Carbonyls halides

Acid halides —CO—halogen Haloformyl -carbonyl halide... 

Numerous carbonyl halides, of which the best known are octahedral compounds of the type [M(C0)4X2] are obtained by the action of halogen on Fe(CO)5, or CO on MX3 (M = Ru, Os). Stepwise substitution of the remaining CO groups is possible by X or other ligands such as N, P and As donors. 

It has generally been concluded that the photoinitiation of polymerization by the transition metal carbonyls/ halide system may occur by three routes (1) electron transfer to an organic halide with rupture of C—Cl bond, (2) electron transfer to a strong-attracting monomer such as C2F4, probably with scission of-bond, and (3) halogen atom transfer from monomer molecule or solvent to a photoexcited metal carbonyl species. Of these, (1) is the most frequently encountered. 

The block copolymer produced by Bamford s metal carbonyl/halide-terminated polymers photoinitiating systems are, therefore, more versatile than those based on anionic polymerization, since a wide range of monomers may be incorporated into the block. Although the mean block length is controllable through the parameters that normally determine the mean kinetic chain length in a free radical polymerization, the molecular weight distributions are, of course, much broader than with ionic polymerization and the polymers are, therefore, less well defined,... 

Acid halides -oyl halide -carbonyl halide lialocarbony ... 

Metal carbonyls form several complexes but those of major interest in MOCVD are the carbonyl halides and the carbonyl-nitric-oxide complexes. 

The carbonyl halides have the general formula Mx(C0)yX2 with X being fluorine, chlorine, bromine, or iodine. With the notable exception of nickel, most metals form carbonyl halides including all the metals listed in Table 3.4. 

A particularly interesting case is that of the platinum metal group which, in addition to platinum (Pt), comprises ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), and palladium (Pd). These carbonyl halides are usually the most practical precursors for metal deposition because of their high volatility at low temperature. Indeed two of them, palladium and platinum, do not form carbonyls but only carbonyl halides. So does gold. 

The hydrogen reduction of the metal halides, described in Sec. 1.2, is generally the favored reaction for metal deposition but is not suitable for the platinum-group metals since the volatilization and decomposition temperatures of their halides are too close to provide efficient vapor transport. 1 1 For that reason, the decomposition of the carbonyl halide is preferred. The exception is palladium which is much more readily deposited by hydrogen reduction than by the carbonyl-halide decomposition. 

Preparation of Carbonyl Halides. The carbonyl halides are generally produced by the direct reaction of the metal halide and CO, usually at high pressure and at the temperature range of 140-290°C. A typical reaction is 1 1... 

Some examples of carbonyl halides are shown in Table 3.6. 

CVD Reactions. The platinum halides are volatile with a decomposition pointtooclose to thevaporizati on pointtomakethempracticalfor C VD transport. Platinum canbe deposited by the decomposition of the acetylacetonate, although carbonaceous impurities remain in the deposit. The carbonyl halides, specifically dicarbonyl dichloride, are more satisfactory precursors. The decomposition reaction is as follows ... 

Carboxylation of aromatic rings with carbonyl halides... 

The Reaction of Manganese Carbonyl Halides with CNC H, and CNCH3 (Tetrahydrofuran) ... 

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface, (3) generation of surface hot-spots due to cavitational micro-jets, and (4) direct trapping with CO of reactive metallic species formed during the reduction of the metal halide. The first three mechanisms can be eliminated, since complete reduction of transition metal halides by Na with ultrasonic irradiation under Ar, followed by exposure to CO in the absence or presence of ultrasound, yielded no metal carbonyl. In the case of the reduction of WClfc, sonication under CO showed the initial formation of tungsten carbonyl halides, followed by conversion of W(C0) , and finally its further reduction to W2(CO)io Thus, the reduction process appears to be sequential reactive species formed upon partial reduction are trapped by CO. 

Reactions of metal carbonyls with halogens lead to the formation of carbonyl halide complexes by substitution reactions or breaking metal-metal bonds. The reaction... 

The reaction of CO with some metal halides results in the formation of metal carbonyl halides directly, as illustrated in the following examples ... 

Martynov, I.V., Yu.L. Kruglyak, and S.I. Malekin. "Carbonyl Halide Oxime /S-Chloroalkyl Fluoro-phosphates," Soviet Patent 241433, April 18, 1969 (In Russian). 

Table 12a. Standard enthalpy of formation, A/ff(g), enthalpy of disruption, AHjy, and metal-halogen bond enthalpy contribution, (M-X), in metal carbonyl halides (kJ mol-1)...

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