Page 792 - Advanced Organic Chemistry Part B - Reactions & Synthesis

768 O O
C C
Cl Cl
CHAPTER 8 Rh Rh + 2 Rh Rh
Cl Cl
Reactions Involving C C
Transition Metals O O Ref. 310

-Allyl complexes of palladium were described in Section 8.2.1. Similar
-allyl complexes of nickel can be prepared either by oxidative addition on Ni(0) or
by transmetallation of a Ni(II) salt. Some reactions of these allyl nickel species are
discussed in Section 8.3.1.
Br
2 CH 2 CHCH Br + 2 Ni(CO) 4 Ni Ni + 8 CO
2
Br
Ref. 311

2 CH 2 CHCH MgBr + NiBr 2 Ni + 2 MgBr 2
2
Ref. 312

Organic ligands having a cyclic array of four carbon atoms have been of
particular interest in connection with the chemistry of cyclobutadiene. Organometallic
compounds containing cyclobutadiene as a ligand were first prepared in 1965. 313
The carbocyclic ring in the cyclobutadiene–iron tricarbonyl complex reacts as an
aromatic ring and can undergo electrophilic substitutions. 314 Subsequent studies showed
that oxidative decomposition of the complex can liberate cyclobutadiene, which is
trapped by appropriate reactants. 315 Some examples of these reactions are given in
Scheme 8.17.
One of the most familiar of the -organometallic compounds is ferrocene, a
neutral compound that is readily prepared from cyclopentadienide anion and iron(II). 316

–
2 + FeCl 2 Fe

Numerous chemical reactions have been carried out on ferrocene and its derivatives. 317
The molecule behaves as an electron-rich aromatic system, and electrophilic substi-
tution reactions occur readily. Reagents that are relatively strong oxidizing agents,
such as the halogens, effect oxidation at iron and destroy the compound.

310 J. Chatt and L. M. Venanzi, J. Chem. Soc., 4735 (1957).
311 E. J. Corey and M. F. Semmelhack, J. Am. Chem. Soc., 89, 2755 (1967).
312
D. Walter and G. Wilke, Angew. Chem. Int. Ed. Engl., 5, 151 (1966).
313 G. F. Emerson, L. Watts, and R. Pettit, J. Am. Chem. Soc., 87, 131 (1965); R. Pettit and J. Henery,
Org. Synth., 50, 21 (1970).
314
J. D. Fitzpatrick, L. Watts, G. F. Emerson, and R. Pettit, J. Am. Chem. Soc., 87, 3254 (1965).
315 R. H. Grubbs and R. A. Grey, J. Am. Chem. Soc., 95, 5765 (1973).
316 G. Wilkinson, Org. Synth., IV, 473, 476 (1963).
317
A. Federman Neto, A. C. Pelegrino, and V. A. Darin, Trends in Organometallic Chem., 4, 147 (2002).