Insertion reactions of difluorovinylidene 1b into H-2, CH4, and CD4 have been observed in argon matrixes at 20-40 K. These reactions are controlled by diffusion of trapped species rather than by activation barriers, indicating that the activation barriers are very small (<1 kcal/mol) or absent. In contrast, no insertion was observed into CF4 or C2H4. With C2H4, addition to the double bond to give (difluoromethylene)cyclopropane (5) is the only pathway. This was rationalized by ab initio (MP2/6-31G(d,p)) and DFT (B3LYP/6-311++G-(d,p)) calculations, which predict activation barriers of essentially zero for the H-2 and CH4 insertion, but 40 and 3 kcal/mol for the insertion into CF4 and C2H4, respectively.