_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Organocopper and -silver compounds
Table 3.12. Coordination environments in Me 2 MX. (M = B.Al.Ga.In.Tl)
Compound
Coordination
number of M
Environment of
M
('CMCt
Me,BF
(Me,AICI),
(Me,InCI)n
Me,TICI
(Me, TIOPh),
(Me 2 TISPh),
(2, 3, 5, 6-C 6 F 4 H) 2 TIBr
Me,Tlacac
3
4
5
6
4
4
5
6
Trigonal planar
Tetrahedral
Trigonal bipyramidal
Octahedral
Distorted tetrahedral
Distorted tetrahedral
Trigonal bipyramidal
Distorted pentagonal
bipyramid (one equatorial
site vacant)
120
127
167
180
173
163
144,150
170
group from Me 3 TI to form air-stable dimethylthallium derivatives.
Me,Tl + HX -----> Me 2 TIX + CH.
Me,Tl + X 2 ----. Me 2 TIX + CH,X
The halides Me 2 TIX (X= C, Br, I) are high melting solids, which are sparingly
soluble in ali but strongly coordinating solvents. The fiu oride Me 2 TIF and
hydroxide Me 2 TIOH. which are prepared from the ehi oride and AgF or Ag,O
respectively in aqueous suspension, are very soluble in water. The hydroxide is
apparently dissociated in solution into Me 2 TI+ and OH- ions. The Me 2 TI+ ion is
isoelectronic with Me 2 Hg and has a similar linear geometry.
The structures of severa! dimethylthallium derivatives ha ve been determined
in the solid state by X-ray crystallography. Some results are summarized in
Table 3.12 and in Fig. 3.21. Thallium adopts coordination numbers offour, five
and six. The trend to higher coordination numbers going down a Group is noted
for Si to Pb (p. 102 ).
3.1 O Organocopper and -silver compounds
3 .10.1 Organocopper compounds in organic synthesis
Copper compounds have been used for many years in organic chemistry. The
Ullmann synthesis of biphenyls in which an aryl iodide is heated with copper
metal to temperatures over 200oC is considered to involve arylcopper intermediates
rather than free radicals. The presence of 2- and 4-nitro groups aids coupling;
2-nitro-iodobenzene can be coupled by Cu+ O ,SCF 3 in ammoniacal solution even
at room temperature.
Copper(I) iodide reacts with monoalkyl and arylethynes in aqueous ammonia
giving insoluble yellow, redor brown derivatives [Cu-C=CR]n. These reactions
resemble those of mercury(II) (p. 61 ). These 'acetylides' couple with aryl iodides
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