Synthesis, reactivity, and crystal structures of ferrocene-substituted amidinate derivatives

Article abstract of DOI:10.1016/S0022-328X(01)00973-1

Reaction of FcLi (Fc=ferrocenyl) with DCC (DCC=l,3-dicyclohexylcarbodiimide), followed by the addition of water, yields the ferrocene-containing amidine Fc(NCy)NHCy in 50% yield. The amidine is readily deprotonated by LiN(SiMe₃)₂ or

Full text of DOI:10.1016/S0022-328X(01)00973-1

Journal of Organometallic Chemistry 637–639 (2001) 521–530
www.elsevier.com/locate/jorganchem
Synthesis, reactivity, and crystal structures of ferrocene-substituted
amidinate derivatives
John R. Hagadorn 1, John Arnold *
Department of Chemistry, Uni6ersity of California, 526 Latimer Hall, Berkeley, CA 94720-1460, USA
Received 19 April 2001; received in revised form 15 May 2001; accepted 17 May 2001
Abstract
Reaction of FcLi (Fc=ferrocenyl) with DCC (DCC=l,3-dicyclohexylcarbodiimide), followed by the addition of water, yields
the ferrocene-containing amidine Fc(NCy)NHCy in 50% yield. The amidine is readily deprotonated by LiN(SiMe3)2 or
NaN(SiMe3)2 to yield alkali metal amidinates, [FcC(NCy)2]Li and [FcC(NCy)2]Na, in high yields. These serve as convenient
sources of [FcC(NCy)2]− for a wide range of salt-metathesis reactions with transition metal halides. Reactions of [FcC(NCy)2]Li
with 0.5 equivalents MX2 (M=Fe, Co; X=Cl, Br) form the paramagnetic 4-coordinate derivatives [FcC(NCy)2]2M. Reaction of
[FcC(NCy)2]Na with CpFe(CO)2I affords the carbamoyl derivative CpFe(CO)[FcC(NCy)N(Cy)C(O)]. Although not thermally
labile, a CO ligand is readily lost upon UV irradiation to give the amidinate derivative CpFe(CO)[FcC(NCy)2]. The addition of
13CO (50 psig) to a solution of CpFe(CO)[FcC(NCy)2] results in the rapid exchange of CO at 25 °C. Heating this solution to
80 °C results in the partial formation of the carbamoyl species by a formal CO insertion into an FeꢀN bond. Reaction of
[FcC(NCy)2]Li with 0.5 equivalents [Rh(CO)2(m-Cl)]2 forms orange [FcC(NCy)2]Rh(CO)2 in good yield. Cyclic voltammetry
measurements in THF reveal a quasi-reversible oxidation at E1/2= +0.46 V followed by an irreversible oxidation at +1.49 V (vs.
Cp2Fe). Chemical oxidation of [FcC(NCy)2]Rh(CO)2 with AgBF4 generates the amidine-containing product {[FcC(NCy)-
NHCy]Rh(CO)2}[BF4]. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Amidinates; Ferrocene ligands; Cobalt; Iron; Rhodium
1. Introduction
pendant donors [8]. Toward this end, we recently re-
ported the first Fc-substituted (Fc=ferrocenyl) amidi-
nate, which by virtue of the redox-active Fc-unit, has
potential in a wide range of applications such as metal-
containing polymers, polymetallic complexes, and elec-
trochemically controlled (‘redox switched’) catalysts [9].
Here, we give a detailed report of the synthesis and
characterization of several new Fe(II) and Rh(I) deriva-
tives of the Fc-containing amidinate ligand.
Transition metal amidinate complexes have been at-
tracting significant interest for over 20 years due to
their diverse structural and reaction chemistry [1]. No-
tably, they have been used for the preparation of
metal–metal bonded species [2], dinitrogen complexes
[2a,3], and catalysts for a wide range of bond forming
reactions (CꢀC and CꢀN) [4], including olefin polymer-
izations [5]. With the current interest in organometallic
chemistry of controlling structure/reactivity through lig-
and modification, a wide range of new amidinates has
been reported in the last several years. These include
typical [RC(NR%)2]− amidinates [6], tethered bis(amidi-
nates) [7], chiral versions [5c,7], and amidinates with
2. Experimental
2.1. General considerations
Standard Schlenk-line and glove box techniques were
used throughout the preparative procedures except in
the work-up of air-stable FcC(NCy)NHCy (Cy=cyclo-
hexyl, Fc=ferrocenyl). Ferrocene, AgBF4, and t-BuLi
were purchased from Strem and used as received. 1,3-
* Corresponding author. Fax: +1-508-437-7852.
E-mail address: arnold@socrates.berkeley.edu (J. Arnold).
1 Current Address: Department of Chemistry and Biochemistry,
University of Colorado, Boulder, CO 80309-0215, USA.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00973-1

522
J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
Dicyclohexylcarbodiimide (DCC) was purchased from
Sigma and used as received. FeCl2 and CoBr2 were
purchased from Strem and dried at 150 °C/l0−2 mmHg
overnight. LiN(SiMe3)2 [10], NaN(SiMe3)2 [11], [Rh-
(CO)2(m-Cl)]2 [12], and CpFe(CO)2I [13] were prepared
following literature procedures. Tetrahydrofuran
(THF), Et2O, and hexanes were distilled from sodium/
benzophenone under nitrogen. Toluene was distilled
from sodium under nitrogen. CH2Cl2 was distilled from
CaH2 under nitrogen. C6D6 was vacuum transferred
from sodium/benzophenone. CDCl3 was vacuum trans-
ferred from CaH2. Melting points were determined in
sealed capillary tubes under nitrogen and are uncor-
rected. 1H- and 13C{1H}-NMR spectra were recorded at
ambient temperatures unless stated otherwise. Chemical
shifts (l) are given relative to residual protium in the
deuterated solvent at 7.15 and 7.24 ppm for C6D6 and
CDCl3, respectively. IR samples were prepared as min-
eral oil mulls and taken between KBr plates. Elemental
analyses were determined within the College of Chem-
istry, University of California, Berkeley. Cyclic voltam-
b-C5H4), 3.55 (m, 1H, Cy), 2.21 (m, 2H, Cy), 1.80–1.10
(m, 18H, Cy). 13C{1H}-NMR (C6D6): l=151.3, 81.4,
69.5, 69.4, 68.2, 58.3, 48.9, 36.5, 33.7, 26.5, 25.3. IR
(cm−1): 3420 (m, wNꢀH), 1619 (vs, wCꢁN), 1490 (s), l301
(w), 1256 (w), 1181 (w), 1156 (w), 1106 (w), 1023 (w),
1003 (w), 888 (w), 830 (m), 722 (w), 568 (w), 488 (w).
Anal. Found: C, 70.41; H, 8.46; N, 7.05. Calc. for
C23H32N2Fe: C, 70.41; H, 8.22; N, 7.14%.
2.2.2. {[FcC(NCy)2]Li(Et2O)}2
Toluene (200 ml) cooled to −78 °C was added to
FcC(NCy)NHCy (17.1 g, 43.6 mmol) and LiN(SiMe3)2
(7.30 g, 43.6 mmol) forming a clear orange solution.
After stirring overnight at room temperature (r.t.), the
solution was concentrated to a viscous dark orange
solution. Addition of Et2O (100 ml) followed by cooling
to −40 °C yielded the product as orange crystals (13.4
g). A second crop yielded additional crystals (4.9 g).
1
Total yield: 89%. M.p.: 225–230 °C. H-NMR (C6D6):
l=5.0–4.1 (br, 9H, C5H5, C5H4), 3.26 (q, 4H, Et2O),
2.6–1.2 (br, 22H, Cy), 1.11 (t, 6H, Et2O). IR (cm−1):
1492 (s), 1342 (m), 1305 (w), 1153 (w), 1106 (w), 1064
(w), 1024 (w), 1002 (w), 982 (w), 888 (w), 818 (m), 742
(w), 722 (w), 498 (w), 473 (w). Anal. Found: C, 68.89;
H, 8.62; N, 5.82. Calc. for C27H41N2FeLiO: C, 68.65;
H, 8.75; N, 5.93%.
metry measurements were conducted with 10−2
M
solutions (in CH2Cl2 or THF) using 0.1 M [Bu4N]PF6
as the supporting electrolyte. The salt was purified by
recrystallization prior to use [14]. A standard three-elec-
trode assembly consisting of a platinum working, plat-
inum auxiliary, and a silver reference was used for the
measurements. Magnetic moments were determined
using Evans’ method [15]. Single crystal X-ray structure
determinations were performed at CHEXRAY, Univer-
sity of California, Berkeley.
2.2.3. [FcC(NCy)2]2Fe(Et2O)0.25
Tetrahydrofuran (30 ml) was added to a 100-ml
round-bottomed flask containing FeCl2 (0.135 g, 1.06
mmol) and [FcC(NCy)2]Li(Et2O) (1.00 g, 2.13 mmol) to
form an orange–brown solution. After stirring
overnight, the volatile materials were removed under
reduced pressure. The orange solid was extracted with
CH2Cl2 (25 ml) and filtered through a Celite pad on a
fritted disk. Concentration to saturation, followed by
the addition of Et2O (20 ml) and cooling to −40 °C
afforded the product as orange crystals (0.55 g, 61%).
M.p.: 216–218 °C. IR (cm−1): 1451 (vs, br), 1376 (m),
1306 (w), 1232 (w), 1204 (w), 1054 (s, br), 901 (m), 824
(m), 722 (m), 562 (m), 533 (w), 522 (w), 497 (m), 479
(m). Anal. Found: C, 65.69; H, 7.52; N, 6.48. Calc. for
2.2. Syntheses
2.2.1. FcC(NCy)NHCy
Ferrocene (100 g, 538 mmol) was evacuated for 2 h
in a 2-l round-bottomed flask. Tetrahydrofuran (300
ml) and hexanes (300 ml) were added forming an
orange suspension. At 0 °C, a pentane solution of
t-BuLi (328 ml, 538 mmol) was added dropwise over
1.5 h. The reaction mixture was allowed to warm to
ambient temperature over 2 h. After stirring overnight,
a THF (100 ml) solution of DCC (111 g, 538 mmol)
was added dropwise over 30 min. After stirring the
orange suspension overnight, degassed H2O (19.4 ml,
1080 mmol) was added dropwise forming a dark orange
solution and a white solid. The orange solution was
decanted, and the volatile materials were removed using
a rotary evaporator. The resulting orange solid was
sublimed overnight at 65 °C/l0−2 mmHg to remove
unreacted Cp2Fe and DCC. The remaining solid was
crystallized from boiling hexanes to yield orange prisms
of the product. Two crops: 106 g, 50% yield. M.p.:
C47H64.5Fe3N4O0.25: C, 65.86; H, 7.58; N, 6.54%. veff
5.02 mB.
=
2.2.4. [FcC(NCy)2]2Co(Et2O)
Ethyl ether (100 ml) was added to a 250-ml round-
bottomed flask containing CoBr2 (1.00 g, 4.57 mmol)
and [FcC(NCy)2]Li(Et2O) (4.30 g, 9.14 mmol) to form a
brown suspension. After stirring overnight, the volatile
materials were removed under reduced pressure, and
the brown solid was extracted with toluene (60 ml). The
solution was filtered through a Celite pad on a fritted
disk and concentrated to 20 ml. The addition of hex-
anes (20 ml) and cooling to −40 °C afforded an ochre
solid (2.85 g, 74%). Recrystallization from Et2O gave
1
109.5–111.0 °C. H-NMR (C6D6): l=4.63 (d, J=6.8
Hz, 1H, NH), 4.28 (t, J=1.8 Hz, 2H, a-C5H4), 4.18 (m,
1H, Cy), 3.99 (s, 5H, C5H5), 3.93 (t, J=1.8 Hz, 2H,

J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
523
analytically pure product co-crystallized with solvent.
M.p.: 203–207 °C. IR (cm−1): 1631 (w), 1451 (vs, br),
1376 (m), 1364 (m), 1308 (w), 1236 (w), 1204 (w), 1159
(w), 1120 (w), 1108 (w), 1076 (w), 1030 (w), 1002 (w),
990 (w), 902 (m), 824 (m), 572 (m), 497 (w), 479 (w).
Anal. Found: C, 65.42; H, 7.55; N, 6.29. Calc. for
to 50 ml. The addition of hexanes (100 ml) and cooling
to −40 °C yielded the product as dark red crystals (3.5
g). A second crop was obtained by concentration and
cooling to −40 °C. Total yield: 4.65 g, 26.5%. M.p.:
1
176–185 °C. H-NMR (C6D6): l=4.43 (s, 5H, C5H5),
4.04–4.02 (m, 7H, C5H5+a-C5H4), 3.87 (t, J=1.7 Hz,
2H, b-C5H4), 3.60 (m, 2H, Cy), 1.9–1.0 (m, 20H, Cy).
13C{1H}-NMR (C6D6): l=223.2, 166.1, 79.3, 74.9,
69.8, 69.1, 68.0, 55.5, 38.2, 36.5, 26.3, 26.2. IR (cm−1):
1922 (vs, wCO), 1523 (m), 1465 (vs, br), 1377 (s), 1307
(w), 1231 (w), 1122 (w), 1106 (w), 1089 (w), 1056 (w),
1001 (w), 900 (w), 836 (w), 823 (w), 808 (w), 722 (w),
559 (w), 528 (w), 502 (w), 482 (w). Anal. Found: C,
64.30; H, 6.83; N, 4.85. Calc. for C29H36Fe2N2O: C,
64.47; H, 6.72; N, 5.18%.
C50H72COFe2N4O: C, 65.58; H, 7.92; N, 6.12%. veff
4.62 mB.
=
2.2.5. Preparation of [FcC(NCy)2]Na
Hexanes (200 ml) were added to FcC(NCy)NHCy
(22.0 g, 56.2 mmol) and NaN(SiMe3)2 (10.3 g, 56.2
mmol) forming an orange suspension. After stirring
overnight, the orange solid was collected by filtration
and dried under reduced pressure affording an orange
powder (22.6 g, 97.0%).
2.2.8. [FcC(NCy)2]Rh(CO)2
2.2.6. CpFe(CO)[FcC(NCy)N(Cy)C(O)]
Toluene (35 ml) was added to [Rh(CO)2(m-Cl)]2
(0.337 g, 0.867 mmol) and [FcC(NCy)2]Li(Et2O) (0.816
g, 1.73 mmol) forming a cloudy, orange–brown solu-
tion. After stirring for 5 h, the volatile materials were
removed under reduced pressure. The orange–brown
solid was extracted with hexanes (80 ml) and filtered
through a pad of Celite on a fritted disk. Concentration
of the solution to 60 ml and cooling to −40 °C
afforded the product as orange crystals (0.52 g). Total
yield from two crops: 0.78 g, 82%. M.p.: 134–136 °C.
1H-NMR (C6D6): l=4.15 (t, J=1.9 Hz, 2H, a-C5H4),
3.97 (s, 5H, C5H5), 3.96 (t, J=1.9 Hz, 2H, b-C5H4),
3.84 (m, 2H, Cy), 1.67 (m, 8 H, Cy), 1.48 (m, 2H, Cy),
1.4–1.0 (m, 10H, Cy). 13C{1H}-NMR (C6D6): l=188.4
(d, 1JRhꢀC=67.1 Hz), 182.3 (2JRhꢀC=4.4 Hz), 72.7,
70.0, 70.0, 69.2, 54.4, 37.0, 26.0, 25.8. IR (cm−1): 2052
(vs), 1977 (vs), 1511 (m), 1462 (m), 1451 (s), 1377 (m),
1361 (m), 1237 (m), 1123 (w), 1107 (w), 1080 (w), 1029
(w), 1004 (w), 821 (m), 569 (m), 519 (m), 475 (m). Anal.
Found: C, 54.50; H, 5.65; N, 5.09. Calc. for
C25H31FeN2O2Rh: C, 54.57; H, 5.68; N, 5.09%.
Toluene (100 ml) was added to CpFe(CO)2I (2.32 g,
7.65 mmol) and [FcC(NCy)2]Na (3.17 g, 7.65 mmol) to
form a black solution. After a few minutes, the solution
became orange–brown with the formation of a yellow
precipitate. The solution was stirred overnight and then
filtered through a pad of Celite on a fritted disk.
Concentration to 20 ml and cooling to −40 °C yielded
the product as an orange solid (1.00 g). The addition of
hexanes (20 ml) to the mother liquor followed by
cooling to −40 °C yielded a second crop as orange–
red crystals. Total yield 2.50 g, 57.5%. M.p.: 194–
1
195 °C. H-NMR (C6D6): l=4.69 (m, 1H, a-C5H4),
4.54 (s, 5H, C5H5), 4.18 (m, 1H, a-C5H4), 3.96 (s, 5H,
C5H5), 3.96 (m, 1H, b-C5H4), 3.93 (m, 1H, b-C5H4),
3.56 (m, 1H, Cy), 3.04 (m, 2H, Cy), 2.33 (m, 1H, Cy),
1.8–0.9 (m, 17H, Cy). 13C{1H}-NMR (C6D6): l=
233.8, 220.3, 166.0, 84.1, 76.2, 71.6, 70.2, 70.0, 69.3,
68.1, 62.4, 60.4, 37.6, 35.4, 32.6, 31.3, 27.3, 27.2, 25.9,
25.8, 25.7, 25.7. IR (cm−1): 1902 (vs, wCO), 1630 (s,
wCꢁO), 1514 (m, wCꢁN), 1459 (s, br), 1377 (s), 1212 (m),
1157 (w), 1118 (w), l061 (w), 998 (w), 964 (w), 924 (w),
876 (w), 829 (w), 814 (w), 795 (w), 727 (w), 666 (w), 570
(w), 496 (w), 474 (w). Anal. Found: C, 64.00; H, 6.57;
N, 4.91. Calc. for C30H36Fe2N2O2: C, 63.40; H, 6.38; N,
4.93%.
2.2.9. {[FcC(NCy)NHCy]Rh(CO)2}[BF4]
Methylene chloride (20 ml) was added to powdered
[FcC(NCy)2]Rh(CO)2 (0.152 g, 0.276 mmol) and AgBF4
(54.8 mg, 0.282 mmol) to form a burgundy-colored
solution. Within a few minutes a silver precipitate was
observed. After 3 h, the volatile materials were removed
under reduced pressure. The red–violet residue was
extracted with CH2Cl2 (20 ml) and filtered. The solu-
tion was concentrated to 7 ml and cooled to −40 °C.
After sitting overnight, the solution was filtered again
to remove some silver-colored precipitate, and Et2O (10
ml) was added. Within a few hours, red crystals of the
product were isolated (50 mg, 29%). M.p. (dec):
2.2.7. CpFe(CO)[FcC(NCy)2]
Toluene (200 ml) was added to CpFe(CO)2I (10.0 g,
32.9 mmol) and [FcC(NCy)2]Na (13.6 g, 32.9 mmol)
forming a black solution. After a few minutes, the
solution became orange–brown with the formation of a
yellow precipitate. The solution was stirred overnight
and then filtered through a pad of Celite on a fritted
disk into a long quartz tube (ca. 2.5 cm diameter). The
solution was irradiated in an UV chamber for 24 h
under N2. 1H-NMR spectroscopic analysis of an
aliquot of the solution confirmed the absence of start-
ing material. The solution was filtered and concentrated
1
167 °C. H-NMR (CDCl3): l=5.78 (s, 1H, NH), 5.00
(s, 1H, a-C5H4), 4.78 (s, 2H, b-C5H4), 4.59 (s, 1H,
a-C5H4), 4.40 (s, 5H, C5H5), 4.05 (m, 1H, Cy), 3.04 (m,
1H, Cy), 2.25 (m, 1H, Cy), 2.0–1.0 (m, 19H, Cy).

524
J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
13C{1H}-NMR (CDCl3, 75.5 MHz): l=183.4 (d,
ferred to a Siemens SMART diffractometer/CCD area
detector [16], centered in the beam (Mo–Ka; u=
1
1JRhꢀC=72.1 Hz), 182.5 (d, JRhꢀC=69.4 Hz), 180.0 (d,
2JRhꢀC=4.2 Hz), 75.2, 73.7, 71.9, 69.9, 67.0, 59.6, 58.8,
34.9, 34.3, 33.9, 31.6, 25.1, 25.0, 24.6, 24.6, 24.4, 24.3.
IR (cm−1): 3208 (m), 2086 (vs), 2016 (vs), 1611 (s),
1460 (vs, br), 1377 (s), 1280 (m), 1094 (m, br), 844 (w),
825 (w), 740 (w), 611 (w), 490 (w), 473 (w). Anal.
Found: C, 46.95; H, 5.05; N, 4.37. Calc. for
C25H32BF4FeN2O2Rh: C, 47.06; H, 5.05; N, 4.39%.
,
0.71073 A; graphite monochromator), and cooled by a
nitrogen low-temperature apparatus. Preliminary orien-
tation matrix and cell constants were determined by
collection of 60 10-s frames, followed by spot integra-
tion and least-squares refinement. A hemisphere of data
was collected using 0.3°ꢀ scans. The raw data were
integrated (XY spot spread=1.60°, Z spot spread=
0.60°) and the unit cell parameters refined using SAINT
.
2.3. X-ray crystallographic studies
Data analysis and absorption correction was performed
using XPREP. The data were corrected for Lorentz and
polarization effects, but no correction for crystal decay
was applied. The structure was solved and refined with
the TEXSAN [17] software package using direct methods
and expanded using Fourier techniques. The quantity
minimized by the least-squares program was ꢀw(ꢁFoꢁ−
ꢁFcꢁ)2, where w is the weight of a given observation. The
p-factor, used to reduce the weight of intense reflec-
tions, was set to 0.030 throughout the refinement. The
Table 1 lists a summary of crystallographic data for
all crystallographically characterized compounds. De-
tails of individual data collections and solutions are
given below.
2.3.1. General procedure
A crystal of appropriate size was mounted on a
quartz fiber using Paratone-N hydrocarbon oil, trans-
Table 1
Crystal data and collection parameters
Compound
FcC(NCy)NHCy
CpFe(CO)-
CpFe(CO)-
[FcC(NCy)2]
C29H36N2OFe2
540.30
[FcC(NCy)2]-
Rh(CO)2
C25H31N2O2RhFe
550.29
{[FcC(NCy)NHCy]-
Rh(CO)2}[BF4]
C25H32BF4O2RhFeN2
638.14
[FcC(NCy)N(Cy)C(O)]
C30H36N2O2Fe2
568.32
Empirical formula
Formula weight
Space group
Temperature (°C)
Unit cell dimensions
C23H32FeN2
392.37
(
(
P212121 (c19)
P212121 (c19)
P1 (c2)
Pba2 (c32)
P1 (c2)
−150
−104
−93
−93
−97
,
a (A)
39.547(1)
9.3790(2)
10.7050(2)
9.9667(1)
17.9689(4)
28.9218(5)
10.0875(2)
11.6278(2)
13.0580(1)
83.185(1)
68.016(1)
64.307(1)
1278.11(4)
2
19.0364(5)
21.0181(6)
5.8973(2)
10.0949(3)
10.9287(3)
13.0603(4)
108.915(1)
97.231(1)
99.928(1)
1316.9(1)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
3970.6(1)
8
5179.6(2)
8
2359.6(2)
4
Z
Diffractometer
Radiation
Siemens SMART
Mo–Ka
Siemens SMART
Mo–Ka (u=0.71073 A) Mo–Ka
Siemens SMART
Siemens SMART
Mo–Ka
Siemens SMART
Mo–Ka (u=0.71073 A)
,
,
,
,
,
(u=0.71073 A)
Graphite
(u=0.71073 A)
Graphite
(u=0.71073 A)
Graphite
Monochromator
Detector
Graphite
Graphite
CCD area detector CCD area detector
CCD area detector CCD area detector CCD area detector
Scan type, width
Scan speed
ꢀ, 0.3°
ꢀ, 0.3°
ꢀ, 0.3°
ꢀ, 0.3°
ꢀ, 0.3°
10 s frame−1
Hemisphere
3–46.5
30 s frame−1
Hemisphere
3–46.5
20 s frame−1
Hemisphere
3–46.5
10 s frame−1
Hemisphere
3–46.5
30 s frame−1
Hemisphere
3–46.5
Reflections measured
2q Range (°)
v (mm−1
)
0.768
1.15
1.16
1.336
1.229
Tmin, Tmax
Crystal dimensions
(mm)
0.622, 0.760
0.30×0.32×0.32
0.822, 0.897
0.22×0.15×0.09
0.797, 0.880
0.22×0.20×0.11
0.773, 0.861
0.14×0.13×0.10
0.853, 0.923
0.12×0.11×0.08
Color
Number of reflections
measured
Orange
16 799
Orange–red
21 373
Red
5255
Orange
9966
Red
5529
Number of unique
reflections
3283
7426
3561
3539
3681
Number of observations 2685
6145
3110
2533
2923
Number of parameters
R, Rw (%)
Goodness-of-fit
475
3.10, 3.67
1.25
649
2.67, 3.16
1.07
307
3.47, 4.98
1.92
279
2.55, 3.02
1.00
329
3.96, 5.11
1.76

J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
525
analytical forms of the scattering factor tables for the
neutral atoms were used, and all scattering factors
were corrected for both the real and imaginary com-
ponents of anomalous dispersion [18].
grown from hexanes at 5 °C. Data collection and
processing proceeded as stated above.
The unit cell parameters and systematic absences
indicated a primitive orthorhombic cell. The choice of
the acentric space group Pba2 (c 32) was confirmed
by successful solution of the structure. All non-hydro-
gen atoms were refined anisotropically. Hydrogen
atoms were assigned idealized positions and were in-
cluded in structure factor calculations but were not
refined. Initial refinement of the incorrect absolute
structure (Flack parameter=0.945(9)) gave residuals
of R=3.07% and Rw=3.63%. The atomic coordi-
nates were inverted and the Flack parameter refined
to 0.013(8) indicating that the correct absolute struc-
ture was used. The final residuals improved signifi-
cantly (R=2.55%, Rw=3.02%).
2.3.2. FcC(NCy)NHCy
Crystals suitable for X-ray diffraction studies were
grown over several days by the slow cooling of a
boiling hexanes solution to r.t. Data collection and
processing proceeded as stated above.
The unit cell parameters indicated a primitive or-
thorhombic cell. Systematic absences indicated the
space group P212121 (c19); this was confirmed by
the successful refinement of the model. All non-hy-
drogen atoms were refined anisotropically. Amine hy-
drogens were located in a difference Fourier map,
and their positions were refined. All remaining hydro-
gens were assigned idealized positions and were in-
cluded in structure factor calculations, but were not
refined. The Flack parameter was refined to 0.53, in-
dicative of inversion twinning. Friedel mates were av-
eraged.
2.3.6. {[FcC(NCy)NHCy]Rh(CO)2}[BF4]
Crystals suitable for X-ray diffraction studies were
grown from CH2Cl2–Et2O at −40 °C. Data collec-
tion and processing proceeded as stated above.
The unit cell parameters indicated a primitive tri-
clinic cell. The choice of the centric space group was
confirmed by successful solution of the structure. All
non-hydrogen atoms were refined anisotropically. The
amidine hydrogen was located in a difference Fourier
and refined isotropically. All remaining hydrogen
atoms were assigned idealized positions and were in-
cluded in structure factor calculations but were not
refined.
2.3.3. CpFe(CO)[FcC(NCy)N(Cy)C(O)]
Crystals suitable for X-ray diffraction studies were
grown over several days by vapor diffusion of hex-
anes into an Et2O solution of the compound. Data
collection and processing proceeded as stated above.
The unit cell parameters indicated a primitive or-
thorhombic cell. Systematic absences indicated the
space group P212121 (c19); this was confirmed by
the successful refinement of the model. All non-hy-
drogen atoms were refined anisotropically. Hydrogen
atoms were assigned idealized positions and were in-
cluded in structure factor calculations but were not
refined. The Flack parameter was refined to 1.006(3),
indicating that the incorrect absolute configuration
had been used (R=3.89%, Rw=4.74%). Atomic co-
ordinates were inverted and the Flack parameter
refined to −0.036(2). The final residuals improved
significantly (R=2.67%, Rw=3.16%).
3. Results and discussion
3.1. Ligand synthesis and characterization
Deprotonation of ferrocene with one equivalent t-
BuLi in THF–hexanes forms a mixture of ferrocenyl
lithium (FcLi), the 1,1%-dilithio species (FcLi2), and
unreacted ferrocene [19]. This mixture reacts readily
with DCC to generate amidinate products, with FcC-
(NCy)2Li being the major species formed. It is note-
worthy that an attempt to prepare the N,N%-bis(tri-
methylsilyl) analogue by similar methodology has
been reported to give no reaction [1a], apparently due
to the lower electrophilicity of the trimethylsilyl-sub-
stituted carbodiimide. In order to isolate pure ligand,
the mixture was hydrolyzed with excess water, and
the solvent was stripped to afford an orange mixture
consisting of FcC(NCy)NHCy, Fc[C(NCy)NHCy]2
[20], and Cp2Fe (Scheme 1).
2.3.4. CpFe(CO)[FcC(NCy)2]
Crystals suitable for X-ray diffraction studies were
grown from hexanes at −40 °C. Data collection and
processing proceeded as stated above.
The unit cell parameters indicated a triclinic cell.
The choice of the centric space group was confirmed
by the successful solution of the structure. All non-
hydrogen atoms were refined anisotropically. Hydro-
gen atoms were assigned idealized positions and were
included in structure factor calculations but were not
refined.
Sublimation of the mixture at 65 °C/10−2 mmHg
removed ferrocene and carbodiimide; pure FcC-
(NCy)NHCy was then obtained in 50% yield by crys-
tallization of the residue from boiling hexanes.
2.3.5. [FcC(NCy)2]Rh(CO)2
Crystals suitable for X-ray diffraction studies were

526
J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
1
assigned to wCꢁN and wNꢀH, respectively. H-NMR spec-
troscopic data of C6D6 solutions show a single species
with two distinct triplets of equal intensities at 4.28 and
3.93 ppm arising from the substituted-Cp ligand and a
singlet at 3.99 ppm from the other Cp ligand. Cyclic
voltammetry reveals a quasi-reversible oxidation at
Scheme 1.
E
1/2= +0.31 V relative to the Cp2Fe/[Cp2Fe]+ couple
(Fig. 1). The DEp of 250 mV is only slightly greater
than that measured for Cp2Fe (220 mV) under
analogous conditions. The solid-state structure was de-
termined by X-ray crystallography. A drawing of one
of the two independent molecules (per asymmetric unit)
is shown in Fig. 2 with related metrical parameters in
Table 2. Since the two molecules are essentially struc-
turally identical, only one will be discussed. As ex-
pected, the amidine functionality displays localized
,
single and double CN bonds of 1.467(6) and 1.289(6) A
for N(2)ꢀC(11) and N(1)ꢀC(11), respectively. Due to
the high quality of the data set, the amidine-hydrogen
bound to N(2) was located in a difference Fourier map,
and it was refined isotropically. The N(1)ꢀC(11)ꢀ
N(2)ꢀC(18) torsion angle is only 8.6(9)°, and the ge-
ometry at N(2) is planar (combined angles=360°).
These data suggest p-delocalization over N(1)ꢀC(11)ꢀ
N(2) similar to that found in organic amides. The
substituted-Cp plane is roughly perpendicular to the
NCN group, intersecting at 71°.
Fig. 1. Cyclic voltammogram of
a M solution of FcC-
10−2
(NCy)NHCy in CH2Cl2 measured at 50 mV s−1 (referenced to Cp2Fe
couple).
3.2. Synthesis and characterization of Group 1 and
transition metal deri6ati6es
The free-base FcC(NCy)NHCy was easily converted
to the lithium salt by deprotonation with LiN(SiMe3)2
in toluene. Concentration of the solution followed by
the addition of Et2O resulted in crystallization of the
etherate, {[FcC(NCy)2]Li(Et2O)}2, in 90% yield. The
sodium derivative was prepared similarly using
NaN(SiMe3)2, however, the product was isolated as an
orange powder from hexanes.
Fig. 2. ORTEP view of one of the two independent molecules of
FcC(NCy)NHCy drawn with 50% thermal ellipsoids.
Similar to other lithium amidinates, {[FcC(NCy)2)-
Li(Et2O)}2 functions as a useful reagent in salt-metathe-
sis reactions with metal halides. For example, treatment
of FeCl2 with two equivalents of [FcC(NCy)2]Li(Et2O)
in THF, followed by crystallization from CH2Cl2–
Et2O, afforded orange crystals of the trimetallic [FcC-
(NCy)2]2Fe in good yield (Scheme 2). A similar reaction
with CoBr2 in Et2O gave [FcC(NCy)2]2Co, also in good
yield. We note that these compounds are rare examples
of monomeric homoleptic amidinates of Fe(II) and
Co(II) [6e]. We attribute their stability to the relatively
high degree of steric protection provided by the cyclo-
hexyl groups. Magnetic susceptibility measurements (by
Evans’ solution NMR method) gave veff values typical
for high spin Fe(II) and Co(II) (5.02 and 4.62 mB,
respectively). In an attempt to prepare a mixed cy-
clopentadienyl-amidinate derivative, CpFe(CO)2I was
Table 2
,
Selected bond lengths (A) and bond angles (°) for FcC(NCy)NHCy
Fe1ꢀC1
Fe1ꢀC3
Fe1ꢀC5
Fe1ꢀC7
Fe1ꢀC9
N1ꢀC11
N2ꢀH1
2.072(5)
2.042(5)
2.054(5)
2.042(5)
2.052(5)
1.289(6)
0.88(6)
Fe1ꢀC2
Fe1ꢀC4
Fe1ꢀC6
Fe1ꢀC8
Fe1ꢀC10
N2ꢀC11
2.074(5)
2.053(5)
2.057(5)
2.051(5)
2.072(5)
1.370(6)
C11ꢀN1ꢀC12
C11ꢀN2ꢀH1
N1ꢀC11ꢀN2
N2ꢀC11ꢀC10
120.8(4)
114(3)
121.5(4)
112.3(4)
C11ꢀN2ꢀC18
C18ꢀN2ꢀH1
N1ꢀC11ꢀC10
125.0(4)
121(3)
126.0(4)
Infrared spectroscopy of air-stable FcC(NCy)NHCy
reveals absorbances at 1619 and 3420 cm−1 which are

J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
527
Table 3
reacted with [FcC(NCy)2]Li(Et2O) in toluene. The ini-
,
Selected bond lengths (A) and bond angles (°) for CpFe(CO)-
[FcC(NCy)N(Cy)C(O)]
tially black solution became orange–brown within a
few minutes indicating the absence of any CpFe(CO)2I.
The isolation of pure product, however, proved to be
difficult due to the moderate solubility of the byproduct
LiI. This problem was remedied by the use of the
ether-free sodium salt [FcC(NCy)2]Na. Stirring the re-
actants in toluene overnight afforded an orange–red
Fe(1)ꢀN(1)
Fe(1)ꢀC(6)
O(1)ꢀC(6)
N(1)ꢀC(8)
N(2)ꢀC(8)
1.975(3)
1.731(4)
1.163(4)
1.315(4)
1.380(4)
Fe(1)ꢀC(1–5)ave
Fe(1)ꢀC(7)
O(2)ꢀC(7)
2.119
1.904(4)
1.223(4)
1.442(5)
N(2)ꢀC(7)
N(1)ꢀFe(1)ꢀC(6)
C(6)ꢀFe(1)ꢀC(7)
C(7)ꢀN(2)ꢀC(8)
Fe(1)ꢀC(7)ꢀO(2)
Fe(1)ꢀC(7)ꢀN(2)
N(1)ꢀC(8)ꢀN(2)
92.9(2)
90.3(2)
113.5(3)
129.0(3)
112.8(3)
115.7(3)
N(1)ꢀFe(1)ꢀC(7)
Fe(1)ꢀN(1)ꢀC(8)
Fe(1)ꢀC(6)ꢀO(1)
Fe(1)ꢀC(7)ꢀO(2)
O(2)ꢀC(7)ꢀN(2)
81.8(1)
114.8(2)
178.1(4)
129.0(3)
118.0(3)
Scheme 2.
Scheme 4.
solution and yellow precipitate. Work-up in toluene–
hexanes followed by cooling to −40 °C afforded pure
CpFe(CO)[FcC(NCy)N(Cy)C(O)] as microcrystalline
orange–red solid in good yield (Scheme 3).
Despite reports of
a
closely related reaction
(CpFe(CO)2Cl+Li(amidinate)) yielding an unstable
product [1b], our product proved to be air-stable in
Et2O solution, as well as thermally stable in boiling
benzene. Characterization by IR spectroscopy revealed
an intense absorption at 1902 cm−1 assignable to the
terminal wCO and additional absorptions at 1630 and
1514 cm−1 for CꢁO and CꢁN stretches of the car-
bamoyl-type ligand. For comparison, the related Mn
complex Mn(CO)4[PhC(NPh)N(Ph)C(O)] features an
absorption at 1673 cm−1 assigned to wCꢁO [21].
13C{1H}-NMR spectroscopic data also support the for-
mulation of the product with downfield signals at l
223.8 and 220.3 ppm for the carbonyl carbons (absolute
assignments are not made). The structure was further
confirmed by X-ray crystallography. A drawing of one
of the two independent molecules per asymmetric unit
is shown in Fig. 3 with corresponding metrical parame-
Scheme 3.
,
ters in Table 3. The N(l)ꢀC(8) distance of 1.315(4) A is
longer than expected for a double bond, and the
,
N(2)ꢀC(8) interaction of 1.380(4) A is shorter than
expected for a single bond (compare to N(2)ꢀC(7),
,
1.442(5) A). This suggests significant contribution from
the zwitterionic resonance form shown in Scheme 4.
Additionally, the geometry at N(2) is nearly planar with
the sum of the angles equaling 357.5°.
The carbonyl ligand of CpFe(CO)[FcC(NCy)-
N(Cy)C(O)] was found to be thermally inert. Heating
C6D6 solutions of the complex in the presence of 13CO
(14 psig) to 85 °C overnight failed to incorporate any
Fig. 3. ORTEP view of CpFe(CO)[FcC(NCy)N(Cy)C(O)] drawn with
50% thermal ellipsoids.

528
J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
labeled CO into the Fe complex. Likewise, heating a
benzene solution to reflux under N2 overnight failed to
give any reaction. Photolysis, however, led to the loss
of CO and the formation of air-sensitive CpFe(CO)-
[FcC(NCy)2] (Scheme 3). For convenience, the reaction
can be carried out using a solution of CpFe(CO)[FcC-
(NCy)N(Cy)C(O)] generated in situ from CpFe(CO)2I
and [FcC(NCy)2]Na. Following this preparation, the
dark red product was readily isolated in 27% yield. IR
spectroscopic data shows a strong absorption at 1929
cm−1 assigned as wCO, which is blue-shifted relative to
the related parameter of CpFe(CO)[FcC(NCy)-
N(Cy)C(O)] (wCO=1902 cm−1). Characterization by
13C{1H}-NMR spectroscopy reveals a signal at l 223.2
ppm for the carbonyl ligand. The solid-state structure,
as determined by X-ray crystallography, was consistent
with the spectroscopic data. An ORTEP view of the
molecule is shown in Fig. 4 with related bond lengths
and angles in Table 4. As expected, the FeꢀN bonds of
the amidinate ligand are nearly identical at 1.995(3) and
,
2.009(2) A. The carbonyl ligand is typical, with an
,
FeꢀC(1) distance of 1.738(3) A and an FeꢀC(1)ꢀO(1)
angle of 177.0(3)°.
In contrast to the carbarmoyl-type derivative, the
carbonyl ligand of CpFe(CO)[FcC(NCy)2] readily ex-
changes with 13CO (50 psig) in C6D6 solution at 25 °C
(Scheme 3). The reaction likely proceeds via the 16-elec-
tron intermediate CpFe[FcC(NCy)2], formed by disas-
sociative loss of CO, although an h1-amidinate ligand
cannot be ruled out. When the same solution was
heated to 80 °C for 7 h, 65% conversion to the doubly
labeled carbamoyl derivative was observed.
We anticipated that oxidizing the ferrocenyl group of
FcC(NCy)2 might alter the donor properties of the
ligand. In order to probe the effect of this oxidation, we
sought to prepare a metal carbonyl derivative that
would be preferentially oxidized at the Fc site. This
would allow us to monitor the wCO (by IR spectroscopy)
as a function of ligand oxidation state. The molecule we
prepared for this purpose is [FcC(NCy)2]Rh(CO)2. As
shown in Scheme 5, the lithium salt readily reacted with
[Rh(CO)2(m-Cl)]2 in toluene to form the desired product
in good yield.
Fig. 4. ORTEP view of CpFe(CO)[FcC(NCy)2] drawn with 50% ther-
mal ellipsoids.
IR spectroscopy revealed two intense absorptions at
2052 and 1977 cm−1 assigned to the terminal car-
bonyls. 13C{1H}-NMR spectroscopic data, which
showed a doublet at l 182.3 ppm (2JRhꢀC=4.4 Hz) for
the amidine (NCN) carbon, suggested that the complex
was monomeric in solution. X-ray crystallography
proved this to be the case in the solid-state as well.
Shown in Fig. 5 is an ORTEP diagram with related
bond angles and lengths in Table 5. The square-planar
rhodium features an h2-amidinate ligand and a pair of
terminal carbonyls. The RhꢀN bonds are essentially
Table 4
,
Selected bond lengths (A) and bond angles (°) for CpFe(CO)-
[FcC(NCy)2]
Fe(1)ꢀN(1)
Fe(1)ꢀC(1)
O(1)ꢀC(1)
N(2)ꢀC(7)
1.995(3)
1.738(3)
1.165(4)
1.337(4)
Fe(1)ꢀN(2)
Fe(1)ꢀC(2ꢀ6)ave
N(1)ꢀC(7)
2.009(2)
2.104
1.326(4)
N(1)ꢀFe(1)ꢀN(2)
N(2)ꢀFe(1)ꢀC(1)
Fe(1)ꢀN(2)ꢀC(7)
65.4(1)
95.8(1)
92.1(2)
N(1)ꢀFe(1)ꢀC(1)
Fe(1)ꢀN(1)ꢀC(7)
Fe(1)ꢀC(1)ꢀO(1)
95.9(1)
93.1(2)
177.0(3)
,
identical (avg. 2.066 A) as are the RhꢀC bonds (avg.
,
1.857 A). The substituted-Cp plane intersects the NCN
plane at a dihedral angle of 47°.
As shown in Fig. 6, cyclic voltammetry measure-
ments of [FcC(NCy)2]Rh(CO)2 (taken at 200 mV s−1
)
reveal a quasi-reversible oxidation of the Fc-group at
1/2= +0.46 V (vs. Cp2Fe) with an additional irre-
E
versible oxidation at +1.49 V. Chemical oxidation of
[FcC(NCy)]Rh(CO)2 with 1 equivalent of AgBF4 in
CH2Cl2 appeared to occur quickly, with a silver precip-
itate forming within minutes. Following methylene
chloride work-up, the product was isolated as red crys-
tals from CH2Cl2–Et2O in 29% yield. IR spectroscopy
revealed an absorption at 3208 cm−1, which appeared
to be due a NꢀH stretch and a strong absorption at
Scheme 5.

J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
529
ordinate rhodium adopts square-planar geometry. As
,
expected, the RhꢀN(1) bond (2.063(5) A) is shorter
,
than the dative RhꢀN(2) bond (2.131(5) A). This results
in a trans influence that is observed as a slight elonga-
,
tion of the RhꢀC(2) bond (1.864(7) A) compared to
RhꢀC(1) (1.846(7) A) (Table 6). Interestingly, unlike all
,
of the structurally characterize, Fc-containing amidi-
nates, the substituted-Cp plane is nearly coplanar with
the NCN amidine plane (dihedral angle=7°). It ap-
pears likely that this is simply caused by steric repul-
sions; the cyclohexyl group bound to N(2) is directed
away from the Cp-hydrogens.
In conclusion, we have reported a convenient large-
scale synthesis of the ferrocene-containing amidinate
ligand FcC(NCy)2. This ligand can be used for the
stabilization of a wide range of transition metal deriva-
tives which feature good solubility and crystallization
properties. Although electrochemical studies suggest
that oxidation of the ferrocenyl moiety is possible, the
isolation of ferrocenium-containing derivatives has
proven to be difficult. Further study of the redox
properties will be necessary for the development of
redox-switchable ligands.
Fig. 5. ORTEP view of [FcC(NCy)2]Rh(CO)2 drawn with 50% thermal
ellipsoids.
Table 5
,
Selected bond lengths (A) and bond angles (°) for [FcC-
(NCy)2]Rh(CO)2
RhꢀN1
RhꢀC1
O1ꢀC1
N1ꢀC3
C3ꢀC4
2.062(4)
1.861(6)
1.132(6)
1.324(7)
1.487(7)
RhꢀN2
RhꢀC2
O2ꢀC2
N2ꢀC3
2.069(4)
1.852(6)
1.142(6)
1.343(6)
N1ꢀRhꢀN2
N1 ꢀRhꢀC2
N2ꢀRhꢀC2
RhꢀC1ꢀO1
63.8(2)
166.3(2)
102.4(2)
178.9(6)
N1ꢀRhꢀC1
N2ꢀRhꢀC1
C1ꢀRhꢀC2
RhꢀC2ꢀO2
104.0(2)
167.8(2)
89.7(2)
178.4(5)
Fig. 7. ORTEP view of {[FcC(NCy)NHCy]Rh(CO)2}[BF4] drawn with
50% thermal ellipsoids.
Fig. 6. Cyclic voltammogram of a 10−2 M solution of [FcC(-
NCy)2]Ph(CO)2 in THF measured at 200 mV s−1 (referenced to
Cp2Fe couple).
Table 6
,
Selected bond lengths (A) and bond angles (°) for {[FcC(NCy)-
NHCy]Rh(CO)2}[BF4]
RhꢀN1
RhꢀC1
O1ꢀC1
N1ꢀC3
C3ꢀC4
2.063(5)
1.846(7)
1.149(8)
1.279(7)
1.436(8)
RhꢀN2
RhꢀC2
O2ꢀC2
N2ꢀC3
2.131(5)
1.864(6)
1.136(7)
1.481(7)
1611 cm−1, likely from a CN double bond. Addition-
ally, the H-NMR spectrum contained a singlet at 5.78
1
ppm that integrated to a single hydrogen, further sug-
gesting the formation of an amidine functionality. As
shown in Fig. 7, X-ray crystallography revealed the
product to be {[FcC(NCy)NHCy]Rh(CO)2}[BF4],
which contains ferrous Fc-group and a coordinated
h2-amidine. Similar to [FcC(NCy)2]Rh(CO)2, the 4-co-
N1ꢀRhꢀN2
N1ꢀRhꢀC2
N2ꢀRhꢀC2
RhꢀC1ꢀO1
63.6(2)
167.2(2)
103.8(2)
178.0(6)
N1ꢀRhꢀC1
N2ꢀRhꢀC 1
C1ꢀRhꢀC2
RhꢀC2ꢀO2
105.6(2)
169.0(2)
87.1(3)
179.4(6)

530
J.R. Hagadorn, J. Arnold / Journal of Organometallic Chemistry 637–639 (2001) 521–530
[6] (a) J.A.R. Schmidt, J. Arnold, Chem. Commun. (1999) 2149;
(b) P.J. Stewart, A.J. Blake, P. Mountford, Organometallics 17
(1998) 3271–3281;
(c) Y. Zhou, D.S. Richeson, Inorg. Chem. 35 (1996) 2448;
(d) A. Littke, N. Sleiman, C. Bensimon, D.S. Richeson, G.P.A.
Yap, S.J. Brown, Organometallics 17 (1998) 446;
(e) B. Vendemiati, G. Prini, A. Meetsma, B. Hessen, J.H.
Teuben, O. Traverso, Eur. J. Inorg. Chem. 3 (2001) 707–711.
[7] (a) J.R. Hagadorn, J. Arnold, Angew. Chem. Int. Ed. Engl. 37
(1998) 1729;
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 157181–157185. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
(b) G.D. Whitener, J.R. Hagadorn, J. Arnold, J. Chem. Soc.
Dalton Trans. (1999) 1249.
[8] (a) K. Kiincaid, C.P. Gerlach, G.R. Giesbrecht, J.R. Hagadorn,
G.D. Whitener, A. Shafir, J. Arnold, Organometallics 18 (1999)
5360;
Acknowledgements
(b) M.J.R. Brandsma, E.A.C. Brussee, A. Meetsma, B. Hessen,
J.H. Teuben, Eur. J. Inorg. Chem. (1998) 1867.
[9] For a recent review of this general area, see the following and
references therein: A.M. Allgeier, C.A. Mirkin, Angew. Chem.
Int. Ed. Engl. 37 (1998) 894.
We thank the DOE (contract no. DE-AC03-
76SF00098) for support of this work.
[10] E.H. Amonoo-Neizer, R.A. Shaw, D.O. Skovlin, B.C. Smith,
Inorg. Synth. 8 (1966) 19.
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