Variation of bonding modes in homoleptic tin(II) 1-azaallyls

Article abstract of DOI:10.1039/a701971h

The homoleptic tin(II) compounds Sn[N(R)C(Bu^t)-C(H)C₆H₃Me₂-2,5] ₂0 1, Sn[N(R)C(Bu^t)C(H)R]₂ 2 and R₂CC(Ph)N(R)Sn[N(R)C(Ph)CR₂] 3 (R = SiMe₃) are p

Full text of DOI:10.1039/a701971h

�
View Article Online / Journal Homepage / Table of Contents for this issue
Variation of bonding modes in homoleptic tin(ii) 1-azaallyls†
Peter B. Hitchcock, Jin Hu, Michael F. Lappert, Marcus Layh and John Severn
The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ
t
1
The homoleptic tin(II) compounds Sn[N(R)C(Bu )-
h -enamido ligands with the free electron pair pointing away
t
from the ligands. The N(1)–Sn–N(1A) angle of 111.2° is only
C(H)C
CC(Ph)N(R)Sn[N(R)C(Ph)CR
prepared and structurally characterised.
6
H
3
Me
2
-2,5]
2
1, Sn[N(R)C(Bu )C(H)R]
2
2
and
) are
slightly larger than in the mononuclear tin(ii) amides
R
2
2
] 3 (R SiMe
=
3
5
6
Sn[N(SiMe
3
)
2
]
2
2 2 3 2 2
(104.7°) or Sn[N(Me) (CH ) CMe ]
(
109.7°). The arrangement of the ligands is such that the
aromatic rings are within the van der Waals range above and
below the Sn atom [Sn–C(2) 3.151, Sn–C(7) 3.188 Å]. A similar
The important series of first-row triatom-centred, monoanionic
ligands [XYZ] include allyl, triazenide and amidinate, with
2
t
7
the carboxylate probably the archetype. Open-chain, structur-
6 4 2 2
interaction has been reported in 1,2-C H [N(CH Bu )] Sn. The
1
ally characterised 1-azaallyl ligands are of recent date. In
enamido character of the 1-azaallyl ligand in 1 is evident from
the short Sn–N(1), long N(1)–C(1) and a short C(1)–C(2)
distance (Table 1), as well as 13C NMR shifts which are
consistent with N(1)–C(1) being a single and C(1)–C(2) a
double bond.
1
2
3
2
[
Li(LLA)]
2
, rac-[Zr(LLA)
2
Cl
2
] and rac-[Yb(LLA) ], the [LLA]
2
3
ligand behaved in an h -chelating bridging (Li) or terminal (Zr,
t
3
Yb) fashion [LLA = N(R)C(Bu )C(H)R, R = SiMe ]. We now
report that the latter reflects on only one possible mode of
1
3
Changing the 2,5-dimethylphenyl group of the h -ligand
terminal 1-azaallyl–metal (M) bonding (MA, h -iminoalkyl),
1
system in 1 by a trimethylsilyl group alters the ligand bonding
while another, MB, represents an h -enamidometal isomer.
3
mode to h . Thus the X-ray structure of 2 (Fig. 2)‡ shows that,
This is illustrated by reference to the three homoleptic
in contrast to 1, C(2) and N(1) are both within bonding range of
the tin atom but compared to 1 the Sn–N(1) distances are longer
1
2
-azaallyltin(ii) complexes, having the structures SnB
and Sn(A)B 3, the variation in structural types being due to
2 2
1, SnA
1
3
(Table 1). The C(1)–C(2) and C(1)–N(1) distances and the
C
changing the substituents on the NCC skeleton:
NMR spectral chemical shifts show iminoalkyl rather than
enamido character, as evident by comparison with
Sn[NC H C(SiMe ) -2]
5 4 3 2 2
.8 It is interesting to note that C(1) is
t
t
Sn[N(R)C(Bu )C(H)C
6
H
3
Me
2
-2,5]
2
1, Sn[N(R)C(Bu )C(H)R]
] 3 (R = SiMe ).
2
2
and R
2
CC(Ph)N(R)Sn[N(R)C(Ph)CR
2
3
bent towards the metal [the angle between the adjacent planes
SnN(1)C(2) and N(1)C(1)C(2) is 37°] leading to a Sn–C(1)
C
N
C
N
C
C
M
C
M
C
M N
distance of 2.729(2) Å. Therefore an alternative description of 2
9
5 5 2
is as a bent sandwich complex similar to Sn(h-C Me ) .
The X-ray structure of crystalline 3‡ shows that introducing
a second trimethylsilyl group at C(2) or C(5) probably increases
the steric demand of the ligand to such an extent that the
bis(chelate) arrangement is no longer viable; thus, an inter-
mediate situation between that of 1 and 2 is observed, wherein
MA
MB
The yellow (1, 2) and orange (3) tin complexes were readily
synthesised (78–84%) from SnCl and 2 equiv. of Li[N(R)C-
2
t
4a
t
(
Bu )C(H)Ar] [obtained
Ar = C Me -2,5], K(LLA), or Li[N(R)C(Ph)CR
pared4b from LiCR
(thf) + PhCN] in diethyl ether or pentane
from LiCH(R)
2
+
Bu CN,
2
1
6
H
3
2
] [pre-
3
1
one ligand is h - and the other is h -coordinated. Table 1 shows
3
2
relevant interatomic distances and NMR spectral chemical
solution at ambient temperature. A single-crystal X-ray diffrac-
tion study‡ shows that 1 (Fig. 1) is coordinated by two
3
shifts. Important differences for the h -coordinated ligand in 3
compared with 2 are a shorter Sn–N(1) and a longer Sn–C(2)
distance in 3 and a much smaller dihedral angle between the
planes N(1)SnC(2) and N(1)C(1)C(2) of only 12.7°. That a
higher coordination number than three in 3 is probably avoided
C(10)
C(8)
by the increased bulk of the ligand (compared with that in 2) is
C(7)
also supported by variable-temperature 1H and 13C NMR
C(9)
C(6)
Si
N(1)
C(4)
Si(2)
C(5)
C(2)
Sn
C(1)
N(1′)
C(3)
C(11)
C(2)
C(1)
N(1′)
Sn
C(3)
C(2′)
N(1)
Si(1)
Fig. 2 Partial molecular structure of 2 (core atoms only) with selected bond
angles (°): N–Sn–NA 146.98(6), N–Sn–C(2) 57.99(6), N–Sn–C(2A) 97.25,
C(2)–Sn–C(2A) 89.44(8)
Fig. 1 Partial molecular structure of 1 (core atoms only)
Chem. Commun., 1997
1189

View Article Online
spectroscopic experiments which show the two ligands to be
Footnotes
equivalent in solution down to 290 °C, indicating that there is
*
†
‡
E-mail: m.f.lappert@sussex.ac.uk
No reprints available.
Crystal data for 1: C34H N Si Sn, M = 667.68, monoclinic, space group
56 2 2
1
a rapid intramolecular exchange between the h - and
3
h -coordinated ligand. Comparing 2 and 3 with 1 it may be that
the preference for the enamido structure in 1 is due to electronic
rather than steric reasons.
C2/c (no. 15), a = 13.006(4), b = 15.957(3), c = 17.735(10) Å, b
= 98.74(3), U = 3638(2) Å , Z = 4, D = 1.22 g cm , F(000) = 1408,
c
3
23
2
1
In conclusion, we believe that the following features (i) and
ii) are particularly noteworthy. (i) Compounds 1–3 serve as a
l(Mo-Ka) = 0.71073 Å, m = 0.79 mm . Data were collected at 293(2)
K on a Enraf-Nonius CAD4 diffractometer in the w–2q mode in the range
(
2
< q < 25°. The structure was solved by direct methods (SHELXS 86) and
2
good example to demonstrate how comparatively small differ-
ences in the backbone of a 1-azaallyl ligand may significantly
influence their metal complex bonding modes. (ii) Enamido–
metal bonding now shown in the tin(ii) complexes 1 and 3 has
only recently been crystallographically established for some
refined by full-matrix least squares on all F (SHELXL 93) with absorption
correction by y-scans. All non-hydrogen atoms were anisotropic, and
hydrogen atoms were included in the riding mode with Uiso(H) = 1.2
U
eq(C) or 1.5 Ueq for Me groups. Final residuals for 3190 independent
reflections were R = 0.057, wR = 0.086 and for the 2442 with I > 2s(I),
R1 = 0.037, wR2 = 0.077.
2: C24 Si Sn, M = 603.8, monoclinic, space group C2/c (no. 15),
a = 11.387(5), b = 16.675(6), c = 18.390(8) Å, b = 106.07(3), U
1
2
alkali-metal 2-methylpyridine or related derivatives,1
Li[NC {C(SiMe
postulated for group 1 and 2 metal complexes, which when
0,11
e.g.
)Ph}-2](tmen); such structures are widely
11
H
5 4
3
H N
56 2
4
3
23
12
= 3355.4 Å , Z = 4, D = 1.20 g cm , F(000) = 1280, l(Mo-
prepared in situ are valuable C–C bond-forming synthons;
there is NMR spectroscopic structural evidence for
c
2
1
Ka) = 0.71073 Å, m = 0.92 mm . 3060 independent reflections were
collected at 173(2) K on a Enraf-Nonius CAD4 diffractometer in the w–2q
mode in the range 2 < q < 25°. The structure was solved by heavy-atom
methods (SHELXS 86) and refined by full-matrix least squares on F (Enraf-
Nonius MolEN) with absorption correction by DIFABS. All non-hydrogen
atoms were anisotropic, and hydrogen atoms were included in the riding
mode with Uiso(H) = 1.2 Ueq(C) or 1.5 Ueq for Me groups. Final residuals
for 2623 reflections [with I > 2s(I)] were R = 0.025, RA = 0.030.
t
n
[
2 3 x n
M{N(H)C(Bu )CHPr }{OP(NMe ) } ] (M = Li, x = 1 or
M = Na, x = 2)1 and [Li{N(Ph)CNCH(CH
3a
2 3 2 x n
) CH } (thf) ]
3b
x = 0, or x = 1 = n).1 The [NC
2
(
5
H
4
C(SiMe
3
)
2
-2] ligand has
1
been found in an h -mode in the homoleptic mercury(ii)
complex, but it is the tautomeric (cf. MB) iminoalkyl ligated
species.14
3
64 2 6 1
: C34H N Si Sn, M = 788.1, monoclinic, space group P2 /c (no. 14),
We thank EPSRC and SPECS-BIOSPECS for the award of a
CASE studentship for J. S., EPSRC for a fellowship for J. H.
and the European Commission for a category 30 HMCR
fellowship for M. L.
a = 19.249(4), b = 12.400(3), c = 19.820(5) Å, b = 112.83(2), U
=
=
refinement were identical to those for 1. Final residuals for 7663
independent reflections were R = 0.096, wR = 0.106 and for the 5008
with I > 2s(I), R = 0.048, wR = 0.088.
Atomic coordinates, bond lengths and angles, and thermal parameters
have been deposited at the Cambridge Crystallographic Data Centre
3
23
4360(2) Å , Z = 4, D
0.77 mm21. Conditions for data collection and
0.71073 Å, m
c
= 1.20 g cm , F(000) = 1664, l(Mo-Ka)
=
1
2
Table 1 Some important structural and NMR spectroscopic data on the
1
2
(1-azaallyl)tin(ii) complexes 1–3
Complex
(CCDC). See Information for Authors, Issue No. 1. Any request to the
CCDC for this material should quote the full literature citation and the
reference number 182/463.
Property
CNa
1
2
3
2
4
—
3
1
b
d(Sn–N, h ) /Å
2.130(3)
—
2.153(4)
2.288(4)
2.775(4)
2.531(5)
1.365(6)
1.461(6)
1.432(5)
1.317(6)
3
b
References
d(Sn–N, h ) /Å
d[Sn–C(1)]/Å
d[Sn–C(2)]/Å
2.510(2)
2.729(2)
2.295(2)
—
1.463(3)
—
(2.791)
(3.151)
1.349(5)
—
1.435(4)
—
1
2
3
P. B. Hitchcock, M. F. Lappert and D.-S. Liu, J. Chem. Soc., Chem.
Commun., 1994, 2637.
P. B. Hitchcock, S. A. Holmes, M. F. Lappert and S. Tian, J. Chem. Soc.,
Chem. Commun., 1994, 2691.
1
b
C–C(h ) /Å
3
b
C–C(h ) /Å
1
b
C–N(h ) /Å
P. B. Hitchcock, M. F. Lappert, D.-S. Liu and E. J. Ryan, Polyhedron,
3
b
C–N(h ) /Å
1.298(3)
1
995, 14, 2745.
1
19
1
d[ Sn{ H}]
61.5
152.6
104.4
2387.2
202.5
50.0
237.3
185.7
100.6
4
5
(a) D.-S. Liu, unpublished work; (b) M. Layh, unpublished work.
T. Fjeldberg, H. Hope, M. F. Lappert, P. P. Power and A. J. Thorne,
J. Chem. Soc., Chem. Commun., 1983, 639.
1
3
1
d[ C{ H}, C(1)]
1
3
1
d[ C{ H}, C(2)]
6
R. W. Chorley, P. B. Hitchcock, M. F. Lappert, W.-P. Leung,
P. P. Power and M. M. Olmstead, Inorg. Chim. Acta, 1992, 198–200,
a
CN = coordination number. b The designations of h and h relate to the
1
3
enamido or chelate mode of the ligand-to-metal bonding, respectively.
2
03.
7
8
H. Braunschweig, B. Gehrhus, P. B. Hitchcock and M. F. Lappert, Z.
Anorg. Allg. Chem., 1995, 621, 1922.
B. S. Jolly, M. F. Lappert, L.M. Engelhardt, A. H. White and
C. L. Raston, J. Chem. Soc., Dalton Trans., 1993, 2653; L. M.
Engelhardt, B. S. Jolly, M. F. Lappert, C. L. Raston and A. H. White,
J. Chem. Soc., Chem. Commun., 1988, 336.
Si(3)
Si(2)
C(2)
9
P. Jutzi, F. Kohl, P. Hofmann, C. Kr u¨ ger and Y.-H. Tsay, Chem. Ber.,
1
980, 113, 757; J. L. Atwood, W. E.Hunter, A. H. Cowley, R. A. Jones
and C. A. Stewart, J. Chem. Soc., Chem. Commun., 1981, 925.
10 U. Pieper and D. Stalke, Organometallics, 1993, 12, 1201.
Sn
C(1)
C(3)
N(1)
C(6)
Si(1)
C(5)
1
1 W.-P. Leung, L.-H. Weng, T.-J. Wang and T. C. W. Mak, Organomet-
allics, 1995, 14, 4832.
2 cf. J. K. Whitesell and M. A. Whitesell, Synthesis, 1983, 517.
13 (a) N. Kallman and D. B. Collum, J. Am. Chem. Soc., 1987, 109, 7466;
(b) P. C. Andrews, D. R. Armstrong, M. MacGregor, R. E. Mulvey and
D. Reed, J. Chem. Soc., Chem. Commun., 1989, 1341.
Si(6)
1
C(4)
N(2)
Si(5)
Si(4)
1
4 M. J. Henderson, R. I. Papasergio, C. L. Raston, A. H. White and
M. F. Lappert, J. Chem. Soc., Chem. Commun., 1986, 672.
Fig. 3 Partial molecular structure of 3 (core atoms only) with selected bond
angles (°): N(1)–Sn–N(2) 109.9(1), N(1)–Sn–C(2) 59.33(1), N(2)–Sn–C(2)
113.2(2), C(4)–N(2)–Si(4) 116.4(3), C(4)–N(2)–Sn 105.0(3), Si(4)–
Received in Basel, Switzerland, 20th March 1997; Com.
7/01971H
N(2)–Sn 137.6(2)
1190
Chem. Commun., 1997