Biphenolate phosphine complexes of tin(IV)

Article abstract of DOI:10.1021/ic701006r

The preparation and structural characterization of tin(IV) complexes supported by (2,2′-phenylphosphino)bis(4,6-di-tert-butylphenolate) ([OPO]^2-) are described. The reaction of in-situ prepared Li ₂[OPO] with SnCl₄ in THF at -35°C produced [OPO]SnCl₂(THF) as a THF adduct. Addition of SnCl₄ to a THF solution of H₂[OPO] in the presence of 2 equiv of NEt₃ at room temperature led to the formation of the ate complex {[OPO]SnCl₃}(HNEt₃). The metathetical reactions of Li ₂[OPO] with R₂SnCl₂ (R = Me, n-Bu) in THF at -35°C generated the corresponding five-coordinate dialkyl complexes [OPO]SnR₂. In addition to the multinuclear NMR spectroscopic data for all new compounds, X-ray structures of [OPO]SnCl₂(THF), [OPO]SnMe₂, and [OPO]Sn(n-Bu)₂ are presented.

Full text of DOI:10.1021/ic701006r

Inorg. Chem. 2007, 46, 7587−7593
Biphenolate Phosphine Complexes of Tin(IV)
Lan-Chang Liang,*,† Yu-Ning Chang,† Han-Sheng Chen,† and Hon Man Lee‡
Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen
UniVersity, Kaohsiung 80424, Taiwan, and Department of Chemistry, National Changhua
UniVersity of Education, Changhua 50058, Taiwan
Received May 24, 2007
The preparation and structural characterization of tin(IV) complexes supported by (2,2
di-tert-butylphenolate) ([OPO]2-) are described. The reaction of in-situ prepared Li2[OPO] with SnCl4 in THF at
35 C produced [OPO]SnCl2(THF) as a THF adduct. Addition of SnCl4 to a THF solution of H2[OPO] in the
presence of 2 equiv of NEt3 at room temperature led to the formation of the “ate” complex [OPO]SnCl3 (HNEt3).
The metathetical reactions of Li2[OPO] with R2SnCl2 (R Me, n-Bu) in THF at 35 C generated the corresponding
′-phenylphosphino)bis(4,6-
−
°
{
}
)
−
°
five-coordinate dialkyl complexes [OPO]SnR2. In addition to the multinuclear NMR spectroscopic data for all new
compounds, X-ray structures of [OPO]SnCl2(THF), [OPO]SnMe2, and [OPO]Sn(n-Bu)2 are presented.
Introduction
[OPO]2- are currently receiving considerable attention,
particularly for group 4 chemistry, due, at least in part, to
their potential use as homogeneous catalyst precursors for
polymerization of terminal olefins and ring-opening polym-
erization of heterocyclic molecules.15-24 Interestingly, it has
been demonstrated that the bond distances of Ti-P in
titanium(IV) complexes of [OPO]2-14 are shorter than those
of Ti-S in the corresponding complexes of the sulfide-
bridged 2,2′-thiobis(6-tert-butyl-4-methylphenolate) ligand21,25,26
as evidenced by single-crystal X-ray diffraction analysis. This
phenomenon is notably unusual in consideration of the
relative atomic size and hardness of these donor atoms but
We are currently exploring the coordination chemistry of
main-group and transition metals involving o-phenylene-
derived hybrid chelating ligands that contain both soft and
hard donors.1-14 For instance, the structural characterization
of a series of group 4 complexes supported by the tridentate
biphenolate phosphine ligand (2,2′-phenylphosphino)bis(4,6-
di-tert-butylphenolate) ([OPO]2-) has recently been de-
scribed.14 The chelating (poly)phenolate ligands such as
* To whom correspondence should be addressed. E-mail: lcliang@
mail.nsysu.edu.tw.
† National Sun Yat-sen University.
‡ National Changhua University of Education.
(1) Liang, L.-C. Coord. Chem. ReV. 2006, 250, 1152-1177.
(2) Chien, P.-S.; Liang, L.-C. Inorg. Chem. 2005, 44, 5147-5151.
(3) Huang, M.-H.; Liang, L.-C. Organometallics 2004, 23, 2813-2816.
(4) Lee, W.-Y.; Liang, L.-C. Dalton Trans. 2005, 1952-1956.
(5) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics 2003, 22,
3007-3009.
(15) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 429-447.
(16) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. ReV. 2004,
104, 6147-6176.
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128, 13062-13063.
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(19) Kim, Y.; Jnaneshwara, G. K.; Verkade, J. G. Inorg. Chem. 2003, 42,
1437-1447.
(7) Liang, L.-C.; Huang, M.-H.; Hung, C.-H. Inorg. Chem. 2004, 43,
2166-2174.
(20) van der Linden, A.; Schaverien, C. J.; Meijboom, N.; Ganter, C.;
Orpen, A. G. J. Am. Chem. Soc. 1995, 117, 3008-3021.
(21) Fokken, S.; Spaniol, T. P.; Kang, H. C.; Massa, W.; Okuda, J.
Organometallics 1996, 15, 5069-5072.
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3547.
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353-357.
(22) Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Makromol. Chem.,
Rapid Commun. 1989, 10, 349-352.
(23) Schaverien, C. J.; van der Linden, A. J.; Orpen, A. G. Polym. Prepr.
(Am. Chem. Soc., Polym. DiV.) 1994, 35, 672-673.
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A.; Okuda, J. Organometallics 2000, 19, 2498-2503.
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Chem. 2002, 663, 158-163.
(10) Liang, L.-C.; Lin, J.-M.; Lee, W.-Y. Chem. Commun. 2005, 2462-
2464.
(11) Liang, L.-C.; Chien, P.-S.; Lin, J.-M.; Huang, M.-H.; Huang, Y.-L.;
Liao, J.-H. Organometallics 2006, 25, 1399-1411.
(12) Liang, L.-C.; Chien, P.-S.; Huang, Y.-L. J. Am. Chem. Soc. 2006,
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(13) Chang, Y.-N.; Liang, L.-C. Inorg. Chim. Acta 2007, 360, 136-142.
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2673.
10.1021/ic701006r CCC: $37.00
Published on Web 07/31/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 18, 2007 7587

Liang et al.
Scheme 1
Table 1. Selected NMR Dataa
likely suggestive of a stronger chemical bond for the former
than the latter. In view of the close resemblances of Ti(IV)
to Sn(IV)27 and the potential transmetalation characteristic
of tin complexes with other metal halides,28,29 we have set
out to explore the coordination chemistry of [OPO]2-
involving Sn(IV). In this contribution, we describe the
preparation and structural characterization of a series of tin-
(IV) complexes containing [OPO]2-, including X-ray struc-
tures of [OPO]SnCl2(THF), [OPO]SnMe2, and [OPO]Sn(n-
Bu)2. Interestingly, both facial and meridional coordination
modes are observed for [OPO]2- in this study, in spite of
the intrinsic pyramidal nature of the phosphorus donor. It is
worth noting that compounds described herein represent rare
examples of structurally characterized biphenolate phosphine
complexes of main-group metals,13 although ligands of this
type have been known since 1980.30
1J
1J
31P
119Sn
119SnP
117SnP
compd
δ
δ
[OPO]SnCl2(THF)b
{[OPO]SnCl3}(HNEt3)
[OPO]SnMe2
-58.9
-56.5
-76.5
-76.5
-55.1
-37.6
342.1
309.4
1886
1802
1920
1047
842
2009
1094
881
[OPO]Sn(n-Bu)2
a All spectra were recorded in C6D6 at room temperature unless otherwise
noted; chemical shifts in ppm, and coupling constants in Hz. b Data obtained
in THF due to low solubility in C6D6.
1
as only one set of THF resonances is observed in the H
NMR spectrum of a C6D6 solution containing [OPO]SnCl2-
(THF) and an excess amount of THF (e.g., 10 equiv). The
solubility of [OPO]SnCl2(THF), however, is too low in all
commonly used solvents to acquire interpretable low-
temperature 1H NMR spectra. The determination of the static
structure of this molecule in solution is thus hampered and
inconclusive. The tin atom may be observed in a saturated
THF solution as a doublet resonance centered at -55.1 ppm
Results and Discussion
1
with JPSn of 1886 Hz (Table 1) in the 119Sn{1H} NMR
It has been shown that attempts to prepare [OPO]TiCl2-
(THF) from the reactions of Li2[OPO] with 1 equiv of TiCl4-
(THF)2 in a variety of solvents led to a complicated mixture
from which the bis-ligand complex Ti[OPO]2 may be
selectively isolated.14 Subsequent comproportionation of Ti-
[OPO]2 with TiCl4(THF)2 produced effectively the desired
[OPO]TiCl2(THF). In contrast, the analogous metathetical
reaction of Li2[OPO] with SnCl4 in THF at -35 °C generated
[OPO]SnCl2(THF) (Scheme 1) as a pale yellow solid as
judged by the 1H and 31P{1H} NMR spectra. The phosphorus
donor of [OPO]SnCl2(THF) in C6D6 appears as a singlet
resonance at -61.7 ppm in the 31P{1H} NMR spectrum, a
value that is significantly shifted upfield as compared to those
of Li2[OPO] (-32 ppm)13 and [OPO]TiCl2(THF) (18 ppm).14
The tert-butyl groups in [OPO]SnCl2(THF) are observed as
spectrum, indicating the coordination of the phosphorus
donor to the tetravalent tin center. Attempts to obtain
satisfactory analysis data for [OPO]SnCl2(THF) were unsuc-
cessful, due presumably to the facile dissociation of the
coordinated THF molecule and/or the incorporation of
cocrystallized toluene molecule upon recrystallization (vide
infra).
Though indeterminate in solution, the solid-state structure
of [OPO]SnCl2(THF) was established by an X-ray diffraction
study. Colorless crystals of [OPO]SnCl2(THF) suitable for
X-ray diffraction analysis were grown from a concentrated
toluene solution at -35 °C. Crystallographic details are
summarized in Table 2. As depicted in Figure 1, [OPO]SnCl2-
(THF) is a six-coordinate species with the coordinated THF
molecule trans to one of the phenolate oxygen atoms of the
fac-[OPO]2- ligand. As a result, this compound is C1-
symmetric in the solid state. The Cs symmetry found for
[OPO]SnCl2(THF) in solution thus presumably arises from
the facile dissociation and recoordination of the THF
molecule as illustrated in Scheme 2. The Sn-O(phenolate),
Sn-O(THF), and Sn-Cl distances are all within the expected
values for a six-coordinate tin(IV) complex.31-34 The Sn-P
1
two sharp singlet resonances in the H NMR spectrum at
room temperature, consistent with a Cs-symmetric geometry
for this complex. Reminiscent of what has been reported for
[OPO]TiCl2(THF),14 the coordinated THF molecule is pre-
sumably labile and tends to dissociate from the Sn(IV) center
(27) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; Wiley-Interscience: New York, 1999;
p 695.
(28) Clark, K. A. F.; George, T. A.; Brett, T. J.; Ross, C. R., II; Shoemaker,
R. K. Inorg. Chem. 2000, 39, 2252-2253.
(29) Clark, K. A. F.; George, T. A. Inorg. Chem. 2005, 44, 416-422.
(30) Tzschach, A.; Nietzschmann, E. Z. Chem. 1980, 20, 341-342.
(31) Smith, G. D.; Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1992, 11, 1064-1071.
7588 Inorganic Chemistry, Vol. 46, No. 18, 2007

Biphenolate Phosphine Complexes of Tin(IV)
Table 2. Crystallographic Data for [OPO]SnCl2(THF), [OPO]SnMe2,
and [OPO]Sn(n-Bu)2
{[OPO]SnCl2
{[OPO]SnMe2}
Compound
Formula
(THF)}(toluene)
(pentane)
C45H61Cl2O3PSn
870.50
C41H63O2PSn
737.57
Fw
crystal size (mm3)
0.32 × 0.28 × 0.15
0.27 × 0.23 × 0.17
D
calc (Mg/m3)
1.267
1.208
crystal syst
space group
a (Å)
b (Å)
c (Å)
Triclinic
P1h
Monoclinic
P21/n
13.2078(5)
20.1362(8)
15.8305(7)
90
105.598(2)
90
4055.1(3)
4
11.2833(2)
13.1780(3)
16.6922(5)
77.8660(10)
75.9260(10)
73.4790(10)
2281.39(9)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Figure 1. Molecular structure of [OPO]SnCl2(THF) with thermal ellipsoids
drawn at the 35% probability level. The asymmetric unit cell contains one
disordered toluene molecule, which is omitted for clarity. Selected bond
distances (Å) and angles (deg): Sn(1)-O(2) 2.049(3), Sn(1)-O(1) 2.053-
(3), Sn(1)-O(3) 2.221(3), Sn(1)-Cl(2) 2.3401(12), Sn(1)-Cl(1) 2.4049-
(12), Sn(1)-P(1) 2.5311(11), O(2)-Sn(1)-O(1) 93.89(12), O(2)-Sn(1)-
O(3) 83.79(13), O(1)-Sn(1)-O(3) 173.10(12), O(2)-Sn(1)-Cl(2) 88.24(8),
O(1)-Sn(1)-Cl(2) 95.25(9), O(3)-Sn(1)-Cl(2) 91.18(10), O(2)-Sn(1)-
Cl(1) 169.01(9), O(1)-Sn(1)-Cl(1) 95.13(9), O(3)-Sn(1)-Cl(1) 86.52-
(10), Cl(2)-Sn(1)-Cl(1) 97.15(5), O(2)-Sn(1)-P(1) 80.50(8), O(1)-
Sn(1)-P(1) 77.55(8), O(3)-Sn(1)-P(1) 95.63(10), Cl(2)-Sn(1)-P(1)
166.10(4), Cl(1)-Sn(1)-P(1) 95.35(4).
Z
T (K)
200(2)
150(2)
diffractometer
radiation, (Å)
2 range (deg)
index ranges (h;k;l)
Kappa CCD
Mo KR, 0.71073
4.18 < 2 < 50.72
-13, 13; -15, 15;
-20, 20
29396
8327
0.0725
0.748
SMART APEX II
Mo KR, 0.71073
3.20 < 2 < 57.64
-12, 13; -23, 17;
-24, 24
33224
10512
0.0275
0.700
total no. of reflns
no. of indep reflns
Rint
Absorp coeff (mm-1
)
no. of data/restraints/
parameters
8327/0/453
10512/97/452
derivatives of aryl phosphines such as SnPh[P(C6H4-2-S)3]
(2.5161(11) Å),29 SnPh[P(C6H3-3-SiMe3-2-S)3] (2.5132(14)
Å),29 and SnPh[P(C6H3-5-Me-2-S)3] (2.5124(9) Å).28,29 The
molecular structure of [OPO]SnCl2(THF) resembles closely
that of [OPO]TiCl2(THF).14 The [OPO]2- ligand in both
[OPO]SnCl2(THF) and [OPO]TiCl2(THF) adopts a facial
coordination mode with the dihedral angle of the two
O-M-P planes being 96.2° for Sn and 100.9° for Ti. The
somewhat smaller dihedral angle found for [OPO]SnCl2-
(THF) than [OPO]TiCl2(THF) is consistent with the longer
Sn-O(phenolate) bond distances (2.049(3) and 2.053(3) Å)
than Ti-O(phenolate) (1.848(8) and 1.858(7) Å). Interest-
ingly, the Sn-P distance is in the former complex is slightly
shorter than Ti-P (2.596(3) Å) in the latter, despite the
smaller octahedral covalent radius of Ti(IV) (1.36 Å) than
Sn(IV) (1.45 Å).27 The Sn(1)-Cl(1) distance of 2.405(1) Å
is slightly longer than the Sn(1)-Cl(2) distance of 2.340(1)
Å, consistent with the relatively higher trans influence of
the phenolate oxygen atom than the phosphorus donor in
[OPO]2-. As anticipated, the Sn-O(THF) distance of 2.221-
(3) Å is longer than the Sn-O(phenolate) lengths.
goodness of fit
final R indices [I > 2(I)]
1.090
1.050
R1 ) 0.0504
wR2 ) 0.1249
R1 ) 0.0744
wR2 ) 0.1454
-0.703 to 0.839
R1 ) 0.0413
wR2 ) 0.1139
R1 ) 0.0634
wR2 ) 0.1240
-0.872 to 0.942
R indices (all data)
residual density (e/Å3)
Compound
[OPO]Sn(n-Bu)2
C42H63O2PSn
749.58
0.25 × 0.14 × 0.11
Formula
Fw
Crystal size (mm3)
D
calc (Mg/m3)
1.227
Crystal syst
space group
a (Å)
b (Å)
c (Å)
Monoclinic
P21/n
10.9360(7)
19.4210(13)
19.1740(14)
90
R (deg)
â (deg)
94.957(4)
90
4057.1(5)
4
γ (deg)
V (Å3)
Z
T (K)
200(2)
diffractometer
radiation, λ (Å)
2θ range (deg)
index ranges (h;k;l)
total no. of reflns
no. of indep reflns
Rint
Kappa CCD
Mo KR, 0.71073
4.20 < 2 < 50.02
-13, 12; -22, 23; -22, 18
28062
Addition of SnCl4 to a THF solution of H2[OPO] in the
presence of 2 equiv of NEt3 at room temperature produced
the “ate” complex {[OPO]SnCl3}(HNEt3) (Scheme 3). This
result is notably different from what has been observed for
the titanium(IV) chemistry, which led instead to the forma-
tion of the bis-ligand complex Ti[OPO]2 under similar
conditions.14 The propensity to form a six-coordinate
7124
0.1217
0.701
Absorp coeff (mm-1
no. of data/restraints/parameters
goodness of fit
)
7124/96/471
1.033
final R indices [I > 2σ(I)]
R1 ) 0.0765
wR2 ) 0.1725
R1 ) 0.1321
wR2 ) 0.2007
-0.618 to 1.145
R indices (all data)
residual density (e/Å3)
(32) Smith, G. D.; Fanwick, P. E.; Rothwell, I. P. J. Am. Chem. Soc. 1989,
111, 750-751.
(33) Darensbourg, D. J.; Ganguly, P.; Billodeaux, D. Macromolecules 2005,
38, 5406-5410.
distance of 2.531(1) Å, however, is notably shorter than those
found in six-coordinate tin(IV) complexes of alkylphosphines
such as SnF4(Et2PCH2CH2PEt2) (2.6058(9) Å),35 SnCl4(Et2-
PCH2CH2PEt2) (2.6481(17) Å),35 and trans-SnF4(PCy3)2
(2.6538(11) Å)35 but comparable to those of five-coordinate
(34) Lado, A. V.; Poddel’sky, A. I.; Piskunov, A. V.; Fukin, G. K.; Baranov,
E. V.; Ikorskii, V. N.; Cherkasov, V. K.; Abakumov, G. A. Inorg.
Chim. Acta 2005, 358, 4443-4450.
(35) Davis, M. F.; Clarke, M.; Levason, W.; Reid, G.; Webster, M. Eur. J.
Inorg. Chem. 2006, 2773-2782.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7589

Liang et al.
Scheme 2
Scheme 3
Scheme 4
{[OPO]SnCl3}- and [OPO]SnCl2(THF) rather than a five-
coordinate [OPO]SnCl2 is likely reflective of the highly
electrophilic nature of the putative [OPO]SnCl2. Surprisingly,
{[OPO]SnCl3}(HNEt3) is much more soluble than [OPO]-
SnCl2(THF) even in nonpolar solvents, although the former
coordinating solvents (e.g., THF or diethyl ether) or the
eliminated LiCl salt, a phenomenon that is in sharp contrast
to that of the dichloride derivative (vide supra). This result
is reflective of a less electrophilic tin(IV) center of the dialkyl
complexes than that of the putative five-coordinate dichloride
species due to the difference in electronegativity of these
1
complex is characteristic of an ion pair. The H NMR
1
spectrum of {[OPO]SnCl3}(HNEt3) in C6D6 exhibits two
sharp singlet resonances for the tert-butyl groups, indicating
the presence of a symmetry plane in this molecule. The
phosphorus donor appears as a singlet resonance at -56.5
donor atoms (C, 2.55; Cl, 3.16).36 The H NMR spectrum
of [OPO]SnMe2 in C6D6 at room temperature reveals two
sharp singlet resonances at 1.70 and 1.33 ppm for the tert-
butyl groups of [OPO]2- and two doublet resonances at 0.53
(3JHP ) 3 Hz) and 0.44 ppm (3JHP ) 2 Hz) with tin satellites
for the tin-bound methyl groups, consistent with Cs symmetry
for this molecule. The Cs symmetry is anticipated in view
of the inherent pyramidal geometry of the phosphorus donor.
The phenolate oxygen atoms are likely positioned axially in
a trigonal bipyramial structure on the basis of their relatively
high electronegativity as compared to those of the other donor
1
ppm flanked by 117Sn and 119Sn satellite signals with JSnP
of 1920 and 2009 Hz, respectively Consistently, the 119Sn-
{1H} NMR spectrum reveals a doublet resonance centered
at -37.6 ppm due to the coupling between 119Sn and 31P
nuclei.
The metathetical reactions of Li2[OPO] with R2SnCl2 (R
) Me, n-Bu) in THF at -35 °C generated the corresponding
five-coordinate dialkyl complexes [OPO]SnR2 (Scheme 4).
Interestingly, these dialkyl species are not associated with
(36) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 93.
7590 Inorganic Chemistry, Vol. 46, No. 18, 2007

Biphenolate Phosphine Complexes of Tin(IV)
Figure 3. Molecular structure of [OPO]Sn(n-Bu)2 with thermal ellipsoids
drawn at the 35% probability level. Selected bond distances (Å) and angles
(deg): Sn(1)-C(35) 2.128(7), Sn(1)-C(39) 2.146(8), Sn(1)-O(1) 2.178-
(5), Sn(1)-O(2) 2.183(6), Sn(1)-P(1) 2.480(2), C(35)-Sn(1)-C(39) 119.7-
(3), C(35)-Sn(1)-O(1) 100.3(3), C(39)-Sn(1)-O(1) 94.5(3), C(35)-
Sn(1)-O(2) 98.5(3), C(39)-Sn(1)-O(2) 95.6(3), O(1)-Sn(1)-O(2) 150.5(2),
C(35)-Sn(1)-P(1) 116.7(2), C(39)-Sn(1)-P(1) 123.6(3), O(1)-Sn(1)-
P(1) 76.0(1), O(2)-Sn(1)-P(1) 75.4(1).
Figure 2. Molecular structure of [OPO]SnMe2 with thermal ellipsoids
drawn at the 35% probability level. The asymmetric unit cell contains one
disordered pentane molecule, which is omitted for clarity. Selected bond
distances (Å) and angles (deg): C(1)-Sn(1) 2.119(3), C(2)-Sn(1) 2.129-
(4), O(1)-Sn(1) 2.154(2), O(2)-Sn(1) 2.150(2), P(1)-Sn(1) 2.5118(7),
C(1)-Sn(1)-C(2) 121.53(16), C(1)-Sn(1)-O(2) 103.99(12), C(2)-Sn-
(1)-O(2) 89.89(13), C(1)-Sn(1)-O(1) 103.31(12), C(2)-Sn(1)-O(1)
91.80(12), O(2)-Sn(1)-O(1) 146.73(9), C(1)-Sn(1)-P(1) 109.96(12),
C(2)-Sn(1)-P(1) 128.51(11), O(2)-Sn(1)-P(1) 76.77(6), O(1)-Sn(1)-
P(1) 76.29(6).
of 359.99° for [OPO]SnMe2 and 360° for [OPO]Sn(n-Bu)2.
The dihedral angle between the two O-Sn-P planes in
[OPO]SnMe2 (160.3°) and [OPO]Sn(n-Bu)2 (173.0°) is
notably wider than those of the fac-[OPO]2--derived [OPO]-
SnCl2(THF) and [OPO]TiCl2(THF) (vide supra) but smaller
than the ideal value of 180° due likely to the constraint
imposed by the two fused five-membered chelate rings and
the distortion arisen from the pyramidal phosphorus donor.
The O-Sn-O bond angle ([OPO]SnMe2, 146.73(9)°; [OPO]-
Sn(n-Bu)2, 150.5(2)°) is thus relatively small, and the two
o-phenylene rings are tilted away from the phosphorus-bound
phenyl group with respect to the [OPO]2- coordination plane.
The preference for [OPO]2- to adopt the meridional instead
of facial geometry in a trigonal bipyramid is reminiscent of
what has been reported for 5-coordinate tin(IV) complexes
atoms present in this molecule (Bent’s rule).37,38 The sym-
metry plane of this compound thus coincides with the
equatorial plane that contains the tin center and the two
R-carbon atoms. As a result, the two tin-bound methyl groups
are chemically inequivalent. The phosphorus donor in [OPO]-
SnMe2 appears as a singlet resonance at -76.5 ppm flanked
1
by 117Sn and 119Sn satellite signals with JSnP of 1047 and
1094 Hz, respectively. The tin atom is observed as a doublet
resonance at 342.1 ppm in the 119Sn{1H} NMR spectrum, a
value that is shifted significantly downfield as compared to
those of [OPO]SnCl2(THF) and {[OPO]SnCl3}(HNEt3). The
discrepancy in 119Sn chemical shifts observed for five-
coordinate [OPO]SnMe2 and six-coordinate [OPO]SnCl2X
(X ) THF, Cl-) is consistent with the lower coordination
number39 for the former than the latter. Similar phenomena
were also found for [OPO]Sn(n-Bu)2.
Colorless crystals of [OPO]SnMe2 and [OPO]Sn(n-Bu)2
suitable for X-ray diffraction analysis were grown from a
concentrated pentane solution at -35 °C. Figures 2and 3
illustrate the molecular structures of [OPO]SnMe2 and [OPO]-
Sn(n-Bu)2, respectively. Consistent with the solution NMR
spectroscopic data, these compounds are Cs-symmetric, five-
coordinate species. The coordination geometry of these
complexes is best described as distorted trigonal bipyramidal
with the two phenolate oxygen atoms occupying the axial
positions. The tin center lies perfectly on the equatorial plane
as indicated by the sum of the three equatorial bond angles
40
of [ONO]2- such as Sn[(OCH2CH2)2NMe](t-Bu)2 and
Sn[(O2CCH2)2NCH2-m-tolyl](n-Bu)2.41 Though anticipated
in view of the Bent’s rule, the meridional geometry of
[OPO]2- found in [OPO]SnMe2 and [OPO]Sn(n-Bu)2 is
virtually unprecedented for [XPX]2-- or [LPL]-derived (X
) anionic donor, L ) neutral donor) five-coordinate
complexes as indicated by the Cambridge Structural Database
to date. With the incorporation of a phosphorus donor at the
central position, the tridentate di(donor)/phosphine ligands
are usually forced to adopt a facial coordination mode in
five-coordinatespeciesduetoitsintrinsicpyramidgeometry.42-48
The Sn-P distance of 2.5118(7) Å in [OPO]SnMe2 and
(40) Swisher, R. G.; Holmes, R. R. Organometallics 1984, 3, 365-369.
(41) Mancilla, T.; Carrillo, L.; Zamudio Rivera, L. S.; Camacho, C. C.; de
Vos, D.; Kiss, R.; Darro, F.; mahieu, B.; Tiekink, E. R. T.; Rahier,
H.; Gielen, M.; Kemmer, M.; Biesemans, M.; Willem, R. Appl.
Organomet. Chem. 2001, 15, 593-603.
(42) Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M. Organo-
metallics 1999, 18, 428-437.
(43) MacLachlan, E. A.; Fryzuk, M. D. Organometallics 2005, 24, 1112-
1118.
(37) Bent, H. A. J. Chem. Educ. 1960, 37, 616-624.
(38) Bent, H. A. Chem. ReV. 1961, 61, 275-311.
(39) Granger, P. In NMR of Newly Accessible Nuclei; P. Laszlo, Ed.;
Academic Press: New York, 1983; Vol. 2, pp 400-402.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7591

Liang et al.
X-ray Crystallography. Table 2 summarizes the crystallographic
data for [OPO]SnCl2(THF), [OPO]SnMe2, and [OPO]Sn(n-Bu)2.
Data were collected on a Bruker-Nonius Kappa CCD diffractometer
or a SMART APEX II diffractometer with graphite monochromated
Mo KR radiation (λ ) 0.7107 Å). Structures were solved by direct
methods and refined by full matrix least-squares procedures against
F2 using WinGX crystallographic software package or SHELXL-
97. All full-weight non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were placed in calculated positions. In
[OPO]SnMe2, one of the tert-butyl groups is disordered with the
methyl substituents being in the ratio of ca. 74:26 over two
conformations. In [OPO]Sn(n-Bu)2, one tert-butyl and one n-butyl
groups are disordered with the methyl or n-butyl (excluding CR)
moieties being in the ratio of ca. 55:45 and ca. 37:63, respectively,
over two conformations. A semiempirical absorption correction was
applied using the SADABS program.51
2.480(2) Å in [OPO]Sn(n-Bu)2 is slightly shorter than that
of 2.531(1) Å in [OPO]SnCl2(THF), a result that is ascribed
to the higher percentage of s character that the Sn-P bond
possesses in the hybrid orbitals for the former (sp2) than the
latter (d2sp3).37,38 Consistently, the Sn-O distances in [OPO]-
SnR2 (R ) Me, 2.152 Å average; R ) n-Bu, 2.181 Å
average) are longer than those of [OPO]SnCl2(THF) (2.052
Å average). The Sn-C bond lengths of [OPO]SnR2 are
comparable to those reported for five-coordinate organotin-
40
(IV) complexes such as Sn[(OCH2CH2)2NMe](t-Bu)2 and
Sn[(O2CCH2)2NCH2-m-tolyl](n-Bu)2.41
Conclusions
In summary, we have prepared a series of five- and six-
coordinate tin(IV) complexes of the tridentate biphenolate
phosphine ligand [OPO]2- and established the solution and
solid-state structures of these molecules by multinuclear
NMR spectroscopy and X-ray crystallography, respectively.
Of particular interest are the divergent coordination modes
of [OPO]2-, which may bind to tin(IV) either facially or
meridionally depending on the overall geometry of the
derived complexes. The meridional geometry of [OPO]2-
verified in this study is particularly remarkable in view of
the involvement of a pyramidal phosphorus donor at the
central position in the chelating ligand employed. Studies
directed to delineate the reactivity of these compounds are
currently under way.
Synthesis of [OPO]SnCl2(THF). Solid H2[OPO] (200 mg, 0.39
mmol) was dissolved in THF (4 mL), and the solution was cooled
to -35 °C. To this was added n-BuLi (0.48 mL, 1.6 M in hexane,
Aldrich, 0.77 mmol, 2 equiv) dropwise. The reaction mixture was
stirred at room temperature for 1 h. The resultant solution was
cooled to -35 °C again, and a prechilled solution of SnCl4 (101
mg, 0.39 mmol) in THF (10 mL) at -35 °C was added dropwise.
The reaction mixture was stirred at room temperature for 16 h and
evaporated to dryness under reduced pressure. The solid thus
obtained was extracted with diethyl ether (20 mL × 2) and filtered
through a pad of Celite. The combined filtrate was evaporated to
dryness under reduced pressure to afford a pale yellow solid, which
was washed with pentane (1 mL × 3) and dried in vacuo; yield
251 mg (84%). Colorless crystals suitable for X-ray diffraction
analysis were grown from a concentrated toluene solution at
Experimental Section
1
-35 °C. H NMR (C6D6, 200 MHz): δ 7.88 (m, 2, Ar), 7.66 (d,
2, Ar), 7.50 (dd, 2, Ar), 7.03 (m, 3, Ar), 3.63 (t, 4, OCH2CH2),
1.69 (s, 18, CMe3), 1.18 (s, 22, CMe3 + OCH2CH2). H NMR
General Procedures. Unless otherwise specified, all experiments
were performed under nitrogen using standard Schlenk or glovebox
techniques. All solvents were reagent grade or better and purified
by standard methods. 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
1
(CDCl3, 200 MHz): δ 7.68 (m, 2, Ar), 7.50 (m, 2, Ar), 7.45 (m, 3,
Ar), 7.22 (d, 2, Ar), 3.64 (t, 4, OCH2CH2), 1.71 (t, 4, OCH2CH2),
1.42 (s, 18, CMe3), 1.21 (s, 18, CMe3). 31P{1H} NMR (C6D6, 80.95
MHz): δ -61.70. 31P{1H} NMR (CDCl3, 80.95 MHz): δ -62.40.
31P{1H} NMR (THF, 202.31 MHz): δ -58.85 (1JPSn ) 1886,
1
119
constants (J), in hertz. H NMR spectra are referenced using the
1
JPSn ) 1802). 119Sn{1H} NMR (THF, 186.38 MHz): δ -55.11
residual solvent peak at δ 7.16 for C6D6 and δ 7.27 for CDCl3. 13
C
117
1
119
(d, JPSn ) 1886).
NMR spectra are referenced using the residual solvent peak at δ
128.39 for C6D6. The assignment of the carbon atoms is based on
the DEPT 13C NMR spectroscopy. 31P NMR spectra are referenced
externally using 85% H3PO4 at δ 0. 119Sn NMR spectra are
referenced externally using SnMe4 (at δ 0)39 or a saturated SnCl2
(anhydrous) solution in THF (at δ 236).49 Routine coupling
constants are not listed. All NMR spectra were recorded at room
temperature in specified solvents unless otherwise noted. Elemental
analysis was performed on a Heraeus CHN-O Rapid analyzer.
Materials. Compounds H2[OPO]50 and Li2[OPO]13 were pre-
pared according to the literature procedures. All other chemicals
were obtained from commercial vendors and used as received.
Synthesis of {[OPO]SnCl3}(HNEt3). Neat SnCl4 (0.02 mL, 0.17
mmol) was added to a mixture of H2[OPO] (88.3 mg, 0.17 mmol)
and NEt3 (37.8 mg, 0.37 mmol, 2.2 equiv) in THF (6 mL) at room
temperature. The reaction solution was stirred at room temperature
for 17 h and evaporated to dryness under reduced pressure. The
solid residue was triturated with pentane (2 mL × 2) and dissolved
in toluene (6 mL). The toluene solution was filtered through a pad
of Celite and evaporated to dryness under reduced pressure to afford
1
the product as a pale yellow solid; yield 92 mg (65%). H NMR
(C6D6, 500 MHz): δ 8.47 (br s, 1, NH), 7.97 (dd, 2, Ar), 7.67 (d,
2, Ar), 7.59 (dd, 2, Ar), 7.04 (m, 3, Ar), 2.40 (dq, 6, NCH2Me),
1.82 (s, 18, CMe3), 1.23 (s, 18, CMe3), 0.71 (t, 9, NCH2Me). 31P-
1
{1H} NMR (C6D6, 202.31 MHz): δ -56.52 (1JPSn ) 2009, JPSn
119
117
(44) Morello, L.; Yu, P. H.; Carmichael, C. D.; Patrick, B. O.; Fryzuk, M.
D. J. Am. Chem. Soc. 2005, 127, 12796-12797.
(45) Ma, J.-F.; Kojima, Y.; Yamamoto, Y. J. Organomet. Chem. 2000,
616, 149-156.
(46) Paine, T. K.; Weyhermuller, T.; Slep, L. D.; Neese, F.; Bill, E.; Bothe,
E.; Wieghardt, K.; Chaudhuri, P. Inorg. Chem. 2004, 43, 7324-7338.
(47) Dunbar, K. R.; Haefner, S. C.; Pence, L. E. J. Am. Chem. Soc. 1989,
111, 5504-5506.
(48) Luo, H.; Setyawati, I.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1995, 34,
2287-2299.
(49) Burke, J. J.; Lauterbur, P. C. J. Am. Chem. Soc. 1961, 83, 326-331.
(50) Siefert, R.; Weyhermuller, T.; Chaudhuri, P. J. Chem. Soc., Dalton
Trans. 2000, 4656-4663.
) 1920). 31P{1H} NMR (THF, 80.95 MHz): δ -58.61. 119Sn{1H}
NMR (C6D6, 186.38 MHz): δ -37.61 (d, JPSn ) 2009). 13C-
1
119
{1H} NMR (C6D6, 125.70 MHz): δ 164.88 (d, JCP ) 13.32, C),
139.71 (d, JCP ) 4.15, C), 138.98 (d, JCP ) 7.79, C), 134.88 (d,
JCP ) 10.43, CH), 131.20 (d, JCP ) 3.27, CH), 129.23 (d, JCP
)
11.94, CH), 128.87 (s, CH), 126.16 (s, CH), 124.06 (d, JCP ) 61.84,
C), 110.35 (d, JCP ) 68.26, C), 46.87 (s, NCH2Me), 36.47 (d, JCP
(51) Sheldrick, G. M. SADABS, version 2.04; University of Go¨ttingen:
Go¨ttingen, Germany, 2002.
7592 Inorganic Chemistry, Vol. 46, No. 18, 2007

Biphenolate Phosphine Complexes of Tin(IV)
) 2.26, CMe3), 34.77 (s, CMe3), 32.09 (s, CMe3), 30.49 (s, CMe3),
8.84 (s, NCH2Me). Anal. Calcd for C40H61Cl3NO2PSn: C, 56.93;
H, 7.29; N, 1.66. Found: C, 56.59; H, 7.29; N, 1.73.
pale yellow solid thus obtained was dissolved in pentane (6 mL).
The pentane solution was filtered through a pad of Celite and
evaporated to dryness to afford the product as a pale yellow solid;
yield 133 mg (92%). Crystals suitable for X-ray diffraction analysis
were grown from a concentrated pentane solution at -35 °C; yield
Synthesis of [OPO]SnMe2. Solid H2[OPO] (200 mg, 0.39 mmol)
was dissolved in THF (4 mL), and the solution was cooled to
-35 °C. To this was added n-BuLi (0.48 mL, 1.6 M in hexane,
Aldrich, 0.77 mmol, 2 equiv) dropwise. The reaction mixture was
stirred at room temperature for 1 h. The resultant solution was
cooled to -35 °C again, and a prechilled solution of Me2SnCl2
(85 mg, 0.39 mmol) in THF (10 mL) at -35 °C was added
dropwise. The reaction mixture was stirred at room temperature
for 16 h and evaporated to dryness under reduced pressure. The
pale yellow solid thus obtained was dissolved in pentane (6 mL).
The pentane solution was filtered through a pad of Celite and
evaporated to dryness to afford the product as a pale yellow solid;
yield 248 mg (96%). Colorless crystals suitable for X-ray diffraction
analysis were grown from a concentrated pentane solution at -35
1
61 mg (43%). H NMR (C6D6, 500 MHz): δ 7.888 (dd, 2, Ar),
7.779 (d, 2, Ar), 7.345 (ddd, 2, Ar), 6.816 (m, 3, Ar), 1.729 (s, 18,
CMe3), 1.582 (m, 4, Sn(CH2)3CH3), 1.480 (m, 2, Sn(CH2)3CH3),
1.331 (s, 18, CMe3), 1.283 (m, 2, Sn(CH2)3CH3), 1.236 (q, 2, Sn-
(CH2)3CH3), 1.162 (q, 2, Sn(CH2)3CH3), 0.730 (t, 3, Sn(CH2)3CH3),
0.695 (t, 3, Sn(CH2)3CH3). 31P{1H} NMR (C6D6, 202.31 MHz): δ
1
-76.520 (1JPSn ) 881, JPSn ) 842). 31P{1H} NMR (THF, 80.95
119
117
MHz): δ -76.922. 119Sn{1H} NMR (C6D6, 186.38 MHz): δ
309.444 (d, JPSn ) 881). 13C{1H} NMR (C6D6, 125.70 MHz):
1
119
δ 168.39 (d, JCP ) 15.59, C), 140.07 (d, JCP ) 4.53, C), 138.75 (d,
JCP ) 8.17, C), 132.56 (d, JCP ) 12.82, CH), 130.81 (d, JCP
2.65, CH), 130.13 (s, CH), 129.71 (d, JCP ) 11.94, CH), 129.38
(d, JCP ) 60.46, C), 126.54 (d, JCP ) 1.89, CH), 108.43 (d, JCP
)
1
°C. H NMR (C6D6, 500 MHz): δ 7.92 (dd, 2, Ar), 7.79 (d, 2,
)
Ar), 7.37 (dd, 2, Ar), 6.83 (m, 1, Ar), 6.78 (m, 2, Ar), 1.70 (s, 18,
77.81, C), 36.50 (d, JCP ) 2.77, CMe3), 34.74 (s, CMe3), 32.03 (s,
CMe3), 30.27 (s, CMe3), 28.55 (s, Sn(CH2)3Me), 28.36 (s, Sn(CH2)3-
Me), 27.49 (s, Sn(CH2)3Me), 26.97 (s, Sn(CH2)3Me), 23.72 (s, Sn-
(CH2)3Me), 16.56 (d, JCP ) 11.94, Sn(CH2)3Me), 14.07 (s,
Sn(CH2)3Me), 13.91 (s, Sn(CH2)3Me). Anal. Calcd for C42H63O2-
PSn: C, 67.30; H, 8.47. Found: C, 67.38; H, 8.49.
CMe3), 1.33 (s, 18, CMe3), 0.53 (d, 3, 3JHP ) 3, 2JHSn ) 67, SnCH3),
3
2
0.44 (d, 3, JHP ) 2, JHSn ) 77, SnCH3). 31P{1H} NMR (C6D6,
202.31 MHz): δ -76.479 (1JPSn ) 1094, JPSn ) 1047). 31P-
1
119
117
{1H} NMR (THF, 80.95 MHz): δ -77.733. 119Sn{1H} NMR
(C6D6, 186.38 MHz): δ 342.127 (1JPSn ) 1094). 13C{1H} NMR
119
(C6D6, 125.70 MHz): δ 168.00 (d, JCP ) 14.71, C), 140.42 (d, JCP
) 2.263, C), 138.93 (d, JCP ) 4.59, C), 132.47 (d, JCP ) 6.41,
Acknowledgment. We thank the National Science Coun-
cil of Taiwan for financial support (NSC 95-2113-M-110-
001) of this work, Ms. Chao-Lien Ho (NSYSU) and Ru-
Rong Wu (National Cheng Kung University) for technical
assistance with NMR experiments, Mr. Ting-Shen Kuo
(National Taiwan Normal University) for solving the X-ray
structures of [OPO]SnCl2(THF) and [OPO]Sn(n-Bu)2, and
the National Center for High-Performance Computing (NCHC)
for the access to chemical databases.
CH), 130.99 (d, JCP ) 1.82, CH), 130.23 (s, CH), 129.85 (d, JCP
)
5.97, CH), 126.50 (d, JCP ) 1.76, CH), 108.78 (s, C), 108.15 (s,
C), 36.50 (s, CMe3), 34.77 (s, CMe3), 32.03 (s, CMe3), 30.23 (s,
CMe3), 1.66 (s, SnMe), -5.06 (d, 2JCP ) 12.82, SnMe). Anal. Calcd
for C36H51O2PSn: C, 64.98; H, 7.72. Found: C, 65.07; H, 8.05.
Synthesis of [OPO]Sn(n-Bu)2. Solid H2[OPO] (100 mg, 0.19
mmol) was dissolved in THF (4 mL), and the solution was cooled
to -35 °C. To this was added n-BuLi (0.24 mL, 1.6 M in hexane,
Aldrich, 0.38 mmol, 2 equiv) dropwise. The reaction mixture was
stirred at room temperature for 1 h. The resultant solution was
cooled to -35 °C again, and a prechilled solution of (n-Bu)2SnCl2
(58.7 mg, 0.19 mmol) in THF (4 mL) at -35 °C was added
dropwise. The reaction mixture was stirred at room temperature
for 16 h and evaporated to dryness under reduced pressure. The
Supporting Information Available: X-ray crystallographic data
in CIF format for [OPO]SnCl2(THF), [OPO]SnMe2, and [OPO]-
Sn(n-Bu)2. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC701006R
Inorganic Chemistry, Vol. 46, No. 18, 2007 7593