Sterically encumbered acyclic diphosphazanes: synthesis, conformations and coordination behavior

Abstract

The reaction between λ ³-diphosphazane [EtN(PCl₂)₂] and the sodium salts of substituted phenols affords sterically encumbered diphosphazanes [EtN{P(OR)₂}₂] (R = -C₆H₃ⁱPr₂-2,6 (1), -C₆H₃Me₂-2,6 (2) and -C₆H₂Me₃-2,4,6 (3)). When the same reaction was carried out with bulky sodium 2,4-di-tert-butyl-4-methylphenoxide, only a monosubstitution takes place to result in the formation of [EtN{PCl(OR)}₂] (R = -C₆H₂^tBu₂-2,6-Me-4) (4). Further reaction of 2 with [Mo(CO)₄(NBD)] produces cis-[(EtN{P(OC₆H₃Me₂-2,6)₂}₂)Mo(CO)4] (5). Diphosphazanes 1-4 and the metal derivative 5 have been characterized by means of their analytical data and EI-MS, IR and multinuclear NMR (¹H and ³¹P) spectral data. The solid-state structure of the diphosphazanes 1, 2 and 4, and the molybdenum complex 5 have been determined by X-ray diffraction studies. Irrespective of the size of substituent, the bulky groups on the phosphorus and nitrogen are on the same side of the P-N-P skeleton with a local C2v symmetry. The central nitrogen remains almost trigonal planar in all the compounds.