The synthesis of cis bis alkyl, acyl alkyl, alkoxycarbonyl alkyl, bis alkoxycarbonyl, alkoxycarbonyl alkyloxalyl and bis alkyloxalyl tetracarbonyl iron is described These complexes constitute the first homogeneous series of models for the study of the mono and polycarbonylation reactions. Their thermolysis display different results according to the nature of the ligands which undergo the reductive elimination. The carbon-carbon coupling process is not observed for two alkyl ligands bound to the metal via sp³ carbons; however, it becomes very easy between an alkyl and an acyl or an alkoxycarbonyl (sp^2-sp³ coupling). Our results also demonstrate that bis alkoxycarbonyl complexes do not induce the formation of oxalates which are only formed in high yields by thermolysis of the alkoxycarbonyl alkyloxalyl compounds. The alkoxy group of the alkoxycarbonyl ligands are very labile and this property led us to synthetize cations bearing only one alkoxycarbonyl ligand.