A novel fluorene-containing κ4-P2N 2-tetradentate platinum(II) complex

Article abstract of DOI:10.1039/b816351k

Base induced P,N-chelation, C-C coupling and methylene C-H deprotonation affords an unusual fluorene containing square-planar Pt^II complex Pt(κ⁴-P₂N₂-Ph₂PCHNNCC ₁₂H₈)₂

Full text of DOI:10.1039/b816351k

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A novel fluorene-containing j4-P2N2-tetradentate platinum(II) complex†
Mark R. J. Elsegood, Andrew J. Lake and Martin B. Smith*
Received 18th September 2008, Accepted 6th November 2008
First published as an Advance Article on the web 17th November 2008
DOI: 10.1039/b816351k
Base induced P,N-chelation, C–C coupling and methylene
C–H deprotonation affords an unusual fluorene contain-
4
ing square-planar PtII complex Pt(j -P2N2-Ph2PCH NN-
=
CC12H8)2 which has been isolated and structurally charac-
terised.
Acyclic tridentate and tetradentate ligands based on symmetric
or nonsymmetric donor atom combinations (N, P, O, S) con-
tinue to attract much attention. Neutral or anionic tridentate
and tetradentate ligand systems containing N/P donor sets
are especially appealing for their diverse coordination modes
and uses in metal based catalysis.1,2 Furthermore chiral P2N2-
ligands have successfully been employed in a range of asymmetric
transformations using metal based catalysts.2b,c,3,4 We recently
described a readily synthesised PNN¢N¢¢-tetradentate ligand and
its diverse bonding capabilities to a range of late transition-metals.5
Fluorene, diazofluorene or fluorenone groups have been used
in organic synthesis6 and for the preparation of metal complexes7
including organometallic acetylides,8 oligomers9 and polymers.10
However examples of monodentate or bidentate phosphine lig-
ands bearing one or two fluorene groups are sparsely documented
in the literature.11 Herein we describe the synthesis and character-
isation of a novel PtII coordinated P2N2-tetradentate ligand util-
ising a straightforward to prepare fluorene functionalised tertiary
phosphine. A pivotal step in this transformation is the unusual
C–C coupling or dimerisation reaction, a feature previously ob-
served in carbodiimide,12a ketomalonate,12b 2-(arylazo)phenol,12c
fulvene12d and phosphorus substituted alkene chemistry.12e
Fig. 1 Molecular structure of 2. All C–H hydrogen atoms except those
on N(1) and N(3) are omitted for clarity. Selected bond distances
˚
(A) and angles (deg) (values in square brackets are for the second
molecule): P(1)–O(1) 1.4929(13) [1.4914(13)]; O(1)–P(1)–C(1) 112.79(8)
[113.28(8)], P(1)–C(1)–N(1) 112.64(12) [111.56(13)], C(1)–N(1)–N(2)
115.86(14) [116.55(15)], N(1)–N(2)–C(2) 122.30(15) [121.62(16)].
These are linked through intermolecular N–H ◊ ◊ ◊ O H-bonding
˚
[N(1) ◊◦◊ ◊ O(2) 2.813(2), H(1) ◊ ◊ ◊ O(2) 2.02(2) A, N(1)–H(1) ◊ ◊ ◊ O(2)
˚
150(2) ; N(3) ◊ ◊ ◊ O(1) 2.798(2), H(3) ◊ ◊ ◊ O(1) 2.04(2) A, N(3)–
H(3) ◊ ◊ ◊ O(1) 147(2)◦]. The P(1)–C(1)/P(2)–C(27) [1.8336(19),
1.8347(19)], C(1)–N(1)/C(27)–N(3) [1.445(2), 1.441(2)] and N(2)–
C(2)/N(4)–C(28) [1.297(2), 1.303(2)] distances are all as antic-
ipated whereas the N(1)–N(2)/N(3)–N(4) distances are rather
short [1.334(2), 1.330(2)]13,14 suggesting some possible p-electron
delocalisation.
Reaction of Ph2PCH2OH and 9-fluorenone hydrazone,
=
H2NN CC12H8, in CH3OH gave the new tertiary phosphine
The yellow dichloroplatinum(II) complex 3 was prepared by
reaction of PtCl2(cod) with two equiv. of 1 in dichloromethane.
Confirmation of the cis stereochemistry was ascertained by
1
31P{ H} NMR and FT - IR spectroscopy. The molecular structure
(1)
of 3 was elucidated by a single crystal X-ray study (Fig. 2).† The
molecule lies on a two-fold axis. Upon coordination the P(1)–C(1),
C(1)–N(1), N(1)–N(2) and N(2)–C(2) bond lengths are similar to
those of 2 (vide infra for notable comparisons with 4). There is
also an intramolecular N–H ◊ ◊ ◊ Cl H-bond [N(1) ◊ ◊ ◊◦Cl(1) 3.206(2),
=
Ph2PCH2NHN CC12H8 1 in excellent yield (93%) as a yellow
solid which displayed the anticipated spectroscopic properties
(eqn (1)). Oxidation of 1 with aq. H2O2 (27.5%) gave the
phosphine oxide Ph2P(O)CH2NHN CC12H8 2 which has been
structurally characterised (Fig. 1).‡ In the solid state 2 exists
˚
H(1) ◊ ◊ ◊ Cl(1) 2.62(3) A, N(1)–H(1) ◊ ◊ ◊ Cl(1) 128(3) ].
Since the amine proton in 3 is acidic we reasoned deprotonation
with base should promote P,N-coordination of the cis coordinated
=
t
ligands.1b,c Treatment of 3 with BuOK gave 4 and was obtained
in 64% yield as a dark orange solid following isolation from
as a dimer pair with two molecules in the asymmetric unit.
1
CH3OH (Eqn. (2)). In the 31P{ H} NMR spectrum of 4 a new
downfield phosphorus resonance at d(P) 55.3 ppm (1JPtP 3300 Hz)
was observed indicating both phosphorus donor atoms are within
five-membered chelate rings. Interestingly the 1H NMR spectrum
(298 K) showed, in addition to broad signals in the aromatic region
attributed to the fluorene and phenyl hydrogens, a new doublet
Department of Chemistry, Loughborough University, Loughborough, UK
LE11 3TU. E-mail: m.b.smith@lboro.ac.uk; Fax: +44 1509 223925;
Tel: +44 1509 222553
† Electronic supplementary information (ESI) available: Experimental
procedures, spectroscopic data and additional X-ray figures. CCDC
reference numbers 702768–702770. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b816351k
2
[d(H) 5.75 ppm, JPH 32 Hz. c.f. 4.65 ppm for 3] consistent with
30 | Dalton Trans., 2009, 30–32
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Fig. 2 Molecular structure of 3. The disordered diethyl ether sol-
vent molecule and all C–H hydrogen atoms except those on N(1)
˚
are omitted for clarity. Selected bond distances (A) and angles (deg):
Fig. 3 (a) Ball and stick model of 4. All C–H hydrogen atoms except
those on C(1) and C(27) and the toluene solvent molecule are omitted
Pt(1)–P(1) 2.2420(6), Pt(1)–Cl(1) 2.3603(6), P(1)–C(1) 1.871(3), C(1)–N(1)
1.451(4), N(1)–N(2) 1.332(3), N(2)–C(2) 1.305(4); P(1)–Pt(1)–P(1A)
101.61(3), P(1)–Pt(1)–Cl(1) 85.36(2), P(1)–Pt(1)–Cl(1A) 172.04(2),
Cl(1)–Pt(1)–Cl(1A) 87.95(3), Pt(1)–P(1)–C(1) 107.80(9), P(1)–C(1)–N(1)
110.94(19), C(1)–N(1)–N(2) 119.4(2), N(1)–N(2)–C(2) 119.1(2).
˚
for clarity. Selected bond distances (A) and angles (deg): Pt(1)–P(1)
2.2341(11), Pt(1)–P(2) 2.2436(11), Pt(1)–N(2) 2.007(3), Pt(1)–N(4)
2.007(3), P(1)–C(1) 1.820(5), C(1)–N(1) 1.299(5), N(1)–N(2) 1.345(5),
N(2)–C(2) 1.477(5), C(2)–C(28) 1.597(6), C(28)–N(4) 1.473(5), N(4)–N(3)
1.332(4), N(3)–C(27) 1.309(5), C(27)–P(2) 1.820(5); P(1)–Pt(1)–P(2)
112.31(4), N(2)–Pt(1)–N(4) 81.68(13), Pt(1)–P(1)–C(1) 97.43(15),
P(1)–C(1)–N(1) 119.3(3), C(1)–N(1)–N(2) 116.7(4), N(1)–N(2)–C(2)
116.5(3), N(2)–C(2)–C(28) 105.2(3), C(2)–C(28)–N(4) 104.9(3),
C(28)–N(4)–N(3) 117.6(3), N(4)–N(3)–C(27) 116.5(4), N(3)–C(27)–P(2)
118.9(3), C(27)–P(2)–Pt(1) 97.61(15). (b) Space filling view of 4 showing
the twisted orientation of the two fluorene groups.
=
the presence of two CHPPh2 hydrogens (by integration). The
13C{ H} NMR spectrum of 4 revealed the absence of a fluorene
1
=
N C resonance suggesting loss of double bond character.
two fluorene groups is ca. 50◦ indicating significant twisting
presumably to minimise steric interactions between these planar
aromatic rings. The X-ray structure of 4 is unique and represents
the first crystallographic example of a complex bearing a MP2C4N4
metallacyclic ring.16
(2)
In conclusion, we have shown that in one-step a coordinated
P-monodentate phosphine bearing a fluorene auxillary group can
undergo sequential P,N-chelation, C–C coupling and methylene
C–H deprotonation togive aremarkable P2N2-tetradentate ligand.
Further studies are now underway to probe the generality of this
reaction and investigate the mechanistic pathway associated with
this transformation. These results will be published in due course.
An X-ray crystallographic study† shows the unprecedented for-
mation of a P2N2-coordinated ligand at a square-planar PtII centre
in 4 (Fig. 3). The coordination sphere about Pt(1) comprises two cis
Pt–P–C–N–N five-membered chelate rings and a third Pt–N–C–
Acknowledgements
C–N metallocyclic ring formed by carbon carbon coupling
12c,15
˚
[C(2)–C(28) 1.597(6) A]
between both fluorene groups from
We would like to thank the EPSRC and Loughborough University
for funding (AJL). Johnson and Matthey are gratefully acknowl-
edged for the generous loan of precious metal salts.
each cis chelated P,N-tertiary phosphine. The PtII centre lies
0.0375 A out of the P(1)/N(2)/N(4)/P(2) coordination plane.
˚
Within each Pt–P–C–N–N ring it is clear that a change in
hybridisation (sp3 to sp2) about C(1) and C(27) has occurred
as indicated by the significant contraction of the C–N bond
Notes and references
˚
‡ Crystal data: For 2, C26H21N2OP: Mr = 408.42, triclinic, space group
lengths [1.299(5), ◦1.309(5) A] and enlarged P–C–N bond angles
¯
[119.3(3), 118.9(3) ].1b,c The N(1)–N(2) [1.345(5) A] and N(3)–N(4)
[1.332(4) A] bond lengths remain similar to those of 2 and
3 and suggest some p-electron delocalisation may exist in the
C(1)–N(1)–N(2)/C(27)–N(3)–N(4) backbones. However the
N(2)–C(2)/N(4)–C(28) distances [1.477(5), 1.473(5) A] are consid-
erably longer than found in 2 and 3 implying these should formally
be viewed as single bonds. Each Pt–P–C–N–N ring can be de-
scribed as near planar [N(1) deviates by 0.0560 A from the Pt(1)–
P1, a = 12.6349(7), b = 13.7094(8), c = 13.7679(8), a = 71.744(2),
˚
◦
3
˚
b = 84.887(2), g = 71.011(2) , V = 2141.3(2) A , T = 150(2) K, Z =
˚
4, m(Mo-Ka) = 0.148 mm-1, 9889 independent reflections measured,
dcalc = 1.267 g cm-3, R1 = 0.0446 (for 7137 data with I > 2s(I)),
wR2 = 0.1181 (all data) and 547 refined parameters. CCDC reference
number 702768. For 3·Et2O, C52H42Cl2N4PPt·C4H10O: Mr = 1124.94,
monoclinic, space group I2/a, a = 20.0646(8), b = 10.7880(4), c =
˚
3
˚
23.7050(9), b = 111.046(2), V = 4788.8(3) A , T = 150(2) K, Z = 4,
m(Mo-Ka) = 3.154 mm-1, 5835 independent reflections measured, dcalc
=
1.560 g cm-3, R1 = 0.0208 (for 4567 data with I > 2s(I)), wR2 = 0.0471
(all data), and 313 refined parameters. CCDC reference number 702769.
For 4·C7H8, C52H38N4P2Pt·C7H8: Mr = 1068.03, monoclinic, space group
P21/n, a = 12.0681(6), b = 15.7231(8), c = 25.0731(13), b = 98.648(2),
˚
˚
P(1)–C(1)–N(1)–N(2) plane; N(4) deviates by 0.0694 A from the
Pt(1)–P(2)–C(27)–N(3)–N(4) plane]. The average torsion angle
[C(3)–C(2)–C(28)–C(29), C(14)–C(2)–C(28)–C(40)] between the
3
-1
˚
V = 4703.5(4) A , T = 150(2) K, Z = 4, m(Mo-Ka) = 3.096 mm , 10772
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independent reflections measured, dcalc = 1.508 g cm-3, R1 = 0.0374 (for
7718 data with I > 2s(I)), wR2 = 0.0732 (all data), and 596 refined
parameters. CCDC reference number 702770.
8 (a) W.-Y. Wong, K.-Y. Ho and K.-H. Choi, J. Organomet. Chem., 2003,
670, 17; (b) W.-Y. Wong, K.-H. Choi, G.-L. Lu, J.-X. Shi, P.-Y. Lai,
S.-M. Chan and Z. Lin, Organometallics, 2001, 20, 5446.
9 Z. Zhao, S. Yu, L. Xu, H. Wang and P. Lu, Tetrahedron, 2007, 63,
7809.
1 For recent examples of P2N and N2P-coordination, see: (a) M. D.
Palacios, M. C. Puerta, P. Valerga, A. Lledo´s and E. Veilly, Inorg.
Chem., 2007, 46, 6958; (b) E. Ben-Ari, G. Leitus, L. J. W. Shimon and
D. Milstein, J. Am. Chem. Soc., 2006, 128, 15390; (c) D. Vuzman,
E. Poverenov, L. J. W. Shimon, Y. Diskin-Posner and D. Milstein,
Organometallics, 2008, 27, 2627.
10 X. Liu, R. Zhu, Y. Zhang, B. Liu and S. Ramakrishna, Chem. Commun.,
2008, 3789.
11 (a) C. A. Fleckenstein and H. Plenio, Organometallics, 2008, 27, 3924;
(b) C. Freund, N. Barros, H. Gornitzka, B. Martin-Vaca, L. Maron and
D. Bourissou, Organometallics, 2006, 25, 4927.
2 For recent examples of P2N2-coordination, see:(a) A. A. Mikhailine,
E. Kim, C. Dingels, A. J. Lough and R. H. Morris, Inorg. Chem., 2008,
47, 6587; (b) C. Sui-Seng, F. Freutel, A. J. Lough and R. H. Morris,
Angew. Chem., Int. Ed., 2008, 47, 940; (c) Z.-R. Dong, Y.-Y. Li, J.-S.
Chen, B.-Z. Li, Y. Xing and J.-X. Gao, Org. Lett., 2005, 7, 1043; (d) S.
Burger, B. Therrien and G. Su¨ss-Fink, Eur. J. Inorg. Chem., 2003, 3099.
3 R. Noyori and S. Hashiguchi, Acc. Chem. Res., 1997, 30, 97.
4 M. Althaus, C. Bonaccorsi, A. Mezzetti and F. Santoro,
Organometallics, 2006, 25, 3108.
5 S. E. Durran, M. R. J. Elsegood, S. R. Hammond and M. B. Smith,
Inorg. Chem., 2007, 46, 2755.
6 S. Kobayashi, R. Yazaki, K. Seki and Y. Yamashita, Angew. Chem., Int.
Ed., 2008, 47, 5613.
12 (a) C. Villiers, P. Thue´ry and M. Ephritikhine, Chem. Commun., 2006,
392; (b) M. Pasquali, C. Floriani, A. Chiesi-Villa and C. Guastini,
Inorg. Chem., 1981, 20, 349; (c) S. Halder, R. Acharyya, S.-M. Peng,
G.-H. Lee, M. G. B. Drew and S. Bhattacharya, Inorg. Chem., 2006, 45,
9654; (d) F.-J. K. Rehmann, A. J. Rous, O. Mendoza, N. J. Sweeney, K.
Strohfeldt, W. M. Gallagher and M. Tacke, Polyhedron, 2005, 24, 1250;
(e) K. Izod, W. McFarlane, B. V. Tyson, W. Clegg, R. W. Harrington
and S. T. Liddle, Organometallics, 2003, 22, 3684.
13 L. R. Sutton, A. J. Blake, W.-S. Li and M. Schro¨der, J. Chem. Soc.,
Dalton Trans., 1998, 279.
14 M. Yamamura, N. Kano and T. Kawashima, Inorg. Chem., 2006, 45,
6497.
15 H. Wang and F. P. Gabbai, Org. Lett., 2005, 7, 283 and references
7 (a) J. Zhang, M. Gandelman, L. J. W. Shimon and D. Milstein,
Organometallics, 2008, 27, 3526; (b) C. J. Adams, J. Chem. Soc., Dalton
Trans., 1999, 2059.
therein.
16 D. B. Grotjahn, D. Combs, S. Van, G. Aguirre and F. Ortega, Inorg.
Chem., 2000, 39, 2080.
32 | Dalton Trans., 2009, 30–32
This journal is
The Royal Society of Chemistry 2009
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