Carbonyl halides structure

Carbonyl Halides and Hydrides. Fe2(CO) reacts with HBr or HI and Fe(CO)j with HBr under u.v. light to yield the halogeno-complexes [Fe(CO)3.X]2. Structure (16) is postulated, on the basis of the close similarity in i.r. spectra with those of [Fe(CO)3SR]2 complexes. 

The palladium-catalyzed carbonylation of isomeric vinylic halides shows the reaction to be reasonably stereospecific and proceed with retention of the original halide structure. The degree of specificity, however, depends somewhat on the reaction conditions. Low reaction temperatures and/or excess triarylphosphine favor the stereospecific reaction (11). 

My co-worker H. Lagally showed that the thermal decomposition of Fe(CO)4I2 afforded successively Fe(CO)2I2, Fe(CO)2I, and CO-free Fel. For these decomposition products of Fe(CO)4I2 a polymeric structure with iodine bridges is postulated. A study of the reaction FeI2 + 4 CO Fe(CO)4I2, also in collaboration with Lagally, further established the metastable or labile nature of iron carbonyl halides (63). 

THEORETICAL DESCRIPTIONS OF THE ELECTRONIC STRUCTURES OF THE CARBONYL HALIDES... 

Formaldehyde (methanal, COH ) is an apposite starting point for a discussion of the electronic structure of the carbonyl halides, as its orbital interactions are relatively simple. Like the carbonyl halides, the ground state of COHj is planar with C2y symmetryt, and its molecular orbitals can be constructed from those of carbon monoxide and the Is atomic orbitals of two hydrogen atoms (see Fig. 17.1). Its valence electron configuration is ... 

Empirical trends in the electronic structure of the carbonyl halides... 

In the Sections above, various aspects of the electronic structure of the carbonyl halides have been discussed in some detail, and it is now appropriate to consider what insight this knowledge yields concerning their chemical reactivity. In particular, their reactivity towards nucleophilic and electrophilic substitutions will be examined. 

The carbonyl halides, COX2 (X = F, Cl and Br), are all hydrolytically unstable substances. Mixed carbonyl halides such as COCIBr are also known. The compound CO(NH2)2 is urea. In the molecular structures of both urea and COCl2 the C—O bond length is somewhat longer than the expected value for a C=0 double bond, whereas the N—C and Cl—C distances are somewhat shorter than expected for single bonds. These facts lead to the conclusion that these molecules may be viewed as resonance hybrids (10-X). X x x... 

The structures of the carbonyl halides present little problem where they are dimeric or polymeric they are invariably bridged through the halogen atoms and not by carbonyl bridges, for example, in (22-V) and (22-Vl). The... 

The most stable carbonyl halides of group 10 metals are those of platinum. [PtX2(CO)2] and [PtX2(CO)]2 are prepared by reaction of PtX2 (X = C1, Br, I) with carbon monoxide under pressure. These compounds have the following structures ... 

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