Malonodinitrile CH2(CN)2 as synthon for the preparation of unprecedented N-metalla- and N-phosphino-β-diimine ligands

Article abstract of DOI:10.1021/om010105q

Unprecedented N-phosphino-β-diimine ligands 4 and 5 have been prepared from a facile one-pot synthesis using malonodinitrile, CH₂(CN)₂, the Schwartz reagent [Cp₂Zr(H)Cl]_n (1), and the corresponding chlorophosphines R₂PCl 2 and 3. An alkyl aluminum complex and the corresponding bidentate lithium salt ligand have been isolated. We showed that the reactivity of the N-phosphino-β-diimine compound 4 and that of the corresponding N-thiophosphino-β-diimine derivative 6 with HCl are completely different. The chemistry reported suggests unique and interesting chelating behavior which may differ from that of existing β-diimine ligands.

Full text of DOI:10.1021/om010105q

1716
Organometallics 2001, 20, 1716-1718
Ma lon od in itr ile CH2(CN)2 a s Syn th on for th e
P r ep a r a tion of Un p r eced en ted N-Meta lla - a n d
N-P h osp h in o-â-d iim in e Liga n d s
Alexandrine Maraval, Damien Arquier, Alain Igau,*,† Yannick Coppel,
Bruno Donnadieu, and J ean-Pierre Majoral*
Laboratoire de Chimie de Coordination, CNRS, UPR 8241, 205 Route de Narbonne,
31077 Toulouse Cedex 04, France
Received February 9, 2001
Summary: Unprecedented N-phosphino-â-diimine ligands
4 and 5 have been prepared from a facile one-pot
synthesis using malonodinitrile, CH2(CN)2, the Schwartz
reagent [Cp2Zr(H)Cl]n (1), and the corresponding chlo-
rophosphines R2PCl 2 and 3. An alkyl aluminum
complex and the corresponding bidentate lithium salt
ligand have been isolated. We showed that the reactivity
of the N-phosphino-â-diimine compound 4 and that of
the corresponding N-thiophosphino-â-diimine derivative
6 with HCl are completely different. The chemistry
reported suggests unique and interesting chelating be-
havior which may differ from that of existing â-diimine
ligands.
of the â-diiminates were needed.7 Electronic properties
are another important feature to consider in ligand
design, but the routes described for the preparation of
â-diimine ligands do not allow a large variety of groups
on the nitrogen atoms. Main group elements linked on
the imino nitrogen atoms, as differently coordinated
phosphorus moieties, could be a way to tune the coor-
dination ability of the â-diiminate system A. Part of our
studies in the interactions of main group elements with
zirconocene complexes have been devoted to the syn-
thesis of new heterosubstituted imino ligands.8 Herein
we report, starting with malonitrile and following a
hydrozirconation/transmetalation reaction process, the
synthesis of unprecedented N-phosphino-â-diketiminate
ligands. Malonodinitrile, CH2(CN)2, has been used
widely in organic synthesis as a stabilized nucleophile
in some of the most important carbon-carbon bond
forming reactions, the Michael addition,9 and Knoev-
enagel condensation.10 To the best of our knowledge,
malonodinitrile has not yet been used as a synthon for
the preparation of stable imine-enamine compounds.
Bidentate, monoanionic, nitrogen-based L-X- ligands
are the subject of intense studies.1 Among this class of
compounds, â-diiminates of the type A which form six-
membered chelate rings are of particular interest.2-5
Even though the list of successful applications of â-di-
iminate ligands A is steadily growing,6 by comparison
with the analogous â-diketonates (“acac” complexes),
their chemistry is largely undeveloped, although they
offer the potential advantages of modulating steric and
electronic properties by varying the nature of the
substituents bonded to the nitrogen atoms. In all the
systems that have been active in catalytic processes,
sterically demanding substituents on the nitrogen atoms
* Corresponding authors. Fax: 05 61 55 30 03.
† E-mail: igau@lcc-toulouse.fr.
In a first experiment, malonodinitrile, CH2(CN)2, was
successively treated with 2 equiv of the Schwartz’s
reagent [Cp2Zr(H)Cl]n, 1, and 2 equiv of Ph2PCl, 2, to
form the N-phosphino-â-diketimine 4 in 77% isolated
yield (Scheme 1).11 The parent ion detected [M + 1]+ in
mass spectrometry was in agreement with the general
formula [CH4(CN)2(PR2)2] for 4. The 31P NMR spectrum
(1) For the use of R-diimine ligands see for example: Feldman, J .;
McLain, S. J .; Parthasarathy, A.; Marshall, W. J .; Calabrese, J . C.;
Arthur, S. D. Organometallics 1997, 16, 1514. Kilian, C. M.; Tempel,
D. J .; J ohnson, L. K.; Brookhart, M. J . Am. Chem. Soc. 1996, 118,
11664. J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267, and references therein. Dipyridylmethanides: Gorni-
tzka, H.; Stalke, D. Organometallics 1997, 13, 4398. C2-symmetric
semicorrins complexes: Pfaltz, A. Acta Chem. Scand. 1996, 50, 189,
and references therein.
(2) N-Aryl-â-diketiminates: (a) McGeachin, S. G. Can. J . Chem.
1968, 46, 1903. Scheibe, G. Chem. Ber. 1923, 56, 137. (b) Parks, J . E.;
Holm, R. H. Inorg. Chem. 1968, 7, 1408.
(3) N-Trimethylsilyl-â-diketiminates: Hitchcock, P. B.; Lappert, M.
F.; Layh, M. Chem. Commun. 1998, 201. Deelman, B.-J .; Lappert, M.
F.; Lee, H.-K.; Mak, T. C. W.; Leung, W.-P.; Wei, P.-R. Organometallics
1997, 16, 1247.
(4) Lithium 3-sila- and 3-germa-â-diketiminates: Hitchcock, P. B.;
Lappert, M. F.; Layh, M. Chem. Commun. 1998, 2179.
(5) For a recent review of related macrocyclic ligands prepared by
amine condensations with 2,4-pentanedione see: Mountford, P. Chem.
Soc. Rev. 1998, 27, 105. Knorr, R.; Weib, A. Chem. Ber. 1982, 115,
139.
(6) Gibson, V. C.; Segal, J . A.; White, A. J . P.; Williams, D. J . J .
Am. Chem. Soc. 2000, 122, 7120. Cui, C.; Roesky, H. W.; Hao, H.;
Schmidt, H.-G.; Noltemeyer, M. Angew. Chem., Int. Ed. Engl. 2000,
39, 1815. Budzelaar, P. H. M.; Moonen, N. N. P.; de Gelder, R.; Smits,
J . M. M.; Gal, A. W. Eur. J . Inorg. Chem. 2000, 753. Bertilsson, S. K.;
Tedenborg, L.; Alonso, D. A.; Andersson, P. G. Organometallics 1999,
18, 1261.
1
of 4 displayed a singlet at 51.2 ppm. H and 13C NMR
spectra exhibited (besides the chemical shifts corre-
sponding to the protons and carbons of the aromatic
(7) (a) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J .
Inorg. Chem. 1998, 1485. (b) Cheng, M.; Lobkovsky, E. B.; Coates, G.
W. J . Am. Chem. Soc. 1998, 120, 11018. (c) Deelman, B.-J .; Hitchcock,
P. B.; Lappert, M. F.; Leung, W.-P.; Lee, H.-K.; Mak, T. C. W.
Organometallics 1999, 18, 1444. (d) Quian, B.; Scanlon, J ., IV; Smith,
M. R., III. Organometallics 1999, 18, 1693.
(8) Boutonnet, F.; Dufour, N.; Straw, T.; Igau, A.; Majoral, J .-P.
Organometallics 1991, 10, 3939. Maraval, A.; Donnadieu, B.; Igau, A.,
Majoral, J .-P. Organometallics 1999, 18, 3183.
(9) J ung, M. E. In Comprehensive Organic Chemistry; Trost, B. M.,
Fleming, I., Semmelhack, M., Eds.; Pergamon Press: Oxford, 1991;
Vol. 4, p 1.
(10) Tietze, L. F.; Beifuss, U. In Comprehensive Organic Chemistry;
Trost, B. M., Fleming, I., Heathcock, L. C. H., Eds.; Pergamon Press:
Oxford, 1991; Vol. 2, p 358.
10.1021/om010105q CCC: $20.00 © 2001 American Chemical Society
Publication on Web 04/03/2001

Communications
Organometallics, Vol. 20, No. 9, 2001 1717
Sch em e 1. Syn th esis of N-P h osp h or u s-â-d iim in e Liga n d s 4-6
rings) the signals in the region expected for a CHdN-
1
aldimine group [δ H 7.60 and δ 13C 160.8 ppm] and a
CH-alkene enamine fragment [δ 1H 4.90 and δ 13C 99.9
1
ppm]. In H NMR the large low-field shift of the N-H
proton [δ 1H 11.79 ppm] established the structure as a
hydrogen-bonded chelate form.2b The chemical shift
equivalence of the two Ph2P-NCH fragments in 4 is
accommodated by a rapid tautomeric conversion. One
characteristic band in IR appeared at 1625 cm-1, which
can be assigned to the imine-enamine stretching mode
of 4.13 Under the same experimental conditions, 5 was
formed after treatment of malonodinitrile with 2 equiv
of 1 followed by addition of 2 equiv of (iPr2N)2PCl, 3, to
the resulting reaction mixture. The â-diimine compound
5 displays the same spectroscopic features as those
observed for 4.11 To confirm the spectroscopic assign-
ments and to have a better insight into the molecular
structure of the latter â-diimine species prepared, an
X-ray diffraction study was carried out on the phos-
phinesulfide product 6 obtained after addition of ele-
mental sulfur on 4 (Figure 1).14 The molecule has a C2
symmetry; consequently the hydrogen atom H(N) on the
N atom is statistically distributed on two sites related
by the 2-fold axis. All the atoms in 6 except those of the
aryl groups lie in the same plane. As expected, the
C(2)-N (1.317 Å) and C(1)-C(2) (1.381 Å) bonds in the
N-C-C-C-N skeleton are halfway from a single and
double bond and are equivalent to those found in six-
F igu r e 1. Molecular structure of 6. Selected bond lengths
[Å] and angles [deg]: C(1)-C(2) 1.381(4), C(2)-N 1.317(4),
N-P 1.685(3), P-S 1.9349(12); C(1)-C(2)-N 124.0(3),
C(2)-C(1)-C(2A) 124.4(4), C(2)-N-P 123.1(3), C(2)-N-
H(N) 111(3), N-P-S 114.70(11).
membered aromatic rings.17 Therefore, the simplest
picture to consider for compounds 4-6 is the superposi-
tion of the two tautomers a and b (Scheme 1).
The first attempts to identify the metalated compound
resulting from the addition of malonitrile to 1 were not
1
satisfactory, as they gave by H NMR several sets of
resonances impossible to assign. However, when a
catalytic amount of MeI (10%) was added to the mal-
1
(11) 4: 77% yield, 31P{1H} NMR (C6D6) δ 51.2 (s); 1H NMR (C6D6)
onodinitrile/1 reaction mixture, the H NMR spectrum
3
4
δ 4.90 (tt, J HH ) 6.1 Hz, J HP ) 0.9 Hz, 1H, CH), 7.39-7.57 (m, 20H,
Ph), 7.60 (ddd, 3J HH ) 3J HH ) 6.1 Hz, 3J HP ) 18.0 Hz, 2H, CHN), 11.79
became considerably simplified to show the formation
of 7 as the unique product of the reaction. At 293 K in
3
2
(tt, J HH ) 6.1 Hz, J HP ) 6.1 Hz, 1H, NH); 13C{1H} NMR (C6D6) δ
3
3
99.9 (t, J CP ) 13.0 Hz, CH), 130.5 (s, p-Ph), 130.9 (d, J CP ) 7.8 Hz,
m-Ph), 133.7 (d, 2J CP ) 20.5 Hz, o-Ph), 141.5 (d, 1J CP ) 11.8 Hz, i-Ph),
160.8 (d, 2J CP ) 28.0 Hz, CHN); C27H24N2P2 (438.45), calcd C 73.96, H
5.52, N 6.39, found C 73.43, H 5.41, N 6.27; FT-IR (KBr) 1625 cm-1
ν(CdN); MS (DCI/NH3) m/z 439 [M + H]+. 5: 31P{1H} NMR (C6D6) δ
89.6 (s); 1H NMR (C6D6) δ 1.02 (d, J HH ) 6.6 Hz, 24H, CH3), 1.17 (d,
3
3J HH ) 6.6 Hz, 24H, CH3), 3.68 (m, 8H, CHCH3), 4.74 (t, J HH ) 8.0
3
3
3
Hz, 1H, CH), 6.71 (ddd, J HH
)
3J HH ) 8.0 Hz, J HP ) 15.1 Hz, 2H,
CHN), 11.82 (m br, 1H, NH); C27H60N6P2 (530.76), calcd C 61.10, H
11.39, N 15.83, found C 60.88, H 11.25, N 15.78; FT-IR (KBr) 1632
cm-1 ν(CdN); MS (DCI/CH4) m/z 531 [M + H]+.
both proton and carbon NMR spectra, only one signal
was observed for the two CH-N groups of the â-diket-
imine skeleton (δ 1H 7.48 ppm, δ 1H 157.6 ppm),
indicative of a process that rapidly interconverts on the
NMR time scale the two imine-enamine isomers. The
CH-N protons appear as a doublet of doublets (3J H(2)-H(1)
(12) Buchwald, S. L.; LaMaire, S. J .; Nielsen, R. B.; Watson, B. T.;
King, S. M. Org. Synth. 1993, 71, 77. Buchwald, S. L.; LaMaire, S. J .;
Nielsen, R. B.; Watson, B. T.; King, S. M. Tetrahedron Lett. 1987, 28,
3895.
(13) Tsybina, N. M.; Vinokurov, V. G.; Protopopova, T. V.; Skoldinov,
A. P. J . Gen. Chem. USSR 1966, 36, 1383.
(14) Crystal data for 6:
space group C2/c, T ) 293 K, a ) 17.118(3) Å, b ) 15.059(3) Å, c )
11.543(2) Å, â ) 119.89(3)°, V ) 2579.8(8) Å3, Z ) 4, µ ) 0.349 mm-1
C27H24N2P2S2, Mr ) 502.54, monoclinic,
3
) 5.8 Hz, J H(2)-H(N) ) 12.6 Hz). An excitation-sculpted
.
STOE imaging plate diffraction system (IPDS) diffractometer, 6340
reflections collected, 2029 independent, Rint ) 0.0723, final R indices
[I>2σ(I)], R1 ) 0.0406, wR2 ) 0.0787, (all data) R1 ) 0.0958, wR2 )
0.0916. The structure was solved by direct methods with SIR9215 and
refined by least-squares procedures on F2 with SHELX97.16
(15) SIR92 program for automatic solution of crystal structures by
direct methods: Altomare, A.; Cascarano, G., Giacovazzo, G.; Guagia-
rdi, A.; Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr.
1994, 27, 435.
singly selective 1D TOCSY NMR experiment allowed
the assignment of the H(N) proton.18 TOCSY transfers
were detected to the two aldimine H(2) protons and to
the H(N) proton which appears as a very broad peak (δ
6.94 ppm, half-height line width ∆ν ≈ 500 Hz). It was
(17) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. In Structure Correlation; Bu¨rgi, H.-B., Dunitz, J . D.,
Eds.; VCH: Weinheim, 1994; Vol. 2, pp 808-811.
(16) Sheldrick, G. M. SHELXL97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Germany, 1997.

1718 Organometallics, Vol. 20, No. 9, 2001
Communications
Sch em e 2. Rea ctivity of th e
Sch em e 3. Rea ctivity of N-P h osp h in o-â-d iim in e
N-P h osp h in o-â-d iim in e Liga n d 4
Liga n d s 4 a n d 6 w ith HCl
clear from this experiment that the H(N) proton was
involved in an exchange that is in the intermediate
range on the NMR time scale.19 Interestingly, before
the addition of MeI, 7 was detected among the other
zirconated species formed in the reaction mixture
obtained from malonitrile and 1. This clearly demon-
strated that MeI induced the rearrangement of the
different zirconocene intermediates to the thermody-
namic product of the reaction 7. However, alkylation on
nitrogen did not occur.20,21 In the reaction resulting in
the quantitative formation of the N-phosphino-â-dialdi-
mine compounds 4 and 5, the chlorophosphine deriva-
tives R2PCl 2 and 3 may have played the same role as
MeI to induce the unique formation of 7 in the reaction
mixture. In that case the transmetalation reaction took
place at the nitrogen center to give the corresponding
imino-N-phosphine products. It is important to note that
chlorophosphines R2PCl were reported to induce the
migration of the metal fragment ZrCp2Cl along a
saturated carbon chain, followed then by the electro-
philic substitution reaction to give the corresponding
phosphorus product.22
iminate ligand, 1H and 13C NMR of 9 showed the
presence of the methyl groups on the aluminum metal
1
fragment at δ H -0.45 and δ 13C -6.4 ppm.
Interestingly addition of HCl (2 equiv) on 4 resulted
in the cleavage of the P-N bond to give a diphenyl-
chorophosphine compound as the sole phosphorus prod-
uct of the reaction along with an organic product which
has not yet been fully identified but which may be
attributed to the corresponding parent compound C2H6N2.
Starting from the thiophosphino â-diiminate derivative
6, addition of HCl (1 equiv) led to the quantitative
formation of the corresponding vinamidinium compound
10, which has been fully characterized by NMR spec-
troscopy and an X-ray crystal structure analysis.23
In summary, we have described a highly efficient
method for the preparation of unprecedented N-phos-
phino-â-diketiminate ligands 4-6 via a mild one-pot
synthesis starting from commercially available reagents
(for the preparation of 4: malonitrile, MeI, Schwartz’s
reagent, 1, and chlorodiphenylphosphine, 2). The gen-
eral applicability of this method for the synthesis of new
N-(hetero)substituted â-diketiminate ligands and the
activity of the corresponding aluminum complexes (i.e.,
9) in olefin polymerization are in development. Vin-
amidinium salts as product 10 easily obtained from the
corresponding neutral N-phosphino-â-diketiminate com-
pounds belongs to the family of polymethine dyes, which
are a fundamental group of organic dyes widely used
for practical purposes. This class of derivatives are also
of special preparative value due to their reactivity
toward electrophiles (at Câ) and nucleophiles (CR).24 We
have preliminary demonstrated that the isolated and
stable metalated compound 7 is the appropriate synthon
for the preparation of a large variety of compounds; it
can be viewed as the formal “unmasked” trianionic
trimethine-cyanine parent compound B.
n
Addition at -78 °C in THF of 1 equiv of BuLi on 4
led quantitatively to the formation of the corresponding
â-diiminate lithium salt 8 as a (THF)2 adduct (Scheme
1
2). In H NMR complete disappearance of the NH signal
1
[δ H 11.79 ppm] was observed. The chemical shifts in
1
both H [δ 7.94 and 5.05 ppm] and 13C [δ 165.4 and 98.3
ppm] NMR spectra are consistent with the CHdN
aldimine and the central methine CH fragments, re-
spectively, in the anionic bidentate ligand 8. The â-di-
imine 4 reacted with AlMe3 to eliminate methane,
affording quantitatively the diiminate complex 9 (δ 13P
1
55.1 ppm) (Scheme 2). All the NMR data (13P, H, and
13C) indicated symmetric ligand environments. Besides
the signals corresponding to the backbone of the â-di-
(18) The selective Gaussian-shaped pulse was applied at the central
methine proton. Braun, S.; Kalinowski, H. O.; Berger, S. 100 and More
Basic NMR Experiments; VCH: Weinheim, 1996. Claridge, T. D. W.
High-Resolution NMR Techniques in Organic Chemistry, Tetrahedron
Organic Chemistry Series; Baldwin, J . E., Williams, F. R. S., R. M.,
Eds.; Pergamon: New York, 1999; Vol. 19, pp 201 and 328.
(19) Complete studies of the structure of 7 from NMR experiments
at variable temperature (from 273 to 193 K: 2D NMR experiments
(gs-DQFCOSY, gs-HMQC), 1D GROESY experiments) will be reported
elsewhere.
Ack n ow led gm en t. Financial support of this work
by the CNRS, France, is gratefully acknowledged.
(20) Organozirconocene-Zr(IV) complexes react with a large variety
of electrophiles and participate in most of the processes involving the
formation of carbon-carbon bonds; see: Negishi, E. In Comprehensive
Organic Chemistry; Trost, B. M., Fleming, I., Paquette, L. A., Eds.;
Pergamon Press: Oxford, 1991; Vol. 5, p 1163. For recent symposiums
on zirconocene chemistry, see: Negishi, E. Recent Advances in the
Chemistry of Zirconocene and Related Compounds, Tetrahedron Sym-
posia-in-print No. 57; Tetrahedron 1995, 51 (special issue). Wipf, P.;
J ahn, H. Tetrahedron, 1996, 52, 12853.
(21) Substitution of a zirconocene fragment ZrCp2X N-linked to an
imine function by an alkyl group has not yet been reported.
(22) Zablocka, M.; Boutonnet, F.; Igau, A.; Dahan, F.; Majoral, J .
P.; Pietrusiewicz, K. M. Angew. Chem., Int. Ed. Engl. 1993, 32, 1735.
Zablocka, M.; Igau, Majoral, J . P.; Pietrusiewicz, K. M. Organometallics
1993, 12, 603.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails for the preparation of 5, 8, 9, and 10; spectroscopic and
X-ray crystal analysis data for 6 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
OM010105Q
(23) Details of the structure will be reported elsewhere.
(24) Tyutyulkov, N.; Fabian, J .; Melhorn, A.; Dietz, F.; Tadjer, A.
Polymethine Dyes, Structure and Properties; St Kliment Ohridski
University Press: Sofia, 1991. Kachkovski, A. D. Polymethine Dyes.
In Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed.; J ohn
Wiley & Sons: New York, 1996; Vol. 19, pp 1004-1030.