(Phosphacyclopentadienyl)indium(I) derivatives: Synthesis and X-ray crystal structure of [In(η5-P3C2But2)]

Article abstract of DOI:10.1021/om980877v

Co-condensation of indium vapor and tert-butylphosphaethyne at 77 K yields two new, volatile In-(1) complexes: [In(η⁵-P₃C₂Bu^t₂)] (1) and [In(η⁵-P₂C₃Bu^t₃)] (2). A single-crystal X-ray diffraction experiment on 1 reveals a discrete molecular structure, involving half-sandwich coordination of the P₃C₂Bu^t₂ ring around the indium center. 1 may be independently prepared by treating InI with the newly synthesized, base-free ligand salt K(P₃C₂Bu^t₂).

Full text of DOI:10.1021/om980877v

Organometallics 1999, 18, 793-795
793
Notes
(P h osp h a cyclop en ta d ien yl)in d iu m (I) Der iva tives:
Syn th esis a n d X-r a y Cr ysta l Str u ctu r e of
[In (η5-P 3C2Bu t )]
2
Charlotte Callaghan, Guy K. B. Clentsmith, F. Geoffrey N. Cloke,*
Peter B. Hitchcock, J ohn F. Nixon,* and David M. Vickers
The Chemistry Laboratory, School of Chemistry, Physics and Environmental Sciences,
The University of Sussex, Falmer, Brighton, Sussex BN1 9QJ , U.K.
Received October 26, 1998
Summary: Co-condensation of indium vapor and tert-
butylphosphaethyne at 77 K yields two new, volatile In-
(I) complexes: [In(η5-P3C2But )] (1) and [In(η5-P2C3But )]
act as precursors for semiconducting films and de-
vices.13-19 Our success in the synthesis of unusual,20-22
low-valent transition metal complexes by metal vapor
synthesis (MVS) techniques provided the incentive to
apply these methods to main-group metals. In this work
we report the synthesis and structure of new, volatile,
2
3
(2). A single-crystal X-ray diffraction experiment on 1
reveals a discrete molecular structure, involving half-
sandwich coordination of the P3C2But ring around the
2
and thermally stable In(I) complexes, [In(η5-P3C2But )]
indium center. 1 may be independently prepared by
2
treating InI with the newly synthesized, base-free ligand
(1) and [In(η5-P2C3But )] (2), by MVS techniques and
3
salt K(P3C2But ).
2
the determination of the molecular structure of 1. In
addition we report the independent synthesis of 1 by
more conventional means, utilizing the newly synthe-
In tr od u ction
sized, base-free ligand salt K(P3C2But ).
2
An early and now classic example of subvalent main-
group-metal chemistry is the reaction of InCl3 with an
excess of NaC5H5 to give [In(η5-C5H5)] upon sublima-
tion.1 For many years [In(η5-C5H5)] remained the sole
representative of this class of compounds,2-8 and despite
recent interest in subvalent main-group chemistry in
which ligands other than cyclopentadienyl derivatives
are utilized,9-11 examples of In(I) complexes are less
numerous compared to those of In(III) due to the pro-
pensity of the former to undergo disproportionation to
the zerovalent metal and In(III).12 The revival in low-
valent indium chemistry and the appearance of further
examples of In(I) and In(II) complexes in the literature
is due in part to the potential of indium compounds to
Resu lts a n d Discu ssion
Co-condensation of indium vapor and ButCtP at 77
K afforded a deep brown matrix, which gave a brown
oil after workup. The mass spectrum of this material
gave signals at m/z 384 and 346, consistent with the
formation of In(P2C3But )+ and In(P3C2But )+, respec-
3
2
tively, along with the spectrum base peak at m/z 115,
representing In+. Evidently the naked metal atoms in
the matrix had cyclized ButCtP units to give both (P2C3-
But ) and (P2C3But ) rings.23 Sublimation of the MVS
2
3
product yielded a yellow powder which gave the same
mass spectrum, and the more soluble component, [In-
(P2C3But )] (2), could be removed by recrystallization of
3
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R.; Buttrey, L. A. Organometallics 1990, 9, 2488.
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Fettinger, J . C.; Pazik, J . C.; Victoriano, L. Organometallics 1989, 8,
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Dietrich, A. J . Organomet. Chem. 1989, 363, 243.
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R.; Fettinger, J . C.; Blom, R. Organometallics 1988, 7, 1051.
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Chem. 1996, 35, 943.
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Engl. 1993, 32, 748.
(17) Fischer, R. A.; Behm, J .; Priermeier, T.; Scherer, W. Angew.
Chem., Int. Ed. Engl. 1993, 32, 746.
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R. S.; Xue, Z. Appl. Phys. Lett. 1989, 55, 2760.
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1998, 797.
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Am. Chem. Soc. 1996, 118, 7630.
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therein.
(11) Frazer, A.; Piggot, B.; Hursthouse, M. B.; Mazid, M. J . Am.
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10.1021/om980877v CCC: $18.00 © 1999 American Chemical Society
Publication on Web 01/20/1999

794 Organometallics, Vol. 18, No. 4, 1999
Notes
Ta ble 1. 13C{1H} NMR Sp ectr oscop ic Da ta for
[In (η5-P 3C2Bu t2)] (1) in d 6-Ben zen e a t 75.1 MHz
nucleus
chem shift/ppm
J C-P(M)/Hz
J C-P(X) + J C-P(X′)/Hz
C(ring)
C(CH3)3
CH3
221.4
41.6
37.6
9.5
20.4
67.1
9.7
12.8
92.1
Ta ble 2. Bon d Len gth s (Å) a n d Bon d An gles (d eg)
Obser ved in [In (η5-P 3C2Bu t2)] (1)
In-P1
In-C1
P1-C1
P1-P1′
3.035(3)
2.981(9)
1.748(10)
2.111(5)
In-P2
In-centroid
P2-C1
3.108(4)
2.598(9)
1.781(10)
C1-P1-P1′
C2-C1-P1
100.2(3)
119.8(6)
P1-C1-P2
C1-P2-C1′
119.8(6)
100.0(7)
trum at 183.2 ppm, and its 1H NMR spectrum re-
vealed the expected signals in a 2:1 ratio at 1.52 and
1.36 ppm arising from the chemically different tert-butyl
groups.
Single crystals of 1 suitable for an X-ray diffraction
experiment were grown from hexanes, and the solid-
state structure is shown in Figure 1. Relevant bond
distances and angles are listed in Table 2. The
P3C2But ring is η5-ligated to the metal, and the
2
In(P3C2But ) units lie on a crystallographic mirror plane
2
and are linked into chains by weak interactions between
the indium centers and alternate P3C2But rings. The
2
F igu r e 1. (a) ORTEP view of, and numbering scheme for,
structure confirms the half-sandwich coordination of the
ring around the indium center, and the In-centroid
distance is 2.598 Å, which is comparable to metal to
ring-centroid distances of cyclopentadienyl complexes
of In(I), which range from 2.726 Å (for [In(η5-C5H5)])24
to 2.53 Å (for [In(η5-C5H4SiMe3)]).5 However, when
intermonomer distance is considered (i.e. the distance
between an indium atom and the alternate ligand along
the chain), the distance of 3.526 Å observed for 1 is
exceptionally long in comparison with the [In(η5-C5H4R)]
systems, for which intermonomer distances lie within
0.2 Å of intramolecular indium ring-centroid bond
lengths.4 In addition, the closest In-In contacts of 1 are
greater than 6.1 Å, which are comparable to those
observed in [In(pz)3BH] (pz ) 3,5-di-tert-butylpyraz-
[In(η5-P3C2But )] (1). (b) Chem 3D view of the crystal
2
packing of 1.
the sublimate from toluene or petroleum ether to give
1
pure [In(P3C2But )] (1), identified by means of H and
2
31P{1H} NMR spectroscopy. 1 could be synthesized in
near-quantitative yield by heating InI and the base-free
ligand salt K(P3C2But ) in refluxing toluene for 24 h (eq
2
1). The 31P{1H} NMR spectrum of 1 in d6-benzene
olyl)10 and [In(C6H3-2,6-Trip2)] (Trip ) C6H2-2,4,6-Pri ).9
3
Evidently the increased steric protection offered by the
larger heterocycle and the tert-butyl groups is sufficent
to diminish aggregation entirely, in contrast to the trend
set by the [In(η5-C5H4R)] series in which the tendency
to form zigzag polymeric chains is marked; likewise,
when more sterically demanding cyclopentadienyl de-
rivatives are employed, aggregation is again observed
(cf. the dimeric [In(η5-C5(CH2Ph)5)]2 and the hexa-
meric [In(η5-C5Me5)]6). As is observed with the tris-
(pyrazolyl)borate complexes of In(I),10,11 the solid-state
reveals the typical AB2 pattern associated with an η5-
ligated, 1,2,4-substituted P3C2 ring (a triplet at 259.5
ppm and a doublet at 255.9 ppm, J P-P′ ) 50.9 Hz) or a
fluxional η1 complex undergoing fast 1,2-shifts. The
appearance of the 13C{1H} NMR spectrum is rather
more complicated, since each carbon nucleus couples to
sets of one chemically and two magnetically different
phosphorus nuclei. Multiplets are observed at 221.4,
41.6, and 37.6 ppm, arising from the ring, quaternary,
and methyl carbon nuclei, respectively. Spectral simula-
tion allows extraction of the carbon-phosphorus cou-
pling constants associated with the AM[X]2 spin systems
(Table 1).
structure of 1 consists of clearly discrete InP3C2But
2
units.
While the metal center of 1 is expected to be a Lewis
base, its reactivity is unremarkable. No evidence for
adduct formation was obtained by NMR spectroscopy
when solutions of 1 were treated with Lewis acids such
as [Pt(PPh3)2Cl2]2(µ-Cl)2 and [V(η5-C5H5)2]. Attempts to
oxidize the indium center by addition of iodine led to
decomposition. The solubility of 1 tends to suggest a
monomer in solution, in agreement with the solid-state
1
As expected, the H NMR spectrum of 1 consists of a
singlet at 1.37 ppm due to the tert-butyl protons. The
more soluble indium derivative 2, presumably the 1,3-
diphosphacyclopentadienyl complex [In(η5-P2C3But )],
3
which is recovered from the supernatant of crystalline
1, could not be isolated as a pure material but was
characterized by a singlet in its 31P{1H} NMR spec-
(24) Frasson, E.; Menegus, F.; Panattoni, C. Nature 1963, 199, 1087.

Notes
Organometallics, Vol. 18, No. 4, 1999 795
metal to give a clear dark solution from which the solvent was
removed in vacuo. The resultant oil was sublimed onto a liquid-
nitrogen cold finger (10-3 mBar, 80 °C) to give a yellow oil (40
mg). Extraction of the yellow oil into toluene (2 mL) and cooling
data, and if this is the case, the poor ability of the In
center as a Lewis base more likely represents an
electronic effect rather than a steric one. In(I) com-
plexes, such as [In(pz)3BH]10,25 or [In(C6H3-2,6-Trip2)],9
contain similarly bulky steric groups but are neverthe-
less quite potent Lewis bases. It is suggested that the
reduced donor ability of the In center of 1 is related to
1
to -50 °C yielded pale yellow crystals of 1 (20 mg). H NMR
(d6-benzene): δ 1.49 (s, CH3C). 31P{1H} NMR (d6-benzene): δ
259.5.(t, 1P, J P-P′ ) 50.8 Hz), 255.5 (d, 2P, J P-P′ ) 50.8 Hz).
MS (70 eV) (%): m/z 346 (40, M+), 331 (10, M+ - CH3), 231
(10, M+ - In), 115 (100, In+). Anal. Calcd for C10H18InP3: C,
34.71; H, 5.24. Found: C, 34.65; H, 5.18.
the electronic properties of the P3C2But ring, which is
2
overall more electron-withdrawing than the cyclopen-
tadienyl systems.26
2 could be obtained as a pale yellow powder by removing
the solvent from the supernatant solution of crystalline 1 (5
4
mg). 1H NMR (d6-benzene): δ 1.52 (t, 18H, J H-P ) 1 Hz,
Con clu sion s
4
But), 1.36 (t, 9H, J H-P ) 1 Hz, Bu′t). 31P{1H} NMR: δ 183.2
(s). MS (70 eV) (%): m/z 384 (42%, M+), 246 (15%, M+
-
In this work is presented a well-characterized ex-
ample of an In(I) complex. Further work, including the
extension of this chemistry to gallium and aluminum
and an appraisal of 1 as a precursor for the deposition
of semiconducting indium phosphide films, is underway.
Me3CCtCCMe3), 115 (100, In+). Analysis was not obtained.
1 could also be synthesized by heating finely ground InI
(0.38 g, 1.57 mmol) and K(P3C2But ) (0.48 g, 1.57 mmol) in
2
toluene (30 mL) at reflux for 24 h. Removal of the solvent and
sublimation of the residue gave pure 2 as a pale yellow powder
(0.36 g, 92.3%).
K(P 3C2Bu t2). BunLi (21.3 mL, 0.053 mol) was added to
P(SiMe3)3 (13.3 g, 0.053 mol) in Et2O (100 mL) at 0 °C.
Potassium menthoxide in heptane (105 mL, 0.055 mol) was
added directly, and the mixture was stirred for 12 h, at the
end of which time a caramel color had developed. This solution
was then added to ButC(OSiMe3)dPSiMe3 (27.89 g, 0.106 mol)
in toluene (40 mL) at 0 °C in an ampule. The ampule was
evacuated and heated to 50 °C for 48 h, during which time
an orange solid precipitated and the solution became dark
red. The orange solid was collected on a frit, washed with
toluene (3 × 10 mL volumes), and dried under vacuum to give
Exp er im en ta l Section
General procedures are detailed elsewhere.22,27 Indium
metal and InI (99.999% purity) were supplied by Aldrich.
P(SiMe3)3, ButC(OSiMe3)dPSiMe3, and ButCtP were synthe-
sized according to literature procedures.28,29 Solutions of potas-
sium menthoxide (approximately 0.50 mol L-1) in heptane
were prepared by treating menthol (Aldrich) in heptane with
excess potassium metal (BDH) and heating the mixture to
reflux for 24 h, followed by filtration and dilution to a 0.52
mol L-1 titer. BunLi (Acros) was used as supplied as a 2.5 mol
L-1 solution in hexane. Unless otherwise stated, all procedures
were carried out under dry dinitrogen or argon. Microanalyses
were performed by Mikroanalytisches Labor Pascher.
K(P3C2But ) as a light beige powder (4.82 g, 33.6%). A second
2
crop of product could be obtained by heating the combined
filtrate and toluene washings to 50 °C for a further 36 h (1.89
g, 13.1%). 1H NMR (d5-pyridine): δ 2.05 (s, But). 31P{1H} NMR
(d5-pyridine): δ 252.8 (t, 1P, J P-P′ ) 48.7 Hz), 244.8 (d, 2P,
J P-P′ ) 48.7 Hz). Anal. Calcd for C10H18KP3: C, 44.44; H, 6.71.
Found: C, 44.05; H, 6.76.
[In (η5-P 3C2Bu t 2)] (1) a n d [In (η5-P 2C3Bu t 3)] (2). Co-
condensation at 77 K of indium vapor (1.67 g, 14.5 mmol) from
a
resistively heated alumina crucible with an excess of
ButCtP (20 g, 0.20 mol) over 1.5 h resulted in the formation
of a deep brown matrix, which was warmed to room temper-
ature under vacuum. The apparatus was then opened to an
external trapping system, and unreacted ButCtP (12 g) was
collected in an external trap at 77 K. After 4 h the reaction
vessel was refilled with dinitrogen and the matrix washed into
a Schlenk receiver with hexanes (2 L). This mixture was then
filtered through a flame-dried bed of Celite to remove colloidal
Ack n ow led gm en t. The advice and assistance of Dr.
Tony Avent is acknowledged for the NMR spectra and
simulations. Also thanked is Dr. Ali Abdul-Sada for
acquiring the mass spectra. Financial assistance was
obtained from the EPSRC in the form of a scholarship
to D.M.V. and a fellowship to G.K.B.C.
(25) Kuchta, M. C.; Parkin, G. Main Group Chem. 1996, 1, 291.
(26) Bartsch, R.; Datsenko, S.; Ignatiev, N. V.; Mu¨ller, C.; Nixon, J .
F.; Pickett, C. J . J . Organomet. Chem. 1997, 529, 375.
(27) Cloke, F. G. N.; Hitchcock, P. B.; Love, J . B. J . Chem. Soc.,
Dalton Trans. 1995, 25.
(28) Becker, G.; Schmidt, H.; Uhl, G.; Uhl, W. Inorg. Synth. 1990,
27, 243.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, bond lengths, and bond angles for
1. This material is available free of charge via the Internet at
http://pubs.acs.org.
(29) Becker, G. Z. Anorg. Allg. Chem. 1977, 430, 66.
OM980877V