Synthesis and structure of cyclic gold(I) phosphanyl complexes [{Au(PR2)}n]

Article abstract of DOI:10.1002/anie.200390270

Gold(I) Phosphanyl Complexes, such as [Au(PR₂)]_n, have been known for more than 25 years. However, the solid-state structure of such complexes, as well as their nature in solution, has remained somewhat of a mystery. The figure displays the cyclic and polymeric forms that are possible (L = endgroup). The structures of the complexes, and the occurrence of Au...Au interactions are discussed.

Full text of DOI:10.1002/anie.200390270

Communications
2,4,6-Me3C6H2), and PIs2 (4, Is = 2,4,6-(iPr)3C6H2)), whose
novel cyclic structures were determined by X-ray crystallog-
raphy.[3]
Treatment of the known compounds [Au(PHR2)(Cl)][4]
and the novel [Au(PHIs2)(Cl)] (5) with aqueous ammonia in
THF or CH2Cl2 caused precipitation of the white, toluene-
soluble and air-stable [{Au(PR2)}n] complexes 1–4
(Scheme 1). 31PNMR spectra of these crude products
showed the presence of several species (for 1 and 3: four
species; for 2: five or ten species depending on reaction time;
for 4: only one form). Recrystallization of 1 from toluene
gave a mixture of two compounds which could not be
separated, but on one occasion crystals of one of these forms
were isolated. Recrystallization of 2 from toluene yielded a
mixture of two compounds; the less soluble one was isolated
after further recrystallization. Heating 3 in toluene caused
partial conversion to a major product, which then crystallized
preferentially. After isolation, these materials were charac-
terized by elemental analyses, multinuclear NMR and IR
spectroscopies, and MALDI mass spectrometry (molecular
ions were observed).
Gold–Phosphanyl Structures
Synthesis and Structure of Cyclic Gold(i)
Phosphanyl Complexes [{Au(PR2)}n]**
Diana M. Stefanescu, Holming F. Yuen,
David S. Glueck,* James A. Golen, and
Arnold L. Rheingold
Since their discovery in 1976, homoleptic gold(i) phosphanyl
complexes of the form [{Au(PR2)}n] have remained a
mysterious class of compounds.[1] The parent, and most
investigated of the family, [{Au(PPh2)}n], is insoluble; its
color was reported to depend on the base used in its
preparation from [Au(PHPh2)(Cl)] or related precursors.[2]
Parish and co-workers prepared several related [{Au(PR2)}n]
complexes (R = Et, n-octyl, p-MeC6H4, p-(tBu)C6H4), which
could be obtained in soluble and insoluble forms, that were
proposed to be either cyclic or linear chain polymers.[2d] NMR
studies of these materials, although made difficult by precip-
itate formation, suggested that several species were present in
solution. Mössbauer spectra indicated the expected linear
coordination with two phosphanyl ligands binding to a gold
center, but structural details were not available.[2d,f] We report
here that using bulkier R groups enables the synthesis of
soluble gold phosphanyl complexes of the form [{Au(PR2)}n]
(PR2 = PCy2 (1, Cy = c-C6H11), P(tBu)2 (2), PMes2 (3, Mes =
NH4OH
[Au(PHR2)Cl]
[{Au(PR2)}n]
PR2 = PCy2 (1), P(tBu)2 (2),
PMes2 (3), PIs2 (4)
Scheme 1. Synthesis of AuI–Phosphanyl Complexes.
The crystal structures of cyclic [{Au(PCy2)}6]·2C7H8
(1·2C7H8), [{Au(P(tBu)2)}6]·C7H8 (2·C7H8), [{Au(PMes2)}4]
(3), and [{Au(PIs2)}3](4) are shown in Figures 1–4.[5] Toluene
molecules are not illustrated in these figures, but in both
1·2C7H8 and 2·C7H8, they are present in the channels between
the rings, which stack to yield an extended structure. Not
surprisingly, an increase in the size of the Psubstituents leads
[*] Prof. D. S. Glueck, D. M. Stefanescu, H. F. Yuen
Department of Chemistry and Dartmouth Molecular Materials
Group
6128 Burke Laboratory
Dartmouth College, Hanover, New Hampshire, 03755 (USA)
Fax: (+1)603-646-3946
E-mail: Glueck@Dartmouth.edu
Prof. J. A. Golen, Prof. A. L. Rheingold
Department of Chemistry
University of Delaware
Newark, Delaware, 19716 (USA)
[þ] Permanent address:
Department of Chemistry and Biochemistry
University of Massachusetts Dartmouth
North Dartmouth, Massachusetts, 02747 (USA)
Figure 1. ORTEP diagram of [Au(PCy2)]6·2C7H8 (1·2C7H8). The hydro-
gen atoms and solvent molecules are not shown. Selected bond
lengths [Š] and angles [8]: Au1-P1 2.3116(12), Au1-P3 2.3150(12), Au2-
P2 2.3132(12), Au2-P1 2.3166(13), Au3-P2a 2.3145(12), Au3-P3
2.3223(12); P1-Au1-P3 174.09(4), P2-Au2-P1 168.83(4), P2a-Au3-P3
174.39(4).
[**] We thank the NSF for support, including an REU fellowship for
H.F.Y.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Angewandte
Chemie
Figure 4. ORTEP diagram of [{Au(PIs2)}3] (4). The hydrogen atoms
Figure 2. ORTEP diagram of [{Au(P(tBu)2)}6]·C7H8 (2·C7H8). The hydro-
gen atoms and solvent molecule are not shown. Selected bond lengths
[Š] and angles [8]: Au1-P1 2.3287(12), Au1-P2 2.3306(12), Au2-P2
2.3324(12), Au2-P3 2.3363(12), Au3-P1a 2.3280(12), Au3-P3
2.3295(12); P1-Au1-P2 174.85(4), P2-Au2-P3 178.12(4), P1a-Au3-P3
176.86(4).
and disorder in the isopropyl groups are not shown. Selected bond
lengths [Š] and angles [8]: Au1-P3 2.332(2), Au1-P1 2.335(2), Au1···Au3
3.0661(4), Au1···Au2 3.0821(4), Au2-P1 2.314(2), Au2-P2 2.319(2),
Au2···Au3 3.0970(5), Au3-P3 2.321(2), Au3-P2 2.323(2); P3-Au1-P1
157.30(7), P1-Au2-P2156.47(8), P3-Au3-P2157.02(8).
slightly longer than that in the precursor [Au(PH(tBu)2)(Cl)]
(2.230(2) Š).[4] Aurophilic interactions[6] are clearly present in
the {Au3} triangle of 4, with Au···Au separations ranging from
3.0661(4) to 3.0970(5) Š, and may also be important in 3, with
Au···Au separations of 3.3414(14) and 3.4448(12) Š observed.
In contrast, the shortest Au···Au separations in 1·2C7H8 and
2·C7H8 are 3.8992(3) and 3.9183(3) Š, respectively.
Although the ring in 1·2C7H8 is almost planar (mean
deviation from the plane is 0.1116 Š) and that in 4 is planar
(mean deviation 0.0075 Š), 2·C7H8 and 3 adopt puckered
structures (Figure 5). The structure of 3 may be described as
“butterfly-like”, with an angle between the planes of
125.24(9)8, or as a plane of Au atoms with Patoms alternating
above and below the plane. In the twisted 2·C7H8, two planes
of P atoms (P1, P2, P3, P1a and P1, P2a, P3a, P1a) intersect at
an angle of 34.15(2)8.
Figure 3. ORTEP diagram of [{Au(PMes2)}4] (3). The hydrogen atoms
are not shown. Selected bond lengths [Š] and angles [8]: Au1-P1
2.311(6), Au1-P2 2.318(6), Au1···Au2 3.3414(14), Au2-P1a 2.312(6),
Au2-P2 2.320(6); P1-Au1-P2 170.3(2), P1a-Au2-P2 163.8(2).
Hexameric 1·2C7H8 and 2·C7H8 have the same nuclearity
as [{Au(S(2,4,6-(iPr)3C6H2)}6], in which the {Au6S6} ring
adopts
a
chair conformation.[3a,e] However, 1·2C7H8 is
almost planar and the twisted ring in 2·C7H8 is closer to a
boat conformation. The structure of the cyclic tetramer 3 may
be compared to that of [{Au(N(SiMe3)2)}4], which contains a
to a decreased ring size, presumably to reduce unfavorable
steric interactions.
À
As expected, the P-Au-P angles are close to linear, and the
phosphorus atoms are approximately tetrahedral (Table 1).
planar {Au4N4} core. The shorter Au N bond length
(2.082(3) Š) is accompanied by reduced Au···Au distances
(3.0100(3) and 3.0355(3) Š).[3f] In contrast, the {Au4S4} core in
[{Au(S{SiO(tBu)3})}4] is folded as in 3 with an angle of 157.38
with respect to the S–S diagonal,[3c]
À
The Au Pbond lengths are similar in all four complexes, and
À
the average Au Pbond length in 2·C7H8 (2.3309(12) Š) is
but [{Au(SC(SiMe3)3)}4] is planar
Table 1: Selected bond lengths [Š] and angles [8] in the gold(i) phosphanyl complexes 1·2C7H8, 2·C7H8, 3,
and 4.
and [{Au(TeC(SiMe3)3)}4] adopts a
butterfly structure with a dihedral
angle of 144.98(6)8.[3b]
Complex
1·2C7H8
2·C7H8
3
4
À
Several planar complexes with a
{Au3} triangle supported by bridging
ligands are known, but these
include two-atom bridges and
nine-membered rings.[7] In contrast,
Au P (av)
2.3155(13)
172.44(4)
108.18(18)
117.51(5)
105.8(2)
2.3309(12)
176.61(4)
106.93(17)
115.76(5)
113.5(2)
2.315(6)
167.0(2)
114.6(7)
94.2(2)
2.324(2)
156.93(8)
115.2(3)
83.06(7)
110.9(4)
P-Au-P (av)
Au-P-C (av)
Au-P-Au (av)
C-P-C (av)
105.4(9)
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Communications
((AuPMes2)6), 2529.86 (Au6(PMes2)5), 2333.22 ((AuPMes2)5),
2202.19, 2153.50, 2108.03, 2063.85 (Au5(PMes2)4), 1883.82, 1867.24
((AuPMes2)4), 1783.39, 1717.12, 1641.44, 1597.32 (Au4(PMes2)3),
1417.18, 1317.02, 1236.70, 1174.88, 951.23.
Received: November 8, 2002 [Z50508]
[1] R. J. Puddephatt, P. J. Thompson, J. Organomet. Chem. 1976, 117,
395 – 403.
[2] a) J. Vicente, M. T. Chicote, P. G. Jones, Inorg. Chem. 1993, 32,
4960 – 4964; b) J. Vicente, M. T. Chicote, I. Saura-Llamas, M.-C.
Lagunas, J. Chem. Soc. Chem. Commun. 1992, 915 – 916; c) T. A.
Annan, R. Kumar, D. G. Tuck, J. Chem. Soc. Dalton Trans. 1991,
11 – 18; d) D. B. Dyson, R. V. Parish, C. A. McAuliffe, R. G.
Pritchard, R. Fields, B. Beagley, J. Chem. Soc. Dalton Trans. 1989,
907 – 914; e) T. A. Annan, R. Kumar, D. G. Tuck, J. Chem. Soc.
Chem. Commun. 1988, 446 – 448; f) D. B. Dyson, R. V. Parish,
C. A. McAuliffe, R. Fields, Hyperfine Interact. 1988, 40, 327 – 330.
[3] For related structures of AuI chalcogenolates and of an amide,
see: a) I. Schroter, J. Strahle, Chem. Ber. 1991, 124, 2161 – 2164;
b) P. J. Bonasia, D. E. Gindelberger, J. Arnold,Inorg. Chem. 1993,
32, 5126 – 5131; c) W. Wojnowski, B. Becker, J. Sassmanhausen,
E.-M. Peters, K. Peters, H. G. von Schnering, Z. Anorg. Allg.
Chem. 1994, 620, 1417 – 1421; d) M. R. Wiseman, P. A. Marsh,
P. T. Bishop, B. J. Brisdon, M. F. Mahon,J. Am. Chem. Soc. 2000,
122, 12598 – 12599; e) D. J. LeBlanc, C. J. L. Lock, Acta Crystal-
logr. Sect. C 1997, 53, 1765 – 1768; f) S. D. Bunge, O. Just, W. S.
Rees, Jr., Angew. Chem. 2000, 112, 3199 – 3200; Angew. Chem.
Int. Ed. 2000, 37, 3082 – 3084.
Figure 5. The Au–P rings have different shapes: almost planar in
1·2C7H8, twisted in 2·C7H8, butterfly in 3, and planar in 4.
the shorter bridges in 4 lead to unusually bent P-Au-P angles
(average 156.93(8)8). We are not aware of other simple
[{AuX}n] complexes with trinuclear structures; the closest
precedent is the Au–Nb raft cluster [{Au(Cp02NbH2)}3] (Cp’ =
h5-C5H4SiMe3), which also features bridging hydrides.[8] These
comparisons suggest that ring size and conformation in these
classes of homoleptic compounds depend strongly on the
substituents and the possibility of Au···Au interactions.
In conclusion, X-ray crystallographic studies of gold(i)
phosphanyl complexes have for the first time established the
structures of this class of compounds as cyclic oligomers.
31PNMR spectroscopy showed that several species, presum-
ably rings of different sizes, exist in solution, and that they can
interconvert in some cases. These advances pave the way for
further investigation of the structure and reactivity of AuI
phosphanyl complexes and their potential applications.[9]
[4] a) H. Schmidbaur, G. Weidenhiller, A. A. M. Aly, O. Steigel-
mann, G. Muller, Z. Naturforsch. B 1989, 44, 1503 – 1508; b) H.
Schmidbaur, A. A. M. Aly, Z. Naturforsch. B 1979, 34, 23 – 26.
[5] Crystallographic data for 1–4: recorded at 223(2) K (1·2C7H8 and
3), 150(2) K (2·C7H8), and 218(2) K (4) with MoKa (0.71073 Š)
ꢀ
radiation: 1·2C7H8: triclinic, space group P1, a = 11.7057(7), b =
15.2817(9), c = 15.3080(9) Š, a = 63.2510(10), b = 73.1750(10),
g = 88.0730(10)8, Z = 2, R1 = 0.0313 for 10891 (I > 2s(I)) data;
2·C7H8: monoclinic, space group C2/c, a = 30.0553(16), b =
8.8627(5), c = 29.4648(16) Š, b = 115.4920(10)8, Z = 4, R1 =
0.0278 for 8504 (I > 2s(I)) data; 3: monoclinic, space group
C2/c, a = 23.830(5), b = 12.160(2), c = 27.254(6) Š, b =
108.322(4)8, Z = 8, R1 = 0.0728 for 5526 (I > 2s(I)) data; 4:
orthorhombic, space group Pna21, a = 24.6277(14), b =
15.3421(9), c = 23.5866(14) Š, Z = 4, R1 = 0.0474 for 19538 (I >
2s(I)) data; CCDC 196576–196579 (complexes 1·2C7H8, 2·C7H8,
3, and 4, respectively) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB21EZ, UK; fax: (+ 44)1223-336-033; or deposit@
ccdc.cam.ac.uk).
Experimental Section
A representative synthesis is described. Full details of the synthesis
and characterization of the other complexes are in the Supporting
Information.
3: Aqueous ammonia (approximately 5 mL, 29.6%, 78 mmol)
was added to a solution of [Au(PHMes2)(Cl)] (340 mg, 0.68 mmol) in
THF (10 mL); a white precipitate was formed. After stirring for
30 min, the solvent was pumped off, and the resulting white solid was
washed with water (30 mL) to give 3 (220 mg, 69%). 31P{1H} NMR
([D8]toluene, 121.4 MHz): d = À17.0 (major), À18.8 (minor), À23.4
(minor), À36.1 ppm (minor). This material could be dissolved in
heated toluene (708C). Slow evaporation of toluene at room temper-
ature yielded a single product, shown to be a cyclic tetramer by X-ray
crystallography (Yield 42%).
[6] a) H. Schmidbaur, Gold Bull. 2000, 33, 3 – 10; b) H. Schmidbaur,
Chem. Soc. Rev. 1995, 24, 391 – 400.
[7] A. L. Balch, M. M. Olmstead, J. C. Vickery, Inorg. Chem. 1999,
38, 3494 – 3499, and references therein.
[8] A. Antinolo, J. K. Burdett, B. Chaudret, O. Eisenstein, M.
Fajardo, F. Jalon, F. Lahoz, J. A. Lopez, A. Otero, J. Chem. Soc.
Chem. Commun. 1990, 17 – 19.
[9] a) G. Landgraf in Gold. Progress in Chemistry, Biochemistry and
Technology (Ed.: H. Schmidbaur), Wiley, Chichester 1999,
pp. 143 – 171; b) C. F. Shaw III in Gold. Progress in Chemistry,
Biochemistry and Technology (Ed.: H. Schmidbaur), Wiley,
Chichester, 1999, pp. 259 – 308.
Elemental analysis (%) calcd for C72H88Au4P4: C 46.36, H 4.76.
Found: C 46.20, H 4.58. 31P{1H} NMR (C6D6, 121.4 MHz): d =
1
À36.1 ppm; H NMR (C6D6, 300 MHz): d = 6.70 (16H), 2.65 (48H),
2.07 ppm (24H). IR (KBr): n˜ = 3015, 2954, 2915, 1715, 1592, 1546,
1454, 1392, 1292, 1246, 1015, 838, 700, 615, 554, 423 cmÀ1. MALDI -
TOF-MS
(Cyano-4-hydroxycinnamic
acid):
m/z
2799.65
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