Formyl complexes kinetic stability

Several trends in the kinetic stability of formyl complexes are evident in Tables I and II. First, formyl complexes of third row transition metals... 

Kinetic Stability of Metal Formyl Complexes. Metal formyl complexes have approximately the same kinetic stability as the corresponding metal acetyl complexes. Thermal decomposition of (CH3CH2)4N [(C6-H50)3P] (CO)3FeCHO" in THF at 65°C gives a mixture of two metal hydrides in a 4 1 ratio (CO)4FeH , formed by loss of phosphite and... 

Now that we have an eflScient route to metal formyl complexes, we can study the thermodynamic stability of these complexes. We have found that metal formyls are much less thermodynamically stable than the corresponding metal hydrides. Thus, metal formyl species have never been observed in the reactions of metal hydrides with CO because of the thermodynamic instability of the formyl complexes and not because of their kinetic instability. 

A hydride is one of the simplest nucleophiles, and Casey ° and Gladysz have prepared kinetically stable formyl complexes by the direct attack of hydride on a number of neutral chromium-, molybdenum-, and iron-carbonyl complexes (Equation 11.2). Although these complexes are relatively electron rich, because they possess zero-valent metal centers, the negative charge in the product can be stabilized by the remaining -ir-ac-cepting CO ligands. 

Below about 200 °C, the photo-decomposition of acetaldehyde becomes involved as a result of the increased stability of the formyl and acetyl radicals. The occurrence of new elementary steps, in addition to those already mentioned, renders the kinetics of the reaction rather complex. 

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