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

Organotransition metal chemistry
/OMe BX3
(OC)5M=C -- 0 -
"-.R -45 C
',/
o
c
o
c
X-M=C-R + X2BOMe + CO
1\,
c
o
c
o
These are rather labile and decompose at 30°-50°C liberating RC=CR. The sp
carbon atom has two orthogonal p-orbitals which can form two n-bonds with
appropriate metal orbitals. The short M-C distance (1.67 Â where X= 1, M
= Cr, R = Me) indicates a triple bond.
A vinylidene complex is formed when W(C0) 4 (dppe) is heated with phenylethyne
in THF. This is reversibly protonated, affording a cationic carbyne. The
carbonylligand trans to the triple bond can be substituted by halide or by neutral
ligands.
Phc=cH
THF
a: ~
mer [(dppe)(C0) 3 W=C=CHPh)
While electrophiles (e.g. H+) attack the {3-carbon atom in vinylidenes,
nucleophiles add to the a-position yielding 17 1 -vinyl complexes.
N
E
1 N- + 1
[M]--C=CHR <------ [M]=C=CHR __:______. [M] + =C-CHR
Carbyne ( alkylidyne) complexes are implicated in the metathesis of alkynes
(p. 377).
7.2.3 Bridged methylene complexes
The CH 2 (CR 2 ) group acts not only as a terminalligand but can, like CO, forma
bridge between two metal atoms. These metal atoms can be the same or different.
It has been suggested that any ţl-CH 2 compound can probably exist if the
corresponding ţl-carbonyl is known. One preparation involves the addition of
Fischer carbenes to coordinatively unsaturated complexes.
\/
/R le\
[M']: + [M]=C --- [Mj-[M]; cf. [M1
"-.R'
236
R
R'
\ 1 /
"- / c ,.....c
+ C=C --+ [Mj-11 or [M'] 1'
/ "-. C '-.C/
1 \ '