Synthesis of 2-silyl substituted phospharuthenocenes and an elaboration into the first phospharuthenocene-phosphine

Article abstract of DOI:10.1039/b208736g

A [1,5] shift protocol transiently hindering the 2-position of phospholide anions provides an access to sterically unencumbered phospharuthenocenes and the first phospharuthenocene-phosphine.

Full text of DOI:10.1039/b208736g

Synthesis of 2-silyl substituted phospharuthenocenes and an elaboration
into the first phospharuthenocene-phosphine
Duncan Carmichael,* François Mathey,* Louis Ricard and Nicolas Seeboth
Laboratoire Hétéroéléments et Coordination, UMR CNRS 7653, DCPH Ecole Polytechnique, 91128
Palaiseau cedex, France. E-mail: Duncanc@mars.polytechnique.fr; francois.mathey@polytechnique.fr;
Fax: +331 69333990
Received (in Cambridge, UK) 6th September 2002, Accepted 24th October 2002
First published as an Advance Article on the web 8th November 2002
A [1,5] shift protocol transiently hindering the 2-position of
phospholide anions provides an access to sterically un-
encumbered phospharuthenocenes and the first phosphar-
uthenocene-phosphine.
treatment of potassium phospholides 2a,b with i-Pr3SiCl,14
a
KOt-Bu-induced [1,5] silyl shift-deprotonation sequence11
provided the corresponding 2-triisopropylsilylphospholides
5a,b in excellent yield. These anions were conveniently
complexed to [RuCp*Cl]4 in situ and the pale yellow air-stable
phospharuthenocene products [RuCp*(PC4Me2{i-Pr3Si}R)]
The potential of phosphametallocenes as ligands for enantiose-
lective catalysis,1 a promising area currently dominated by iron
derivatives,2 has been underlined inter alia by recent reports of
the spectacular performance of the phosphaferrocene-phos-
phine ligand (+)13,4 in the enantioselective isomerisation of
unprotected allylic alcohols.4 Ruthenium-based homologues
provide an obvious means of varying the electronic and steric
properties of the phosphametallocene ligand but they have not
found uses in catalysis to date, presumably because the few
known (monophospholyl)ruthenocenes5 all bear sterically de-
manding groups which are likely to impede coordination at the
phosphorus lone pair. Given (a) the stability of phosphar-
uthenocenes across the range of mono-,5 di- and tri-6 and
penta7-phospholyl ligands, (b) the potential for elaborating
phospharuthenocenes by simple electrophilic aromatic substitu-
tion reactions8 and (c) precedents for increasing either catalyst
TOF9 or enantioselectivity10 through judiciously substituting Fe
by Ru, it seemed important to prepare, investigate and
functionalise a simple monophospharuthenocene.
Fig. 1 Molecular structure of [RuCp*(PC4PhHMe2)]2 4. Selected bond
lengths (Å) and angles (°): Ru(1)–Ru(1)A, 2.6471(8); Ru(1)–P(1), 2.250(1);
Ru(1)–P(1)A, 2.240(1); P(1)–C(1), 1.798(3); C(1)–C(2), 1.339(4); C(2)–
C(3), 1.476(4); C(3)–C(4), 1.359(3); P(1)–C(4), 1.825(3); Ru(1)–P(1)–
Ru(1)A, 72.25(3); P(1)–Ru(1)–P(1)A, 107.75(3). Primed and unprimed atoms
are related by a centre of symmetry.
Previous studies have suggested that only phospharutheno-
cenes bearing bulky groups are easily accessible5 and our
exploratory reactions between non-encumbered phospholides
and [RuCp*Cl]4 showed that hindrance blocks a kinetically
facile formation of phospholyl-bridged dimers. Thus reaction of
[RuCp*Cl]4 with phospholide 2a11 gave only traces ( < 5%) of
the desired phospharuthenocene 3a, with the product being
predominantly ( > 80%) a 1+1 mixture of two complexes
showing 31P NMR resonances (201 and 203 ppm) in a zone
indicative of ligands bridging metal–metal bonds.12† One of
these compounds, the dimer 4, was obtained as monocrystals
suitable for an X-ray structural determination (Fig. 1).‡ Its
thermal conversion into 3a (toluene, 110 °C, 2 days) was
unsatisfactory and provoked extensive decomposition.
Scheme 1 Reagents and conditions: i: i-Pr3SiCl (1 eq.), THF, 20 °C, 30 min,
ii: KOt–Bu (1 eq.), THF, 278 °C to rt, 1 h, iii: [Cp*RuCl]4 (0.25 eq.), THF,
20 °C, 5 min, iv: (CF3CO)2O (2 eq.), BF3OEt2 (2 eq.), CH2Cl2, rt, 2 h, v:
NaOMe (1 eq.), THF, 278 °C to rt, 30 min, vi: LiAlH4 (2 eq.), THF, 20 °C,
10 min, vii: MsOH (1.2 eq.), CH2Cl2–MeOH, 278 °C, 30 s, then HPPh2 (2
eq.), rt, 20 min.
To encumber the phospholide anion reversibly and activate
the phospharuthenocene products towards electrophilic aro-
matic substitution, a simple and potentially general synthesis of
2-silylphospholide anions13 was developed (Scheme 1). After
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13C{1H} NMR d 98.3 [d, 1JPC 58.3 Hz, PCCH2], 96.1 [d, 2JPC 6.8 Hz, CMe],
92.0 [d, 2JPC 4.5 Hz, CMe], 88.1 [s, Cp*], 80.8 [d, 1JPC 58.8 Hz, PCH], 60.6
[d, 2JPC 23.6 Hz, CH2O], 14.2 [s, CMe], 11.3 [s, Cp*], 10.5 [s, CMe] ppm.
MS (EI, 70 eV): m/z (%) 377 (100) [M+ 2 H], 359 (53) [M+ 2 H3O], 346
(35) [M+ 2 CH4O]. 9: (CDCl3, 298 K) 31P{1H} NMR d 212.7 [d, 3JPP 28.7
Hz, PPh2], 244.9 [d, 3JPP 28.7 Hz, PRu] ppm. 13C{1H} NMR d 140–127
2
[ArC], 94.5 [d, JPC 6.7 Hz, CMe], 93.3 [dd, JPC 58.4, 18.9 Hz, PCCH2],
92.1 [dd, JPC 8.3, 6.4 Hz, CMe], 87.4 [s, Cp*], 80.3 [d, 1JPC 59.0 Hz, PCH],
29.7 [dd, JPC 19.2, 14.7 Hz, CH2P], 14.6 [s, CMe], 11.2 [s, Cp*], 11.0 [d,
4JPC 2.3 Hz, CMe] ppm. MS (EI, 70 eV): m/z (%) 546 (2) [M+], 360 (100)
[M+ 2 PPh2H].
‡ Crystal data: For 4: from THF. C44H54P2Ru2, M = 846.95, monoclinic,
space group P21/n, a = 11.087(5), b = 14.757(5), c = 12.041(5) Å, b =
96.340(5)°, U = 1958.0(14) Å3, Z = 2, Dc = 1.437 g cm23, F(000) = 872.
Monochromated Mo-Ka radiation l = 0.71070 Å. m = 0.883 cm21, T =
150 K. Of 5702 independent reflections measured over h: 215 to 15, k: 220
to 18, l: 216 to 15° from an orange plate of ca. 0.20 3 0.20 3 0.12 mm on
a Kappa CCD diffractometer, 4346 with I > 2s(I) were refined on F2 using
direct methods in SHELXL. wR2 = 0.1072, R1 = 0.0388, GoF = 1.075.
For 6a: C31H47PRuSi from CH2Cl2–EtOH. M = 579.82, monoclinic, space
Fig. 2 Molecular structure of [RuCp*(PC4Ph(Sii-Pr3)Me2)] 6a. Selected
bond lengths (Å): Ru(1)–P(1), 2.405(1); Ru(1)–C(1), 2.228(2); Ru(1)–C(2),
2.186(2); Ru(1)–C(3), 2.195(2); Ru(1)–C(4), 2.275(2); P(1)–C(1),
1.798(2); C(1)–C(2), 1.431(2); C(2)–C(3), 1.436(2); C(3)–C(4), 1.439(2);
P(1)–C(4), 1.795(2).
group P21/c, a
= 8.939(5), b = 42.464(5), c = 8.166(5) Å, b =
110.070(5)°, U = 2911(2) Å3, Z = 4, Dc = 1.323 g cm23, F(000) = 1224,
m = 0.652 cm21. 8165 independent reflections from a pale yellow crystal
of ca. 0.20 3 0.20 3 0. 20 mm were collected, over h: 212 to 12, k: 253
to 59, l: 211 to 11°, and 6814 were refined using the methods above. wR2
= 0.0791, R1 = 0.0313, GoF = 1.034. CCDC 193091 and 193092. See
http://www.rsc.org/suppdata/cc/b2/b208736g/ for crystallographic files in
CIF or other electronic format.
6a,b were isolated by chromatography (silica, pentane, 6b, rf
ca. 0.2) or crystallisation (MeOH, 6a). Crowding in 6a is clearly
reflected in the centroid-C(4)–Si(1) angle of 18.0° (Fig. 2).
As anticipated, compounds 6 show useful reactivity towards
electrophiles. Protodesilylation using TMSCl–methanol led
quantitatively to the parent phospharuthenocenes 3 and treat-
ment of either 3 or 6 with [CF3CO]+[F3BO2CCF3]2 2b,15 gave
the corresponding 2-(trifluoroacetyl)phospharuthenocenes 7.
The utility of these complexes was confirmed by transformation
of 7b into the potentially versatile10,16 (2-phospharuthenocene)-
methanol derivative 8 and its classical elaboration into the target
(2-phospharuthenocene)methylphosphine 9 (Scheme 1).
It seems clear that the methodology developed above
provides the means to transform readily available phospholide
anions into a wide variety of a-functionalised phosphar-
uthenocenes. No organic phospharuthenocene chemistry has
been described prior to this article but complexes 3–9 are stable
and easy to handle, and the simplicity of their functional group
transformations makes them good candidates for more sophisti-
cated elaboration. The approach described here is particularly
well-suited to the synthesis of Cp*-substituted phosphametallo-
cenes which, when employed as enantiopure ligands, seem
likely to deliver better ee’s than their Cp-derived analogues.
Given the relationship of 9 to the ligand class exemplified by 1,
further phospharuthenocene work is in progress.
1 Recent reviews: L. Weber, Angew. Chem., Int. Ed., 2002, 41, 563; D.
Carmichael and F. Mathey, Top. Curr. Chem., 2002, 220, 27; C. Ganter,
J. Chem. Soc., Dalton Trans, 2001, 3541.
2 Lead references: S. O. Agustsson, H. Chunhua, U. Englert, T. Marx, L.
Wesemann and C. Ganter, Organometallics, 2002, 21, 2993; R. Shintani
and G. C. Fu, Org. Lett., 2002, 4, 3699; M. Ogasawara, K. Yoshida and
T. Hayashi, Organometallics, 2001, 20, 3913.
3 S. Qiao and G. C. Fu, J. Org. Chem., 1998, 63, 4168; for the Cp based
analogue, see also: C. Ganter, L. Brassat and B. Ganter, Chem. Ber.-
Recueil, 1997, 130, 1771.
4 K. Tanaka, S. Qiao, M. Tobisu, M. M.-C. Lo and G. C. Fu, J. Am. Chem.
Soc., 2000, 122, 9870; K. Tanaka and G. C. Fu, J. Org. Chem., 2001, 66,
8177.
5 D. Carmichael, L. Ricard and F. Mathey, J. Chem. Soc., Chem.
Commun., 1994, 1167; M. Ogasawara, K. Yoshida, T. Nagano and T.
Hayashi, Organometallics, 2002, 21, 3062; where the authors also
report an unstable Fe(CO)4 complex.
6 R. Bartsch, F. G. N. Cloke, J. C. Green, R. M. Matos, J. F. Nixon, R. J.
Suffolk, J. L. Suter and D. J. Wilson, J. Chem. Soc., Dalton Trans.,
2001, 1013 and refs therein.
7 O. J. Scherer, T. Bruck and G. Wolmershauser, Chem. Ber., 1988, 121,
935.
8 This chemistry is quite well developed for phosphaferrocenes; see: F.
Mathey, Coord. Chem. Rev., 1994, 137, 1.
We thank CNRS, Ecole Polytechnique and the EC (COST
action D12-026) for support.
9 H. C. L. Abbenhuis, U. Burckhardt, A. Gramlich, A. Martelletti, J.
Spencer, I. Steiner and A. Togni, Organometallics, 1996, 15, 1614.
10 T. Hayashi, A. Ohno, L. Shi-je, Y. Matsumoto, E. Fukuyo and K.
Yanagi, J. Am. Chem. Soc., 1994, 116, 4223.
Notes and references
† Selected spectroscopic data: 3a: (CDCl3, 298 K) 31P NMR d 242.7 [d,
2JPH 35.8 Hz] ppm. 3b: (CDCl3, 298 K) 31P{1H} NMR d 254.1 ppm.
11 S. Holand, M. Jeanjean and F. Mathey, Angew. Chem., Int. Ed., 1997,
36, 98; N. Seeboth, DEA thesis, Ecole polytechnique, 2002.
12 A. J. Carty, D. MacLaughlin and D. Nucciarone, in Phosphorus-31 nmr
spectroscopy in stereochemical analysis. Organic compounds and metal
complexes, ed. L. D. Quin and J. G. Verkade, VCH, 1987, p. 559.
13 Efficient syntheses of 2,5-disilyl substituted phospholides using zirco-
nocene chemistry are available (e.g. P. J. Fagan and W. A. Nugent, J.
Am. Chem. Soc., 1988, 110, 2310) and we have confirmed that 3b can
be prepared by protodesilylation of the product obtained from
[Li(PC4Me2-2,5-{SiMe3}2)] and [RuCp*Cl]4. However, extrapolating
these methods to unsymmetrically substituted pro-(planar-chiral) phos-
pholides remains relatively difficult: J. Hydrio, M. Gouygou, F.
Dallemer, J.-C. Daran and G. G. A. Balavoine, J. Organomet. Chem.,
2000, 595, 267; F.-X. Buzin, PhD thesis, Ecole polytechnique, 2001.
14 t-BuMe2SiCl may also be employed. Use of TMSCl is compromised by
a competing P-desilylation upon reaction with KOt-Bu.
2
1
13C{1H} NMR d 93.0 [d, JPC 7.4 Hz, CMe], 87.4 [s, Cp*], 80.7 [d, JPC
59.6 Hz, PCH], 13.4 [s, CMe], 11.1 [s, Cp*] ppm. MS (EI, 70 eV): m/z (%)
347 (100) [M+ 2 H], 332 (58) [M+ 2 H 2 CH3]. 4: (C6D6, 333 K) 31P{1H}
NMR d 203.1 ppm. 5a: (THF, 298 K) 31P{1H} NMR d 123.8 ppm. 5b:
31P{1H} NMR d 113.3 ppm. 6a: (THF, 298 K) 31P{1H} NMR d 22.6 ppm.
6b: (CDCl3, 298 K) 31P{1H} NMR d 221.1 ppm. 13C{1H} NMR d 97.3 [d,
2JPC 4.5 Hz, CMe], 96.3 [d, 2JPC 8.2 Hz, CMe], 87.3 [s, Cp*], 83.7 [d, 1JPC
62.2 Hz, PCH], 83.4 [d, 1JPC 81.3 Hz, PCSi], 19.4 [4C, s, SiCCH], 19.3 [2C,
s, SiCCH], 15.0 [s, CMe], 14.3 [s, CMe], 12.7 [2C, s, SiCH], 12.6 [1C, s,
SiCH], 11.0 [s, Cp*] ppm. MS (EI, 70 eV): m/z (%) 505 (87) [MH+], 462
(100) [MH+-C3H7]. 7a: (CDCl3, 298K) 31P{1H} NMR d 220.4 [q, 4JPF 59.5
Hz] ppm. 7b: (CDCl3, 298 K) 31P{1H} NMR d 228.1 [q, JPF 61.4 Hz]
4
ppm. 13C{1H} NMR d 187.0 [dq, 2JPC 23.0 Hz 2JFC 33.3 Hz, COCF3], 112.4
1
2
2
[q, JFC 294.3 Hz, C], 100.4 [d, JPC 8.0 Hz, CMe], 94.1 [d, JPC 4.6 Hz,
CMe], 90.2 [s, Cp*], 87.0 [dq, 1JPC 58.6, 3JFC 4.6 Hz, PCCO], 81.0 [d, 1JPC
71.3 Hz, PCH], 13.9 [s, CMe], 12.5 [s, CMe], 10.4 [s, Cp*] ppm. MS (EI,
15 H. L. Hassinger, R. M. Soll and G. W. Gribble, Tetrahedron Lett., 1998,
39, 3095.
16 L. Brassat, B. Ganter and C. Ganter, Chem.-Eur. J., 1998, 4, 2148.
70 eV): m/z (%) 444 (54) [M+], 428 (37) [M+ 2 O], 344 (33) [M+
2
COCF3], 57 (100). 8: (CDCl3, 298 K) 31P{1H} NMR d 248.0 ppm.
CHEM. COMMUN., 2002, 2976–2977
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