Chemistry Reference
In-Depth Information
Table 2.1 Common Tolman cone angles y and exact ligand cone angles y1.
y1 (Pd)
Min. (1)
10
Cone angle y
(1)
9c
Max. (1)
10
Entry
Ligand
1
P
3
87
2
PMe
3
118
120
3
P(CF
3
)
3
137
4
PPhMe
2
122
149
5
PPh
2
Me
136
151
6
PPh
3
145
170
7
P(p-tol)
3
145
171
8
P(C
6
F
5
)
3
184
9
P(o-tol)
3
194
176
208
10
P(mesityl)
3
212
159
15
11
PCy
2
Ph
12
PPh
2
(t-Bu)
157
167
13
PPh(t-Bu)
2
170
187
14
PEt
3
132
136
169
15
P(n-Bu)
3
132
136
169
16
P(i-Pr)
3
160
169
177
17
PCy
3
170
18
P(i-Bu)
3
143
214
19
P(s-Bu)
3
160
182
9
(194
12b
)
20
P(t-Bu)
3
188
176
15
21
P(1-adamantyl)
2
(n-Bu)
198
12b
22
P(t-Bu)
2
(neopentyl)
210
12b
23
P(t-Bu)(neopentyl)
2
B
180
9
(227
12b
)
24
P(neopentyl)
3
25
P(OMe)
3
107
26
P(OPh)
3
128
246
15
27
2-(Di-tert-butylphosphino)biphenyl
(JohnPhos)
2-Dicyclohexylphosphino-2
0
,6
0
-
dimethoxybiphenyl (SPhos)
240
15
28
2-Dicyclohexylphosphino-2
0
,4
0
,6
0
-
triisopropylbiphenyl (XPhos)
256
15
29
angle
ΒΌ
109.51) of the phosphorus atom is not always valid. Additionally, the
substituents are folded back to make a minimum cone when flexibility in the
ligand is present, which may not always be a reasonable assumption. To
address these limitations, Allen and co-workers recently developed an
innovative method for determining ''exact ligand cone angles'' utilizing a
mathematical approach.
10
They define the exact ligand cone angle (y1) as the
angle of the most acute right circular cone which contains all of the atoms of
the ligand (described by spheres with the atom's corresponding van der
Waals radius) and is tangent to up to three of the atoms (Figure 2.2). The
models are constructed from either X-ray data or DFT-optimized structures
and, importantly, no approximations are used. Thus, only the Cartesian
coordinates are required to determine y1. For ligands that can adopt
multiple conformations, y1 is determined as a range between a maximum y1
and a minimum y1. In certain cases, the value of y1 is vastly different from
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