2 Homometallic Alkoxides

446 Alkoxo and Aryloxo Derivatives of Metals
2.1 Mono-aryloxides
2.1.1 Simple Mono-phenoxides
The conventional substitution chemistry of phenol as well as the importance of
substituted phenols as commercial anti-oxidants and monomers in the production of
phenylene-oxide polymers make available to the inorganic and organometallic chemist
a selection of typically inexpensive ligands. The introduction of alkyl substituents onto
the phenoxide ring, usually by Friedel–Crafts and related electrophilic substitution
reactions 6 can readily be achieved. The strong ortho-metallation directing effect of
either the parent or protected phenolic group can be used to build substituted phenols
via the lithiated nucleus (Scheme 6.1), e.g. by reaction with ketones. 7 Aryl groups can
be introduced into the ortho position by Suzuki coupling 8 or by arylation with bismuth 9
or lead 10 reagents. Alternative strategies include construction of the phenoxide nucleus
via initial condensation reactions followed by aromatization (Scheme 6.1). Alkyl
substituents in the para position exert little steric influence within the coordination
sphere but can help control solubility and modify the spectroscopic properties of
metal derivatives. In contrast, the choice of suitable alkyl substituents in either one
Np
R
Ar
Bu t
Br Br
+
O
+
O
Bu t
OH
O
Np
R
Ar
Bu t
Br
(i) 2Bu n Li
(ii)
O
(iii) H + /H2O R R
base Pd/C
OH
Np
Ar
Bu t
Bu t
OH
OH
Np
Ar
BiNp3Cl2
Bu t
OH
base Pd/C
Np
R
Ar
Bu t
Np
OH
OH
R = H, Ph, Me, Pr i ; Ar = Ph, l-Naphthyl
tetramethylguanidine
Scheme 6.1
OH
Pd/C
Np
R
Ar
Bu t
Np
Bu t
Bu t
OH
Np