Transition-Metal Derivatives of Phosphinophosphazenes: X-ray Crystal Structures of N₃P₃Cl₄PhPPh₂, N₃P₃Cl₄PhPPh₂Cr(CO)₅, and N₃P₃Cl₄PhPPh₂•Ru₃(CO)₁₁

The phosphinophosphazene N₃P₃Cl₄PhPPh₂ (1) has been synthesized by the reaction of the triethylborane-stabilized phosphazene anion in Li[N₃P!₃Cl₄PhBEt₃] (4) with PPh₂Cl. The arsinophosphazene N₃P₃Cl₄PhAsPh₂ (12), the first example of a phosphazene with a P-As bond, was similarly synthesized from 4 and AsPh₂Cl. The phosphino group of 1 undergoes facile coordination to low-valent transition-metal fragments; coordination to skeletal nitrogen atoms of the phosphazene ring was not detected. Reaction of 1 with (i) Cr(CO)₆ (under ultraviolet irradiation) or Cr(CO)₅THF or with (ii) Fe₂(CO)₉ affords the mononuclear complexes N₃P₃Cl₄PhPPh₂•Cr(CO)₅ (5), and N₃P₃Cl₄PhPPh₂•Fe(CO)₄ (6), respectively. Heating of 1 with Ru₃(CO)₁₂ gives the polynuclear species N₃P₃Cl₄PhPPh₂-Ru₃(CO)₁₁ (7). The structures of 1, 5, and 7 have been determined by X-ray diffraction. Crystals of 1 are monoclinic, space group P2₁/c, with a = 18.007 (7) Å, b = 8.447 (3) Å, c = 16.999 (6) Å, β = 116.95 (3)°, V= 2304.8 ų, and Z = 4. Crystals of 5 are monoclinic, space group P2₁/c, with a = 17.245 (9) Å, b = 17.901 (2) Å, c = 9.990 (7) Å, β = 93.95 (6)°, V= 3076.6 ų, and Z = 4. Crystals of 7 are monoclinic, space group P2₁, with a = 9.498 (6) Å, b = 35.275 (12) Å, c = 13.457 (4) Å,β = 108.05 (3)°, V = 4286.7 ų, and Z = 4. The P-P bonds of 1, 5, 6, and 7 and the P-As bond of 12 are sources of hydrolytic instability and were shown (in the cases of 1, 6, and 12) to undergo nucleophilic cleavage with sodium trifluoroethoxide. High polymeric phosphazenes bearing backbone-bound phosphino groups have been synthesized in solution but are also hydrolytically sensitive and decompose on attempted isolation.