Reaction of gold(III) oxo complexes with alkenes. Synthesis of unprecedented gold alkene complexes, [Au(N,N)(alkene)][PF6]. Crystal structure of [Au(bipyip)(η2-CH2=CHPh)] [PF6] (bipyip = 6-

Article abstract of DOI:10.1039/b404890c

Gold alkene complexes [Au(bipy^R)(η²-alkene)] [PF₆] (bipy^R = 6-alkyl-2,2′-bipyridine) have been obtained by reaction of gold(III) oxo complexes [Au₂(bipy ^R)₂(μ-O)₂][PF<

Full text of DOI:10.1039/b404890c

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Reaction of gold(III) oxo complexes with alkenes. Synthesis of
unprecedented gold alkene complexes, [Au(N,N)(alkene)][PF6]. Crystal
structure of [Au(bipyip)(h2-CH2NCHPh)][PF6] (bipyip =
6-isopropyl-2,2A-bipyridine)†
Maria A. Cinellu,*a Giovanni Minghetti,a Sergio Stoccoro,a Antonio Zuccaa and Mario Manasserob
a Dipartimento di Chimica, Università di Sassari, via Vienna 2, I-07100 Sassari, Italy.
E-mail: cinellu@uniss.it
b Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Università di Milano, Centro CNR, via
Venezian 21, I-20133 Milano, Italy. E-mail: m.manassero@istm.cnr.it
Received (in Cambridge, UK) 2nd April 2004, Accepted 21st May 2004
First published as an Advance Article on the web 17th June 2004
Gold alkene complexes [Au(bipyR)(h2-alkene)][PF6] (bipyR
=
resonances of the corresponding carbon atoms are likewise shifted
upfield with coordination-induced shift Dd 252.4 ppm for the
methyne and 256.4 ppm for the methylene carbon. These upfield
shifts are similar to those found in the comparable three-coordinate
6-alkyl-2,2A-bipyridine) have been obtained by reaction of
gold(III) oxo complexes [Au2(bipyR)2(m-O)2][PF6]2 with alkenes.
The crystal structure of the styrene adduct [Au(bipyip)(h2-
CH2NCHPh)][PF6] (bipyip = 6-isopropyl-2,2A-bipyridine) has
been solved by X-ray analysis.
copper( ) olefin complexes supported by chelating nitrogen ligands
I
(Dd(H) 20.1 to 22.0 ppm; Dd(C) 240 to 250 ppm).8,9 Addition
of one equivalent of styrene to a CD2Cl2 solution of 2a causes
broadening of the vinylic protons of the coordinated styrene,
indicating fast intermolecular exchange at room temperature.
Variable temperature 1H NMR spectra of complex 2c indicate at
room temperature a dynamic process involving rotation of the
coordinated styrene around the metal–olefin bond. The calculated
DGrot‡ value (50.3 kJ.mol21 at 243 K)† is in the range previously
reported for similar d10 olefin complexes with a-diimmine
ligands.8e,9a,b,10
Gold(III) oxo complexes1 are a new entry into the relatively small
family of late transition metal oxo complexes.2 The chemistry of
this class of compounds has been of interest for many years. Among
the various aspects of the reactivity displayed by metal oxo
complexes is the capability of transferring oxygen atoms to organic
and inorganic substrates.2,3
In the course of our investigations of the reactivity of the oxo
complexes [Au2(bipyR)2(m-O)2][PF6]2 (bipyR = 6-alkyl-2,2A-bi-
pyridine) we found that PPh3 is stoichiometrically converted into
Olefin gold complexes have been known for many years,11
however, only a small number of isolable complexes have been
reported12 and only a few of them have been structurally
characterized.13 Furthermore the available X-ray data are relevant
to species incomparable to compounds 2a–2d.
OPPh3; the gold( ) complex [Au(PPh3)2][PF6] and the free
I
bipyridine ligand are also quantitatively obtained from the
reaction.1a In view of these encouraging results we decided to
extend this reaction to alkenes. Alkene oxidation by oxygen atom
transfer reaction from late transition metal oxo complexes is, at
present, an objective of particular interest.
The m-oxo complexes [Au2(bipyR)2(m-O)2][PF6]2 1 (R = Me a,
CH2Me b, CHMe2 c, CH2CMe3 d) react with excess alkene in
acetone or acetonitrile solution under different experimental
conditions to give, albeit in low yield, unexpected alkene adducts,
[Au(bipyR)(alkene)][PF6] (alkene = styrene 2, a-methylstyrene,
ethylene and norbornene).4,5 Few examples of alkene complexes
obtained by reaction of a late transition metal oxo complex have
been reported.6
The reaction with styrene was used as a model and studied with
all the complexes in order to assess the possible influence of the
alkyl substituent at the 6 position on the reactivity of the oxo
complexes.‡ In no case is the reaction quantitative—average yield
is in the range 15–45%. Most of the starting material is recovered
when the reaction is carried out in anhydrous solvents, while
complete conversion of the oxo complexes is accomplished in the
presence of water, after a long reaction time.‡ Variable amounts of
metallic gold and organic products arising from oxidation of
alkenes are also formed in all cases.4,5 To the best of our
knowledge, alkene oxidation by an isolated late transition metal
oxo complex is still rare.6b,7
The thermally stable styrene adducts [Au(bipyR)(h2-
CH2NCHPh)][PF6] (2a–d)† give satisfactory elemental analyses
and their molecular ions M+ have been detected by FAB mass
spectrometry. The 1H NMR spectra at room temperature, recorded
in various solvents, show that both the CH and CH2 resonances are
shifted upfield compared to free styrene. For example, in CDCl3 the
methyne proton resonates at d 5.43 (Dd 21.29) and the methylene
protons at d 4.07 (Dd 21.68 ppm) and 4.03 (Dd 21.21 ppm). The
The structure of 2c§ consists of the packing of [Au(bipyip)(h2-
styrene)]+ cations, PF62 anions and MeCN molecules in the molar
ratio 2 : 2 : 1. Fig. 1 shows an ORTEP view of the cation, and
principal bond parameters are reported in the figure caption. The
orientation of the olefin is coplanar with the bipyridine backbone,
which chelates the gold centre with a bite angle of 75.1(2)°. The
dihedral angle between the metal coordination plane and the C(14)–
C(15)–C(16) plane is 77.2(3)° which means that there is a bending
back angle of 12.8(3) ° of the phenyl ring with respect to the ideal
orthogonal coordination. Gold–carbon distances, Au–C(14)
2.114(6) and Au–C(15) 2.098(5) Å, are slightly shorter or similar to
those found in two gold(
) alkene complexes (2.21(2), 2.15(2) Å13c
I
and 2.14(4), 2.11(4) Å13b) (consider the high standard deviations of
the four latter distances). The bond length between Au and the CH
carbon atom, 2.114(6) Å, is slightly longer than that of the other
Au–C contact, 2.098(5) Å. This is a common feature of metal-
coordinated styrene, compare with e.g. Cu–C distances of 2.014(5)
and 1.985(6) Å in the cationic Cu(
) styrene complex [Cu(bipy)(h2-
I
styrene)][ClO4] 3.8b The C(14)–C(15) distance, 1.384(8) Å, is
slightly longer than in free styrene (1.346(20) Å)14 and in 3
(1.358(10) Å)8b and comparable to that found in the neutral b-
diketiminate complex [Cu(Me2NN)(h2-CH2NCHPh)] (1.373(6)
Å).8e The Au–N distances, 2.150(3) and 2.217(5) Å are very long,
probably because of the trans-influence of the styrene molecule.
The elongation of the Au–N(2) bond, 2.217(5) Å, compared to the
Au–N(1) bond, 2.150(3) Å, is probably due to the steric hindrance
of the bulky isopropyl substituent. A similar effect has been found
previously, for instance, in 1d.1c
The coordinated styrene is readily displaced from 2d by
triphenylphosphine, as shown by a proton spectrum recorded
straight after the addition of one equivalent of PPh3.
[Au(PPh3)2][PF6] is quantitatively isolated from the reaction with
two equivalents of PPh3.
† Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/cc/b4/b404890c/
1618
C h e m . C o m m u n . , 2 0 0 4 , 1 6 1 8 – 1 6 1 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

View Article Online
Pentium III computer. CCDC 236738. See http://www.rsc.org/suppdata/cc/
b4/b404890c/ for crystallographic data in .cif or other electronic format.
1 (a) M. A. Cinellu and G. Minghetti, Gold Bull., 2002, 35, 11; (b) M. A.
Cinellu, G. Minghetti, M. V. Pinna, S. Stoccoro, A. Zucca and M.
Manassero, J. Chem. Soc., Dalton Trans., 2000, 1261; (c) M. A. Cinellu,
G. Minghetti, M. V. Pinna, S. Stoccoro, A. Zucca, M. Manassero and M.
Sansoni, J. Chem. Soc., Dalton Trans., 1998, 1735; (d) M. A. Cinellu,
G. Minghetti, M. V. Pinna, S. Stoccoro, A. Zucca and M. Manassero,
Chem. Commun., 1998, 2397.
2 P. R. Sharp, J. Chem. Soc., Dalton Trans., 2000, 2647; P. R. Sharp,
Comments Inorg. Chem., 1999, 21, 85.
3 Active Oxygen in Chemistry, ed. C. S. Foote, J. S. Valentine, A.
Greenberg and J. F. Liebman, Chapman and Hall, London, 1995; Active
Oxygen in Biochemistry, ed. J. S. Valentine, C. S. Foote, A. Greenberg
and J. F. Liebman, Chapman and Hall, London, 1995; Biomimetic
Oxidations Catalyzed by Transition Metal Complexes, ed. B. Meunier,
Imperial College Press, London, 2000; Metal-Oxo and Metal-Peroxo
Species in Catalytic Oxidations, ed. B. Meunier, Springer, Berlin, 2000;
vol. 97; R. H. Holm, Chem. Rev., 1987, 87, 1401; L. Que, Jr. and W. B.
Tolman, Angew. Chem., Int. Ed., 2002, 41, 1114; M. Taki, S. Itoh and
S. Fukuzumi, J. Am. Chem. Soc., 2002, 124, 998 and references
therein.
4 Part of this work has been presented in oral form: M. A. Cinellu, G.
Minghetti, D. Bacciu, S. Stoccoro, A. Zucca and M. Manassero,
Abstracts of Papers, Gold 2003, New Industrial Applications of Gold,
Vancouver, Canada, September 28–October 1, 2003, No.1113.
5 Full characterization of complexes with a-methylstyrene, ethylene and
norbornene is on-going and will be reported in a full paper.
6 (a) B. Flint, J.-J. Li and P. R. Sharp, Organometallics, 2002, 21, 997; (b)
E. Szuromi, H. Shan and P. R. Sharp, J. Am. Chem. Soc., 2003, 125,
10522.
Fig. 1 ORTEP view of the [Au(bipyip)(h2-styrene)]+ cation. Ellipsoids are
drawn at the 30% probability level. Selected bond distances (Å) and angles
(°): Au–N(1) 2.150(3), Au–N(2) 2.217(5), Au–C(14) 2.114(6), Au–C(15)
2.098(5), C(14)–C(15) 1.384(8), C(14)–C(16) 1.488(6) Å, N(1)–Au–N(2)
75.1(2), N(1)–Au–C(14) 119.6(2), N(1)–Au–C(15) 157.8(2), N(2)–Au–
C(14), 165.4(2), N(2)–Au–C(15) 127.0(2), C(14)–Au–C(15) 38.4(2),
C(15)–C(14)–C(16) 126.3(5)°.
7 T. Hosokawa, M. Takano and S.-I. Murahashi, J. Am. Chem Soc., 1996,
118, 3990.
On the whole the spectroscopic and structural data, taken
together, point to a non negligible p contribution in the olefin–gold
bond.
We are grateful to the University of Sassari for financial support
(60%) and to the Regione Autonoma della Sardegna (RAS) for a
grant to M.A.C. (L.R.9/8/1950, n.43).
8 (a) M. Munakata, S. Kitagawa, S. Kosome and A. Asahara, Inorg.
Chem., 1986, 25, 2622 and references therein (b) H. Masuda, K.
Machida, M. Munakata, S. Kitagawa and H. Shimono, J. Chem. Soc.,
Dalton Trans., 1988, 1907; (c) L. Cavallo, M. E. Cucciolito, A. De
Martino, F. Giordano, I. Orabona and A. Vitagliano, Chem. Eur. J.,
2000, 6, 1127; (d) B. F. Straub, F. Eisenträger and P. Hoffmann, Chem.
Commun., 1999, 2507; (e) X. Dai and T. H. Warren, Chem. Commun.,
2001, 1998.
9 Larger values are found for analogous d10 metal complexes (M = Pd,
Pt) with more electron accepting alkenes (Dd(H) 23.0 to 23.5 ppm;
Dd(C) 290 to 2120 ppm). See for example: (a) R. van Asselt, C. J.
Elsevier, W. J. J. Smeets and A. L. Spek, Inorg. Chem., 1994, 33, 1521;
(b) K. J. Cavell, D. J. Stufken and K. Vrieze, Inorg. Chim. Acta, 1980,
47, 67; (c) M. W. van Laren, M. A. Duin, C. Klerk, M. Naglia, D.
Rogolino, P. Pelagatti, A. Bacchi, C. Pelizzi and C. J. Elsevier,
Organometallics, 2002, 21, 1546; (d) M. L. Ferrara, F. Giordano, I.
Orabona, A. Panunzi and F. Ruffo, Eur. J. Inorg. Chem., 1999, 1939; (e)
L. Canovese, F. Visentin, G. Chessa, C. Santo, P. Uguagliati, L. Maini
and M. Polito, J. Chem. Soc., Dalton Trans., 2002, 3696; (f) M. L.
Ferrara, I. Orabona, F. Ruffo, M. Funicello and A. Panunzi, Organome-
tallics, 1998, 17, 3832.
Notes and references
‡
Reactions of compounds 1a–1d with styrene. Anhydrous solvent:
styrene (2 mmol) was added to a solution of 1 (0.2 mmol) in acetonitrile (40
cm3) (1a and 1b) or acetone (40 cm3) (1c and 1d). The resulting yellow
solution was stirred for 3 days at room temperature and then filtered through
Celite. The solution was evaporated to dryness and the residue extracted
with CHCl3 (3 3 15 cm3). The combined chloroform extracts were filtered
and concentrated to a small volume. Addition of diethyl ether gave a whitish
precipitate of compound 2 (2a, 15%; 2b, 20%; 2c 25%; 2d, 45%). Unreacted
complex 1 was recovered from the insoluble residue (1a, 66%; 1b, 61%; 1c,
50%; 1d, 30%).
Aqueous solvent: to a solution of 1a (0.320 g, 0.3 mmol) in acetonitrile
(50 cm3) styrene (6 mmol) and water (5 cm3) were added. The resulting
solution was stirred under Ar for 7 days at room temperature. Concentration
of the filtered solution gave a white precipitate of 2a which was recovered
by filtration under vacuum. Recrystallization from dichloromethane gave
the analytical sample (0.130 g, 35%). Compounds 2c and 2d were obtained
similarly from 1c and 1d, respectively. In contrast to 2a, 2c and 2d were
extracted with CHCl3 (3 3 15 cm3) after evaporation to dryness of the
filtered solution. (2c, 31 %; 2d, 46%).
10 L. Canovese, F. Visentin, P. Uguagliati and B. Crociani, J. Chem. Soc.,
Dalton Trans., 1996, 1921.
11 A. J. Chalk, J. Am. Chem. Soc., 1964, 86, 4733.
12 H. Schmidbaur, A. Grohmann and M. E. Olmos in Gold Progress in
Chemistry, Biochemistry and Technology, ed. H. Schmidbaur, John
Wiley and Sons. New York, 1999, pp. 728–730; A. Grohmann and H.
Schmidbaur, ‘Gold’ in Comprehensive Organometallic Chemistry, ed.
J. L. Wardell, E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon-
Elsevier, Oxford, 1995, vol. 3, pp. 44–47; R. J. Puddephatt, ‘Gold’, in
Comprehensive Organometallic Chemistry, ed. G. Wilkinson, F. G. A.
Stone and E. W. Abel., Pergamon Press, Oxford, 1982, vol. 2, pp.
809–812; R. J. Puddephatt, The Chemistry of Gold, Elsevier, The
Netherlands, 1978, pp. 148–151.
13 (a) M. Håkansson, H. Eriksson and S. Janger, J. Organomet. Chem.,
2000, 602, 133; (b) R. M. Dávila, R. J. Staples and J. P. Fackler, Jr.,
Organometallics, 1994, 13, 418; (c) D. Belli Dell’Amico, F. Calder-
azzo, R. Dantona, J. Strähle and H. Weiss, Organometallics, 1987, 6,
1207.
§ Crystal data for 2c·0.5MeCN: C22H23.5Au1F6N2.5P, Mr
= 664.88,
monoclinic, space group P21/c (no. 14), a = 13.717(1), b = 12.833(1), c =
15.272(2) Å, b = 114.15(1)°, U = 2453.1(4) Å3, Z = 4, dc = 1.800 g
cm23, T = 223 K, m = 61.1 cm21, F(000) = 1284. Reflections measured
33327, independent 5027 with Rint = 0.027. Final R2 (F2, all reflections) =
0.054, R2w = 0.090, conventional R1 = 0.032 for 291 variables. Bruker
SMART CCD area-detector, Mo–Ka radiation (l = 0.71073 Å), w scan
mode, qmin = 3°, qmax = 26°. Structure solved by direct methods and
refined by full-matrix least squares. Atom C(13) is disordered and split into
two half atoms, C(13a) and C(13b), with occupancy factors = 0.50; only
C(13a) has been drawn in Fig. 1. The half MeCN molecule is disordered
around an inversion centre. The programme used was Personal SDP on a
14 J. C. Cochran, K. Hagen, G. Paulen, Q. Shen, S. Tom, M. Traetteberg
and C. Wells, J. Mol. Struct., 1997, 413–414, 313.
C h e m . C o m m u n . , 2 0 0 4 , 1 6 1 8 – 1 6 1 9
1619