Synthesis and characterisation of two monomeric crystalline thallium(I) β-diketiminates

Article abstract of DOI:10.1039/b413666g

Treatment of the appropriate sodium β-diketiminate NaL or NaL′ with an equivalent portion of TlCl in thf under mild conditions furnishes in good yield the first structurally characterised thallium β-diketiminates: the monomeric, orange, crystalline Tl(I)

Full text of DOI:10.1039/b413666g

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Synthesis and characterisation of two monomeric crystalline thallium(I)
b-diketiminates{
Yanxiang Cheng, Peter B. Hitchcock, Michael F. Lappert* and Meisu Zhou
Received (in Cambridge, UK) 7th September 2004, Accepted 15th November 2004
First published as an Advance Article on the web 15th December 2004
DOI: 10.1039/b413666g
Treatment of the appropriate sodium b-diketiminate NaL or
NaL9 with an equivalent portion of TlCl in thf under mild
conditions furnishes in good yield the first structurally
characterised thallium b-diketiminates: the monomeric,
ð1Þ
orange, crystalline Tl(I) complexes TlL and TlL9
[L
5
{N(SiMe3)C(Ph)}2CH,
L9
5
{N(C6H3Pri2-
2,6)C(H)}2CPh].
Although the +1 oxidation state is common for inorganic thallium
compounds, low molecular aggregated organic univalent Tl
compounds are rare.1,2 Crystalline monomers include the singly
coordinated organothallium compound Tl[C6H3(C6H2Pri3-
The orange, sharp melting, crystalline b-diketiminates 1 and 2
gave satisfactory microanalyses{ and multinuclear NMR§ and
mass{ spectra as well as single crystal X-ray data".
29,49,69)2-2,6],3 and
a
series of triply N-coordinated
A feature of the 13C{1H} NMR spectra of 1 and 2 and the 1H
NMR spectrum of 2 was the presence of doublets due to coupling
to the 203Tl (29%) and 205Tl (71%) spin-K isotopes.§ These
splittings were large but unexceptional for Tl compounds.14 For
example, the 1H NMR spectrum of 2 in toluene-d8 or C6D6
Tl tris(pyrazolyl)borates,
h
the
first
of
which
was
i
ꢂ
ꢀ
ꢁ
ꢃ
4
Tl NC But CðHÞCðHÞN 3BH [av. l(Tl–N) 2.585 A], one
˚
modification of Tl[g5-C5(CH2Ph)5],5 and [Mg(pmdeta)][Tl(g5-
C5H5)2].6 Even with bulky ligands, aggregation is a feature,
3
showed J(1H–203,205Tl) 5 127.3 Hz. The individual peaks of the
involving formation of (i) Tl–Tl bonds [the first example was
7
Tl2{Si(SiMe3)3}2, with l(Tl–Tl) 2.9142(5) A]; (ii) close Tl Tl
doublets were broad due to efficient CSA (Chemical Shift
Anisotropy) relaxation of the Tl isotopes, as confirmed by the
observation that the broadening increased when changing from a
300 MHz to a 500 MHz spectrometer and that upon cooling the
doublets coalesced to broad singlets at 213 K as Tl relaxation
became yet more efficient. Coupling of 1H or 29Si signals was not
observed in the 1H or 29Si{1H} (INEPT) NMR spectra of 1 even
at 328 K using the lower field spectrometer; the signals were
sufficiently broad that coupling of , ca. 20 Hz would not have
been noted. {For TlL-, coupling was observed in the 13C{1H}
…
˚
t
contacts, as in [Tl{(NBu )2SiMe2}3]2, l(Tl Tl) 3.16 ¡ 0.03 A; (iii)
8
…
˚
i
p-arene Tl interactions, as in [Tl{N(SiMe3)(C6H3Pr 2-2,6)}]4,
…
9
…
˚
Cent(g-arene) Tl 3.11 A]; or (iv) ligand-bridged dimers, as in
crystalline [Tl{m-N(SiMe3)2}]2,10a which dissociates into the
monomer in the vapour.10b
Metal b-diketiminates are increasingly useful spectator ligands.11
Notable illustrations are provided by the isolation of the first
monomeric Al(I) and Ga(I) complexes ML0 [M 5 Al,12a Ga;12b
L0 5 {N(C6H3Pri2-2,6)C(Me)}2CH]; although InL0 proved elusive,
it has also recently been obtained in modest yield, but was
photolabile and slowly decomposed in the dark in an aromatic
solvent.12c
3
NMR spectrum [4J(13C–Tl) 9.4, J(13C–Tl) 44.7 (endocyclic) and
1
43.4 (CH3) Hz], but not the H NMR spectrum13}. The CH3 1H
NMR signals of 2 appeared as doublets at 293 K, attributed to
restricted rotation about the N–Cipso and/or C–C (e.g., C15–C19)
bonds.
We now report the first structurally characterised crystalline Tl
b-diketiminates, the monomeric TlL and TlL9 [L
5
Crystalline
1 (Fig. 1) is a discrete monomer." The
{N(SiMe3)C(Ph)}2CH, L9 5 {N(C6H3Pri2–2,6)C(H)}2CPh]. The
only other Tl b-diketiminate in the literature is TlL-, employed as
a precursor to [CuL-(g2-CH2LCHR)] [L- 5 {N(C6H3Me2-
2,6)C(Me)}2CH, R 5 H or Ph].13
TlN1C1C2C3N2 ring has the boat conformation. The Tl, C2,
Si1, Si2, C4 and C10 atoms are 21.23, 20.15, +0.69, +0.62, +0.14
˚
and +0.18 A out of the N1C1C3N2 plane. The angle between the
latter plane and the C1C2C3, TlN1N2, and the C4 or C10 phenyl
plane is 14.5, 40.4, and 50 or 46u, respectively. The bond lengths
and angles are similar to those of [NaL(thf)2] (see suppl. data),
Treatment of thallium(I) chloride with NaL{ or NaL9{ in thf
and crystallisation from hexane yielded the crystalline complex TlL
(1) or TlL9 (2) in high yield, eqn. (1).{
3
…
shown schematically in Fig. 2. There is an g -Ph Tl0 close
˚
contact (3.634, 3.304 and 3.508 A for C10, C15 and C14,
…
˚
respectively; Tl Tl(2 2 x, 1 2 y, 1 2 z) 6.464 A) and no
{ Electronic supplementary information (ESI) available: (i) synthesis of
NaL(thf)2 and NaL9; (ii) X-ray data for 1, 2 and NaL(thf)2. See http://
www.rsc.org/suppdata/cc/b4/b413666g/
…
significant Tl CH3 contacts, while the Tl Tl(1 2 x, 1 2 y, 1 2 z)
…
˚
distance of 4.21 A is well outside any possible bonding
*m.f.lappert@sussex.ac.uk
interaction.
752 | Chem. Commun., 2005, 752–754
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are 89u, 84u and 36u, respectively. The endocyclic bond lengths are
closely similar to those in 1. The most marked differences in
endocyclic bond angles are those centred at the nitrogen atoms,
which are more than 10u wider in 2 than in 1, while the angle at C2
is 3.5u narrower and at C1 or C3 ca. 2u wider than in 1. The
…
…
˚
Tl C20 distance is 3.88 A, which may imply a weak Tl HC
agostic interaction. The bonding in the b-diketiminato ligand of
both 1 and 2 shows significant p-delocalisation.
In summary, we have prepared the first structurally charac-
terised b-diketiminates of thallium: the monomeric, crystalline
complexes Tl[{N(R1)C(R2)}2CR3] (1: R1 5 SiMe3, R2 5 Ph,
R3 5 H; and 2: R1 5 C6H3Pri2-2,6, R2 5 H, R3 5 Ph); they are
potentially useful as convenient precursors for a wider range of
compounds (cf. ref. 13). Compounds 1 and 2 are also noteworthy
in being extremely rare examples of monomeric organic thallium(I)
compounds, and having the low metal coordination number of
two.
˚
Fig. 1 Molecular structure of 1. Selected bond lengths (A) and angles (u):
Tl–N1 2.456(3), Tl–N2 2.449(3), N1–C1 1.330(5), N2–C3 1.314(5), C1–C2
1.408(6), C2–C3 1.416(5), C1–C4 1.513(5), C3–C10 1.502(5), N1–Si1
˚
1.736(3), N2–Si2 1.744(3) A; N1–Tl–N2 78.0(1), Tl–N1–C1 116.5(2), Tl–
We thank the Royal Society for the award of a Sino-British
(Y. C.) and a K. C. Wong (M. Z.) Fellowship, Dr R. Sablong for
providing the data for NaL(thf)2 (Fig. 2) and Drs A. G. Avent and
A. V. Protchenko for useful discussions.
N2–C3 117.0(3), N1–C1–C2 126.6(4), N2–C3–C2 126.3(4), C1–C2–C3
128.5(3)u.
Yanxiang Cheng, Peter B. Hitchcock, Michael F. Lappert* and
Meisu Zhou
Chemistry Department, University of Sussex, Brighton, UK BN1 9QJ.
E-mail: m.f.lappert@sussex.ac.uk
Notes and references
Fig. 2 Molecular structure of crystalline [NaL(thf)2] with selected bond
˚
˚
lengths (A) and angles (u): a 2.358(6), b 1.341(8), c 1.402(7) A; a 87.6(3), b
121.4(4), c 127.5(6), d 134.3(8)u.
{ Synthesis: A solution of NaL (see ESI) (0.68 g, 1.75 mmol) in thf (15 ml)
was added to a suspension of TlCl (0.42 g, 1.75 mmol) in thf (5 ml) at
ambient temperature. The mixture was stirred for ca. 12 h, then filtered.
The filtrate was concentrated and the residue was crystallised from hexane
at 227 uC, yielding orange crystals of 1 (0.82 g, 82%) (Found: C, 44.4; H,
5.08; N, 4.89. C21H29N2Si2Tl requires C, 44.2; H, 5.13; N, 4.91%), mp 123–
125 uC; EI-MS: m/z (%) 571 (MH+, 25), 365 [(M 2 Tl)+, 100]. The orange,
crystalline 2 (80%) (Found: C, 59.3; H, 6.25; N, 4.06. C33H41N2Tl requires
C, 59.2; H, 6.17; N, 4.18%), mp 178–179 uC, [EI-MS: m/z (%) 670 (M+, 59)],
was obtained similarly from NaL9(see ESI) and TlCl.
Crystalline 2 (Fig. 3) is a monomer, but has a nearer
…
neighbouring molecule than 1, the Tl Tl9 distance being
˚
3.76 A." The Tl, C4, C10 and C22 atoms are 20.48, 20.10,
˚
+0.22 and +0.12 A out of the N1C1C2C3N2 plane. The angle
between the latter plane and the C10, C22 and C4 phenyl planes
§ NMR Spectral data (293 K, C6D6, Bruker DPX 300) 1: 1H: d 7.38–7.41
(m, 4 H, Ph), 7.03–7.11 (m, 6 H, Ph), 5.25 (s, 1 H, CH), 0.04 (s, 18 H,
SiMe3); 13C{1H}: d 170.9 (d, 2JCTl 48.4 Hz, C1, C3), 149.1 (d, 3JCTl 46.8 Hz,
(C4, C10)], 127.6–127.9 (3 singlets, Ph), 111.5 (d, 3JCTl 103.3 Hz, C2), 3.48
(d, 3JCTl 138.9 Hz, SiMe3); 29Si{1H}: d 0.9. 2: 1H: d 8.47 (d, 3JHTl 127.3 Hz,
2 H, NCH), 6.8–7.4 (m, 11 H, aromatic H), 3.29 (brs, 4 H, CHMe2), 1.14
[d, 6JHTl 6.9 Hz, 12 H, CH(CH3)2], 1.07 [d, 6JHTl 6.9 Hz, 12 H, CH(CH3)2];
13C{1H}: d 157.6 (C1, C3), 149.3 (br, C10), 143.8 (C4), 141.9 (C11, C15),
[128.7, 126.5, 125.2 (C5, C6, C13)], 124.1 (C7), 123.7 (C12, C14), 28.3 (d,
4JCTl 50 Hz, C16), 24.8 (CH3), 24.6 (d, 5JCTl 66 Hz, CH3) (no signal for C2
observed). The numbering of the carbon atoms corresponds to Figs. 1 (1)
or 3 (2).
" CCDC numbers: 1: 249920; 2: 249921; [NaL(thf)2]: 249922. See http://
www.rsc.org/suppdata/cc/b4/b413666g/ for crystallographic data in .cif or
other electronic format. 1: C21H29N2Si2Tl, M 5 570.01, monoclinic, space
˚
group P21/n (No. 14), a 5 9.9885(2), b 5 19.6876(3), c 5 12.2915(3) A,
3
˚
˚
b 5 107.184(1)u, U 5 2309.2(1) A , Z 5 4, m(Mo-Ka, l 5 0.71073 A) 5
7.11 mm21, T 5 173(2) K, R1 5 0.025 for 3658 (I . 2s(I)) data,
wR2 5 0.067 (all data). 2: C33H41N2Tl, M 5 670.05, triclinic, space group
¯
˚
P1 (No. 2), a 5 9.3632(2), b 5 12.0547(3), c 5 13.6277(3) A, a 5 72.045(1),
˚
3
b 5 84.102(1), c 5 88.813(1)u, U 5 1455.41(6) A , Z 5 2, m(Mo-Ka) 5
5.57 mm21, T 5 173(2) K, R1 5 0.026 for 4919 (I . 2s(I)) data,
wR2 5 0.056 (all data).
˚
Fig. 3 Molecular structure of 2. Selected bond lengths (A) and angles (u):
Tl–N1 2.471(3), Tl–N2 2.423(3), N1–C1 1.311(4), N2–C3 1.309(5), C1–C2
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˚
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