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

General reactions of transition metal complexes
Electron rich complexes are strong nucleophiles. This is illustrated by some
reactions with methyl iodide, which may be compared with attack by a tertiary
amine:
11Mel +
Fe[P(OMel,L- [MeFe(P(OMe),),] [PF.r
11INH 4 PF 6
Mei
Ni(PMe,). -----> [MeNi(PMe,).] + [I] ..
CI! 3 CN
Mei 1
Me,N ----> Me 4 N r-
In these reactions (2(a), 2(b), 3(a) in Table 5.8). the coordination number of
the metal increases by one, while the electron configuration remains the same.
The structural relationships are shown in Fig. 5.16 by vertical arrows ( J1 ).
Halogens behave as electrophiles towards nucleophilic complexes. There are
two common modes of reaction, e.g.
18e,
six-coordinate
!Se
seven-coordinate
co x,
M(C0) 4 L 1 ~M(CO),L 1 -----> M(CO),L 1 X 1
+CO
1 he.
!ive-coordinate
(unsaturated)
18 e
seven-coordinate
The first is analogous to the reaction just described ( H ), but the second involves
expulsion of o ne carbonylligand. This probably proceeds by dissociation of CO to
give an unsautrated 16-electron intermediate. followed by addition of X 2 • (A
synchronous mechanism could also operate.) The general reaction pathway is
along the route horizontal ( ~) then diagonal ( //) in Fig. 5.16.
When counting electrons it is recommended that ali bonds are treated as
covalent. Thus a single bond M-X (X= H, CI etc.) is considered as being derived
from M· and x·, rather than from M + and :X- or from M:- and X+. In this way
possible confusion over assignment of a formal oxidation state to the metal is
avoided. Ligands (X= H, F. CI. Br, I. CN, alkyl. aryl. acyl etc.) which form single
two-electron bonds are therefore treated as one-electron donors.
Examples:
HCo(C0) 4 : l(H) + 9(Co) + (4 x 2)(4C0) = 18
Mn(CO)_;: 7(Mn) + 10( SCO) + 1 (negative charge) = 18
Fe(C0) 4 1 1 :8(Fe)+8(4C0)+(2 x 1)(2!)= 18
HNi(PMe,); :1(H) + lO(Ni) + 8(4PMe,)- 1 (positive charge) = 18
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