Chemistry Reference
In-Depth Information
One extremely interesting pair of tungsten compounds are the species
all-trans
-
[W (O C
6
H
3
Ph
2
-2,6)
2
Cl
2
(PMe
2
Ph)
2
]
180
and
all-trans
-[W(OC
6
H
4
Me-4)
2
Cl
2
(PMe
2
Ph)
2
].
181
The former compound is paramagnetic (high-spin) with a W-OAr distance of 1.966
(4) A while the diamagnetic (low-spin) 4-methylphenoxide compound has distances
of only 1.848 (5) A and 1.840 (5) A. Two factors are possibly at work here. First the
steric bulk of the 2,6-diphenylphenoxide ligand may inhibit its approach to the metal
centre leading to lower
-bonding and smaller splitting of the d
xz
and d
yz
orbitals above
the d
xy
orbital. There is also the possibility that the 2,6-diphenylphenoxide ligand is
a poorer
-donor that the 4-methylphenoxide leading to the high-spin situation. In
another study it was found possible to finely tune the singlet - triplet energy gap of
related d
2
-W(
IV
) systems [W(OC
6
H
3
Ph-
1
-C
6
H
4
2
(L)
2
] by changing substituents on
the donor pyridine and bipyridine ligands L.
182
Short M-OAr distances and large M-O-Ar angles are also common for nonchelated,
terminal aryloxide derivatives of the electropositive lanthanide metals (Table 6.19). The
M-OAr distances for isostructural, monomeric molecules in this case correlate well
with the metal ionic radius (lanthanide contraction) and also increase with coordination
number.
183
When one begins to consider structural parameters (and indeed chemistry)
1e
of later
d-block metal aryloxides one is confronted with a different situation. This is highlighted
by the values of
O
,
C
calculated for later transition metal alkyl, aryloxide compounds
(Table 6.4). It can be seen that values range from close to zero to positive numbers,
i.e.
in some compounds the M-OAr bond lengths exceed M-C(alkyl) bond lengths! This
is a dramatically different picture from that seen for early transition metal compounds.
Table 6.4
Metal - ligand bond lengths for mixed alkyl, aryloxides of later transition
metals
Bond length ( A)
O
,
C
( A)
Compound
M-O
M-C
Ref.
[Pt
OC
6
H
5
Me(bipy)]
2.001 (5)
2.023 (6)
C0.02
i
[Pt
OC
6
H
5
(I)Me
2
bipy
]
2.014 (5)
2.051 (7)
C0.03
i
[(TMEDA)Pd
OC
6
H
5
Me
]
2.024 (3)
2.010 (5)
C0.01
ii
[(TMEDA)Pd
OC
6
H
4
NO
2
-4
Me
]
2.029 (4)
1.997 (7)
C0.03
ii
trans
-[Pd
OC
6
H
5
Me
PMe
3
2
]
2.106 (3)
2.039 (4)
C0.07
iii
[Pd
PPh
2
C
6
H
4
CH
2
NMe
2
OC
6
H
5
Me]
2.088 (5)
2.020 (7)
C0.09
iv
cis
-[Pd
OC
6
H
5
Me(DMPE)]
2.098 (6)
2.101 (9)
0
v
cis
-[Pt
OC
6
H
5
Me
PMe
3
2
]
2.128 (4)
2.08 (1)
C0.05
vi
cis
-[Au
OC
6
H
5
Me
2
PPh
3
]
2.09 (1)
2.00 (1), 2.03 (3)
C0.07
vii
i
G.M. Kapteijn, M.D. Meijer, D.M. Grove, N. Veldman, A.L. Spek, and G. van Koten,
Inorg.
Chim. Acta
,
264
, 211 (1997).
ii
G.M. Kapteijn, A. Dervisi, D.M. Grove, H. Kooijman, M.T. Lakin, A.L. Spek, and G. van
Koten,
J. Am. Chem. Soc.
,
117
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iii
Yong-Joo Kim, Kohtaro Osakada, A. Takenaka, and A. Yamamoto,
J. Am. Chem. Soc.
,
112
,
1096 (1990).
iv
M.
Kapteijn,
M.P.R.
Spee,
D.M.
Grove,
H.
Kooijman,
A.L.
Spek
and
G.
van
Koten,
Organometallics
,
15
, 1405 (1996).
v
A.L. Seligson, R.L. Cowan, and W.C. Trogler,
Inorg. Chem.
,
30
, 3371 (1991).
vi
K. Osakada, Yong-Joo Kim, and A. Yamamoto,
J. Organomet. Chem.
,
382
, 303 (1990).
vii
T. Sone, M. Iwata, N. Kasuga, and S. Komiya,
Chem. Lett.
, 1949 (1991).
