The reaction of the phosphinidene complex [Cp*P{W(CO)5}2] (1 a) with diphenyldiazomethane leads to [{W(CO)5}Cp*P=NN{W(CO)5}=CPh2] (2). Compound 2 is a rare example of a phosphadiazadiene ligand (R‐P=N−N=CR′R′′) complex. At temperatures above 0 °C, 2 decomposes into the complex [{W(CO)5}PCp*{N(H)N=CPh2)2] (3), among other species. The reaction of the pentelidene complexes [Cp*E{W(CO)5}2] (E=P, As) with diazomethane (CH2NN) proceeds differently. For the arsinidene complex (1 b), only the arsaalkene complex 4 b [{W(CO)5}2{η1:2‐(Cp*)As=CH2}] is formed. The reaction with the phosphinidene complex (1 a) results in three products, the two phosphaalkene complexes [{W(CO)5}2{η1:2‐(R)P=CH2}] (4 a: R=Cp*, 5: R=H) and the triazaphosphole derivative [{W(CO)5}P(Cp*)‐CH2‐N{W(CO)5}=N‐N(N=CH2)] (6 a). The phosphaalkene complex (4 a) and the arsaalkene complex (4 b) are not stable at room temperature and decompose to the complexes [{W(CO)5}4(CH2=E−E=CH2)] (7 a: E=P, 7 b: E=As), which are the first examples of complexes with parent 2,3‐diphospha‐1,3‐butadiene and 2,3‐diarsa‐1,3‐butadiene ligands.