Preparation and Properties of tetrahedro-Tetraphosphorus Complexes of Rhodium and Iridium. Molecular and Electronic Structure of 2-P4)(PPh3)2>

Article abstract of DOI:10.1021/ja00263a010

White phosphorus dissolved in dichloromethane or diethyl ether at -78 deg C reacts with the Rh(I) or Ir(I) complexes (M = Rh, X = Cl, Br, I, L = PPh3; M = Rh, X = Cl, L = P(p-tol)3, P(m-tol)3, AsPh3; M = Ir, X = Cl, L = PPh3) to form yellow or orange tetrahedro-tetraphosphorus complexes . 31P NMR spectroscopy of in CD2Cl2 at low temperatures shows the P4 ligand to be η²-coordinated and deshielded by ca. 240 ppm relative to free P4.The P4 units act as A₂B₂ spin systems coupling to two 31P nuclei of PPh3 ligands (X2) and to 103Rh (I = 0.5) to give an overall A₂B₂MX₂ spin system.The vibrational frequencies of the P4 molecule in the rhodium complexes have been identified by infrared and Raman spectroscopy and are found to be from 15 to 90 cm^-1 lower in energy than the corresponding frequencies in free P4.An X-ray structure determination on *2CH2Cl2 at 185 K shows the crystals to be triclinic, space group P1<*>, with a = 11.853(2) Angstroem, b = 12.568(8) Angstroem, c = 14.505(2) Angstroem, α = 104.41(4) degree, β = 103.42(13) degree, γ = 84.22(4) degree, V = 2033.5(19) Angstroem³, D₀ = 1.58 g cm^-3, Z = 2, and D_c = 1.562 g cm^-3.The P4 molecule is η²-bonded to the rhodium atom (mean Rh-P = 2.293 Angstroem) with the metal-bonded P-P edge standing perpendicular to the remaining coordination plane of the metal.The phosphine ligands are bent away from the tetraphosphorus group toward the chlorine ( support the analogy between η²-bonded P4 and η²-bonded alkene or S2; the "back-bonding" component may be traced to a three-orbital-four-electron interaction between P4 and the RhCl(PH3)2 fragment.Xα calculations show that the most important contribution to the Rh-P4 covalent bond comes from an equatorial in-plane ? overlap of Rh4d_yz with a P4 2P?^*_<*> orbital.There is also a contribution from ? overlap of an Rh(4d_z², 4d_x2_-y2, 5s) hybrid orbital with a P4 2P(p_?, ?_<*>, s_?) hybrid.The calculated P-P bond order is 0.4 for the bonded edge and 1.0 for the opposite tetrahedral edge of the P4 ligand.In an EPA glass at liquid nitrogen temperature (X = Cl, Br) shows five absorptions in the 700-260-nm region.These are assigned to one-electron transitions, with good agreement between the obdserved and calculated energies.The absorptions owe most of their intensity to metal -> P4 and metal -> phosphine charge transfer.