The new 16-electron ruthenium compounds (v5-C5Me5)Ru(L)CI [(l), L = PPri,; (2), L = PCy3) (Cy = cyclohexyl) were prepared from [ ( ~p -C ~M e ~) R u C l l ~ and PPri3 or PCy3, respectively, and the X-ray crystal structure of (1) has been determined; reactions of the title compounds with CO, C2H4, pyridine, and PhSiH3 are described.A plethora of mechanistic and synthetic information has been reported regarding compounds of the type (qS-CSHS)FeL2X, and related Ru and 0 s systems. 1 In many instances reactive 16-electron intermediates formed via thermal or photoinduced dissociation of L play an important role in the chemistry of these species.2 Here we report the preparation, characterization, and initial reactivity studies of stable, co-ordinatively unsaturated 'half sandwich' compounds (qs-CsMeS) Ru( PR3)Cl.Combination of methylene chloride solutions of PR3 [4 equiv.; R = Pri or Cy, (Cy = cyclohexyl)] and [(qs-CSMeS)-RuC1I43 (1 equiv.) at room temperature produced an immediate colour change from dark orange to deep blue. The highly crystalline 16-electron complexes (q~-CSMeS)Ru(L)C1 [(1), L = PPri,; (2), L = PCy3] were isolated as blue crystals from pentane in 92 and 82% yields, respectively (equation 1).Both reactions are quantitative in [zH,]benzene by IH n.m.r. spectroscopy. Compounds (1) and (2) were charac-and R u C ~] ~.

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The aims of this preliminary study were to establish the efficacy and minimum effective dose of TG(5)(FdDO3A)(52) gadolinium dendrimer for contrast-enhanced, three-dimensional (3D) time of flight (TOF) magnetic resonance angiography (MRA) of the body. In a dose ranging study in eight rabbits (Group A), each of two animals received 0.03; 0.02; 0.01; or 0.005 mmol/kg of the agent for 3D-TOF MRA of the pelvic circulation in the axial and coronal planes. An additional nine animals (Group B) received a dose of 0.02 mmol/kg for 3D-TOF MRA of the mediastinum, abdomen or of the lower limbs. Quantitative and qualitative analyses of the images from Group A demonstrated a dose-related reduction in saturation effects and improved visualization of vascular structures, with maximal augmentation of the contrast-to-noise ratio (CNR) at 0.03 mmol/kg. The dose of 0.02 mmol/kg was found to be the minimal effective dose at the three vascular regions.