Formation of an unusual tetralithium diplatinum complex [Pt(C≡CBut)2(PPh2O)2Li 2(μ-H2O)(Me2CO)2]2 containing μ3-PPh2O- liga

Article abstract of DOI:10.1039/a705522f

The very unusual complex [Pt(C≡CBu^t)₂(PPh₂O)₂Li ₂(μ-H₂O)(Me₂CO)₂]₂ 2 is obtained by the reaction of 'Li₂[Pt(C≡CBu^t)₄]' with

Full text of DOI:10.1039/a705522f

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Formation of an unusual tetralithium diplatinum complex
[Pt(C·CBut)2(PPh2O)2Li2(m-H2O)(Me2CO)2]2 containing m3-PPh2O2 Ligands
Larry R. Falvello,a Juan Fornie´s,*a Elena Lalinde,*b Antonio Mart´ın,a Teresa Morenob and Jorge Sacrista´nb
a Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n, Universidad de Zaragoza-Consejo
Superior de Investigaciones Cient´ıficas, 50009 Zaragoza, Spain
b Departamento de Qu´ımica, Universidad de La Rioja, 26001, Logron˜o, Spain
The very unusual complex [Pt(C·CBut)2(PPh2O)2Li2(m-
employed.9 Complex 1 was characterised analytically and
spectroscopically.
H2O)(Me2CO)2]2
2 is obtained by the reaction of
‘Li2[Pt(C·CBut)4]’ with an excess of PPh2H in acetone–
ethanol and possesses an unusual linear chain of four Li
atoms sandwiched between two square planar dianionic
units trans-2OPPh2{Pt(C·CBut)2}PPh2O2, to which it is
bound through m3-PPh2O2 bridging ligands.
The identity of complex 2 has been established by X-ray
structure analysis† which revealed the unexpected tetra-
lithiumdiplatinum
species
[Pt(C·CBut)2(PPh2O)2Li2(m-
H2O)(Me2CO)2]2.‡ Molecule A (Fig. 1) is formed by two
identical dianionic fragments ‘trans-2OPPh2{Pt(C·CBut)2}P-
Ph2O2’ which act as didentate ligands, bridging the four Li
centers pairwise through the oxygen atoms. Each PPh2O2
ligand is Pt–P bonded [Pt(1)–P(1,2) 2.301(2), 2.306(2) Å] and
as mentioned bridges two Li centres [Li–O range
1.907(10)–1.969(10) Å], giving two planar Li2O2 rings,
Li(1,2)O(1,2A) and Li(1A,2A)O(1A,2), which are rigorously copla-
nar. The central atoms are connected by two H2O molecules
[O(5), O(5A)]. All this results in a final linear disposition of four
non-bonded Li atoms [Li(2)···Li(1,2A) 2.610(13), 2.848(19) Å],
Li(1)–Li(2)–Li(2A) 176.7(6)°], which is very similar to the Li
disposition in the compound recently described by Roesky and
coworkers,7 Li4[(MeGa)6(m3-O)2(ButPO3)6]·4thf. This struc-
tural feature contrasts with the most prevalent structural motif,
cubane-like, found in other tetralithium derivatives10 which has
been rationalised using ring-stacking ideas.11 The Li atoms in
Platinum–alkynyl chemistry has long been the subject of
intensive study1 and recently there has been a growing interest
in the synthesis of polymetallic species derived from dianionic
(C222, C2RC222, etc.) or substituted (pyridyl, bipyridyl,
ruthenocenyl, ferrocenyl, etc.) building blocks due to their
increasing importance in materials science.1,2 The family of
alkynyl Pt complexes, particularly that of mononuclear hetero-
leptic derivatives which are stabilised by tertiary phosphine
ligands is now quite large.1,2d,e,3 The chemistry of monomeric
derivatives containing other types of ligands is comparatively
less developed1,3a,4 and analogous complexes containing secon-
dary phosphines as additional ligands have not been explored.
The presence of acidic protons in this type of ligand (PR2H)
probably prevents the use of the most general synthetic routes
such as the reaction of halides with alk-1-ynes (base, CuI-
catalysed)1,2d,e,3b,4d or with metal acetylide reagents.1,4 Re-
cently, we have reported the preparation of trans-
[Pt(C·CBut)2(PPh3)2]5 in high yield by partial displacement of
the alkynyl groups with PPh3 from the reactive species
Li2[Pt(C·CBut)4], prepared ‘in situ’. We report here the
application of this method to the diphenylphosphine ligand,
which allows not only the preparation of the homologous
complex trans-[Pt(C·CBut)2(PPh2H)2] 1 but also the synthesis
of an unexpected tetralithium diplatinum compound 2, which
contains lithium atoms in the form of an unusual linear chain of
four Li atoms stabilised by m3-PPh2O2 and m-OH2 bridging
ligands. Complex 2 represents the second alkynyl–platinum
lithium complex crystallographically characterised,6 and also
the second example reported containing one small chain of four
sandwiched Li ions.7
The tetraalkynylplatinatelithium species ‘Li2[Pt(C·CBut)4]’
was initially formed by addition of LiC·CBut to [PtCl2(tht)2]
(molar ratio 5.5:1) as previously reported.5,8 Treatment of the
colourless solution obtained by dissolving Li2[Pt(C·CBut)4] in
acetone–ethanol with an excess of PPh2H (1:3, N2 atmosphere)
causes the slow precipitatiion (7 h of stirring) of trans-
[Pt(C·CBut)2(PPh2H)2] 1 as a white microcrystalline solid
(25% yield on the Pt starting material). Prolonged stirring (7 h)
of the resulting filtrate under aerobic conditions produces the
separation of a new white solid. Recrystallization of this solid
from hot acetone yields the crystalline tetralithium diplatinum
diphenylphosphinite complex 2 in ca. 45% yield. During our
efforts to optimise the synthesis of complex 1 we observed that
the relative yields of 1 and 2 vary with the presence of air in the
reaction system (25–52% 1 to 45–11% 2, on the Pt starting
material). This fact clearly indicates that the presence of
PPh2O2 ligands in complex 2 stems from the partial oxidation
of the PPh2H ligand to PPh2OH under the reaction conditions
Fig. 1 Molecular structure of 2. Ellipsoids depicted at their 50% probability
level. Important molecular geometry parameters include: interatomic
distances (Å): Li(1)–O(1) 1.907(10), Li(1)–O(2A) 1.927(10), Li(2)–O(2A)
1.957(11), Li(2)–O(1) 1.969(10), Li(2)–O(5) 2.0481(10), Li(2)–O(5A)
2.048(10), Pt(1)–C(1) 2.001(6), Pt(1)–C(7) 2.006(6), C(1)–C(2) 1.207(8),
C(7)–C(8) 1.203(8). Bond angles (°): O(3)–Li(1)–O(4) 99.0(4),
O(1)–Li(1)–O(2A) 96.9(4), Li(1)–O(1)–Li(2) 84.6(4), Li(1)–O(2A)–Li(2)
84.4(4), O(1)–Li(2)–O(2A) 93.9(4), O(5)–Li(2)–O(5A) 91.9(4), Li(2)–
O(1)–P(1) 119.1(4), O(1)–P(1)–Pt(1) 111.65(15), O(2)–P(2)–Pt(1)
112.62(15), Pt(1)–C(1)–C(2) 175.8(5), C(1)–C(2)–C(3) 173.4(7), Pt(1)–
C(7)–C(8) 177.0(5), C(7)–C(8)–C(9) 175.0(7). Primed atoms are related by
inversion centre to unprimed ones.
Chem. Commun., 1998
141

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‡ The crystal structure determination† reveals that there are two independ-
ent, but very similar, half-molecules per asymmetric unit. For simplicity, we
will discuss here only the molecule denoted by A.
each [Li(1,2)O2] unit are chemically different. Thus the internal
Li atoms [Li(2), Li(2A)] have tetrahedral coordination, being
bonded to the O atoms [O(5), O(5A)] of the two bridging water
ligands, while the external Li atoms [Li(1), Li(1A)] interact with
two terminal acetone molecules [Li(1)–O(3),(4) 1.981(10),
1.997(10) Å]. Both the distortion from tetrahedral geometry at
the Li centres and the Li–O bond lengths are in good agreement
with those observed in other Li compounds containing similar
LiO4 tetrahedral coordination environments.10–12 On the other
hand, it is also remarkable that although a variety of metal
coordination modes have been observed for diorgano-
phosphinite ligands,9a,12b,13 to our knowledge, complex 2 is the
1 R. Nast, Coord. Chem. Rev., 1982, 47, 89.
2 (a) Inorganic Materials, ed. D. W. Bruce and D. O’Hare, Wiley, 2nd
edn., 1996, p. 460; (b) W. Beck, B. Niemer and M. Weiser, Angew.
Chem., Int. Ed. Engl., 1993, 32, 923; (c) N. J. Long, Angew. Chem., Int.,
Ed. Engl., 1995, 34, 21; (d) R. Faust, F. Diederich, V. Gramlich and P.
Seiler, Chem. Eur. J., 1995, 1, 111; (e) A. Harriman, M. Hissler, R.
Ziessel, A. D. Cian and J. Fisher, J. Chem. Soc., Dalton Trans., 1995,
4067 and references therein.
3 (a) J. Manna, K. D. John and M. D. Hopkins, Adv. Organomet. Chem.,
1995, 38, 79; (b) M. I. Bruce, M. Ke and P. J. Low, Chem. Commun.,
1996, 2405; (c) J. Manna, J. A. Whiteford and P. J. Stang, J. Am. Chem.
Soc., 1996, 118, 8731.
4 (a) J. Fornie´s and E. Lalinde, J. Chem. Soc., Dalton Trans., 1996, 2587;
(b) I. Ara, J. R. Berenguer, J. Fornie´s, E. Lalinde and M. T. Moreno,
Organometallics, 1996, 15, 1820; (c) R. J. Cross and M. F. Davidson,
J. Chem. Soc., Dalton Trans., 1986, 1987; (d) S. Tanaka, T. Yoshida, T.
Adachi, T. Yoshida, K. Onitsuka and K. Sonogashira, Chem. Lett.,
1994, 877; (e) S. L. James, G. Verspui, A. L. Spek and G. van Koten,
Chem. Commun., 1996, 1309.
3
first example in which this ligand acts with a m3-k :P,O,OA
bonding mode, bridging two hard Li atoms (m-O) and also being
P-bonded to a soft Pt centre. The P–O bond distances in 2
[1.537(4), 1.539(4) Å] are comparable to those observed for
structurally characterised [PPh2–O]2 complexes displaying a
m-O,m-P metal bridging mode.13 The square-planar coordina-
tion at Pt is unexceptional, exhibiting, as expected, essentially
linear acetylenic fragments (see Fig. 1).
In accord with the solid structure, the IR spectrum of 2 shows,
in addition to a medium n(C·C) band at 2092 cm21, the
presence of water (3646, 3402, 1611 cm21) and typical
absorptions for n(PNO) (996, 1006, 1030 cm21), characteristic
of phosphinito-bridged complexes.13 In the 31P NMR spectrum
5 J. R. Berenguer, J. Fornie´s, F. Mart´ınez, J. C. Cubero, E. Lalinde, M. T.
Moreno and A. J. Welch, Polyhedron, 1993, 12, 1797.
6 [Pt2(C·CPh)4(PEt3)2(Bun)2(m-Li)2]: A. Sebald, B. Wrackmeyer, Ch. R.
Theocharis and W. Jones, J. Chem. Soc., Dalton Trans., 1984, 747.
7 M. G. Walawalkar, R. Murugaval, A. Voigt, H. W. Roesky and H. G.
Schmidt, J. Am. Chem. Soc., 1997, 119, 4656.
8 P. Espinet, J. Fornie´s, F. Mart´ınez, M. Toma´s, E. Lalinde, M. T.
Moreno, A. Ruiz and A. J. Welch, J. Chem. Soc., Dalton Trans., 1990,
791.
9 The formation of phosphinito complexes starting from PPh2H has been
previously observed: J. Vicente, M. T. Chicote and P. G. Jones, Inorg.
Chem., 1993, 32 4960.
10 M. A. Beswick and D. S. Wright, Comprehensive Organometallic
Chemistry II, ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Elsevier,
1995, vol. 1, pp. 1–34; E. Weiss, Angew. Chem., Int. Ed. Engl., 1993, 32,
1501; K. Gregory, P. v. R. Schleyer and R. Snaith, Adv. Inorg. Chem.,
1994, 37, 47; D. Seebach, Angew. Chem., Int. Ed. Engl., 1988, 27,
1624.
1
a singlet shifted far downfield (d 67.37, JPtP 2510 Hz) is
observed,indicative of P oxidation to PV.13 The 1H NMR
spectrum of 2 in CD3COCD3 exhibits a singlet at d 0.46 due to
equivalent alkynyl groups (C2But); however, the difficulty in
assigning OH bands, even after addition of D2O, does not allow
us to determine with certainty whether the H2O molecules
remain coordinated in solution.
The Li-ionic conductivity of the Li derivative 2 has also been
measured using the well known complex impedance method,14
but it is near zero. This fact is in agreement with previous results
obtained for other tetrahedral LiO4 derivatives.15
We thank the Direccio´n General de Ensen˜anza Superior
(Spain, Projects PB95-0003C02-01 02 and PB95-0792) and the
University of LaRioja (API-97/B13) for financial support.
11 R. E. Mulvey, Chem. Soc. Rev., 1991, 20, 167.
12 (a) Lithium Chemistry—A Theoretical and Experimental Overview, ed.
A.-M. Sapse and P. v. R. Schleyer, Wiley, New York, 1995, ch. 9 and
references therein; (b) M. A. Beswick, N. L. Cromhout, C. N. Harmer,
J. S. Palmer, P. R. Raithby, A. Steiner, K. L. Verhorevoort and D. S.
Wright, Chem. Commun., 1997, 583.
Footnotes and References
13 Homonuclear examples, see: D. E. Fogg, N. J. Taylor, A. Meyer and
A. J. Carty, Organometallics, 1987, 6 2252; N. W. Alcock, P.
Bergamini, T. M. Gomes-Carniero, R. D. Jackson, J. Nicholls, A. G.
Orpen, P. G. Pringle, S. Sostero and O. Traverso, J. Chem. Soc., Chem.
Commun., 1990, 980; V. Riera, M. A. Ruiz, F. Villafane, C. Bois and Y.
Jeannin, Organometallics, 1993, 12, 124. Heteronuclear examples, see:
P. M. Veitch, J. R. Allen, A. J. Blake and M. Schroder, J. Chem. Soc.,
Dalton Trans., 1987, 2853; D. M. Roundhill, R. P. Sperline and W. B.
Beaulieu, Coord. Chem. Rev., 1978, 26, 263.
14 B. V. R. Chowdari, K. Radhakrishnan, K. A. Thomas and G. V. Subba
Rao, Mater. Res. Bull., 1989, 24, 221.
15 H. Aono, N. Imanaka and G.-Y. Adachi, Acc. Chem. Res., 1994, 27,
265.
* E-mail: juan.fornies@posta.unizar.es
† Crystal data for 2·0.5Me2CO: C43.50H53Li2O5.50Pt, M = 934.77, triclinic,
space group P1 (no. 2), a = 13.858(3), b = 13.858(3), c = 24.693(7) Å, a
= 83.79(3), b = 87.53(2), g = 65.02(2)°, U = 4590(2) Å3, Z = 2, T = 173
K, m = 3.166 mm21, graphite monochromated Mo-Ka radiation, l =
0.71073 Å, colourless prism with dimensions 0.56 3 0.46 3 0.30 mm,
Siemens AED2/STOE diffractometer with Oxford Cryogenics low-tem-
perature attachement, w–q scans, data collection range 4 < 2q < 48°,
semiempirical absorption correction based on y scans, transmission factors
0.889–0.577, 1001 refined parameters with 13628 unique (Rint = 0.026)
reflections (15 247 measured). Full-matrix least-squares refinement of this
model against F2 (program SHELXL 9316) converged to final residual
indices R1 = 0.033, wR2 = 0.070. (R factors defined in ref. 16), GOF 1.05.
Final difference electron density maps showed four peaks > 1 e Å23 (1.98,
1.43, 1.31, 1.03; largest diff. hole 21.21) lying closer than 1.12 Å from the
Pt atoms. CCDC 182/698.
16 G. M. Sheldrick, SHELXL-93, a Program for Crystal Structure
Refinement, University of Go¨ttingen, Germany, 1993.
Received in Basel, Switzerland, 30th July 1997; 7/05522F
142
Chem. Commun., 1998