In terms of grammar, というの (> っていうの) is a complementiser, a device that captures a sentence (with a subject and the verb) and authorize it to work like a noun.
The adjective 羨ましい can indicate the source of envy as well as the experiencer of the emotion:
Pay attention of the topicalized noun, 彼の地位. It's a noun. In order for a sentence to appear at this position, it must first be cast into noun by way of the toiuno-complementiser.