Fluoro carbon complexes bonding

Addition reactions of the Si-Si bonds across carbon-carbon triple bonds have been most extensively studied since the 1970s by means of palladium catalysts. In the early reports, palladium complexes bearing tertiary phosphine ligands, mostly PPh3, were exclusively employed as effective catalysts, enabling the alkyne bis-silylation with activated disilanes, i.e., disilanes with electronegative elements on the silicon atoms such as hydro [36], fluoro [37], chloro [38], and alkoxy-disilanes [39,40] and those with cyclic structure (Scheme 4) [41-44]. The bis-silylation reactions could be successfully applied to terminal alkynes and acetylenedicarboxylates to give (Z)-l,2-bis(silyl)alkenes, which are otherwise difficult to synthesize. 

Oxidative addition of fluorinated aromatics to give metal(aryl) fluoro complexes has been observed frequently for complexes of group 10 metals, but rarely otherwise. The reactions include the insertion of an Ni(PEt3)2 unit into a carbon-fluorine bond in hexafluorobenzene (Scheme 5). The very slow conversion (4 weeks) was initially reported by Fahey and Mahan full spectroscopic and crystallographic characterization of the product was performed by Perutz et al " Mechanistic studies and density functional theory (DFT) calculations give strong evidence for precoordination of the aromatic substrate followed by a concerted oxidative addition. " " Oxidative addition has also been... 

Our group has devoted two articles for the study of systems where the chiral subunits are bonded to a boron or to a metallic atom (Scheme 3.28). In both cases, the weakness of the bonds formed can be easily broken. In the first case, a series of bisdiphenylborates and the effect of the fluoro substitution on the relative stability of the homo vs. heterochiral complexes have been studied by means of DFT calculations (B3LYP/6-31G ) [29]. In addition, the corresponding isoelectronic structures, in which the boron has been substituted by a carbon or a positively charged nitrogen, have been considered. In all the cases, the homo and heterochiral complexes present D2 and S4 symmetries, respectively. 

The silver-carbon bond in compounds containing a perfluoroalkyl group is considerably more stable than in non-fluorinated compounds. The synthesis can be accomplished by the nucleophilic addition of silver fluoride to fluoro-olefines. A typical example of this reaction is given in equation 9. The complexes are soluble in organic solvents and have been isolated as the 1 1 complexes with acetonitrile [RAg(CH3CN)]23. 

In fully substituted R3Si-PR2-type compounds, P-Si bonds are broken by water, oxygen, carbon dioxide, carbon disulphide and some metal carbonyl complexes. Diphosphines are formed by reaction with some phosphine halides or fluoro-phosphoranes (Figure 9.10). Other Si-P bond-breaking reactions are (6.564), (6.578) and (6.600). 

ESR spectra of many a metal-carbon bonded complexes have been investigated (Table 4.8). Numerous four-coordinate MR4-type complexes have symmetry lower than tetrahedral, for example, [Cr(CH2SiMe3)4] , [V(CH2SiMe3)4], [Cr(CH2SiMe3)4], etc. The compound ReMe has a structure of a distorted octahedron because of the Jahn-Teller effect. In contrast to ReF, the distortion of ReMeg is not dynamic. This situation may be due to a considerably larger lODq value for the methyl complex compared to the fluoro derivative. Based on ESR spectra, a square-antiprism structure was proposed for [ReMcg] . 

---