The α-iminophospholide ligands

Article abstract of DOI:10.1021/ja060100q

The reaction of phospholide ions with imidoyl chlorides in the presence of ^tBuOK gives the α-iminophospholides that are isolated as their trimethylstannyl derivatives. These derivatives in turn react with metal chlorides to give complexes of th

Full text of DOI:10.1021/ja060100q

Published on Web 05/27/2006
The r-Iminophospholide Ligands
Joanna Grundy, Bruno Donnadieu, and Franc¸ois Mathey*
UCR-CNRS Joint Research Chemistry Laboratory, Department of Chemistry, UniVersity of California RiVerside,
RiVerside, California 92521-0403
Received January 13, 2006; E-mail: fmathey@citrus.ucr.edu
Ligands incorporating a delocalized -NdC-CdN- core (e.g.,
2,2′-bipyridines and 1,4-diazadienes) play a central role in coordina-
tion chemistry and homogeneous catalysis. The analogous -Pd
C-CdP- ligands have also been studied to some extent. 2,2′-
Biphosphinines (1) display strong π-accepting properties and
stabilize transition metal centers in low oxidation states.1 Stabilized
1,4-diphosphadienes, such as 2, have already found some interesting
catalytic applications.2 The dissymmetrical -PdC-CdN- ligands
are only represented today by 2,2′-pyridylphosphinines (3).3 Their
chemistry is rather disappointing because the two subunits behave
independently. This finding can be easily rationalized if we consider
the electronic properties of imines and phosphaalkenes. The π-bond
of H2CdNH appears at -12.49 eV, whereas the π-bond of H2Cd
PH is much higher in energy at -10.30 eV.4 This huge gap prevents
any sizable delocalization within a -PdC-CdN- unit. To restore
some cooperativity between the sp2-N and sp2-P centers, the
simplest option is to stabilize the PdC double bond by incorporation
into an aromatic ring. This led us to consider the R-iminophos-
pholide ions (4) as a potential solution.
From these data (especially the short C2-C3 bond at 1.396 Å, and
the significantly contracted P-C1 bond at 1.742 Å), it is quite clear
that the electronic structure of 5 is better represented by a mesomeric
formulation (eq 1).
A NBO analysis fully confirms this point: charge at P +0.236,
charge at N -0.694 e. Thus, the nitrogen will be the donor and
phosphorus the acceptor center. This theoretical study clearly
establishes the full cooperativity between the two sp2-coordinating
centers of 5.
The synthesis of R-iminopyrrolides cannot be transposed for
obtaining R-iminophospholides. However, some time ago, we
described a simple method which converts R-unsubstituted into
R-functional phospholides using a [1,5] shift of the functional group
from P to CR.8 We thus studied the reaction of phospholides with
imidoyl chlorides.9 The chemistry is described in eq 2.
An additional interest of these ligands lies in their analogy with
the well-known R-iminopyrrolides, whose applications in polym-
erization catalysis have been studied in some depth recently.5
To get a more precise idea of the electronic properties of such
P,N-ligands, we first decided to perform a DFT study of a
representative species 5 with Li+ as the counterion at the B3LYP/
6-311++G(3df,2p) level of theory.6 The computed structure is
shown in Figure 1.
The R-phenyl group has been introduced for steric protection of
the phosphorus coordinating center. The R-iminophospholide (8)
gives a 31P resonance at 87.8 ppm in THF. The reaction with
trimethyltin chloride gives 9,10 which can be isolated by crystal-
lization. The overall yield of 9 from 6 can reach 40%. The X-ray
crystal structure of 9 is shown in Figure 2).
Figure 1. Computed structure of lithium 2-(N-methylimino)phospholide
(5). Main bond lengths (Å) and angles (deg): P-C1 1.742, P-C4 1.795,
C1-C2 1.395, C2-C3 1.396, C3-C4 1.404, C4-C8 1.426, C8-N 1.299,
P-Li 2.366, N-Li 1.914; C1-P-C4 90.33, P-C4-C8 126.26, C4-C8-N
124.26, N-Li-P 98.70, P-C4-C8-N 16.40.
The lithium ion is not η5-coordinated to the phosphole ring as
in nonfunctional phospholides7 but chelated between phosphorus
and nitrogen. The structure of the ligand is essentially planar except
for a slight displacement of the imino nitrogen away from the plane
on the same side as lithium (P-C4-C8-N dihedral angle ) 16.4°).
Figure 2. X-ray crystal structure of phosphole 9. Main bond lengths (Å)
and angles (deg): P1-Sn1 2.5349(8), P1-C1 1.795(3), P1-C4 1.803(3),
C1-C2 1.372(4), C2-C3 1.455(4), C3-C4 1.377(4), C4-C5 1.473(4),
C5-N1 1.284(3); C1-P1-Sn1 95.51(9), C4-P1-Sn1 95.80(9), C1-P1-
C4 90.44(12), P1-C4-C5 121.39(19), C4-C5-N1 119.2.
9
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J. AM. CHEM. SOC. 2006, 128, 7716-7717
10.1021/ja060100q CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
References
(1) Selected references: (a) Rosa, P.; Me´zailles, N.; Ricard, L.; Mathey, F.;
Le Floch, P. Angew. Chem., Int. Ed. 2000, 39, 1823. (b) Me´zailles, N.;
Rosa, P.; Ricard, L.; Mathey, F.; Le Floch, P. Organometallics 2000, 19,
2941. (c) Rosa, P.; Me´zailles, N.; Ricard, L.; Mathey, F.; Le Floch, P.;
Jean, Y. Angew. Chem., Int. Ed. 2001, 40, 1251.
(2) Selected references: (a) Minami, T.; Okamoto, H.; Ikeda, S.; Tanaka,
R.; Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2001, 40, 4501. (b)
Ozawa, F.; Yamamoto, S.; Kawagishi, S.; Hiraoka, M.; Ikeda, S.; Minami,
T.; Ito, S.; Yoshifuji, M. Chem. Lett. 2001, 972. (c) Ozawa, F.; Okamoto,
H.; Kawagishi, S.; Yamamoto, S.; Minami, T.; Yoshifuji, M. J. Am. Chem.
Soc. 2002, 124, 10968.
(3) (a) Bre`que, A.; Santini, C. C.; Mathey, F.; Fischer, J. Inorg. Chem. 1984,
23, 3463. (b) Schmid, B.; Venanzi, L. M.; Albinati, A.; Mathey, F. Inorg.
Chem. 1991, 30, 4693. (c) Schmid, B.; Venanzi, L. M.; Gerfin, T.;
Gramlich, V.; Mathey, F. Inorg. Chem. 1992, 31, 5117.
Figure 3. Ligand structure in copper complex 10. Selected bond lengths
(Å): P2-C5 1.7557(16), P2-C2 1.7760(16), N1-C1 1.296(2), N1-C12
1.433(2), C1-C2 1.457(2), C1-C18 1.509(2), C2-C3 1.405(2), C3-C4
1.421(2), C3-C19 1.512(2), C4-C5 1.393(2), C4-C20 1.512(2), C5-C6
1.477(2), C6-C11 1.398(2), C6-C7 1.399(2), C7-C8 1.389(2), C8-C9
1.387(2), C9-C10 1.383(3), C10-C11 1.393(2), C12-C13 1.390(2), C12-
C17 1.390(2), C13-C14 1.387(2), C14-C15 1.387(3), C15-C16 1.383-
(3), C16-C17 1.390(2), Cu1-Cu2 2.6046(3), Cu1-Cu3 2.7041(3), Cu1-
Cu4 2.5495(3), Cu2-Cu3 2.5691(3), Cu2-Cu4 2.7330(3), Cu3-Cu4
2.6101(3).
(4) Lacombe, S.; Gonbeau, D.; Cabioch, J.-L.; Pellerin, B.; Denis, J.-M.;
Pfister-Guillouzo, G. J. Am. Chem. Soc. 1988, 110, 6964.
(5) For two recent reviews, see: (a) Yoshida, Y.; Matsui, S.; Fujita, T. J.
Organomet. Chem. 2005, 690, 4382. (b) Mashima, K.; Tsurugi, H. J.
Organomet. Chem. 2005, 690, 4414.
(6) Frisch, M. J.; et al. Gaussian 03, revision B.05; Gaussian, Inc.: Pittsburgh,
PA, 2003.
(7) Douglas, T.; Theopold, K. H. Angew. Chem., Int. Ed. Engl. 1989, 28,
1367.
(8) Holand, S.; Jeanjean, M.; Mathey, F. Angew. Chem., Int. Ed. Engl. 1997,
36, 98.
(9) Cunico, R. F.; Pandey, R. K. J. Org. Chem. 2005, 70, 5344.
(10) A solution of 1-phenyl-3,4-dimethylphosphole (2 mL, 10 mmol) in
tetrahydrofuran (40 mL) and tBuOK (1.23 g, 11 mmol) was freeze-thaw-
degassed twice in a thick-walled glass ampule sealed with a Teflon valve.
The mixture was heated (under a static vacuum) to 140 °C for 8 h.
Volatiles were removed in vacuo, then the mixture was redissolved in
tetrahydrofuran (40 mL), cooled to -78 °C, and N-phenylacetimidoyl
chloride (15 mmol, 2.3 g, 2.01 mL) added via syringe. After the solution
was allowed to warm to ambient temperature, it was stirred for 30 min,
then tBuOK (1.12 g, 10 mmol) was added and warmed to 40 °C for 1 h,
then cooled to 0 °C, and trimethyltin chloride (2.1 g, 11 mmol) added.
The mixture was stirred for 1 h, then volatiles were removed in vacuo.
The product was extracted with hexane (3 × 20 mL) and crystallized
from hexane to give pale yellow crystals of pure phosphole 9 (40% yield,
1.86 g): 31P NMR CDCl3 δ -46.4 (1JPSn ) 552 Hz); 1H NMR CDCl3 δ
7.30-7.15 (m, C6H5), 6.96 (1H, m, Ph), 6.69 (2H, m, Ph), 2.39 (3H, d,
The structure is characterized by the E stereochemistry at the
CdN double bond, probably for steric reasons, a highly pyramidal
phosphorus atom (sum of the angles at P ) 281.7°) and a very low
delocalization within the ring. In fact, this is the most pyramidal
phosphole whose structure has been recorded to date.11 Stan-
nylphosphole (9) is a convenient precursor for the transition metal
complexes of the R-iminophospholide (8). As an example, its
reaction with copper(I) chloride leads to a red diamagnetic
tetrameric complex [Cu(8)]4 (10) in 92% yield.12 The iminophos-
pholide acts as a bridging five-electron µ2-P, η1-N-ligand as shown
in Figure 3). Each copper atom has 16 electrons in its valence shell
if we ignore the copper-copper bonds. Thus, clusterization takes
place to bring the electron count up to 18 electrons. It is interesting
to compare this situation to that found in the other structurally
characterized copper-phosphide complex [Cu(phen)(PPh2)]3, where
the 18e rule is fulfilled without metal-metal bonds.13 Broadly
speaking, the structure of the ligand in 10 is intermediate between
those of 5 and 9. This means that some delocalization is still
effective in 10. It is anticipated that tuning the steric bulk of the
nitrogen substituent of 8 will permit the isolation of interesting
monomeric electron-deficient complexes.
4JPH ) 1.6 Hz, 5JSnH ) 17 Hz, CH3), 2.17 (3H, d, 4JPH ) 1.6 Hz, 5JSnH
)
)
4
3
14 Hz, CH3), 2.08 (3H, d, JPH ) 1.2 Hz, CH3), -0.08 (9H, d, JPH
2.1, 2JSnH ) 49.2, SnCH3); 13C NMR CDCl3 δ 165.9 (CdN), 153.11 (Cipso
-
Ph), 151.8 (PC(ring)), 148.1 (PCC(ring)), 146.3 (PC(ring)), 142.2 (PCC(ring)),
138.6 (CipsoPh), 129.1 (C6H5), 129.0 (C6H5), 128.3 (C6H5), 126.5 (C6H5),
3
122.8 (C6H5), 119.7 (C6H5), 22.5 (d, JPC ) 7.3 Hz, CH3), 16.6 (CH3),
3
2
15.1 (CH3), -8.5 (d, Sn(CH3)3, JPC ) 5.5 Hz, JSnC ) 312 Hz).
(11) Mattmann, E.; Simonutti, D.; Ricard, L.; Mercier, F.; Mathey, F. J. Org.
Chem. 2001, 66, 755.
(12) A solution of phosphole 9 (1.15 mmol, 0.54 g) in dichloromethane (10
mL) was added dropwise to a suspension of CuCl (1.15 mmol, 0.11 g) in
dichloromethane (20 mL) at 0 °C. The mixture was allowed to warm to
ambient temperature and stirred for 8 h. The resulting red solution was
dried in vacuo, then redissolved in dichloromethane. The solution was
kept at -5 °C for 8 h, resulting in the formation of pure red crystals of
1
the tetrameric complex 10 (92%, 0.48 g): 31P NMR C6D6 δ -128.0; H
Acknowledgment. The authors thank the University of Cali-
fornia, Riverside, and the CNRS for the financial support of this
work.
NMR C6D6 δ 7.23-6.73 (m, C6H5), 6.76 (1H, m, Ph), 6.69 (2H, m, Ph),
2.37 (3H), 2.34 (3H), 1.88 (3H); 13C NMR C6D6 δ 169.5 (CdN), 149.4
(PCC(ring)), 141.4 (PC(ring)), 138.8 (PC(ring)), 133.1 (C6H5), 131.4 (C6H5),
126.7 (C6H5), 124.9 (C6H5), 124.9 (C6H5), 124.1 (C6H5), 124.1 (C6H5),
123.1 (C6H5), 22.8 (CH3), 19.3 (CH3), 15.7 (CH3).
(13) Meyer, C.; Gru¨tzmacher, H.; Pritzkow, H. Angew. Chem., Int. Ed. Engl.
Supporting Information Available: Complete ref 6. X-ray crystal
structure analysis of compounds 9 and 10. This material is available
free of charge via the Internet at http://pubs.acs.org.
1997, 36, 2471.
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