Synthesis and molecular structures of the first phosphoranylidene complexes of rare earth metals

Article abstract of DOI:10.1039/b514439f

Metallation of the donor-functionalised ylide ligand Ph₃P=CH-(o- CH₃OC₆H₄) with homoleptic alkyl and aryl complexes of yttrium and lutetium furnished unprecedented phosphoranylidene complexes, featuring a centra

Full text of DOI:10.1039/b514439f

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LETTER
www.rsc.org/njc | New Journal of Chemistry
Synthesis and molecular structures of the first phosphoranylidene
complexes of rare earth metalswz
Konstantin A. Rufanov,* Bernd H. Muller, Anke Spannenberg* and Uwe Rosenthal
¨
Received (in Durham, UK) 11th October 2005, Accepted 24th November 2005
First published as an Advance Article on the web 9th December 2005
DOI: 10.1039/b514439f
Metallation of the donor-functionalised ylide ligand
Ph3PQCH–(o-CH3OC6H4) with homoleptic alkyl and aryl
complexes of yttrium and lutetium furnished unprecedented
phosphoranylidene complexes, featuring a central l2-M2C2 core.
For our study we have chosen the known chelating phos-
phoranylidene ligand Ph3PQCH-(o-CH3OC6H4) 1,18 whose
structure we determined for comparison purposes (Fig. 1).y
In the early stages of our investigation we attempted to
metallate 1 with rather stable Cp#2Lu(THF)CH3 (Cp# = [1,3-
(SiMe3)2C5H3]) and M[N(SiMe3)2]3 (M = Y, Lu) complexes.
However, NMR-monitoring of these reactions revealed only
the simple substitution of the THF molecule or reversible
formation of unstable adducts, similar to those described
earlier.14 The metallation of 1, however, was not observed.
Although the protonolysis of the more reactive homoleptic
alkyl- or aryl-complexes of the types Ln(CH2SiMe3)3(THF)n
(n = 2, 3) or Ln(o-Me2NCH2C6H4)3 with different CH acids,
such as Cp and acetylenes, is well established,19–21 such
reactions have not been reported for phosphoranylidenes.
Initially
we
discovered
that
reaction
of
Lu(CH2SiMe3)3(THF)2 with 1 leads to exhaustive protonoly-
sis. Indeed, NMR monitoring of the reaction mixture revealed
the gradual growth of a new broad 31P signal at 12.2 accom-
panied by the decline of the sharp signal of 1 at 10.8. The
reaction, which is complete after 2 d, furnished yellow, micro-
crystalline material in 46% yield. Single crystals were obtained
from a saturated benzene solution that had been standing at
10 1C for several weeks. The broad 1H resonances for the
aromatic protons and the methoxy group suggest that 3 dis-
plays a dynamic behaviour in solution and that the ethereal
ligands are hemi-labile.22
Scheme 1
The organometallic chemistry of rare earth metals, which to
date has been dominated by metallocene complexes, has
recently received some impetus towards the search for new
ligand systems to expand its scope beyond this traditional
realm.1–8 In contrast to main-group9–11 and transition me-
tals,12 there are no examples of the activation of the CH
protons of ylenes by rare-earth metals. Because the increased
Lewis acidity of the lanthanides may lead to reactivity patterns
that are different from those for transition metals, we were
encouraged to develop new synthetic approaches towards
lanthanide complexes of these phosphorus-ylide ligands.
Previously Schumann has found that Ph3PQCH2 and
Ph3PQCHSiMe3 simply substitute THF in the complexes
Cp2LuX(THF) (X = But, Cl),13 while (C5Me5)2LuMe reacts
with ortho-metallation of one of the phenyl substituents and
formation of a 5-membered cyclic ylide complex,14–16 rather
than in metallation of the QCH2 group (Scheme 1). Similar
donor–acceptor adducts were later reported for other rare
earth metals.17
We also studied the metallation of 1 with the thermally
more stable and less reactive yttrium complex
Y(o-Me2NCH2C6H4)3, intending to synthesize heteroleptic
mono-ylide complex 4 (Scheme 2). A reaction of equimolar
amounts of 1 and the metal complex furnished, after heating at
65 1C for 5 h, unexpectedly a similar product of the exhaustive
protonolysis of 1, namely 5. This yellow microcrystalline
material has very low solubility in common solvents and
was characterized by 1H-, 31P-NMR and elemental analysis
and shown to be an analogue of binuclear complex 3. Re-
crystallization of 5 from boiling THF furnished, upon slow
cooling of the solution, the light yellow complex 5a. The
molecular structures of 3 and 5a differ only in the number of
coordinated THF molecules. Each lutetium atom in 3 is
coordinated by only one THF donor ligand and the molecule
has a center of inversion, with both lutetium atoms having
distorted octahedral coordination geometry. In compound 5a,
by contrast, one yttrium is six-coordinate, bearing one THF
ligand, while the other is seven-coordinate, bearing two THF
ligands (Fig. 2).23
Leibniz-Institut fur Organische Katalyse an der Universitat Rostock,
¨
¨
Albert-Einstein-Straße 29A, 18059 Rostock, Germany. E-mail:
k_rufanov@gmx.de; Fax: +49 (0)381 1281 5000
w Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/b514439f
z Dedicated to Prof. Dmitry A. Lemenovskii on occasion of his 60th
birthday
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New J. Chem., 2006, 30, 29–31 | 29

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Fig. 2 ORTEP drawing of the molecular structure of 5a. All hydro-
gen atoms are omitted; for non-metallated Ph-rings and co-ordinated
THF ligands only ipso-C and oxygen atoms are shown for clarity. 50%
probability thermal ellipsoids are presented only for the labelled
atoms.
Fig. 1 ORTEP drawing of the molecular structure of 1; 50% prob-
ability thermal ellipsoids are presented.z
The difference in bond lengths within the central m2-M2C2
core is larger for 5a (D = 0.18 A) than for 3 (D = 0.14 A), but
the poor crystal quality of 3 (R1 = 0.0843) prohibits detailed
comparisons of the bond lengths and angles of 3 with those of
1 and 5a. Selected structural parameters of the structures of
the free ligand 1 and of 5a are given in Table 1.
Table 1 Selected bond lengths/A and angles/1 for 1 and 5a
1
5a
Y–C(shortest)
Y–C(longest)
Y–CPh
Y–OTHF
Y–OOMe
P–CYlide
P–CPh
CYlide–CAryl
CAryl–OOMe
C–P–C
2.396(6)
2.576(6)
2.480(7)–2.572(6)
2.408(5), 2.450(5), 2.471(4)
2.431(4), 2.577(4)
1.701(6), 1.714(6)
1.807(7)–1.851(6)
1.449(9), 1.455(8)
1.398(7), 1.404(8)
104.4(3)–115.4(3)
117.8(4), 119.9(4)
85.4(2), 87.5(2)
93.2(2), 93.7(2)
The shortest Y–C bond in the m2-Y2C2 core is of 2.396(6) A
long, and it lies in a range typical for neutral, low-coordinated,
non-Cp complexes of yttrium with at least two hard-donor
ligands.24a The THF molecules form strong bonds with the
yttrium atoms with a maximum bond length of 2.47 A, which
is a similar value to those found in other Y–THF adducts.24
One of the Y–O bonds to the methoxy groups is much longer
and indicates weaker bonding. The phosphonium centers are
1.693(2)
1.818(2)–1.831(2)
1.452(2)
1.382(2)
103.4(1)–120.2(1)
132.0(1)
P–CYlide–CAryl
CYlide–Y–CYlide
Y–C–Y
nearly tetrahedral with a narrower range of C–P–C angles 110
(ꢁ5)1 and significantly smaller P–CYlideꢂCAryl angle 119(ꢁ1)1
than that in the free ligand 1—112(ꢁ8)1 and 1321, respectively.
These new phosphoranylidene complexes of lutetium and
yttrium should be important both for our understanding of
fundamental bonding concepts of organometallic chemistry
and as catalyst precursors. Full details of our results on rare
earth complexes in this series will be discussed in a forth-
coming paper.
Acknowledgements
The authors thank Prof. H. Schumann and Dr S. I. Troyanov
for fruitful discussions, Dr B. Ziemer (Humboldt Universitat
¨
zu Berlin) for crystallographic studies of 1 and 3 and Dipl.-
Ing. S. Schutte (Technische Universitat Berlin) and Petra
¨
Bartles for technical assistance. Financial support through
the DFG programmes (SPP 1166, GrK 352 and GrK 1213)
is gratefully acknowledged.
Scheme 2 Synthesis of binuclear phosphoranylidene complexes 3
and 5.
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y Synthetic and analytical details for the starting reagents are
given in the ESI. Synthesis of 3: a 0.5 M benzene solution of
Lu(CH2SiMe3)3(THF)2 (5 mL, 2.5 mmol) was slowly added to a
stirred solution of 1 (956 mg, 2.5 mmol) in benzene (5 mL) at room
temperature. The reaction mixture was then stirred and heated at 45
1C. It gradually changed in colour from orange-red to dark yellow.
After 2 d a small amount of precipitate formed that was filtered off and
the resulting solution was reduced in volume to approx. 5 mL and very
slowly cooled down to 10 1C for crystallization. After several weeks
light yellow crystals formed. The product was filtered off, washed with
pre-cooled benzene (2 mL) and dried under vacuum. Yield 0.72 g
(46%). 1H NMR (300 MHz, C6D6, +23 1C): d 7.89–6.95 (br m, Aryl-
groups and solvated C6H6), 3.60 (br s, CH2–O, THF), 2.75 (br s, CH3–
O), 1.70 (br t, CH2–CH2–O, THF). 31P NMR (121.5 MHz, C6D6,
+23 1C): d 12.2 (br s). Elemental analysis was calculated for
C60H56Lu2O4P2(C6H6)4, C 64.45%, H 5.15%, Lu 22.35%, observed
C 63.92%, H 5.28%, Lu 22.17%. Synthesis of 5: a 0.5 M THF solution
of Y(o-Me2NCH2C6H4)3 (5 mL, 2.5 mmol) was added to a stirred
solution of 1 (956 mg, 2.5 mmol) in toluene (30 mL). The orange
solution was slowly heated to 65 1C and allowed to stir at this
temperature for 5 h, while it gradually deepened in colour and a
bright yellow precipitate deposited. After slow cooling to room
temperature, the dark red solution was decanted and the yellow solid
was washed with toluene (2 ꢃ 5 mL) and dried under high vacuum.
Yield 0.60 g (42%) of C52H40O2P2Y2(C4H8O)(C9H13N). 1H NMR
(300 MHz, C5D5N, +23 1C): d 7.89–7.15 (br m, Aryl-groups), 3.65 (br
s, CH2–O, THF), 3.54 (s, Me2NCH2), 3.45 (br s, CH3–O), 2.19 (s,
Me2N), 1.59 (br t, CH2–CH2–O, THF). 31P NMR (121.5 MHz,
C5D5N, +23 1C): d 36.8. Elemental analysis was calculated for
References
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C65H61NO3P2Y2,
C 68.25%, H 5.37%, N 1.22%, observed C
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z Data were collected on a STOE IPDS diffractometer using graphite
monochromated Mo-Ka radiation (l = 0.71073 A). The structures
were solved by direct methods and refined by full-matrix least-squares
techniques against F2 using SHELX-97 software package.25 Crystal
ꢀ
data: for 1: C26H23OP, M = 382.41, triclinic, space group P1, a =
9.746(2) A, b = 10.046(2) A, c = 10.715(2) A, a = 73.76(2)1, b =
85.61(2)1, g = 89.94(2)1, V = 1004.0(3) A3, Z = 2, Dc = 1.265 g
cmꢂ3, m(Mo-Ka) = 0.151 mmꢂ1. T = ꢂ123 1C, crystal dimensions
0.76 ꢃ 0.40 ꢃ 0.08 mm, 6420 reflections were measured, 3401 were
symmetry independent and 2577 were observed [I > 2s(I)], R1
=
22 Poor solubility of 3 at lower temperatures prohibits study of its
dynamic behaviour with NMR in more detail.
0.0376 and wR2 = 0.0945 (all data). CCDC reference number 245413.
For 3: C84H80Lu2O4P2, M = 1565.36, monoclinic, space group P21/c,
a = 14.192(5) A, b = 12.461(4) A, c = 20.490(5) A, b = 105.51(3)1, V
= 3491.6(18) A3, Z = 2, Dc = 1.489 g cmꢂ3, m(Mo-Ka) = 2.908
mmꢂ1. T = ꢂ93 1C, crystal dimensions 0.40 ꢃ 0.28 ꢃ 0.20 mm, 17113
reflections were measured, 4979 were symmetry independent and 2802
were observed [I > 2s(I)], R1 = 0.0843 and wR2 = 0.2278 (all data).
The intensities were corrected for Lorentz polarization and absorption
effects using ABSCOR, a modification of DIFABS (Tmin = 0.366,
23 Two solvate C6H6 molecules per asymmetric unit of 3 and one
solvate THF molecule per asymmetric unit of 5a have been found.
24 See for example: (a) W. J. Evans, J. C. Brady and J. W. Ziller, J.
Am. Chem. Soc., 2001, 123, 7711; (b) S. Arndt, P. M. Zeimentz, T.
P. Spaniol, J. Okuda, M. Honda and K. Tatsumi, Dalton Trans.,
2003, 3622; (c) P. G. Hayes, G. C. Weich, D. J. H. Emslei, C. L.
Noack and W. E Piers, Organometallics, 2003, 22, 1577; (d) S.
Bambirra, D. van Leusen, A. Meetsma, B. Hessen and J. H.
Teuben, Chem. Commun., 2003, 522.
Tmax
C68H72O6P2Y2,
=
0.558).26 CCDC reference number 245412. For 5a:
ꢀ
1225.02, triclinic, space group P1,
M
=
a
=
25 (a) G. M. Sheldrick, Programm for solution of crystal structures,
SHELXL-97, Universitat Gottingen, 1997, 22; (b) G. M. Sheldrick,
12.513(3) A, b = 14.455(3) A, c = 19.023(4) A, a = 86.89(3)1, b =
75.64(3)1, g = 70.68(3)1, V = 3144.4(11) A3, Z = 2, Dc = 1.294 g
cmꢂ3, m(Mo-Ka) = 1.936 mmꢂ1. T = ꢂ73 1C, crystal dimensions 0.45
ꢃ 0.25 ꢃ 0.20 mm, 40601 reflections were measured, 11055 were
¨
¨
Programm for the refinement of crystal structures, SHELXL-97,
Universitat Gottingen, 1997, 22.
26 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, A39,
¨
¨
symmetry independent and 6310 were observed [I > 2s(I)], R1
=
158.
0.0624 and wR2 = 0.1511 (all data). CCDC reference number 286123.
For crystallographic data in CIF or other electronic format see DOI:
10.1039/b514439f.
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This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006
New J. Chem., 2006, 30, 29–31 | 31