The development and chemistry of novel phosphacarbons and their derivatives

The exploration of low-coordinate phosphorus chemistry resulted in the synthesis of a range of novel phosphorus species which were duly characterised and subjected to extensive reactivity studies; potential applications and implications for the field are outlined. The group 14 chloropropargyls R3EC≡CCH2Cl (E = Si, Sn; R = nBu, Ph, Me2Ph, nPr, iPr) were prepared from HC≡CCH2Cl and the respective R3ECl. While attempts to convert R3EC≡CCH2Cl to R3EC≡CCH2PX2 (X = Cl, NEt2) via the Grignard reaction and addition of ClPX2 were unsuccessful, reactions with LiPR’2 effected conversion to group 14 propargylphosphines R3EC≡CCH2PR’2 (E = Si, Sn; R3 = nBu3, Ph3, Me2Ph, nPr3, iPr3; R’ = Ph, SiMe3). The addition of neat I2 to R3SiC≡CCH2P(SiMe3)2 afforded impure samples of R3SiC≡CCH2PI2 (R3 = Me2Ph, nPr3, nBu3) that could not be isolated from pentane solutions; attempts to convert R3SiC≡CCH2P(SiMe3)2 to R3SiC≡CC≡P with AgOTf and DABCO were unsuccessful. The synthesis of PhC≡CCH2PR’2 (R’ = Ph, SiMe3) was achieved by reaction with LiPR’2, while the Grignard reaction followed by addition to ClP(NEt2)2 afforded the novel allene Ph((NEt2)2P)C=C=CH2; reactions with HCl and MeI occurred exclusively at phosphorus. The syntheses of phosphaalkenes C6H4(1-C(OSiMe3)=PR’)(R) (R = 2-Me, 3-Me, 3-CN, 4-CN, 4-CO2Me, 4-COCl; R’ = H, SiMe3) were attempted by Becker condensation of C6H4(1- COCl)(R) and R’P(SiMe3)2. These reactions were studied in some detail in order to ascertain the principle reaction products, for which tentative identities were assigned. Phosphaalkenes E-/ZC6H4(1-C(OSiMe3)=PSiMe3)(2-Me) and E-/Z-C6H4(1-C(OSiMe3)=PSiMe3)(3-Me) were isolated and characterised spectroscopically. A library of meta- and para-substituted phosphomides C6H4(R)C(O)PPh2 (R = 3-Me, 3-CN, 3-CH2Cl, 4-CN, 4-CO2Me) was synthesised by reaction of HPPh2 with the respective acyl chlorides C6H4(R)COCl. Following standard literature methods for assessing electronic characteristics, IR data evidenced extensive delocalisation of the phosphorus lone pair into the carbonyl region in all cases, though coordination chemistry evidenced coordination exclusively via the phosphorus lone pair, indicative of little delocalisation. Novel di-phosphomides C5H3E(2,6-C(O)PPh2)2 (E = CH, N) were generated by addition of C5H3E(COCl)2 to HPPh2 and their behaviour as tridentate pincer ligands assessed by reaction with transition metals. The reaction of MeP(SiMe3)2 with C5H3E(2,6-C(O)PPh2)2 (E = CH, N) generated unprecedented diphosphametacyclophanes {3-CO-C6H4-C(O)PMe}2 and {2-CO-C5H3N-C(O)PMe}2; {3-COC6H4-C(O)PMe}2 is the first example of a metacyclophane that incorporates multiple phosphorus centres within the ligand skeleton, and was characterised crystallographically