Reaction of Pentelidene Complexes with Diazoalkanes: Stabilization of Parent 2,3‐Dipnictabutadienes

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 }=CPh 2 ] ( 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=CPh 2 ) 2 ] ( 3 ), among other species. The reaction of the pentelidene complexes [Cp*E{W(CO) 5 } 2 ] (E=P, As) with diazomethane (CH 2 NN) proceeds differently. For the arsinidene complex ( 1 b ), only the arsaalkene complex 4 b [{W(CO) 5 } 2 {η 1:2 ‐(Cp*)As=CH 2 }] is formed. The reaction with the phosphinidene complex ( 1 a ) results in three products, the two phosphaalkene complexes [{W(CO) 5 } 2 {η 1:2 ‐(R)P=CH 2 }] ( 4 a : R=Cp*, 5 : R=H) and the triazaphosphole derivative [{W(CO) 5 }P(Cp*)‐CH 2 ‐N{W(CO) 5 }=N‐N(N=CH 2 )] ( 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 (CH 2 =E−E=CH 2 )] ( 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.