Stepwise Formation of a 1,3‐Butadiene Analogue of Mixed Heavier Group 15 Elements

The reaction of the phosphinidene complex Cp*P{W(CO)₅}₂] ( 1 a ) with di‐tert‐butylcarboimidophosphene leads to the P? C cage compound 6 and the Lewis acid–base adduct Cp*P{W(CO)₅}₂(CNtBu)] ( 2 a ). In contrast, the arsinidene complex shows a different reactivity. At low temperatures, the arsaphosphene complex {W(CO)₅}{η²‐(Cp*)As?P(tBu)}{W(CO)₅}] ( 3 ) is formed. At these temperatures, 3 reacts further with a second equivalent of carboimidophosphene to form {W(CO)₅}{η²‐{(Cp*)(tBu)P}As?P(tBu)}{W(CO)₅}] ( 5 ), probably by the insertion of a phosphinidene unit (tBuP) into an As? C bond. In contrast, at room temperature 3 reacts further by a radical‐type reaction to form {(tBu)P?As? As?P(tBu)}{W(CO)₅}₄] ( 4 ). Compound 4 is the first example of a neutral, 1,3‐butadiene analogue containing only mixed heavier Group 15 elements. It consists of two P?As double bonds connected by arsenic atoms.