Imidazole → imidazolidine. Preparation by reduction of [Os(H)(CO)(PPh3)2(PyaiR)]+/0[Os(H)(CO)(PPh3)2(PyaiR)]+/0 with NaBH4 and characterisation of the products (PyaiR = 1-alkyl-2-{3′-(pyridylazo)}imidazole)