The synthesis of the first phophanylphosphonate, Mes*PH-PO(OEt)2 (2-H), in which the P(III) centre is not coordinated by a M(CO)5 (M = W, Mo, Cr) fragment is reported. The title compound reacts with LDA under the formation of 2-Li which is best described as the enolate form with a high double bond character between the two phosphorus centres. 2-Li is shown to engage in the phospha-Wittig-Horner reaction and converts aldehydes into phosphaalkenes that are metal-free and thus available for future manipulations at the phophorus lone pair. Using a selection of aldehydes with aliphatic, aromatic or vinylic substituents as substrates, phosphaalkene formation proceeds in high yields and high E-selectivity. The selectivity is however compromised during purification on standard silica which was found to promote E/Z isomerization.

More than just a carbon copy: The reaction of a phospha-Wittig-Horner reagent with diacetylenic ketones (see scheme) results in a cascade of reactions that can lead to both an oxaphosphole-terminated cumulene system and an alkene-bridged bis-phosphole. The reaction outcome is determined by the nature of the acetylene termini, with phenyl groups stabilizing a carbene intermediate that dimerizes to give the bis-phosphole product.

P,P-Dichlorophosphines 2a−c (RPCl 2 , R = Ph (a), t-Bu (b), 2,4,6-Me 3 Ph (c)) and P,P-dibromophosphines 4d,e (RPBr 2 , R = (i-Pr) 3 SiCC (d) and H 2 CCH (e)) react with triethylphosphite under Michaelis−Arbuzov conditions to give phosphinodiphosphonates 3a−e in quantitative yields. After complexation to W(CO) 5 and treatment with CH 3 ONa, phospha-Wittig−Horner reagents 9a,b are obtained on a multigram scale in good overall yield. Phospha-Wittig−Horner reagents with unsaturated substituents at III P (10d,e) can be prepared in analogous procedures; however, they prevail in an unusual ylide form that allows conjugation between the lone pair and the acetylene and vinyl π-systems, respectively. Phosphinophosphonate 9a has been characterized by X-ray crystallography and is shown to react smoothly with acetone within minutes. The resulting W(CO) 5 -coordinated phosphaalkene is shown to dimerize to a 1,2-diphosphitane or to undergo a 1,3-proton shift depending on the reaction conditions. In addition, a one-pot synthetic sequence starting from W(CO) 5 -coordinated phosphinodiphosphonates 5d,e has been developed to engage compounds with vinyl and acetylene substituents in phospha-Wittig−Horner reactions.

The phospha-Peterson reaction between a lithiated secondary phosphane, MesP(Li)TMS, and an aldehyde affords Mes-phosphaalkenes which, upon methanol addition and P-oxidation, react with a second carbonyl compound site specifically to produce unsymmetric alkenes. The E/ Z selectivity of the one-pot cross coupling is largely determined by the electronic nature of the aryl substituent of the first aldehyde, with electron-donating groups giving rise to increased amounts of Z-alkenes.

Triphenylphosphaalkenes 1a-c were prepared in good to excellent yields in a modified phospha-Peterson reaction between PhP(Li)TMS and benzophenones with different para-substituents at the C-phenyl groups (a: R = H, b: R = Ooctyl, c: R = F). Owing to the low kinetic stabilization that is provided by the P-phenyl group, compounds 1a-c engage in [a]