Cyclic and short-chain linear phosphazenes with hindered aryloxy side groups

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A series of short-chain and cyclic phosphazenes bearing o-dichloro- and o-dimethyl-phenoxy groups have been synthesised, and their structures studied by X-ray crystallography. These compounds are small-molecule models for the corresponding linear high polymers. Structural parameters: N3P3Cl5(OC6H3Cl2-o)1, a= 8.081(4), b= 8.074(2), c= 25.868(3)A, β= 91.11(2)°, space group P21/c, Z= 4; gem-N3P3Cl4(OC6H3Cl2-o)22, a= 18.856(5), b= 8.002(2), c= 16.124(2)A, β= 114.89(2)°, space group P21/c, Z= 4; N3P3Cl2(OC6H3Cl2-o)44, a= 7.975(3), b= 18.373(4), c= 22.225(3)A, β= 90.35(2)°, space group P21/n, Z= 4; [NP(OC6H3Cl2-o)2]35, a= 12.021(4), b= 19.938(5), c= 18.379(11)A, β= 90.84(5)°, space group P21/n, Z= 4; gem-N4P4Cl4(OC6H3Cl2-o)46, a= 10.806(2), b= 10.861(2), c= 17.075(7)A, α= 89.33(4), β= 80.79(3), γ= 68.44(2)°, space group P1, Z= 2; gem-N3P3Cl4(OC6H3Me2-o)27, a= 9.470(3), b= 18.481(12), c= 13.087(8)A, β= 94.56(4)°, space group P21/n, Z= 4; [NP(OC6H3Me2-o)2]38, a= 20.560(5), b= 20.580(9), c= 22.085(4)A, α=β=γ= 90.0°, space group P4/ncc, Z= 8; OPCl2NP(OC6H3Cl2-o)39, a= 14.319(4), b= 16.837(4), c= 20.660(8)A, space group Pbca, Z= 8; OPCl(OC6H3Me2-o)NPCl(OC6H3Me2-o)NP(OC6H3Me2-o)310, a= 15.212(3), b= 18.965(1), c= 14.559(2)A, β= 102.96(2)°, space group P21/c, Z= 4. Despite the bulkiness of the o-dichloro- and o-dimethyl-phenoxy groups, their introduction into the phosphazene structure followed a geminal substitution pathway during the early stages of the reaction. In the reactions with the linear short-chain oligomers these nucleophiles preferentially attacked at the terminal PCl3 rather than at the PCl units in the middle of the chain or those associated with the phosphoryl group. The structure of compound 10 revealed a distorted trans-trans conformation for the PN skeleton, in contrast to the cis-trans arrangement generally believed to exist for linear phosphazene high polymers.