Synthesis and structure of 6-aminofulvene-2-aldiminate complexes

Article abstract of DOI:10.1021/ic101524b

We report here a synthetic route to bis(N,N'-aryl)-6-aminofulvene-2- aldimine (AFA) ligand systems, specifically Ph₂-AFAH and Dip ₂-AFAH. The synthesis and structural characterization of a series of Cu(I) complexes [(Ph₂-AFA)-Cu(CNPh)₂](2), [(Ph ₂-AFA)Cu(CNPr)] (3), and [(Dip₂-AFA)Cu(CNiPr)] (4), from the reaction of the corresponding lithiated AFA systems with Cu-Cl derivatives are reported; notably in the case of [(Ph₂-AFA)Cu(CNPh)₂] studies have revealed the existence of two structural isomers (2a and 2b), both of which can be isolated and structurally characterized. Density functional theory (DFT) calculations suggest that the two crystal forms are comparatively close in energy, and geometry optimization reveals a convergence of these two forms to a geometry that more closely resembles the solid-state structure of isomer 2b, having a CH ... π interaction. The reactions of the AFA compounds Ph₂-AFAH and Dip₂-AFAH with ZnMev and AlMe ₃ have also been investigated, and the results of these reactions are described here.

Full text of DOI:10.1021/ic101524b

Inorg. Chem. 2011, 50, 937–948 937
DOI: 10.1021/ic101524b
Synthesis and Structure of 6-Aminofulvene-2-aldiminate Complexes
Alexander M. Willcocks,† Alexander Gilbank,† Stephen P. Richards,† Simon K. Brayshaw,† Andrew J. Kingsley,‡
Raj Odedra,‡ and Andrew L. Johnson*,†
†Department of Chemistry, University of Bath, Bath, BA2 7AY, United Kingdom, and
‡SAFC-Hitech, Power Road, Bromborough, Wirral, CH62 3QF, United Kingdom
Received July 29, 2010
We report here a synthetic route to bis(N,N 0-aryl)-6-aminofulvene-2-aldimine (AFA) ligand systems, specifically Ph2-
AFAH and Dip2-AFAH. The synthesis and structural characterization of a series of Cu(I) complexes [(Ph2-AFA)-
Cu(CNPh)2] (2), [(Ph2-AFA)Cu(CNiPr)] (3), and [(Dip2-AFA)Cu(CNiPr)] (4), from the reaction of the corresponding
lithiated AFA systems with Cu-Cl derivatives are reported; notably in the case of [(Ph2-AFA)Cu(CNPh)2] studies
have revealed the existence of two structural isomers (2a and 2b), both of which can be isolated and structurally
characterized. Density functional theory (DFT) calculations suggest that the two crystal forms are comparatively close
in energy, and geometry optimization reveals a convergence of these two forms to a geometry that more closely
resembles the solid-state structure of isomer 2b, having a CH π interaction. The reactions of the AFA compounds
Ph2-AFAH and Dip2-AFAH with ZnMe2 and AlMe3 have also been investigated, and the results of these reactions are
described here.
3 3 3
Introduction
tous cyclopentadienyl ligands. Of particular interest have
been ligand systems such as β-diketiminate (A),1 amino-
troponiminate (B),2 anilido-iminate ligands (C),3 and 1,2-
cyclopentadienyl diimine ligands4 (D and E), as represented
in Figure 1, all of which are mono anionic ligands with similar
ligand architectures. In all cases, these ligands can be tuned
electronically and sterically by varying their alkyl or aryl
substituents. Subsequently, many main group element, tran-
sition metal, and lanthanide metal complexes containing these
ligands have been prepared, and their chemistries studied.
In this context, 6-aminofulvene-2-aldimine (AFA) systems
(E), which have features in common with β-diketiminate,
amino-troponiminate, anilido-iminate ligands, and 1,2-cy-
clopentadienyl diimine ligands (D), have been known since
1963.5 Despite this, it is only recently that AFA-systems have
attracted interest as ligands because of their potential to bind
to metal atoms via one of two possible bonding modes; either
through the diimine donor groups (E), or the cyclopentadie-
nyl unit (E0).4c-f To-date, AFA-complexes of very few metals
have been described in the literature [Mg, Zn, Fe, Ru, and
The synthesis and development of ligand systems is of
particular importance in the development of organometallic
chemistry, as specific ligand-sets impart a dominant influence
over both the physical and electronic properties of the metal
centers within subsequent complexes. To this end, consider-
able effort has been directed toward the synthesis monoanionic
ligand systems, as replacements (or alternatives) to the ubiqui-
*To whom correspondence should be addressed. Phone: 44 (0)1225
384467. Fax: 44 (0)1225 386231. E-mail: a.l.johnson@bath.ac.uk.
(1) (a) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; MacDougall, D. J.;
Mahon, M. F.; Procopiou, P. A. Dalton Trans. 2009, 9715. (b) Jana, A.;
Objartel, I.; Roesky, H. W.; Stalke, D. Dalton Trans. 2010, 39, 4647. (c) Solis-
Ibarra, D.; Gomora-Figueroa, A. P.; Zavala-Segovia, N.; Jancik, V. Eur. J. Inorg.
Chem. 2009, 4564. (d) Shimokawa, C.; Itoh, S. Inorg. Chem. 2005, 44, 3010.
(e) Dove, A. P.; Gibson, V. C.; Hormnirun, P.; Marshall, E. L.; Segal, J. A.; White,
A. J. P.; Williams, D. J. Dalton Trans. 2003, 3088. (f) Stender, M.; Eichler, B. E.;
Hardman, N. J.; Power, P. P.; Prust, J.; Noltemeyer, M.; Roesky, H. W. Inorg.
Chem. 2001, 40, 2794.
(2) (a) Datta, S.; Roesky, P. W.; Blechert, S. Organometallics 2007, 26,
4392. (b) Datta, S.; Gamer, M. T.; Roesky, P. W. Dalton Trans. 2008, 2839.
(c) Datta, S.; Gamer, M. T.; Roesky, P. W. Organometallics 2008, 27, 1207.
(d) Lohnwitz, K.; Molski, M. J.; Luhl, A.; Roesky, P. W.; Dochnahl, M.; Blechert,
S. Eur. J. Inorg. Chem. 2009, 1369. (e) Meyer, N.; Roesky, P. W. Organome-
tallics 2009, 28, 306. (f) Dochnahl, M.; Lohnwitz, K.; Pissarek, J. W.; Roesky,
P. W.; Blechert, S. Dalton Trans. 2008, 2844. (g) Meiners, J.; Herrmann, J. S.;
Roesky, P. W. Inorg. Chem. 2007, 46, 4599.
(4) (a) Ong, C. M.; Stephan, D. W. Inorg. Chem. 1999, 38, 5189. (b) Etkin,
N.; Ong, C. M.; Stephan, D. W. Organometallics 1998, 17, 3656. (c) Bailey, P. J.;
Lorono-Gonzalez, D.; Parsons, S. Chem. Commun. 2003, 1426. (d) Bailey, P. J.;
Melchionna, M.; Parsons, S. Organometallics 2007, 26, 128. (e) Bailey, P. J.;
Collins, A.; Haack, P.; Parsons, S.; Rahman, M.; Smith, D.; White, F. J. Dalton
Trans. 2010, 39, 1591. (f) Johnson, A. L.; Willcocks, A. M.; Raithby, P. R.;
Warren, M. R.; Kingsley, A. J.; Odedra, R. Dalton Trans. 2009, 922.
(5) (a) Hafner, K.; Vopel, K. H.; Ploss, G.; Konig, C. Justus Liebigs Ann.
Chem. 1963, 661, 52. (b) Hafner, K.; Vopel, K. H.; Ploss, G.; Konig, C. Org.
Synth. 1967, 46, 52. (c) Ohta, B. K.; Perrin, C. L. Chem. Abstr. 1999, 217, U155.
(3) (a) Liu, X. M.; Gao, W.; Mu, Y.; Li, G. H.; Ye, L.; Xia, H.; Ren, Y.;
Feng, S. H. Organometallics 2005, 24, 1614. (b) Mcheik, A.; Katir, N.; Castel,
A.; Gornitzka, H.; Massou, S.; Riviere, P.; Hamieh, T. Eur. J. Inorg. Chem. 2008,
5397. (c) Long, J. M.; Gao, H. Y.; Liu, F. S.; Song, K. M.; Hu, H.; Zhang, L.; Zhu,
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r
2011 American Chemical Society
Published on Web 01/05/2011
pubs.acs.org/IC

938 Inorganic Chemistry, Vol. 50, No. 3, 2011
Willcocks et al.
crystals (8.3 g, 74%). Elemental analysis calcd for C19H16N2; C:
83.78, H: 5.93, N: 10.29, Found; C: 83.80, H: 5.90, N: 10.30. 1H
3
NMR (300.22 MHz, 298 K, CDCl3), δ: 6.27 (t, 1H, CH, J =
3
3.67 Hz), 6.87 (d, 2H, CH, J = 3.67 Hz), 7.08-7.16 (m, 2H,
C6H5), 7.21-7.24 (m, 2H, C6H5), 7.3-7.39 (m, 1H, C6H5), 8.09
(d, 2H, CH, 3J = 6.18 Hz), 15.41 (s, 1H, NH). 13C {1H} NMR
(75.49 MHz, 298 K, CDCl3), δ: 119.5, 121.3, 122.5, 125.2, 129.9,
135.1, 145.7, 151.0.
Synthesis of Dip2-AFAH. Dip2-AFAH was made using the
procedure described for Ph2-AFAH, substituting 2,6-diisopro-
pylaniline (18.9 mL, 100 mmol) for aniline. Bright yellow
crystals of Dip2-AFAH were obtained (12.4 g, 68%). Elemental
analysis calcd for C31H40N2C; C: 84.48, H: 9.16, N: 6.36, Found;
C: 84.60, H: 9.20, N: 6.28. 1H NMR (300.22 MHz, 298 K,
CDCl3), δ: 1.18 (d, 24H, Ph(CH(CH3)2)2 3J = 6.79 Hz), 3.21
(sept, 4H, Ph(CH(CH3)2)2, 3J = 6.79 Hz), 6.51 (t, 1H, CH, 3J =
Figure 1. Monoanionic imine based ligands (A-D) with a structural
relationship to the AFA system (E), and the two known tautomeric
coordination modes of the AFA ligand (E and E0).
3
3.65 Hz), 7.08 (d, 2H, CH J = 3.65 Hz), 7.15-7.29 (m, 6H,
C6H3), 7.92 (d, 2H, CH, 3J = 7.15 Hz), 14.48 (t, 1H, NH, 3J =
7.15 Hz). 13C {1H} NMR (75.49 MHz, 298 K, CDCl3), δ: 24.2,
28.4, 119.7, 121.1, 123.7, 123.7, 133.6, 142.3, 142.4, 157.7.
Synthesis of [(Ph2-AFA)Cu(CNPh)2], (2b). In a dry Schlenk
tube, under an inert atmosphere of argon, stoichiometric quan-
tities of lithium hexamethyldisilylamide (2.00 mmol, 0.335 g)
and Ph2-AFAH (2.00 mmol, 0.544 g) were combined in a
tetrahydrofuran (THF) solution (20 mL). The reaction mixture
was then stirred for 1 h, followed by the addition of [(PhNC)2-
Cu(μ2-Cl)]2 (0.61 g, 1.00 mmol) in THF (20 mL) and further
stirring for 16 h. After which time the volatiles were removed
under reduced pressure. Dry hexane (20 mL) was added to the
resultant residue, and was left to stir for 15 min. The volatiles
were then removed under reduced pressure. This process was
repeated three times in total to remove any residual THF.
Further hexane (50 mL) was added, and the slurry was filtered
through Celite to remove any insoluble materials, and the volatiles
removed in vacuo. This resulted in a dark brown crude product
that was purified by recrystallization (hexane) to afford 2b as
orange crystals (0.651 g, 81%). Elemental analysis calcd for
C33H25N4Cu; C: 73.25, H: 4.66, N: 10.35, Found; C: 73.92, H:
Pd].4c-e More recently we have reported AFA-complexes
containing copper.4f Here we describe an improved general
synthesis for AFA ligand systems and describe the synthesis
of selected copper, aluminum, and zinc complexes.
Experimental Section
General Data. All preparations were performed under an
atmosphere of dry, O2-free argon, employing standard vacuum
and Schlenk line techniques. Solvents were reagent grade, dis-
tilled under an inert argon atmosphere from appropriate drying
agents, and degassed using the freeze-pump-thaw method
prior to use. All organic reagents were purified by conventional
methods. [(PhNC)2Cu(μ2-Cl)]2,4f [(iPrNC)Cu(μ3-Cl)]4,6 and
6-dimethylamino fulvene7 were prepared according to literature
procedures. Phenyl-isocyanide and isopropyl-isocyanide were
prepared using modified literature procedures.8 The organome-
tallic reagents, ZnMe2 and AlMe3 were provided by SAFC-
Hitech as neat liquids and made into 2 M stock solutions in
toluene. All other materials, unless otherwise stated, were purchased
from commercial sources. 1H and 13C spectra were recorded on a
Bruker Avance 300 MHz spectrometer, using internal refer-
ences. Coupling constants are given in hertz. Elemental analyses
of the ligand systems were performed “in-house” at the Depart-
ment of Chemistry, University of Bath. Elemental analysis of
the complexes 2-6 were performed by Elemental Microanalysis
Ltd.
1
5.04; N: 10.15. H NMR (300 MHz, 296 K, CDCl3), δ: 6.32
3
3
(triplet, J = 3.57 Hz, 1H, CHCHCH), 6.90 (doublet, J =
3.54 Hz, 2H, CHCHCH), 7.05-7.21 (m, 10H, C6H5), 7.27-7.44
(m, 10H, C6H5), 8.28(s, 2H, PhNCH). 13C{1H} NMR (75.50 MHz,
296 K, CDCl3), δ: 115.6, 118.7, 1122.8, 123.9, 126.5, 128.8, 129.6,
129.8, 134.8, 150.3, 156.5, 162.7.
Synthesis of [(Ph2-AFA)Cu(CNiPr)], (3). In a dry Schlenk
tube, under an inert atmosphere of argon, stoichiometric quan-
tities of lithium hexamethyldisilylamide (2.00 mmol, 0.335 g)
and Ph2-AFAH (2.00 mmol, 0.544 g) were combined in THF
(20 mL). The reaction mixture was then stirred for 1 h, followed
by the addition of [(iPrNC)Cu(μ3-Cl)]4 (0.336 g, 0.50 mmol) in
THF (20 mL) with further stirring for 16 h. The volatiles were
removed under reduced pressure. Dry hexane (20 mL) was
added to the resultant residue, and was left to stir for 15 min.
The volatiles were removed under reduced pressure. This process
was repeated a total of three times to remove any residual THF.
Further hexane (50 mL) was added, and the slurry was filtered
through Celite to remove any insoluble materials with subsequent
removal of the volatiles in vacuo. This resulted in a dark brown
crude product that was purified by recrystallization (hexane) to
afford 3 as orange crystals (0.651 g, 81%). Elemental analysis
calcd for C23H22CuN3; C: 68.38, H: 5.49, N: 10.40, Found; C:
67.50, H: 5.33, N: 11.14. 1H NMR (300.22 MHz, 298 K, CDCl3),
Synthesis of Ph2-AFAH. In separate dry Schlenk tubes, and
under an inert atmosphere of argon, solutions of oxalyl chloride
(3.6 mL. 41.32 mmol) in dichloromethane (DCM) (30 mL) and
dimethyl formamide (3.18 mL. 41.32 mmol) in DCM (30 mL)
were prepared. Both Schlenks were cooled to 0 °C, and the solution
of oxalyl chloride was added dropwise to that of dimethyl
formamide. This mixture was then allowed to stir for 2 h, and
warmed to room temperature. After rapid addition of a solution
of 6-(dimethylamino)fulvene (5 g, 41.32 mmol) in DCM (20 mL)
to the slurry, the reaction mixture was then left to stir for a further
16 h, after which time the volatiles were removed under reduced
pressure. To the resultant solid, an excess of aniline (9.1 mL.
100 mmol) and ethanol (40 mL) was added, and the mixture was
refluxed for 16 h. Thin layer chromatography (1:10, ethyl acetate/
hexane) confirmed the completion of the reaction, and the volatiles
were then removed under reduced pressure. The resultant crude
product was purified by column chromatography (hexane) and
recrystallization (hexane) to afford Ph2-AFAH as bright orange
3
δ: 1.22 (d, 6H, CH(CH3)2, J = 6.70 Hz), 3.66 (sept, 1H, CH-
(CH3)2, 3J = 6.70 Hz), 6.37 (t, 1H, CH, 3J = 3.62 Hz), 6.99 (d,
2H, CH, 3J = 3.62 Hz), 7.02-7.09 (m, 4H, C6H5), 7.14-7.20 (m,
2H, C6H5), 7.22-7.29 (m, 4H, C6H5), 8.30 (s, 2H, CH). 13C {1H}
NMR (75.49 MHz, 298 K, CDCl3), δ: 23.0, 47.4, 116.5, 118.5,
122.9, 124.2, 128.9, 135.5, 156.2, 162.8. No resonance for
CNCH(CH3)2 was observed.
(6) Kruck, T.; Terfloth, C. Chem. Ber. 1993, 126, 1101.
(7) Lou, Y.; Chang, J.; Jorgensen, J.; Lemal, D. M. J. Am. Chem. Soc.
2002, 124, 15302.
(8) (a) Ugi, I.; Meyr, R. Org. Synth. 1961, 41, 101. (b) Ugi, I.; Meyr, R.;
Lipinski, M.; Bodesheim, F.; Rosendahl, F. Organic Syntheses 1961, 41, 13.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 939
Table 1
Dip2-AFAH: Tol
2a
2b
3
4
6
empirical formula
formula weight
T/K
C38H48N2
532.78
150(2)
C33H25CuN4
541.11
150(2)
C33H25CuN4
541.11
150(2)
C23H22CuN3
403.98
150(2)
C35H46CuN3
572.29
150(2)
C33H45AlN2
496.69
150(2)
crystal system
space group
monoclinic
P21/c
10.6560(5)
20.2830(4)
15.3220(7)
triclinic
P1
triclinic
P1
orthorhombic
P212121
8.11400(10)
11.1000(2)
21.9760(4)
triclinic
P1
orthorhombic
P212121
11.4890(2)
14.4270(2)
18.4190(4)
˚
a (A)
9.9170(3)
10.8650(4)
14.5300(6)
106.4740(10)
97.129(2)
112.271(2)
1341.18(8)
2
11.1110(8)
11.5390(7)
11.9660(10)
66.999(2)
76.739(2)
72.760(3)
1337.44(17)
2
9.0040(2)
9.7290(2)
19.8460(6)
97.1120(10)
91.9950(10)
106.002(2)
1653.95(7)
2
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
V
99.118(2)
3269.8(2)
4
1.082
0.620
1160
1979.28(6)
4
1.356
1.115
840
3052.98(9)
4
1.081
0.089
1080
Z
F
calc mg/m-3
1.340
0.843
1.344
0.845
1.149
0.686
μ(Mo-KR), mm-1
F(000)
crystal size, mm
560
0.20 ꢀ 0.13 ꢀ
560
0.20 ꢀ 0.13 ꢀ
612
0.15 ꢀ 0.13 ꢀ
0.15 ꢀ 0.10 ꢀ
0.22 ꢀ 0.1 ꢀ
0.10 ꢀ 0.10 ꢀ
0.10
8.53 to 30.53
30682
0.10
3.53 to 27.48
23329
0.08
8.53 to 23.26
11011
0.08
3.11 to 24.71
22140
0.10
3.25 to 24.71
15385
0.08
4.00 to 27.06
56503
θ range (deg)
reflections collected
independent reflections [R(int)]
reflections observed [I > 2σ(I)]
max.,min transmission
goodness-of-fit
8791 [0.1103]
5211
0.9938, 0.9908
1.017
6046 [0.0432]
4863
0.9204, 0.8495
1.039
3649 [0.1555]
2213
0.9354, 0.8491
0.972
3369 [ 0.0675]
2294
0.9161, 0.7915
1.059
5632 [0.0314]
4918
0.9346, 0.9041
1.050
6684 [0.1243]
4600
0.9934, 0.9912
0.975
final R1 (wR2) [I > 2σ(I)]
final R1 (wR2) (all data)
absolute structure parameter
0.0613 (0.1238)
0.1240 (0.1551)
0.0393 (0.0842)
0.0572 (0.0934)
0.0562 (0.1051)
0.1163 (0.1270)
0.0314 (0.0755)
0.0435 (0.0814)
-0.020(16)
0.0327 (0.0782)
0.0410 (0.0831)
0.0435 (0.0844)
0.0882 (0.0960)
0.01(14)
-3
˚
largest diff. peak and hole, e A
0.214 and -0.191 0.337 and -0.544 0.327 and -0.499 0.420 and -0.587 0.310 and -0.246 0.182 and -0.182
Synthesis [(Dip2-AFA)Cu(CNiPr)], (4). In a dry Schlenk tube,
under an inert atmosphere of argon, stoichiometric quantities
of lithium hexamethyldisilylamide (2.00 mmol, 0.335 g) and
Dip2-AFAH (0.881 g, 2.00 mmol) were combined in THF
(20 mL). The reaction mixture was then stirred for 1 h, followed
by the addition of [(iPrNC)Cu(μ3-Cl)]4 (0.336 g, 0.50 mmol) with
further stirring for 16 h. The volatiles were removed under reduced
pressure. Dry hexane (50 mL) was added to the resultant residue,
and this was left to stir for 15 min. The volatiles were removed
under reduced pressure. This process was repeated a total
of three times to remove any residual THF. Further hexane
(20 mL) was added, and the slurry was filtered through Celite to
remove any insoluble materials with subsequent removal of the
volatiles in vacuo. This resulted in a dark brown crude product
that was purified by crystallization (hexane) to afford 4 as orange
crystals (0.732 g, 64%). Elemental analysis calcd for C35H46-
CuN3; C: 73.45, H: 8.10, N: 7.34, Found; C: 73.06, H: 8.15, N:
C6H5), 7.28-7.35 (m, 4H, C6H5), 8.06 (s, 2H, CH). 13C {1H}
NMR (75.49 MHz, 238 K, CDCl3), δ: -9.1, 117.7, 120.2, 124.2,
126.5, 129.1, 140.6, 148.7, 163.5.
Synthesis of [(Dip2-AFA)AlMe2] (6). In a dry Schlenk tube,
under an inert atmosphere of argon, THF (20 mL) was added to
Dip2-AFAH (0.881 g, 2.00 mmol). To this solution trimethyl
aluminum (2 M in toluene) (2.00 mmol, 1 mL) was added and the
reaction mixture was allowed to stir for 16 h, after which time
any insoluble material was separated by filtration and the solution
concentrated by removal of the volatiles in vacuo. This was
followed by storage of the solution at -28 °C to afford yellow
crystals of 6 (0.360 g, 36%). Elemental analysis calcd for
C34H49Al1N2; C: 79.80, H: 9.13, N: 5.64, Found; C: 79.18, H:
9.77, N: 5.60. 1H NMR (300.22 MHz, 300 K, CDCl3), δ: -1.01
3
(s, 6H, Al(CH3)2), 1.15 (d, 6H, PhCH(CH3)2, J = 6.86 Hz),
1.28 (d, 6H, PhCH(CH3)2, 3J = 6.86 Hz), 3.28 (sept, 6H,
3
3
Ph(CH(CH3)2)2, J = 6.86 Hz), 6.48 (t, 1H, CH, J = 3.68
Hz), 7.06 (d, 2H, CH, 3J = 3.68 Hz), 7.19-7.30 (m, 6H, C6H3),
7.93 (s, 2H, CH). 13C {1H} NMR (75.49 MHz, 298 K, CDCl3),
δ: -10.8, 23.4, 25.8, 28.8, 118.5, 120.2, 124.3, 127.5, 140.6, 143.9,
144.49, 166.6.
1
7.36. H NMR (300.22 MHz, 300 K, CDCl3), δ: 0.96 (d, 6H,
CNCH(CH3)2, J = 6.59 Hz), 1.18 (d, 12H, Ph(CH(CH3)2)2,
3
3
3J = 6.84 Hz), 1.21 (d, 12H, Ph(CH(CH3)2)2, J = 6.84 Hz),
3.34-3.50 (m, 5H, Ph(CH(CH3)2)2 and CNCH(CH3)2), 6.36 (t,
1H, CH, 3J = 3.55 Hz), 6.94 (d, 2H, CH, 3J = 3.55 Hz),
7.10-7.18 (m, 6H, C6H3), 8.03 (s, 2H, CH). 13C {1H} NMR
(75.49 MHz, 298 K, CDCl3), δ: 22.7, 23.5, 24.4, 28.1, 47.1, 115.2,
117.9, 123.4, 124.7, 134.1, 140.8, 151.3, 164.5. No resonances for
CNCH(CH3)2 observed.
Synthesis of [(Ph2-AFA)2Zn], (7). In a dry Schlenk and under
an inert atmosphere of argon THF (20 mL) was added to Ph2-
AFAH (0.544 g, 2.00 mmol). To this solution, dimethyl zinc (1 M in
Toluene) (2.00 mmol, 2 mL) was added, and the reaction mixture
was allowed to stir for 16 h, after which time any insoluble
material was separated by filtration, and the solution concen-
trated by removal of the volatiles in vacuo. This was followed by
storage of the solution at -28 °C to afford 7 as yellow crystals
(0.322 g, 49%). Elemental analysis calcd for C38H30N4Zn1; C:
Synthesis of [(Ph2-AFA)AlMe2], (5). In a dry Schlenk tube,
under an inert atmosphere of argon, THF (20 mL) was added to
Ph2-AFAH (0.544 g, 2.00 mmol). To this solution trimethyl
aluminum (2 M in toluene) (2.00 mmol, 1 mL) was added, and
the reaction mixture was allowed to stir for 16 h, after which time
any insoluble material was separated by filtration and the solution
concentrated by removal of the volatiles in vacuo. This was
followed by storage of the solution at -28 °C to afford 5 as
yellow crystals (0.322 g, 49%). Elemental analysis; calcd for
C21H21Al1N2; C: 76.81, H: 6.45, N: 8.53, Found; C: 76.63, H:
6.62, N: 8.39. 1H NMR (300.22 MHz, 298 K, CDCl3), δ: -0.91
(s, 6H, Al(CH3)2), 6.46 (t, 1H, CH, 3J = 3.65 Hz), 7.10 (d, 2H,
CH, 3J = 3.65 Hz), 7.10-7.16 (m, 4H, C6H5), 7.20-7.25 (m, 2H,
1
75.06, H: 4.97, N: 9.21, Found; C: 74.98, H: 5.01, N: 9.23. H
NMR (300.22 MHz, 298 K, CDCl3), δ: 6.39 (t, 2H, CH, 3J =
3.65 Hz), 6.80-6.86 (m, 8H, m-C6H5), 6.94-7.07 (m, 16H, {12H
o/p-C6H5, 4H, CH}), 8.06 (s, 4H, CH). 13C {1H} NMR (75.49
MHz, 238 K, CDCl3), δ: 118.2, 118.9, 122.2, 125.2, 129.1, 140.0,
151.9, 163.1
Crystallography. Experimental details relating to the single-
crystal X-ray crystallographic studies are summarized in Table 1.
For all structures, data were collected on a Nonius Kappa CCD

940 Inorganic Chemistry, Vol. 50, No. 3, 2011
Willcocks et al.
Scheme 1. Synthesis of the AFA Complexes [(Ph2-AFA)Cu(CNPh)]
(1) and [(Ph2-AFA)Cu(CNPh)2] (2) Formed from [(η5-C5H5)Cu-
(CNPh)]4f
coordination chemistry, which could prove to be extensive
given the rich chemistry of the related dicarbonyl substituted
cyclopentadienide complexes.15
Inspired by the previously published multistep procedure
for the synthesis of AFA ligand systems reported by Sanz and
co-workers,16 which is itself based upon earlier work by
Muller-Westerhoff,17 we have developed a modified procedure
that is capable of providing a much wider range of N-sub-
stituted AFA ligands, than described here, in moderate to
high yields. The first step consists of the selective monosub-
stitution of 6-dimethylamino-fulvene by the Vilsmeir-Haack
reagent, [Me2NdC(H)Cl]Cl, formed in situ by the reaction of
dimethyl formamide and oxalyl chloride.18 Reaction of these
two reagents is complete after several hours forming the
intermediate [C5H3{C(H)NMe2}2]Cl. In the second step, re-
moval of solvent under vacuum followed by addition of an
ethanolic solution containing an excess (>2 equiv) of the
desired primary amine, or aniline, results in the formation
of the corresponding N,N0-disubstituted AFA ligand system
(Scheme 2), which can be purified by column chromatography.
The ligands systems reported here, Ph2-AFAH and Dip2-
AFAH, were obtained in isolated yields of 74% and 68%,
respectively, which in comparison to previously reported
synthetic procedures represents a significant improvement.16,17
In the case of both ligand systems, the isolated materials are
yellow air stable systems with a notable tendency to crystal-
lize, an advantageous feature in terms of their purification
and characterization. During the course of these investiga-
tions crystals suitable for single crystal X-ray diffraction studies
of both Ph2-AFAH and Dip2-AFAH were isolated and shown
to be identical to the previously reported systems.4e,19 Recrys-
tallization of the Dip2-AFAH ligand system from toluene
yielded crystals of the toluene solvate system Dip2-AFAH:
Tol, the molecular structure of which is shown in Figure 2.
Table 2 shows selected bond lengths and angles.
diffractometer at 150(2) K using Mo-KR radiation (λ =
˚
0.71073 A). Structure solution and refinements were performed
using SHELX869 and SHELX9710 software, respectively. Cor-
rections for absorption were made in all cases. All hydrogens
attached to carbon atoms were included at calculated positions
and refined using the riding model. In the case of the ligand
system, [(Dip)2-AFAH]:Tol, the N-H hydrogen atom was
found in the difference Fourier map and was freely refined.
The asymmetric unit of [(Ph2-AFA)Cu(CNiPr)], 3, consists of
one full molecule of the copper complex. The coordinated
CNiPr ligand is disordered with respect to the central core,
and has been refined and modeled over two positions, in a 62%
to 38% occupancy ratio. To obtain a stable convergence,
refinement of both the major and the minor component of
disorder were refined with isotropic displacement parameters.
Disorder is also present in complex 4, [(Dip2-AFA)Cu(CNiPr)],
in which one of the four isopropyl groups of the {Dip2-AFA}
ligand is disordered over two positions, in a 53% to 47%
occupancy ratio. As with 3, to obtain a stable convergence, refine-
ment of both the major and the minor component of disorder in 4
were refined with isotropic displacement parameters.
Computational Methods. Density functional calculations
were performed using the B3LYP11 hybrid density functional
under the Gaussian09 package.12 The SDD pseudopotential
and associated basis set13 were used for copper, and the
6-31G(d)14 basis set was used for all other atoms. To give
corrected “experimental” geometries, the hydrogen atoms
were optimized with the PM6 functional, with the non-hydrogen
atoms kept fixed (X-ray geometries systematically under-
estimate X-H distances). Subsequent full geometry optimi-
zations were performed with B3LYP/6-31G(d) and frequency
calculations were used to confirm the stationary points were
true minima. For the compound 2b, there were problems with
the initial internal coordinates, and hence a preliminary
optimization in Cartesian coordinates was performed, prior
to a final optimization using internal coordinates.
A comparison with the non-solvated Dip2-AFAH recently
reported by Bailey et al.4e shows little, if any, difference
between the two crystal systems. In both cases, the molecular
structures contain a planar {C5(CN)2} backbone (the mean
deviation from planarity for the atoms N(1), C(1)-C(7),
˚
N(2) is 0.0203(11) A) with the pendant 2,6-diisopropylphenyl
units approaching a perpendicular orientation to the {C5(CN)2}
plane [C(11)-C(16)/N(1),C(1)-C(7),N(2) = 80.11(5) °;
C(21)-C(26)/N(1),C(1)-C(7),N(2) = 89.02(4) °], an obser-
vation whichis incontrast to the Ph2-AFAH system, in which
the phenyl rings are closer to coplanarity with the {C5(CN)2}
backbone [{C5(CN)2}/phenyl angles of 19.0 and 6.7°].19
Despite the obvious steric differences between the Ph2-AFAH
Results and Discussion
We have recently reported the formation of the AFA
complexes [(Ph2-AFA)Cu(CNPh)] (1) and [(Ph2-AFA)Cu-
(CNPh)2}] (2) via the double migratory insertion of phenyl
isocyanide, Ph-NC, into two vicinal sp2 C-H bonds of the
η5-coordinated cyclopentadienyl group in the complex [(η5-
C5H5)Cu(CNPh)] (Scheme 1).
and Dip2-AFAH ligands, the N N distances in both systems
3 3 3
˚
˚
are comparable [2.781(2) A in Dip2-AFAH cf. 2.51 A in
Ph2-AFAH],19 which is presumably a result of the intermo-
lecular hydrogen bond present in both systems. A cursory
Motivated by these results, we have sought a higher
yielding route to AFA ligand systems to further explore their
Scheme 2. Modular “one-pot” Synthesis of AFA Ligand System Precursors

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 941
Figure 2. Molecular structure of the solvated ligand system Dip2-AFAH in the solvated complex Dip2-AFAH Tol . Thermal ellipsoids are shown at 50%
3
probability, and hydrogen atoms have been removed for clarity.
Table 2. Selected Bond Lengths and Angles for Dip2-AFAH Tol
comparison of the bond lengths around the {C5(CN)2} back-
bone indicates that while the C-C and C-N bonds are
midway between single and double bonds in character there is
some localization of electron density resulting in an alternating
pattern of “single/long” and “double/short” bonds around
the molecule (Figure 2).
Initial attempts to form copper complexes of the {Ph2-AFA}
and {Dip2-AFA} ligand systems focused on the reaction of
[Cu-(Mes)]5 (Mes =2,4,6-trimethylphenyl) with stoichiometric
amounts of the ligands Ph2-AFAH and Dip2-AFAH in
tetrahydrofuran (THF). In both cases, only unreacted ligand
was isolated from the reaction mixtures. The kinetic stability
of organo-copper systems such as mesityl-copper has been
previously attributed to the high degree of aggregation encoun-
tered in Cu(I)-aryl systems and strong three-center two-electron
3
˚
Selected Bond Lengths (A)
N(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(6)-C(2)
1.324(2)
1.379(2)
1.436(2)
1.375(3)
1.459(2)
2.781(2)
0.88(3)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-N(2)
1.414(3)
1.394(2)
1.428(2)
1.289(2)
N(1) N(2)
H(1N) N(2)
3 3 3
1.974(3)
3 3 3
N(1)-H(1N)
Selected Bond Angles (deg)
N(1)-C(1)-C(2)
N(2)-C(7)-C(6)
N(1)-H(1N)-N(2)
127.04(4)
126.63(4)
159 (2)
C(1)-N(1)-C(11)
C(7)-N(2)-C(21)
121.13(13)
116.54(13)
(3c-2e-) bonding found in these systems.20 These features,
coupled with the sterically restricted access of the organo-
copper reagent to the acidic N-H group of the AFA ligand,
presumably render the reactants kinetically inert toward
each other.
(9) Sheldrick, G. M. SHELX-86, Computer Program for Crystal Structure
€
€
Determination; University of Gottingen: Gottingen, Germany, 1986.
(10) Sheldrick, G. M. SHELX-97, Computer Program for Crystal Struc-
€
€
ture Refinement; University of Gottingen: Gottingen, Germany, 1997.
(11) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C. T.; Yang,
W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
Treatment of Ph2-AFAH with lithium bis(trimethylsilyl)-
amide (or n-butyl lithium) in THF, followed by reaction with
[(PhNC)2Cu(μ2-Cl)]2, provides the complex [(Ph2-AFA)Cu-
(CNPh)2] (2), and represents an alternative pathway for the
production of complex 2 (Scheme 3), which has previously
beensynthesizedby the insertion of phenylisocyanide into the
C-H bonds of [(η5-C5H5)Cu(CNPh)].4f After workup and
recrystallization from hexane at -40 °C, crystals were iso-
lated in 81% yield. Both the 1H NMR spectrum of 2, which
shows resonances at δ 6.40 (t), 7.01 (d), and 8.35 ppm (s)
associated with the AFA ligand and a multiplet between
δ 7.12-7.42 ppm corresponding to the 20 H of the aromatic
groups, and also the elemental analysis of the complexes
made by both routes are the same (within experimental error).
However, isolation of the product from the salt-metathesis
route followed by recrystallization from hexane at -40 °C
yielded crystals with very different asymmetric unit cell dimen-
sions (Table 1) to those previously isolated from the insertion
reaction.4f
(12) Frisch, M. J. Gaussian 09, revision A.02; Gaussian, Inc.: Wallingford,
CT, 2009.
(13) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987, 86,
866.
(14) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
724. (b) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(15) (a) Vaughn, A. E.; Barnes, C. L.; Duval, P. B. Angew. Chem., Int. Ed.
2007, 46, 6622. (b) Enk, B.; Kopacka, H.; Wurst, K.; Muller, T.; Bildstein, B.
Organometallics 2009, 28, 5575. (c) Klass, K.; Duda, L.; Kleigrewe, N.; Erker,
G.; Froehlich, R.; Wegelius, E. Eur. J. Inorg. Chem. 1999, 11. (d) Oberhoff, M.;
Duda, L.; Karl, J.; Mohr, R.; Erker, G.; Froehlich, R.; Grehl, M. Organometallics
1996, 15, 4005. (e) Calucci, L.; Englert, U.; Pampaloni, G.; Pinzino, C.; Volpe, M.
J. Organomet. Chem. 2005, 690, 4844. (f) Blankenbuehler, M. T.; Selegue, J. P.
J. Organomet. Chem. 2002, 642, 268. (g) Wallace, C. E.; Selegue, J. P.; Carrillo,
A. Organometallics 1998, 17, 3390. (h) Layfield, R. A.; Humphrey, S. M.
Organometallics 2005, 24, 6063. (i) Lindsay, A. J.; Kim, S.; Jacobson, R. A.;
Angelici, R. J. Organometallics 1984, 3, 1523. (j) Snyder, C. A.; Selegue, J. P.;
Tice, N. C.; Wallace, C. E.; Blankenbuehler, M. T.; Parkin, S.; Allen, K. D. E.;
Beck, R. T. J. Am. Chem. Soc. 2005, 127, 15010.
(16) Sanz, D.; Perez-Torralba, M.; Alarcon, S. H.; Claramunt, R. M.;
Foces-Foces, C.; Elguero, J. J. Org. Chem. 2002, 67, 1462.
(17) Mueller-Westerhoff, U. J. Am. Chem. Soc. 1970, 92, 4849.
(18) Jarrahpour, A.; Zarei, M. Tetrahedron 2009, 65, 2927.
(19) Ammon, H. L.; Mueller-Westerhoff, U. Tetrahedron 1974, 30, 1437.
(20) van Koten, G. J. Organomet. Chem. 1990, 400, 283.

942 Inorganic Chemistry, Vol. 50, No. 3, 2011
Willcocks et al.
Scheme 3. Synthesis and Attempted Synthesis of Group 11 Metal-AFA Complexes
A closer inspection of the crystals using single crystal X-ray
diffraction revealed a new structural isomer of 2 (i.e., 2b); For
comparison, the molecular structure of the original iso-
mer (2a) is shown in Figure 3, and the molecular structure
of the newly isolated structural isomer (2b) is shown in
Figure 4. Selected bond lengths and angles for 2a and 2b
are shown in Table 3.
serving to highlight the considerable differences in Cu-CNPh
bonding environments in the two complexes.
Both complexes possess AFA backbones, {C5(CN)2}, that
are near planar; the mean deviation from planarity for the
˚
atoms N(1), C(1)-C(7), N(2) is 0.0776(20) A in 2a and
˚
0.0538(41) A in 2b. The Cu-N distances in 2a and 2b are
˚
very similar [2a; Cu(1)-N(1), 2.0530(18) A and Cu(1)-N(2),
˚
˚
Although the copper centers in both 2a and 2b are four-
coordinate, with the two nitrogen atoms of the AFA ligand
and the divalent carbon atoms of two phenyl isocyanide
ligands coordinated to the metal centers, only complex 2a has
angles about the Cu center that are close to an ideal tetrahedral
(see table 3). In direct contrast, complex 2b has a highly
distorted geometry, with two angles, N(2)-Cu(1)-C(41) and
C(31)-Cu(1)-C(41), which are greater that 120° [123.62(19)°
and 123.2(2)° respectively]. Figure 5 shows a least-squares
overlay of the two complexes (2a in green; 2b in red). While
the imine substituents on the AFA ligands are, not unsurpris-
ingly, orientated differently in both complexes, the core
{Cu-C5(CN)2} fragments, in both complexes shows good
2.0366(17) A: 2b; Cu(1)-N(1) 2.0366(17) A and Cu(1)-N(2)
˚
2.069(4) A] (in the two adducts). As with previously reported
systems,4a,b,d,e 2a and 2b display a distortion such that the
metal center is displaced out of the plane of the AFA ligand
˚
˚
by 0.36 A and 0.72 A, respectively, a direct consequence
of the dihedral angles between the N(1)-Cu(1)-N(2) plane
and the N(1)-C(1)-C(7)-N(2) plane [2a, 17.71(11)°: 2b,
35.19(23)°] in the two complexes.
The coordination environment about the copper center in
2b is possibly best described as distorted trigonal pyramidal,
with the nitrogen atoms of the {Ph2-AFA} ligand [N(1) and
N(2)] and one of the two phenyl isocyanide carbon atoms
[C(41)] occupying the basal positions, with the copper center
˚
˚
correlation, with an error of displacement of 0.0844 A,
displaced out of the plane [N(1)-N(2)-C(41)] by 0.569 A.
Figure 3. Molecular structure of complex 2a. Thermal ellipsoids are shown
at 50% probability, and hydrogen atoms have been removed for clarity.
Figure 4. Molecular structure of complex 2b. Thermal ellipsoids are shown
at 50% probability, and hydrogen atoms have been removed for clarity.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 943
Table 3. Selected Bond Lengths and Angles for the Structural Isomers, Complexes 2a and 2b
˚
selected bond lengths (A)
selected bond angles (deg)
2a
2b
2a
2b
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-C(31)
Cu(1)-C(41)
N(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(2)-C(6)
C(7)-N(2)
C(31)-N(3)
C(41)-N(4)
N(1)-C(11)
N(2)-N(22)
2.0530(18)
2.0366(17)
1.907(2)
1.917(2)
1.308(3)
1.415(3)
1.421(3)
1.384(3)
1.391(3)
1.414(3)
1.426(3)
1.447(3)
1.294(3)
1.164(3)
1.164(3)
1.429(3)
1.437(3)
2.024(5)
2.069(4)
1.943(6)
1.877(6)
1.299(7)
1.416(8)
1.411(7)
1.400(8)
1.381(7)
1.381(7)
1.421(7)
1.457(7)
1.315(7)
1.158(6)
1.164(7)
1.437(7)
1.439(6)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-C(31)
N(1)-Cu(1)-C(41)
N(2)-Cu(1)-C(31)
N(2)-Cu(1)-C(41)
C(31)-Cu(1)-C(41)
105.87(7)
108.15(8)
112.54(8)
112.01(8)
100.67(8)
116.96(10)
104.46(17)
92.72(19)
107.6(2)
99.7(2)
123.62(19)
123.2(2)
Cu(1)-C(31)-N(3)
C(31)-N(3)-C(32)
Cu(1)-C(41)-N(4)
C(41)-N(4)-C(42)
174.7(2)
178.2(2)
171.24(19)
173.6(2)
159.6(5)
174.8(5)
171.0(5)
179.1(5)
Cu(1)-N(1)-C(1)
Cu(1)-N(2)-C(7)
127.28(15)
130.80(15)
123.7(4)
125.4(3)
C(33)-H(33) {C5}CT = 141.66°].21 This molecular geo-
3 3 3
metry is in stark contrast to the pseudo tetrahedral geometry
encountered in complex 2a.
A comparison of the two Cu-C bond distances in 2a
˚
˚
[Cu(1)-C(31), 1.907(2) A and Cu(1)-C(41), 1.917(2) A]
shows that the two bonds are similar to each other, whereas
the comparable distances in 2b [Cu(1)-C(31), 1.943 A;
Cu(1)-C(41), 1.877(6) A] reveal a difference in the Cu-C
˚
˚
bonding in the two metal ligand interactions with the ‘basal’
isocyanide group displaying a significantly shorter bond
distance to the copper center, than the ‘apical’ group. This
short Cu-C bond distance is, in fact, comparable to the
Cu-C bond distance found in the three coordinate system
[(Ph2-AFA)Cu(CNPh)] (1).4f
To shed light upon the reasons for the two different
isomeric forms for compound 2, gas phase Density
Functional Theory (DFT) calculations were performed.
A comparison of the energies of the two forms based
upon the experimental determined geometries (solid
state) reveals that of the isomers crystallographically
characterized, complex 2a was the lowest energy con-
formation (ΔE = 9.4 kJ/mol) (Figure 6). Upon geometry
optimization (gas phase), both forms give similar geometries,
differing only in the orientation of the peripheral phenyl rings
of the diimine ligand. The associated energy changes of 55.5
and 63.4 kJ/mol respectively are not unsurprising given the
difference between solid state DFT systems and gas-phase
systems.
Figure 5. Least-squares overlay of the two complexes 2a (green) and 2b
(red), demonstrating the significant structural differences in the phenyl
isocyanide coordination to the copper centers.
These two DFT optimized, gas-phase forms, have similar
energies, with the form derived from 2b being slightly more
stable (ΔE = 1.5 kJ/mol). In both cases, the optimized
geometries more closely resembled form 2b, in which the
The apical position is occupied by the carbon atom of the
second phenyl isocyanide group [C(31)], although the co-
ordination environment of this group is further distorted
from ideal, such that the ligand is orientated toward
the {C5(NC)2} core of the AFA ligand; the angle between
the N(1)-Cu(1)-N(2) plane and the vector described by the
bond Cu(1)-C(31) being 100.13(5)°. The apical isocyanide
ligand is further distorted with a nonlinear angle at C(31)
[Cu(1)-C(31)-N(3) = 156(5)°], which directs the phenyl
group toward the {C5}-ring of the AFA ligand. This orienta-
tion preference of the apical phenyl isocyanide group is
apical phenyl isocyanide is involved in a CH π interaction
3 3 3
between the {C5}-ring of the AFA ligand and one of the
ortho-CH groups of the isocyanide ligand. Figure 7 shows the
optimized molecular structure of complex 2 derived from the
experimentally determined geometries of complex 2a. Exam-
ination of the calculated bond lengths and angles in the
optimized complex 2 (Figure 7) reveals a high degree of
rationalized by the presence of a weak C-H π interaction
3 3 3
between a C-H group [C(33)-H(33)] on the phenyl isocya-
(21) (a) Madhavi, N. N. L.; Katz, A. K.; Carrell, H. L.; Nangia, A.;
Desiraju, G. R. Chem. Commun. 1997, 2249. (b) Madhavi, N. N. L.; Katz, A. K.;
Carrell, H. L.; Nangia, A.; Desiraju, G. R. Chem. Commun. 1997, 1953.
nide and the electron rich {C5}-ring of the AFA ligand
˚
˚
[C(33)-{C5}CT = 3.750(4) A; H(33)-{C5}CT = 2.958 A;

944 Inorganic Chemistry, Vol. 50, No. 3, 2011
Willcocks et al.
Figure 6. Representation of the relative energies of the crystallographically determined structures 2a and 2b, and their optimized molecular structures,
obtained at the B3LYP/6-31G(d) level.
˚
Figure 7. Optimized geometry of [(Ph2-AFA-Ph)Cu(CNPh)2] obtained at the B3LYP/6-31G(d) level, showing relevant calculated distances (A), and
calculated bond angles (deg).
symmetry, such that the molecule possesses a mirror plane
defined by {CNC} atoms of the two phenyl isocyanide ligands
and the copper center which bisects the molecule. A brief
comparison of the solid state structure of complex 2b, and
the geometry optimized system, 2, reveals that the copper
center is displaced further out of the plane of the AFA ligand
the phenyl group is directed toward the {C5}-ring of the AFA
ligand, revealing an interesting C-H π interaction be-
3 3 3
tween the {C5}-ring of the AFA ligand (which is known to carry
substantial negative charge)4c and a C-H group [C(33)-
˚
H(33)] on the phenyl isocyanide [C(33)-{C5}CT = 3.87 A;
˚
H(33)-{C5}CT = 2.79 A; C(33)-H(33) {C5}CT = 171.92°],
3 3 3
˚
which presumably contributes to the stability of this isomeric
form, and that of 2b.
[0.820 A] than in 2b, and consequently possesses greater
dihedral angles between the N(1)-Cu(1)-N(2) plane and the
N(1)-C(1)-C(7)-N(2) plane [38.47°].
The ‘apical’ isocyanide ligand in the DFT optimized
structure of 2 also shows less distortion than that observed
in solid-state 2b with a nonlinear angle at C(31) [Cu(1)-
C(31)-N(3) = 163.88°]; as in the solid-state structure of 2b
While computational studies show that there is a moderate
change in the relative energies of complexes 2a and 2b upon
geometry optimization (gas-phase), what is more significant
is the observation that there is only a small energy difference
(ΔE = 9.4 kJ/mol) between the two molecular structures 2a

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 945
Figure 9. Molecular structure of complex 4. Disorder in one of the
isopropyl groups of the 2,6-diisopropylphenyl substituent [C(11)] ligand
has been omitted for clarity and the major component of the disorder
[C(17A)-C(18A)-C(18B) with 53% occupancy] is shown as isotropic. All
anisotropic atoms are shown with thermal ellipsoids at 50% probability.
Figure 8. Molecular structure of complex 3. Disorder in the isopropyl
isocyanide ligand has been omitted for clarity, and the major component
of the disorder [C(31)-N(3A)-C(32A)-C(33A)-C(34A) with 63% occupancy]
is shown as isotropic. All anisotropic atoms are shown with thermal
ellipsoids at 50% probability.
δ = 1.18 and 1.21 ppm, both accounting for 12H each. The
observed inequivalence is a result of restricted rotation about
the N-aryl bond, resulting in two distinct methyl environ-
ments: within the “bite” of the ligand, and outside the “bite”
of the ligand.
and 2b derived from the solid-state geometries. The similar
energies, and the absence of significant differences in geome-
tries, strongly suggest that the existence of two forms in the
solid state is a consequence of different packing effects, arising
from the differences in crystallization conditions.
As part of the study we have attempted to control the
crystallization conditions in an effort to selectively isolate
either of the two isomeric forms of 2. Despite multiple attempts,
we have been unsuccessful in determining the precise condi-
tions that would selectively allow isolation of one isomer over
another, and given the relatively small energy differences and
the large number of potential variables in terms of factors such
as temperature, rate of cooling, and concentration, this is not
surprising. Similarly, attempts to interconvert between iso-
meric forms have also been fraught with difficulties.
Treatment of the sterically more demanding AFA ligand,
Dip2-AFAH, with lithium bis(trimethylsilyl)amide (or n-butyl
lithium) in THF followed by reaction with [(PhNC)2Cu(μ2-
Cl)]2 failed to provide the 2,6-diisopropylphenyl derivatized
analogues of 2a or 2b. Only unreacted ligand was isolated
from the reaction mixture, suggesting that the steric bulk of
{Dip2-AFA} precludes complex formation.
In contrast, reaction of Li[Ph2-AFA] and Li[Dip2-AFA],
formed in situ, with stoichiometric amounts of [(iPrNC)-
Cu(μ3-Cl)]4 results in the formation and isolation of the
complexes [(Ph2-AFA)Cu(CNiPr)] (3) and [(Dip2-AFA)Cu-
(CNiPr)] (4), respectively. The1H NMR spectra of both 3 and
4 show the coordination of both CNiPr and AFA ligands
to the copper metal center. Upon coordination, the doublet
associated with the imine {H-CdN} group changes to
become sharp singlet resonances [δ = 8.30 ppm (3); δ =
8.03 ppm (4)], which is accompanied by the shifting of several
peaks. In the case of the {Dip2-AFA} ligand, coordination to
the copper center results in an inequivalence of the methyl
groups of the 2,6-diisopropyl phenyl substituent, with the 1H
NMR spectrum of 4 showing the presence of two doublets at
Recrystallization of complexes 3 and 4 (separately) from
hexane, yields crystals of the corresponding compound of
suitable quality for single crystal X-ray diffraction studies.
The molecular structures of both complexes are shown in
Figures 8 and 9, respectively, and selected bond lengths and
angles are shown in Table 4. Both complexes feature three
coordinate trigonal planar metal centers, with the nitrogen
atoms of the AFA ligands and divalent carbon of the
isocyanide ligand occupying the three-coordination sites.
˚
The Cu-N distances [3: Cu-N = 1.962(2) and 1.961(2) A; 4:
˚
Cu-N = 1.975(16) and 1.9341(15) A] and Cu-C distances
˚
˚
[3: Cu-C = 1.866(11) A; 4: Cu-C = 1.858(2) A] in complexes
3 and 4 are comparatively shorter than the corresponding
distances observed in complexes 2a and 2b.
While the sum of the angles about each copper center
P
indicates near perfect planar geometry [
= 359.94° (3)
Cu
and 360° (4)] (the copper atom in both systems resides frac-
tionally above the plane of the three atoms, N(1), N(2), and
˚
˚
C(31) by 0.0287 A in 3 and 0.0028 A in 4) a closer inspection
of the geometry about the copper centers reveals asymmetric
coordination environments; with the AFA-Cu bite angle
(N-Cu-N) of both complexes being the smallest angle
[N(1)-Cu(1)-N(2); 113.43(10)° (3), and 110.79(7)° (4)] and
the largest angle being that subtended between N(2)-Cu(1)-
C(31) [124.06(18)° (3), 132.86(8)° (4)].
Despite this asymmetry, there is very little difference in the
core bonding features of the {Cu-AFA} coordination which
would explain the significant differences in bond angles between
the twosystems; average Cu-N bond lengthsare comparable
˚
˚
[1.961 A (3) vs 1.955 A (4)], although there is a difference
between the two Cu-N bonds in complex 4 [Cu(1)-N(1)
˚
˚
1.9758(16) A; Cu(1)-N(2) 1.9341(15) A]. The relative

946 Inorganic Chemistry, Vol. 50, No. 3, 2011
Willcocks et al.
Table 4. Selected Bond Lengths and Angles for [(Ph2-AFA)Cu(CNiPr)] (3) and [(Dip2-AFA)Cu(CNiPr)] (4)
3
4
3
4
˚
Selected Bond Lengths (A)
Cu(1)-N(1)
Cu(1)-N(2)
N(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(6)-C(2)
1.962(2)
1.961(2)
1.314(4)
1.404(4)
1.419(4)
1.390(4)
1.457(4)
1.9758(16)
1.9341(15)
1.301(2)
1.418(3)
1.410(3)
1.392(3)
1.455(3)
Cu(1)-(C31)a
C(31)-N(3)a
1.867(5) 1.866(11)
1.145(6) 1.154(12)
1.858(2)
1.151(3)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-N(2)
1.387(4)
1.416(4)
1.414(4)
1.314(4)
1.388(3)
1.413(3)
1.413(3)
1.306(2)
Selected Bond Angles (deg)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-C(31)a
N(2)-Cu(1)-C(31)a
113.43(10)
110.79(7)
Cu(1)-C(31)-N(3)a
Cu(1)-N(1)-C(11)
Cu(1)-N(2)-C(21)
177.6(5)
178.5(9)
115.4(2)
173.35(19)
113.42(12)
116.28(11)
122.45(18)
123.9(3)
124.06(18)
120.2(3)
116.35(8)
132.86(8)
117.17(18)
a Disorder in the isopropyl isocyanide groups modeled over two positions [C(31A)-N(3A)-C(32A)-C(33A)-C(34A)] (63% occupancy) and [C(31B)-
N(3B)-C(32B)-C(33B)-C(34B)] (37% occupancy).
Scheme 4. Synthesis of Aluminum and Zinc AFA Complexes
orientation of the AFA aryl substituents in the two complexes
is different, which is apparent from Figures 8 and 9, with the
angles subtended between the phenyl ring substituents on
{Ph2-AFA} and the plane defined by the {C5(CN)2} plane, in
complex 3 [45.11(7)° and 48.06(7)°] closer to coplanar than
those in the {Dip2-AFA} system, [72.72° and 82.57°]. Assum-
ing the orientation of the AFA substituents to be a factor in
the solid-state deformation, it may be expected that the {Dip2-
AFA} complex [(Dip2-AFA)Cu(CNiPr)] (4) would be the most
symmetric of these complexes, as the approximate coplanarity
of the aryl substituents provides a less sterically restricted
environment for {CuCNiPr} coordination; however, this is not
found to be the case.
The large N(2)-Cu(1)-C(31) angle in complex 4 results in
a pronounced distortion of the isopropyl isocyanide coordi-
nation such that the ligand is displaced toward one side of the
ligand’s maw (specifically toward the aryl substituent C(11)-
C(16)). This distortion is further amplified by a nonlinear
coordination, of the isopropyl isocyanide at the Cu atom
[Cu(1)-C(31)-N(3) = 173.35(19)°] compared to near the
more linear coordination observed in complex 3 [Cu(1)-
C(31)-N(3) = 177.35(19)°].
Attempts to synthesize gold(I) AFA complexes by the
reaction of lithiated AFA ligands with [ClAu(PPh3)] and
[ClAu(THT)] in THF resulted in the initial formation of a
dark orange solution which rapidly darkened and turned
black, depositing gold metal on the walls of the reaction vessel.
Successive attempts to isolate stable complexes from these
reactions have, to-date, been unsuccessful. In contrast, re-
lated reactions between metalated β-diketiminate ligands and
[ClAu(THT)], or metalated aminotroponiminate ligands with
[ClAu(PPh3)], have been shown to yield complexes containing
Au(I).22
Reaction of either Dip2-AFAH or Ph2-AFAH with AlMe3
in THF affords the dimethyl derivatives, [(Ph2-AFA)AlMe2]
(5) and [(Dip2-AFA)AlMe2] (6), respectively (Scheme 4). The
yellow complexes could be isolated in high yields, direct from
the reaction mixture, but recrystallization from suitable solvents
(THF and toluene) resulted in reduced overall yields (36-
49%). Nevertheless, what appeared to be single crystals of
[(Ph2-AFA)AlMe2], however, have been obtained. Unfortu-
nately the crystals and subsequent X-ray diffraction data
were not of satisfactory quality to refine the molecular struc-
ture. In the case of [(Dip2-AFA)AlMe2] crystals suitable
for single crystal X-ray analysis experiments were isolated.
The molecular structure of the complex 6 is shown in
Figure 10, and selected bond lengths and angles are shown in
Table 5.
As with the copper complexes 1-4, the AFA ligand in 6
binds to the metal center via the imine nitrogen atoms. Two
methyl groups around the aluminum center complete the
metals pseudo tetrahedral coordination sphere. The Al-N
˚
bond lengths [Al(1)-N(1) = 1.9426(17) A; Al(1)-N(2) =
˚
1.9487(14) A] are fractionally longer than those observed in
both the comparable 2,6-diisopropylphenyl substituted dike-
i
timinato complex [{HC(CMeN(C6H3 Pr2)}AlMe2], [1.928(2)
23
˚
A], and the related 1,2-cyclopentadienyl diimine complex
described by Stephan and co-workers [1.853(9) A],4a and are
˚
probably a consequence of the larger N-Al-N bite angle
observed for 6[N(1)-Al(1)-N(2) = 104.32(9)° (cf. 96.18(9)°23
and 99.72(7)°,4a respectively)]. In contrast, the Al-C distances
˚
˚
in 6 [Al(1)-C(101)=1.950(2) A; Al(1)-C(102)=1.963(2) A]
are directly comparable to similar bonds in the two pre-
˚
viously mentioned related complexes [cf. 1.964(3) A and
4a,23
˚
1.953(2) A, respectively].
As with complexes 1-4, the AFA backbone in complex 6 is
very close to planar, with the mean deviation from planarity
˚
for the atoms N(1), C(1)-C(7), N(2) being 0.0530(16) A, but
˚
the aluminum center is located 0.87 A out of this plane. This
(22) (a) Dias, H. V. R.; Flores, J. A. Inorg. Chem. 2007, 46, 5841.
(b) Meiners, J.; Herrmann, J. S.; Roesky, P. W. Inorg. Chem. 2007, 46, 4599.
(23) Qian, B. X.; Ward, D. L.; Smith, M. R. Organometallics 1998, 17,
3070.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 947
Figure 10. Molecular structure of complex 6. Thermal ellipsoids are shown at 50% probability and hydrogen atoms have been removed for clarity.
Table 5. Selected Bond Lengths and Angles for Complex 6
at δ = -0.91 and -1.01 ppm respectively, suggesting a rapid
interchange between the two distinct methyl environments
˚
Selected Bond Lengths (A)
observed in the solid-state structure of 6.
Al(1)-N(1)
Al(1)-N(2)
N(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(6)-C(2)
N(1)-C(11)
N(2)-C(22)
1.9426(17) Al(1)-C(101)
1.9487(14) Al(1)-C(102)
1.330(2)
1.950(2)
1.963(2)
Treatment of ZnMe2 with Ph2-AFAH in THF affords the
bis-AFA complex, [(Ph2-AFA)2Zn] (7) exclusively. While
complex 7 has previously been reported by Bailey and co-
workers as the product from the reaction of ZnCl2 with
Na[Ph2-AFA],4d we had hoped controlled reaction of the
parent ligand system with dimethyl zinc would afford com-
plexescomparable to the methyl magnesium derivative [(Cy2-
AFA)MgMe(THF)], also reported by Bailey.4c Attempts to
react the lithiated ligand [(Ph2-AFA)Li] with MeZnCl also
resulted inthe isolation of complex 7, presumably a result of a
Schlenk equilibrium, in which complex 7 is a thermodynamic
sink (Scheme 5).
1.398(2)
1.412(2)
1.396(3)
1.455(2)
1.465(2)
1.455(2)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-N(2)
1.385(3)
1.412(3)
1.406(3)
1.311(2)
Selected Bond Angles (deg)
C(101)-Al(1)-C(102) 116.78(10) N(1)-Al(1)-C(102) 109.07(8)
N(1)-Al(1)-N(2)
N(1)-Al(1)-C(101)
N(1)-C(1)-C(2)
N(2)-C(7)-C(6)
104.32(7) N(2)-Al(1)-C(101) 112.38(8)
108.07(9) N(2)-Al(1)-C(102) 105.48(8)
128.49(17) C(1)-N(1)-C(11)
130.05(16) C(7)-N(2)-C(21)
115.44(16)
114.79(14)
Crystals of compound 7, suitable for single crystal X-ray
diffraction, were obtained during the course of this study
(Table 1). The molecular structure determined in this study is
identical (within experimental error) to that previously de-
termined by Bailey et al.4d
displacement of the metal center out of the plane of the AFA
ligand results in an acute angle of 40.87(16)° between the
{AlN2} plane and the mean plane defined by the two imine,
CdN, bonds.
In contrast, reaction of ZnMe2 (or MeZnCl) with the more
sterically demanding ligand system, Dip2-AFAH, failed to
result in any observable reaction, irrespective of the reaction
stoichiometries used, solvent systems, or conditions em-
ployed. Similar observations regarding this ligand system
have been reported by others; for example, the failure to
synthesize the mono- or bis-Dip2-AFA complexes of palla-
dium, and have been attributed to the size of the 2,6-
diisopropylphenyl substituents, which in some cases not only
prevent initial coordination but precludes complexation
completely.4e
Displacement of the Al center above the plane of the
ligand, also allows the steric burden within the maw of ligand
to be relieved by a slight twisting of the 2,6-diisopropylphenyl
substituents toward the space vacated by the {AlMe2} group;
such that the angle between the {C5(CN)2} plane of the ligand
and each phenyl ring is significantly more acute [{C5(CN)2}/
C(11)-C(16) = 73.5°; {C5(CN)2}/C(21)-C(26) = 61.6°] than
corresponding angles found in both the free ligand, Dip2-
AFAH, and complex 4.
1
The H NMR spectra of complexes 5 and 6 show the
presence of a single resonance for the methyl groups on Al
Scheme 5. Proposed Reaction Pathway to Complex 7

948 Inorganic Chemistry, Vol. 50, No. 3, 2011
Willcocks et al.
Conclusions
that is, the bulky 2,6-diisopropylphenyl substituent, has a
significant effect on the chemistry of these ligands, and in
several cases reaction of the {Dip2-AFA} ligand system with
metal reagents resulted in no observable reaction, which we
attribute to a kinetic rather than thermodynamic effect.
In summary, we have described a one-pot synthesis for aryl
substituted AFA ligands, and reported the subsequent reac-
tion chemistry of these species with selected copper, gold,
aluminum, and zinc reagents. It is hoped that with the
development of this ligand synthesis we can further expand
the known coordination chemistry of these ligand systems.
Reaction of Li[Ph2-AFA] with [(PhNC)2Cu(μ2-Cl)]2 re-
sulted in the isolation of two independent structural isomers
of the complex [{Ph2-AFA}Cu(CNPh)2]2, 2, both of which
can be structurally characterized, suggesting a highly flexible
system, both electronically and coordinatively. DFT calcula-
tions and geometry optimization of these systems reveal
minimal energy differences between these two solid-state
forms, consistent with our hypothesis that the observed
differences are the consequence of different packing effects
arising from the differences in crystallization conditions.
The introduction of sterically demanding N-substituents,
Acknowledgment. We acknowledge the financial sup-
port of the University of Bath and the EPSRC for the
award of a CASE for New Academics (A.M.W.). We
thank UMICORE AG & Co. KG for a generous gift of
precious metal compounds. A.L.J. thanks Prof. P. R.
Raithby (UoB) and Dr. M. S. Hill (UoB) for helpful
comments and fruitful discussions.
Supporting Information Available: X-ray crystallographic
files in CIF format. Further details about the geometry of
complexes 2a and 2b. This material is available free of charge
via the Internet at http://pubs.acs.org.