2 Homometallic Alkoxides

484 Alkoxo and Aryloxo Derivatives of Metals
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)(PEt3⊳2] undergoes
only 10% insertion of CO2 (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)3L2] (LDPMe3, L2D diars)
show much less tendency to insert electrophiles compared to the methoxide analogues.
Neither phenoxide reacts with CO2 whereas only the PMe3 derivative will insert CS2.In
contrast both methoxides insert both CO2 and CS2. 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⊲DNPh⊳⊲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
CS2 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 CO2, COS,andCS2into 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 CO2. 250,251 The insertion
of CO2 into zinc aryloxides was shown to proceed via direct attack by the nucleophilic
oxygen. Hence a vacant site at the metal was not needed but small orthosubstituents
were essential. The complex [Zn(OC6H2Me3-2,4,6)2(py)2] reacted with
13CO2 to form a mono(aryl carbonate). 250 In contrast [Cd(OC6H3Ph2-2,6)2(thf)2] failed
to react with CO2 but did undergo insertion with COS and CS2. 251 The product of CS2
insertion was crystallized from benzene yielding the dimeric species [(ArOCS2)Cd( 2-
OAr)2Cd(S2COAr)] (OAr D OC6H3Ph2-2,6). Although highly disordered, the molecular
structure was confirmed by an X-ray diffraction study. 251
The addition of CS2 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(S2COAr)] 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 2CH2CH2PPh2⊳2g has been shown to react with SO2 to produce the corresponding
sulfonates, [M(ttp)(SO2OPh).SO2]. 253
Thallium phenoxide undergoes insertion of SO2 to produce [Tl(SO2OPh)]. 254