A mononuclear indium(I) carbene analogue

Article abstract of DOI:10.1039/b406017b

The 'one pot' reaction between K[N(SiMe₃)₂], InI and the β-diimine ligand precursor [H(NDippCMe)₂CH] (Dipp = C ₆H₃Prⁱ₂-2,6) gave [In{(NDippCMe)₂CH}] 1, the first example of a two-coordinate, neutral, In(1) singlet 'carbene analogue'.

Full text of DOI:10.1039/b406017b

A mononuclear indium( ) carbene analogue
I
Michael S. Hill*a and Peter B. Hitchcockb
a Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London, UK SW7
2AZ. E-mail: mike.hill@imperial.ac.uk; Fax: +44 (0)20 7594 5804; Tel: +44 (0)20 7594 5709
b The Chemistry Laboratory, University of Sussex, Falmer, Brighton, East Sussex, UK BN1 9QJ
Received (in Cambridge, UK) 23rd April 2004, Accepted 8th June 2004
First published as an Advance Article on the web 20th July 2004
The ‘one pot’ reaction between K[N(SiMe3)2], InI and the b-
diimine ligand precursor [H(NDippCMe)2CH] (Dipp
C6H3Pri2-2,6) gave [In{(NDippCMe)2CH}] 1, the first example
of a two-coordinate, neutral, In( ) singlet ‘carbene analogue’.
scopic and analytical data were consistent with the X-ray structure
obtained from single crystals grown at room temperature from
hexane solution. Compound 1 is monoclinic (P21/n) and iso-
=
I
structural with the Al(
I
) and Ga(
) derivatives V and VI.5,6 The
I
molecular structure, illustrated in Fig. 1, comprises well separated
monomers with a V-shaped two-coordinate geometry at indium.
The In–N(1)–C(1)–C(2)–C(3)–N(2) heterocycle is effectively
planar (rms deviation of least squares plane = 0.0067 Å). The In–N
bond lengths [2.268(3), 2.276(3) Å] are longer than those in
previously reported In(III) derivatives bearing the same ligand (e.g.
[In{(NDippCMe)2CH}X2]: X = I; 2.121(2), 2.147(1), X = Me;
2.190(1), 2.204(1) Å)13 and the In(II) complex [In{(NDippC-
Me)2CH}Cl]2 (2.169(4), 2.172(4) Å)11 which contains a direct In–
The search for Group 13 and 14 species that are formally analogous
to singlet carbenes has gathered pace in recent years.1 Monomeric
derivatives, I (X = anionic substituent; E = C, Si, Ge, Sn or Pb),
are known for the Group 14 elements,2 isoelectronic Group 13
species, II (X = anionic substituent; L = neutral donor; E = B, Al,
Ga, In, Tl) are rare. Schmidbaur and Jones have reported the
heterocyclic anions III and IV, both of which contain gallium in a
formal +1 oxidation state,3,4 and Roesky and Power have described
syntheses of the neutral six electron aluminium(
I
) and gallium(
I
) b-
In bond, but shorter than those in monomeric In(
I
) tris-
tris(3,5-di-tert-butylpyrazolyl)-
), average ca. 2.49 Å]14c which contain an
diketiminato derivatives V and VI.5,6 It is reasoned that the doubly
occupied HOMO of all four compounds is mainly an aluminium or
gallium sp orbital. The availability of this lone pair has been shown
in coordination and reaction chemistry.7 In view of the increasing
stability of the univalent state as Group 13 is descended,8 it is
surprising that indium complexes analogous to III–VI have not
(pyrazolyl)borates
hydroboratoindium(
[e.g.
I
additional In–N interaction.14 The N(1)–M–N(2) angle
[81.12(10)°] in 1 is more acute than those in the Al(
I) [89.86(8)°]
and Ga( ) [87.53(5)°] derivatives, and the remaining endocylic
I
angles in the chelate ligand are significantly wider than those
observed in V and VI. As a result, the indium centre of 1 protrudes
from the cavity provided by the ligand to a greater extent than the
aluminium or gallium cations in V or VI. The isolation of 1
vindicates Power’s surmise regarding the probable stability of this
been reported. The In(
I) halides are readily available and a number
of In(
I
) s-alkyl and s-aryl derivatives have been synthesised from
them by treatment with organolithium reagents.9,10 Although an
attempted synthesis of the indium analogue (1) of V and VI resulted
in disproportionation to indium(III), indium(II) and indium(0)
products, Power has suggested that this compound should be
obtainable under the correct conditions.11 After our successful
syntheses of b-diketiminato compounds of Group 2 elements from
the potassium compound and the alkaline earth iodides,12 we
compound and shows that the In( ) centre is indeed stabilised
I
towards disproportionation by the b-diketiminato ligand. It is
unclear why 1 can be obtained from the potassium b-diketiminate
and InI but not from the lithium b-diketiminate and InCl. It appears
that the outcome of the metathesis is determined by the properties
of intermediates produced during the reaction rather than by the
attempted to synthesise the elusive In(
procedure.
I
) derivative 1 by a similar
stability of the In( ) carbene analogue. In the work described by
I
Power it seems that these intermediates gave predominantly
disproportionation products.11
Compound 1 is the first example of a neutral monovalent indium
‘carbene analogue’. In( ) species are isoelectronic with the
I
stannylenes, the most intensively studied Group 14 carbenoid
species. Experiments to delineate the coordination and reaction
chemistry of 1 will be reported in future publications.
[In{(NDippCMe)2CH}] (Dipp = C6H3Pri2-2,6) (1) was obtained
by a simple ‘one pot’ reaction of equimolar quantities of
K[N(SiMe3)2], InI and H(NDippCMe)2CH in THF at 278
°C.†Some disproportionation was evident from the deposition of
indium metal as the solution was warmed to room temperature, but
extraction with hexane and crystallisation gave compound 1 in
reasonable (36% unoptimised) yield as pale yellow, thermally
stable crystals. We have not yet identified further products from this
reaction, although it is likely that mixtures of iodoindium(II) and
iodoindium(III) compounds are produced.11 Compound 1 is photo-
labile but stable in hexane solution and in the solid state if stored in
the absence of light. In aromatic solvents however decomposition,
accompanied by the deposition of elemental indium, occurs over a
48 hour period even in the dark. Compound 1 has been
characterised by 1H and 13C NMR spectroscopy, elemental analysis
and a single crystal X-ray structure determination.‡The spectro-
Fig. 1 Thermal ellipsoid plot (30%) of 1. H atoms omitted for clarity.
Selected bond lengths (Å) and angles (°): In–N(1) 2.268(3), In(1)–N(2)
2.276(3), N(1)–C(1) 1.324(4), N(1)–C(6) 1.445(4), N(2)–C(3) 1.323(4),
N(2)–C(18) 1.439(4), C(1)–C(2) 1.398(4), C(2)–C(3) 1.403(4), N(1)–In–
N(2) 81.12(10), In–N(1)–C(1) 130.3(2), In–N(2)–C(3) 130.3(2), N(1)–
C(1)–C(2) 124.6(3), C(1)–C(2)–C(3) 129.5(3), C(2)–C(3)–N(2) 124.2(3).
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C h e m . C o m m u n . , 2 0 0 4 , 1 8 1 8 – 1 8 1 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

3 (a) E. S. Schmidt, A. Jockisch and H. Schmidbaur, J. Am. Chem. Soc.,
1999, 121, 9758; (b) E. S. Schmidt, A. Schier and H. Schmidbaur, J.
Chem. Soc., Dalton Trans., 2001, 505.
4 R. J. Baker, R. D. Farley, C. Jones, M. Kloth and D. M. Murphy, J.
Chem. Soc., Dalton Trans., 2002, 3844.
We thank the Royal Society for the provision of a University
Research Fellowship. Dedicated to the memory of Professor Colin
Eaborn FRS.
5 C. Cui, H. W. Roesky, H.-G. Schmidt, M. Noltemeyer, H. Hao and F.
Cimpoesu, Angew. Chem., Int. Ed., 2000, 39, 4274.
6 N. J. Hardman, B. E. Eichler and P. P. Power, Chem. Commun., 2000,
1991.
Notes and references
7 (a) N. J. Hardman, C. Cui, H. W. Roesky, W. H. Fink and P. P. Power,
Angew. Chem., Int. Ed., 2001, 40, 2172; (b) N. J. Hardman, P. P. Power,
J. D. Gorden, C. L. B. Macdonald and A. H. Cowley, Chem. Commun.,
2001, 1866; (c) N. J. Hardman, R. J. Wright, A. D. Philip and P. P.
Power, J. Am. Chem. Soc., 2003, 125, 2667; (d) R. J. Baker, C. Jones, M.
Kloth and J. A. Platts, Angew. Chem., Int. Ed., 2003, 42, 2660; (e) R. J.
Baker, C. Jones and J. A. Platts, J. Am. Chem. Soc., 2003, 125, 10534;
(f) R. J. Baker, C. Jones and J. A. Platts, Dalton Trans., 2003, 3673.
8 A. J. Downs, Chemistry of Aluminium, Gallium, Indium and Thallium,
Chapman and Hall, London, 1993.
† THF (50 mL) was added to a mixture of InI (1.00 g, 4.14 mmol),
K[N(SiMe3)2] (0.83 g, 4.14 mmol) and [H(NDippCMe)2CH] (1.73 g, 4.14
mmol) at 278 °C. Warming to room temperature in the absence of light
produced a grey slurry. Volatiles were removed and the solid residue
extracted with hexane (30 mL). Filtration and concentration of the filtrate
produced compound 1 as pale yellow crystals suitable for X-ray diffraction
analysis (0.80 g, 36%). Anal. Calc.(found) for C29H41InN2: C 65.41 (65.72);
H 7.78 (7.83); N 5.26 (5.15)%. Mp 203–205 °C (dec). 1H NMR (270 MHz,
toluene-d8) d 1.15 (d, 12H, 3JHH = 6.9 Hz, CHMe2), 1.23 (d, 12H, 3JHH
=
3
6.9 Hz, CHMe2), 1.72 (s, 6H, CMe), 3.19 (sept, 4H, JHH = 6.9 Hz,
CHMe2), 5.00 (s, 1H, CH), 7.14 (m, 6H, ArH). 13C{1H} NMR (67.94 MHz,
toluene-d8) d 23.8 (CHMe2), 24.3 (CMe), 25.7 (CHMe2), 28.3 (CHMe2),
98.1 (g-CH), 123.9 [m-C(Dipp)], 125.5 [p-C(Dipp)], 142.1 [o-C(Dipp)],
144.9 [i-C(Dipp)], 163.8 (CN).
9 For example, s-alkyls: (a) R. D. Schluter, A. H. Cowley, D. A. Atwood,
R. A. Jones and J. L. Atwood, J. Coord. Chem., 1993, 30, 25; (b) W.
Uhl, A. Janschak, W. Saak, M. Kaupp and R. Wartchow, Organome-
tallics, 1998, 17, 5009.
10 s-Aryls: (a) S. T. Haubrich and P. P. Power, J. Am. Chem. Soc., 1998,
120, 2202; (b) R. J. Wright, A. D. Philips, N. J. Hardman and P. P.
Power, J. Am. Chem. Soc., 2002, 124, 8538.
11 M. Stender and P. P. Power, Polyhedron, 2002, 21, 525.
12 M. S. Hill, P. B. Hitchcock and M. Crimmin, unpublished observa-
tions.
13 M. Stender, B. E. Eichler, N. Hardman, P. P. Power, J. Prust, M.
Noltemeyer and H. W. Roesky, Inorg. Chem., 2001, 40, 2794.
14 (a) A. Frazer, B. Piggott, M. B. Hursthouse and M. Mazid, J. Am. Chem.
Soc., 1994, 116, 4127; (b) H. V. R. Dias, L. Huai, W. Jin and S. G. Bott,
Inorg. Chem., 1995, 34, 1973; (c) M. C. Kuchta, H. V. R. Dias, S. G.
Bott and G. Parkin, Inorg. Chem., 1996, 35, 943.
‡ Crystal data at 173(2) K for 1 with Mo-Ka radiation (l = 0.71073 Å):
C29H41InN2, M = 532.46, monoclinic, P21/n (No. 14), a = 12.5576(4), b
= 16.0978(7), c = 14.1307(5) Å, b = 105.421(2)°, V = 2753.68(18) Å3,
Z = 4, Dc = 1.28 g cm23, m = 0.88 mm21, R1 = 0.038 for 3674 [I > 2s(I)]
data; wR2 = 0.099 for all data. Data collection Kappa CCD. Refinement
using SHELXL-97. CCDC 238162. See http://www.rsc.org/suppdata/cc/
b4/b406017b/ for crystallographic data in .cif format.
1 (a) M. Driess and H. Grützmacher, Angew. Chem., Int. Ed. Engl., 1996,
35, 829; P. P. Power, Chem. Rev., 1999, 99, 3463.
2 M. Weidenbruch, Eur. J. Inorg. Chem., 1999, 373.
C h e m . C o m m u n . , 2 0 0 4 , 1 8 1 8 – 1 8 1 9
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