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 }=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 (CH2 NN) 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.