Beiträge zur Chemie des Phosphors. 64 [1]. Zur quasicyclischen Konformation der Organylphosphide M2(PR)n′ [MK,Na]

Contributions to the Chemistry of Phosphorus. 64. About the Quasicyclic Conformation of the Organylphosphides M₂(PR)_n′M = K, Na] The organyl tetraphosphides M₂(PR)₄ (M = K, Na) and – as can be assumed with a high probability – the corresponding triphosphides M₂(PR)₃ exhibit a quasicyclic conformation with a twofold intramolecular metal bridge between the terminal P atoms. This structure becomes evident from the following ³¹P n.m.r. spectroscopic observations for the tetraphosphides: For the salts M₂(PR)₄ (M = K, Na) only a single configuration isomer is observed indicating that a configuration selecting “cyclization reaction” takes place. Beyond it, the ²J_PP coupling constants have the same range of magnitude as in five-membered heterocyclophosphanes. Moreover, the ³J_PP couplings between the “terminal” P atoms possess unusual high values. The alternative monocyclic structure with a single metal bridge is not compatible with a configuration rule for five-membered phosphanes which describes the relation of magnitudes of cis- and trans-²J_PP couplings.