Addition polymerization, the most general method of preparation for organic polymers, has successfully been extended to P=C bonds. The polymerization of a phosphaalkene has been initiated by thermolysis or with alkyllithium reagents. The unprecedented poly(methylenephosphine)s are easily oxidized using oxygen or sulfur to give air stable macromolecules. A molecular weight (M(w)) of 35000 g/mol for the poly(methylenephosphine sulfude) was estimated by light-scattering GPC.

Phosphaalkenes (MesP=CRR': R = R' = Ph (1a); R = R' = 4-FC6H4 (1b); R = Ph, R' = 4-FC6H4 (1c); R = R' = 4-OMeC6H4 (1d); R = Ph, R' = 4-OMeC6H4 (1e); R = Ph, R' = 2-pyridyl (1f)) are prepared from the reaction of MesP(SiMe3)2 and O=CRR' in the presence of a trace of KOH or NaOH. The base-catalyzed phospha-Peterson reaction is quantitated by NMR spectroscopy, and isolated yields of phosphaalkene between 40 and 70% are obtained after vacuum distillation and/or recrystallization. The asymmetrically substituted phosphaalkenes (1c, 1e, 1f) form as 1:1 mixtures of E and Z isomers; however, X-ray crystallography reveals that the E isomers crystallize preferentially. Interestingly, E-1e and E-1f readily isomerize in solution in the dark, although the rate of isomerization is much faster when samples are exposed to light. X-ray crystal structures of 1b, E-1e, and E-1f reveal that the P=C bond lengths (average of 1.70 A) are in the long end of the range typically found in phosphaalkenes (1.61-1.71 A). Attempts to prepare isolable P-adamantyl phosphaalkenes following this route were unsuccessful. Although AdP=CPh2 (2a) is detected by 31P NMR spectroscopy, attempts to isolate this species afforded the 1,2-diphosphetane (AdPCPh2)2 (3a), which was characterized by X-ray crystallography.

Since Beckers synthesis of the first stable phosphaalkene in 1976, [1] these compounds, which contain a P=C bond and were once considered exotic, now constitute a major branch of phosphorus chemistry. Applications for these compounds are even being developed.[2-4] The ability of P = C bonds, in many instances, to "copy" the well-established chemistry of isolobal C=C bonds has attracted considerable attention. [2, 3a, d] In molecular chemistry, the remarkable analogy between phosphaalkenes and alkenes is evidenced by phospha variants of a number of reactions, including 1,2-addition, [4+2]cycloaddition, Peterson and Wittig olefination, h 2 coordination to metal centers, and Cope and allylic rearrangements. One of the most important reactions of C = C bonds is the addition polymerization of olefins, which is used to produce many commodity polymers. The absence of an analogous polymer chemistry for P=C bonds prompted us to investigate addition polymerization as a potential route to new phosphine polymers. We recently reported the first addition polymerization of the phosphaalkene 1[5] (Mes = 2,4,6-trimethylphenyl) to give the poly(methylenephosphine) 2 (M w % 10 4 g mol À1 by GPC versus polystyrene), an alternating PÀC polymer. [6]

The secondary vinylphosphines Ar(F)P(H)C(R)[double bond]CH(2) [2a, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = CH(3); 2b, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = C(6)H(5); 2c, Ar(F) = 2,4,6-(CF(3))(3)C(6)H(2), R = CH(3)] were prepared by treating the corresponding dichlorophosphine Ar(F)PCl(2) (1) with H(2)C[double bond]C(R)MgBr. In the presence of catalytic base (DBU or DABCO) the vinylphosphines (2a-c) undergo quantitative 1,3-hydrogen migration over 3 d to give stable and isolable phosphaalkenes Ar(F)P=C(R)CH(3) (3a, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = CH(3); 3b, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = C(6)H(5); 3c, Ar(F) = 2,4,6-(CF(3))(3)C(6)H(2), R = CH(3)). Under analogous conditions, only 90% conversion is observed in the base-catalyzed rearrangement of MesP(H)C(CH(3))[double bond]CH(2) to MesP[double bond]C(CH(3))(2). Presumably, the increase in acidity of the P-H group when electron-withdrawing groups are employed (i.e. 2a-c) favors quantitative rearrangement to the phosphaalkene tautomer (3a-c). Thus, the double-bond migration reaction is a convenient and practical method of preparing new phosphaalkenes with C-methyl substituents.

Since Beckers synthesis of the first stable phosphaalkene in 1976, [1] these compounds, which contain a P=C bond and were once considered exotic, now constitute a major branch of phosphorus chemistry. Applications for these compounds are even being developed.[2-4] The ability of P = C bonds, in many instances, to "copy" the well-established chemistry of isolobal C=C bonds has attracted considerable attention. [2, 3a, d] In molecular chemistry, the remarkable analogy between phosphaalkenes and alkenes is evidenced by phospha variants of a number of reactions, including 1,2-addition, [4+2]cycloaddition, Peterson and Wittig olefination, h 2 coordination to metal centers, and Cope and allylic rearrangements. One of the most important reactions of C = C bonds is the addition polymerization of olefins, which is used to produce many commodity polymers. The absence of an analogous polymer chemistry for P=C bonds prompted us to investigate addition polymerization as a potential route to new phosphine polymers. We recently reported the first addition polymerization of the phosphaalkene 1[5] (Mes = 2,4,6-trimethylphenyl) to give the poly(methylenephosphine) 2 (M w % 10 4 g mol À1 by GPC versus polystyrene), an alternating PÀC polymer. [6]