Christa Siebert

Cations of the [5LFe(CO)2]+ Type and Radicals of the 5LFe(CO)2 Type

This section deals with the unsaturated 17-electron species [5LFe(CO)2]. and the cationic 16-electron species [5LFe(CO)2]+. The short-lived radicals could only be characterized in some cases using a UV flash/IR monitoring apparatus.

Cations of the [ 5 LFe(CO) 2 1 L] + Type

This section comprises all compounds in which the 1L ligand is connected to the iron atom with a single bond and contains a positive charge at any position of the ligand. Compounds with the 5L ligand other than C5H5, i.e., with the Cp*Fe(CO)2 group (Fp*) instead of C5H5Fe(CO)2 (Fp*), are restricted to a few species and added at the end of the appropriate subsection.

Other Compounds of the 5 LFe(CO) 2 1 L Type

The section collects all compounds derived from C5H5Fe(CO)2R in which the C5H5 ligand (Cp) is replaced by substituted Cp ligands (Cp*) or by other 5L ligands. The compounds are arranged as follows: C5H4R’ compounds (see Section 1.5.2.3.17.1) C5H3R’2, C5H2R’3, C5HR’4 or C5R’5 compounds (see Section 1.5.2.3.17.2) other 5L ligands (see Section 1.5.2.3.17.3)

Anions of the [5LFe(CO)2 1L]+ Type

In this section, anionic compounds of mainly the type [C5H5Fe(CO)2 1L]- are collected in which the 1L ligand contains a negative charge. With exception of the first complex, which bears a deprotonated carboxylic group (Fp-substituted acetic acid), the salts are derived by formal addition of Fp- to CH2=C=O (I), CO2 (II, E=O), and CS2 (II, E=S). Two complexes containing C5H4CH3 and C5(CH3)5 as the 5L ligands are described at the end of the section.

Radical Ions Derived from 5 LFe(CO) 2 1 L Compounds

In this section 17-electron compounds of the type [5LFe(CO)2 1L]·+ and 19-electron compounds of the type [5LFe(CO)2 1L]·- are described in which the 5L ligands are represented by unsubstituted or substituted cyclopentadienyl groups. In general, the 17-electron systems (II) were obtained as short-lived intermediates by electrochemical oxidation of the corresponding neutral 5LFe(CO)2R complexes such as I which, in the presence of a donor molecule, result in the formation of highly reactive acyl complexes of the type [5LFe(CO)(2D)COR]·+ (e.g. III, IV) [5]. The 19-electron species were intermediates in the reduction-assisted migratory insertion [3, 6]. Mechanistic considerations based on the application of the configuration mixing (CM) model to the migratory insertion, assisted by either prior oxidation or reduction are given [6].

Organogallium-Germanium Compounds

This compound is formed by decomposition of K[Ga(CH3)2(GeH3)Cl]-1.5CH3OCH2CH2OCH3 (see p. 418) in C6H5CH3 at -15°C over a period of 2 h. Removal of KCl and solvent (pumping at -15°C for 2 d), followed by distillation at 25 to 30°C under high vacuum, yielded a colorless liquid consisting of a mixture of the compound (76%) and Ga(CH3)2H (based on analyses). The products could not be separated because Ga(CH3)2GeH3 decomposes slowly at 25°C to give Ga(CH3)2H and (GeH2)n.

Organogallium-Transition Metal Compounds

This chapter contains transition metal (M) compounds with Ga-M bonds. Other organogal-lium derivatives of transition metals without such a bond are described in Sections 13.6.2.1 to 13.6.2.4. With organogallium species five types of complexes have been described in the literature. Formula I represents adducts of Ga(C6H5)3 with anionic 18-electron complexes (no adducts with neutral species are known). Compounds with a three-coordinate Ga atom are described with Formulas II and III; the latter complexes have only been identified in solution. Compounds with a four-membered M-Ga-M-Ga ring (Formula IV) are only known as iron carbonyl derivatives and contain one molecule of a base at each Ga atom for stabilization. The base-free derivative of IV (No. 11 in Table 73) was also described but only characterized by IR spectroscopy. Incorporation of N-bases (C5H5N, tetramethylethylenediamine, 2,2′-bipyridyl) causes the molecule to monomerize to give compounds of Formula V, containing a formally “subvalent” Ga atom.

Organogallium-Phosphorus and -Arsenic Compounds

The compounds in this section, listed in Table 71, are of the GaR2ER2’ type (E = P or As, R’ = H only for No. 7), except for No. 6, which contains a Ga(CH3)Cl unit.

Compounds of Organogallium Anions

The compounds in this section are arranged in a way similar to that of the previous sections, i.e., the description begins with tetraorganylgallates, [GaR4]-, and is followed by [GaRnX4-n]- anions (n = 1 to 3) where X stands for hydrogen, halogen, pseudohalogen, oxygen groups, etc. Finally, very extended subsections deal with organogallium pyrazolyl anions bonded to transition metal fragments via the second N atom of pyrazolyl, thus acting as anionic donor ligand with respect to the transition metal. Depending on the type of the transition metal moiety, these compounds may be neutral or ionic.

Organogallium-Boron Compounds

The compound was first prepared by treating Ga(CH3)3 repeatedly with B2H6 at — 45°C until no further reaction was apparent [1]. In a more recent paper, Ga(CH3)3 was allowed to react with a fivefold excess of B2H6 at -15°C for 3 h and was isolated in a 20 to 42% yield by trap-to-trap distillation of the volatiles in a vacuum system [6]. An 80% yield was obtained from the reaction of Ga(CH3)2Cl with an excess of powdered LiBH4 at -15°C with pumping for 4 h and vacuum fractionation as above. This method was suitable for the preparation of Ga(CH 3 ) 2 BD 4 using LiBD4 [6]. The formation from GaH(BH4)2 and Ga(CH3)3 at -45°C, along with GaH(CH3)BH4, is indicated in a reaction scheme in [5].