Cα,Cortho-Dimetalated phosphazene complexes

Article abstract of DOI:10.1039/b707320h

The first C_α,C_ortho dilithium complex of a phosphazene has been synthesized as a single stereoisomer and has been structurally characterized in solution; the complex is monomeric, with the dianion acting as an N-C_ortho and O-C_α chelate. Transmetallation with Me₃SnCl and PhHgCl afforded the first C _α,C_ortho homo- and hetero-bimetallic phosphazene complexes, which contain a desymmetrised Ph₂PN moiety. The Royal Society of Chemistry.

Full text of DOI:10.1039/b707320h

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Ca,Cortho-Dimetalated phosphazene complexes{{
Jesu´s Garc´ıa Lo´pez,a Ignacio Ferna´ndez,a Manuel Serrano Ruizb and Fernando Lo´pez Ortiz*a
Received (in Cambridge, UK) 15th May 2007, Accepted 23rd July 2007
First published as an Advance Article on the web 28th August 2007
DOI: 10.1039/b707320h
The first Ca,Cortho dilithium complex of a phosphazene has
been synthesized as a single stereoisomer and has been
structurally characterized in solution; the complex is mono-
meric, with the dianion acting as an N–Cortho and O–Ca chelate.
Transmetallation with Me3SnCl and PhHgCl afforded the first
Ca,Cortho homo- and hetero-bimetallic phosphazene complexes,
which contain a desymmetrised Ph2PN moiety.
Ortho- and a-lithiated phosphazenes have seen widespread use in
organic and organometallic chemistry.1 These monoanions can act
as chelating ligands to give four- (A),2 five- (B),3 and six-membered
(C4 and D5) metallocycles (Fig. 1). Double deprotonation of
phosphazenes has been achieved exclusively at the position a to the
phosphorus of bis(phosphazenyl)methanes.6 The dianions E are
valuable precursors for a wide range of metal complexes.1,7 Access
to a,o-dilithiated phosphazenes might open new prospects in this
Scheme 1 Synthesis of dilithium phosphazene 6 and reactivity toward
area of chemistry. Lappert and co-workers isolated complex 2
through lithiation of CH2(SiMe3)P(Ph)2LNSiMe3 (1) with nBuLi
in hexane (Fig. 1).8 The formation of 2 was assumed to proceed via
an ortho-lithiated species.
Me3SnCl.
for H1 at d 0.4 ppm and the four multiplets signal [d 6.7 (t, H8),
6.72 (q, H9), 7.4 (dd, H10), 7.95 (d, H7) ppm] arising from the
ortho deprotonated phenyl ring [Fig. 2(a)].11 The 13C{31P,1H}
NMR spectrum acquired at 295 uC showed two quartets [d 1.83,
We have previously proposed the participation of a,o-dianions
of phosphazenes 3 as key intermediates in the synthesis of spiro
1,2-oxaphosphetanes 5 (Scheme 1).9 The process would involve the
ortho lithiation of the a monoanions 4.5 The work described here
concerns the first synthesis and structural characterization of a
Ca,Cortho dilithium phosphazene 6 in solution and its application in
the synthesis of the bimetallic tin(IV) and tin(IV)–mercury(II)
complexes 7 and 10, respectively. The solid-state structure of the
compound 7 is also described.
1J(13C7Li) 17.0 Hz; 209.27, J(13C7Li) 30.3 Hz, ppm] assigned to
1
C1 and C6, respectively [Fig. 2(b), S5, ESI{]. The multiplicity of
C1 and C6 reveals the binding of each carbon to only one lithium
atom. This fact, together with the absence of significant changes in
the NMR spectra of a diluted sample of 6 (0.062 M), suggests that
the dianion is a monomer. At 2100 uC the 7Li{1H} spectrum
consists of two doublets [d 1.2, J(31P7Li) 3.2 Hz; 2.3, J(31P7Li)
7.1 Hz, ppm] [Fig. 2(c)]. The 31P,7Li coupling of 3.2 Hz is very
similar to that found in chelates D (Fig. 1).5 Hence, the high field
lithium signal of 6 can be assigned to Li1, which is coordinated to
Ca and the oxygen of the CO group of the phosphazenyl moiety.
The large deshielding of the carbon C12 [DdC12(6/3) = 12.9 ppm]
2
2
Treatment of 3 with 2.2 equiv. of RLi (R = sBu, tBu) in THF at
270 uC for 30 min afforded an orange solution of 6 (Scheme 1),§
which was investigated by NMR methods.10 a,o-Dilithiation was
evidenced in the 1H NMR spectrum at 290 uC by the broad signal
Fig. 1 Different types of lithium phosphazenes.
a
´
Area de Qu´ımica Orga´nica, Universidad de Almer´ıa, Carretera de
Sacramento s/n, 04120, Almer´ıa, Spain. E-mail: flortiz@ual.es;
Fax: 34 950 015478; Tel: 34 950 015478
b
´
Area de Qu´ımica Inorga´nica, Universidad de Almer´ıa, Carretera de
Sacramento s/n, 04120, Almer´ıa, Spain
Fig. 2 NMR spectra of 6 in THF-d8: (a) expansions of the 1H spectrum
(500.13 MHz) measured at 290 uC. (b) Expansions of the C1 and C6
signals of the 13C{31P,1H} spectrum (125.76 MHz) measured at 295 uC.
{ Dedicated to Prof. Vicente Gotor on the occasion of his 60th birthday.
{ Electronic supplementary information (ESI) available: Experimental and
spectroscopic details. See DOI: 10.1039/b707320h
7
(c) Li{1H} spectrum (194.37 MHz) measured at 2100 uC.
4674 | Chem. Commun., 2007, 4674–4676
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and the decrease in the 31P,13C coupling [D1JPC12(6/3) = 217.9 Hz]
atoms Sn1 and Sn2, respectively. The Sn1–O1 (284.0 pm) and
Sn2–N1 (272.2 pm) distances are shorter than the sum of the
corresponding van der Waals radii (Sn/O: 370.0 pm; Sn/N:
372.0 pm), thus indicating the existence of Sn–O and Sn–N
contacts.15 In agreement with this coordination the Sn–C bond
distances of the methyl groups anti to the O/N donor atoms are
slightly larger than the other Sn–CH3 bonds: Sn1–C31 215.9(5) pm;
Sn1–C32/33, av. 212.7 pm; Sn2–C42 218.1(5) pm; Sn2–C41/43, av.
213.4 pm. The geometry at the tin atoms can be considered as
being located on the tetrahedral-trigonal bipyramidal path.16 The
values Dgh(Sn1) = 28u and Dgh(Sn2) = 47u indicate that the tin
atom Sn2 exists in a five-coordinate geometry best described as a
distorted trigonal bipyramid, whereas the Sn1 configuration is
closer to a distorted tetrahedron. The Sn2–N1 coordination gives
rise to an almost planar five-membered ring [torsion angles N1–
P1–C21–C22 of 5.8(4)u, P1–C21–C22–Sn2 of 20.1(5)u]. The Sn2
atom is part of a six-membered ring showing a puckered half-chair
conformation with a planar bay defined by the PNCO moiety
[torsion angles P1–N1–C53–O1 of 5.7(6)u, C51–P1–N1–C53 of
56.6(4)u, N1–P1–C51–Sn1 of 268.9(3)u]. This is the first time that
are consistent with this assignment.1c,5
2
The large magnitude of J(31P7Li2) establishes the existence of
PN–Li coordination. The double chelation in 6 will add rigidity to
the complex. This hypothesis was verified by 1D gROESY
measurements at 290 uC (ESI{). Selective irradiation of H1
produced NOE on the ortho protons H10 and H12 of both
aromatic rings, whereas irradiation of H2 gave NOE only on H10.
The NOEs observed indicate that complex 6 is configurationally
stable, the relative configuration is l, and it exists in a conformation
in which H1 is gauche with respect to both P-phenyl rings and anti
with respect to the nitrogen. These results imply that the initially
formed a anion 4 directs the ortho deprotonation with excellent
diastereoselectivity. To the best of our knowledge, this is the first
report on the desymmetrisation of a Ph2PN moiety by directed
ortho lithiation. a,o-Dianions have previously been characterised
only for a few alkyl phenyl sulfones12 and one sulfoximine.12d
Although the dianions do not showed Ca–Li contacts, these
systems proved to mimic the reactivity of a,a-dilithiosulfones
toward alkylating reagents.12a,d,13
a
a,o-bis(stannyl)phosphazene has been characterized.17
Dianion 6 remains unaltered for three days in the temperature
range from 290 to 270 uC. Above 270 uC, 6 undergoes
cyclocondensation with loss of MeOLi. The process is completed
in a few minutes at 235 uC. Subsequent addition of benzaldehyde
furnishes 5 (R1 = H, R2 = Me, R3 = H, R4 = Ph) quantitatively.9
The reaction of 6 with 2 equiv. of Me3SnCl at 290 uC during
15 h led, after aqueous workup, to the bis(stannane) 7 in high yield
(Scheme 1), together with small amounts of the diastereomer 8
(6%) (ratio 7 : 8 of 12.5 : 1), and the ortho monostananne 9 (19%).
The three compounds were separated by column chromatography
and identified on the basis of the NMR data. Recrystallization of 7
from hexane at 230 uC gave colourless crystals, which were
studied by X-ray methods."
Phosphazenes bearing one tin(II) atom at the a15b–d,18 or ortho15a
carbon and two tin(II) atoms at the a position7b have been
described previously. It is worth noting that the solid-state
structure of 7 shows the same molecular arrangement as the
precursor 6 in solution.
This success with 7 prompted us to investigate the usefulness of
dianion 6 as scaffold for accessing to hetero-bimetallic complexes.
To our delight, stepwise addition of PhHgCl and Me3SnCl to 6 at
290 uC afforded a-stannyl-o-mercurated phosphazene 10 in good
yields (mixture of 10, 11 and 12 in a ratio of 73 : 17 : 10)
(Scheme 2).19 Purification by column chromatography furnished
pure complexes 10–12. Their structures were assigned based on
multinuclear magnetic resonance spectroscopy measurements.
Compound 10 is characterised by a 31P signal at d 35.34 ppm
showing 119Sn and 199Hg satellites. The corresponding metallic
nuclei appear as doublets at d (119Sn) 7.55 ppm, 2J(119Sn31P)
The solid structure of 7 displays two SnMe3 groups s-bonded to
the phosphazenyl ligand at the Ca and Cortho positions (Fig. 3). The
Sn–C distances fall within the expected range for Sn–C(alkyl/aryl)
bonds.14 The CLO and PLN groups are directed toward the tin
3
32.8 Hz,20 and d(199Hg) 2701.9 ppm, J(199Hg31P) 90.5 Hz. A
detailed NMR study will be published elsewhere. Compounds 10
and 11 are the first examples of heterodinuclear Sn,Hg-
phosphazene complexes.
In summary, the first a,o-dilithium phosphazene 6 has been
synthesized as a single stereoisomer. The solution structure shows
the characteristic motifs of monolithiated Ca and Cortho phospha-
zenes. The CO–Li and PN–Li coordination of 6 leads to a rigid
monomeric complex that is configurationally stable. The desym-
metrisation of the Ph2PLN moiety achieved in the formation of
dianion 6 is transferred very efficiently to Ca,Cortho homo- and
Fig. 3 ORTEP drawing of 7. Selected bond lengths (pm) and angles (u):
P1–N1 160.9(23), P1–C51 177.5(4), N1–C53 134.9(5), C53–O1 122.7(5),
Sn1–C51 220.9(4), Sn1–C31 215.9(5), Sn1–C32 212.7(5), Sn1–C33
212.8(5), Sn2–C22 217.0(4), Sn2–C41 213.2(4), Sn2–C42 218.1(5), Sn2–
C43 213.6(4); C32–Sn1–C33 113.9(2), C32–Sn1–C31 108.6(2), C33–Sn1–
C31 107.1(2), C32–Sn1–C51 118.80(17), C33–Sn1–C51 108.87(18),
C31–Sn1–C51 97.88(19), C41–Sn2–C43 119.49(18), C41–Sn2–C22
116.52(17), C41–Sn2–C42 99.3(2), C43–Sn2–C22 113.62(18), C43–Sn2–
C42 103.0(2), C22–Sn2–C42 100.19(17).
Scheme 2 Synthesis of heterodinuclear Sn,Hg-phosphazene complexes
10 and 11.
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A. Murso and D. Stalke, Chem.–Eur. J., 2004, 10, 3622; (d) G. C. Welch,
W. E. Piers, M. Parvez and R. McDonald, Organometallics, 2004, 23,
1811; (e) for X = P see: M. T. Gamer and P. W. Roesky, Z. Anorg. Allg.
Chem., 2001, 627, 877; (f) M. S. Hill, P. B. Hitchcock and
S. M. A. Karagoumi, J. Organomet. Chem., 2004, 689, 722.
hetero-dinuclear phosphazene complexes 7 and 10, respectively.
Complexes 6, 7 and 10 could serve as precursors for a variety of
bimetallic complexes via transmetallation reactions. This area of
chemistry is currently under investigation.
´
5 I. Ferna´ndez, J. M. Alvarez-Gutie´rrez, N. Kocher, D. Leusser, D. Stalke,
This research was supported by the Ministerio de Educacio´n y
Ciencia (MEC) (project: CTQ2005-1792BQU). J. G. L. thanks
MEC for a doctoral fellowship.
J. Gonza´lez and F. Lo´pez-Ortiz, J. Am. Chem. Soc., 2002, 124, 15184.
6 (a) A. Mu¨ller, B. Neumu¨ller and K. Dehnicke, Z. Anorg. Allg. Chem.,
1997, 623, 1306; (b) C. M. Ong and D. W. Stephan, J. Am. Chem. Soc.,
1999, 121, 2939; (c) A. Kasani, R. P. K. Babu, R. McDonald and
R. G. Cavell, Angew. Chem., Int. Ed., 1999, 38, 1483.
7 For recent references, see: (a) W.-P. Leung, Z.-X. Wang, H.-W. Li,
Q.-C. Yang and T. C. W. Mak, Angew. Chem., Int. Ed., 2001, 40, 2501;
(b) W. D. Jones, G. Lin, R. A. Gossage, R. McDonald and R. G. Cavell,
Organometallics, 2003, 22, 2832; (c) T. Cantat, N. Me´zailles, L. Ricard,
Y. Jean and P. Le Floch, Angew. Chem., Int. Ed., 2004, 43, 6382; (d)
M. Fang, N. D. Jones, R. Lubowski, J. Tjathas, M. J. Ferguson and
R. G. Cavell, Angew. Chem., Int. Ed., 2006, 45, 3097; (e) T. Cantat,
L. Ricard, N. Me´zailles and P. Le Floch, Organometallics, 2006, 25,
6030.
8 (a) P. B. Hitchcock, M. F. Lappert and Z.-X. Wang, Chem. Commun.,
1997, 1113; (b) P. B. Hitchcock, M. F. Lappert and Z.-X. Wang,
J. Organomet. Chem., 2006, 691, 2748.
9 J. Garc´ıa-Lo´pez, E. Peralta-Pe´rez, A. Force´n-Acebal, S. Garc´ıa-Granda
and F. Lo´pez-Ortiz, Chem. Commun., 2003, 856.
10 0.14 M Samples in THF-d8 (ESI{). Attempts to recrystallize 6 from
THF were unsuccessful.
11 The signal of the methyl protons H2 buried under the solvents was
unraveled through a 1D gTOCSY spectrum (ESI{).
Notes and references
§ Synthesis of 6: To a solution of 26 mg (91 mmol) of 3 in dry THF-d8
(0.3 mL) prepared in a dried 5-mm NMR tube at 270 uC were added
132 mL (0.199 mmol) of sBuLi (1.3 M solution in n-hexane). The sample
was transferred to the magnet with the probehead previously cooled to
290 uC. The extra signals shown in the spectra correspond to the solvent of
the organolithium base, which was not eliminated. The same procedure was
used for the reactions carried out in bulk. NMR data for 6 in THF-d8: 1H
NMR (500.13 MHz, 290 uC) d 0.4 (br s, H1), 1.34 (dd, H2, JPH = 20.5,
JHH = 8.2 Hz), 3.55 (s, H4), 6.70 (br t, H8, JPH = 2.0, JHH = 6.8 Hz), 6.72
(q, H9, JPH = JHH = 6.8 Hz), 7.24 (m, H13), 7.25 (m, H14), 7.4 (dd, H10,
JPH = 10.9, JHH = 6.8 Hz), 7.69 (m, H12), 7.95 (d, H7, JHH = 6.8 Hz). 13
C
NMR (125.76 MHz, 295 uC) d 1.83 (dq, C1, JPC = 51.9, JCLi = 17.0 Hz),
11.58 (C2), 51.45 (C4), 121.3 (d, C9, JPC = 16.0 Hz), 124.5 (C8), 127.62
(C10), 127.79 (d, C13, JPC = 9.0 Hz), 128.87 (d, C14, JPC = 3.1 Hz), 131.0
(d, C12, JPC = 7.5 Hz), 140.06 (d, C11, JPC = 81.8 Hz), 142.28 (d, C7, JPC
=
=
24.9 Hz), 145.44 (d, C5, JPC = 110.7 Hz), 165.08 (C3), 209.27 (m, C6, JCLi
7
30.3 Hz). 31P NMR (202.46, 2100 uC) d 43.81. Li NMR (194.37 MHz,
2100 uC) d 1.2 (d, Li2, JPLi = 3.2 Hz), 2.3 (d, Li1, JPLi = 7.1 Hz).
" Crystal data for 7: C22H34NO2Sn2, Mr = 612.85, crystal size: 0.25 6 0.18
12 (a) J. Vollhardt, H.-J. Gais and K. L. Lukas, Angew. Chem., Int. Ed.
Engl., 1985, 24, 610; (b) W. Hollstein, K. Harms, M. Marsch and
G. Boche, Angew. Chem., Int. Ed. Engl., 1987, 26, 1287; (c) H.-J. Gais
and J. Vollhardt, Tetrahedron Lett., 1988, 29, 1529; (d) J. F. K. Mu¨ller,
M. Neuburger and M. Zehnder, Helv. Chim. Acta, 1997, 80, 2182.
13 H.-J. Gais, W. A. Ball and J. Bund, Tetrahedron Lett., 1988, 29, 781.
14 (a) R. A. Howie, E. S. Paterson and J. Wardell, J. Organomet. Chem.,
1983, 259, 71; (b) A. J. Davenport, D. L. Davies, J. Fawcett and
D. R. Russell, J. Chem. Soc., Dalton Trans., 2002, 3260.
¯
6 0.109 mm, triclinic, space group P1, a = 9.249(5), b = 11.414(5), c =
3
˚
˚
13.629(5) A, a = 77.744(5), b = 80.155(5), c = 68.041(5)u, V = 1297.3(10) A ,
Z = 2, Dc = 1.569 g cm23, F000 = 608, T = 150(2) K; m = 2.002 mm21. 6932
reflections measured, 4449 independent (Rint = 0.0187), 261 parameters,
final R indices R1 [I = 2s(I)] = 0.0337 and wR2 (all data) = 0.0869, GOF on
2
3
˚
F = 1.081, max./min. residual electron density = 1.150/20.722 e A . Data
were collected on a BRUKER Smart-Apex CCD area-detector diffract-
˚
ometer, using Mo-Ka radiation (l = 0.71069 A). The intensities were
15 Range of SnrN distances in phosphazenyl Sn(II) complexes: 225.6(6)–
2.589(5) pm. (a) S. Wingerter, H. Gornitzka, R. Bertermann,
S. K. Pandey, J. Rocha and D. Stalke, Organometallics, 2000, 19,
3890; (b) W.-P. Leung, Q. W.-Y. Ip, S.-Y. Wong and T. C. W. Mak,
Organometallics, 2003, 22, 4604; (c) P. B. Hitchcock, M. F. Lappert and
Z.-X. Wang, J. Organomet. Chem., 2006, 691, 2748; (d) W.-P. Leung,
K.-W. Wong, Z.-X. Wang and T. C. W. Mak, Organometallics, 2006,
25, 2037.
measured using the v scan method. Empirical absorption correction was
applied. The structure was solved by direct methods SIR97 and refined by
full-matrix least-squares on F2 using SHELXTL97 software package.
Anisotropic thermal factors were assigned to all the non-hydrogen atoms.
All the diagrams were generated by using the SHELXTL 97 and ORTEP
programs. CCDC 621431. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b707320h
16 The position on this path is defined by Dgh = gheq 2 ghax, with gheq
and ghax being the sum of the equatorial and axial angles, respectively.
The limiting values are 0u for a tetrahedron and 90u for a trigonal
bipyramid. U. Kolb and M. Dra¨ger, Organometallics, 1991, 10, 2737.
17 For Ca,Cortho-monometallic bis(phosphazenyl)methanides, see ref. 7c.
See also: (a) M. W. Avis, K. Vrieze, J. M. Ernsting, C. Elsevier,
N. Veldman, A. L. Spek, K. V. Katti and C. L. Barnes, Organometallics,
1996, 15, 2376; (b) M. Fang, N. D. Jones, M. J. Ferguson, R. McDonald
and R. G. Cavell, Angew. Chem., Int. Ed., 2005, 44, 2005.
1 For recent reviews, see: (a) K. Izod, Coord. Chem. Rev., 2002, 227, 153;
(b) A. Steiner, S. Zacchini and P. I. Richards, Coord. Chem. Rev., 2002,
227, 193; (c) F. Lo´pez-Ortiz, Curr. Org. Synthesis, 2006, 3, 187.
2 (a) F. Lo´pez-Ortiz, E. Pela´ez-Arango, B. Tejerina, E. Pe´rez-Carren˜o and
S. Garc´ıa-Granda, J. Am. Chem. Soc., 1995, 117, 9972; (b) A. Mu¨ller,
B. Neumu¨ller and K. Dehnicke, Angew. Chem., Int. Ed. Engl., 1997, 36,
2350; (c) P. B. Hitchcock, M. F. Lappert, P. G. H. Uiterweerd and
Z.-X. Wang, J. Chem. Soc., Dalton Trans., 1999, 3413; (d) M. Said,
M. Thornton-Pett and M. Bochmann, Organometallics, 2001, 20, 5629;
(e) B. Neumu¨ller, A. Mu¨ller and K. Dehnicke, Z. Anorg. Allg. Chem.,
2002, 628, 100.
3 (a) A. Steiner and D. Stalke, Angew. Chem., Int. Ed. Engl., 1995, 34,
1752; (b) L. Boubekeur, L. Ricard, N. Me´zailles, M. Demange,
A. Auffrant and P. Le Floch, Organometallics, 2006, 25, 3091.
4 For X = C see:(a) P. B. Hitchcock, M. F. Lappert and Z.-X. Wang,
J. Chem. Soc., Dalton Trans., 1997, 1953; (b) J. D. Masuda, P. Wei and
D. W. Stephan, Dalton Trans., 2003, 3500; (c) N. Kocher, D. Leuser,
18 W.-P. Leung, Z.-X. Wang, H.-W. Li, Q.-C. Yang and T. C. W. Mak,
J. Am. Chem. Soc., 2001, 123, 8123.
19 For ortho mercurated phosphazenes, see: (a) J. Vicente, J. A. Abad,
R. Clemente, J. Lo´pez-Serrano, M. C. Ram´ırez de Arellano, P. G. Jones
and D. Bautista, Organometallics, 2003, 22, 4248; (b) S. D. J. Brown,
W. Henderson, K. J. Kilpin and B. K. Nicholson, Inorg. Chim. Acta,
2007, 360, 1310.
20 Complexes 7/10 and 8/11 show similar 119Sn NMR data for the tin atom
bonded at the a carbon (see ESI{).
4676 | Chem. Commun., 2007, 4674–4676
This journal is ß The Royal Society of Chemistry 2007