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Highly strained methylenephosphiranes are formed in the reaction of the new electrophilic phosphinidene complex [iPr(2)N-P=Fe(CO)(4)] with allenes. Remarkably, reaction with diallenes at 0 degrees C also leads to a phosphirane, which rearranges upon warming to room temperature to a bis-isopropylidenephospholene (see scheme).

The phosphinidene complex iPr 2 N−PFe(CO) 4 was prepared as a storable phosphirane solution from Collman's reagent and iPr 2 NPCl 2 in the olefins 1-pentene and 1-hexene. The carbenelike reagent is able to hop under very mild conditions (>−25 °C) from one olefin to another and to alkynes to give the more stable phosphirenes that likewise display dynamic covalent behavior. The olefinic solutions are effective reservoirs for the highly reactive phosphinidene complex, as is illustrated in its N−H and O−H insertion reactions with amines, alcohols, and carboxylic acids and in its P−C bond formation with Grignard reagents.

The (phosphaalkenyl)lithium carbenoid (Z)-Mes*PdCClLi (2; Mes* ) supermesityl ) 2,4,6tri-tert-butylphenyl) was transmetalated with MgBr 2 , ZnCl 2 , and HgCl 2 to furnish the new (phosphavinylidene)metal carbenoids Mes*PdCClMX ((Z)-5a, MX ) MgBr; (E)-5b, MX ) ZnCl; (E)-5c, MX ) HgCl), while with 0.5 equiv of the metal halide, the bis(phosphaalkenyl)metal carbenoids (Mes*PdCCl) 2 M ((Z,Z)-6a, M ) Mg; (E,E)-6b, M ) Zn; (E,E)-6c, M ) Hg) were formed. Compounds 2 and 5a were reacted with carbonyl compounds under 1,2addition, leading to the β-phosphaallyl alcohols 7-10. Bromine-lithium exchange at -90 °C between (Z)-Mes*PdCBrSiMe 3 ((Z)-14) and n-butyllithium furnished (E)-/(Z)-Mes*PdCLiSiMe 3 ((E)-/(Z)-16; E:Z ) 1:1. Transmetalation of (E)-/(Z)-16 with MgBr 2 or ZnCl 2 furnished only the trans-metal isomer of Mes*PdCMXSiMe 3 ((Z)-18a, MX ) MgBr; (E)-18b, MX ) ZnCl). From (E)-/(Z)-16, a new access to the phosphaallene Mes*PdCdCPh 2 (20) was obtained by reaction with benzophenone.

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Generating the transient electrophilic tungsten pentacarbonyl-phenylphosphinidene complex PhP=W(CO) 5 in the presence of 2,7-dimethylocta-2,3,5,6-tetraene leads to the formation of a 3,4-di-A C H T U N G T R E N N U N G substituted phosphole or a complexed phospholene, depending on the reaction conditions. The formation of the phospholene results from the reaction of PhP=W(CO) 5 with the diallene, while the formation of the phosphole arises from reaction with 3,4-diisopropylidene-cyclobutene, which is formed in situ from the isomerization of the conjugated allene.