Synthesis and structural characterisation of divalent transition metal complexes containing an unsymmetrical benzamidinate ligand

Article abstract of DOI:10.1039/b303527a

The unsymmetrical benzamidinate ligand [PhC(NSiMe₃)(NAr)] ^- (Ar = 2,6-Me₂C₆H₃), denoted L ^-, and its lithium derivative [LiL(TMEDA)] (1) (TMEDA = N,N,N′,N′-tetramethylethylenediamine) have

Full text of DOI:10.1039/b303527a

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Synthesis and structural characterisation of divalent transition metal
complexes containing an unsymmetrical benzamidinate ligandy
Hung Kay Lee,* Tung Suet Lam, Chi-Keung Lam, Hung-Wing Li and Sze Man Fung
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong SAR, P. R. China. E-mail: hklee@cuhk.edu.hk; Fax: +852-2603-5057;
Tel: +852-2609-6331
Received (in Montpellier, France) 28th March 2003, Accepted 28th April 2003
First published as an Advance Article on the web 21st July 2003
The unsymmetrical benzamidinate ligand [PhC(NSiMe3)(NAr)]ꢀ (Ar ¼ 2,6-Me2C6H3), denoted Lꢀ, and
its lithium derivative [LiL(TMEDA)] (1) (TMEDA ¼ N,N,N0,N0-tetramethylethylenediamine) have been
prepared. Treatment of 1 with MCl2 (M ¼ Mn, Co, Fe or Ni) afforded the corresponding divalent transition
metal benzamidinates with interesting molecular structures. The reaction of two equivalents of 1 with MnCl2
or CoCl2 afforded the centrosymmetric binuclear complexes [(ML2)2ꢁ(TMEDA)] (M ¼ Mn 2, Co 5). On the
other hand, the reaction of FeCl2 with 1, in an appropriate stoichiometric ratio, led to the mononuclear
mono(benzamidinate) [FeL(Cl)(TMEDA)] (3) and the bis(benzamidinate) [FeL2(TMEDA)] (4) complexes.
The addition of two equivalents of 1 to NiCl2 yielded the mononuclear [NiL2] (6). X-Ray crystallography
revealed that the k2-benzamidinate ligand Lꢀ is bonded to the metal centre of these complexes in an
unsymmetrical fashion. The TMEDA ligand in 2–5 exhibits different coordination modes. It acts as a
chelating ligand in 3, as a monodentate ligand in 4, and as an unusual N,N0-bridging ligand in 2 and 5.
mononuclear Ni(II) derivative [NiL2] (6). Common to these
Introduction
complexes is the k2 coordination of the benzamidinate ligand
Lꢀ. The TMEDA ligand in 2–5 shows different coordina-
tion behaviour, namely as a chelating ligand in 3, a monodentate
ligand in 4 and a rare N,N0-bridging ligand in 2 and 5.
Over the past decades, considerable research efforts have been
devoted to the development of various ancillary ligands as
alternatives to cyclopentadienyl ligands in organometallic
chemistry. Accordingly, the studies of alkoxy, amido and ami-
dinato ligands have attracted much interest. Amidinate ligands
of the type [RC(NR0)2]ꢀ (R, R0 ¼ H, alkyl, aryl or SiMe3)
have proven to be versatile in supporting a wide range of main
group, transition metal, and f element compounds.1–20 They
offer a greater potential in ligand design (and thus a modifica-
tion of the reactivities of their corresponding metal complexes)
over the Cp ligands by virtue of their different steric and elec-
tronic properties due to the different substituents R and R0.
Although the chemistry of early transition metal amidinates
is well-developed, that of low-valent late transition metal deri-
vatives has received relatively less attention.1,2,4,5,12,13e,13i,14,18–20
Currently, we are interested in the chemistry of metal
complexes supported by sterically demanding amido21–23 and
amidinato ligands.23,24 By treating the lithium anilide [Li-
{N(SiMe3)(Ar)}(TMEDA)]25 (Ar ¼ 2,6-Me2C6H3 ; TMEDA ¼
N,N,N0,N0-tetramethylethylenediamine) with benzonitrile, we
have successfully isolated the lithium benzamidinate [Li{PhC-
(NSiMe3)(NAr)}(TMEDA)]. The new unsymmetrical ligand
has been shown to be versatile in supporting a number of main
group and transition metal complexes with intriguing mole-
cular structures.23,24 Herein we report the preparation and
molecular structures of a series of divalent transition metal
benzamidinate complexes derived from [PhC(NSiMe3)-
(NAr)]ꢀ (Lꢀ) namely the binuclear Mn(II) and Co(II) benzami-
dinates [(ML2)2ꢁ(TMEDA)] (M ¼ Mn 2, Co 5), the mononuclear
Fe(II) benzamidinate chloride [FeL(Cl)(TMEDA)] (3) and
the Fe(II) bis(benzamidinate) [FeL2(TMEDA)] (4), and the
Experimental
General procedures
All reactions were carried out under a purified nitrogen atmo-
sphere using modified Schlenk techniques. Solvents were dried
over and distilled from calcium hydride (hexane) or sodium
benzophenone (diethyl ether, THF, and toluene), and degassed
twice by freeze-thaw cycles before use. Anhydrous metal(II)
chlorides were purchased from Aldrich and used as received.
Benzonitrile was dried over and distilled from phosphorus
pentoxide. The lithium anilide [Li{N(SiMe3)(Ar)}(TMEDA)]
was prepared according to published procedures.25
1H and 13C{1H} NMR spectra were recorded on a Bruker
DPX 300 spectrometer. Chemical shifts were referenced to
residual solvent protons at d ¼ 7.15 for C6D6 . EI mass spectra
were taken from solid state samples using a ThermoFinnigan
MAT 95 XL mass spectrometer. Melting points were recorded
on an Electrothermal melting point apparatus and are uncor-
rected. Elemental analyses were performed by MEDAC Ltd.,
Brunel University, UK. Magnetic moments were measured in
benzene solutions at 300 K by the Evans method26 using a
JEOL 60 MHz NMR spectrometer. Cyclic voltammetry was
carried out by using a BAS CV-50W Voltammetric Analyzer.
The electrochemical cell used in our studies consisted of a pla-
tinum ball working electrode, a silver wire reference electrode,
and a platinum foil auxiliary electrode. All sample solutions
were prepared in CH2Cl2 with (Bun4N)(PF6) (0.15 M) as the
supporting electrolyte. Chemical potentials were internally
referenced to the FeCp2+/FeCp2 redox couple.
y Electronic supplementary information (ESI) available: inclination
angles in complexes 1–6. See http://www.rsc.org/suppdata/nj/b3/
b303527a//
1310
New J. Chem., 2003, 27, 1310–1318
DOI: 10.1039/b303527a
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2003

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Syntheses
stirring at room temperature for 12 h, a blue solution with
a grey precipitate was obtained. The solution was filtered
through celite and then concentrated to ca. 3 mL. Allowing
the solution to stand at ambient temperature for one day gave
compound 5 as dark blue crystals (1.95 g, 1.38 mmol, 56%).
The compound was washed with hexane three times and dried
in vacuo, mp 69–71 ꢂC, meff ¼ 3.40 mB per Co atom. EI-MS (70
eV): m/z (%) 648 (12) [CoL2]+, 633 (10) [CoL2 ꢀ Me]+, 351 (6)
[CoL]+, 296 (96) [L]+. Anal. found: C, 66.75; H, 7.71; N,
9.38%; calcd for C78H108Co2N10Si4 : C, 66.16; H, 7.69; N,
9.89%.
[LiL(TMEDA)] (1). To a solution of C6H5CN (1.5 mL, 14.7
mmol) in diethyl ether (30 mL) at 0 ꢂC was slowly added a
yellow solution of [Li{N(SiMe3)(Ar)}(TMEDA)] (4.63 g, 14.7
mmol) in diethyl ether (20 mL). The reaction mixture was stir-
red at room temperature for 12 h to give an orange solution,
which was filtered through celite and then concentrated to
ca. 10 mL under reduced pressure. Crystallisation at ambient
temperature afforded compound 1 as colourless crystals. The
product was washed with hexane and dried in vacuo (4.56 g,
10.9 mmol, 74%), mp 116–118 ꢂC. 1H NMR (300.13 MHz,
C6D6): d 7.36–7.38 (m, 2 H, C6H3Me2), 6.98–7.04 (m, 4 H,
C6H5), 6.87–6.92 (m, 1 H, C6H5), 6.77 (t, J ¼ 7.5 Hz, 1 H,
C6H3Me2), 2.39 (s, 6 H, C6H3Me2), 1.99 (s, 12 H, NMe2),
1.77 (s, 4 H, NCH2), 0.12 (s, 9 H, SiMe3). 13C{1H} NMR
(75.47 MHz, C6D6): d 173.6, 151.6, 144.2, 130.8, 127.2,
126.8, 126.7, 122.1, 120.8, 56.6, 45.6, 19.9, 3.48. EI-MS (70
eV): m/z (%) 296 (22) [L]+, 281 (11) [L ꢀ Me]+, 208 (8)
[L ꢀ NSiMe3]+, 176 (33) [L ꢀ NAr]+, 73 (71) [SiMe3]+. Anal.
found: C, 69.10; H, 9.48; N, 13.51%; calcd for C24H39N4LiSi:
C, 68.86; H, 9.39; N, 13.38%.
[NiL2] (6). To a slurry of NiCl2 (0.42 g, 3.24 mmol) in diethyl
ether (20 mL) at 0 ꢂC was added dropwise a solution of 1 (2.71
g, 6.48 mmol) in diethyl ether (10 mL). The reaction mixture
was warmed slowly to room temperature and stirred for 12 h.
All the volatiles were removed under reduced pressure and the
residue was extracted with toluene (30 mL) and then filtered
through celite. The filtrate was concentrated to ca. 3 mL. Com-
pound 6 was obtained as purple crystals after allowing the
solution to stand at ambient temperature (1.46 g, 2.24 mmol,
69%). The product was washed three times with hexane and
dried in vacuo, mp 193–195 ꢂC (dec.). 1H NMR (300.13
MHz, C6D6): d 7.57–7.53 (m, 10 H, C6H3Me2 and C6H5),
7.18–7.16 (m, 6 H, C6H3Me2), 3.29 (s, 12 H, C6H3Me2), 0.23
(s, 18 H, SiMe3). 13C{1H} NMR (75.47 MHz, C6D6): d
143.2, 137.9, 135.0, 130.1, 128.5, 128.0, 127.6, 125.2, 20.4,
2.3. EI-MS (70 eV): m/z (%) 649 (6) [M]+, 354 (3) [NiL]+,
296 (100) [L]+, 281 (62) [L ꢀ Me]+. Anal. found: C, 65.94; H,
7.11; N, 8.73%; calcd for C36H46N4NiSi2 : C, 66.56; H, 7.14;
N, 8.62%.
.
[(MnL2)2 (TMEDA)] (2). To a stirred suspension of MnCl2
(0.21 g, 1.67 mmol) in diethyl ether (20 mL) at 0 ꢂC was slowly
added a solution of [LiL(TMEDA)] (1) (1.41 g, 3.37 mmol) in
diethyl ether (10 mL). The reaction mixture was stirred at
room temperature for 12 h. All the volatiles were removed
under reduced pressure and the residue was extracted with
toluene (30 mL). The extract was concentrated to ca. 8 mL
to afford the title compound as colourless crystals (0.72 g,
0.51 mmol, 61%), mp 158–160 ꢂC (dec.), meff ¼ 3.59 mB per
Mn atom. EI-MS (70 eV): m/z (%) 644 (12) [MnL2]+, 629
(10) [MnL2 ꢀ Me]+, 351 (6) [MnL]+, 296 (95) [L]+. Anal.
X-Ray crystallography
found: C, 67.37; H, 7.76; N, 9.45%; calcd for C78H108
Mn2N10Si4 : C, 66.54; H, 7.73; N, 9.95%.
-
Single-crystals of complexes 1–6 suitable for crystallographic
studies were mounted in glass capillaries and sealed under
nitrogen. Details of crystal parameters, data collection and
structural refinement are summarised in Table 1. Data were
collected on a Bruker SMART CCD diffractometer at 293 K
using graphite-monochromated Mo–Ka radiation (l ¼
[FeL(Cl)(TMEDA)] (3). A slurry of FeCl2 (0.34 g, 2.68
mmol) in diethyl ether (10 mL) was cooled to ꢀ78 ꢂC. To this
was added dropwise a solution of 1 (1.12 g, 2.68 mmol) in the
same solvent (20 mL). After stirring at ꢀ78 ꢂC for 20 min, the
solution was allowed to warm slowly to room temperature and
stirred for a further period of 12 h. All the volatiles were then
removed in vacuo and the residue was extracted with toluene
(30 mL). The yellowish-brown solution was filtered and then
concentrated to ca. 3 mL. Allowing the solution to stand at
ambient temperature for one day gave compound 3 as yellow
crystals (0.78 g, 1.55 mmol, 58%). The product was washed
three times with hexane and dried in vacuo, mp 100–102 ꢂC
(dec.), meff ¼ 5.13 mB . EI-MS (70 eV): m/z (%) 296 (50) [L]+,
281 (40) [L ꢀ Me]+, 224 (84) [L ꢀ SiMe3]+, 207 (96) [L ꢀ
NSiMe3]+. Anal. found: C, 56.75; H, 7.83; N, 11.28%; calcd
for C24H39FeN4SiCl: C, 57.31; H, 7.81; N, 11.13%.
˚
0.71073 A). The structures were solved by direct phase deter-
mination using the computer program SHELX-97 on an
IBM compatible personal computer and refined by full-matrix
least-squares methods with anisotropic thermal parameters for
the non-hydrogen atoms.27 Hydrogen atoms were introduced
in their idealised positions and included in structure factor
calculations with assigned isotropic temperature factors.28
CCDC reference numbers 192352–55 and 207044–45. See
http://www.rsc.org/suppdata/nj/b3/b303527a/ for crystallo-
graphic files in CIF or other electronic format.
Results and discussion
Syntheses
[FeL2(TMEDA)] (4). To a suspension of FeCl2 (0.44 g, 3.47
mmol) in diethyl ether (20 mL) at 0 ꢂC was added dropwise a
solution of 1 (2.91 g, 6.94 mmol) in the same solvent (10 mL).
The reaction mixture was stirred at room temperature for 12 h
to afford an olive-green solution. The solution was filtered and
concentrated to ca. 3 mL to give the title compound as yellow
crystals (1.85 g, 2.43 mmol, 70%). The product was washed
three times with hexane and dried in vacuo, mp 118–120 ꢂC
(dec.), meff ¼ 4.96 mB . EI-MS (70 eV): m/z (%) 646 (18)
[FeL2]+, 631 (19) [FeL2 ꢀ Me]+, 296 (98) [L]+. Anal. found:
C, 65.61; H, 8.29; N, 11.19%; calcd for C42H62FeN4Si2 : C,
66.11; H, 8.19; N, 11.01%.
The lithium reagent [LiL(TMEDA)] (1) is easily accessible via
the reaction of [Li{N(SiMe3)(Ar)}(TMEDA)] (Ar ¼ 2,6-Me2-
C6H3) with benzonitrile in diethyl ether. The lithium anilide
[Li{N(SiMe3)(Ar)}(TMEDA)] was prepared according to a
modified literature procedure.25 As shown in Scheme 1, lithia-
tion of 2,6-dimethylaniline with LiBun in diethyl ether, followed
by quenching of the resulting solution with one equivalent of
trimethylsilyl chloride, gave the silylated aniline [HN(SiMe3)-
(Ar)]. Subsequent lithiation of [HN(SiMe3)(Ar)] with LiBun,
in the presence of TMEDA, gave the corresponding lithium
anilide [Li{N(SiMe3)(Ar)}(TMEDA)]. Reaction of the lithium
anilide with one equivalent of benzonitrile afforded the
lithium benzamidinate 1 as colourless crystals in 74% yield.
The reaction of [Li{N(SiMe3)(Ar)}(TMEDA)] with benzoni-
.
[(CoL2)2 (TMEDA)] (5). A solution of 1 (2.06 g, 4.92 mmol)
in diethyl ether (10 mL) was added slowly to a slurry of CoCl2
(0.32 g, 2.46 mmol) in diethyl ether (20 mL) at 0 ꢂC. Upon
trile involves
a direct insertion of the amido ligand
New J. Chem., 2003, 27, 1310–1318
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Table 1 Crystallographic data for complexes 1–6
1
2ꢁC6H5CH3
3
4
5
6
Molecular formula
Molecular weight
Crystal system
Space group
C24H39LiN4Si
418.62
C78H108Mn2N10Si4ꢁC7H8 C24H39ClFeN4Si C42H62FeN6Si2 C78H108Co2N10Si4 C36H46N4NiSi2
1500.12
Monoclinic
502.98
Triclinic
763.01
Monoclinic
1415.96
Triclinic
649.66
Triclinic
Monoclinic
P21/n (No. 14) C2/c (No. 15)
¯
P1 (No. 2)
¯
P21/n (No. 14) P1 (No. 2)
¯
P1 (No. 2)
˚
a/A
8.2152(8)
25.198(2)
13.140(1)
90
32.691(5)
13.883(2)
20.286(3)
90
7.9613(8)
10.053(1)
18.026(2)
92.056(2)
98.285(2)
101.881(2)
2
10.414(4)
18.633(7)
23.860(9)
90
10.9563(9)
11.6745(9)
17.633(1)
108.250(2)
104.354(2)
95.475(2)
1
12.3641(9)
12.4981(9)
14.485(1)
97.980(1)
109.071(2)
114.916(1)
2
˚
b/A
˚
c/A
a/ꢂ
b/ꢂ
g/ꢂ
Z
93.696(2)
90
106.162(4)
90
93.964(8)
90
4
4
4
3
˚
U/A
2714.5(4)
18 162
8843(2)
29 380
10 738
4078
1393.9(2)
9892
6618
4619(3)
26 108
11 011
5889
2038.1(3)
13 501
9622
1816.0(2)
12 250
8591
Reflections collected
Unique data measured 6527
Obs. data [I ꢃ 2s(I)]
R1 [I ꢃ 2s(I)]a
wR2 [I ꢃ 2s(I)]a
R1 (all data)a
wR2(all data)a
Rint
2794
3894
6064
0.0465
6473
0.0404
0.0478
0.1213
0.1258
0.1496
0.0503
0.0530
0.1206
0.1635
0.1511
0.0808
0.0424
0.0923
0.0853
0.1083
0.0225
0.0503
0.1340
0.1026
0.1540
0.0379
0.1172
0.0802
0.1161
0.0560
0.1312
0.0215
0.1241
0.0134
a
R1 ¼ S | |Fo| ꢀ |Fc| |/S |Fo|; wR2 ¼ {S [w(F2o ꢀ Fc2)2]/S [w(Fo2)2]}1/2
[N(SiMe3)(Ar)]ꢀ into the –C N functionality, followed by a
1,3-silyl migration.
Whilst complexes 2–5 are paramagnetic species (vide infra), the
nickel derivative 6 is a diamagnetic compound. The 1H and 13
=
=
C
The transition metal derivatives 2–6 were readily prepared
by treating 1 with the corresponding metal dichloride in the
appropriate stoichiometric ratio (Scheme 2). The binuclear
Mn(II) and Co(II) benzamidinate complexes [(ML2)2ꢁ
(TMEDA)] (M ¼ Mn 2, Co 5), isolated as colourless and dark
blue crystals, respectively, were synthesised by treating the
appropriate metal dichloride with two equivalents of 1 in
diethyl ether. In contrast, an analogous reaction of NiCl2 with
1 gave the mononuclear [NiL2] (6) as purple crystals. For the
Fe(II) derivatives, treatment of anhydrous FeCl2 with one
molar equivalent of 1 in diethyl ether at ꢀ78 ꢂC yielded the
mono(benzamidinate) complex [FeL(Cl)(TMEDA)] (3),
whereas the addition of two equivalents of 1 to FeCl2 at 0 ꢂC
followed by stirring at room temperature for 12 h gave the
bis(benzamidinate) derivative [FeL2(TMEDA)] (4). Both com-
plexes 3 and 4 were isolated as yellow crystals. It is noteworthy
that mono(amidinate) complexes of transition metals are rare.
Complex 3 may be considered as an intermediate compound
during the course of reaction to the corresponding bis(benz-
amidinate) 4. Thus, the preparation of 3 requires a strict and
proper control of reaction stoichiometry and conditions.
Complexes 2–6 were isolated as highly air-sensitive com-
pounds. They are readily soluble in diethyl ether, THF and
toluene, but only sparingly soluble in saturated hydrocarbons.
NMR spectra of 6 elicit one single set of signals, which are
assignable to a pair of equivalent Lꢀ ligands. No paramagnetic
shifts were observed in the NMR spectra, suggesting that the
compound adopts a diamagnetic 16-electron configuration
with a pseudo-square-planar geometry in solution.
It is believed that the TMEDA ligand provides coordination
saturation to the metal centres, which contributes to the stabi-
lity of the present complexes 2–5. Interestingly, the TMEDA
ligand shows three different coordination modes in these com-
plexes: it acts as a bidentate N,N0-chelating ligand in 3, a
monodentate ligand in 4, and an unusual N,N0-bridging ligand
in 2 and 5. In general, the coordination number of a metal
complex is determined by the bulky nature of the supporting
ligands around the metal centre. An increase in steric encum-
brance around a metal centre generally results in a lowering
of its coordination number. Since complex 3 is sterically less
crowded (as compared to 2, 4 and 5), the TMEDA ligand
can coordinate to its metal centre in the commonly observed
N,N0-chelating fashion. On the other hand, the presence of
an additional benzamidinate ligand around each metal centre
in 2, 4 and 5 prohibits the TMEDA from binding in a chelating
mode. The unusual N,N0-bridging TMEDA ligand in com-
plexes 2 and 5 is noteworthy. A few examples of this unusual
coordination mode of TMEDA have been reported for some
main group metal hydrides, alkyls, and amides,29 but are rarely
observed in transition metal chemistry.30 Recently, we have
reported a binuclear cobalt(II) amido compound that contains
an unusual bridging TMEDA ligand.22c
X-Ray crystal structures
Crystals of complexes 1–6 suitable for X-ray diffraction studies
were obtained from toluene. The molecular structures of 1–6
with the atom numbering schemes are depicted in Figs. 1–6,
respectively. Selected bond distances and angles of the com-
pounds are listed in Tables 2–7.
The crystal structures of 1–6 reveal that each Lꢀ ligand is
bonded to the metal centre as a bidentate, four-electron donor
ligand. This leads to the formation of a highly strained four-
member M–N–C–N metallacycle. The bonding parameters
within each benzamidinate ligand are normal. The amidinate
N–C–N backbone consists of almost identical N–C distances
Scheme 1
1312
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Scheme 2
(see Tables 2–7), which are close to the average value of the
the central carbon atom of the N–C–N moiety [1.492(3)–
˚
1.512(3) A], as well as the C–N distances between the Ar
˚
substituent and the Namidinate atom [1.414(2)–1.434(4) A]
are typical for Csp2–Csp2 and Csp2–Nsp2 single bond distances,
˚
˚
=
observed N C [1.302(7) A] and N–C [1.360(8) A] bonds
reported for other amidines.31 The Ph and Ar substituents of
the Lꢀ ligand are not co-planar with the plane of the N–C–N
motif (see Table S1 in the electronic supplementary informa-
tiony). Moreover, the C–C distances between the Ph ring and
Fig. 2 Molecular structure of the centrosymmetric [(MnL2)2ꢁ
(TMEDA)]ꢁC7H8 (2ꢁC7H8) (30% thermal ellipsoids) with the atomic
labelling scheme. The solvated toluene molecule is omitted for clarity.
Fig. 1 Molecular structure of [LiL(TMEDA)] (1) (30% thermal
ellipsoids) with the atomic labelling scheme.
New J. Chem., 2003, 27, 1310–1318
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Fig. 5 Molecular structure of the centrosymmetric [(CoL2)2ꢁ
(TMEDA)] (5) (30% thermal ellipsoids) with the atomic labelling
scheme.
Fig. 3 Molecular structure of [FeL(Cl)(TMEDA)] (3) (30% thermal
ellipsoids) with the atomic labelling scheme.
respectively. All of these observations exclude the possibility
of any conjugation between the amidinato N–C–N moiety
and the Ph or Ar substituents. The observed Si–Namidinate
Apparently, the more electron-withdrawing Ar substituent
may force the negative charge on Lꢀ to locate mainly on the
N atom bearing the Ar ring and, hence, a shorter M–N(Ar)
distance may result. However, the almost identical C–N dis-
tances of the N–C–N moiety in each of the present complexes
(see Tables 2–7) suggest that the electronic effect may not
be the dominating factor in determining the unsymmetrical
coordination mode of the Lꢀ ligand in these complexes.
The Li–Namidinate distances are comparable to those of
˚
distances in 1–6, ranging from 1.695(2)–1.741(1) A, are com-
parable to those reported for other silylamido systems.32
The lithium benzamidinate 1. Compound 1 crystallises in a
monoclinic crystal system with space group P21/n. The mono-
nuclear compound consists of a lithium cation bound by an
k2-benzamidinate anion and a chelating TMEDA ligand,
resulting in a distorted tetrahedral environment around the
metal centre. The unsymmetrical nature of the Lꢀ ligand leads
to a slightly unsymmetrical coordination of Lꢀ to the lithium
centre, as evidenced by the slightly different Li–Namidinate dis-
31
˚
2.023 A (ave.) reported for [Li{PhC(NPh)2}(TMEDA)] and
(ave.) for, [Li{(2,6-(p-ButC6H4)2C6H3)C(NPri)2}-
˚
1.997
A
(TMEDA)]13h but slightly shorter than those of 2.076(6)–
31
˚
2.188(6) A in the monomeric [Li{PhC(NPh)2}(PMEDTA)]
˚
and 2.144
A
(ave.) in the dimeric [Li{(p-MeC6H4)C-
tances of 2.009(3) and 2.032(3) A in 1. In addition to its inher-
(NSiMe3)2}(THF)2]2 .33 The Li–Namidinate distances in 1 are
˚
˚
similar to the Li–N distances of 1.98(3)–2.03(3) A reported
ently unsymmetrical nature, the unsymmetrical binding of the
Lꢀ ligand to the metal centre in 1 (and also in 2–6, vide infra)
may also be related to the steric and electronic properties of
the SiMe3 and Ar substituents attached to the amidinato nitro-
gens (Chart 1). Since the SiMe3 group is sterically more
demanding than the Ar substituent, the M–N(SiMe3) bonds
are longer as compared to the M–N(Ar) distances. In addition
to steric considerations, an electronic effect is also expected to
exert a substantial influence on the M–N bond distances.
for the isoelectronic lithium guanidinate [Li{(NC6H11)2-
C[N(SiMe3)2]}]2 .34
The transition metal derivatives 2–6. The mononuclear com-
plex [FeL(Cl)(TMEDA)] (3) crystallises in the triclinic
¯
space group P1, whilst the bis(benzamidinate) derivative
Fig. 4 Molecular structure of [FeL2(TMEDA)] (4) (30% thermal
ellipsoids) with the atomic labelling scheme. Disorder of the uncoordi-
nated NMe2 group of the TMEDA ligand is not shown for clarity.
Fig. 6 Molecular structure of the centrosymmetric [NiL2] (6) (30%
thermal ellipsoids) with the atomic labelling scheme.
1314
New J. Chem., 2003, 27, 1310–1318

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ꢂ
Selected bond distances (A) and angles (ꢂ) for [LiL-
Table 4 Selected bond distances (A) and angles ( ) for [FeL(Cl)-
(TMEDA)] (3)
˚
˚
Table
(TMEDA)] (1)
2
Li(1)–N(1)
Li(1)–N(3)
2.032(3)
2.112(4)
2.348(4)
1.328(2)
1.414(2)
68.5(1)
Li(1)–N(2)
Li(1)–N(4)
2.009(3)
2.102(4)
1.323(2)
1.505(3)
1.695(2)
87.3(1)
Fe(1)–N(1)
Fe(1)–N(3)
2.083(2)
2.297(2)
2.2766(8)
1.325(3)
1.428(3)
61.87(7)
120.92(6)
125.83(8)
116.0(2)
122.5(2)
123.8(2)
87.0(1)
Fe(1)–N(2)
Fe(1)–N(4)
2.260(2)
2.204(2)
1.314(3)
1.512(3)
1.722(2)
78.58(9)
112.74(7)
153.54(9)
121.5(2)
95.1(1)
Li(1)–Cl(1)
N(2)–C(1)
N(1)–C(8)
N(1)–C(1)
C(1)–C(2)
Si(1)–N(2)
Fe(1)–Cl(1)
N(2)–C(1)
N(1)–C(8)
N(1)–C(1)
C(1)–C(2)
Si(1)–N(2)
N(1)–Li(1)–N(2)
N(1)–Li(1)–N(3)
N(2)–Li(1)–N(3)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(1)–C(8)
C(1)–N(2)–Li(1)
Si(1)–N(2)–Li(1)
N(3)–Li(1)–N(4)
N(1)–Li(1)–N(4)
N(2)–Li(1)–N(4)
N(1)–C(1)–C(2)
C(1)–N(1)–Li(1)
C(8)–N(1)–Li(1)
C(1)–N(2)–Si(1)
N(1)–Fe(1)–N(2)
N(1)–Fe(1)–Cl(1)
N(1)–Fe(1)–N(4)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(1)–C(8)
C(1)–N(2)–Fe(1)
Si(1)–N(2)–Fe(1)
N(3)–Fe(1)–N(4)
N(4)–Fe(1)–Cl(1)
N(2)–Fe(1)–N(3)
N(1)–C(1)–C(2)
C(1)–N(1)–Fe(1)
C(8)–N(1)–Fe(1)
C(1)–N(2)–Si(1)
129.8(2)
118.9(2)
118.2(2)
120.5(2)
122.3(2)
86.9(1)
127.6(2)
130.4(2)
121.3(2)
86.1(1)
151.2(2)
133.0(1)
141.1(2)
130.2(2)
140.1(1)
139.9(1)
˚
[FeL2(TMEDA)] (4) crystallises in the monoclinic space group
P21/n. Both complexes display a distorted trigonal bipyrami-
dal geometry. Complex 3 consists of a chloride ligand, a biden-
tate benzamidinate and a N,N0-chelating TMEDA. The
chlorine atom Cl(1), the benzamidinate nitrogen N(1) and
the amino nitrogen N(4) of the TMEDA constitute the trigo-
nal plane (sum of bond angles around the Fe centre ¼ 359.5ꢂ),
ꢂ), whereas the nitrogen atoms N(2) and N(3) occupy the axial
positions with N(2)–Fe(1)–N(3) ¼ 153.54(9)ꢂ. For the bis(ben-
zamidinate) complex 4, the Fe centre is chelated by two benza-
midinate ligands and a monodentate TMEDA. Disorder of
the uncoordinated NMe2 terminus of the TMEDA ligand
was observed (not shown in Fig. 3). The equatorial plane of
the trigonal bipyramidal structure is composed of the benzami-
dinate nitrogens N(1), N(3) and the amino nitrogen N(5) from
the TMEDA (sum of bond angles around the Fe centre ¼
360.0ꢂ). The axial positions are occupied by nitrogens N(2)
and N(4) with N(2)–Fe(1)–N(4) ¼ 159.76(8)ꢂ. Deviation of
the N(2)–Fe(1)–N(3) angle in 3 and the corresponding N(2)–
Fe(1)–N(4) angle in 4 from linearity may be ascribed to the
small bite of the Lꢀ ligand.
reported for [Fe{FcC(NCy)2}2ꢁ0.25Et2O]13e and 2.020
A
(ave.) for [Fe{ButC(NCy)2}2].20 They are also longer than
˚
those of 1.997(8)–2.109(9) A reported for the Fe(III) compound
[Fe{PhC(NSiMe3)2}2Cl].5b
The centrosymmetric binuclear complexes [(ML2)2ꢁ
(TMEDA)] (2 and 5) are isostructural. The Mn(II) derivative,
which crystallises in the monoclinic space group C2/c, was
obtained in a solvated form with co-crystallised toluene in a
molar ratio of 1:1, whereas no solvent of crystallisation was
observed for the Co(II) derivative 5, which crystallises in the
¯
triclinic space group P1. Each M(II) centre in the two com-
plexes is bound by a pair of k2-benzamidinate ligands, forming
a {MN4} moiety. Coordination by one amino nitrogen of the
TMEDA ligand completes a distorted trigonal bipyramidal
configuration around the metal centre. It is noteworthy that
the TMEDA ligand in 2 and 5 links two {MN4} moieties
together by coordinating in an unusual N,N0-bridging mode.
Similarly, the benzamidinate ligand Lꢀ coordinates to the
M(II) centre of 2 and 5 in an unsymmetrical manner, leading
to the unsymmetrical M–Namidinate bond lengths of 2.177(3)–
˚
˚
2.223(3) A in 2 and 2.016(1)–2.246(1) A in 5. The Mn–Namidinate
distances in 2 are comparable to the corresponding distances of
The observed Fe–Namidinate distances, which range from
4
2.186(4)–2.219(4) A for [Mn{PhC6H4C(NSiMe3)2}2], 2.177(2)–
˚
˚
˚
2.083(2)–2.260(2) A in 3 and 2.095(2)–2.240(2) A in 4, reveal
that Lꢀ binds unsymmetrically to the Fe(II) centre, with the
Fe–N(SiMe3) distances being longer than the Fe–N(Ar) dis-
tances. The N atom attached to the SiMe3 group occupies
the axial position, whilst the one bearing the Ar ring occupies
the equatorial position. The Fe–Namidinate distances of 3 and 4
18
2.348(2) A for [Mn{HC(NCy)2}2(TMEDA)], and 2.155(2)–
˚
˚
2.188(2) A for the terminal amidinate ligands of the dimeric
[Mn{HC(NCy)2}{m-HC(NCy)2}]2 .18 However, theyare slightly
˚
longer than those of 2.075(7)–2.096(7)A for the sterically
congested. [Mn{(2,6-Mes2C6H3)C(NPri)2}2].13i The observed
Co–Namidinate distances in 5 are only marginally longer than
˚
are longer than the corresponding distances of 2.037 A (ave.)
ꢂ
ꢂ
˚
˚
Table 3 Selected bond distances (A) and angles ( ) for [(MnL2)2ꢁ
Table 5 Selected bond distances (A) and angles ( ) for [FeL2-
(TMEDA)] (4)
(TMEDA)]ꢁC6H5CH3 (2ꢁC6H5CH3)
Mn(1)–N(1)
Mn(1)–N(3)
2.184(3)
2.177(3)
2.303(3)
1.336(4)
1.434(4)
1.341(4)
1.496(4)
1.716(3)
61.58(9)
135.9(1)
108.4(1)
115.6(3)
122.1(3)
122.4(3)
90.4(2)
Mn(1)–N(2)
Mn(1)–N(4)
N(1)–C(1)
C(1)–C(2)
2.223(3)
2.211(2)
1.329(4)
1.496(4)
1.728(3)
1.333(4)
1.426(4)
Fe(1)–N(1)
Fe(1)–N(3)
2.095(2)
2.109(2)
2.181(2)
1.330(3)
1.434(3)
1.330(3)
1.495(3)
1.728(2)
62.46(8)
128.20(9)
114.74(9)
115.5(2)
122.9(2)
124.5(2)
87.8(2)
Fe(1)–N(2)
Fe(1)–N(4)
N(1)–C(1)
C(1)–C(2)
N(2)–Si(1)
N(4)–C(21)
N(3)–C(28)
2.240(2)
2.211(2)
1.331(3)
1.497(4)
1.727(2)
1.331(3)
1.440(3)
Mn(1)–N(5)
N(2)–C(1)
Fe(1)–N(5)
N(2)–C(1)
N(1)–C(8)
N(3)–C(21)
N(2)–Si(1)
N(4)–C(21)
N(3)–C(28)
N(1)–C(8)
N(3)–C(21)
C(21)–C(22)
N(4)–Si(2)
C(21)–C(22)
N(4)–Si(2)
N(1)–Mn(1)–N(2)
N(1)–Mn(1)–N(3)
N(3)–Mn(1)–N(5)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(1)–C(8)
C(1)–N(2)–Mn(1)
Si(1)–N(2)–Mn(1)
N(3)–C(21)–C(22)
C(21)–N(3)–Mn(1)
C(28)–N(3)–Mn(1)
C(21)–N(4)–Si(2)
N(3)–Mn(1)–N(4)
N(1)–Mn(1)–N(5)
N(2)–Mn(1)–N(4)
N(1)–C(1)–C(2)
61.97(9)
115.8(1)
162.1(1)
122.2(3)
92.3(2)
N(1)–Fe(1)–N(2)
N(1)–Fe(1)–N(3)
N(3)–Fe(1)–N(5)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(1)–C(8)
C(1)–N(2)–Fe(1)
Si(1)–N(2)–Fe(1)
N(3)–C(21)–C(22)
C(21)–N(3)–Fe(1)
C(28)–N(3)–Fe(1)
C(21)–N(4)–Si(2)
N(3)–Fe(1)–N(4)
N(1)–Fe(1)–N(5)
N(2)–Fe(1)–N(4)
N(1)–C(1)–C(2)
C(1)–N(1)–Fe(1)
C(8)–N(1)–Fe(1)
C(1)–N(2)–Si(1)
N(3)–C(21)–N(4)
N(4)–C(21)–C(22)
C(21)–N(3)–C(28)
C(21)–N(4)–Fe(1)
Si(2)–N(4)–Fe(1)
62.51(8)
117.06(9)
159.76(8)
121.6(2)
94.1(2)
C(1)–N(1)–Mn(1)
C(8)–N(1)–Mn(1)
C(1)–N(2)–Si(1)
N(3)–C(21)–N(4)
N(4)–C(21)–C(22)
C(21)–N(3)–C(28)
C(21)–N(4)–Mn(1)
Si(2)–N(4)–Mn(1)
144.5(2)
130.4(2)
115.3(3)
123.7(3)
122.3(3)
90.6(2)
141.4(2)
131.1(2)
114.9(2)
122.5(2)
123.2(2)
88.9(2)
138.6(2)
121.0(3)
91.9(2)
139.2(1)
122.5(2)
93.5(2)
145.4(2)
130.8(2)
143.2(2)
130.3(2)
136.6(2)
140.5(1)
New J. Chem., 2003, 27, 1310–1318
1315

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ꢂ
˚
Table 6 Selected bond distances (A) and angles ( ) for [(CoL2)2ꢁ
(TMEDA)] (5)
Co(1)–N(1)
Co(1)–N(3)
2.029(2)
2.016(2)
2.159(2)
1.324(3)
1.424(3)
1.329(3)
1.500(3)
1.722(2)
62.96(7)
125.32(8)
113.26(7)
115.4(2)
122.5(2)
123.9(2)
86.1(1)
Co(1)–N(2)
Co(1)–N(4)
N(1)–C(1)
C(1)–C(2)
N(2)–Si(1)
N(4)–C(21)
N(3)–C(28)
2.246(2)
2.198(2)
1.327(3)
1.504(3)
1.725(2)
1.318(3)
1.428(3)
Co(1)–N(5)
N(2)–C(1)
N(1)–C(8)
N(3)–C(21)
Chart 1
C(21)–C(22)
N(4)–Si(2)
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(3)
N(3)–Co(1)–N(5)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(1)–C(8)
C(1)–N(2)–Co(1)
Si(1)–N(2)–Co(1)
N(3)–C(21)–C(22)
C(21)–N(3)–Co(1)
C(28)–N(3)–Co(1)
C(21)–N(4)–Si(2)
N(3)–Co(1)–N(4)
N(1)–Co(1)–N(5)
N(2)–Co(1)–N(4)
N(1)–C(1)–C(2)
C(1)–N(1)–Co(1)
C(8)–N(1)–Co(1)
C(1)–N(2)–Si(1)
N(3)–C(21)–N(4)
N(4)–C(21)–C(22)
C(21)–N(3)–C(28)
C(21)–N(4)–Co(1)
Si(2)–N(4)–Co(1)
63.66(7)
121.41(7)
163.76(7)
122.2(2)
95.5(1)
peaks associated with the mononuclear [ML2]+ unit (m/
z ¼ 644 for 2, 649 for 5). For the mononuclear [FeL(Cl)(T-
MEDA)] (3), no molecular ion peak was observed, only the
fragmentation pattern due to the Lꢀ ligand. The mass spec-
trum of [FeL2(TMEDA)] (4) showed signals associated with
the [FeL2]+ species (m/z ¼ 646) as well as its fragments. The
Ni(II) derivative 6 is the only compound in the series that
showed its molecular ion peak at m/z ¼ 649 in its mass
spectrum.
140.6(2)
130.3(2)
114.6(2)
123.3(2)
123.9(2)
86.8(1)
141.9(1)
121.9(2)
94.4(1)
The magnetic moments of complexes 2–5 in benzene solu-
tions at 300 K have been measured by the Evans NMR
method.26 The magnetic moment of 3.59 mB per Mn(II) ion
for the binuclear complex 2 is much lower than the spin-only
value expected for a high-spin d5 electronic configuration.
Although a variable temperature magnetic susceptibility mea-
surement for this compound is not available, it appears that
a plausible mechanism for a Mnꢁ ꢁ ꢁMn interaction may not
be present in the compound. This may be supported by the
solution magnetic moment of 3.40 mB per Co(II) ion for the
analogous binuclear Co(II) derivative 5, which suggests a
high-spin d7 electronic configuration with three unpaired elec-
trons for each Co(II) ion. On the basis of this information, the
observed magnetic moment for each Mn(II) ion in 2 may be
141.6(2)
134.4(2)
137.7(1)
˚
those of 2.006(4)–2.020(4) A reported for [Co{FcC(NCy)2}2ꢁ
Et2O],13e and slightly longer than those of 1.973(4)–1.993(3)
A in [Co{(2,6-Mes2C6H3)C(NPr )2}2].
The mononuclear Ni(II) derivative 6 crystallises in the tricli-
i
13i
˚
¯
nic space group P1. As shown in Fig. 6, the complex consists
of an almost square-planar Ni(II) centre bound by a pair of
trans-chelating Lꢀ ligands. This is in contrast with the closely
related [Ni{PhC(NSiMe3)2}2]2,15c and the bulky [Ni{(2,6-
Mes2C6H3)C(NPri)2}2] derivatives,13i with both of the latter
exhibiting a distorted tetrahedral structure. An unsymmetrical
coordination of Lꢀ to the Ni(II) centre of 6 is also noted. The
ascribed to a S ¼ quartet ground state.35,36 The respective
3
2
magnetic moments of 5.13 and 4.96 mB for the Fe(II) derivatives
3 and 4 are consistent with the spin-only value of 4.90 mB for
four unpaired electrons.
˚
observed Ni–Namidinate distances of 1.908(2)–1.945(2)A in 6 are
shorter than the corresponding bond lengths of 2.007(3)–
15c
˚
2.016(4) A in [Ni{PhC(NSiMe3)2}2].
shorter than those of 1.969(3)–1.977(2)
They are slightly
˚
The redox properties of the present complexes in CH2Cl2
solutions have been studied by cyclic voltammetry. Although
complexes 2, 3 and 5 did not show any redox behaviour within
the limits of solvent decomposition under the conditions of our
studies, the Fe(II) bis(benzamidinate) 4 and the Ni(II) deriva-
tive 6 both exhibited cyclic voltammetric behaviour. The cyclic
voltammogram of 4 (Fig. 7) shows a quasi-reversible reduction
wave at E1/2 ¼ –1.04 V (versus ferrocene) with DEp ¼ 162 mV.
On the other hand, the cyclic voltammogram of 6 (Fig. 8)
consists of two anodic processes, namely an initial quasi-rever-
sible oxidation at E1/2 ¼ 0.17 V (DEp ¼ 165 mV), followed by
an irreversible oxidation at Epa ¼ 0.69 V. Since benzamidines
A in [Ni{(2,6-
Mes2C6H3)C(NPri)2}2],13i but marginally longer than those
0
˚
of 1.904(5) A (ave.) in the binuclear Ni(II) complex of N,N -
di-p-tolylformamidinate [Ni2{MeC(N(C6H4Me–p))2}4].12g
Mass spectrometry, magnetic susceptibility measurements, and
cyclic voltammetry
Although the EI mass spectrum of the lithium derivative 1 only
showed a fragmentation pattern due to the Lꢀ ligand, those
of the binuclear complexes 2 and 5 displayed fragmentation
ꢂ
˚
Table 7 Selected bond distances (A) and angles ( ) for [NiL2] (6)
Ni(1)–N(1)
Ni(1)–N(3)
1.908(2)
1.921(2)
1.319(3)
1.492(3)
1.734(2)
1.330(2)
1.430(3)
68.93(7)
173.70(8)
110.9(2)
125.2(2)
124.9(2)
88.6(1)
Ni(1)–N(2)
Ni(1)–N(4)
1.945(2)
1.937(2)
1.329(2)
1.426(2)
1.320(3)
1.500(3)
1.741(2)
69.09(7)
176.39(8)
123.9(2)
90.4(1)
N(1)–C(1)
C(1)–C(2)
N(2)–C(1)
N(1)–C(8)
N(2)–Si(1)
N(4)–C(21)
N(3)–C(28)
N(3)–C(21)
C(21)–C(22)
N(4)–Si(2)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(3)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(1)–C(8)
C(1)–N(2)–Ni(1)
Si(1)–N(2)–Ni(1)
N(3)–C(21)–C(22)
C(21)–N(3)–Ni(1)
C(28)–N(3)–Ni(1)
C(21)–N(4)–Si(2)
N(3)–Ni(1)–N(4)
N(2)–Ni(1)–N(4)
N(1)–C(1)–C(2)
C(1)–N(1)–Ni(1)
C(8)–N(1)–Ni(1)
C(1)–N(2)–Si(1)
N(3)–C(21)–N(4)
N(4)–C(21)–C(22)
C(21)–N(3)–C(28)
C(21)–N(4)–Ni(1)
Si(2)–N(4)–Ni(1)
137.9(1)
132.1(2)
111.3(2)
124.8(2)
123.4(2)
88.5(1)
139.2(1)
123.7(2)
89.5(1)
138.6(1)
129.8(2)
Fig. 7 Cyclic voltammogram of 4 in a CH2Cl2 solution containing
.
141.6(1)
[Bun4N][PF6] (0.15 M). Scan rate: 50 mV sꢀ1
1316
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1996, 242, 31–42; (c) F. A. Cotton, L. M. Daniels, L. R. Falvello,
J. H. Matonic and C. A. Murillo, Inorg. Chim. Acta, 1997, 256,
269–275; (d ) F. A. Cotton, L. M. Daniels, J. H. Matonic and
C. A. Murillo, Inorg. Chim. Acta, 1997, 256, 277–282; (e) F. A.
Cotton, L. M. Daniels, D. J. Maloney, J. H. Matonic and C. A.
Murillo, Inorg. Chim. Acta, 1997, 256, 283–289; ( f ) F. A. Cotton,
L. M. Daniels, X. Feng, D. J. Maloney, J. H. Matonic and C. A.
Murillo, Inorg. Chim. Acta, 1997, 256, 291–301; (g) F. A. Cotton,
M. Matusz and R. Poli, Inorg. Chem., 1987, 26, 1472–1474.
13 (a) J. R. Hagadorn and J. Arnold, Organometallics, 1994, 13,
4670–4672; (b) J. R. Hagadorn and J. Arnold, J. Am. Chem.
Soc., 1996, 118, 893–894; (c) J. R. Hagadorn and J. Arnold, Orga-
nometallics, 1996, 15, 984–991; (d ) J. R. Hagadorn and J. Arnold,
J. Chem. Soc., Dalton Trans., 1997, 3087–3096; (e) J. R. Hagadorn
and J. Arnold, Inorg. Chem., 1997, 36, 132–133; ( f ) D. Y.
Dawson and J. Arnold, Organometallics, 1997, 16, 1111–1113;
(g) J. R. Hagadorn and J. Arnold, Organometallics, 1998, 17,
1355–1368; (h) J. A. R. Schmidt and J. Arnold, J. Chem. Soc.,
Dalton Trans., 2002, 2890–2899; (i) J. A. R. Schmidt and J.
Arnold, J. Chem. Soc., Dalton Trans., 2002, 3454–3461 and refer-
ences therein.
14 A. Singhal, V. K. Jain, M. Nethaji, A. G. Samuelson, D.
Jayaprakash and R. J. Butcher, Polyhedron, 1998, 17, 3531–3540.
15 (a) D. Walther, R. Fischer, H. Go¨rls, J. Koch and B. Schweder,
J. Organomet. Chem., 1996, 508, 13–22; (b) D. Walther, R.
Fischer, M. Friedrich, P. Gebhardt and H. Go¨rls, Chem. Ber.,
1996, 129, 1389–1393; (c) D. Walther, P. Gebhardt, R. Fischer,
U. Kreher and H. Go¨rls, Inorg. Chim. Acta, 1998, 281, 181–189.
16 (a) P. J. Stewart, A. J. Blake and P. Mountford, Inorg. Chem.,
1997, 36, 1982–1986; (b) P. J. Stewart, A. J. Blake and P.
Mountford, Inorg. Chem., 1997, 36, 3616–3622.
Fig. 8 Cyclic voltammogram of 6 in a CH2Cl2 solution containing
[Bun4N][PF6] (0.15 M). Scan rate: 100 mV sꢀ1
.
are also known to be electrochemically active, assignments of
the redox processes for 4 and 6 appear to be difficult in the
present cases.
Acknowledgements
17 A. Littke, N. Sleiman, C. Bensimon, D. S. Richeson, G. P. A. Yap
and S. J. Brown, Organometallics, 1998, 17, 446–451.
This work was supported by Direct Grants (A/C Nos.:
2060157 and 2060185) of The Chinese University of Hong
Kong. The authors wish to thank Professor Thomas C. W.
Mak for his valuable advice on the X-ray crystallographic
studies.
18 A. Kasani, R. P. Kamalesh Babu, K. Feghali, S. Gambarotta,
G. P. A. Yap, L. K. Thompson and R. Herbst-Irmer, Chem.-
Eur. J., 1999, 5, 577–586.
19 T. Clark, J. Cochrane, S. F. Colson, K. Z. Malik, S. D. Robinson
and J. W. Steed, Polyhedron, 2001, 20, 1875–1880.
20 B. Vendemiati, G. Prini, A. Meetsma, B. Hessen, J. H. Teuben
and O. Traverso, Eur. J. Inorg. Chem., 2001, 707–711.
21 (a) Y. Peng, M.Phil. Thesis, The Chinese University of Hong
Kong, 1999; (b) C. H. Lam, M.Phil. Thesis, The Chinese Univer-
sity of Hong Kong, 2001; (c) S. C. F. Kui, M.Phil. Thesis, The
Chinese University of Hong Kong, 2001.
22 (a) H. K. Lee, Y.-L. Wong, Z.-Y. Zhou, Z.-Y. Zhang, D. K. P. Ng
and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 2000, 539–544;
(b) H. K. Lee, Y. Peng, S. C. F. Kui, Z.-Y. Zhang, Z.-Y. Zhou
and T. C. W. Mak, Eur. J. Inorg. Chem., 2000, 2159–2162; (c)
H. K. Lee, C. H. Lam, S.-L. Li, Z.-Y. Zhang and T. C. W.
Mak, Inorg. Chem., 2001, 40, 4691–4695.
References
1
2
3
J. Barker and M. Kilner, Coord. Chem. Rev., 1994, 133, 219–300.
F. T. Edelmann, Coord. Chem. Rev., 1994, 137, 403–481.
H. W. Roesky, B. Meller, M. Noltemeyer, H.-G. Schmidt, U.
Scholz and G. M. Sheldrick, Chem. Ber., 1988, 121, 1403–1406.
K. Ko¨hler, H. W. Roesky, M. Noltemeyer, H.-G. Schmidt, C.
4
5
Freire-Erdbrugger and G. M. Sheldrick, Chem. Ber., 1993, 126,
921–926.
¨
(a) E. Hartmann, K. Dehnicke and D. Fenske, Z. Anorg. Allg.
Chem., 1989, 575, 10–16; (b) A. Zinn, H. von Arnim, W. Massa,
M. Scha¨fer, J. Pebler and K. Dehnicke, Z. Naturforsch., B: Chem.
Sci., 1991, 46, 1300–1304.
23 T. S. Lam, M.Phil. Thesis, The Chinese University of Hong Kong,
2002.
24 T. S. Lam, H. W. Li, T. C. W. Mak and H. K. Lee, J. Inorg.
Biochem., 2001, 86, 306.
6
(a) D. G. Dick, R. Duchateau, J. J. H. Edema and S. Gambarotta,
Inorg. Chem., 1993, 32, 1959–1962; (b) P. Berno, S. Hao, R.
Minhas and S. Gambarotta, J. Am. Chem. Soc., 1994, 116,
7417–7418.
25 (a) H. Schumann, J. Winterfeld, E. C. E. Rosenthal, H. Hemling
and L. Esser, Z. Anorg. Allg. Chem., 1995, 621, 122–130; (b)
H. Schumann, J. Gottfriedsen, S. Dechert and F. Girgsdies,
Z. Anorg. Allg. Chem., 2000, 626, 747–758.
7
8
D. A. Dobbs and R. G. Bergman, Organometallics, 1994, 13,
4594–4605.
26 D. F. Evans, J. Chem. Soc., 1959, 2003–2005.
27 G. M. Sheldrick, SHELX-97, Package for Crystal Structure
Solution and Refinement, University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
28 D. T. Cromer, J. T. Waber, International Tables for X-Ray Crys-
tallography, Kynoch Press, Birmingham, U.K., 1974.
29 Some examples are: (a) R. B. Hallock, W. E. Hunter, J. L.
Atwood and O. T. Beachley, Jr., Organometallics, 1985, 4, 547–
549; (b) D. O’Hara, J. S. Foord, T. C. M. Page and T. J.
Whitaker, J. Chem. Soc., Chem. Commun., 1991, 1445–1447; (c)
J. L. Atwood, S. G. Bott, F. M. Elms, C. Jones and C. L. Raston,
Inorg. Chem., 1991, 30, 3792–3793; (d ) J. J. Byers, W. T.
Pennington and G. H. Robinson, Acta Crystallogr., Sect. C,
1992, 48, 2023–2024; (e) J. P. Bezombes, P. B. Hitchcock, M. F.
Lappert and P. G. Merle, J. Chem. Soc., Dalton Trans., 2001,
816–821.
(a) R. Gomez, R. Duchateau, A. N. Chernega, J. H. Teuben, F. T.
Edelmann and M. L. H. Green, J. Organomet. Chem., 1995, 491,
153–158; (b) R. Gomez, R. Duchateau, A. N. Chernega, A.
Meetsma, F. T. Edelmann, J. H. Teuben and M. L. H. Green,
J. Chem. Soc., Dalton Trans., 1995, 217–225; (c) R. Duchateau,
C. T. van Wee, A. Meetsma, P. T. van Duijnen and J. H. Teuben,
Organometallics, 1996, 15, 2279–2290; (d ) R. Duchateau, C. T.
van Wee and J. H. Teuben, Organometallics, 1996, 15, 2291–2302.
(a) D. Herskovics-Korine and M. S. Eisen, J. Organomet. Chem.,
1995, 503, 307–314; (b) C. Averbuj, E. Tish and M. S. Eisen,
J. Am. Chem. Soc., 1998, 120, 8640–8646.
9
10 J. C. Flores, J. C. W. Chien and M. D. Rausch, Organometallics,
1995, 14, 1827–1833.
11 (a) F. A. Cotton and W. A. Wojtczak, Polyhedron, 1994, 13, 1337–
1341; (b) F. A. Cotton, L. M. Daniels, C. A. Murillo and X.
Wang, J. Am. Chem. Soc., 1996, 118, 4830–4833; (c) F. A. Cotton,
L. M. Daniels, G. T. Jordan IV, C. Lin and C. A. Murillo, J. Am.
Chem. Soc., 1998, 120, 3398–3401.
12 (a) F. A. Cotton, L. M. Daniels, L. R. Falvello and C. A. Murillo,
Inorg. Chim. Acta, 1994, 219, 7–10; (b) F. A. Cotton, L. M.
Daniels, D. J. Maloney and C. A. Murillo, Inorg. Chim. Acta,
30 M. C. Kerby, B. W. Eichhorn, J. A. Creighton and K. P. C.
Vollhardt, Inorg. Chem., 1990, 29, 1319–1323.
31 J. Barker, D. Barr, N. D. R. Barnett, W. Clegg, I. Cragg-Hine,
M. G. Davidson, R. P. Davies, S. M. Hodgson, J. A. K. Horward,
M. Kilner, C. W. Lehmann, I. Lopez-Solera, R. E. Mulvey, P. R.
Raithby and R. Snaith, J. Chem. Soc., Dalton Trans., 1997,
951–956.
New J. Chem., 2003, 27, 1310–1318
1317

View Article Online
32 M. F. Lappert, P. P. Power, A. R. Sanger, R. C. Srivastava,
Metal and Metalloid Amides, Ellis Horwood, Chichester, 1980,
pp. 235–381 and 465–544.
35 B. Chiswell, E. D. McKenzie and L. F. Lindoy, in Comprehensive
Coordination Chemistry, ed. G. Wilkinson, R. D. Gillard and
J. A. McCleverty, Pergamon, Oxford, 1987, vol. 4.
33 D. Stalke, M. Wedler and F. T. Edelmann, J. Organomet. Chem.,
1992, 431, C1–C5.
34 G. R. Giesbrecht, A. Shafir and J. Arnold, J. Chem. Soc., Dalton
Trans., 1999, 3601–3604.
36 Five-coordinate Mn(II) complexes with an intermediate-spin-
electronic configuration have been reported: C. G. Barraclough,
R. L. Martin, S. Mitra and R. C. Sherwood, J. Chem. Phy.,
1970, 53, 1638–1642 and references therein.
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