Gold(I) ethylene and copper(I) ethylene complexes supported by a polyhalogenated triazapentadienyl ligand

Article abstract of DOI:10.1021/ic800373u

A rare gold(I) ethylene complex and the closely related copper(I) ethylene adduct have been isolated using [N{(C₃F₇)C(2,6-Cl ₂C₆H₃)N}₂]^- as the supporting ligand. [N{(C₃F₇)C(2,6-Cl₂C ₆H₃)-N}₂]Au(C₂H₄) (1) is an air-stable solid. It features a U-shaped triazapentadienyl ligand backbone and a three-coordinate, trigonalplanar gold center. The copper(I) adduct [N{(C₃F₇)C(2,6-Cl₂C₆H ₃)-N}₂]Cu(C₂H₄) (2) also has a similar structure. The ¹³C NMR signal corresponding to the ethylene carbons of 1 appears at about 64 ppm upfield from the free ethylene, while the ethylene carbons of 2 show a relatively smaller (39 ppm) upfield shift. [N{(C₃F₇)C(2,6-Cl₂C₆H ₃)N}₂]M(C₂H₄) (M = Cu, Au) mediate carbene-transfer reactions from ethyl diazoacetate to saturated and unsaturated hydrocarbons.

Full text of DOI:10.1021/ic800373u

Inorg. Chem. 2008, 47, 4448-4450
Gold(I) Ethylene and Copper(I) Ethylene Complexes Supported by a
Polyhalogenated Triazapentadienyl Ligand
Jaime A. Flores and H. V. Rasika Dias*
Department of Chemistry and Biochemistry, The UniVersity of Texas at Arlington, Arlington, Texas 76019
Received February 27, 2008
A rare gold(I) ethylene complex and the closely related copper(I)
ethylene adduct have been isolated using [N{(C3F7)C(2,6-
Cl2C6H3)N}2]- as the supporting ligand. [N{(C3F7)C(2,6-Cl2C6H3)-
N}2]Au(C2H4) (1) is an air-stable solid. It features a U-shaped
triazapentadienyl ligand backbone and a three-coordinate, trigonal-
planar gold center. The copper(I) adduct [N{(C3F7)C(2,6-Cl2C6H3)-
N}2]Cu(C2H4) (2) also has a similar structure. The 13C NMR signal
corresponding to the ethylene carbons of 1 appears at about 64
ppm upfield from the free ethylene, while the ethylene carbons of 2
show a relatively smaller (39 ppm) upfield shift. [N{(C3F7)C(2,6-
Cl2C6H3)N}2]M(C2H4) (M ) Cu, Au) mediate carbene-transfer reactions
Figure 1. 1,3,5-Triazapentadienyl complexes of copper and silver showing
two different coordination modes.
from ethyl diazoacetate to saturated and unsaturated hydrocarbons.
[N{(C3F7)C(Dipp)N}2]AgPPh3 have κ2-bonded U-shaped ligand
backbones,6,7 while t-BuNCAg[N{(C3F7)C(Dipp)N}2] features
a κ1-bonded ligand with a W-shaped backbone (Figure 1).7
In this paper, we report the utility of a 1,3,5-triazapenta-
dienyl ligand in gold(I) ethylene chemistry and some catalytic
properties of the resulting adduct. The related copper
chemistry is also presented. A gold phosphine complex,
[N{(C3F7)C(Ph)N}2]AuPPh3, supported by a 1,3,5-triaza-
pentadienyl ligand has been reported, but X-ray structural
data are not available.5,11 The 19F NMR spectroscopic data
of this molecule indicate the presence of a κ1-bonded
triazapentadienyl ligand. It is also noteworthy that isolable
gold ethylene complexes are very rare12 and structurally
Although 1,3,5-triazapentadienyl systems are closely re-
lated to the popular and widely used 1,5-diazapentadienyl
(ꢀ-diketiminate) ligands,1 they have not received the same
attention as metal ion chelators.2–10 Recently, we reported
the isolation of several thermally stable copper(I) and silver(I)
complexes(includingsomefeaturingCu-COandCu-ethylene
bonds) using 1,3,5-triazapentadienyl anions as auxiliary
ligands.2,6,7 The resulting adducts also display quite interest-
ing and diverse coordination modes. For example, [N-
{(C3F7)C(Dipp)N}2]CuCO (Dipp ) 2,6-(Pri)2C6H3) and
* To whom correspondence should be addressed. E-mail: dias@uta.edu.
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031–3066.
(2) Dias, H. V. R.; Singh, S.; Flores, J. A. Inorg. Chem. 2006, 45, 8859–
8861.
(10) (a) Zhang, J.-P.; Lin, Y.-Y.; Huang, X.-C.; Chen, X.-M. J. Am. Chem.
Soc. 2005, 127, 5495–5506. (b) Kopylovich, M. N.; Tronova, E. A.;
Haukka, M.; Kirillov, A. M.; Kukushkin, V. Y.; Frausto da Silva,
J. J. R.; Pombeiro, A. J. L. Eur. J. Inorg. Chem. 2007, 4621–4627.
(c) Kopylovich, M. N.; Haukka, M.; Kirillov, A. M.; Kukushkin, V. Y.;
Pombeiro, A. J. L. Chem.sEur. J. 2007, 13, 786–791. (d) Walther,
M.; Wermann, K.; Lutsche, M.; Guenther, W.; Goerls, H.; Anders, E.
J. Org. Chem. 2006, 71, 1399–1406. (e) Guzei, I. A.; Crozier, K. R.;
Nelson, K. J.; Pinkert, J. C.; Schoenfeldt, N. J.; Shepardson, K. E.;
McGaff, R. W. Inorg. Chim. Acta 2006, 359, 1169–1176. (f) Guo,
J.-P.; Wong, W.-K.; Wong, W.-Y. Eur. J. Inorg. Chem. 2006, 3634–
3640. (g) Hesse, N.; Froehlich, R.; Humelnicu, I.; Wuerthwein, E.-U.
Eur. J. Inorg. Chem. 2005, 2189–2197. (h) Kajiwara, T.; Ito, T. Eur.
J. Inorg. Chem. 2004, 3084–3088. (i) Guo, J.; Wong, W.-K.; Wong,
W.-Y. Eur. J. Inorg. Chem. 2004, 267–275. (j) Turnbull, M. M.; Wei,
M. Y.; Willett, R. D. J. Coord. Chem. 1995, 35, 11–17.
(3) Dias, H. V. R.; Singh, S. Dalton Trans. 2006, 1995–2000.
(4) Dias, H. V. R.; Singh, S.; Cundari, T. R. Angew. Chem., Int. Ed. 2005,
44, 4907–4910.
(5) Siedle, A. R.; Webb, R. J.; Brostrom, M.; Newmark, R. A.; Behr,
F. E.; Young, V. G., Jr. Organometallics 2004, 23, 2281–2286.
(6) Dias, H. V. R.; Singh, S. Inorg. Chem. 2004, 43, 5786–5788.
(7) Dias, H. V. R.; Singh, S. Inorg. Chem. 2004, 43, 7396–7402.
(8) Siedle, A. R.; Webb, R. J.; Behr, F. E.; Newmark, R. A.; Weil, D. A.;
Erickson, K.; Naujok, R.; Brostrom, M.; Mueller, M.; Chou, S.-H.;
Young, V. G., Jr. Inorg. Chem. 2003, 42, 932–934.
(9) (a) Aris, D. R.; Barker, J.; Phillips, P. R.; Alcock, N. W.; Wallbridge,
M. G. H. J. Chem. Soc., Dalton Trans. 1997, 909–910. (b) Hursthouse,
M. B.; Mazid, M. A.; Robinson, S. D.; Sahajpal, A. J. Chem. Soc.,
Dalton Trans. 1994, 3615–3620. (c) Robinson, V.; Taylor, G. E.;
Woodward, P.; Bruce, M. I.; Wallis, R. C. J. Chem. Soc., Dalton Trans.
1981, 1169–1173. (d) Bottrill, M.; Goddard, R.; Green, M.; Hughes,
R. P.; Lloyd, M. K.; Taylor, S. H.; Woodward, P. J. Chem. Soc., Dalton
Trans. 1975, 1150–1155. (e) Brown, H. C.; Schuman, P. D. J. Org.
Chem. 1963, 28, 1122–1127.
(11) 1,5-Diazapendadienyl complexes of gold are also rare. Dias, H. V. R.;
Flores, J. A. Inorg. Chem. 2007, 46, 5841–5843.
(12) Dias, H. V. R.; Wu, J. Eur. J. Inorg. Chem. 2008, 509–522, and 2008,
2113, and the references cited therein.
4448 Inorganic Chemistry, Vol. 47, No. 11, 2008
10.1021/ic800373u CCC: $40.75  2008 American Chemical Society
Published on Web 04/23/2008

COMMUNICATION
ppm, respectively.13 Similar ethylene 13C NMR chemical
shifts of 1 and [HB(3-(CF3)-5-(Ph)Pz)3]Au(C2H4) but a
significantly different and upfield-shifted proton signal in 1
Scheme 1. Synthesis of Ethylene Adducts of Gold and Copper Using
[N{(C3F7)C(2,6-Cl2C6H3)N}2]H
1
points to an additional contribution to the H NMR shift of
the 1,3,5-triazapentadienyl adduct, which is most likely the
shielding caused by the ligand aryl group ring currents
flanking the ethylene moiety.
We also prepared the analogous copper(I) adduct [N{(C3-
F7)C(2,6-Cl2C6H3)N}2]Cu(C2H4) (2) for a direct comparison.
It was obtained in high yield starting with the free ligand
1
and Cu2O (Scheme 1). The H and 13C NMR (in CDCl3)
signals corresponding to the coordinated ethylene in this
molecule appear at δ ) 3.53 and 84.2 ppm (1JCH ) 161 Hz),
respectively. These are relatively smaller upfield shifts from
the free ethylene signals compared to those observed for the
analogous gold adduct. The upfield shift of the ethylene
protons and, more importantly, the ethylene carbons of
metal-ethylene adducts has been attributed to the increased
shielding caused by the metal-to-ethylene π back-dona-
tion.12,15 Therefore, these NMR data point to significantly
higher π back-bonding in the gold system.
In contrast to gold(I), a number of well-authenticated
copper(I) ethylene adducts are known.12 [HC{(Me)C(2,6-
Me2C6H3)N}2]Cu(C2H4)16 and [t-Bu2P(Me3SiN)2]Cu(C2H4)17
represent two examples of three-coordinate copper ethylene
adducts with relatively electron-rich (compared to that in 2)
auxiliary ligands. The ethylene 13C NMR signal in these adducts
were observed at δ ) 74.7 and 73.0 ppm, respectively.
Treatment of 1 in CDCl3 with excess ethylene yielded two
sharp signals in the 1H NMR spectrum at δ ) 2.71 and 5.39
ppm for the coordinated and free ethylene, respectively. The
same experiment with 2, however, led to the coalescence of
the bound ethylene signal, indicating fast ethylene exchange
on the NMR time scale and the presence of a relatively more
labile M-ethylene bond in the copper system.
characterized examples are limited to [HB(3-(CF3),5-
(R)Pz)3]Au(C2H4) (R ) CF3, Ph)13 and [Au(C2H4)3][SbF6].14
The 1,3,5-triazapentadiene used in this study, [N{(C3F7)-
C(2,6-Cl2C6H3)N}2]H, was synthesized using a procedure
similar to that reported earlier for highly fluorinated 1,3,5-
triazapentadienes.2 It is a colorless crystalline solid with good
solubility in solvents such as toluene, THF, CH2Cl2, and Et2O
but sparingly soluble in n-hexane. The X-ray crystal structure
of [N{(C3F7)C(2,6-Cl2C6H3)N}2]H shows that its NCNCN
backbone adopts a somewhat twisted, W-shaped configura-
tion with a long-short-long-short N-C bond distance
pattern, while the acidic proton is bonded to one of the
terminal nitrogen atoms.
The treatment of [N{(C3F7)C(2,6-Cl2C6H3)N}2]Li (pre-
pared in situ by reacting [N{(C3F7)C(2,6-Cl2C6H3)N}2]H with
n-BuLi) with AuCl in the presence of ethylene led to
[N{(C3F7)C(2,6-Cl2C6H3)N}2]Au(C2H4) (1) in 55% yield
(Scheme 1). It is a yellow solid that does not lose ethylene
under reduced pressure and is air- and light-stable for more
than 1 month at room temperature. A solution of the 1 in
X-ray crystal structures of 1 and 2 are shown in Figure 2.
The gold atom in 1 displays a rare, trigonal-planar coordina-
tion.18 The triazapentadienyl ligand binds to the metal center
in a κ2 fashion with Au-N distances of 2.1467(16) and
2.1549(17) Å. The CdC bond length of the bonded ethylene
[1.405(4) Å] is significantly longer than that of the free
ethylene [1.313(1) Å (X-ray)19 and 1.338 Å (calcd)].14
Crystals of 2 show some twinning, but it was resolved
1
CDCl3 shows no decomposition, as is evident from the H
NMR analysis after 1 week at room temperature in the
absence of light. It is fairly soluble in solvents such as CH2Cl2
and C6H6 but less soluble in n-hexane.
j
satisfactorily. The copper adduct crystallizes in the P1 space
group with two chemically similar molecules in the asym-
metric unit. The basic structure is similar to that of the gold
adduct 1. The Cu-C(ethylene) and Cu-N bond distances
are shorter than the corresponding Au-C and Au-N distances.
This follows the trend expected based on the smaller covalent
The 1H NMR signal corresponding to the ethylene protons
of 1 in CDCl3 appears as a singlet at δ ) 2.71 ppm, which
1
is a quite significant upfield shift from the free ethylene H
NMR signal (δ ) 5.40 ppm).12 The 13C NMR signal of the
coordinated ethylene in 1 appears at 59.1 ppm (1JCH ) 162
Hz), which is again considerably upfield-shifted relative to
the corresponding peak of the free ethylene (δ ) 123.3 ppm
(1JCH ) 156 Hz).12 The NMR data of [HB(3-(CF3)-5-
(Ph)Pz)3]Au(C2H4) have been reported, and its ethylene
proton and carbon resonances appear at δ ) 3.69 and 59.3
(15) (a) Cinellu, M. A.; Minghetti, G.; Cocco, F.; Stoccoro, S.; Zucca, A.;
Manassero, M.; Arca, M. Dalton Trans. 2006, 5703–5716. (b) Hahn,
C. Chem.sEur. J. 2004, 10, 5888–5899.
(16) Dai, X.; Warren, T. H. Chem. Commun. 2001, 1998–1999.
(17) (a) Straub, B. F.; Eisentrager, F.; Hofmann, P. Chem. Commun. 1999,
2507–2508. (b) Straub, B. F.; Gruber, I.; Rominger, F.; Hofmann, P.
J. Organomet. Chem. 2003, 684, 124–143.
(18) Carvajal, M. A.; Novoa, J. J.; Alvarez, S. J. Am. Chem. Soc. 2004,
126, 1465–1477.
(13) Dias, H. V. R.; Wu, J. Angew. Chem., Int. Ed. 2007, 46, 7814–7816.
(14) Dias, H. V. R.; Fianchini, M.; Cundari, T. R.; Campana, C. F. Angew.
Chem., Int. Ed. 2008, 47, 556–559.
(19) Van Nes, G. J. H.; Vos, A. Acta Crystallogr., Sect. B 1979, 35, 2593–
2601.
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COMMUNICATION
Scheme 2. [N{(C3F7)C(2,6-Cl2C6H3)N}2]M(C2H4) (M ) Au, Cu)
Catalyzed Carbene-Transfer Reactions from EDA
3 in 42% yield. The related copper catalyst gave 3 in much
higher yield (74%). The copper adduct also gave a much
higher styrene cyclopropanation product 4 (93%) with no
detectable sp2 C-H bond insertion product (5). The gold
adduct gave 4 in good yield (69%), while a small amount of
5 was also detected (2%). [N{(C3F7)C(2,6-Cl2C6H3)-
N}2]M(C2H4) (M ) Au, Cu) also catalyzes the Büchner
chemistry22 with benzene, producing 6 in comparable yields:
68% (Au) and 67% (Cu). The gold adduct also leads to sp2
C-H bond activation product 7 in about 8% yield. Overall,
these preliminary data are promising and show, for the first
time, that triazapentadienyl complexes of coinage metals are
indeed useful catalysts for a variety of transformations.
Carbene-transfer chemistry mediated by isolable gold adducts
of any type is also rare,23 and the reports in the literature
mainly concern the cationic gold catalysts supported by
N-heterocyclic carbenes.24 As for the copper, tris(pyra-
zolyl)borate complexes are the most widely used in carbene-
transfer chemistry.21
Overall, we describe the isolation and structural characteriza-
tion of three-coordinate gold(I) and copper(I) ethylene adducts
using a polyhalogenated 1,3,5-triazapentadienyl ligand. The
NMR and structural data suggest strong metal-to-ethylene π
back-bonding in the gold adduct 1 (despite the presence of a
weakly donating auxiliary ligand). [N{(C3F7)C(2,6-Cl2C6H3)-
N}2]M(C2H4) (M ) Au, Cu) also mediate carbene-transfer
reactions from EDA to saturated and unsaturated hydrocarbons.
Further studies are underway to explore the coordination
chemistry of triazapentadienyl ligands and catalytic properties
of triazapentadienyl metal adducts.
Figure 2. Molecular structures of 1 (top) and 2 (bottom). Selected bond lengths
(Å) and angles (deg): 1: Au-C21 2.089(2), Au-C22 2.098(2), Au-N1
2.1467(16), Au-N3 2.1549(17), C21-C22 1.405(4); C21-Au-C22 39.22(11),
N1-Au-N3 86.38(6). 2, molecule 1: Cu1-N3 1.946(5), Cu1-N1 1.958(5),
Cu1-C21 2.004(6), Cu1-C22 2.004(6), C21-C22 1.364(9); N3-Cu1-N1
96.4(2), C21-Cu1-C22 39.8(3). 2, molecule 2 (not shown): Cu2-N4 1.933(5),
Cu2-N6 1.950(5), Cu2-C44 1.998(7), Cu2-C43 2.020(7), C43-C44 1.377(10);
N4-Cu2-N6 95.2(2), C44-Cu2-C43 40.1(3).
radius of copper(I) compared to that of gold(I). The CdC
distances 1.364(9) and 1.377(10) Å of coordinated ethylene in
2 are slightly shorter than those of the gold complex 1 (which
is consistent with the NMR data and the low Mfethylene back-
bonding in copper), but the difference is within the 3σ value of
estimated standard deviations.
Efficient carbene-transfer chemistry mediated by polyha-
logenated molecules like [HB(3,5-(CF3)2Pz)3]Ag(THF) and
[HB(3,4,5-Br3Pz)3]Cu(NCMe) suggests that [N{(C3F7)C(2,6-
Cl2C6H3)N}2]M(C2H4) (M ) Au, Cu) may also show
interesting catalytic properties.20,21 Accordingly, we inves-
tigated their ability to facilitate the carbene unit transfer from
ethyl diazoacetate (EDA, a widely used carbene source) to
saturated and unsaturated hydrocarbons like cyclopentane,
styrene, and benzene (Scheme 2). The reaction of cyclopen-
tane with EDA employing [N{(C3F7)C(2,6-Cl2C6H3)-
N}2]Au(C2H4) (5 mol %) afforded C-H activation product
(20) (a) Krishnamoorthy, P.; Browning, R. G.; Singh, S.; Sivappa, R.;
Lovely, C. J.; Dias, H. V. R. Chem. Commun. 2007, 731–733. (b)
Dias, H. V. R.; Browning, R. G.; Polach, S. A.; Diyabalanage,
H. V. K.; Lovely, C. J. J. Am. Chem. Soc. 2003, 125, 9270–9271. (c)
Dias, H. V. R.; Browning, R. G.; Richey, S. A.; Lovely, C. J.
Organometallics 2004, 23, 1200–1202. (d) Dias, H. V. R.; Browning,
R. G.; Richey, S. A.; Lovely, C. J. Organometallics 2005, 24, 5784.
(e) Lovely, C. J.; Browning, R. G.; Badarinarayana, V.; Dias, H. V. R.
Tetrahedron Lett. 2005, 46, 2453–2455.
Acknowledgment. This work has been supported by the
Robert A. Welch Foundation (Grant Y-1289).
Note Added after ASAP Publication. There was an error
in the NMR shift of compound [HB(3-(CF3)-5-(Ph)Pz)3]-
Au(C2H4) in the version published ASAP April 23, 2008;
the corrected version published ASAP May 2, 2008.
(21) Diaz-Requejo, M. M.; Belderrain, T. R.; Nicasio, M. C.; Perez, P. J.
Dalton Trans. 2006, 5559–5566.
Supporting Information Available: X-ray crystallographic data
for [N{(C3F7)C(2,6-Cl2C6H3)N}2]H complexes 1 and 2 (CIF) and
experimental details. This material is available free of charge via
the Internet at http://pubs.acs.org.
(22) Doyle, M. P.; McKervey, M. A.; Tao, Y. Modern Catalytic Methods
for Organic Synthesis with Diazo Compounds; Wiley: New York,
1998; Chapter 6, p 289.
(23) Hashmi, A. S. K. Chem. ReV. 2007, 107, 3180–3211.
(24) Fructos, M. R.; De Fremont, P.; Nolan, S. P.; Mar Dauiiaz-Requejo,
M.; Perez, P. J. Organometallics 2006, 25, 2237–2241.
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