George A. Gray

13C nuclear magnetic resonance of organophosphorus compounds. VI. 13C spin-lattice relaxation times in phosphorus heterocycles

Abstract Carbon-13 spin-lattice relaxation times have been determined for a series of substituted 2,2,3,4,4-pentamethylphosphetanes (four-membered phosphorus heterocycles), including phosphetanes, phosphetanium salts and phosphetane oxides. Nonprotonated carbons have T 1 values of the order of 8–18 sec while protonated carbons have values ranging from 0.6 to 4.0 sec. The rigidity and, in most cases, isotropic nature of the phosphetanes has allowed comparison of T 1 s and subsequent determination of relaxation mechanisms and probing of the ease of internal rotation for each of the several methyl groups on the basic ring backbone. Situations are observed where pseudoequatorial methyl carbons on C-2 and C-4 have relaxation times shorter than those of the presumably more hindered pseudoaxial methyls attached to the same C-2 and C-4 carbons. This points out the danger of directly equating short T 1 values with steric crowding.

Phosphorus-31 relaxation rate studies of Mn2+ - alkaline phosphatase

Abstract Phosphorus-31 NMR relaxation rates for the ternary complex of manganese-alkaline phosphatase-phosphate have been measured and their temperature dependence studied. The exchange of phosphate into the complex is exchange limited with respect to the transverse relaxation rate but is fast with respect to longitudinal relaxation. The data show that the observed phosphate relaxation is an outer-sphere effect. The activation energy for phosphate exchange is E a = 8 Kcal/mole as determined from the temperature dependence of the line width of the phosphorus resonance.

π-Facial selectivities in the coordination of an optically pure fused cyclopentadienyl ligand to arene ruthenium moieties. NMR spectral and structural characterization of a single diastereomer of [(PCp)Ru(Me6C6)]PF6

Abstract Optically pure thallium (1R)-(−)-9,9-dimethyltricyclo[6.1.1.02′6]deca-2,5-dienide (TIPCp) reacts with [(n6-arene)RuCl2]2 (arene = C6H6, MeC6H4, p-MeC6H4CHMe2, Me6C6) and NH4PF6 to form two isomers of the complexes [(n5-PCp)Ru(n6-arene)]PF6. The π-facial stereoselectivity for coordination of PCp is a function of the steric bulk of the arene increasing from a 1:1 (C6H6) to a 14:1 (Me6C6) exolendo isomer ratio. New complexes were characterized by elemental analyses, physical properties, differential pulse voltammetry and 1H and 13C{1H} one- and two-dimensional NMR spectroscopy. The structure of [(n5-PCp)Ru(n6-Me6C6)]PF6 was confirmed by X-ray crystallography. This compound crystallized in the acentric space group C2221 in a unit cell with the following dimensions: a = 11.451(4), b = 13.426(5), c = 31.249(3) A, V= 4804(3) A3, Z = 8. Refinement converged to R(F) = 0.056 for 1723 independent observed (I>3σ(I)) reflections. Ruthenium coordinates to the less sterically hindered exo face of the PCp ligand, anti to the gem-dimethyl group, and is closer to the arene (Ru-ring centroid = 1.73 A) than to the PCp ligand (Ru-ring centroid = 1.79 A).