Chemistry Reference
In-Depth Information
involve attack of the nucleophilic aryloxide oxygen directly on the carbon atom of the
electrophilic substrate. This is supported by a lack of retardation of the insertion product
(
i.e.
no CO dissociation needed) or formation of [M(CO)
6
](
i.e.
no OAr ionization)
when the reaction is carried out under a pressure of CO.
The insertion chemistry of alkyl and hydrido, aryloxy derivatives of the group 10
metals has been studied. Although the phenoxide
trans
-[Pt(H)(OPh)(PEt
3
2
] undergoes
only 10% insertion of CO
2
(1 atm) into the Pt-OPh bond, reaction with PhNCO
cleanly produces the corresponding
N
-phenylcarbamato complex.
243
Similarly the
nickel compounds
trans
-[Ni(H)(OPh)(L)
2
] react with PhNCO but in this case there
is evidence that the reaction is reversible.
244
The 4-methylphenoxide complexes
fac
-[Re(OAr)(CO)
3
L
2
](LD PMe
3
,L
2
D diars)
show much less tendency to insert electrophiles compared to the methoxide analogues.
Neither phenoxide reacts with CO
2
whereas only the PMe
3
derivative will insert CS
2
.In
contrast both methoxides insert both CO
2
and CS
2
.
245
Again mechanistic data pointed
to a direct attack of metal-bound alkoxide(aryloxide) on the electrophilic carbon atom.
The reactivity of copper aryloxides towards a variety of heterocumulenes has been
investigated.
246
,
247
Insertion of RNCS (R D Me, Ph) into copper(
I
) aryloxide bonds has
been shown to lead to a variety of
N
-alkylamino(aryloxy)methanethiolato complexes
depending on the nature of the ancillary ligands. In the absence of any other donor
ligation a cluster compound, [Cuf
2
-SC
D
NPh
OAr
g]
6
has been characterized from
the insertion of PhNCS into a Cu-4-methylphenoxide bond.
248
Recently the effect of
ortho
-substituents upon the oligomerization of Cu(
I
) complexes formed by insertion of
CS
2
and PhNCS into Cu-OAr bonds has been carried out.
249
Some of the insertion
reactions have been shown to be reversible.
The insertion of CO
2
,COS,andCS
2
into Zn-OAr and Cd-OAr bonds has been
studied. The reactivity is important given the fact that discrete zinc aryloxides will
act as catalysts for the copolymerization of epoxides and CO
2
.
250
,
251
The insertion
of CO
2
into zinc aryloxides was shown to proceed
via
direct attack by the nucleo-
philic oxygen. Hence a vacant site at the metal was not needed but small
ortho
-
substituents were essential. The complex [Zn(OC
6
H
2
Me
3
-2,4,6)
2
(py)
2
] reacted with
13
CO
2
to form a mono(aryl carbonate).
250
In contrast [Cd(OC
6
H
3
Ph
2
-2,6)
2
(thf)
2
] failed
to react with CO
2
but did undergo insertion with COS and CS
2
.
251
The product of CS
2
insertion was crystallized from benzene yielding the dimeric species [(ArOCS
2
)Cd(
2
-
OAr)
2
Cd(S
2
COAr)] (OAr D OC
6
H
3
Ph
2
-2,6). Although highly disordered, the molec-
ular structure was confirmed by an X-ray diffraction study.
251
The addition of CS
2
to the thallium aryloxides [Tl(OAr)] (Ar D 4-methyl, 4-butyl,
4-
tert
-butyl, 3,5-dimethylphenyl) has been shown to be a good synthetic route to the
corresponding [Tl(S
2
COAr)] salts, which can be used to generate transition metal
derivatives.
252
5.2.3
Insertion of Sulfur Dioxide
The rhodium and iridium complexes [M(ttp)(OPh)] fM D Rh, Ir; ttp D
PhP(CH
2
CH
2
CH
2
PPh
2
2
g has been shown to react with SO
2
to produce the corre-
sponding sulfonates, [M(ttp)(SO
2
OPh).SO
2
].
253
Thallium phenoxide undergoes insertion of SO
2
to produce [Tl(SO
2
OPh)].
254
