Basicity of N‐(Tetramesityltetraphosphacyclopentylidene)cyclohexylamine: an Unusual Diphospha(III)guanidine Derivative

The nitrogen atom in cyclic hetero‐oligophosphane cyclo‐P4Mes4C(NCy) (1) can be protonated with HCl or HBF4. The resulting cation was isolated as the BF4–, AlCl4– and GaCl4– salts and characterised by NMR spectroscopy, mass spectrometry and X‐ray crystallography. According to quantum mechanical calculations, the basicity of compound 1 is comparable to that of methyl‐substituted monophospha(III)guanidine. The pKα value of 1 was also determined experimentally with indicator bases.