Hexacoordinate phosphorus. 5. Synthesis and characterization of neutral phosphorus(V) compounds containing substituted bidentate amidino ligands derived from carbodiimides

A series of neutral hexacoordinate (λ⁶) phosphorus compounds (1-8) of the general formula ([equation omitted] R = cyclohexyl, isopropyl) have been prepared by an apparent carbodiimide insertion into a P-Cl bond of a pentacoordinate (5) phosphorane. The six-coordinate nature of these derivatives is evidenced by their characteristic high-field ³¹P NMR chemical shifts and is further substantiated by the crystal structure of [equation omitted], where R = cyclohexyl. Crystal data for 5: monoclinic, space group P2₁/c (No. 14), a = 8.548 (3) Å, b-24.280 (8) Å, c = 10.571 (5) Å, β = 111.18 (3)°, V = 2045 ų, Z = 4. Final R and R_w values for 5 are 0.052 and 0.067, respectively. The molecular structure of 5 shows that the two nitrogen atoms of the chloroamidine ligand are equivalently bound to phosphorus (P-N = 1.843 (3), 1.837 (4) A) with slightly elongated bond lengths relative to a normal P-N bond, that the chloroamidine ligand is essentially planar, and that the two Cl atoms and the carbodiimide framework atoms and the ipso carbon of the cyclohexyl substituents lie in the same plane about the X6-phosphorus atom. These X6-phosphoranes are not very reactive. Lithium phenyl substitutes at the chlorine on the ring of [equation omitted] (2), and not on phosphorus, to give [equation omitted] (9), where R = isopropyl. Hydrolysis of 2 gave the phosphoryl compound with a monodentate ligand [equation omitted] (10). A detailed characterization, using multinuclear NMR, infrared, and mass spectroscopic data, of all compounds is reported.