No d Orbitals but Walsh Diagrams and Maybe Banana Bonds: Chemical Bonding in Phosphines, Phosphine Oxides, and Phosphonium Ylides.

Synthesis and second-order nonlinear optical properties of three coordinate organoboranes with diphenylphosphino and ferrocenyl groups as electron donors: crystal and molecular structures of (E)-DCHCHB(mes)2 and DCCB(mes)2 [D P(C6H52, (η-C5H5)Fe(η-C5H4); mes = 2,4,6-(CH3)3C6H2]

Synthesis and Structure of a Base-Stabilized C-Phosphino-Si-Amino Silyne

Displacement of ethene from [Pt(η2-C2H4)(dcpe)] by Ph2PCCMe gives the monomeric η2-alkynylphosphine complex [Pt(η2-Ph2PCCMe)(dcpe)] (5). Reaction of 5 with one equivalent of HCl forms, in benzene, the four-coordinate η1-vinyl–platinum(II) complex [PtCl{C(CHMe)PPh2}(dcpe)] (6) by regiospecific addition of the proton to the alkyne carbon atom bearing the methyl group. In dichloromethane, reversible dissociation of the chloride ion from 6 takes place and the cation [Pt{C(CHMe)PPh2-κP,C1}(dcpe)]+ (6′)
that contains a three-membered methylenephosphaplatinacycle fragment can be observed. Treatment of complex 5 with methyl iodide results in the formation of a phosphonium salt [Pt{η2-C(CH2)CHPPh2Me}(dcpe)]+I−, [8]I, in which the alkynylphosphine has rearranged to the corresponding allene. The alkynylphosphine complex 5 is cleanly oxidised at phosphorus in the presence of sulfur or air to give the corresponding sulfide or oxide [Pt(η2-Ph2P(X)CCMe)(dcpe)] (X = S (9), O (10)). Complexes 5, 6, 8, 9 and 10 have been structurally characterised by single-crystal X-ray diffraction analysis.

Preparation and reactivity of mononuclear platinum(0) complexes containing a η2-coordinated alkynylphosphine

Structural data for substituted benzene derivatives (bond lengths and angles) are summarised. A structural scheme of the deformation of a bonds in the benzene ring under the influence of electron-donating and electron-accepting substituents is based on X-ray diffraction results. The general rule is revealed that the valence angle of a substituted carbon atom in the benzene ring increases with the nuclear potential of the substituents. A correlation is established between such angles and the Taft inductive constants. The structural characteristics of substituted benzenes are compared with those of metal complexes. A list of 258 references is included.

Structural Chemistry of Substituted Benzene Derivatives

A three-dimensional X-ray diffraction analysis of the structure of bis(diphenylphosphino)acetylene, (C6Hs)2PC=CP(C6Hs)2, has been carried out. The crystals are monoclinic, space group P21/n with a= 14"709, b= 8"166, c= 17-836 A, p= 95 ° 13', Z= 4. The parameters determined earlier by Brinkel were refined by a block-diagonal least-squares method with 2717 intensities collected with a Hilger-Watts linear diffractometer. The hydrogen atoms were included in the calculations. The final R value, including all reflexions, was 0.061 (R'=0.0064). The molecule has the expected pyramidal configuration about both phosphorus atoms, but in view of the asymmetric orientation of the benzene rings about the P-C bonds, possesses no symmetry, n-Interaction between the phosphorus atoms and the acetylenic group has been advanced to account for the geometry of the molecule. The torsion angle between the directions of the polar axes of the phosphorus lone-pair orbitals is approximately 90 °. Bond lengths and angles do not differ significantly in the two equivalent parts of the molecule. The mean > P-C(Ph) and > P-C = bond lengths are 1.832 and 1.765/~ respectively, and include an angle of 101.1 ° (e.s.d. 0.004/~, and 0-2°). All benzene rings are essentially planar with some significant inand out-of-plane bendings of the exocyclic bonds. The packing arrangement is described.

J.C.J. Bart

Papers

The crystal and molecular structure of bis(diphenylphosphino)acetylene