Ring Expansions of Nonpolar Polyphosphorus Rings

The reaction of the phosphinidene complex [Cp*P{W(CO)₅ }₂ ] (1 a) (Cp*=C₅ Me₅ ) with the anionic cyclo-P_n ligand complex [(η³ -P₃ )Nb(ODipp)₃ ]^- (2, Dipp=2,6-diisopropylphenyl) resulted in the formation of [{W(CO)₅ }₂ {μ₃ ,η^3:1:1 -P₄ Cp*}Nb(ODipp)₃ ]^- (3), which represents an unprecedented example of a ring expansion of a polyphosphorus-ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO)₅ }₂ ] (E=P: 1 a, As: 1 b) with the neutral complex [Cp'''Co(η⁴ -P₄ )] (Cp'''=1,2,4-tBu₃ C₅ H₂ ) led to a cyclo-P₄ E ring (E=P, As) through the insertion of the pentel atom into the cyclo-P₄ ligand. Starting from 1 a, the two isomers [Cp'''Co(μ₃ ,η^4:1:1 -P₅ Cp*){W(CO)₅ }₂ ] (5 a,b), and from 1 b, the three isomers [Cp'''Co(μ₃ ,η^4:1:1 -AsP₄ Cp*){W(CO)₅ }₂ ] (6 a-c) with unprecedented cyclo-P₄ E ligands (E=P, As) were isolated. The complexes 6 a-c represent unique examples of ring expansions which lead to new mixed five-membered cyclo-P₄ As ligands. The possible reaction pathways for the formation of 5 a,b and 6 a-c were investigated by a combination of temperature-dependent ³¹ P{¹ H} NMR studies and DFT calculations.

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 {η^1:2 -(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 {η^1:2 -(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.