Bis- and tris-phosphinostannane gold complexes featuring Au → Sn dative interactions: Synthesis, structures, and DFT calculations

Article abstract of DOI:10.1016/j.poly.2016.07.010

As part of our interest in the coordination chemistry of heavy Group 14 elements, we have synthesized complexes of general formula [(o-(Ph₂P)C₆H₄)₂SnClPh]AuX (X = Cl (2-Cl), X = Br (2-Br), and X = I (2-I)) in which the chlorostanane unit acts as a σ-acceptor ligand toward gold. The existence of a Au → Sn dative bond is evidenced by a trigonal bipyramidal geometry about the tin atom as well as a distorted square planar geometry about the gold center. While the measured Au–Sn bond distances are crystallographically indistinguishable in this series, theoretical investigations reveal that the strength of the Au → Sn interaction increases in the order 2-I < 2-Br < 2-Cl. These results suggest that the Au → Sn interaction is affected by the ligands around gold. Lastly, we also report the tripodal complex [(o-(Ph₂P)C₆H₄)₃SnCl]AuSnCl₃(4) in which the gold atom is concomitantly coordinated to a Z-type tin ligand and an X-type tin ligand.

Full text of DOI:10.1016/j.poly.2016.07.010

Polyhedron xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Bis- and tris-phosphinostannane gold complexes featuring Au ? Sn
dative interactions: Synthesis, structures, and DFT calculations
⇑
Tzu-Pin Lin, François P. Gabbaï
Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
As part of our interest in the coordination chemistry of heavy Group 14 elements, we have synthesized
complexes of general formula [(o-(Ph2P)C6H4)2SnClPh]AuX (X = Cl (2-Cl), X = Br (2-Br), and X = I (2-I)) in
Received 24 May 2016
Accepted 9 July 2016
Available online xxxx
which the chlorostanane unit acts as a
r-acceptor ligand toward gold. The existence of a Au ? Sn dative
bond is evidenced by a trigonal bipyramidal geometry about the tin atom as well as a distorted square
planar geometry about the gold center. While the measured Au–Sn bond distances are crystallographi-
cally indistinguishable in this series, theoretical investigations reveal that the strength of the Au ? Sn
interaction increases in the order 2-I < 2-Br < 2-Cl. These results suggest that the Au ? Sn interaction is
affected by the ligands around gold. Lastly, we also report the tripodal complex [(o-(Ph2P)C6H4)3SnCl]
AuSnCl3 (4) in which the gold atom is concomitantly coordinated to a Z-type tin ligand and an X-type
tin ligand.
Keywords:
Z ligands
Lewis acids
Tin
Gold
Tripodal ligands
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
Among these, group 14-based systems have drawn special
attention because of the saturated nature of the group 14 acceptor
The interactions between ligands and transition metals have
been an essential subject in inorganic chemistry. Other than the
commonly known L-type (two-electron donors) and X-type ligands
(one-electron donors), Z-type ligands (two-electron acceptors)
have begun to surface in the past decade [1]. Capable of drawing
a pair of d-electrons away from a metal, Z-ligands affect the elec-
tronic structures of transition metals, leading to interesting prop-
erties and reactivity [2]. While a large fraction of the earlier work
focused on boron containing Z-ligands [1d,1f,1g,2a], recent efforts
have shown that that other Lewis acidic main group elements
can also be considered [3].
that achieves hypervalence upon interaction with the metallobasic
transition metal atom. Examples of such complexes include transi-
tion metal silane, germane, and stannane complexes characterized
by dative M ? E bonds (E = Si, Ge, Sn) [4]. Some representative
examples of such complexes are shown in Chart 1. In addition to
the metallastannatrane and metallasilatrane of type I in which
the M ? Si/Sn interaction is supported by four rigid 2-mercapto-
1-methylimidazolide buttresses [4a-d], several groups including
ours have described derivatives which feature two or three o-phos-
phino-phenylene buttresses as in the case of complexes of type II
and III [4e-k]. These recent results demonstrate that heavy Group
Cl
F
E
F
E
N
S
N
S
Ph
E
N
S
N
S
PPh2
N
S
N
S
=
N
N
M
iPr2P Au PiPr2
Ph2P
M
PPh2
Cl
Cl
Cl
I
II
III
(E = Si, Sn;
M = Pd, Pt)
(E = Si, Sn)
(E = Si, Ge, Sn;
M = Cu, Ag, Au)
Chart 1. Selected examples of transition metal silane, germane, and stannane complexes.
⇑
Corresponding author.
http://dx.doi.org/10.1016/j.poly.2016.07.010
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.
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2
T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
14 Lewis acids can coordinate to electron-rich late transition met-
als as -accepting ligands. To better understand the parameters
because of the greater acidity of the fluorostannane moiety and
the greater Lewis basicity of the di-iso-propylphosphino groups.
Shorter P ? Sn contacts (3.125(4) Å) have also been reported in
(o-(Ph2P)C6H4)SnClPh2 which again possesses a more Lewis acidic
chlorostannane unit and a less congested structure allowing for a
closer approach of the Lewis base and Lewis acid [7].
r
governing the strength of the Au ? Sn interactions in such com-
plexes, we herein report the synthesis of new bis- and tris-phosphi-
nostannane gold complexes. The strength of the Au ? Sn
interactions in these complexes have been evaluated using DFT
methods.
Ligand LPhP3 reacted cleanly with (tht)AuCl (tht = tetrahydroth-
iophene) to afford complex 2-Cl as well as the known gold deriva-
tive 1 [8] isolated as a byproduct of the reaction (Scheme 1). The
stability of the latter, which features a short aurophilic interaction
of 2.8594(3) Å, provides the thermodynamic driving force for the
transmetallation reaction. The yield of 2-Cl could be optimized
by addition of two equivalents of (tht)AuCl. Complex 2-Cl has been
fully characterized. The 31P NMR resonance of 2-Cl which features
the expected tin satellites (3J117/119Sn,P = 78/80 Hz), appears at
56 ppm confirming the symmetrical coordination of the phospho-
rus atoms to gold. The 119Sn NMR resonance of 2-Cl (Fig. 1b)
appears as a triplet at -86 ppm (3JSn,P = 80 Hz) which is comparable
to the value reported for [(o-(iPr2P)C6H4)2SnClPh]AuCl (ꢀ80 ppm,
3JSn,P = 67.7 Hz) [4e]. This 119Sn chemical shift of 2-Cl is, however,
distinctly upfield from that of Ph3SnCl (ꢀ45 ppm) [5], in line with
an increase in the coordination number of the tin atom. These
spectroscopic features strongly suggest the presence of a Au ? Sn
interaction.
2. Results and discussions
The reaction of ortho-lithio-diphenylphosphinobenzene with
PhSnCl3 in Et2O afforded the tris-phosphinostannane ligand
(o-(Ph2P)C6H4)3SnPh, hereafter referred to as LPhP3, in moderate
yield (Scheme 1). The 31P NMR spectrum of this ligand displays
one resonance at dꢀ2.51 flanked by two satellites resulting from
coupling with the tin nuclei (3JSn-P = 28.5 Hz). Accordingly, the
119Sn NMR resonance of LPhP3 (Fig. 1a) is split into a quartet
3
(ꢀ144 ppm, JSn-P = 28.5 Hz). The 119Sn chemical shift of LPhP3 is
very close to that observed for Ph4Sn (ꢀ128 ppm) [5], suggesting
the unchanged tetrahedral geometry at the tin center and the
absence of P ? Sn interactions. This view is supported by the crys-
tallographically measured Sn–P separations (Sn–P(1) 3.408(3) Å,
Sn–P(2) 3.457(3) Å, Sn–P(3) 3.494(3) Å) in LPhP3 which could only
be consistent with rather weak P ? Sn interactions (Fig. 2). We
note that (o-(Ph2P)C6H4)3SnF has been described previously [6].
This compound features shorter P ? Sn interactions (3.366(1) Å)
As shown in Fig. 3, the Au-Sn distance (2.9069(6) Å) measured
in complex 2-Cl is shorter than the sum of the van der Waals radii
Ph2
P
Cl
PPh2
Ph
Ph
PPh2
Au
P
Sn
PhSnCl3
Et2O
2 (tht)AuCl
Li
+
Sn
0.5
Au
Ph2P Au PPh2
Cl
CH2Cl2
3
Ph2
Ph2P
PPh2
LPhP3
1
2
-Cl
Scheme 1. Synthesis of LPhP3 and 2-Cl.
Fig. 1. (a) 119Sn NMR spectrum of LPhP3 in CDCl3 and (b) 119Sn NMR spectrum of 2-Cl in CD2Cl2.
Cl1
C55
C37
Sn
Sn
C1
C7
C25
P2
C38
P3
C2
C1
P1
P2
P1
C19
Au
C20
Cl2
Fig. 2. Molecular structures of LPhP3 (left) and 2-Cl (right) in the crystal. Ellipsoids are given at the 50% probability level. Some of the phenyl rings are drawn as thin lines.
Hydrogen atoms and the solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg) for LPhP3: Sn–P(1) 3.408(3), Sn–P(2) 3.457(3), Sn–P(3) 3.494(3),
C(19)–Sn–C(55) 124.6(3), C(1)–C(2)–P(1) 117.6(6), C(19)–C(20)–P(2) 116.5(6), C(37)–C(38)–P(3) 118.4(7), C(2)–C(1)–Sn 121.2(6), C(20)–C(19)–Sn 124.2(6), C(38)–C(37)–Sn
124.2(7). Selected bond lengths (Å) and angles (deg) for 2-Cl: Au–P(2) 2.3052(9), Au–P(1) 2.3113(10), Au–Cl(2) 2.5539(10), Au–Sn 2.9069(6), Sn–C(1) 2.145(4), Sn–C(7) 2.175
(4), Sn–C(25) 2.182(3), Sn–Cl(1) 2.5010(10), P(2)–Au–P(1) 165.48(3), Cl(2)–Au–Sn 165.90(2), Cl(1)–Sn–Au 177.93(3), C(1)–Sn–C(7) 110.01(14), C(1)–Sn–C(25) 126.15(14), C
(7)–Sn–C(25) 123.66(13).
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T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
3
Fig. 3. Molecular structures of complex 2-Br (left) and 2-I (right) in the crystal. Ellipsoids are given at the 50% probability level. Some of the phenyl rings are drawn as thin
lines. Hydrogen atoms and the solvent molecule are omitted for clarity. Selected bond lengths (Å) and angles (deg) for 2-Br: Au–Br 2.6395(8), Au–P(1) 2.3028(16), Au–P(2)
2.3061(16), Au–Sn 2.9015(6), Sn–C(1) 2.148(7), Sn–C(25) 2.167(6), Sn–C(7) 2.182(6), Sn–Cl 2.4930(16), P(1)–Au–P(2) 164.83(6), Br–Au–Sn 165.08(2), Cl–Sn–Au 177.38(5), C
(1)–Sn–C(25) 110.6(3), C(1)–Sn–C(7) 126.7(3), C(25)–Sn–C(7) 122.4(2). Selected bond lengths (Å) and angles (deg) for 2-I: Au–I 2.7983(5), Au–P(1) 2.3109(14), Au–P(2)
2.3160(14), Au–Sn 2.9201(5), Sn–C(1) 2.157(6), Sn–C(25) 2.172(6), Sn–C(7) 2.189(6), Sn–Cl 2.4879(15), P(1)–Au–P(2) 163.69(5), I–Au–Sn 167.601(15), Cl–Sn–Au 177.34(5), C
(1)–Sn–C(25) 110.0(2), C(1)–Sn–C(7) 128.6(2), C(25)–Sn–C(7) 121.0(2).
(4.35 Å) [9], and only slightly exceeds the sum of the covalent radii
(2.75 Å) [10]. The Sn–Cl(1) bond length (2.5010(10) Å) in complex
2-Cl significantly surpasses those of tetra-coordinate organoaryl
tin compounds (2.32 Å in Ph3SnCl) [11], and is close to the value
of 2.62 Å reported for penta-coordinate stannate [Ph3SnCl2]ꢀ [12].
Moreover, the tin coordination geometry is that of an essentially
undistorted trigonal bipyramid as shown by the linearity of the
thermodynamic stability of the Au-X bond. The solvation of the
free halides in the reaction mixture will also influence the fate of
these reactions as explained several decades ago for other soft
metal halide complexes [16]. Examination of the crystal structures
of both complexes (Fig. 3) shows that the Au–Sn distance (2.9015
(6) Å for 2-Br, 2.9201(5) Å for 2-I). While the Au-Sn distance in
2-Br is essentially identical to that in 2-Cl, a measurable increase
is noted for the iodide complex 2-I. This small change originates
from the decreased trans influence of the iodide anion, leading to
a reduction of the gold atom metallobasicity. A more accentuated
version of this effect is known for complexes such as [(o-iPr2P-
(C6H4)]3B)AuCl [17] and [(o-(Ph2P)C6H4)2SbF3]AuCl [18] which
undergo a rather drastic lengthening of the transannular Au ? B
and Au ? Sb, respectively, bond upon abstraction of the chloride
anion. The tin center in both 2-Br and 2-I adopts an undistorted
Cl(1)–Sn–Au angle of 177.93(3)° and the sum of the Ceq–Sn–Ceq
P
angles of 359.8° (hereafter denoted as
C-Sn-C). The molecular
structures of complex 2-Cl unambiguously indicate the coordina-
tion of the stannane moiety to the gold center. The heavier Group
14 element behaves here as a Lewis acid via the low-lying r⁄(Sn–
Cl) orbital. The Au ? Sn interaction in the gold(I) complex 2-Cl
results in an unusual distorted square planar geometry at the gold
center (P(1)–Au–P(2) = 165.48(3)° and Sn–Au–Cl(2) = 165.90(2)°),
a situation reminiscent of that observed in the related gold-borane
complex [(o-(iPr2P)C6H4)2BPh]AuCl [13]. The Au–Cl distance of
2.5539(10) Å is longer than that in (Ph3P)2AuCl (2.500(4) Å) [14]
and [(o-(iPr2P)C6H4)2BPh]AuCl (2.524(1) Å) [13]. Taken collectively,
the structure of 2-Cl is analogous to that of the previously charac-
terized fluorostannane-gold analogue which features a Au ? Sn
bond of 2.891(2) Å [4e].
trigonal bipyramid as indicated by the Cl(1)–Sn–Au angles
P
(177.38(5)° for 2-Br, 177.34(5)° for 2-I) and the
values
C-Sn-C
(359.7° for 2-Br, 359.6° for 2-I). The NMR spectroscopic features
3
(d(31P) 56.0; d(119Sn) ꢀ83, JSn-P = 78 Hz for 2-Br and d(31P)
= 55.9; d(119Sn) ꢀ83, tin satellites not detected for 2-I) show little
change when compared to those of 2-Cl and as such merit no fur-
ther comments.
When TBABr (n-tetrabutylammonium bromide) or TBAI (n-
tetrabutylammonium iodide) is added to the reaction mixture of
LPhP3 and (tht)AuCl, the gold-bromide and gold-iodide complexes
2-Br and 2-I are isolated (Scheme 2). The in situ halide metathesis
reactions suggest that the gold center has a stronger affinity for
softer halide which seems to contradict the fact Au–X bond energy
of trivalent gold complexes of general formula (Ph3P)Au(4-Me-
C6H4)(CF3)(X) decreases in the following order X = Cl > Br > I [15].
This apparent dichotomy can be reconciled by noting that the for-
mation of 2-Br and 2-I from 2-Cl does not involve homolytic cleav-
age of the Au-X bond but instead halide exchange. As such, the
formation 2-Br and 2-I from 2-Cl is not solely guided by the
As a part of these studies, we have also been able to prepare the
mono-phosphinostannane ligand LPh2PCl. As shown in Scheme 3,
reaction of this ligand with (tht)AuCl and TBABr in dry CH2Cl2
afforded the known compound 2-Br as well as a new compound
3 characterized by a 31P NMR resonance at 65 ppm. The structure
of this new compound has been elucidated by X-ray crystallogra-
phy (Fig. 4). It features two 1-dichlorophenylstannyl-
2-diphenylphosphino-benzene ligands bound to
a
single
gold-chloride moiety. Interestingly, the gold-bound chlorine atom
interacts with the two neighboring tin atoms, resulting in an
unusual T-shaped geometry as indicated by the Au–Cl(1)–Sn and
Sn–Cl(1)–Sn’ angles of 84.93(5)° and 169.86(9)°, respectively. The
Ph2
P
Cl
PPh2
Ph
Ph
Au
P
1) 2 (tht)AuCl
2) 1.5 TBAX
Sn
+
Sn
0.5
Au
Ph2P Au PPh2
X
CH2Cl2
Ph2
Ph2P
PPh2
LPhP3
1
2
2
-Br (X = Br), -I (X = I)
Scheme 2. Synthesis of complexes 2-Br and 2-I.
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T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
Cl
Ph
Cl
Ph2P
Sn
Cl
Cl
1) (tht)AuCl
2) TBABr
Sn
PPh2
Au
PPh2
SnPh2Cl
2
-Br +
Cl
MeCN/
Ph2P
Sn
Ph2P
Au PPh2
SnCl3
CH2Cl2
Ph CH2Cl2
(9/1)
Cl
LPh2PCl
3
4
Scheme 3. Synthesis of complexes 3 and 4.
Cl3’
Sn’
Cl2’
P’
Au
Cl1
Au
P
Cl1
Sn
Cl3
Cl2
Fig. 4. Molecular structure of complex 3 in the crystal (left), including a top view along the Cl(3)–Sn–Cl(1)–Sn0–Cl(3)0 axis (right). Ellipsoids are given at the 50% probability
level. Some of the phenyl rings are drawn as thin lines. Hydrogen atoms and the solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Au–P
2.2936(17), Au–Cl(1) 2.860(3), Sn–Cl(1) 2.8793(9), Sn–Cl(2) 2.334(2), Sn–Cl(3) 2.428(2), Au–Cl(1)–Sn 84.93(5), Sn–Cl(1)–Sn0 169.86(9), Cl(3)–Sn–Cl(1) 173.49(7), P–Au–P0
156.73(8).
Cl1
C37
Sn1
P2
C1
C19
P3
P1
Au
Sn2
Cl4
Cl2
Cl3
Fig. 5. Molecular structure of complex 4 in the crystal (left), including a top view along the Sn(2)–Au–Sn(1)–Cl(1) axis (right). Ellipsoids are given at the 50% probability level.
Some of the phenyl rings are drawn as thin lines. Hydrogen atoms and the solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Au–P(3) 2.404
(2), Au–P(1) 2.410(2), Au–P(2) 2.412(2), Au–Sn(2) 2.7181(12), Au–Sn(1) 3.0873(13), Sn(2)–Cl(2) 2.392(2), Sn(2)–Cl(3) 2.410(2), Sn(2)–Cl(4) 2.413(2), Sn(1)–C(37) 2.151(8), Sn
(1)–C(19) 2.169(8), Sn(1)–C(1) 2.174(8), Sn(1)–Cl(1) 2.435(2), P(1)–Au–P(2) 113.94(7), P(3)–Au–P(1) 116.59(7), P(3)–Au–P(2) 117.69(8), Sn(2)–Au–Sn(1) 175.61(2), C(37)–Sn
(1)–C(19) 117.3(3), C(37)–Sn(1)–C(1) 118.5(3), C(19)–Sn(1)–C(1) 122.8(3), Cl(1)–Sn(1)–Au 177.01(5).
concomitant interaction of the two tin atoms with the chloride
anion is reminiscent of the Sn–Cl–Sn motifs formed when biden-
tate tin-based Lewis acids such as o-C6H4(SnClMe2)2 bind chloride
anions [19]. However, the bonds formed between the bridging
chloride and the two symmetrically equivalent tin atoms
(Sn–Cl(1) 2.8793(9) Å) are much longer than those observed in
[o-C6H4(SnClMe2)2Cl]ꢀ (2.5267(11) and 2.4762(11) Å) [19].
This lengthening is explained by the fact that the chloride anion
is also interacting with the gold center through a Au–Cl bond of
2.860(3) Å which, as expected, appears elongated when compared
to that in (Ph3P)2AuCl (2.500(4) Å) [14]. The lengthening of the
Au–Cl bond is to be correlated to a widening of the P–Au–P angle
(156.73(8)°) which is much larger than in (Ph3P)2AuCl (132.1(1)°)
[14]. Last, a parallel can be drawn between the structure of 3 and
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T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
5
Table 1
Selected bond lengths and angles (in Å and deg, respectively) for complexes 2-Cl, 2-Br, 2-I, and 4 as determined crystallographically and optimized computationally.
2-Cl
2-Br
2-I
4
X-ray
DFT
X-ray
DFT
X-ray
DFT
X-ray
DFT
Au–Sn
Au–Xa
Sn–Cl
2.9069(6)
2.554(1)
2.501(1)
177.93(3)
359.8
3.005
2.589
2.535
179.27
359.5
2.9015(6)
2.6395(8)
2.493(1)
177.38(5)
359.7
3.016
2.717
2.537
178.80
359.5
2.9201(5)
2.7983(5)
2.488(1)
177.34(5)
359.6
3.046
2.899
2.528
179.69
359.3
3.087(1)
2.718(1)
2.435
177.01(5)
358.6
3.154
2.852
2.520
179.46
359.4
Au–Sn–Cl
P
C–Sn–C
a
X = Cl for 2-Cl; X = Br for 2-Br; X = I for 2-I; X = SnCl3 for 4.
0.900
(a)
ELF
ELF
Cl
Cl
0.675
Sn
Sn
0.450
0.225
0.000
Au
Sn
Au
Cl
Boys
Boys
Boys
(b)
2-Cl
4
Fig. 6. (a) ELF plots for 2-Cl (left) and 4 (right). The maps are drawn in the plane containing two central heavy atoms and the tin-bound chloride. (b) Plots of the Au-Sn Boys
localized orbital (at 0.03 isovalue) for 2-Cl (left) and 4 (right). Hydrogen atoms are omitted for clarity.
Sn
Au Sn2
Sn1
Cl1
Au
Cl
Cl2
2-Cl
4
Fig. 7. Calculated electron-density maps for complexes 2-Cl (left) and 4 (right) with relevant bond paths and bond critical points. Hydrogen atoms and the diphenyl
substituents at phosphorus are omitted for clarity.
that of a Al–Cl–Al bridged intermediate formed when tBu2Al
An examination of the solid-state structure of 4 reveals that this
new compound features a tris-phosphino-chlorostannane ligand
(o-(Ph2P)C6H4)3SnCl; referred to as LP3Cl) coordinated to a Au–SnCl3
unit (Fig. 5). The Au–Sn(2) bond distance (2.718(1) Å) approaches
the sum of the covalent radii of gold and tin (2.75 Å) and is slightly
shorter than that measured in (PPh3)3AuSnCl3 (2.7523(2) Å) [21].
The shortening of this bond may be correlated to the fact that of
the Sn(1) tin atom engages the gold center in a dative Au ? Sn
(PhHC=)CMes2P-Au-PMes2C(=CHPh)AlCltBu2
undergoes
intramolecular chloride exchange [20].
The concomitant formation of 2-Br and 3 indicates the occur-
rence of uncontrollable exchange reactions at tin. In fact, yet
another derivative (4) can be isolated upon recrystallization of
mixtures of 2-Br and 3 from CH3CN/CH2Cl2 (9/1). Complex 4 was
characterized by elemental analysis and ESI-Mass spectrometry.
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T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
Table 2
Calculated electron density (
q
e, e bohrꢀ3) and Laplacian (r2qe, e bohrꢀ5) at the (3, ꢀ1) BCPs.
2-Cl
2-Br
2-I
4
qe
r
2qe
qe
r
2qe
qe
r
2qe
qe
r
2qe
Au–Sn
Au–Xa
Sn–Cl
0.0343
0.0563
0.0584
0.0428
0.1510
0.1165
0.0336
0.0510
0.0582
0.0416
0.1143
0.1161
0.0317
0.0452
0.0590
0.0399
0.0810
0.1183
0.0263
0.0464
0.0604
0.0344
0.0602
0.1207
a
X = Cl for 2-Cl; X = Br for 2-Br; X = I for 2-I; X = SnCl3 for 4.
interaction of 3.087(1) Å in a direction directly trans from the
trichlorostannate ligand. The Au ? Sn interaction in 4 is longer
and thus weaker than that in 2-Cl (2.9069(6) Å). In line with this
argument, the Sn(1)–Cl(1) distance (2.435(2) Å) measured in 4 is
slightly shorter than that in 2-Cl (2.5010(10) Å). As a result of
the Au ? Sn dative interaction, the Sn(1) atom adopts a nearly per-
the Au ? Sn BCP slightly decreases on going from 2-Cl
(0.0343 e bohrꢀ3 (0.0336 e bohrꢀ3
to 2-Br and 2-I
)
)
(0.0317 e bohrꢀ3) (Table 2). This trend is consistent with the calcu-
lated Au ? Sn bond length which increases in the order 2-Cl
(3.005 Å) < 2-Br (3.016 Å) < 2-I (3.046 Å). These results are in line
with the reported trans influence for halides in square-planar PtII
complexes [32]. The tris-phosphinostannane gold complex 4 pos-
sesses the weakest Au ? Sn interaction among all as indicated by
the electron density at the BCP of the Au ? Sn(1) linkage
(0.0263 e bohrꢀ3). This value can also be correlated to the longer
calculated Au ? Sn(1) distance of 3.154 Å (versus 3.005 Å in
2-Cl). It is also interesting to note that the electron densities
calculated at the Au ? Sn BCP in 2-Cl, 2-Br, and 2-I
(0.0343–0.0317 e bohrꢀ3) are only slightly lower than that of the
Au–SnCl3 bond in 4 (0.0464 e bohrꢀ3). This comparison attests to
the strength of the Au ? Sn interactions. Further insights into the
fect trigonal bipyramidal geometry as indicated by the Au–Sn(1)–
P
Cl(1) angle of 177.01(5)° and the
Moreover, the gold atom displays an unusual pentacoordinate
value equal to 358.6°.
C-Sn-C
geometry approaching that of a trigonal bipyramid (Sn(2)–Au–Sn
P
(1) = 175.61(2)°,
P-Au-P = 348.2°). Altogether, the structure of 4
is unique in that the gold atom is concomitantly coordinated to a
Z-type tin ligand and an X-type tin ligand. We also note that the
geometries around the gold and tin atoms in complex 4 are similar
to those in the fluorostannane gold complex III (Chart 1). However,
the Au ? Sn distance is longer in 4 (3.087(1) Å) than in III (2.9686
(3) Å).
Au–Sn bonds are derived from the Laplacian value (
BCP which determines whether the electron density is locally
concentrated (
2qe < 0) or depleted ( 2qe > 0) [33]. As shown in
r
2qe) at the
In order to better understand the unusual Au ? Sn interactions
present in complexes 2-Cl, 2-Br, 2-I, and 4, DFT calculations have
been carried out using the ADF program [22]. BP86 functional
[23] and a TZP all-electron basis sets [24] were used in all cases.
To account for relativistic effects, a method of Zero Order Regular
Approximation (ZORA) [25] was also applied. The optimized
geometries are close to those observed experimentally (Table 1),
thus suggesting the adequacy of this computational method. The
Au ? Sn bonding situation was then assessed by an Electron Local-
ization Function (ELF) analysis [26] which was shown to be partic-
ularly useful in describing chemical bonds [27] including in
complexes involving Z-ligands bound to gold [28]. In all cases,
one localization domain on gold, which can be correlated to a lone
pair of d-electrons, is clearly pointing toward the tin atom (Fig. 6a,
see SI for the ELF plots of 2-Br and 2-I). Therefore, the ELF plots
indicate the presence of a Au ? Sn dative bond. Interestingly, a
similar donor–acceptor situation could be envisioned in the Au-
SnCl3 ionic bond (complex 4) where the electron localization
around tin is protruding toward the gold atom. Further insights
into these Au–Sn bonds are derived from a Boys localization anal-
ysis [29] which reveals a polarized bonding orbital for 2-Cl (Au:
87%, Sn: 2%) and 4 (Au: 90%, Sn: 1%) (Fig. 6b, see SI for the Boys
plots of 2-Br and 2-I). Contrastingly, the Boys orbital calculated
for the Au–SnCl3 bond in 4 bears a significant contribution from
tin (Au: 9%, Sn: 75%), suggesting the polar nature of the Au–SnCl3
ionic bond.
r
r
Table 2, the positive Laplacian sign at the BCPs suggests the polar
nature of the Au–Sn, Sn–Cl, and Au–X bonds.
3. Conclusion
In summary, we have show that bis- and tris-phosphino-
chlorostannane ligands can coordinate to gold ions, with the tin
center acting as a Z-ligand. The Au ? Sn interaction present in
these complexes results in unusual square planar (2-Cl, 2-Br, 2-I)
and trigonal bipyramidal (4) geometries at gold reminiscent of
the trivalent state. According to the DFT calculations, the Au ?
Sn interaction in 2-Cl is weaker than that in the iso-propylphos-
phino analogue [(o-(iPr2P)C6H4)2SnClPh]AuCl. Furthermore, we
show that the Au ? Sn interaction is also affected by the gold-
bound halide as the electron density at the BCP increases from
0.0317 e bohrꢀ3 (2-I) to 0.0336 e bohrꢀ3 (2-Br) and 0.0343 e bohrꢀ3
(2-Cl). Hence, these results indicate that the strength of the
Au ? Sn dative interaction is influenced by the ligands surround-
ing gold. Finally, we also describe a complex (4) in which the gold
atom is interacting simultaneously with a Z-type tin ligand and an
X-type tin ligand. The structural and computational results
obtained for 4 shows that the X-type tin ligand forms a stronger
interaction with the gold center.
Aside from the qualitative view, the topology of the electron
density of the ADF optimized structures was subjected to an
Atoms-In Molecules (AIM) [30] analysis using the Dgrid program
[31]. This analysis reveals a straight bond path connecting the gold
4. Experimental
4.1. General considerations
and tin atom in 2-Cl with an electron density
q(r) of
0.0343 e bohrꢀ3 at the bond critical point (BCP) (Fig. 7). Analogous
calculations previously carried out on [(o-(iPr2P)C6H4)2SnClPh]
AuCl [4e] afforded electron density of 0.0356 e bohrꢀ3. This differ-
ence suggests that the increase Lewis basicity of the di-iso-propy-
lphosphino moiety of [(o-(iPr2P)C6H4)2SnClPh]AuCl strengthens
the Au ? Sn interaction. Furthermore, the trans influence of the
Trichlorophenylstannane, TBABr, and TBAI (TBA = n-tetrabuty-
lammonium) were purchased from Aldrich and used as received.
Ortho-lithio-diphenylphosphinobenzene [34], ligand LPh2PCl [7],
and (tht)AuCl [35] were prepared according to the reported proce-
dures. Solvents were dried by passing through an alumina column
(MeCN and CH2Cl2) or refluxing under N2 over Na/K (Et2O). NMR
spectra were recorded on Varian Unity Inova 400 FT NMR
gold-bound halide is noticeable as the electron density (qe) at
Please cite this article in press as: T.-P. Lin, F.P. Gabbaï, Polyhedron (2016), http://dx.doi.org/10.1016/j.poly.2016.07.010

T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
7
(399.57 MHz for 1H, 100.47 MHz for 13C, 161.75 MHz for 31P,
149 MHz for 119Sn) spectrometers at ambient temperature. Chem-
ical shifts are given in ppm, and are referenced to residual 1H and
13C solvent signals and external 85% H3PO4 and neat Me4Sn.
(t, JP-C = 7.56 Hz), 136.25 (t, JP-C = 5.81 Hz), 136.37, 154.03, 167.59
(two of the quaternary carbon resonances are not detected); 31P
3
NMR (161.75 MHz, CD2Cl2): d 56.0 (s, JSn-P) = 78 Hz); 119Sn NMR
(149 MHz, CD2Cl2): d ꢀ83 (bs). Anal. Calc. for C42.5H34AuBrCl2P2Sn
(2-Br-0.5CH2Cl2): C, 47.57; H, 3.19. Found: C, 47.25; H, 3.33.
4.2. Synthesis of ligand LPhP3
4.5. Synthesis of complex 2-I
A solution of trichlorophenylstannane (120 mg, 0.397 mmol)
was added to a solution ortho-lithio-diphenylphosphinobenzene
in ether (10 mL). After stirring for 10 min, the brown residue was
extracted with CH2Cl2 (3 ꢁ 10 mL) and filtered over Celite. The sol-
vent was removed to afford a brown solid, which was washed with
hexane (3 ꢁ 10 mL) to afford LPhP3 as a light yellow solid (260 mg,
Solid (tht)AuCl (42.5 mg, 0.133 mmol) was added to a solution
of LPhP3 (65 mg, 0.066 mmol) in dry CH2Cl2 (3 mL). After stirring
for 10 min, solid n-tetrabutylammonium iodide (36.8 mg,
0.100 mmol) was added to the reaction mixture. Slow vapor diffu-
sion of Et2O into the resulting solution resulted in the crystalliza-
tion of both 2-I-0.5CH2Cl2 and 1 (47 mg) over 24 h. Based on
elemental analysis, it was determined that 2-I-0.5CH2Cl2 and 1
had formed and crystallized in a 2:1 ratio resulting in a 44.9% yield
for this reaction. 1H NMR of 2-I (399.57 MHz, CD2Cl2): d 6.49–6.59
66.8% yield). 1H NMR (399.57 MHz, CDCl3):
d 6.85 (t, 12H,
3JH-H = 7.6 Hz), 6.92 (t, 3H, 3JH-H = 7.6 Hz), 7.05 (t, 15H, 3JH-H = 7.2 Hz),
3
3
7.14 (t, 6H, JH-H = 7.6 Hz), 7.25 (t, 3H, JH-H = 7.6 Hz), 7.34 (d, 3H,
3JH-H = 7.6 Hz), 7.53 (d, 2H, JH-H = 6.8 Hz, JSn-H = 50.3 Hz), 7.77
3
3
(d, 3H, JH-H = 7.6 Hz, JSn-H = 50.7 Hz); 13C NMR (100.47 MHz,
(m, 4H), 6.86 (t, 1H, JH-H = 7.1 Hz), 7.28–7.62 (m, 20H), 7.69–7.77
3
3
3
3
3
CDCl3): d 127.46, 127.55, 127.67, 127.87 (d, JP-C = 6.0 Hz), 128.75,
(m, 6H), 8.86 (d, 2H, JH-H = 7.7 Hz, JSn-H = 64.3 Hz); 13C NMR
(100.47 MHz, CD2Cl2): d 129.76, 130.73, 131.04 (t, JP-C = 5.22 Hz),
131.94, 133.32, 133.68 (d, JP-C = 8.28 Hz), 134.11, 134.25, 135.55
(t, JP-C = 6.14 Hz), 136.12 (t, JP-C = 6.14 Hz), 136.39, 154.09, 167.41
(one of the quaternary carbon resonances is not detected); 31P
NMR (161.75 MHz, CD2Cl2): d 55.9 (bs); 119Sn NMR (149 MHz, CD2-
Cl2): d ꢀ83 (bs). Anal. Calc. for C121H96Au4Cl4I2P6Sn2 (2-I-0.5CH2Cl2:
1 = 2: 1): C, 46.04; H, 3.07. Found: C, 46.53; H, 3.59.
129.012 (s, JSn-C
= 50.4 Hz), 133.09 (d, JP-C = 17.5 Hz), 134.95
(s, JSn-C = 46.6 Hz), 137.94 (d, JP-C = 1.2 Hz, JSn-C = 38.2 Hz), 138.36
(d, JP-C = 11.4 Hz), 139.63 (d, JP-C = 20.6 Hz, JSn-C = 64.8 Hz), 144.08
(d, JP-C = 3.0 Hz, JSn-C = 46.6 Hz), 144.48 (d, JP-C = 6.1 Hz,
JSn-C = 18.2 Hz), 154.60 (d, JP-C = 69.4 Hz, JSn-C = 12.3 Hz); 31P NMR
3
(161.75 MHz, CDCl3): d ꢀ2.51 (s, JSn-P = 28.5 Hz); 119Sn NMR
3
(149 MHz, CDCl3): d ꢀ144 (q, JSn-P = 28.5 Hz). Anal. Calc. for
C60H47P3Sn: C, 73.56; H, 4.84. Found: C, 72.68; H, 5.08.
4.6. Synthesis of complexes 3 and 4
4.3. Synthesis of complex 2-Cl
To
a
CH2Cl2 solution (10 mL) of ligand LPh2PCl (83 mg,
Solid (tht)AuCl (26.2 mg, 0.082 mmol) was added to a solution
of LPhP3 (40 mg, 0.041 mmol) in dry CH2Cl2 (3 mL) at room temper-
ature. The reaction was allowed to stir for 15 min. Slow vapor dif-
fusion of Et2O into the resulting solution resulted in the
crystallization of both 2-Cl-0.5CH2Cl2 and 1 (28.7 mg) over 24 h.
Based on elemental analysis, it was determined that 2-Cl-0.5CH2-
Cl2 and 1 had formed and crystallized in a 2:1 ratio resulting in a
47.3% yield for this reaction. 1H NMR of 2-Cl (399.57 MHz, CD2Cl2):
d 6.47–6.57 (m, 4H), 6.85 (t, 1H, 3JH-H = 7.2 Hz), 7.29–7.52 (m, 20H),
0.146 mmol) was added solid (tht)AuCl (46.7 mg, 0.146 mmol)
and TBABr (47.0 mg, 0.146 mmol) in the golve box at room temper-
ature. After stirring for 30 min, the reaction mixture was filtrated
through Celite. Slow vapor diffusion of Et2O into the resulting solu-
tion at ꢀ40 °C resulted in the crystallization of both 2-Br-0.5CH2Cl2
and 3-CH2Cl2-0.5Et2O (39 mg) over 24 h. Complex 3 has been char-
acterized by 31P NMR (161.75 MHz, CD2Cl2) at 64 ppm. Further
recrystallization of the mixture of 2-Br and 3 from dry MeCN/CH2-
Cl2 (9/1) afforded 5 mg of 4-CH2Cl2 in the form of colorless single
crystals which are insoluble in organic solvents such as CD2Cl2.
Anal. Calc. for C55H44AuCl6P3Sn2 (4-CH2Cl2): C, 45.72; H, 3.07.
3
3
7.70–7.76 (m, 6H), 8.86 (d, 2H, JH-H = 7.7 Hz, JSn-H = 63.9 Hz); 13C
NMR (100.47 MHz, CD2Cl2): 129.87, 130.75, 131.19 (t,
d
JP-C = 5.78 Hz), 131.94, 133.43, 133.67 (d, JP-C = 9.50 Hz), 134.26,
134.37, 135.64 (t, JP-C = 7.36 Hz), 136.25 (t, JP-C = 6.54 Hz), 136.38,
154.16, 167.67 (one of the quaternary carbon resonances is not
detected); 31P NMR (161.75 MHz, CD2Cl2): d 56.2 (s, 3J(117/119Sn,
Found: C, 46.55; H, 3.14. HRMS(ESI+): m/z calculated for C54H42
-
AuClP3Sn+ 1135.0870. Found 1135.0908.
4.7. Crystallographical measurements
P) = 78/80 Hz); 119Sn NMR (149 MHz, CD2Cl2):
d
ꢀ86 (t,
3JSn-P = 80 Hz). Anal. Calc. for C121H96Au4Cl6P6Sn2 (2-Cl-0.5CH2Cl2:
1 = 2: 1): C, 48.87; H, 3.25; Cl, 7.15. Found: C, 48.76; H, 3.01; Cl,
7.56.
The crystallographic measurements were performed at 110(2) K
using a Bruker APEX-II CCD area detector diffractometer (Mo K
a
radiation, k = 0.71073 Å) for LPhP3, 2-Br-0.5CH2Cl2, 2-I-0.5CH2Cl2,
3-CH2Cl2-0.5Et2O, and 4-CH2Cl2; and a Siemens SMART-CCD area
4.4. Synthesis of complex 2-Br
detector diffractometer (Mo Ka radiation, k = 0.71073 Å) for 2-Cl-
0.5CH2Cl2. In each case, a specimen of suitable size and quality
was selected and mounted onto a nylon loop. The structures were
solved by direct methods, which successfully located most of the
nonhydrogen atoms. Semi-empirical absorption corrections were
applied [36]. Subsequent refinement on F2 using the SHELXTL/PC
package (version 6.1) [37] allowed location of the remaining
non-hydrogen atoms.
Solid (tht)AuCl (42.5 mg, 0.133 mmol) was added to a solution
of LPhP3 (65 mg, 0.066 mmol) in dry CH2Cl2 (3 mL). After stirring
for 10 min, solid n-tetrabutylammonium bromide (32.1 mg,
0.100 mmol) was added to the reaction mixture. Slow vapor diffu-
sion of Et2O into the resulting solution resulted in the crystalliza-
tion of both 2-Br-0.5CH2Cl2 and 1 (58 mg) over 24 h. Based on
the different crystal morphologies of 2-Br-0.5CH2Cl2 and 1, isola-
tion of the crystals of 2-Br-0.5CH2Cl2 was carried out under a
microscope, affording a pure sample of 2-Br-0.5CH2Cl2 (22 mg) in
30.9% yield. 1H NMR of 2-Br (399.57 MHz, CD2Cl2): d 6.48–6.58
4.8. Computational details
All electrons structural optimizations were carried out on com-
plexes 2-Cl, 2-Br, 2-I, and 4 using the ADF program (2008.01)
[22b,22c,38]. All calculations were carried out using the BP86
[23] functional with all electron a TZP [24] basis set for all atoms.
These calculations were performed using the Zero Order Regular
3
(m, 4H), 6.85 (t, 1H, JH-H = 7.1 Hz), 7.28–7.56 (m, 20H), 7.69–7.77
3
3
(m, 6H), 8.86 (d, 2H, JH-H = 7.8 Hz, JSn-H = 64.6 Hz); 13C NMR
(100.47 MHz, CD2Cl2): d 129.87, 130.70, 131.12 (t, JP-C = 5.78 Hz),
133.41, 133.66 (d, JP-C = 9.89 Hz), 134.25, 134.37, 135.64
Please cite this article in press as: T.-P. Lin, F.P. Gabbaï, Polyhedron (2016), http://dx.doi.org/10.1016/j.poly.2016.07.010

8
T.-P. Lin, F.P. Gabbaï / Polyhedron xxx (2016) xxx–xxx
(f) P. Gualco, M. Mercy, S. Ladeira, Y. Coppel, L. Maron, A. Amgoune, D.
Bourissou, Chem. Eur. J. 16 (2010) 10808;
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Amgoune, D. Bourissou, Organometallics 34 (2015) 1449;
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(j) H. Kameo, K. Ikeda, D. Bourissou, S. Sakaki, S. Takemoto, H. Nakazawa, H.
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Approximation (ZORA) [25]. The topology of the electron density of
the ADF optimized structures was subjected to an Atom-In-Mole-
cule (AIM) [30] analysis using the Dgrid program (version 4.4)
[31]. Visualization of the geometry (including bond paths and bond
critical points) as well as of the electron density map was carried
with the Material Studio program (version 4.4). Electron localiza-
tion function (ELF) [26] plots and the Boys localized orbitals
[29b-d] were visualized in ADF program.
(k) H. Kameo, T. Kawamoto, D. Bourissou, S. Sakaki, H. Nakazawa,
Organometallics 34 (2015) 1440.
Acknowledgment
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This work was supported by the National Science Foundation
(CHE- 1566474), the Welch Foundation (A-1423), Texas A and M
University (Arthur E. Martell Chair of Chemistry). We also
acknowledge Dr. Lisa Pérez for her help with the theoretical
calculations.
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Appendix A. Supplementary data
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CCDC 1481793–1481798 contains the supplementary crystallo-
graphic data for complexes LPhP3, 2-Cl, 2-Br, 2-I, 3, and 4. These
data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.poly.2016.07.010.
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Please cite this article in press as: T.-P. Lin, F.P. Gabbaï, Polyhedron (2016), http://dx.doi.org/10.1016/j.poly.2016.07.010