First organotin complex of a phosphonic diamide RP(O)(NHR)2

Article abstract of DOI:10.1016/j.jorganchem.2006.12.044

Diorganotin dichloride-phosphonic diamide complex, [Ph₂SnCl₂(tBuP(O)(NHⁱPr)₂)₂] (1), is prepared by the addition of two equivalents of ^tBuP(O)(NHⁱPr)₂ to one equivalents of Ph₂SnCl₂ either in the presence or absence of triethylamine. Compound 1 is a rare example of an all-trans SnA₂B₂C₂ complex that contains H-bonded six-membered rings which are made up of six different main group elements.

Full text of DOI:10.1016/j.jorganchem.2006.12.044

Journal of Organometallic Chemistry 692 (2007) 1920–1923
www.elsevier.com/locate/jorganchem
First organotin complex of a phosphonic diamide RP(O)(NHR)2
a,
a
a
Ramaswamy Murugavel *, Ramasamy Pothiraja , Swaminathan Shanmugan ,
a
b
Namrata Singh , Ray J. Butcher
a
Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India
b
Department of Chemistry, Howard University, Washington, DC 20059, USA
Received 9 October 2006; received in revised form 18 December 2006; accepted 22 December 2006
Available online 20 January 2007
Abstract
Diorganotin dichloride-phosphonic diamide complex, [Ph2SnCl2(tBuP(O)(NHiPr)2)2] (1), is prepared by the addition of two equiva-
lents of tBuP(O)(NHiPr)2 to one equivalents of Ph2SnCl2 either in the presence or absence of triethylamine. Compound 1 is a rare exam-
ple of an all-trans SnA2B2C2 complex that contains H-bonded six-membered rings which are made up of six different main group
elements.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Phosphonamide; X-ray structure; Organotin chemistry
1. Introduction
phine oxides, phosphonic amides can coordinate tin
through P@O group and also further react with Sn–X
bonds through the N–H group, thus offering possibilities
for the preparation of tin complexes with Sn–N linkages
stabilized by Sn–O coordination.
Organotin compounds and their complexes with elec-
tron-donor molecules have been studied in detail by vari-
ous physicochemical methods in last four decades. Much
of the interest in such complexes arises from their biologi-
cal and catalytic activity [1]. Phosphoryl-containing com-
pounds have, in particular, been used as effective
complexation agents in organotin chemistry [2]. Previous
work, using both 31P NMR spectroscopic and calorimetric
studies, has indicated that organotin chlorides form pre-
dominantly 1:1 adducts in solution, with evidence of 1:2
and other adducts for both R2SnCl2 and RSnCl3 [1c,3].
A variety of 1:1 and 1:2 adducts of triphenylphosphine
oxide with diorganotin(IV) dihalides are known in the liter-
ature [4]. On the other hand, organophosphonic amides
R2P(O)(NHR) and RP(O)(NHR)2 have not so far been
studied as ligands in organotin chemistry. Unlike phos-
Tin complexes of phosphonic amides assume further
importance due to the recent reports where a series of chi-
ral-phosphoramides were shown to catalyze the enantio-
selective allylation of allyltrichlorosilanes [5]. To elucidate
the relationship between the catalyst structure and its selec-
tivity and reactivity, it is necessary to have a clear under-
standing of the phosphoramide Æ Lewis acid complex
structure. Unfortunately, the complexation of phosphora-
mides to chlorosilanes is very weak [5]. However, phospho-
ramide can bind much better to tin through its phosphoryl
oxygen and hence we have investigated the reaction of
Ph2SnCl2 and PhSnCl3 with a phosphonic diamide. The
results obtained on the synthesis and structure of the first
example of a organotin-phosphonic diamide complex, with
a rare H-bonded six-membered ring with six different main
group elements, are presented herein.
*
Corresponding author. Tel.: +91 22 2576 7163; fax: +91 22 2572 3480.
E-mail address: rmv@chem.iitb.ac.in (R. Murugavel).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.12.044

R. Murugavel et al. / Journal of Organometallic Chemistry 692 (2007) 1920–1923
1921
2. Results and discussion
at d 1.06 and 1.08 ppm (3JHH = 6.5 Hz), due to the cou-
pling of the methine (CH) proton. The corresponding sig-
nals of the CH protons of the isopropyl group appear as
two overlapping septets observed at d 3.26–3.38 ppm
(3JHH = 6.5 Hz). An apparent triplet (which is actually
two overlapping doublets) is observed at d 2.08 ppm, due
to the presence of two different types of N–H protons in
the molecules (2JPH = 11.5 Hz). The appearance of two dif-
ferent N–H doublets is an indication of two different types
of hydrogen bonding interaction for these moieties (vide
infra). The aryl protons show multiplets in the region d
7.30–7.50 to 8.00–8.01 ppm. The 31P NMR spectrum of 1
shows a singlet (d 36.45 ppm) which is only slightly down-
field shifted from the value observed for the parent ligand
tBuP(O)(NHiPr)2 (d 35.5 ppm). The decoupled 119Sn{31P}
NMR spectrum of 1 yields a single resonance at d
86.92 ppm. For comparison, free Ph2SnCl2 shows a signal
in 119Sn NMR at ꢀ32.0 ppm [6].
2.1. Synthesis and spectral characterization
The six coordinate tin compound, [Ph2SnCl2(tBu-
P(O)(NHiPr)2)2] (1), was initially synthesized by the reac-
tion of either Ph2SnCl2 with BuP(O)(NHiPr)2 in presence
t
of Et3N (Scheme 1). In spite of using an HCl scavenger,
no reaction has been observed between Sn–Cl bonds and
the N–H protons of the phosphoramide to result in Sn–N
linkages. This is probably both due to the steric congestion
around the nitrogen as well as a decreased acidity of the N–
H protons.
The reaction between PhSnCl3 and BuP(O)(NHiPr)2
t
does not yield the expected 1:2 product [PhSnCl3(tBu-
P(O)(NHiPr)2)2], but once again results in the formation
of 1 (Scheme 1). Obliviously, a disproportionation of
PhSnCl3 to Ph2SnCl2 and SnCl4 has taken place during
the course of the reaction, thus leading to the formation
of 1. A similar aryl transfer in the case of PhSnCl3 has been
observed previously [6].
2.2. Molecular structure of 1
Since the formation of 1 either from Ph2SnCl2 or
PhSnCl3 did not involve the participation of Et3N, the syn-
thesis of 1 was repeated in the absence of Et3N in order to
optimize the conditions for the preparation of 1 and also to
improve the yield of the reaction. For examples, stirring a
The title compound crystallizes in orthorhombic space
group Pnca with the asymmetric part of the unit cell com-
t
posed of one phenyl group, one BuP(O)(NHiPr)2 group,
one chlorine atom and one-half of the metal. A view of
the molecular structure as ORTEP is shown in Fig. 1. As
shown in Fig. 1, the central tin atom is surrounded by
two phenyl groups (Sn–C(1), 2.146(2); Sn–C(5),
t
1:2 toluene solution of Ph2SnCl2 and BuP(O)(NHiPr)2 at
room temperature followed by warming the mixture to
50 °C for 2 h resulted in quantitative formation of 1. Single
crystals of 1 were obtained from the reaction mixture in
about 85% yield by cooling the solution overnight at 5 °C.
Compound 1 has been characterized by elemental anal-
ysis, IR, and NMR (1H, 31P and 119Sn NMR) spectroscopy
and single crystal X-ray diffraction studies. The IR spec-
trum displays vibration bands for all structural linkages
expected for this compound [7]. For example, the charac-
teristic P@O absorption for the compound was observed
at 1092 cmꢀ1. The N–H stretching vibrations result in the
two different strong absorptions at 3337 and 3268 cmꢀ1
probably indicating two types of the –NH groups in the
complex. Absorptions observed at 2967 and 3053 cmꢀ1
are readily assignable to aliphatic and aromatic C–H
stretching vibrations, respectively.
˚
˚
2.134(2) A), two chloride ions (Sn–Cl, 2.5842(5) A) and
two BuP(O)(NHiPr)2 moiety (Sn–O, 2.193(1) A) in an
t
˚
The 1H NMR spectral data obtained for 1 are suggestive
of the expected structure of this molecule. The protons of
the tert-butyl group on phosphorous appear as a phospho-
rous coupled doublet at d 1.04 ppm (3JPH = 15 Hz). The
two isopropyl groups (NHiPr) of the phosphonamide are
non-equivalent and hence appear as two different doublets
Fig. 1. ORTEP of [Ph2SnCl2(tBuP(O)(NHiPr)2)2] at 50% probability level.
˚
Selected bond distances (A) and angles (°): Sn–O 2.193(1), Sn–Cl
2.5842(5), Sn–C(1) 2.146(2), Sn–C(5) 2.134(2), P(1)–N(1) 1.632(1), P(1)–
N(2) 1.636(1), P(1)–O 1.515(1); O–Sn–O10 177.40(5), Cl0–Sn–Cl 177.76(2),
C(5)–Sn–C(1) 180.0, O–Sn–Cl0 92.16(3), O–P(1)–N(2), 107.99(5), O–P(1)–
C(11) 108.36(6), C(1)–Sn–O 91.30(2), O–P(1)–N(1) 115.66(6), C(1)–Sn–Cl
91.121(8), N(1)–P(1)–N(2) 106.81(6), C(5)–Sn–O 88.70(2), N(1)–P(1)–
C(11) 105.53(6), O–Sn–Cl 87.79(3), N(2)–P(1)–C(11) 112.61(6), C(5)–Sn–
Cl 88.879(8), P(1)–O–Sn 144.62(6).
NHiPr
O
P
Ph
Sn
tBu
Ph2SnCl2
or
Cl
P
benzene
NHiPr
iPrHN
+
NHiPr
NHiPr
tBu
O
O
P
tBu
NHiPr
PhSnCl3
Cl
Ph
Scheme 1. Synthesis of 1.

1922
R. Murugavel et al. / Journal of Organometallic Chemistry 692 (2007) 1920–1923
Fig. 2. Formation of 2-D sheets in 1 through intramolecular N–Hꢁ ꢁ ꢁCl hydrogen bonding.
octahedral geometry. The same types of ligands on the cen-
tral metal are trans to each other, thus producing an all-
trans structure. The trans angles found around the metal
are in the range of 177.40–180.00°, while the cis angles
are in the range of 87.79–91.12°. As a result of coordina-
tion to the tin metal, as expected, the P@O distance
Thus the title compound represents a rare inorganic ring
system involving main group elements. The other N–H
group on each phosphonic diamide is involved in intermo-
lecular hydrogen bonding with the chlorine of a neighbor-
ing molecule. This leads to the formation of sheet-like 2-D
structure as shown in Fig. 2. The non-participation of the
second N–H group in hydrogen bonding is also reflected
˚
(P(1)–O, 1.515(1) A) in this compound is longer than that
found in the parent tBuP(O)(NHiPr)2 (1.489(2) A) [8].
both in IR and H NMR spectroscopy (vide supra).
1
˚
Other bond distances are comparable to the values found
for similar linkages in the literature [7].
3. Conclusion
The presence of Sn–Cl and N–H moieties leads to the
formation of interesting intra- and inter-molecular hydro-
gen bonding. One of the two N–H linkages on each Bu-
A phosphonic diamide has been used as a ligand in
organotin chemistry. The organotin phosphonamide com-
plex [Ph2SnCl2 (tBuP(O)(NHiPr)2)2] has been synthesized
from two different precursor halides and the product has
been structurally characterized. The presence of reactive
Sn–Cl and N–H linkages offer further possibilities in using
molecules of type 1, albeit with smaller substituents on
nitrogen and phosphorus, as precursors for tin–amide com-
plexes stabilized by phosphoryl coordination. Work on this
direction is currently underway.
t
P(O)(NHiPr)2 moiety is involved in hydrogen bonding
with chlorine atom of the same molecule. This N–Hꢁ ꢁ ꢁCl
hydrogen bond completes the formation two spirocyclic
six-membered rings around tin as depicted in Fig. 1. The
architecture of these two six-membered rings is remarkable
due to the fact that they are made up of as many as six dif-
ferent elements coming from as many as five different
groups of the main group (group 1 (H), group 14 (Sn),
group 15 (N, P), group 16 (O), group 17 (Cl)). It is of fur-
ther interest to note that at least three different types of
bonding (covalent, coordinate and hydrogen) are repre-
sented within these six-membered rings, with formal bond
order ranging from fractional to two with varying degrees
of multiple bonding. The existence of such six-membered
rings, to our best knowledge, is unknown in the literature.
4. Experimental
4.1. Synthesis of 1
t
Phosphonic diamide BuPO(NHiPr)2 (440 mg, 2 mmol)
was dissolved in toluene (50 mL), and Ph2SnCl2 (344 mg,

R. Murugavel et al. / Journal of Organometallic Chemistry 692 (2007) 1920–1923
1923
1 mmol) in 15 mL of toluene was added at room tempera-
ture and stirred for overnight to obtain small amount
white precipitate which got dissolved on warming solution
at 50 °C. The solution was stirried at 50 °C for 2 h. Color-
less X-ray diffraction quality crystals of 1 were obtained
after 12 h at 5 °C. Yield: 0.636 g (85%). Mp. 145–147 °C.
Anal. Calc. for C32H60N4P2O2SnCl2: C, 49.00; H, 7.71;
N, 7.14. Found: C, 48.46; H, 7.47; N, 7.07%. IR (KBr,
cmꢀ1): 3337 (s), 3268 (s), 3053 (w), 2967 (s), 2870 (m),
1469 (s), 1431 (s), 1262 (m), 1131 (s), 1092 (vs), 1057
(vs), 1020 (vs), 903 (w), 880 (w), 803 (m), 732 (m), 696
(m), 653 (w), 569 (w), 537 (w), 456 (w). 1H NMR
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.12.044.
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˚
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˚
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˚
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Acknowledgements
This work was supported by DST, New Delhi, in the
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the CSIR, New Delhi, for a Research Fellowship.
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