Structural variation in cobalt halide complexes supported by m-terphenyl isocyanides

Article abstract of DOI:10.1016/j.ica.2010.08.024

Detailed herein are synthetic, spectroscopic and structural studies on trisisocyanide cobalt halide complexes featuring the encumbering m-terphenyl isocyanide CNAr^Mes2 (Mes = 2,4,6-Me₃C₆H ₃). Addition of CNAr

Full text of DOI:10.1016/j.ica.2010.08.024

Inorganica Chimica Acta 364 (2010) 238–245
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Structural variation in cobalt halide complexes supported
by m-terphenyl isocyanides
⇑
Nils Weidemann, Grant W. Margulieux, Curtis E. Moore, Arnold L. Rheingold, Joshua S. Figueroa
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Mail Code 0358, La Jolla, CA 92093-0358, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 21 August 2010
Detailed herein are synthetic, spectroscopic and structural studies on trisisocyanide cobalt halide com-
plexes featuring the encumbering m-terphenyl isocyanide CNArMes2 (Mes = 2,4,6-Me3C6H3). Addition of
CNArMes2 to CoI2 in a 3:1 molar ratio provides the mononuclear complex, CoI2(CNArMes2)3, which can
Dedicated to Professor Arnold L. Rheingold,
a tremendous mentor and great friend, on
the occasion of his 70th birthday.
be oxidized to six-coordinate CoI3(CNArMes2
) upon treatment with 0.5 equivalents of I2. Contrastingly,
3
addition of CNArMes2 to CoBr2 provided the dinuclear complex Br2Co(
l ) irrespective
2-Br)2Co(CNArMes2
3
of the molar ratios employed. FTIR analysis on these Co(II) and Co(III) complexes is used to assess the rel-
ative p
-basicities of the cobalt centers toward the CNArMes2 ligands. Treatment of CoX2 (X = Cl, Br and I)
Keywords:
Isocyanides
Cobalt
with three CNArMes2 ligands followed by the addition of granulated Zn provides the pseudo-tetrahedral
complexes XCo(CNArMes2)3. FTIR, magnetic and X-ray crystallographic studies are used to determine both
Halides
Hydroformylation
X-ray crystallography
the ground state electronic structure and relative
p
-basicities of these complexes.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
bering isocyanides including CN-t-Bu and CNXyl (Xyl = 2,6-
Me2C6H3) mirror the reactivity of CO, rather than diverging from
it [17]. Furthermore, these isocyanides have been shown to stabi-
lize higher coordinate cobalt complexes than are typically available
with carbonyl ligands. This latter fact is demonstrated by the many
examples of penta-coordinate [Co(CNR)5]+ cations [16,18–20],
whereas the analogous pentacarbonyl cobalt cation, [Co(CO)5]+
has only recently been isolated in crystalline form [21].
Longstanding interest in isocyanide complexes of cobalt has
arisen because of their isolobal relationship to the classic binary
carbonyl Co2(CO)8 [1–7]. More specifically, the root of this interest
stems from attempts to model the mononuclear intermediates pro-
posed in industrial hydroformylation (oxo catalysis) initiated by
Co2(CO)8 [8–10]. For example, it has been established that the
combination of Co2(CO)8 and H2 generates two equivalents of
monohydride complex HCo(CO)4 [10]. Interestingly, there is still
debate whether H2 reacts directly with Co2(CO)8, or if the latter
undergoes homolytic cleavage to two Co(CO)4 molecules prior to
the H2 activation step [10,11]. Once formed however, carbon mon-
oxide dissociation from HCo(CO)4 is proposed to form four-coordi-
nate HCo(CO)3, which serves as the catalysis entry point [10].
Despite these proposals, definitive evidence for the presence of
either Co(CO)4 or HCo(CO)3 during hydroformylation catalysis
has remained elusive [12–15].
Accordingly, isocyanides (CNR), which allow for steric and elec-
tronic tunability [16], have been employed to model both the
structural and electronic aspects of such highly reactive cobalt car-
bonyls [1–7]. However, one common drawback to the implementa-
tion of isocyanides in this context has been their limited success
for the simultaneous stabilization of coordinative and electronic
unsaturation in mononuclear cobalt centers. In this regard, encum-
In an effort to stabilize low-coordinate metal isocyanide com-
plexes in general, we have introduced the encumbering m-ter-
phenyl isocyanide ligand, CNArMes2 [22–24]. As part of our
studies, we recently reported a series of homoleptic cobalt tetrais-
ocyanide complexes of the formulation [Co(CNArMes2)4]n in the +1,
0 and ꢀ1 charge states [25]. The neutral species Co(CNArMes2
) is
4
particularly noteworthy as it represents a formal mimic of the
reactive unsaturated carbonyl Co(CO)4.
In order to gain synthetic entry to this tetraisocyanide system,
we found that the salt Na[Co(CNArMes2)4] is accessible from Na/
Hg reduction of CoCl2 in the presence of CNArMes2. Interestingly,
optimization of the reaction conditions predicated that only three
equivalents of CNArMes2 were necessary to achieve both reasonable
yields (ca. 60%) of Na[Co(CNArMes2)4] and full consumption of the
isocyanide. Indeed, when greater than three equivalents of
CNArMes2 are employed, no increase in the yield of Na[Co(C-
NArMes2)4] was achieved. Furthermore, significant quantities of free
CNArMes2 remained. Thus, this protocol seemingly does not yield
low-valent trisisocyanide complexes which may serve as precur-
⇑
Corresponding author. Tel.: +1 858 822 7478.
E-mail address: jsfig@ucsd.edu (J.S. Figueroa).
sors to species such as HCo(CNArMes2
)
or [Co(CNArMes2)3]n
3
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.08.024

N. Weidemann et al. / Inorganica Chimica Acta 364 (2010) 238–245
239
(n = +1, 0 and ꢀ1). Accordingly, herein we present synthetic details
for tris-CNArMes2 cobalt halide complexes which may serve this
purpose. Most importantly, the complexes reported here exhibit
spectroscopic and structural features which provide insight into
C6H3 + Mes) ppm. leff (Evans Method, C6D6 with O(SiMe3)2,
400.1 MHz, 20 °C) = 1.9( 0.1) lB (average of three independent
measurements).
p-basicity properties of cobalt halide fragments toward isocyanide
2.2. Preparation of CoI3(CNArMes2
)
3
ligands.
A mixture of CoI2(CNArMes2
)
3
(0.250 g, 0.188 mmol) and I2
(0.024 g, 0.095 mmol and 0.5 equiv.) was suspended in 5 mL of
Et2O and the reaction mixture was stirred at room temperature for
3 h while gradually producing a purple precipitate. The mixture
was then concentrated to ca. 2.5 mL and a light brown supernatant
was decanted off. The resulting purple solid was washed with Et2O
(4 ꢃ 2.5 mL each), dried in vacuo and collected. Yield: 0.248 g
2. Experimental
All manipulations were carried out under an atmosphere of dry
dinitrogen using standard Schlenk and glovebox techniques. Sol-
vents were dried and deoxygenated according to standard proce-
dures. Unless otherwise stated, reagent grade starting materials
were purchased from commercial sources and used as received.
Benzene-d6 (Cambridge Isotope Laboratories) was degassed and
stored over 4 Å molecular sieves for 2 d prior to use. THF-d8 (Cam-
bridge Isotope Laboratories) was vacuum distilled from Na metal
and stored over 4 Å molecular sieves for 1 d prior to use. The isocy-
anide ligand CNArMes2, ½CoðCNArMes2Þ4ꢁBAr4F and NaBAr4F (ArF = 3,5-
(CF3)2C6H3) were prepared as previously described [22,25,26]. Cel-
ite 405 (Fisher Scientific) was dried under vacuum (24 h) at a tem-
perature above 250 °C and stored in the glovebox prior to use.
Nujol was dried with sodium metal and stored in the glovebox
prior to use. Granulated zinc metal was activated with a 2 M
hydrochloric acid solution, subsequently washed with dry THF in
three cycles and dried under vacuum prior to use.
(0.170 mmol, 90%). X-ray quality crystals of CoI3(CNArMes2
)
3
ꢂ0.5C7H8 were obtained upon diffusion of n-pentane into a concen-
trated solution in toluene at room temperature. Anal. Calc. for
C75H75CoI3N3: C, 61.78; H, 5.19; N, 2.88. Found: C, 60.73; H, 5.29;
N, 2.82% (Repeated combustion analysis attempts did not produce
more accurate results. We suspect this results from the formation
of a small amount of the triiodide complex, CoI2(I3)(CNArMes2)3 dur-
ing oxidation of CoI2(CNArMes2)3). FTIR (Nujol/KBr plates, cmꢀ1):
m
= 2727 (w), 2188 (w) [
m(CN)], 2164 (vs) [m(CN)], 1614 (m)
[m
(C@C)], 1575 (w) [ (C@C)], 1488 (w), 1414 (m), 1274 (w), 1192
m
(vw), 1186 (w), 1160 (vw), 1122 (m), 1073 (w), 1067 (w), 1033
(m), 977 (vw), 916 (vw), 882 (vw), 845 (s), 805 (m), 781 (w), 757
(m), 736 (w), 722 (w), 669 (vw), 603 (w), 561 (w), 543 (vw), 538
(vw), 533 (vw), 520 (w), 481 (w) and 472 (w). 1H NMR
(499.8 MHz, C6D6, 20 °C): d = 2.00 (s, 6H, 2 ꢃ o-CH3, Mes, cis-CNR),
2.21 (s, 12H, 4 ꢃ o-CH3, Mes, trans-CNR), 2.45 (s, 6H, 2 ꢃ p-CH3,
Mes, trans-CNR), 2.52 (s, 3H, 1 ꢃ p-CH3, Mes, cis-CNR), 6.74 (d,
3J(H,H) = 8.0 Hz, 2H, 2 ꢃ m-CH, C6H3, cis-CNR), 6.77 (d, 3J(H,H) =
7.0 Hz, 4H, 4 ꢃ m-CH, C6H3, trans-CNR), 6.86 (t, 3J(H,H) = 7.7 Hz,
2H, 2 ꢃ p-CH, C6H3, trans-CNR), 6.88 (t, 3J(H,H) = 7.5 Hz, 1H, 1 ꢃ p-
CH, C6H3, trans-CNR), 6.94 (s, 8H, 8 ꢃ m-CH, Mes, trans-CNR), 6.96
(s, 4H, 4 ꢃ m-CH, Mes, cis-CNR) ppm. 13C{1H} NMR (125.7 MHz,
C6D6, 20 °C: d = 20.5 (s, 4 ꢃ o-CH3, Mes, cis-CNR), 21.3 (s, 8 ꢃ o-
CH3, Mes, trans-CNR), 21.8 (s, 4 ꢃ p-CH3, Mes, trans-CNR), 21.9
(s, 2 ꢃ p-CH3, Mes, cis-CNR), 126.8 (s), 127.3 (s), 129.46 (s), 129.52
(s), 129.7 (s), 129.8 (s), 130.1 (s), 130.6 (s), 133.9 (s), 134.3 (s),
135.3(s), 135.7 (s), 137.2 (s), 137.3 (s), 140.98 (s), 141.02 (s), 153.1
(s, 2 ꢃ iso-C, trans-CNR) and 161.0 (s, 1 ꢃ iso-C, cis-CNR) ppm.
Solution 1H and 13C{1H} NMR spectra were recorded on Varian
Mercury 300 and 400 spectrometers and a Varian VNMRS 500
spectrometer. 1H and 13C chemical shifts are reported in ppm rel-
ative to SiMe4 (1H and 13C d = 0.0 ppm) with reference to the resid-
ual proton resonances of 7.16 ppm (1H) and 128.06 ppm (13C) for
benzene-d6 and 1.73 ppm (1H) and 25.3 ppm (13C) for THF-d8,
respectively [27]. 19F{1H} NMR spectra were referenced externally
to neat trifluoroacetic acid, F3CC(O)OH (d = ꢀ78.5 ppm versus
CFCl3 = 0.0 ppm). Room temperature FTIR spectra were recorded
on a Thermo-Nicolet iS10 FTIR spectrometer. Samples were pre-
pared as Nujol mulls between KBr plates. The following abbrevia-
tions were used for the intensities of the IR absorption bands:
vs = very strong, s = strong, m = medium, w = weak, vw = very
weak and sh = shoulder. Combustion analyses were performed by
Robertson Microlit Laboratories of Madison, New Jersey (USA).
2.3. Preparation of [CoI2(CNArMes2)4]BAr4F
2.1. Preparation of CoI2(CNArMes2
)
3
A
100 mL Schlenk tube was charged with CoI2 (0.808 g,
2.3.1. Method A
0.245 mmol and 1 equiv.) and CNArMes2 (2.500 g, 0.735 mmol and
3 equiv.) and 25 mL of THF were added to the mixture of the start-
ing materials. The resultant suspension was stirred at ambient
temperature to afford a dark brown solution within 1 h. The solu-
tion was filtered through Celite and all volatiles were then re-
moved in vacuo. The resulting residue was then subjected to
three cycles of stirring in 10 mL Et2O for 15 min, followed by evap-
oration to dryness. Upon the last cycle, a purple-brown powder
was obtained and collected. Yield: 3.378 g (0.240 mmol, 98%). X-
ray quality crystals of CoI2(CNArMes2)3ꢂEt2O were obtained from
slow evaporation of a saturated Et2O solution at room temperature.
Anal. Calc. for C79H85CoI2N3O: C, 67.52; H, 6.10; N, 2.99. Found: C,
A suspension of CoI3(CNArMes2
) (0.100 g, 0.0686 mmol) and
3
CNArMes2 (0.023 g, 0.069 mmol and 1 equiv.) in 5 mL Et2O was trea-
ted dropwise with a colorless Et2O solution of Na[BArF4] (0.060 g,
0.069 mmol and 1 equiv., 5 mL). The reaction mixture was allowed
to stir for 24 h and then filtered to remove liberated NaI. Evapora-
tion of the filtrate afforded ½CoI2ðCNArMes2Þ4ꢁBAr4F as purple powder,
which was washed (Et2O, 3 ꢃ 2.5 mL), dried in vacuo, and collected.
Yield: 0.074 g (0.029 mmol, 43%).
2.3.2. Method B
To an Et2O solution of ½CoðCNArMes2Þ4ꢁBArF4 (0.100 g, 0.044 mmol
and 5 mL) was added solid I2 (0.011 g, 0.044 mmol and 1 equiv.)
and resulted in a the rapid formation of a vibrant purple precipi-
tate. The reaction mixture was stirred for 2 h and then allowed
to settle. A light brown supernatant was then decanted from the
purple solid. The latter was washed with Et2O (3 ꢃ 2.5 mL), dried
in vacuo and collected. Yield: 0.082 g (0.031 mmol, 71%). X-ray
quality crystals of ½CoI2ðCNArMes2Þ ꢁBArF ꢂ2C6H14 were obtained
67.30; H, 5.89; N, 3.11%. FTIR (Nujol/KBr plates, cmꢀ1):
(vw), 2726 (w), 2168 (m) [ (CN)], 2127 (s) [ (CN)], 1733 (vw),
1613 (m) [ (C@C)], 1575 (w) [ (C@C)], 1414 (m), 1274 (w), 1189
(w), 1123 (w), 1071 (vw), 1031 (w), 851 (s), 810 (w), 803 (m),
783 (w), 761 (w), 755 (m), 736 (w), 723 (w), 603 (w), 563 (w),
542 (vw), 529 (w), 517 (w) 474 (vw) and 462 (w). 1H NMR
(400.1 MHz, C6D6, 20 °C): d = 2.14 (s br, 18H, 6 ꢃ p-CH3, Mes),
2.58 (s vbr, 36H, 12 ꢃ o-CH3, Mes) and 6.76 (s vbr, 21H, 21 ꢃ CH,
m = 3109
m
m
m
m
4
4
upon diffusion of n-hexane into
fluorobenzene at room temperature. Anal. Calc. for C138H127CoB-
a
concentrated solution in

240
N. Weidemann et al. / Inorganica Chimica Acta 364 (2010) 238–245
F24I2N4O1.5: C, 62.66; H, 4.84; N, 2.12. Found: C, 62.91; H, 4.56; N,
2.17%. FTIR (Nujol/KBr plates, cmꢀ1):
= 2731 (w), 2167 (vs)
(CN)], 2131 (s) [ (CN)], 1614 (m) [ (C@C)], 1587 (w) [ (C@C)],
1570 (w) [ (C@C)], 1490 (vw), 1403 (w), 1354 (s), 1276 (vs),
(m), 1351 (w), 1272 (w), 1186 (w), 1152 (vw), 1120 (m), 1076 (w
br), 1031 (m br), 857 (m), 849 (m), 804 (m), 785 (w), 757 (s),
737 (w), 722 (vw), 619 (vw), 603 (w), 564 (w), 519 (m), 514 (m)
and 496 (vw). 1H NMR (400.1 MHz, C6D6, 20 °C): d = 2.24 (s br,
18H, 6 ꢃ p-CH3, Mes), 2.70 (s vbr, 36H, 12 ꢃ o-CH3, Mes), 4.47 (s
br, 6H, 6 ꢃ m-CH, C6H3), 6.54 (s br, 12H, 12 ꢃ m-CH, Mes), 13.90
(s br, 3H, 3 ꢃ p-CH, C6H3) ppm. leff (Evans Method, C6D6 with
m
[m
m
m
m
m
1192 (vw), 1176 (m), 1158 (s), 1142 (s), 1126 (vs), 1107 (m),
1098 (w), 1076 (vw), 1033 (w), 954 (vw), 943 (vw), 935 (vw),
930 (vw), 895 (w), 885 (m), 855 (m), 839 (w), 813 (w), 808 (w),
794 (vw), 779 (w), 759 (m), 744 (w), 736 (w), 722 (vw), 717
(vw), 712 (m), 683 (m), 671 (m), 626 (vw), 619 (vw), 603 (w),
578 (vw), 563 (w), 553 (vw), 532 (w), 492 (w) and 449 (vw). 1H
NMR (300.1 MHz, THF-d8, 20 °C): d = 1.11 (t, 9H, 3J(H,H) = 7.0 Hz,
3 ꢃ CH3, Et2O), 1.86 (s, 48H, 16 ꢃ o-CH3, Mes), 2.51 (s, 24H,
8 ꢃ p-CH3, Mes), 3.38 (q, 6H, 3J(H,H) = 7.0 Hz, 3 ꢃ CH2, Et2O), 6.91
(s, 32H, 32 ꢃ m-CH, Mes), 7.21 (d, 8H, 3J(H,H) = 8.00 Hz, 8 ꢃ m-
CH, C6H3), 7.57 (s br, 4H, 4 ꢃ p-CH, C6H3-3,5-(CF3)2), 7.59 (t, 4H,
3J(H,H) = 7.6 Hz, 4 ꢃ p-CH, C6H3), 7.80 (m br, 8H, 8 ꢃ o-CH, C6H3-
3,5-(CF3)2) ppm. 13C{1H} NMR (125.7 MHz, THF-d8, 20 °C):
d = 15.6 (s, 3 ꢃ CH3, Et2O), 21.1 (s, 16 ꢃ o-CH3, Mes), 21.8 (s,
8 ꢃ p-CH3, Mes), 66.2 (s, 3 ꢃ CH2, Et2O), 118.1 (sept, 3J(F,C) = 4 Hz,
4 ꢃ p-C, C6H3-3,5-(CF3)2), 125.4 (q, 1J(F,C) = 273 Hz, 8 ꢃ CF3, C6H3-
3,5-(CF3)2), 126.0 (s), 129.0 (s br, 4 ꢃ iso-C, CNR), 129.9 (qq,
2J(F,C) = 32 Hz, 4J(F,C) = 3 Hz, 8 ꢃ m-C, C6H3-3,5-(CF3)2), 130.7 (s),
132.1 (s), 133.3 (s), 133.9 (s), 135.5 (s), 136.4 (s), 138.0 (s), 141.4,
O(SiMe3)2, 400.1 MHz, 20 °C) = 3.0( 0.1) lB (average of three inde-
pendent measurements).
2.6. Preparation of ClCo(CNArMes2
)
3
A mixture of CoCl2 (0.064 g, 0.491 mmol) and CNArMes2 (0.500 g,
1.473 mmol and 3 equiv.) was suspended in THF (10 mL) and al-
lowed to stir for 2 h. Granular Zn (0.322 g, 4.91 mmol and 10 equiv.)
was then added and resulted in a color change from blue to brown.
The reaction mixture was allowed to stir for 3 h and then decanted
from the excess Zn metal. All volatiles were removed in vacuo and
the resulting residue was extracted with an Et2O/n-pentane mixture
(9:1, 20 mL) and filtered through Celite. Evaporation of the solvent
resulted in an olive-green powder, which was collected. Yield:
0.384 g (0.324 mmol, 66%). X-ray quality crystals of ClCo(CNAr-
Mes2)3ꢂEt2O were obtained from a saturated Et2O solution stored at
ꢀ35 °C. Anal. Calc. for C79H85ClCoN3O: C, 79.94; H, 7.22; N, 3.54.
Found: C, 79.27; H, 7.44; N, 3.46%. FTIR (Nujol/KBr plates, cmꢀ1):
162.7 (q, 1J(13C,11B) = 50 Hz; sept, 1J(13C,10B) = 17 Hz; 4 ipso-C,
´
C6H3-3,5-(CF3)2) ppm.
m
= 2730 (w), 2045 (vs) [
m
(CN)], 1995 (s sh) [
m(CN)], 1613 (m)
2.4. Preparation of Br2Co(
l
2-Br)2Co(CNArMes2
)
3
[m
(C@C)], 1582 (w) [ (C@C)], 1572 (w) [m
m
(C@C)], 1487 (vw sh),
1415 (m), 1300 (vw), 1288 (vw), 1272 (w), 1161 (w), 1105 (vw),
1088 (vw), 1072 (vw), 1301 (m br), 1011 (w sh), 919 (w), 877 (w),
853 (s), 846 (s), 809 (m), 805 (s), 784 (m), 758 (s), 735 (m), 722
(w), 687 (vw), 620 (w), 603 (m), 556 (m), 564 (w), 524 (m), 514
(m) and 496 (vw). 1H NMR (400.1 MHz, C6D6, 20 °C): d = 1.12 (t,
3J(H,H) = 7.0 Hz, 6H, 2 ꢃ CH3, Et2O), 2.10 (s br, 18H, 6 ꢃ p-CH3,
Mes), 2.58 (s vbr, 36H, 12 ꢃ o-CH3, Mes), 3.27 (q, 3J(H,H) = 7.0 Hz,
4H, 2 ꢃ CH2, Et2O), 3.65 (s br, 6H, 6 ꢃ m-CH, C6H3), 6.40 (s br, 12H,
12 ꢃ m-CH, Mes) and 15.50 (s br, 3H, 3 ꢃ p-CH, C6H3) ppm. leff
(Evans Method, C6D6 with O(SiMe3)2, 400.1 MHz, 20 °C) = 3.1( 0.1)
A mixture of CoBr2 (0.043 g, 0.20 mmol) and CNArMes2 (0.100 g,
0.295 mmol and 1.5 equiv.) was dissolved in 5 mL THF, allowed to
stir for 24 h and filtered from insoluble components. All volatiles
were removed under reduced pressure. The resulting residue was
then subjected to three cycles of n-pentane (2 mL) wash, followed
by drying in vacuo. After the last cycle, Br2Co(
was obtained as a pale green powder. Yield: 0.128 g (0.0879 mmol,
89%). X-ray quality crystals of Br2Co( were
2-Br)2Co(CNArMes2
l )
2-Br)2Co(CNArMes2
3
l
)
3
obtained from slow evaporation of a saturated C6D6 solution at
room temperature. Anal. Calc. for C75H75Co2Br4N3: C, 61.87; H,
5.19; N, 2.89. Found: C, 61.66; H, 5.07; N, 2.87%. FTIR (Nujol/KBr
lB (average of three independent measurements).
plates, cmꢀ1):
2155 (m) [ (CN)], 2085 (w) [
(C@C)], 1572 (w) [ (C@C)], 1402 (w), 1275 (m), 1190 (w), 1162
m
= 2731 (w), 2191 (w) [
m
(CN)], 2176 (vs) [
m
(CN)],
2.7. Preparation of BrCo(CNArMes2
)
3
m
m
(CN)], 1612 (m) [
m
(C@C)], 1580 (w)
[m
m
This tan-green complex was prepared in analogous fashion to
(vw), 1070 (w), 1032 (m br), 919 (vw), 855 (m), 848 (m), 808
(m), 785 (w), 778 (w), 756 (/m), 737 (w), 722 (w), 607 (w), 563
(w), 543 (vw) and 525 (w). 1H NMR (400.1 MHz, C6D6, 20 °C):
d = ꢀ3.22 (s br, 3H, 3 ꢃ p-CH, C6H3), ꢀ0.01 (s vbr, 36H, 12 ꢃ o-
CH3, Mes), 3.54 (s br, 18H, 6 ꢃ p-CH3, Mes), 5.17 (s vbr, 6H,
6 ꢃ m-CH, C6H3), 7.03 (s br, 12H, 12 ꢃ m-CH, Mes) ppm.
ClCo(CNArMes2
)
employing 0.124 g (0.567 mmol) of CoBr2 and
3
0.500 g (1.473 mmol, 2.6 equiv.) of CNArMes2 Yield: 0.343 g
(0.279 mmol, 57%). X-ray quality crystals of BrCo(CNArMes2)3ꢂEt2O
were obtained from a saturated Et2O solution stored at ꢀ35 °C. Anal.
Calc. for C79H85BrCoN3O: C, 77.05; H, 6.96; N, 3.41. Found: C, 76.84;
H, 6.77; N, 3.29%. FTIR (Nujol/KBr plates, cmꢀ1):
(vs) [ (CN)], 1990 (s sh) [ (CN)], 1612 (m) [
(C@C)], 1414 (m), 1351 (vw), 1299 (vw), 1289 (vw), 1271 (w),
m
= 2729 (w), 2037
m
m
m(C@C)], 1574 (w)
2.5. Preparation of ICo(CNArMes2
)
3
[m
1186 (w), 1160 (w), 1152 (w), 1120 (m br), 1074 (w), 1066 (w),
1030 (m br), 971 (vw), 937 (vw), 916 (vw), 890 (vw), 849 (s br),
804 (m), 785 (m), 756 (s), 736 (m), 723 (w sh), 669 (vw), 654 (vw),
620 (w) 603 (w), 564 (w), 553 (vw sh), 513 (m) and 495 (w). 1H
NMR (400.1 MHz, C6D6, 20 °C): d = 1.12 (t, 3J(H,H) = 7.0 Hz, 6H,
2 ꢃ CH3, Et2O), 2.17 (s br, 18H, 6 ꢃ p-CH3, Mes), 2.63 (s vbr, 36H,
12 ꢃ o-CH3, Mes), 3.27 (q, 3J(H,H) = 6.9 Hz, 4H, 2 ꢃ CH2, Et2O), 3.95
(s br, 6H, 6 ꢃ m-CH, C6H3), 6.43 (s br, 12H, 12 ꢃ m-CH, Mes) and
A mixture of CoI2(CNArMes2
) (0.650 g, 0.488 mmol) and granu-
3
lated zinc metal (0.160 g, 2.45 mmol and 5.4 equiv.) was sus-
pended in 10 mL of THF and allowed to stir for 48 h. The reaction
mixture gradually changed in color from purple-brown to green-
brown. The reaction mixture was then filtered and all volatiles
were removed in vacuo. The resultant green-brown residue was ex-
tracted with an Et2O/n-pentane mixture (10:1, 15 mL), filtered
through Celite and evaporated to dryness. The resulting olive-
green solid was washed with n-pentane (3 ꢃ 1 mL), dried in vacuo
and collected. Yield: 0.578 g (0.452 mmol, 93%). X-ray quality crys-
tals of ICo(CNArMes2)3ꢂEt2O were obtained from a saturated Et2O
solution stored at ꢀ35 °C. Anal. Calc. for C79H85CoIN3O: C, 74.22;
H, 6.70; N, 3.29. Found: C, 74.01; H, 6.89; N, 3.20. FTIR (Nujol/
14.95 (s br, 3H, 3 ꢃ p-CH, C6H3) ppm.
leff (Evans Method, C6D6 with
O(SiMe3)2, 400.1 MHz, 20 °C) = 3.2( 0.1)
lB (average of three inde-
pendent measurements).
2.8. Crystallographic structure determinations
KBr plates, cmꢀ1):
(CN)], 1613 (m) [
m
m
= 2730 (w), 2048 (vs) [
(C@C)], 1575 (w) [ (C@C)], 1489 (w), 1415
m
(CN)], 1991 (m sh)
Single crystal X-ray structure determinations were carried out
at low temperature on a Bruker P4 or Platform Diffractometer
[m
m

N. Weidemann et al. / Inorganica Chimica Acta 364 (2010) 238–245
241
equipped with a Bruker APEX II detector. All structures were solved
by direct methods with SIR 2004 [28] and refined by full-matrix
least-squares procedures utilizing SHELXL-97 [29]. Crystallographic
data collection and refinement information is listed in Table 3.
CIF files for all structures have been deposited with the Cambridge
Crystallographic Data Center (CCDC) (See Supplementary
material).
3. Results and discussion
To access low-valent, trisisocyanide cobalt complexes, we envi-
sioned that simple pre-coordination of three CNArMes2 ligands to
Co(II) halides would suffice as a suitable synthetic entry point. Sur-
prisingly however, we found that treatment of commercially avail-
able CoCl2 with 3.0 equiv of CNArMes2 in THF solution did not lead
to an isolable complex of the formulation CoCl2(CNArMes2)3. In-
stead, 1H NMR and FTIR analysis of 3:1 CNArMes2/CoCl2 mixtures
in C6D6 solution revealed a complex speciation pattern indicative
of rapid exchange between free and coordinated CNArMes2. While
cobalt dichloride complexes of less encumbering isocyanides are
known, the [CoCl2] fragment presumably lacks sufficient Lewis
acidity to tightly bind three CNArMes2 ligands. Notably, we have
previously observed similar behavior for the interaction of
CNArMes2 and Cu(I) halide salts [22]. In this latter work, it was
found that both the [CuI] and [CuOTf] (OTf = triflate, OSO2CF3) frag-
ments readily bound three CNArMes2 ligands, whereas only two
were accommodated by the relatively less Lewis acidic [CuCl] unit
[30,31].
Fig. 1. Molecular Structure of CoI2(CNArMes2)3. Selected bond lengths (Å) and angles
(°): Co1–I1 2.5555(14), Co1–I2 2.5741(16), Co1–C1 1.844(3), Co1–C2 1.894(3), Co1–
C3 1.869(3), C1–N1 1.153(4), C2–N2 1.150(4), C3–N3 1.158(4), I1–Co1–I2
149.15(2), I1–Co1–C2 103.75(10), C1–Co1–C3 168.16(12), C1–Co1–C2 93.53(14).
sistent with a mononuclear, d7 Co(II) center possessing an S = ½
ground state. Interestingly, the 1H NMR spectrum of CoI2(C-
NArMes2
)
in C6D6, exhibited a single set of paramagnetically
3
Gratifyingly, a similar trend is observed in the case of cobalt.
Thus, simple addition of 3.0 equiv of CNArMes2 to CoI2 in THF solu-
shifted resonances, thus indicating that the five-coordinate com-
plex is likely fluxional in solution. FTIR analysis (Nujol) on CoI2(C-
tion readily provided the trisisocyanide complex CoI2(CNArMes2
)
3
NArMes2
)
revealed the presence of two
m
(CN) bands centered at
3
as an isolable purple-brown crystalline solid (Scheme 1). Crystallo-
graphic structure determination on crystals grown from Et2O re-
2168 and 2127 cmꢀ1. Notably, these
m(CN) stretches are shifted
to higher energy relative to free CNArMes2
[22], thereby indicating significantly limited
(
p
m
(CN) = 2118 cmꢀ1
backbonding be-
)
vealed
a square pyramidal, mononuclear complex with the
CNArMes2 ligands occupying the axial and two basal positions
(Fig. 1). Evans method magnetic moment determination (C6D6/
tween the d7 center and the isocyanide units [32–35].
Despite the presence of three encumbering CNArMes2 ligands, a
(Me3Si)2O, 20 °C) resulted in a leff value of 1.9(1) lB, which is con-
notable structural feature of CoI2(CNArMes2
)
3
is the seeming avail-
ability of a sixth coordination site. To access this site and probe the
redox behavior of the system, we sought to chemically oxidize
CoI2(CNArMes2
CoI2(CNArMes2
)
)
to d6 Co(III) species. Accordingly, treatment of
with 0.5 equiv of I2 in Et2O solution readily pro-
3
3
vided the diamagnetic complex mer-CoI3(CNArMes2
)
3
as deter-
mined by X-ray crystallography (Fig. 2, Scheme 1). Notably, the
mer-configuration of CoI3(CNArMes2
)
is retained in solution as
3
indicated by the 2:1 ratio of CNArMes2 resonances in its 1H NMR
spectrum (C6D6). The FTIR spectrum (Nujol) of CoI3(CNArMes2
)
3
showed two
m
(CN) bands at 2188 and 2164 cmꢀ1, which are further
shifted to higher energy relative to CoI2(CNArMes2)3 (Table 1). Thus,
despite the low-spin d6 configuration,
p-backbonding interactions
to the CNArMes2 ligands are significantly attenuated by oxidized
nature of the Co center in CoI3(CNArMes2)3. Notably however, the
molecular orbital structure pertaining to the C2v mer-configuration
of d6 octahedral complexes does not maximize
p-backbonding
interactions, especially when compared to the analogous fac-iso-
mers [36].
Other six-coordinate Co(III) complexes are also available from
CoI3(CNArMes2)3. Treatment of CoI3(CNArMes2
)
with NaBArF
4
3
(ArF = 3,5-(CF3)2C6H3) in the presence of an additional equivalent
of CNArMes2 cleanly provides the tetraisocyanide salt [CoI2(CNAr-
Mes2)4]BArF4, which possesses a trans diiodide configuration (Fig. 3,
Scheme 1). As an alternative synthesis, [CoI2(CNArMes2)4]BArF can
4
be readily generated by treatment of the salt [Co(CNArMes2)4]BArF
4
with one equiv of I2 [25]. Tetraisocyanide [CoI2(CNArMes2)4]BArF
4
gives rise to
m
(CN) bands (2167 and 2131 cmꢀ1) that are slightly
Scheme 1.
lower in energy relative to its six-coordinate counterpart

242
N. Weidemann et al. / Inorganica Chimica Acta 364 (2010) 238–245
Fig. 2. Molecular structure of CoI3(CNArMes2)3. Selected bond lengths (Å) and angles
(°): Co1–I1 2.6017(10), Co1–I2 2.6021(10), Co1–I3 2.6035(10), Co1–C1 1.870(6),
Co1–C2 1.866(6), Co1–C3 1.847(6), C1–N1 1.151(8), C2–N2 1.154(8), C3–N3
1.158(8), I1–Co1–I1 172.65(4), I1–Co1–I3 91.87(3), I3–Co1–C3 177.46(18), I3–
Co1–C1 87.92(18), C1–Co1–C2 172.3(3), C1–Co1–C3 94.5(2).
Table 1
Solid-state
m
(CN) stretching frequencies for cobalt halide complexes of CNArMes2
(Nujol/KBr plates). Sh = Shoulder.
Compound
m
(CN) (cmꢀ1
)
CoI2(CNArMes2
CoI3(CNArMes2
)
)
2168(m), 2127(s)
2188(w), 2164(vs)
2167(vs), 2131(s)
3
3
½CoI2ðCNArMes2Þ4ꢁBAr4F
Br2Co(
l
2-Br)2Co(CNArMes2
)
3
2191(w), 2176(vs), 2155(m), 2085(w)
2045(vs), 1995(s, sh)
2037(vs), 1990(s, sh)
ClCo(CNArMes2
)
3
)
BrCo(CNArMes2
3
ICo(CNArMes2
)
3
2048(vs), 1991(m, sh)
Table 2
Selected bond lengths and angles for XCo(CNArMes2
)
complexes (X = Cl, Br and I).
3
Complex
ClCo(CNArMes2
)
3
BrCo(CNArMes2
)
3
ICo(CNArMes2
)
3
Bond lengths (Å)
Co1–X1
Co1–C1
Co1–C2
Co1–C3
C1–N1
C2–N2
C3–N3
2.2062(8)
1.913(2)
1.920(2)
1.902(2)
1.167(3)
1.165(3)
1.169(2)
2.3470(3)
1.914(2)
1.919(2)
1.906(1)
1.168(2)
1.168(2)
1.166(2)
2.5327(5)
1.903(3)
1.918(4)
1.912(3)
1.170(4)
1.163(5)
1.167(4)
Bond angles (°)
X1–Co1–C1
X1–Co1–C2
X1–Co1–C3
C1–Co1–C2
C1–Co1–C3
C2–Co1–C3
116.42(6)
109.42(6)
118.62(6)
106.76(9)
98.82(9)
116.57(5)
108.11(5)
118.10(5)
107.23(7)
99.47(7)
116.61(9)
107.5(1)
119.26(9)
103.9(1)
99.1(1)
105.80(9)
106.44(7)
109.3(1)
CoI3(CNArMes2
) (Table 1). Presumably, this fact reflects the in-
3
creased electron density on the Co(III) center provided by the fourth
r
-donating CNArMes2 ligand.
Whereas the reaction between three CNArMes2 ligands and CoI2
proceeded smoothly and completely to a single mononuclear prod-
uct, the reaction between CNArMes2 and CoBr2 proved to be more
complicated. Combination of CNArMes2 and CoBr2 in a 3:1 ratio in

N. Weidemann et al. / Inorganica Chimica Acta 364 (2010) 238–245
243
THF solution afforded the green dinuclear complex Br2Co(
l
2-Br)2
Co(CNArMes2
)
as determined by X-ray crystallography (Fig. 4).
3
While its formation under these conditions is unclear, it is impor-
tant to note that Br2Co( is obtained exclu-
l
2-Br)2Co(CNArMes2
)
3
sively in this reaction irrespective of the equivalency of either
CNArMes2 or CoBr2 employed. However, the highest yields of
Br2Co(
CoBr2 ratio is used (Scheme 2). Interestingly, the square pyrami-
dal/tetrahedral edge-sharing motif in dinuclear Br2Co( 2-Br)2Co(C-
NArMes2
has only been observed in one other cobalt halide
l ) /
2-Br)2Co(CNArMes2 are obtained when a 3:2 CNArMes2
3
l
)
3
coordination complex, namely Cl2Co(
MeC(CH2PPh2)3) [37,38]. The FTIR spectrum of Br2Co(
NArMes2 (CN) bands at 2176 and 2155 cmꢀ1
exhibits two main
l
2-Cl)2Co(triphos) (triphos =
Scheme 2.
l2-Br)2Co(C-
)
m
,
3
again reflecting insignificant
ligands.
p
-backdonation to the CNArMes
Scheme 3.
Fig. 3. Molecular structure of the cation in ½CoI2ðCNArMes2Þ4ꢁBAr4F . Selected bond
lengths (Å) and angles (°): Co1–I1 2.5765(2), Co1–C1 1.907(2), Co1–C2 1.898(2),
C1–N1 1.148(3), C2–N2 1.154(3), I1–Co1–C1 91.53(7), I1–Co1–C2 90.04(7), C1–
Co1–C2 89.73(9).
Fig. 4. Molecular structure of Br2Co(l
2-Br)2Co(CNArMes2)3. Selected bond lengths
(Å) and angles (°): Co1–Br1 2.4096(5), Co1–Br2 2.5599(5), Co2–Br1 2.5205(6), Co2–
Br2 2.4468(5), Co2–Br3 2.3598(6), Co2–Br4 2.3632(6), Co1–C1 1.871(3), Co1–C2
1.901(3), Co1–C3 1.879(3), C1–N1 1.152(4), C2–N2 1.154(4), C3–N3 1.152(4), Br1–
Co1–Br2 91.127(18), Br1–Co1–C1 167.50(9), Br1–Co1–C2 92.92(9), C2–Co1–C3
172.29(13), Br1–Co1–Br2–Co2 ꢀ0.66(2).
Fig. 5. Molecular structure of ClCo(CNArMes2)3. See Table
lengths and angles.
2
for selected bond

244
N. Weidemann et al. / Inorganica Chimica Acta 364 (2010) 238–245
Despite the differing speciation patterns for CNArMes2 com-
as a pseudo-tetrahedral monomer in the solid state. Furthermore,
Evans Method magnetic moment determination (C6D6/(Me3Si)2O,
20 °C) confirmed that each complex possesses an S = 1 ground state
consistent with a d8 metal center in a C3v-symmetric ligand field
plexes of the divalent cobalt halides, each system can be readily
converted into a stable monovalent, trisisocyanide halide complex
upon the addition of granulated Zn (Scheme 3). Thus, treatment of
pre-formed CoI2(CNArMes2)3 with Zn granules in THF solution read-
(X = Cl,
B). The FTIR spectrum of each complex exhibits two
(Table 1), which are shifted to lower energy relative to free
CNArMes2 (CN) = 2118 cmꢀ1) [22]. Thus, reduction to the mono-
valent state is apparently necessary for the Co center in these com-
plexes to more efficiently engage in -backbonding interactions to
three CNArMes2 ligands. Accordingly, isolation of monoiodide
ICo(CNArMes2
is particularly gratifying in that it, along with
leff = 3.1(1)
lB; X = Br,
leff = 3.2(1)
lB; X = I,
leff = 3.0(1)
ily provides the four-coordinate complex ICo(CNArMes2
)
as a
l
m(CN) bands
3
green-brown solid. The monochloro and monobromo complexes,
ClCo(CNArMes2 and BrCo(CNArMes2)3, are obtained in high yields
)
(m
3
by a similar manner, but without the need for pre-coordination
of three CNArMes2 ligands to the Co center (Scheme 3). Notably, this
protocol mirrors that used for the formation of the classic tris(tri-
phenylphosphine) monohalides of cobalt (i.e. XCo(PPh3)3; X = Cl, Br
and I), which were the first reported tetrahedral cobalt complexes
[39].
p
)
3
CoI2(CNArMes2)3 and CoI3(CNArMes2)3, allow for a systematic assess-
ment of both oxidation state and coordination number on
p-basi-
Structural characterization of the XCo(CNArMes2
) complexes
3
city properties of cobalt toward three CNArMes2 ligands.
(X = Cl, Br and I, Figs. 5–7, respectively) confirmed that each exists
4. Summary and conclusions
As detailed above, differing speciation patterns are encountered
upon addition of the encumbering m-terphenyl isocyanide ligand
CNArMes2 to cobalt dihalide salts. In the case of the cobalt dichlo-
ride fragment, productive isocyanide binding leading to a stable
complex does not take place. However, treatment of the more Le-
wis acidic CoI2 and CoBr2 fragments with three CNArMes2 ligands
results in the formation of stable mono- and dinuclear Co trisisocy-
anide complexes, respectively. The diiodide complex, CoI2(C-
NArMes2)3, can be further oxidized with I2 to the six-coordinate,
octahedral complex CoI3(CNArMes2)3, which retains all three isocy-
anide ligands. FTIR analysis of these Co(II) and Co(III) complexes
revealed that minimal
ligands are present. In contrast, FTIR analysis of the Co(I), monoha-
lide complexes XCo(CNArMes2
revealed that significant -backb-
onding interactions are present. These monovalent, monohalide
p
-backbonding interactions to the CNArMes2
)
p
3
CoX(CNArMes2
)3 complexes can be conveniently prepared by treat-
ment of cobalt dihalide salts with three equivalents of CNArMes2
followed by addition of zinc. We are currently probing the ability
of these CoX(CNArMes2
) complexes to serve as precursors to low-
3
coordinate and hydrido trisisocyanide complexes such as the
[Co(CNArMes2)3]ꢀ anion and HCo(CNArMes2)3.
Fig. 6. Molecular structure of BrCo(CNArMes2)3. See Table 2 for selected bond
lengths and angles.
Acknowledgments
We thank UCSD, the Camille and Henry Dreyfus Foundation, the
Hellman Family Foundation and the ACS Petroleum Research Fund
for generous support. Matthew D. Millard is thanked for assistance
with X-ray crystallography.
Appendix A. Supplementary material
CCDC 779035, 779036, 779037, 779038, 779039, 779040 and
779041 contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2010.
08.024.
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