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

Organotransition metal chemistry
4
Ti
tetrakis (norbornyl) titanium
tetrakis (adamantyl)titanium
Tetrakis(adamantyl)titanium, m.p. 235°C, prepared by heating titanium(IV)
chloride, sodium and 1-chloroadamantane in cyclohexane, could be decomposed
for analysis only at 170°C by a mixture of concentrated nitric and hydrofluoric
acids in the presence of hydrogen peroxide! The contrast with tetramethyltitanium
is amazing.
Transfer of a P-hydrogen atom to give a benzyne ( or orthophenylene) complex
as an intermediate can occur in the decomposition of some ry 1 -aryls. Certainly aryl
complexes with ortho-substituents ( e.g. 2, 4, 6-trimethylphenyl, 'mesityl' or 2. 6-
dimethylphenyl, 'o-xylyl') are more robust than their unsubstituted analogues.
trans[CoBr 2 (PEt 2 Ph) 2 ] + 2MesMgBr---> trans[CoMes 2 (PEt 2 Ph),]
golden-yellow crystals,
planar cobalt, 15-electron,
t!etr2.5 B.M.
The related diamagnetic 16-electron nickel complexes trans[NiMes 2 (PR 3 ) 2 ] and
trans[NiXMes (PR 3 U (X= Cl, Br) can be heated unchanged in boiling benzene
and can be stored in air in the crystalline form. (Mes = 2, 4, 6-trimethylphenyl).
An orthophenylene complex has actually been isolated from the decomposition of
a phenyltantalum derivative.
(b) a-HYDROGEN TRANSFER (a-ELIMINATION). A possible decomposition pathway
for alkyls which lack a P-hydrogen atom, but which possess an a-hydrogen is
termed a-hydrogen transfer or IX-elimination. *
*The second term is somewhat misleading as there is no loss of material from the
coordination sphere in the elementary step M-CH 3 ->M(=CH 2 )H. In the case of {3-
220