Taking advantage of Hg-C bonds: Synthesis of the first homoleptic bis-β-diketiminate complex bound through the γ-carbons

Article abstract of DOI:10.1021/om100167e

The most common β-diketiminate ligand, [{N(2,6-ⁱPr ₂C₆H₃)C(Me)}₂CH]^- (BDI), was used to synthesize a new mercury complex in which two BDI ligands are bound to the metal through the γ-carbons in the solid state. In solution, one of the BDI ligands switches to an N,N'-binding mode; this complex is in equilibrium with the homoleptic species. The thermodynamic parameters, ΔH° (-2.52 kcal mol^-1), ΔS° (-9.24 cal mol ^-1 K^-1), and ΔG°₂₉₈ (0.23 kcal mol^-1), were measured using variable-temperature ¹H NMR spectroscopy.

Full text of DOI:10.1021/om100167e

Organometallics 2010, 29, 2911–2915 2911
DOI: 10.1021/om100167e
Taking Advantage of Hg-C Bonds: Synthesis of the First Homoleptic
Bis-β-diketiminate Complex Bound through the γ-Carbons
Lorenzo Ferro, Martyn P. Coles, Iain J. Day, and J. Robin Fulton*
Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, U.K.
Received March 2, 2010
The most common β-diketiminate ligand, [{N(2,6-iPr2C6H3)C(Me)}2CH]- (BDI), was used to
synthesize a new mercury complex in which two BDI ligands are bound to the metal through the
γ-carbons in the solid state. In solution, one of the BDI ligands switches to an N,N0-binding mode;
this complex is in equilibrium with the homoleptic species. The thermodynamic parameters, ΔH°
(-2.52 kcal mol-1), ΔS° (-9.24 cal mol-1 K-1), and ΔG°298 (0.23 kcal mol-1), were measured using
variable-temperature 1H NMR spectroscopy.
The β-diketiminate ligand has seen an explosion in popu-
larity over the past decade.1 It has been deemed a “Cp”
replacement due to its monoanionic nature and the wide
range of easily accessible variants along the β-diketiminate
backbone (R1, R2, R3, R4, and R5; Figure 1), thus influenc-
ing both the steric and electronic nature of the ligand. Two
common nicknames for this ligand class are found: (R1)2-
nacnac, which generally refers to the ligand in which R3 = H,
R2, R4 = Me,2 and R1 = R5, and BDI, which generally refers
to the most popular β-diketiminate ligand, [{N(2,6-iPr2C6H3)-
C(Me)}2CH]-.3,4 The β-diketiminate ligand has a remark-
able ability to stabilize low-valent complexes in some rather
unusual oxidation states. For instance, Jones and co-workers
were able to reduce BDI-MgI to a Mg(I) dimer complex that
possesses a Mg-Mg bond.5 Holland and co-workers utilized
this ligand to synthesize a rare three-coordinate transition-
metal dinitrogen complex, as well as 12-electron complexes
of iron(II).6,7 Hill took advantage of the steric variants along
the β-diketiminate backbone and generated a series of In(I)
complexes ranging from a mononuclear complex when a
bulky N-aryl substituent was used (BDI), a dimer when
methyl groups were placed in the 2-, 4-, and 6-positions of the
N-aryl substituent (R1 and R5), to a hexaindium chain when
methyl groups were placed in the least obstrusive 3- and
5-positions of the N-aryl substituent (R1 and R5).8
Figure 1. Basic skeleton of the β-diketiminate ligand.
By far the most widely used β-diketiminate ligand is [{N-
(2,6-iPr2C6H3)C(Me)}2CH]- (BDIorDipp2nacnac),9 withover
700 crystal structures reported in the Cambridge Structural
Database. With regard to group 12 metals, only the Zn and
Cd complexes of this ligand are known.10-13 Layh and co-
workers have synthesized a β-diketiminate-Hg complex
(L1HgCl) in which the N-aryl substituent (R1 and R5)
possesses tBu groups in the 2- and 5-positions: R2, R4 =
SiMe3 and R3 = H. In this system, the β-diketiminate ligand
is bound through the γ-carbon.14 Attempts to place more
than one β-diketiminate ligand on Hg were not successful.
Lappert and co-workers synthesized a sila-β-diketiminate
ligand, [{N(2,6-iPr2C6H3)C(Me)}2Si(SiMe3)]- (L2), in which
the methine (CH) group is replaced with a Si(SiMe3).15 The
researchers were able to generate a (L2)2Hg complex via a
disproportionation reaction with Hg2Cl2 and Li-L.2 Similar
to the case for L1HgCl, both ligands were bound to the metal
center via the Si backbone.
*To whom correspondence should be addressed, E-mail: j.r.fulton@
sussex.ac.uk.
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031.
(2) Kim, W. K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541.
(3) Aboulkacem, S.; Tyrra, W.; Pantenburg, I. Z. Anorg. Allg. Chem.
2003, 629, 1569.
(4) This abbreviation has also been used to encompass a variety of
different varieties of β-diketiminate ligands; for instance, see: Dove,
A. P.; Gibson, V. C.; Marshall, E. L.; Rzepa, H. S.; White, A. J. P.;
Williams, D. J. J. Am. Chem. Soc. 2006, 128, 9834.
(5) Green, S. P.; Jones, C.; Stasch, A. Science 2007, 318, 1754.
(6) Smith, J. M.; Lachicotte, R. J.; Pittard, K. A.; Cundari, T. R.;
Lukat-Rodgers, G.; Rodgers, K. R.; Holland, P. L. J. Am. Chem. Soc.
2001, 123, 9222.
(9) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(10) Prust, J.; Stasch, A.; Zheng, W. J.; Roesky, H. W.; Alexopoulos,
E.; Uson, I.; Bohler, D.; Schuchardt, T. Organometallics 2001, 20, 3825.
(11) Prust, J.; Most, K.; Muller, I.; Stasch, A.; Roesky, H. W.; Uson,
I. Eur. J. Inorg. Chem. 2001, 1613.
(12) Chisholm, M. H.; Gallucci, J.; Phomphrai, K. Inorg. Chem.
2002, 41, 2785.
(13) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738.
(14) Fernandes, M. A.; Layh, M.; Omondi, B. In Trends in Organo-
metallic Chemistry Research; Cato, M. A., Ed.; Gazelle Book Services:
Lancaster, U.K., 2005; p 107.
(7) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Organometallics
2002, 21, 4808.
(8) Hill, M. S.; Hitchcock, P. B.; Pongtavornpinyo, R. Science 2006,
311, 1904.
(15) Farwell, J. D.; Fernandes, M. A.; Hitchcock, P. B.; Lappert,
M. F.; Layh, M.; Omondi, B. Dalton Trans. 2003, 1719.
r
2010 American Chemical Society
Published on Web 06/15/2010
pubs.acs.org/Organometallics

2912 Organometallics, Vol. 29, No. 13, 2010
Ferro et al.
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for
Compound 1
Hg-C(2)
2.128(3)
1.500(4)
1.501(4)
1.505(4)
1.510(4)
C(1)-N(1)
N(1)-C(6)
C(3)-N(2)
N(2)-C(18)
1.277(3)
1.428(3)
1.272(3)
1.430(3)
C(2)-C(1)
C(2)-C(3)
C(1)-C(4)
C(3)-C(5)
C(2)-Hg-C(2)0
Hg-C(2)-C(1)
Hg-C(2)-C(3)
C(1)-C(2)-C(3)
C(2)-C(1)-N(1)
C(1)-N(1)-C(6)
180.00(10)
107.75(18)
109.81(18)
114.2(2)
118.2(2)
120.2(2)
C(2)-C(1)-C(4)
N(1)-C(1)-C(4)
C(2)-C(3)-N(2)
C(3)-N(2)-C(18)
C(2)-C(3)-C(5)
N(2)-C(3)-C(5)
115.6(2)
126.1(3)
119.0(2)
122.2(2)
115.9(2)
125.0(3)
Table 2. Crystallographic Data for Compound 1a
chem formula
formula wt
temp (K)
C58H82HgN4 0.33CH2Cl2
3
1064.03
173(2)
˚
wavelength (A)
0.710 73
0.19 ꢀ 0.16 ꢀ 0.16
cryst size (mm3)
cryst syst
Figure 2. ORTEP diagram of the dialkylmercury species 1 with
ellipsoids at the 30% probability level. H atoms, except for H2,
are omitted for clarity. Atoms marked with a prime (0) are at
equivalent positions (-x, -y, -z).
trigonal
R3 (No. 148)
space group
˚
a (A)
33.4216(10)
33.4216(10)
12.6432(3)
90
90
120
12 230.4(6)
9
1.37
2.97
3.47-26.72
17 578/5739, 0.047
5104
5739/0/288
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
We have recently synthesized a series of BDI lead aryl-
oxides and alkoxides. The latter complexes show facile re-
activity toward heterocumulenes such as carbon dioxide but
only sluggish reactivity toward aliphatic electrophiles such as
methyl iodide.16-18 As this is in sharp contrast to the re-
activity of late-transition-metal alkoxides,19 we wanted to
explore the other divalent heavy-metal terminal alkoxides in
order to ascertain any reactivity trends. Thus, our attention
turned to mercury and an attempted synthesis of the BDI-
HgCl complex as a precursor to terminal mercury alkoxide
and amido complexes. Addition of LiNiPr2 to BDI-H,
followed by treatment with a suspension of HgCl2 (0.5 equiv)
results in the formation of colorless crystals in 34% yield
(eq 1).20 Crystals suitable for an X-ray diffraction study were
grownbyslowlycoolingasaturatedCH2Cl2 solution (Figure 2).
The molecule lies on an inversion center with the BDI ligand
bound through the γ-carbon, or the “backbone” of the BDI
ligand. Selected bond lengths and angles are shown in Table
1, and data collection parameters are given in Table 2.
Although there are a handful of examples of other C-bound
β-diketiminate ligands,14,21-23 including BDI complexes,9,24-26
this is the first crystallographically characterized compound in
which two β-diketiminate ligands are C-bound to a single metal
3
˚
V (A )
Z
Fc (Mg m-3
)
abs coeff (mm-1
)
θ range for data collecn (deg)
no. of measd/indep rflns, R(int)
no. of rflns with I >2σ(I)
no. of data/restraints/params
goodness of fit on F2
1.032
final R indices (I>2σ(I))
R indices (all data)
largest diff peak and hole (e A
R1 = 0.033, wR2 = 0.060
R1 = 0.042, wR2 = 0.062
0.60 and -0.50
-3
˚
)
a This molecule sits on an inversion center. The unit cell contains
poorly defined CH2Cl2 disordered about a special position which has
been treated as a diffuse contribution to the overall scattering without
specific atom positions by SQUEEZE/PLATON.
center. Although the geometry of the ligands around Hg is
linear, the ligands are in a staggered conformation to each
other, which is similar to the case for the sila analogue.15 The
˚
Hg-C bond length of 2.127(3) A is significantly shorter than
that reported for L HgCl (2.337(2) A) but similar to other
1
˚
dialkylmercury complexes.27,28 The C-C bond lengths of
2
3
˚
1.500(5)-1.501(4) A are similar to those of other sp -sp
(16) Chen, M.; Fulton, J. R.; Hitchcock, P. B.; Johnstone, N. C.;
Lappert, M. F.; Protchenko, A. V. Dalton Trans. 2007, 2770.
(17) Fulton, J. R.; Hitchcock, P. B.; Johnstone, N. C.; Tam, E. C. Y.
Dalton Trans. 2007, 3360.
(18) Tam, E. C. Y.; Johnstone, N. C.; Ferro, L.; Hitchcock, P. B.;
Fulton, J. R. Inorg. Chem. 2009, 48, 8971.
(19) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc.
Chem. Res. 2002, 35, 44.
(20) Simple salt metathesis between lithiated β-diketiminate (BDI-Li)
and HgCl2 resulted in the formation of an intractable mixture of
products; when LiN(TMS)2 was used instead of LiNiPr2, the only
isolated BDI-containing product was BDI-Li.
C-C single bonds.29 A long-range intramolecular nitrogen-
mercury interaction is observed, with a Hg N2 distance of
˚
2.994 A, slightly shorter than their combined van der Waals
3 3 3
˚
radii of 3.10 A. This type of interaction is observed with both
Layh’s mercury complex L1HgCl as well as Lappert’s bis-sila-
β-diketiminate mercury complex (L2)2Hg.14,15
(21) Hadzovic, A.; Janetzko, J.; Song, D. T. Dalton Trans. 2008, 3279.
(22) Kajiwara, T.; Murao, R.; Ito, T. J. Chem. Soc., Dalton Trans.
1997, 2537.
(23) Hadzovic, A.; Song, D. Organometallics 2008, 27, 1290.
(24) Prust, J.; Hohmeister, H.; Stasch, A.; Roesky, H. W.; Magull, J.;
Alexopoulos, E.; Uson, I.; Schmidt, H. G.; Noltemeyer, M. Eur. J. Inorg.
Chem. 2002, 2156.
(25) Tian, X.; Goddard, R.; Porschke, K. R. Organometallics 2006,
25, 5854.
(26) Rake, A.;Zulch, F.;Ding, Y.;Prust, J.;Roesky, H. W.;Noltemeyer,
(27) Grirrane, A.; Resa, I.; del Rio, D.; Rodriguez, A.; Alvarez, E.;
Mereiter, K.; Carmona, E. Inorg. Chem. 2007, 46, 4667.
(28) Matkoviccalogovic, D. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1987, 43, 1473.
M.; Schmidt, H. G. Z. Anorg. Allg. Chem. 2001, 627, 836.
(29) Lide, D. R. Tetrahedron 1962, 17, 125.

Article
Organometallics, Vol. 29, No. 13, 2010 2913
Figure 3. Variable-temperature 1H NMR spectra of 1 and 2 in CD2Cl2.
1
The room-temperature H NMR spectrum of 1 reveals
the expected magnitude of the coupling constant, no
mercury-proton or mercury-carbon coupling could be
observed at either temperature. The solid-state IR spec-
trum (Nujol) revealed three strong bands at 1648, 1624,
and 1589 cm-1; although these bands are similar to those
for other β-diimine compounds,15,32 these data are not
conclusive for either isomer, as N,N0-bound β-diketiminate
complexes have a wide range of stretching frequencies in
the same region.16,18,26 The solution-phase IR spectrum was
equally inconclusive.
the presence of two different compounds in a 3:2 ratio. The
major compound can be assigned to the dialkyl species,
with a γ-CH resonance at δ 3.98 ppm, similar to that
1
reported for L1HgCl. The one-bond H-13C correlation
experiment showed correlation between this proton and a
carbon found at δ 77.7 ppm. The resonances correspond-
ing to the minor compound are reminiscent of an N,N0-
bound β-diketiminate ligand, with a backbone γ-CH
resonance at δ 4.75 ppm. Integrating in an approximately
1:1 ratio with this resonance is a peak at δ 3.71 ppm. The
1H-13C HSQC experiment revealed that the former pro-
ton correlates with a carbon at δ 96.2 ppm, which is in the
same range as for other N,N0-bound β-diketiminate
compounds,12,18,30 and the latter proton correlates with
a carbon at δ 66.7 ppm, a chemical shift similar to that of
the major isomer. No proton-mercury (1H-199Hg) or
carbon-mercury (13C-199Hg) coupling was observed.
The 199Hg{1H} NMR spectrum shows a single resonance
at both room temperature (-990 ppm) and -60 °C (-1086
ppm). The corresponding resonance line widths at half-
height are 144 and 236 Hz, respectively (the data were
processed with 75 Hz exponential line broadening prior to
Fourier transformation). The observed broad line width
can be attributed to the close proximity of the (broad)
resonances for the two species (1 and 2), leading to the
appearance of a single signal, as well as fast relaxation
caused by the chemical shift anisotropy of the 199Hg.31 The
latter contribution can be confirmed by the observation
that the 199Hg line width at half-height is ∼30% larger at
14.1 T than at 9.4 T (190 Hz, with identical processing
parameters). As the line width for this system is larger than
These data are consistent with an equilibrium mixture of
two different mercury species in solution: the major isomer
in which both β-diketiminate ligands are bound through the
γ-carbon (1) and a minor isomer that is still bound to two
different β-diketiminate ligands, but one ligand is bound
through the N-substituents and the other is bound through
the γ-carbon (2; eq 2). Variable-temperature 1H NMR
spectroscopy revealed that 2 is favored at lower tempera-
tures (Figure 3). From these data, we were able to calculate
ΔH° (-2.52 ( 0.06 kcal mol-1), ΔS° (-9.24 ( 0.21 cal
mol-1 K-1), and ΔG°298 (0.23 ( 0.09 kcal mol-1) for the
interconversion between the two isomers. This equilibria is
similar to a bis(2,2,6,6-tetramethylheptane-3,5-dione)-Hg
complex in which an equilibrium is established between a
dialkylmercury species and a mercury complex that is
bound to one ligand through the γ-carbon and the other
ligand through an oxygen atom.33 Interestingly, the re-
searchers were only able to observe proton-mercury cou-
pling at -40 °C; however, a lower field NMR spectrometer
was used, thus significantly decreasing the line width con-
tributions of relaxation due to chemical shift anisotropy.
(32) Carey, D. T.; Cope-Eatough, E. K.; Vilaplana-Mafe, E.; Mair,
F. S.; Pritchard, R. G.; Warren, J. E.; Woods, R. J. Dalton Trans. 2003,
(30) Dove, A. P.; Gibson, V. C.; Marshall, E. L.; Rzepa, H. S.; White,
A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2006, 128, 9834.
(31) Levitt, M. H. Spin Dynamics: Basics of Nuclear Magnetic
Resonance, 2nd ed.; WileyBlackwell: 2008.
1083.
(33) Allmann, R.; Musso, H.; Flatau, K. Chem. Ber. 1972, 105,
3067.

2914 Organometallics, Vol. 29, No. 13, 2010
Ferro et al.
The thermodynamic parameters were not reported for this
latter system.
DFT was also used to calculate the ground-state energies
for compounds 1 and 2. From these data, we were able to
calculate ΔH° (-2.52 ( 0.06 kcal mol-1), ΔS° (-9.24 ( 0.21
cal mol-1 K-1), and ΔG°298 (0.23 ( 0.09 kcal mol-1) for the
interconversion between the two isomers. Because of the low
level of theory applied, the calculated ΔH° value (0.60 kcal
mol-1) was higher than our measured value and the magni-
tude of the calculated ΔS° value (-14 cal mol-1 K-1) was
greater (although still negative). Due to these discrepancies,
the ΔG°298 value (4.9 kcal mol-1) was significantly higher
than our experimental results. However, we were able to
utilize these calculations in order to predict 1H NMR
chemical shifts, and reassuringly, γ-CH for isomer 1 was
calculated to resonate at δ 4.21 ppm, whereas the Hg-bound
γ-CH of isomer 2 was calculated to resonate at δ 3.72 ppm
and γ-CH of the N,N0-bound β-diketiminate ligand of
isomer 2 was calculated to resonate at δ 4.48 ppm.
Isolated crystals of compound 1 are relatively air stable,
but this compound undergoes thermal decomposition
after 48 h at room temperature in solution. Attempts at
selectively protonating one of the BDI ligands to form
mercury alkoxide or sulfide complexes were not success-
ful. Addition of isopropyl alcohol to 1 led to an intractable
mixture of products. Treatment of 1 with 4-methylbenze-
nethiol gave BDI-H as the only BDI-containing com-
pound.
1
The variable-temperature H NMR spectroscopy experi-
ment also revealed that compound 2 exhibits fluxional
behavior on the NMR time scale. At 60 °C, three different
resonances corresponding to the isopropyl methine reso-
nances of 2 are observed at δ 3.33, 2.91, and 2.49 ppm
integrating to four, two, and two protons each, respectively.
The downfield resonance is from the N,N0-bound ligand, and
the upfield resonances are from the γ-bound ligand of 2. At
-60 °C, the isopropyl methine resonance on the N,N0-bound
ligand of 2 appears as two separate broad resonances, indi-
cating two different environments for the four isopropyl
methine protons of this N,N0-bound ligand. This is presum-
ably due to the asymmetry with respect to the γ-bound
ligand. At this lower temperature, the bulkiness of the N-aryl
groups of both ligands prevent facile rotation around the
Hg-C bond. Thus, one aryl group of the N,N0-bound ligand
is closer to the methine proton of the γ-carbon of the γ-
bound ligand than the other aryl group. Using density
functional theory (DFT), we calculated an optimized geo-
metry for compound 2 (Figure 4), which supports this
hypothesis. From these variable-temperature studies, the
ΔGq value for Hg-C bond rotation was determined to be
11 kcal mol-1. Interestingly, the isopropyl methine protons
for the γ-bound ligand of 2 appear as septets above 0 °C
and as broad resonances at -30 °C and are not observed at
-60 °C. Due to the decreasing solubility of 1 and 2, we were
unable to obtain a reliable 1H NMR spectrum below -60 °C
to determine the fate of these disappearing signals at lower
temperatures. However, it can be assumed that there is
further loss of symmetry of the γ-bound ligand due to
restricted rotation around the N-aryl bond; as such, we
would expect four individual signals for each of the isopropyl
methine protons for the γ-bound ligand at temperatures
below -60 °C. Interestingly, only two resonances corre-
sponding to the back-bone methyl groups (N-C(Me)-C-
C(Me)-N) are observed for compound 2, even at -60 °C.
Although the aliphatic and aromatic regions of the 1H NMR
spectrum varied with temperature, due to the overlapping
signals, we were unable to gain any further information from
this data.
Experimental Section
All manipulations were carried out under an atmosphere of
dry nitrogen or argon using standard Schlenk techniques or in
an inert-atmosphere glovebox. Solvents were dried from the
appropriate drying agent, distilled, degassed, and stored over 4
1
A sieves. The H, 13C, and 199Hg NMR spectra were recorded on
˚
a Varian 400 MHz spectrometer or a Varian 600 MHz spectro-
meter. Both spectrometers were equipped with X{1H} broad-
band-observe probes. The 1H and 13C NMR chemical shifts are
given relative to residual solvent peaks, and the 199Hg chemical
shifts were determined from the deuterium lock signal and
quoted relative to HgMe2 at 0 ppm.34 The 1H-13C HSQC and
1H-13C HMBC spectra were recorded using the Varian Chem-
Pack 4.1 sequences gHSQCAD and gHMBCAD. The data for
the X-ray structure were collected at 173 K on a Nonius Kappa
˚
CCD diffractometer (λ(Mo KR) = 0.710 73 A) and refined
using the SHELXL-97 software package.35
[CH{(CH3)2CN-2,6-iPr2C6H3}2]Hg (1). Lithium diisopropyl-
amide (1.20 mmol, 2 M in THF) was added dropwise to a
toluene solution of BDI-H (500 mg, 1.20 mmol). The red
solution was stirred for 30 min, cooled to -78 °C, and added
dropwise to a stirred suspension of HgCl2 (163 mg, 0.60 mmol)
in toluene at -78 °C. This mixture was stirred overnight and
slowly warmed to room temperature. The resulting gray suspen-
sion was filtered through Celite, and the volatiles were evacu-
ated, producing a pale green precipitate that was washed several
times with pentane to afford a white powder in 34% yield (0.24
mol, 213 mg). Colorless crystals suitable for X-ray diffraction
were grown from a concentrated DCM solution stored in an
ethylene glycol bath at 8 °C for 3 days and -12 °C for 1 week. 1H
NMR (399 MHz, CDCl3, 303 K): δ 6.93-7.17 (m, 6H, ArCH),
4.75 (s, 1H, γ-CH), 3.98 (s, 1H, γ-CH), 3.71 (s, 1H, γ-CH), 3.33
(sept, J = 6.4 Hz, 4H, CHMe2), 2.97 (sept, J = 6.8 Hz, 2H,
CHMe2), 2.91 (m, 2H, CHMe2), 2.81 (sept, J = 6.9 Hz, 2H,
(34) Harris, R. K.; Becker, E. D.; De Menezes, S. M. C.; Goodfellow,
R.; Granger, P. Pure Appl. Chem. 2001, 73, 1795.
(35) Sheldrick, G. M. In SHELXL-97, Program for the Refinement of
€ €
Crystal Structures; University of Gottingen, Gottingen, Germany, 1997.
Figure 4. Optimized geometry of 2.

Article
Organometallics, Vol. 29, No. 13, 2010 2915
CHMe2), 2.49 (sept, J = 6.7 Hz, 2H, CHMe2), 1.85 (s, 6H,
NCMe),1.72 (s, 6H, NCMe), 1.51 (s, 6H, NCMe), 1.18 (d, J =
6.8 Hz, 12H, CHMe), 1.14 (d, J = 6.9 Hz, 12H, CHMe), 1.11 (d,
J = 6.8 Hz, 6H, CHMe), 1.10 (d, J = 6.8 Hz, 12H, CHMe), 1.06
(d, J = 6.8 Hz, 6H, CHMe), δ 0.98 (d, J = 6.8 Hz, 12H, CHMe),
0.89 (d, J = 6.7 Hz, 6H, CHMe), 0.85 (d, J = 6.9 Hz, 6H,
CHMe). 13C{1H} NMR (100 MHz, CDCl3): δ 171.38 (NCMe),
169.97 (NCMe), 164.34 (NCMe), 146.46 (o-C), 141.48 (o-C),
137.03 (ipso-C), 136.46 (ipso-C), 123.50 (ArC), 123.21 (ArC),
122.99 (ArC), 122.89 (ArC), 122.76 (ArC), 122.63 (ArC), 121.92
Key Chemical Shifts for 2. N,N0-bound ligand: 1H NMR (399
MHz, CDCl3, 303 K) δ 4.75 (s, 1H, γ-CH), 3.33 (sept, J = 6.4 Hz,
4H, CHMe2), 1.72 (s, 6H, NCMe), 1.18 (d, J = 6.8 Hz, 12H,
CHMe), 1.14 (d, J = 6.9 Hz, 12H, CHMe);13C{1H} NMR (100
MHz, CDCl3) 164.34 (NCMe), (ipso-C), 141.48 (o-C), 141.26 (o-C),
96.23 (γ-C), 27.78 (CHMe), 27.69 (CHMe), 25.32 (NCMe), 24.48
(CHMe). γ-bound ligand: 1H NMR (399 MHz, CDCl3, 303 K) δ
3.71 (s, 1H, γ-CH), 2.91 (m, 2H, CHMe2), 2.49 (sept, J = 6.7 Hz,
2H, CHMe2), 1.51 (s, 6H, NCMe), 0.98 (d, J = 6.8 Hz, 12H,
CHMe), 0.89 (d, J = 6.7 Hz, 6H, CHMe), 0.85 (d, J = 6.9 Hz, 6H,
CHMe); 13C{1H} NMR (399 MHz, CDCl3) δ 169.97 (NCMe),
137.03 (ipso-C), 66.69 (γ-C), 28.21 (CHMe), 28.51 (CHMe), 23.75
(CHMe), 23.20 (CHMe), 22.49 (CHMe), 21.40 (NCMe).
Computational Details. All calculations were performed using
the density function theory in the Gaussian 03 program. The
geometry optimization was performed at the B3LYP level by
using a double-ζ basis set (LanL2DZ) along with the effective
core potential (LanL2ECP) for the Hg atom and the 3-21G basis
set for all other atoms. Zero-point vibrational energy correc-
tions were also included.36,37 1H NMR spectra were estimated
with the gauge invariant atomic orbital DFT (GIAO-DFT)
calculations at the B3LYP/LanL2DZ/3-21G level.
(
ArC), 96.23 (γ-C), 77.72 (γ-C), 66.69 (γ-C), 28.51 (CHMe),
28.51 (CHMe), 28.21 (CHMe), 27.78 (CHMe), 27.69 (CHMe),
25.32 (NCMe), 24.48 (CHMe), 23.75 (CHMe), 23.20 (CHMe),
22.97 (CHMe), 22.49 (CHMe), 21.91 (NCMe), 21.40 (NCMe).
199Hg NMR (71.5 MHz, CDCl3, 303 K): δ -989.7. IR (Nujol,
cm-1): 3050, 1921, 1866, 1806, 1720, 1648 (s), 1624 (s), 1589 (s),
1439 (s), 1358 (s),1328 (s), 1245, 1207 (s), 1188 (s), 1163 (s), 1107,
1068, 1059, 1042, 972, 936, 916, 789 (s), 760 (s), 690, 523. IR
(CCl4, cm-1): 3061 (w), 2963, 2869, 2990 (br), 2004 (br), 1856
(br), 1635, 1549 (br, s), 1461, 1436, 1409, 1382, 1363, 1322, 1253
(s), 1216 (s), 1165 (w). Anal. Calcd: C, 67.25; H, 7.98; N, 5.41.
Found: C, 67.16; H, 8.07; N, 5.39.
Key Chemical Shifts for 1. 1H NMR (399 MHz, CDCl3, 303
K): δ 3.98 (s, 1H, γ-CH), 2.97 (sept, J = 6.8 Hz, 2H, CHMe2),
2.81 (sept, J = 6.9 Hz, 2H, CHMe2), 1.85 (s, 6H, NCMe), 1.11
(d, J = 6.8 Hz, 6H, CHMe), 1.10 (d, J = 6.8 Hz, 12H, CHMe),
0.8 (d, J = 6.8 Hz, 6H, CHMe). 13C{1H} NMR (100 MHz,
CDCl3): δ 171.38 (NCMe), 146.46 (o-C), 136.46 (ipso-C), 77.72
(γ -C), 28.51 (CHMe), 23.20 (CHMe), 22.97 (CHMe), 21.91
(NCMe).
Acknowledgment. We are grateful for financial sup-
port from the EPSRC (LF, Grant No. EP/E032575/1).
Supporting Information Available: Figures giving a van’t Hoff
plot of the equilibria between 1 and 2, variable-temperature 1H
NMR spectra showing resonances between δ 8 and 0 ppm, and
1H-13C gHSQCAD and 1H-13C gHMBCAD spectra, a table
giving Cartesian coordinates of the optimized structures of
1 and 2, text giving the complete ref 31, and a CIF file giving
crystallographic data for complex 1. This material is available
free of charge via the Internet at http://pubs.acs.org.
(36) Frisch, M. J. et al. In Gaussian 03, Revision E.01; Gaussian, Inc.,
Wallingford, CT, 2004.
(37) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.