Alkali metal complexes of a tert -butylphosphine-bridged biphenolate ligand

Article abstract of DOI:10.1021/om100495e

The coordination chemistry of group 1 metals with a potentially tridentate, dianionic biphenolate phosphine ligand that carries a phosphorus-bound tert-butyl group is described. Deprotonation of bis(3,5-di-tert-butyl-2- hydroxyphenyl)-tert-butylphosphine

Full text of DOI:10.1021/om100495e

Organometallics 2010, 29, 6201–6208 6201
DOI: 10.1021/om100495e
Alkali Metal Complexes of a tert-Butylphosphine-Bridged Biphenolate Ligand
Yu-Lin Hsu and Lan-Chang Liang*
Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University,
Kaohsiung 80424, Taiwan, Republic of China
Received May 19, 2010
The coordination chemistry of group 1 metals with a potentially tridentate, dianionic biphenolate
phosphine ligand that carries a phosphorus-bound tert-butyl group is described. Deprotonation of bis(3,5-
di-tert-butyl-2-hydroxyphenyl)-tert-butylphosphine (H2[tBu-OPO]) with two equivalents of n-BuLi, NaH,
or KH in ethereal solutions produces the corresponding alkali metal complexes {[tBu-OPO]M2(solv)x}2
(M = Li, Na, K; solv = DME, THF). An X-ray diffraction study of the lithium derivative reveals a dimeric
structure that contains two [tBu-OPO]Li2(DME) units linked by two dative O-Li bonds; the two lithium
atoms in each monomeric [tBu-OPO]Li2(DME) are bridged by both phenolate oxygen donors with only
one lithium being coordinated to the phosphorus donor. As a result, the Li4O4 moiety in {[tBu-OPO]Li2}2
constitutes three successive Li2O2 tetragons fused in an open cubane structure. The coordination of the
phosphorus donor to lithium in {[tBu-OPO]Li2(DME)}2 is also confirmed by variable-temperature
7
31P{1H} and Li{1H} NMR studies. Interestingly, the sodium complex is composed of two [tBu-
OPO]Na2(DME)2 units linked by a bridging DME; each [tBu-OPO]Na2(DME)2 subunit is structurally
similar to its lithium analogue though adopting one more coordinated DME. The potassium complex also
contains two [tBu-OPO]K2(THF)2 moieties linked with two dative O-K bridges; the structure of the
monomeric [tBu-OPO]K2(THF)2 unit, however, is markedly distinct from those of its lighter congeners. In
addition to the anticipated fac-coordination from the heteroatoms in the biphenolate phosphine ligand, one
of the potassium atoms in monomeric [tBu-OPO]K2(THF)2 is π-bound to one of the aryl rings
incorporated in the [tBu-OPO]2- backbone.
Introduction
phosphine ligand, [PhP(3,5-tBu2C6H2-2-O)2]2- ([Ph-OPO]2-),
have been prepared.13-16 This particular ligand falls into the
category of current interest in chelating biphenolate ancillary
design, in which not only can the aryl substituents be readily
modified for steric and electronic tuning but the ways to link the
two phenolate rings are also versatile.17-29 As a result, rich
Alkali metal complexes are ubiquitous in organic and inorganic
syntheses. They are usually used as starting materials for depro-
tonation, nucleophilic addition, metathetical reactions, etc.1,2
Their unique reactivity also makes them an attractive candidate
as initiators for polymer preparation.3-6 For instance, lithium
aggregates containing alkoxides and/or aryloxides have shown
remarkable activity in ring-opening polymerization (ROP) of
cyclic molecules and, in some cases, in a controlled manner.7
We are currently investigating reaction chemistry involving
metal complexes of hybrid chelating ligands.8-12 In particular,
a series of group 1, 4, 5, and 14 derivatives of a biphenolate
(11) Liang, L.-C.; Chien, P.-S.; Lee, P.-Y. Organometallics 2008, 27,
3082–3093.
(12) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics 2003, 22,
3007–3009.
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(14) Liang, L.-C.; Chang, Y.-N.; Lee, H. M. Inorg. Chem. 2007, 46,
2666–2673.
(15) Liang, L.-C.; Cheng, L.-C.; Tsai, T.-L.; Hu, C.-H.; Guo, W.-H.
Inorg. Chem. 2009, 48, 5697–5703.
(16) Liang, L.-C.; Chang, Y.-N.; Chen, H.-S.; Lee, H. M. Inorg.
Chem. 2007, 46, 7587–7593.
*To whom correspondence should be addressed. E-mail: lcliang@
mail.nsysu.edu.tw.
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2010 American Chemical Society
Published on Web 11/03/2010
pubs.acs.org/Organometallics

6202 Organometallics, Vol. 29, No. 23, 2010
Hsu and Liang
Figure 1. Molecular structures of H2[tBu-OPO] (left) and H2[Ph-OPO] (right) with thermal ellipsoids drawn at the 35% probability level.
˚
structural chemistry has evolved. We have recently shown that
[Ph-OPO]2- appears to have a strong tendency to form bis-
ligated complexes with group 4 and 5 metals.14,15 We envisioned
that such propensity may perhaps be inhibited, at least to some
degree, by replacing the phosphorus-bound phenyl group with a
tert-butyl, the monoligated complexes derived from which
should be more sterically demanding and less electronically
deficient. Having this in mind, we have set out to prepare a
tert-butylphosphine-bridged biphenolate ligand and pursue its
coordination and reaction chemistry. In this contribution, we
describe the preparation of such a ligand and its group 1
derivatives. Interestingly, these alkali metal complexes exhibit
distinct structural motifs from their phosphorus-bound phenyl
counterparts.13 We note that although biphenolate phosphine
ligands have been known since 1980,30 structurally characterized
alkali metal derivatives are extremely rare.13,31
Table 1. Selected Bond Distances (A) and Angles (deg) for
H2[tBu-OPO] and H2[Ph-OPO]
compound
H2[tBu-OPO]
H2[Ph-OPO]
C-O
1.374(4), 1.382(4)
1.832(4), 1.832(4)
1.867(4)
1.367(3), 1.374(3)
1.829(2), 1.831(2)
1.816(2)
107.40(10), 106.38(10),
102.64(10)
P-C(phenolate)
P-tBu or P-Ph
C-P-C
105.16(17), 108.04(18),
109.84(18)
are summarized in Table 1. On the basis of geometry, bond
distances, and bond angles, both molecules are virtually
isostructural to each other, indicating the phosphorus sub-
stituent has little influence on the sterics of these protio
ligands. The electronic effect, however, is perhaps more
noticeable, as evidenced by the JHP values observed for the
hydroxyl protons in the 1H NMR of these molecules.
Deprotonation of H2[tBu-OPO] with two equivalents of
nBuLi at -35 °C in a variety of solvents produced cleanly the
dilithium complex as indicated by 31P{1H} NMR spectros-
copy. Upon lithiation, the 31P chemical shift moves down-
field from -60 to ca. -13 ppm in nonpolar (e.g., toluene,
pentane) or to ca. -22 ppm in polar solvents (e.g., DME,
THF, Et2O). We found that the most convenient method to
isolate a well-defined product from these reactions is perhaps
that conducted in DME solutions, from which the dilithium
complex was obtained quantitatively (Scheme 1) as colorless
prisms after recrystallization from pentane.
An X-ray diffraction study revealed that the lithium
complex is an approximately C2-symmetric dimer composed
of two [tBu-OPO]Li2(DME) units linked by two dative O-Li
bonds (Figure 2, Table 2). The two lithium atoms in each
monomeric [tBu-OPO]Li2(DME) are bridged by both phe-
nolate oxygen donors. As a result, the Li4O4 moiety in {[tBu-
OPO]Li2}2 constitutes three fused Li2O2 tetragons in an open
cubane motif. The four atoms in each Li2O2 tetragon are
approximately coplanar, as evidenced by the corresponding
torsion angles and the sum of internal angles. The dihedral
angles between the central tetragon and the two peripheral
ones are 133.28° and 136.73°. These wide angles are ascrib-
able to steric congestion imposed by each monomeric moi-
ety. The C2 axis coincides with the normal vectors penetrat-
ing the center of the central Li2O2 tetragon.
Results and Discussion
The tert-butyl-substituted ligand precursor bis(3,5-di-tert-
butyl-2-hydroxyphenyl)-tert-butylphosphine (H2[tBu-OPO])
may be readily prepared with conditions similar to those of
its phenyl analogue.32 In situ lithiation of 2-bromo-4,6-di-tert-
butylphenol with two equivalents of nBuLi in diethyl ether at
-35 °C followed by addition of tert-butyldichlorophosphine
generated, after anaerobic aqueous workup, H2[tBu-OPO] as
an off-white solid in 58% yield. Solution NMR data are
indicative of Cs symmetry for this molecule. The hydroxyl
protons are detected as a doublet resonance at 7.61 ppm with
JHP = 12 Hz. In comparison, the corresponding JHP value for
H2[Ph-OPO] is 8 Hz.32 The phosphorus atom resonates at
-60 ppm, a signal that is shifted more upfield than that of
H2[Ph-OPO] (-50 ppm)32 but consistent with what is anti-
cipated in view of the more electron-releasing nature for a tert-
butyl group.
In order to compare the structural parameters of H2[tBu-
OPO] and H2[Ph-OPO], we attempted X-ray diffraction
studies for both molecules. Single crystals of H2[tBu-OPO]
and H2[Ph-OPO] were both grown from a concentrated
acetonitrile solution at -35 °C. The solid-state structures
are depicted in Figure 1. Selected bond distances and angles
In comparison with the phosphorus-bound phenyl deriv-
ative [Ph-OPO]Li2(DME)2 (Figure 3),13 the monomeric
unit in {[tBu-OPO]Li2(DME)}2 is notably short of one coor-
dinated DME. The formation of a dimeric {[tBu-OPO]Li2-
(DME)}2 instead of [tBu-OPO]Li2(DME)2, however, reflects
the less electron-deficient nature for monomeric [tBu-OPO]-
Li2(DME) than [Ph-OPO]Li2(DME), considering DME is a
much better coordinating base than dative phenolate oxygen
atoms. Such discrepancy is consistent with a recent result
(26) Takeuchi, D.; Nakamura, T.; Aida, T. Macromolecules 2000, 33,
725–729.
(27) Floriani, C.; Corazza, F.; Lesueur, W.; Chiesi-Villa, A.; Guastini,
C. Angew. Chem., Int. Ed. 1989, 28, 66–67.
(28) Corazza, F.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg.
Chem. 1991, 30, 145–148.
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(30) Tzschach, A.; Nietzschmann, E. Z. Chem. 1980, 20, 341–342.
(31) Carmichael, C. D.; Fryzuk, M. D. Dalton Trans. 2008, 800–806.
(32) Siefert, R.; Weyhermuller, T.; Chaudhuri, P. J. Chem. Soc.,
Dalton Trans. 2000, 4656–4663.

Article
Organometallics, Vol. 29, No. 23, 2010 6203
Scheme 1
found for these lithium atoms with one of the O-bound aryl
˚
˚
carbons (2.513(7) A for Li(1) and 2.459(8) A for Li(4)). These
distances are well within the sum of lithium and carbon van der
Waals radii of 3.45 A.34 Interestingly, the coordination geometry
˚
of Li(2) and Li(3) is trigonal monopyramidal, with O(2) and
O(3) being the corresponding apical donor.
Solution NMR data of {[tBu-OPO]Li2(DME)}2 at room
temperature are indicative of Cs symmetry for this molecule,
suggesting a fluxional process involving presumably the
formation of monomeric [tBu-OPO]Li2(DME) via dative
O-Li bond dissociation. This hypothesis is in accord with
the structurally characterized, mononuclear [Ph-OPO]Li2-
(DME)2.13 The 1H NMR spectrum exhibits two doublets for
aryl protons and two singlets for aryl tert-butyls. The integral
of DME signals relative to that of [tBu-OPO]2- empirically
confirms the presence of {[tBu-OPO]Li2(DME)}2. In the pre-
sence of an excess amount of DME (e.g., 2 equiv), solutions of
{[tBu-OPO]Li2(DME)}2 exhibit only one set of resonances for
DME protons, a result that is ascribable to facile exchange
between coordinated and free DME molecules. The coordinated
DME in {[tBu-OPO]Li2(DME)}2 is thus labile and tends to
dissociate. Indeed, standing a C6D6 or toluene-d8 solution of
{[tBu-OPO]Li2(DME)}2 at room temperature for several hours
led to observation of some precipitates. The 1H NMR spectra of
such solutions are too complicated to be interpretable, but are
reflective of the formation of C1-symmetric molecules. We
tentatively ascribe this result to, at least in part, the dissociation
of one coordinated DME from {[tBu-OPO]Li2(DME)}2. Ac-
cordingly, the 31P{1H} NMR of these C6D6 and toluene-d8 solu-
tions reveals two broad singlets, which, upon addition of an
excess amount of DME, merge to give one singlet at -20.7 ppm
as what is observed for a freshly prepared sample. Consistently,
prolonged heating of solid {[tBu-OPO]Li2(DME)}2 under dy-
namic vacuum to 60 °C for 3 h led to a decrease in coordinated
DME, as indicated by 1H NMR. A variable-temperature 31P{1H}
NMR study in toluene-d8 at -80 °C revealed two distinct
1:1:1:1 quartet resonances at -23.3 and -30.1 ppm with coupl-
ing constants of 41 and 60 Hz, respectively, indicating the coor-
dination of the soft phosphorus donors to hard, quadrupolar 7Li
atoms (I = 3/2, natural abundance 92.6%). The magnitude of
these coupling constants is similar to those found for other
lithium phosphine complexes such as Li[N(o-C6H4PPh2)2]-
(THF)2 (34 Hz),12,35 [Li(THF)2][o-(2,6-Me2C6H3N)C6H4PPh2]
Figure 2. Molecular structure of {[tBu-OPO]Li2(DME)}2 with
thermal ellipsoids drawn at the 35% probability level. All
methyls of the tert-butyl groups are omitted for clarity.
reported by Fryzuk et al.; when THF is used in the place of
DME for the preparation of [Ph-OPO]Li2 adducts, coordi-
nation of the dative phenolate oxygen to lithium becomes
comparable, and thus a dimeric {[Ph-OPO]Li2(THF)2}2 is
isolable (Figure 3).31 The distinct conformations of [Ph-
OPO]Li2(DME)2 and {[Ph-OPO]Li2(THF)2}2 also underscore
the significance of coordinating solvent effect (DME versus
THF). Though {[tBu-OPO]Li2(DME)}2 and {[Ph-OPO]Li2-
31
(THF)2}2 are conformationally comparable, the three suc-
cessive Li2O2 tetragons comprise an open cubane structure for
the former but a ladder configuration for the latter. A similar
ladder configuration is also found for {[SPS]Li2(DME)}2
([SPS]2- = [PhP(3-Me3SiC6H3-2-S)2]2-).33
The bond distances and angles of {[tBu-OPO]Li2(DME)}2
are essentially similar to those of [Ph-OPO]Li2(DME)213 and
{[Ph-OPO]Li2(THF)2}2.31 The phosphorus donor in the
monomeric [tBu-OPO]Li2(DME) unit is found to coordinate
to only one of the lithium atoms. The slightly shorter P-Li
t
˚
distances in {[ Bu-OPO]Li2(DME)}2 (2.420(6) and 2.440(6) A)
than {[Ph-OPO]Li2(THF)2}2 (2.499(3) A)31 are consistent with
˚
the stronger electron-releasing nature for the tert-butyl substit-
uents. In comparison, the P-Li distance in [Ph-OPO]Li2-
(DME)2 is rather longer (2.573(5) A).13 As anticipated in view
˚
of the inherent geometry imposed by the phosphorus donor, the
[tBu-OPO]2- ligand adopts a facial coordination mode with
respect to Li(2) and Li(3). The geometry of Li(1) and Li(4) is
perhaps best described as a distorted tetrahedron with the
dihedral angle of two chelating O-Li-O planes being 72.44°
and 65.38°, respectively. An additional close contact is also
(34) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry:
Principles of Structure and Reactivity, 4th ed.; Harper Collins: New York,
1993.
(33) Froelich, N.; Hitchcock, P. B.; Hu, J.; Lappert, M. F.; Dilworth,
J. R. J. Chem. Soc., Dalton Trans. 1996, 1941–1946.
(35) Liang, L.-C.; Chien, P.-S.; Lin, J.-M.; Huang, M.-H.; Huang,
Y.-L.; Liao, J.-H. Organometallics 2006, 25, 1399–1411.

6204 Organometallics, Vol. 29, No. 23, 2010
Hsu and Liang
Figure 3. ChemDraw drawings of [Ph-OPO]Li2(DME)2,13 {[Ph-OPO]Li2(THF)2}2,31 and {[Ph-OPO]K2(DME)2}2.13
t
Table 2. Selected Bond Distances (A), Bond Angles (deg), and Torsion Angles (deg) for {[ Bu-OPO]Li2(DME)}2
˚
Li(1)-O(1) 1.893(6)
Li(2)-O(2) 2.124(7)
Li(4)-O(4) 1.920(7)
Li(4)-O(7) 2.011(7)
Li(4)-O(8) 2.027(7)
Li(4)-O(3) 2.151(7)
Li(1)-O(6) 2.006(7)
Li(2)-P(1) 2.420(6)
Li(1)-O(2) 2.063(7)
Li(3)-O(2) 1.875(6)
Li(1)-O(5) 2.078(7)
Li(3)-O(4) 1.955(6)
Li(2)-O(3) 1.850(6)
Li(3)-O(3) 2.075(6)
Li(2)-O(1) 1.909(7)
Li(3)-P(2) 2.440(6)
O(1)-Li(1)-O(6) 126.9(3)
O(1)-Li(1)-O(2) 98.7(3)
O(6)-Li(1)-O(2) 110.0(3)
O(1)-Li(1)-O(5) 110.9(3)
O(6)-Li(1)-O(5) 79.9(3)
O(2)-Li(1)-O(5) 133.8(3)
O(3)-Li(2)-O(1) 137.6(4)
O(3)-Li(2)-O(2) 100.8(3)
O(1)-Li(2)-O(2) 96.1(3)
O(3)-Li(2)-P(1) 139.2(3)
O(1)-Li(2)-P(1) 81.3(2)
Li(3)-O(3)-Li(2)-O(2) -3.06
O(2)-Li(2)-P(1) 82.0(2)
O(2)-Li(3)-O(4) 139.3(4)
O(2)-Li(3)-O(3) 101.8(3)
O(4)-Li(3)-O(3) 97.8(3)
O(2)-Li(3)-P(2) 138.9(3)
O(4)-Li(3)-P(2) 78.7(2)
O(3)-Li(3)-P(2) 82.2(2)
O(4)-Li(4)-O(7) 130.2(4)
O(4)-Li(4)-O(8) 110.9(3)
O(7)-Li(4)-O(8) 80.2(3)
O(4)-Li(4)-O(3) 96.3(3)
Li(3)-O(3)-Li(4)-O(4) 8.63
O(7)-Li(4)-O(3) 104.3(3)
O(8)-Li(4)-O(3) 140.2(4)
Li(1)-O(1)-Li(2) 86.6(3)
Li(3)-O(2)-Li(1) 122.8(3)
Li(3)-O(2)-Li(2) 77.7(2)
Li(1)-O(2)-Li(2) 77.0(2)
Li(2)-O(3)-Li(3) 79.5(3)
Li(2)-O(3)-Li(4) 127.4(3)
Li(3)-O(3)-Li(4) 77.9(2)
Li(4)-O(4)-Li(3) 86.6(3)
Li(2)-O(2)-Li(1)-O(1) 9.39
1
(34 Hz),36 [Li(THF)2][o-(2,6-iPr2C6H3N)C6H4PPh2] (38 Hz),37
[(2,4,6-Me3C6H2)NLi-2-(4-MeC6H3)]2PPh(dioxane) (40 Hz),38
Li[N(o-C6H4PiPr2)2](THF) (46 Hz),35 Li[N(o-C6H4PCy2)2]-
(THF) (48 Hz),35 [(Me2PCH2)3CO]Li3[C(CHPMe2)3] (58
Hz),39 and the lithium phosphide derivative [Li(tmeda)]2[1,2-
C6H4(PPh)2] (35 Hz).40 Consistently, the 7Li{1H} NMR
spectrum at -80 °C exhibits two doublet (3.0 ppm, JPLi
=
60 Hz; 1.6 ppm, 1JPLi = 41 Hz) and two singlet (-0.8 and -0.9
ppm) resonances, confirming the phosphorus donor in each
dinuclear unit is bound to one rather than two lithium centers.
The reaction of H2[tBu-OPO] with an excess amount of
NaH in DME at -35 °C afforded quantitatively colorless
prisms of {[tBu-OPO]Na2(DME)2}2(μ-DME) (Scheme 2) suit-
able for X-ray diffraction analysis. Reminiscent of its lithium
analogue, solution NMR data of the sodium complex are con-
sistent with Cs symmetry, with two distinct signals for aryl
(36) Liang, L.-C.; Lee, W.-Y.; Yin, C.-C. Organometallics 2004, 23,
3538–3547.
(37) Liang, L.-C.; Lee, W.-Y.; Hung, C.-H. Inorg. Chem. 2003, 42,
5471–5473.
1
(38) MacLachlan, E. A.; Fryzuk, M. D. Organometallics 2005, 24,
1112–1118.
protons and two for aryl tert-butyl groups in the H NMR
spectrum. The phosphorus donors resonate at -23.6 ppm.
Figure 4 depicts the molecular structure of {[tBu-OPO]Na2-
(DME)2}2(μ-DME). Selected bond distances, bond angles, and
€
(39) Muller, G.; Feustel, A. Organometallics 2003, 22, 3049–3058.
(40) Hitchcock, P. B.; Lappert, M. F.; Leung, W.-P.; Yin, P. J. Chem.
Soc., Dalton Trans. 1995, 3925–3932.

Article
Organometallics, Vol. 29, No. 23, 2010 6205
Scheme 2
congeners, attempts to grow X-ray quality crystals of the
potassium complex from DME solutions were not success-
ful. Colorless prisms of {[tBu-OPO]K2(THF)2}2 suitable for
X-ray diffraction analysis, however, were isolated in 93%
yield after recrystallization from THF solutions (Scheme 3).
Surprisingly, DME is not incorporated in this molecule on
the basis of X-ray structural investigation, a result that is
somewhat consistent with the facile dissociative nature of
coordinated DME in {[tBu-OPO]Li2(DME)}2 (vide supra).
Instead, the potassium complex contains two coordinated
THF molecules per [tBu-OPO]2- ligand, as indicated by 1H
NMR. It is noteworthy that {[tBu-OPO]K2(THF)2}2 adopts
fewer ethereal oxygen donors than the previously established
{[Ph-OPO]K2(DME)2}2.13 Reminiscent of lithium and so-
dium complexes, {[tBu-OPO]K2(THF)2}2 exhibits solution
Cs symmetry on the NMR time scale at room temperature, as
evidenced by two distinct signals for aryl protons and two for
aryl tert-butyl groups in the 1H NMR spectrum. The phos-
phorus donors resonate at -17.7 ppm.
Figure 4. Molecular structure of {[tBu-OPO]Na2(DME)2}2-
(μ-DME) with thermal ellipsoids drawn at the 35% probability
level. All methyls of the tert-butyl groups are omitted for clarity.
torsion angles are summarized in Table 3. As illustrated, this
sodium complex contains two [tBu-OPO]Na2(DME)2 units
linked by one bridging DME. The molecule is approximately
Ci-symmetric; the inversion center lies at the central point
between two methylene carbons in the bridging DME. Each
oxygen donor in the bridging DME is bound to both sodium
atoms in the [tBu-OPO]Na2(DME)2 subunit; so are both oxy-
gen donors in [tBu-OPO]2-. Interestingly, each [tBu-OPO]Na2-
(DME)2 unit is structurally similar to its lithium analogue but
adopts one more η2-DME, consistent with the larger atomic size
of the former. In contrast to the nearly planar Li2O2 found in
monomeric [tBu-OPO]Li2(DME), the Na2O2 moiety in the
[tBu-OPO]Na2(DME)2 subunit adopts a butterfly-like struc-
ture. A close contact is also found for Na(2) with both O-bound
aryl carbons, where the corresponding distances of 2.975(3) and
The molecular structure of {[tBu-OPO]K2(THF)2}2 is
depicted in Figure 5. Selected bond distances, bond angles,
and torsion angles are summarized in Table 4. As illustrated,
this molecule contains two [tBu-OPO]K2(THF)2 units linked
with two K-O bridges. The structure is approximately
Ci-symmetric, with the inversion center lying at the central
point of the bridging K2O2 square plane. In comparison, the
four potassium atoms in dimeric {[Ph-OPO]K2(DME)2}2 are
connected by six heteroatoms in two [Ph-OPO]2- ligands
(Figure 3).13 In contrast to what is found for {[tBu-OPO]Li2-
(DME)}2 and {[tBu-OPO]Na2(DME)2}2(μ-DME), the two
potassium atoms in the monomeric [tBu-OPO]K2(THF)2
˚
2.883(3) A are well within the sum of sodium and carbon van
34
˚
der Waals radii of 3.95 A. The coordination number for
unit are not bridged by both oxygen donors in [tBu-OPO]2-
.
metallic elements in {[tBu-OPO]Na2(DME)2}2(μ-DME) is thus
larger than that for {[tBu-OPO]Li2(DME)}2. The conformation
of the [tBu-OPO]Na2(DME)2 subunit is coincidentally identical
Instead, they are connected by one THF and one oxygen
donor in the biphenolate phosphine ligand. Interestingly,
one of the aryl rings in [tBu-OPO]2- is π-bound to K(2). The
13
to that of the previously established [Ph-OPO]Li2(DME)2
though the phosphorus substituents incorporated in the biphe-
˚
K-C distances (ranging from 3.007(5) to 3.275(5) A) are
comparable to those of {[Ph-OPO]K2(DME)2}2 (ranging
nolate phosphine ligands are different. The P-Na distance of
2.8757(14) A is comparable to other phosphine sodium com-
from 3.126(3) to 3.210(3) A),13 [K(η5-C5H5)]x (ranging from
˚
˚
2.955(5) to 3.140(6) A),43 K(η5-C5H5)(18-crown-6) (ranging
˚
plexes such as Na4[iPr2PCHdC(O)Ph]4 (2.852(2) A) and
41
˚
from 2.969(6) to 3.131(7) A),44 [K4(p-tert-butylcalix[4]arene-
˚
n
42
˚
Na2[( Pr2P)2CCH2]2(THF)6 (2.9172(16) and 2.9043(16) A).
45
4H)(THF)5]2 (ranging from 3.005(4) to 3.180(4) A), and
˚
Treatment of H2[tBu-OPO] with an excess amount of KH
in DME at -35 °C afforded cleanly the potassium complex,
as evidenced by 31P{1H} NMR. In contrast to its lighter
[(THF)3K][(μ-OC6H3Me2-2,6)2Y(OC6H3Me2-2,6)2(THF)2]
(43) Dinnebier, R. E.; Behrens, U.; Olbrich, F. Organometallics 1997,
16, 3855–3858.
(44) Neander, S.; Tio, F. E.; Buschmann, R.; Behrens, U.; Olbrich, F.
J. Organomet. Chem. 1999, 582, 58–65.
(45) Gueneau, E. D.; Fromm, K. M.; Goesmann, H. Chem.;Eur. J.
2003, 9, 509–514.
(41) Fryzuk, M. D.; Gao, X. L.; Rettig, S. J. Can. J. Chem. 1995, 73,
1175–1180.
(42) Izod, K.; McFarlane, W.; Tyson, B. V.; Clegg, W.; Harrington,
R. W. Dalton Trans. 2004, 4074–4078.

6206 Organometallics, Vol. 29, No. 23, 2010
Hsu and Liang
t
˚
Table 3. Selected Bond Distances (A), Bond Angles (deg), and Torsion Angles (deg) for {[ Bu-OPO]Na2(DME)2}2(μ-DME)
O(1)-Na(2) 2.273(3)
O(3)-Na(1) 2.424(3)
O(7)-Na(1) 2.461(2)
P(1)-Na(1) 2.8757(14)
O(1)-Na(1) 2.340(2)
O(4)-Na(1) 2.460(3)
O(2)-Na(1) 2.317(2)
O(2)-Na(2) 2.318(3)
O(5)-Na(2) 2.387(3)
O(6)-Na(2) 2.377(3)
Na(2)-O(1)-Na(1) 79.70(8)
Na(1)-O(2)-Na(2) 79.25(8)
O(2)-Na(1)-O(1) 92.37(8)
O(2)-Na(1)-O(3) 171.23(10)
O(1)-Na(1)-O(3) 96.38(9)
O(2)-Na(1)-O(7) 91.87(9)
O(1)-Na(1)-O(7) 85.60(8)
O(3)-Na(1)-O(7) 89.39(9)
Na(1)-O(1)-Na(2)-O(2) 28.48
O(2)-Na(1)-O(4) 101.52(9)
O(1)-Na(1)-O(4) 165.59(10)
O(3)-Na(1)-O(4) 69.71(9)
O(7)-Na(1)-O(4) 97.63(9)
O(2)-Na(1)-P(1) 69.31(6)
O(1)-Na(1)-P(1) 68.33(6)
O(3)-Na(1)-P(1) 113.51(8)
O(7)-Na(1)-P(1) 146.36(8)
O(4)-Na(1)-P(1) 112.96(7)
O(1)-Na(2)-O(2) 94.09(9)
O(1)-Na(2)-O(6) 114.99(11)
O(2)-Na(2)-O(6) 118.28(11)
O(1)-Na(2)-O(5) 124.74(11)
O(2)-Na(2)-O(5) 134.47(11)
O(6)-Na(2)-O(5) 69.38(10)
Scheme 3
˚
respect to K(1). The P-K distance of 3.1734(17) A is notably
shorter than those found in {[Ph-OPO]K2(DME)2}2 (3.3853(9),
13
˚
3.5868(9), and 3.3317(9) A).
Several phenolate complexes are known to initiate cataly-
tic ROP of heterocyclic molecules.13,29,54 The catalytic activ-
ities of {[tBu-OPO]M2(solv)x}2 with respect to ROP of ε-
caprolactone (ε-CL) were examined. Preliminary results are
summarized in Table 5. Gel permeation chromatography
(GPC) analyses of the resulting products reveal a monomo-
dal trace with a reasonably narrow molecular weight dis-
tribution (Mw/Mn < 1.5) though the measured molecular
weights are rather low, particularly that derived from {[tBu-
OPO]Na2(DME)2}2(μ-DME). These products are thus best
described as oligomers. In contrast, high molecular weight
polymers were obtained with catalytic analogues derived
from the [Ph-OPO]2- ligand.13 Data listed in entries 1 and
4 highlight the discrepancy between {[tBu-OPO]Li2(DME)}2
and [Ph-OPO]Li2(DME)2. Nevertheless, the monomer con-
versions for reactions catalyzed by {[tBu-OPO]M2(solv)x}2
are typically high. These results imply that chain transfer
reactions frequently occur and concomitantly generate an
active, presumably new, species to reinitiate a new propagat-
ing chain. It is likely that the identity of the catalytically
active species is nearly uniform, though not single-site, as
suggested by the measured Mw/Mn values.
Figure 5. Molecular structure of {[tBu-OPO]K2(THF)2}2 with
thermal ellipsoids drawn at the 35% probability level. All
methyls of the tert-butyl groups and methylenes of THF are
omitted for clarity.
(ranging from 3.288(9) to 3.400(10) A). The η6-coordina-
46
˚
tion for an arene to potassium has also been reported
elsewhere.47-50 The structural discrepancies found for the
potassium complex in comparison with its lighter analogues
likely reflect the larger atomic size and the preferred
π-coordination mode for the former. It is interesting to note
that crystallographically characterized potassium complexes
of tri(hydrocarbyl)phosphine are extremely rare.13,51-53 The
[tBu-OPO]2- ligand adopts a facial coordination mode with
(46) Evans, W. J.; Ansari, M. A.; Ziller, J. W.; Khan, S. I. J.
Organomet. Chem. 1998, 553, 141–148.
(47) Chadwick, S.; Englich, U.; Ruhlandt-Senge, K. Organometallics
Conclusions
1997, 16, 5792–5803.
(48) Hull, K. L.; Carmichael, I.; Noll, B. C.; Henderson, K. W.
Chem.;Eur. J. 2008, 14, 3939–3953.
(49) Gueneau, E. D.; Fromm, K. M.; Goesmann, H. Chem.;Eur. J.
We have prepared a series of group 1 metal complexes of
[tBu-OPO]2- and established the solution and solid-state
structures of these molecules by multinuclear NMR spec-
troscopy and X-ray crystallography. These complexes, as
elucidated by X-ray diffraction studies, generally constitute
two subunits of the type [tBu-OPO]M2(solv)x; they are either
2003, 9, 509–514.
(50) Frenzel, C.; Jorchel, P.; Hey-Hawkins, E. Chem. Commun. 1998,
1363–1364.
(51) Karsch, H. H.; Graf, V. W.; Reisky, M. Chem. Commun. 1999,
1695–1696.
(52) Gamer, M. T.; Roesky, P. W. Organometallics 2004, 23, 5540–
5544.
(53) Izod, K.; Young, J.; Clegg, W.; Harrington, R. W. Dalton Trans.
(54) Chisholm, M. H.; Lin, C.-C.; Gallucci, J. C.; Ko, B.-T. Dalton
Trans. 2003, 406–412.
2005, 1658–1663.

Article
Organometallics, Vol. 29, No. 23, 2010 6207
t
Table 4. Selected Bond Distances (A), Bond Angles (deg), and Torsion Angles (deg) for {[ Bu-OPO]K2(THF)2}2
˚
O(1)-K(2) 2.596(4)
O(3)-K(2) 2.664(4)
K(1)-O(2)0 2.545(4)
K(1)-K(1)0 3.682(2)
K(1)-K(2) 3.7580(17)
O(1)-K(1) 2.673(3)
O(4)-K(2) 2.746(4)
O(2)-K(1)0 2.545(4)
O(2)-K(1) 2.683(4)
O(4)-K(1) 2.863(4)
P(1)-K(1) 3.1734(17)
K(2)-O(1)-K(1) 90.99(11)
K(1)0-O(2)-K(1) 89.51(11)
K(2)-O(4)-K(1) 84.12(10)
O(2)0-K(1)-O(1) 164.82(12)
O(2)0-K(1)-O(2) 90.49(11)
O(1)-K(1)-O(2) 100.33(11)
K(1)-O(2)-K(1)-O(2) 0.00
O(2)0-K(1)-O(4) 116.23(12)
O(1)-K(1)-O(4) 72.68(11)
O(2)-K(1)-O(4) 99.60(11)
O(2)0-K(1)-P(1) 121.20(9)
O(1)-K(1)-P(1) 57.27(8)
O(2)-K(1)-P(1) 61.33(8)
O(4)-K(1)-O(1)-K(2) -44.34
O(4)-K(1)-P(1) 118.58(9)
O(1)-K(2)-O(3) 146.22(14)
O(1)-K(2)-O(4) 75.82(11)
O(3)-K(2)-O(4) 90.15(15)
Table 5. Catalytic ROP of ε-CLa
atoms is based on the DEPT 13C NMR spectroscopy. 31P
and 7Li NMR spectra are referenced externally using 85%
H3PO4 at δ 0 and LiCl in D2O at δ 0, respectively. Routine
coupling constants are not listed. All NMR spectra were re-
corded at room temperature in specified solvents unless other-
wise noted. Elemental analysis was performed on a Heraeus
CHN-O Rapid analyzer.
GPC analyses were carried out at 45 °C on a JASCO instru-
ment equipped with two Waters Styragel HR columns in series
and a JASCO RI-2031 refractive index detector. HPLC grade
THF was supplied at a constant flow rate of 1.0 mL/min with a
JASCO PU-2080 isocratic HPLC pump. Molecular weights (Mn
and Mw) were determined by interpolation from calibration
plots established with polystyrene standards.
conv
(%)b Mn(calc)c Mn(GPC)d Mw/Mn
d
entry
initiator
1
2
{[tBu-OPO]Li2(DME)}2
{[tBu-OPO]Na2(DME)2}2-
(μ-DME)
100
94
22.8
21.5
2.9
0.5
1.44
1.48
3
{[tBu-OPO]K2(THF)2}2
96
100
21.9
22.8
2.5
28.5
1.43
1.53
413 [Ph-OPO]Li2(DME)2
e
a Conditions: [initiator] = 1.2 mM, 200 equiv of ε-CL, toluene, 80 °C,
3 h; reaction parameters were not optimized; Mn values are reported in
kg mol-1 unit. b Determined by 1H NMR analysis. c Calculated from fw
of ε-CL ꢀ 200 ꢀ conversion, assuming one propagation chain per
initiator. d Measured by GPC in THF, calibrated with polystyrene
standards. e [initiator] = 1.4 mM, 12 h.
X-ray Crystallography. Data were collected on a Bruker-
Nonius Kappa CCD diffractometer with graphite-monochro-
connected by M-O bridges (M = Li, K) or linked with a
μ2-DME molecule (M = Na). Interestingly, the alkali metal
centers within the [tBu-OPO]Li2(DME) and [tBu-OPO]Na2-
(DME)2 subunits are connected by both phenolate oxygen
donors in [tBu-OPO]2-, whereas those in [tBu-OPO]K2-
(THF)2 are linked by one coordinated THF and one pheno-
late oxygen donor. Of particular note is the construction of
an open cubane structure constituted by three fused Li2O2
tetragons in {[tBu-OPO]Li2(DME)}2. These structural motifs
are notably different from those of analogous compounds
derived from a phenylphosphine-bridged biphenolate ligand,13
a result that is ascribable to the influences induced by distinct
phosphorus substituents and coordinating solvents employed.
In general, the biphenolate phosphine ligand adopts the antici-
pated facial coordination mode in all cases. On the basis of the
Cs symmetry observed with solution NMR data for all the alkali
metal complexes, such a coordination mode appears to be
maintained in solution. Variable-temperature 31P{1H} and 7Li-
{1H} NMR studies confirm the coordination of the soft
phosphorus donor to the hard lithium center in {[tBu-OPO]Li2-
(DME)}2. Preliminary catalytic studies reveal that these alkali
metal complexes are active initiators for ring-opening oligomer-
ization of ε-CL. Studies involving preparation of transition
metal complexes of [tBu-OPO]2- and reaction chemistry de-
rived thereafter will be the subjects of further reports.
˚
mated Mo KR radiation (λ = 0.7107 A). Structures were solved
by direct methods and refined by full matrix least-squares
procedures against F2 using WinGX crystallographic software
package. All full-weight non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were placed in calculated
positions. In H2[Ph-OPO], one tert-butyl group is disordered
with the methyl substituents being in the ratio of 59:41 over two
conformations. The structure of {[tBu-OPO]Li2(DME)}2 con-
tains disordered pentane molecules. Attempts to obtain a sui-
table disorder model failed. The SQUEEZE procedure of the
Platon program55 was used to obtain a new set of F2 (hkl) values
without the contribution of solvent molecules, leading to the
presence of significant voids in the structure. The refinement
reduced the R1 value to 0.0761. One tert-butyl group in {[tBu-
OPO]Li2(DME)}2 is disordered with the methyl substituents
being in the ratio of 50:50 over two conformations. In {[tBu-
OPO]Na2(DME)2}2(μ-DME), two tert-butyl groups are disor-
dered with the methyl substituents being in the ratio of 40:60
over two conformations. In {[tBu-OPO]K2(THF)2}2, one tert-
butyl group is disordered with the methyl substituents being in
the ratio of 52:48 over two conformations. CCDC reference
numbers are 777005-777009.
Synthesis of H2[tBu-OPO]. To a diethyl ether solution (20 mL)
of 2-bromo-4,6-di-tert-butylphenol (4.278 g, 15.0 mmol) at -35 °C
was added nBuLi (12 mL, 2.5 M in hexane, 30.0 mmol). After being
stirred at room temperature for 1 h, the solution was cooled to
t
-35 °C again, and a diethyl ether solution (20 mL) of BuPCl2
(1.2 g, 7.5 mmol) at -35 °C was added. The reaction mixture was
stirred at room temperature for 12 h and quenched with degassed
deionized water (20 mL). The product was extracted with degassed
dichloromethane (10 mL ꢀ 2). The dichloromethane solutions were
combined, dried over MgSO4, and evaporated to dryness under
reduced pressure. The residue was dissolved in diethyl ether (3 mL)
and MeCN (15 mL) was added to allow for precipitation of the
product as an off-white solid; yield 2.17 g (58%). Pale yellow crys-
tals suitable for X-ray diffraction analysis were grown from a con-
centrated MeCN solution at -35 °C. 1H NMR (C6D6, 500 MHz):
δ 7.91 (dd, 2, JHP=4.0, JHH=2.0, Ar), 7.61 (d, 2, JHP=12.0, OH),
7.55 (d, 2, 4JHH=2.0, Ar), 1.54 (s, 18, CMe3), 1.33 (s, 18, CMe3),
Experimental Section
General Procedures. Unless otherwise specified, all experi-
ments were performed under nitrogen using standard Schlenk or
glovebox techniques. All solvents were reagent grade or better
and purified by standard methods. All other chemicals were
obtained from commercial vendors and used as received. The
NMR spectra were recorded on Varian Unity or Bruker AV
instruments. Chemical shifts (δ) are listed as parts per million
downfield from tetramethylsilane and coupling constants (J)
1
and peak widths at half-height (Δν1/2) are in hertz. H NMR
spectra are referenced using the residual solvent peak at δ 7.16
for C6D6. 13C NMR spectra are referenced using the internal
solvent peak at δ 128.39 for C6D6. The assignment of the carbon
(55) Spek, A. L. PLATON-A Multipurpose Crystallographic Tool;
Utrecht University: The Netherlands, 2003.

6208 Organometallics, Vol. 29, No. 23, 2010
Hsu and Liang
3
1.11 (d, 9, JHP = 15.0, PCMe3). 13C{1H} NMR (C6D6, 125.7
were removed in vacuo to give {[tBu-OPO]K2(DME)}2 as an off-
white solid; yield 196 mg (98%). The off-white solid was
dissolved in THF (1 mL). The THF solution was cooled to
-35 °C to give the product as colorless prisms suitable for X-ray
diffraction analysis; yield 201 mg (93%, corresponding to the
protio ligand employed). 1H NMR (C6D6, 500 MHz): δ 7.48 (br
s, 4, ArH), 7.32 (s, 4, ArH), 3.42 (m, 16, OCH2CH2), 1.60 (s, 36,
MHz): δ 157.87 (d, JCP = 21.12, C), 141.99 (d, JCP = 1.76, C),
136.31 (d, JCP = 1.76, C), 129.25 (d, JCP = 1.89, CH), 127.18
(s, CH), 116.87 (d, JCP = 6.91, C), 35.87 (d, JCP = 2.26, ArCMe3),
1
34.93 (s, ArCMe3), 32.18 (s, ArCMe3), 32.08 (d, JCP = 2.26,
P
PCMe3), 30.18 (s, ArCMe3), 28.66 (d, 2JCP = 12.95, PCMe3). 31
NMR (C6D6, 202.3 MHz): δ -59.54. Anal. Calcd for C32H51O2P:
C, 77.05; H, 10.31. Found: C, 76.97; H, 10.15.
3
ArCMe3), 1.45 (d, 18, JHP = 11.5, PCMe3), 1.42 (m, 16,
Synthesis of {[tBu-OPO]Li2(DME)}2. To a prechilled DME
solution (6 mL) of H2[tBu-OPO] (200 mg, 0.4 mmol) at -35 °C
was added dropwise n-BuLi (0.5 mL, 1.6 M in hexane,
0.8 mmol). The reaction solution was stirred at room tempera-
ture for 1 h and filtered through a pad of Celite. All volatiles
were removed in vacuo. Pentane (1 mL) was added. The pentane
solution was cooled to -35 °C to give the product as colorless
prisms suitable for X-ray diffraction analysis; yield 234 mg
(98%). 1H NMR (C6D6, 500 MHz): δ 7.73 (d, 4, J = 3.0, ArH),
7.45 (d, 4, J = 2.0, ArH), 2.96 (s, 8, OCH2), 2.91 (s, 12, OCH3),
OCH2CH2), 1.37 (s, 36, ArCMe3). 13C{1H} NMR (C6D6,
125.7 MHz): δ 171.06 (br m, C), 167.59 (s, C), 136.57 (s, C),
130.11 (s, CH), 125.63 (s, C), 123.67 (s, CH), 68.11 (s, OCH2),
35.94 (s, ArCMe3), 34.56 (s, ArCMe3), 32.78 (s, ArCMe3), 31.53
(br s, PCMe3), 30.68 (s, ArCMe3), 30.37 (d, JCP = 14.20,
PCMe3), 26.08 (s, OCH2CH2). 31P{1H} NMR (C6D6, 202.3
MHz): δ -17.72. Attempts to obtain satisfactory analysis data
of {[tBu-OPO]K2(THF)2}2 were not successful. Anal. Calcd
for (C32H49K2O2P)2(DME)2: C, 65.00; H, 8.95. Found: C,
64.71; H, 8.71.
General Procedures for ROP of ε-CL Outlined in Table 5.
A toluene solution of {[tBu-OPO]M2(solv)x}2 (1.2 mM) was
added to a toluene solution of ε-CL (200 equiv). Toluene was
added, if necessary, to make the total volume of the reaction
solution 5 mL. The solution was transferred to a Teflon-sealed
reaction vessel and heated to 80 °C for 3 h. After being cooled to
room temperature, the reaction solution was quenched with a
methanol solution of HCl (1 M). The solution was filtered
through a pad of Celite, and all volatiles were removed under
dynamic vacuum upon heating until the weights of the resulting
viscous residues remained constant.
3
1.55 (s, 36, ArCMe3), 1.46 (d, 18, JHP = 13.5, PCMe3), 1.38
(s, 36, ArCMe3). 13C{1H} NMR (C6D6, 125.7 MHz): δ 167.93
(d, JCP = 12.00, C), 137.92 (s, C), 135.77 (s, C), 128.92 (s, CH),
125.17 (s, CH), 71.41 (s, OCH2), 59.42 (s, OCH3), 35.80
(s, ArCMe3), 34.64 (s, ArCMe3), 32.52 (s, ArCMe3), 31.63
(s, ArCMe3), 30.99 (d, JCP = 4.15, PCMe3), 30.41 (d, JCP
=
14.71, PCMe3). 31P{1H} NMR (C6D6, 202.3 MHz): δ -20.73.
7Li{1H} NMR (C6D6, 194 MHz): δ 0.87. Anal. Calcd for
(C72H118Li4O8P2)(DME)3: C, 68.52; H, 10.14. Found: C, 68.81;
H, 10.54.
Synthesis of {[tBu-OPO]Na2(DME)2}2(μ-DME). To a pre-
chilled DME solution (8 mL) of H2[tBu-OPO] (300 mg, 0.6 mmol)
at -35 °C was added a prechilled DME suspension (2 mL) of
NaH (42 mg, 1.8 mmol). The reaction solution was stirred at
room temperature for 1 h and filtered through a pad of Celite.
The filtrate was concentrated under reduced pressure until the
volume became ca. 1 mL and cooled to -35 °C to give the
product as colorless prisms suitable for X-ray diffraction anal-
Acknowledgment. We thank the National Science
Council of Taiwan for financial support (NSC 96-2628-
M-110-007-MY3, 96-2738-M-110-001, and 96-2918-I-
110-011), Ms. Ting-Ting Tsai for preparing NMR sam-
ples of {[tBu-OPO]Li2(DME)}2 in C6D6, Mr. Ting-Shen
Kuo (NTNU) for assistance with X-ray crystallography,
Ms. Ching-Wei Lu (NTU), Ms. I-Chuan Chen (NCHU),
and Ms. Chia-Chen Tsai (NCKU) for elemental analysis,
Ms. Chao-Lien Ho (NSYSU), Ms. Mei-Yueh Chien
(NCHU), and Ms. Ru-Rong Wu (NCKU) for assistance
with NMR, Prof. Jyh-Tsung Lee for the access to a GPC
instrument, and the National Center for High-perfor-
mance Computing (NCHC) for accesses to chemical
databases. We are also grateful to reviewers for insightful
comments.
1
ysis; yield 438 mg (95%). H NMR (C6D6, 500 MHz): δ 7.62
(s, 4, ArH), 7.45 (s, 4, ArH), 2.95 (s, 20, OCH2), 2.85 (s, 30,
OCH3), 1.60 (s, 36, ArCMe3), 1.46 (d, 18, 3JHP = 12.5, PCMe3),
1.42 (s, 36, ArCMe3). 13C{1H} NMR (C6D6, 125.7 MHz): δ
169.91 (d, JCP = 12.82, C), 136.92 (s, C), 132.95 (s, C), 129.78
(s, CH), 124.40 (s, CH), 71.40 (s, OCH2), 59.11 (s, OCH3), 35.81
(s, ArCMe3), 34.64 (s, ArCMe3), 32.69 (s, ArCMe3), 31.59
(d, JCP = 5.91, PCMe3), 30.90 (s, ArCMe3), 30.06 (d, JCP
=
13.83, PCMe3). 31P{1H} NMR (C6D6, 202.3 MHz): δ -23.62
(Δν1/2 = 140). With multiple attempts, we were unable to obtain
satisfactory data analysis for this compound due likely to the
lability of coordinated DME. The NMR spectra are provided in
the Supporting Information (Figures S1-S3).
Supporting Information Available: NMR spectra of {[tBu-
OPO]Na2(DME)2}2(μ-DME) and X-ray crystallographic data
in CIF format for H2[tBu-OPO], H2[Ph-OPO], {[tBu-OPO]Li2-
(DME)}2, {[tBu-OPO]Na2(DME)2}2(μ-DME), and {[tBu-OPO]-
K2(THF)2}2. This material is available free of charge via the
Internet at http://pubs.acs.org.
Synthesis of {[tBu-OPO]K2(THF)2}2. To a prechilled DME
solution (4 mL) of H2[tBu-OPO] (150 mg, 0.3 mmol) at -35 °C
was added a prechilled DME suspension (1 mL) of KH (36 mg,
0.9 mmol). The reaction solution was stirred at room tempera-
ture for 1 h and filtered through a pad of Celite. All volatiles