X-ray structural determination of a bulky phosphine complex: Chloro {tris(2,4,6-trimethoxyphenyl)phosphine} gold(I), {AuC1[P(C9H11O3)3]}

Article abstract of DOI:10.1016/S0277-5387(00)00527-1

The title compound, {AuC1[P(C₉H₁₁O₃)₃]}, has three fold symmetry in the solid state. The Au-C1 and Au-P bond lengths are 2.294 and 2.255 ?, respectively, and the Au atom has nearly linear coordination geometry, with P-Au-C1 176.03(9)°. The extreme bulkiness of the phosphine ligand is shown by the mean cone angle of 188° (based on O atoms defining the cone), though the cone angle is considerably smaller than 214° for trimesitylphosphine in the known analogous complex. The shorter Au-P bond distance than for Ag-P (2.379(1) ?) in the corresponding known silver chloride complex of tris(2,4,6-trimethoxyphenyl)phosphine tentatively supports an earlier conclusion that gold is smaller than silver.

Full text of DOI:10.1016/S0277-5387(00)00527-1

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Polyhedron 19 (2000) 2211–2213
X-ray structural determination of a bulky phosphine complex:
chloro{tris(2,4,6-trimethoxyphenyl)phosphine}gold(I),
{AuCl[P(C9H11O3)3]}
Elmer C. Alyea *, George Ferguson, Shanmugaperumal Kannan
Department of Chemistry and Biochemistry, Uni6ersity of Guelph, Guelph, Ont., Canada N1G 2W 1
Received 15 March 2000; accepted 11 May 2000
Abstract
The title compound, {AuCl[P(C9H11O3)3]}, has three fold symmetry in the solid state. The AuꢀCl and AuꢀP bond lengths are
,
2.294 and 2.255 A, respectively, and the Au atom has nearly linear coordination geometry, with PꢀAuꢀCl 176.03(9)°. The extreme
bulkiness of the phosphine ligand is shown by the mean cone angle of 188° (based on O atoms defining the cone), though the cone
angle is considerably smaller than 214° for trimesitylphosphine in the known analogous complex. The shorter AuꢀP bond distance
,
than for AgꢀP (2.379(1) A) in the corresponding known silver chloride complex of tris(2,4,6-trimethoxyphenyl)phosphine
tentatively supports an earlier conclusion that gold is smaller than silver. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Bulky phosphine; X-ray structure; Cone angle; Two-coordinate gold complex.
state (Fig. 1). The dihedral angles between the aryl ring
planes and the relevant AuꢀPꢀCln1(n=1, 2, 3) planes
are 50.4(3), 56.7(3)and 15.3(3)° for planes C11–C16,
C21–C26 and C31–C36, respectively. The three aryl
1. Introduction
Our long-standing interest in the steric effects of
bulky phosphine ligands [1,2] led us some years ago to
determine the crystal structure of chloro(trimesitylphos-
phine)gold(I) containing the bulkiest known phosphine
[3]. Another related bulky phosphine, tris(2,4,6-
trimethoxyphenyl)phosphine, has garnered recent atten-
tion [4]. Since several crystallographic studies of mono
tertiarylphosphine gold(I) chloride complexes have been
reported [5–28] we undertook the structural determina-
tion of the title compound to provide a relative steric
profile of tris(2,4,6-trimethoxyphenyl)phosphine, partic-
ularly as compared with other bulky phosphines.
2. Results and discussion
Chloro{tris(2,4,6 - trimethoxyphenyl)phosphine}gold-
(I) (1) has approximate threefold symmetry in the solid
* Corresponding author. Tel.: +1-519-824-4120, Ext. 3031; fax:
+1-519-766-1499.
E-mail address: alyea@chembio.uoguelph.ca (E.C. Alyea).
Fig. 1. A view of (1) with the atomic numbering scheme; displacement
ellipsoids are drawn at the 30% probability level.
0277-5387/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0277-5387(00)00527-1

2212
E.C. Alyea et al. / Polyhedron 19 (2000) 2211–2213
Table 1
bond angle (176.03(9)°) in (1) are comparable with
those reported in other structural studies of species
containing the R3PꢀAuꢀCl fragment (R3P=triaryl- or
trialkyl-phosphine). For comparison, relevant AuꢀCl
and AuꢀP bond lengths and PꢀAuꢀCl angles for some
selected structures of this type, revealed in a search of
the Cambridge Structural Database [30], are shown in
,
Summary of dimensions (A, °) for some chloro(monophos-
phine)gold(I) complexes
Structure
AuꢀCl
AuꢀP
ClꢀAuꢀP Reference
[(MeO)3C6H2]3PAuCl 2.294(2)
(Mesityl)3PAuCl
Ph3PAuCl
(Cyclohexyl)3PAuCl
(Ethyl)3PAuCl
2.255(2)
176.03(9) this work
2.2716(19) 2.2634(15) 178.01(8) [3]
2.279(3)
2.279(5)
2.305(8)
2.306(8)
2.288(2)
2.281(3)
2.288(2)
2.235(3)
2.242(4)
2.232(9)
2.231(8)
2.227(2)
2.243(2)
2.235(2)
2.234(2)
2.249
179.6(1) [5]
177.0(2) [7]
178.5(3) [9]
178.9(3)
176.1(1) [10]
179.4(1) [11]
175.1(1) [12]
178.3(1) [13]
,
Table 1. The AuꢀP bond length of 2.255(2) A (1) is
slightly less than the AuꢀP bond distance in chloro-
,
trimesitylphosphine (2.2634(15) A), but comparable to
Ph(Me2C4H2)PAuCl
(o-Tolyl)3PAuCl
(m-Tolyl)3PAuCl
Ph(cyclohexyl)2PAuCl 2.234(3)
Ph(anthracenyl)2PAuCl 2.281
Ph2(2-trimethylsiloxy)- 2.285
PAuCl
Ph2(trimethylsily-
methyl)PAuCl
(Me2N)3PAuCl
,
those found in Cy3PAuCl (2.242(4) A) and (o-
,
tolyl)3PAuCl (2.243(2) A). The AgꢀP bond distance in
previously reported chloro{tris[trimethoxyphenyl)phos-
173.9
177.3
[14]
[16]
,
phine]}silver(I) is 2.379(1) A and a weak Ag···O interac-
2.229
,
tion of 2.818(3) A gives rise to a PꢀAgꢀCl angle of
175.0(1)° [4]. This longer distance for the AgꢀP bond
compared to the AuꢀP one in the present complex is in
keeping with the recent conclusion that gold is smaller
than silver based on a structural comparison of the
analogous bis(trimesitylphosphine) cations [31]. How-
ever, since our much earlier structural analysis of the
[Ag(Pmes3)2] cation indicated that significant in-
tramolecular steric distortions occur within that cation
[32], the recent conclusion based on comparing the
[M(Pmes3)2] cations is clearly flawed. Our present com-
parison of the analogous LꢀMꢀCl complexes provides
more valid evidence for the conclusion that gold is
indeed smaller than silver. However, the presence of
other intramolecular interactions which are still signifi-
cant in the present complex (such as the Au···O interac-
tions) suggests that caution should still be exercised in
making such a conclusion, i.e. a definitive study should
involve a smaller phosphine.
2.292
2.236
2.222
176.9
177.9
[20]
[25]
2.289
rings of the bulky triarylphosphine ligand have very
similar geometries. The P atom is displaced 0.18(1),
0.22(1) and 0.09(1) A from the aromatic plane and the
ortho methoxy O atoms are displaced in the opposite
direction (e.g. O12 −0.04(1), O16 +0.09(1) A). There
are also weak interactions between the Au atom and
the three immediately adjacent methoxy oxygens (O32,
O12 and O22, Au···O separations 2.922(1), 3.112(1) and
3.122(1) A. Comparable values for the known
analogous Ag complex are: 2.818(3), 3.038(3) and
3.140(3) A [4]. In the analogous trimesitylphosphine
complex the significant Au···H interactions to the ortho
methyl groups (mean contacts Au···C 3.229 A and
Au···H 2.40 A) were characterized as ‘remote agostic’
[29]. Whether the same designation of an attractive
interaction is applicable for (1) is not as clear from the
structural data. All six ortho methoxy groups in (1)
have their methyl groups oriented so that they are
remote from the central P atom and are turned away
from the Au atom. In the trimesitylphosphine complex
,
,
,
,
,
,
In order to quantify the relative bulkiness of the
tris(2,4,6-trimethoxyphenyl)phosphine and trimesit-
ylphosphine ligands, we calculated the cone angles of
these ligands from the crystallographic data for the two
analogous gold complexes. By calculating semi-cone
angles (q/2) using the ‘ligand-profile’ concept [1] with
,
CꢀH at 1.08 A, resultant average cone angles [2] of 188°
,
the mean PꢀCn1ꢀCn6 angle (117.3(6) A) (where n=1,
and 214° were obtained for tris(2,4,6-trimethoxy-
phenyl)phosphine and trimesitylphosphine, respectively.
The smaller estimated steric size of the former ligand is
commensurate with the folding back of the methoxy
groups and the observed structural data for the title
complex.
2, 3) is 6.7° less than the mean PꢀCn1ꢀCn2 angles
(124.0(6)°). Comparable angles in the present complex
are 118.8(17) and 125.2(17)°, respectively. For the
analogous 1:1 silver chloride and bromide complexes
studied by Baker et al. [4], these angles follow the same
trends. The mean AuꢀPꢀC angle and the mean CꢀPꢀC
angle in (1) are 110.5(8) and 108.4(10)°, respectively;
comparable values for the corresponding trime-
sitylphosphine complex are 107.6(2) and 111.2(3)°, at-
testing to the greater ortho interactions due to the larger
steric bulk of the Pmes3 ligand (see below). The com-
parable mean angles in the known silver chloride com-
plex are identical to those found in (1) [4].
3. Experimental
3.1. Compound synthesis and NMR spectral data
The compound was synthesized by stirring tris(2,4,6-
trimethoxyphenyl)phosphine with (dimethylsulfide)-
,
The AuꢀCl bond length (2.294(2) A) and PꢀAuꢀCl

E.C. Alyea et al. / Polyhedron 19 (2000) 2211–2213
2213
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503 K (dec). Spectral data: 31P-NMR (CDCl3): −32.9.
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OCH3); 6.02 (d, 4 Hz, 6H, phenyl) ppm.
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C27H33AuClO9P, M=764.92, Tetragonal, a=
3
,
,
15.3343(9), c=12.3291(11) A, U=2899.1(3) A , T=
294 K, space group P43, graphic monochromated Mo
,
Ka radiation, u=0.71073 A, Z=4, Dcalc=1.753 Mg
m
−3, F(000)=1512, colourless crystals with dimen-
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Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre, CCDC No. 141601 for compound 1. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (Fax: +44-1223-336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
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Acknowledgements
[30] Cambridge Structural Database System (CSDS), Database 5.18,
Cambridge Crystallographic Data Centre, University Chemical
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E.C.A. thanks NSERC (Canada) for a research
grant.
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