],[33] [{(Me4C5-SiMe2-
PAr)Y(THF)(μ-H)}2] (Ar = 2,4,6-C6H2tBu3) [2.724(1) Å], [{Me4C5-
SiMe2–P–C6H2(2,4-tBu)2(6-CMe2CH2)}Y(THF)2] [2.789(2) Å],
[(Me4C5-SiMe2-PPh)Y(THF)(μ-H)2(μ-PhP-SiMe2–C5Me4)Y(THF)2]
[2.826(2) Å],[16] and [(κ3-Tp*)(Cp)Y(PPh2)(THF)] [Tp* = tris(3,5-
dimethylpyrazolyl)-hydroborate] [2.845(2) Å].[35]
=
1,3- Experimental Section
R
=
General Details: An argon-filled MBraun UNIlab glove box equipped
with a –30 °C freezer was employed for the manipulation and storage
of all air-sensitive compounds, and reactions were performed on a
double manifold high vacuum line using standard techniques.[40]
A
Fisher Scientific Ultrasonic FS-30 bath was used to sonicate reaction
mixtures where indicated. A VWR Clinical 200 Large Capacity Centri-
fuge (with 28° fixed-angle rotors that hold 12 × 15 mL or 6 × 50 mL
tubes) in combination with 15 mL Kimble Chase glass centrifuge
tubes was used when required (inside the glovebox). Residual oxy-
gen and moisture was removed from the argon stream by passage
through an Oxisorb-W scrubber from Matheson Gas Products. Diethyl
ether, THF, toluene, benzene and hexanes were initially dried and
distilled at atmospheric pressure from Na/Ph2CO. Hexamethyldisilox-
ane [O(SiMe3)2] was dried and distilled at atmospheric pressure from
Na. Unless otherwise noted, all proteo solvents were stored over an
appropriate drying agent {pentane, hexanes, hexamethyldisiloxane
[O(TMS)2/O(SiMe3)2]: Na/Ph2CO/tetra-glyme; Et2O: Na/Ph2CO} and in-
troduced to reactions through vacuum transfer with condensation at
–78 °C. The deuterated solvents (ACP Chemicals) C6D6, [D8]THF and
[D8]toluene were dried with Na/Ph2CO.
The Y–I distance of 2.964(1) Å in 3 is also within the range
previously reported for yttrium iodido compounds. For exam-
ple, the Y–I distances are 2.9287(3) and 2.9464(3) Å in
[{HC(CMeNAr)2}YI2(THF)],[36] 2.947(1)–2.979(1) Å in [Y{P(SiMe3)-
Ar}I2(thf)3] (Ar
=
2,6-C6H3iPr2),[34] and 3.0161(8)
Å
in
[YI{N(SiMe3)2}2(CH2PPh3)].[37] The Y–OTHF distances of 2.322(5)
and 2.336(5) Å are typical,[36,38] whereas the Y–O(1) distance of
2.508(4) Å is substantially elongated, reflecting the poor donor
ability of a diarylether ligand, combined with steric constraints
imposed by the rigidity of the XP2 pincer ligand framework.
1
Between 25 °C and –90 °C, solution H NMR spectra of 3 in
[D8]THF indicate apparent C2v symmetry, consistent with rapid
migration of the YI(THF)2 unit from one side of the plane of the
ligand backbone to the other. Compound 3 gave rise to a 31P
The 4,5-Dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene,[41]
[Y(CH2SiMe3)3(THF)2],[42] 2,4,6-triisopropylphenyldichlorophos-
1
NMR signal at δ = 1.28 ppm with a J31P,89Y coupling of 162 Hz.
phine,[43] and NaCH2SiMe3
starting materials were prepared ac-
[44]
This coupling is slightly larger than those observed for the ter-
minal yttrium phosphido complexes [Y{P(SiMe3)Ar}I2(thf)3] (Ar =
C6H3iPr2-2,6) (157 Hz),[34] [(CpTMS2)2Y(PHR)(THF)] [CpTMS2 = 1,3-
C5H3(SiMe3)2; R = SitBu3] (144 Hz)[33] and [(Y{P(SiMe3)2}2-
{μ-P(SiMe3)2})2] (122 Hz),[39] and significantly larger than those
reported for the aforementioned intact and cyclometallated
Me4C5-SiMe2-PAr complexes (53–84 Hz).[16]
cording to literature procedures. 1,3,5-triisopropylbenzene, xanthone,
KH (30 wt.-% in mineral oil), LiCH2SiMe3 (1.0 in pentane), nBuLi
(1.6 in hexanes), Br2, YI3, YCl3, NaOtBu and LiAlH4 were purchased
M
M
from Sigma–Aldrich. Solid LiCH2SiMe3 was obtained by removal of
pentane in vacuo, and solid KH was obtained by filtration and wash-
ing with hexanes. YI3(THF)3.5 and YCl3(THF)3.5 were obtained by re-
fluxing the anhydrous yttrium trihalide in THF for 24 h followed by
removal of the solvent in vacuo. Argon (99.999 % purity) and ethyl-
ene (99.999 % purity) were purchased from Praxair.
In an attempt to isolate an XP2 yttrium monoalkyl complex,
two routes were employed; alkane elimination and salt metath-
esis. The alkane elimination reaction between [Y(CH2SiMe3)3-
(THF)2] and H2XP2 (C6D6 solvent, 20 °C) yielded only unreacted
H2XP2, and the products of [Y(CH2SiMe3)3(THF)2] thermal de-
composition. The salt metathesis reaction between 3 and
NaCH2SiMe3 (1 or 2 equiv. in THF) afforded a major product
Combustion elemental analyses were performed on a Thermo
EA1112 CHNS/O analyzer at McMaster University and by Midwest
Microlab, LLC, Indianapolis, Indiana. NMR spectroscopy [1H, 13C(1H),
31P(1H), DEPT-Q, COSY, HSQC, HMBC] was performed on Bruker AV-
200, DRX-500 and AV-600 spectrometers. All H NMR and 13C NMR
1
1
believed to be [(XP2)Y(CH2SiMe3)2(THF)n]– by H NMR spectro-
spectra were referenced relative to SiMe4 through a resonance of the
employed deuterated solvent or proteo impurity of the solvent; C6D6
(δ =7.16 ppm), d8-Tol (2.08, 6.97, 7.01, 7.09 ppm), [D8]THF (1.72,
3.58 ppm) for 1H NMR; and C6D6 (δ =128.0 ppm), d8-Tol (20.43,
125.13, 127.96, 128.87, 137.48 ppm), [D8]THF (25.31, 67.21 ppm) for
13C NMR spectroscopy. 31P{1H} NMR spectra were referenced using
an external standard of 85 % H3PO4 in D2O (δ =0.0 ppm). Herein,
numbered proton and carbon atoms refer to the positions of the
xanthene backbone, as shown in Scheme 1. Inequivalent ortho iso-
propyl protons are labeled A and B, so that the corresponding carbon
resonances can be identified. X-ray crystallographic analyses were
performed on suitable crystals coated in Paratone oil and mounted
on a SMART APEX II diffractometer with a 3 kW Sealed tube Mo
generator in the McMaster Analytical X-ray (MAX) Diffraction Facility.
In all cases, non-hydrogen atoms were refined anisotropically and H
atoms were generated in ideal positions and then updated with each
cycle of refinement.
scopy. However, the reaction was not clean, and despite numer-
ous attempts, this “ate” complex could not be isolated in pure
form.
Conclusions
The rigid POP pincer pro-ligand, H2XP2, was synthesized in two
steps from XBr2. Double deprotonation with excess KH yielded
[K2XP2(dme)n] (1; n = 2.5–4) with a rhombus-shaped K2P2 core,
or [K4(XP2)2(THF)4] (2) featuring the first cubic K4P4 cage struc-
ture, depending on purification conditions. Reaction of 1 with
[YI3(THF)3.5] afforded [(XP2)YI(THF)2] (3) in which Y is displaced
1.55 Å out of the P(1)/C(4)/C(5)/P(2) plane of the XP2 ligand,
contrasting the coordination behavior of yttrium to XN2, the
amido-analogue of the XP2 dianion. However, the reaction to
form 3 is low yielding due to the formation of multiple products
including tris(2,4,6-triisopropylphenyl)triphosphirane, {P(Tripp)}3,
indicative of poor ligand stability in the presence of strong Lewis
acids.
CCDC 1544974 (for 1), 1544974 (for 2), 1544974 (for 3), and 1544977
{for [(PTripp)3]} contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre.
XP2Cl2: A 1.6
M solution of nBuLi in hexanes (12.3 mL, 19.6 mmol)
was added to a solution of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimeth-
Eur. J. Inorg. Chem. 2017, 2920–2927
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© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
ylxanthene (4.72 g, 9.82 mmol) in THF (120 mL) at –78 °C, and the
reaction mixture was stirred at –78 °C for 6 h. A solution of (2,4,6-
H, ortho-, para-CHMe2), 1.17, 1.17 (s, 2 × 18 H, CMe3 rac and meso)
ppm. 13C NMR (C6D6, 126 MHz): δ = 155.43, (ortho-CCHMe2), 151.12
triisopropylphenyl)dichlorophosphine (6.0 g, 19.6 mmol) in THF (para-CCHMe2), 149.71, 149.31 (Xanth-C11), 145.98, 145.87 (Xanth-C2),
(45 mL) was then added, and the reaction mixture and was warmed
to room temperature and stirred for 40 h. Solvent was removed in
vacuo and the resulting yellow solid was dissolved in toluene
(75 mL), centrifuged and the mother liquors were decanted and the
solvents evaporated to dryness. To the resulting tacky yellow solid,
hexanes (60 mL) was added followed by sonication and solvent re-
moval in vacuo to yield XP2Cl2 as a free-flowing off-white solid (6.1 g,
73 %). This product is an approximate 1:1 mixture of diastereomers,
129.36, 128.94 (Xanth-C10), 127.81, 127.68 (Xanth-C1H or Xanth-C3H),
122.02, 121.87, 121.71 (Ar-CH, 2 × Xanth-C1H or Xanth-C3H), 35.26,
35.07, 34.67 (2 × Xanth-C9Me2, CMe3), 34.94 (para-CHMe2), 33.49,
31.42 (CMe2 meso), 33.39, 33.35, 33.31 (ortho-CHMe2), 32.07 (CMe2
rac), 31.63 (CMe3), 25.43, 25.38 (ortho-CHMe2), 24.45, 24.43, 24.25,
24.19 (ortho-CHMe2, para-CHMe2) ppm. 31P NMR (C6D6, 81 MHz): δ =
1
1
–93.07 (d, JP,H = 225 Hz), –93.77 (d, JP, H = 229 Hz) ppm. C53H76P2O:
calcd. C 80.46, H 9.68. Range from duplicate analyses on 4 different
and was of sufficient purity to proceed to the next step of the ligand batches: C 76.49; H 9.72 to C 74.78, H 8.70. These data correspond
synthesis (diastereomers were not identified as rac or meso, since
both diastereomers gave rise to only one CMe2 signal in the H and
to (C53H76P2O)·nLiCl (n = 1–1.5), since C53H76P2OLiCl is C 76.36, H
9.19, and C53H76P2OLi1.5Cl1.5 is C 74.47, H 8.96.
1
13C NMR spectra, presumably due to overlapping signals in the case
of the Cs-symmetric meso isomer). However, the diastereomers (re-
ferred to as A and B) could be separated by sonication in hexanes
(4 mL per g of product) followed by centrifugation and separation
of the solid from the mother liquors. The solid is > 95 % diastereomer
A (isolated in 26 % yield from the crude) while the mother liquors
are enriched in diastereomer B (a 3:1 B:A ratio is typical). NMR spectro-
scopic data for diastereomer A: 1H NMR (C6D6, 600 MHz): δ = 7.43,
7.15 (s, 2 × 2 H, Xanth-CH1 and Xanth-CH3), 7.23 (s, 4 H, Ar-H), 4.25,
[K2(XP2)(DME)2.5] (1): Solid KH (0.126 g, 3.16 mmol) was added to a
solution of H2[XP2]·nLiCl (n = 1), (1.0 g, 1.20 mmol) in DME (40 mL),
and the reaction was stirred at 24 °C for 72 h in the glove box. The
orange reaction mixture was filtered, and the filtrate was evaporated
to dryness in vacuo. Addition of hexanes (15 mL), centrifugation, and
evaporation of the mother liquors to dryness afforded [K2(XP2)-
(DME)2.5] (1.1 g, 80 %) as an orange solid. Crystals of [K2(XP2)(DME)4]
1
were grown by cooling a concentrated DME solution to –30 °C. H
NMR (C6D6, 600 MHz): δ = 7.43 (s, 4 H, Ar-H), 6.78, 6.65 (s, 2 H, Xanth-
3
3
4.26 (sept, JH,H = 6.5 Hz, 2 × 2 H, ortho-CHMe2), 2.76 (sept, JH,H
=
=
3
CH1 and Xanth-CH3), 4.54 (sept, JH,H = 6.5 Hz, 4 H, ortho-CHMe2),
3
7.0 Hz, 2 H, para-CHMe2), 1.45 (s, 6 H, CMe2), 1.30, 1.26 (d, JH,H
3
3.06 (sept, JH,H = 7.0 Hz, 2 H, para-CHMe2), 2.99 (s, 10 H, 2.5 equiv.
3
6.5 Hz, 2 × 12 H, ortho-CHMe2), 1.20, 1.19 (d, JH,H = 7.0 Hz, 2 × 6 H,
para-CHMe2), 1.17 (s, 18 H, CMe3) ppm. 13C NMR (C6D6, 126 MHz):
δ = 156.40 (ortho-CCHMe2), 152.54 (para-CCHMe2), 150.56 (Xanth-
C11), 144.97 (Xanth-C2), 130.64 (d, Ar-Cipso), 129.83 (Xanth-C10), 127.81,
125.85 (Xanth-C1H and Xanth-C3H), 122.94 (Ar-CH), 34.76 (para-
CHMe2), 33.42 (CMe2), 32.31, 32.15 (2 × ortho-CHMe2), 31.42 (CMe3),
26.03, 24.40 (2 × ortho-CHMe2), 24.02, 23.89 (2 × para-CHMe2) ppm.
31P NMR (C6D6, 243 MHz): δ = 75.52 ppm. NMR spectroscopic data for
DME-CH2), 2.88 (s, 15 H, 2.5 equiv. DME-CH3), 1.86 (s, 6 H, CMe2), 1.52
3
3
(d, JH,H = 6.5 Hz, 12 H, ortho-CHMe2), 1.45 (d, JH,H = 7.0 Hz, 12 H,
3
para-CHMe2), 1.38 (d, JH,H = 6.5 Hz, 12 H, ortho-CHMe2), 1.30 (s, 18
H, CMe3) ppm. 13C NMR (C6D6, 126 MHz): δ = 155.16 (ortho-CCHMe2),
146.78 (para-CCHMe2), 144.70 (Xanth-C11), 144.27 (Xanth-C2), 141.18
(Ar-Cipso), 126.34 (Xanth-C10), 123.75, 110.69 (Xanth-C1H and Xanth-
C3H), 120.69 (Ar-CH), 71.46 (DME-CH2), 58.49 (DME-CH3), 35.12 (para-
CHMe2), 34.61 (Xanth-C9Me2 and/or CMe3), 34.16 (CMe2), 33.73
(ortho-CHMe2), 31.96 (CMe3), 26.07, 25.00 (2 × ortho-CHMe2),
24.72 (para-CHMe2) ppm. 31P NMR (C6D6, 81 MHz): δ = –83.73 ppm.
C63H99K2O6P2 (1092.62): calcd. C 69.25, H 9.13; found C 69.69,
H 8.98.
1
diastereomer B: H NMR (C6D6, 600 MHz): δ = 7.55, 7.41 (s, 2 × 2 H,
Xanth-CH1 and Xanth-CH3), 7.24 (s, 4 H, Ar-H), 4.31, 4.32 (sept, 3JH,H
=
3
6.7 Hz, 2 × 2 H, ortho-CHMe2), 2.78 (sept, JH,H = 6.8 Hz, 2 H, para-
3
CHMe2), 1.36 (s, 6 H, CMe2), 1.32, 1.27 (d, JH,H = 6.7 Hz, 2 × 12 H,
3
ortho-CHMe2), 1.24 (d, JH,H = 6.8 Hz, 12 H, para-CHMe2), 1.13 (s, 18
H, CMe3) ppm. 13C NMR (C6D6, 126 MHz): δ = 156.38 (ortho-CCHMe2),
151.25 (Xanth-C11), 149.15 (para-CCHMe2), 147.46 (Xanth-C2), 131.50
(Xanth-C10), 130.62 (Ar-Cipso), 127.83, 124.94 (Xanth-C1H and Xanth-
C3H), 122.80 (Ar-CH), 34.73 (para-CHMe2), 31.83, 31.60 (2 × ortho-
CHMe2), 31.70 (CMe2), 31.49 (CMe3), 25.62, 24.99 (2 × ortho-CHMe2),
24.46, 24.40 (2 × para-CHMe2) ppm. 31P NMR (C6D6, 243 MHz): δ =
76.81 ppm. C53H74Cl2OP2 (860.02): calcd. C 74.01, H 8.67; found C
73.85, H 8.95.
[K4(XP2)2(THF)4] (2): [K2(XP2)(dme)2.5] (1) (95 mg, 0.087 mmol) was
dissolved in THF (12 mL) and stirred at 24 °C for 5 h, followed by
removal of solvent in vacuo. The resulting amber colored solid was
recrystallized from hexanes (1.5 mL) to yield [K4(XP2)2(THF)4] (38 mg,
1
21.6 %) as red-orange crystals. H NMR (C6D6, 600 MHz): δ = 7.43 (s,
4
8 H, Ar-H), 6.87 (d, JH,H = 2.29 Hz, 4 H, Xanth-CH1), 6.61 (broad s, 4
H, Xanth-CH3), 4.37 (sept, 3JH,H = 7.01 Hz, 8 H, ortho-CHMe2), 3.55 (m,
3
16 H, 4 equiv. THF-C2,5H2), 3.07 (sept, JH,H = 7.01 Hz, 4 H, para-
3
CHMe2), 1.88 (s, 12 H, CMe2), 1.50 (d, JH,H = 6.99 Hz, 24 H, A-ortho-
H2XP2·nLiCl (n = 1–1.5): A solution of XP2Cl2 (4.0 g, 4.65 mmol) in
toluene (60 mL) was added to a solution of LiAlH4 (0.194 g,
5.11 mmol) in diethylether (200 mL) at –78 °C. The reaction mixture
was stirred for 2 h before warming to room temperature and stirring
for an additional 24 h. The solvent was removed in vacuo followed
by centrifugation in toluene (45 mL) and evaporation of the mother
liquor to dryness to yield a pale yellow solid. Hexanes (35 mL) was
added followed by centrifugation and evaporation of the mother
liquor. The resulting white solid was heated under vacuum at 60 °C
for 2 d to remove all remaining solvent, yielding H2XP2·nLiCl (n = 1–
3
CHMe2), 1.46 (d, JH,H = 7.02 Hz, 24 H, para-CHMe2), 1.41 (m, 16 H,
3
4 equiv. THF-C3,4H2), 1.34 (d, JH,H = 6.99 Hz, 24 H, B-ortho-CHMe2),
1.33 (s, 36 H, CMe3) ppm. 13C NMR (C6D6, 126 MHz): δ = 154.99
(ortho-CCHMe2), 147.06 (para-CCHMe2), 144.57 (Xanth-C2), 126.98
(Xanth-C10), 124.07 (Xanth-C3H), 120.80 (Ar-CH), 110.75 (Xanth-C1H),
67.82 (THF-C2,5H2), 35.12 (para-CHMe2), 34.83 (Xanth-C9Me2), 34.66
(CMe3), 33.69 (ortho-CHMe2), 33.54 (CMe2), 31.95 (CMe3), 25.94 (B-
ortho-CHMe2), 25.80 (THF-C3,4H2), 25.04 (A-ortho-CHMe2), 24.69
(para-CHMe2) ppm. 31P NMR (C6D6, 81 MHz): δ = –85.14 ppm.
C122H180K4O6P4 (2023.05): calcd. C 72.43, H 8.97; found C 72.38, H
8.75.
1
1.5) (3.20 g, 87 %). H NMR (C6D6, 600 MHz): δ = 7.34, 6.88 (m, 2 × 4
H, Xanth-CH1 and Xanth-CH3 rac and meso), 7.27 (s, 8 H, Ar-H, rac
1
1
and meso), 6.37 (d, JH,P = 229 Hz, 2 H, P-H), 6.17 (d, JH,P = 225 Hz, [(XP2)YI(THF)2] (3) and (PTripp)3: [K2(XP2)(dme)2.5] (1) (0.250 g,
3
2 H, P-H), 4.01, 4.00 (2 sept, JH,H = 6.5 Hz, 2 × 4 H, ortho-CHMe2 rac
and meso), 2.83, 2.82 (2 sept, 3JH,H = 7.0 Hz, 2 × 2 H, para-CHMe2 rac
and meso), 1.54 (s, 6 H, CMe2 rac), 1.53, 1.51 (s, 2 × 3 H, CMe2 meso),
1.30, 1.27 (d, 3JH,H = 6.5 Hz, 2 × 12 H, ortho-CHMe2), 1.25–1.23 (m, 48
0.228 mmol) and [YI3(THF)3.5] (0.166 g, 0.228 mmol) were stirred in
THF (25 mL) for 72 h at 24 °C. The bright yellow solution was filtered
and the solvent was removed in vacuo. The resulting yellow solid
was slurried in hexanes (8 mL) before the mixture was centrifuged
Eur. J. Inorg. Chem. 2017, 2920–2927
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and the mother liquors were evaporated to dryness to provided im-
pure [(XP2)YI(THF)2] (3; 0.110 g) as an orange solid. 5 mL of O(SiMe3)2
was added to the impure solid followed by centrifugation. The result-
ing solid was isolated and dried in vacuo yielding pure [(XP2)YI(THF)2]
(0.048 g, 18 % yield). The remaining mother liquors contain a mixture
of products, including (PTripp)3, and X-ray quality crystals of (PTripp)3
were obtained by cooling a concentrated hexanes solution of this
mixture to –30 °C. X-ray quality crystals of 3 were grown by cooling
a concentrated hexanes solution of 3 to –30 °C. Solid samples of
[(XP2)YI(THF)2] were observed to lose THF slowly under dynamic vac-
uum, and the sample used for NMR spectroscopic characterization
contained just 1.5 equiv. of THF. 1H NMR ([D8]THF, 600 MHz): δ = 7.11
[11]
[12]
[13]
[14]
[15]
(s, 4 H, Ar-H), 6.74 (d, 4JH,H = 2.0 Hz, 2 H, Xanth-CH1), 5.94 (dd, 4JH,H
=
[16]
[17]
[18]
[19]
3
3
2.0, JP,H = 8.0 Hz, 2 H, Xanth-CH3), 4.40 (sept, JH,H = 7.0 Hz, 4 H,
ortho-CHMe2), 3.62 (m, 6 H, 1.5 equiv. THF-C2,5H2), 2.92 (sept, JH,H
=
3
7.0 Hz, 2 H, para-CHMe2), 1.77 (m, 6 H, 1.5 equiv. THF-C3,4H2), 1.54 (s,
6 H, CMe2), 1.28 (d, 3JH,H = 7.0 Hz, 12 H, para-CHMe2), 1.24 (d, 3JH,H
=
[20]
[21]
[22]
3
7.0 Hz, 12 H, A-ortho-CHMe2), 1.01 (d, JH,H = 7.0 Hz, 12 H, B-ortho-
CHMe2), 0.99 (s, 18 H, CMe3) ppm. 13C NMR ([D8]THF, 126 MHz): δ =
155.69 (ortho-CCHMe2), 149.28 (para-CCHMe2), 144.06 (Xanth-C2),
136.51 (d, Ar-Cipso), 128.02 (Xanth-C10), 123.94 (Xanth-C3H), 121.66
(Ar-CH), 114.83 (Xanth-C1H), 35.24 (para-CHMe2), 34.66 (CMe3), 34.53
(ortho-CHMe2), 34.45 (Xanth-C9Me2), 33.11 (CMe2), 31.49 (CMe3), 26.18
(B-ortho-CHMe2), 25.66 (A-ortho-CHMe2), 24.34 (para-CHMe2) ppm.
[23]
[24]
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N. R. Andreychuk, D. J. H. Emslie, Angew. Chem. Int. Ed. 2013, 52, 1696–
1699; Angew. Chem. 2013, 125, 1740.
31P NMR ([D8]THF, 81 MHz): δ = 1.28 (d, JY,P = 162 Hz) ppm.
1
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Acknowledgments
D. J. H. E. thanks Natural Sciences and Engineering Research
Council of Canada (NSERC) for a Discovery Grant and an Strategic
Grant in collaboration with NOVA Chemicals. K. S. A. M. thanks
the Government of Ontario for an OGS – Queen Elizabeth II Grad-
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Keywords: Cage compounds · Phosphido ligand · Pincer
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Received: April 20, 2017
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