Tautomerism of hydrophosphoryl compounds and their features as ligands in metal complex catalysis. Quantum-chemical simulations by the density functional method

The density functional method (gradient-corrected nonempirical functional PBE, basis TZ2p) was used to perform a large-scale study of the mechanism of tautomerization of hydrophosphoryl compounds RR′P (H)O ? RR′POH (R,R′ = Alk, Ar, OR, NR₂). It was shown that intramolecular proton transfer in this rearrangement is forbidden (activation barriers 43.3–60 kcal mol^?1), and, in the absence of carrier molecules, it occurs as synchronous transfer of two protons in fairly strong dimeric associates (2.50–10.5 kcal mol^?1) formed due to O-H···O, O-H···P, and C-H···O hydrogen bonding. The process involves six-membered transition states with activation barriers of 5–15 kcal mol^?1. The contribution of tunneling into the rate constants at 300–400 K, according to estimates in terms of the reaction-path Hamiltonian formalism, reaches 20–40% and increases as the temperature decreases. The mechanism of ethylene hydroformylation in a model complex of a hydrophosphoryl compound with Pt(II) [(H₂PO)₂H]Pt(PH₃)(H)] was considered to reveal factors responsible for the high efficiency of such complexes in the reaction studied. It was found that the key stages of the catalytic cycle involve reversible proton migration in the ?PH₂OH··· O=P chain of the quasi-chelate ring, which provides fine tuning of the electron distribution in the catalytic node and thus functions as a molecular switcher.     

Matrix Groups Related to the Quaternion Group and Spherical Orbit Codes

We consider a finite matrix group with 3⁴· 2¹⁶ elements, which is a subgroup of the infinite group , where is the regular representation of the quaternion group and C is a matrix that transforms the regular representation Q to its cellwise-diagonal form. There is a number of ways to define the matrix C. Our aim is to make the group similar in a certain sense to a finite group. The eventual choice of an appropriate matrix C done heuristically. We study the structure of the group and use this group to construct spherical orbit codes on the unit Euclidean sphere in R⁸. These codes have code distance less than 1. One of them has 3²· 2⁸ = 2304 elements and its squared Euclidean code distance is 0.293. Communicated by: V. A. Zinoviev     

PMR spectra of dimers of cyclopentadienyl compounds

The PMR spectra of cyclopentadine endo-dimer, its 1y-acetoxy-derivative and the dimer of spiro-heptadiene have been thoroughly studied. The assignment is proved by the use of spindecoupling experiments and the INDOR-technique. The relative signs of several coupling constants were found and used for the assignment. General trends in the proton chemical shifts and coupling constants are discussed for the derivatives of the cyclopentadiene dimer and for the substituted cyclopentadiene dimers.