Complexes dihydrogen

Diiridium(I) complexes, dihydrogen uptake, 7, 289 Diiridium(III) polyhydrides, synthesis and reactivity, 7, 410 Diiron carbonyl complexes with cyclopentadienyl ligands... 

Square wave electrochemical analyses confirmed that the affinity of the receptors for dihydrogen phosphate increase with increasing numbers of oxygen atoms in the bridging chain, however the fact that there is no observed increase in the electrochemical response between one and two oxygen atoms indicates that in these two receptors, complexed dihydrogen phosphate occupies the same location within the cavity, relative to the ferrocene moiety. 

Fig. 6.14 The difference INS spectrum (FDS, LANSCE) of complexed dihydrogen. The points are [W(CO)3(H2) P(cyclohexyl)3 2] - [W(CO)3(D2) P(cyclohexyl)3 2], Redrawn from [42] with permission from the American Chemical Society.

Fig. 6.16 The INS spectrum of complexed dihydrogen, in [W(CO)3(H2) P(isopropyl)3 2] calculated by DFT (B3LYP/LANL2DZL). (a) All atoms included and (b) only the dihydrogen ligand. Note that (b) is xlO ordinate expanded relative to (a) and only the fundamentals (without phonon wings) are plotted, TOSCA parameters assumed.

Many bodies of water become eutrophic when excess phosphate from detergents and fertilizer washes in. This overenrichment results in undesirable algal blooms. Agents that complex phosphate may allow it to be removed from treated wastewater, recovered, and reused. The first com plexing agent (7.22) (where X = S) complexes dihydrogen phosphate with a K of 820 and acetate with a K of 470 chloride, hydrogen sulfate, nitrate, and perchlorate are held much more weakly.91 The Kfor the second one with phosphate (7.23 where R is H) is 12,000.92... 

Procedure. A vitamin B complex tablet Is crushed and placed In a beaker with 20.00 mL of a 50% v/v methanol solution that Is 20 mM In sodium tetraborate and contains 100.0 ppm of o-ethoxybenzamIde. After mixing for 2 min to ensure that the B vitamins are dissolved, a 5.00-mL portion Is passed through a 0.45- xm filter to remove Insoluble binders. An approximately 4-nL sample Is loaded Into a 50- xm Internal diameter capillary column. For CZE the capillary column contains a 20 mM pH 9 sodium tetraborate/sodlum dIhydrogen phosphate buffer. For MEKC the buffer Is also 150 mM In sodium dodecylsulfate. A 40-kV/m electric field Is used to effect both the CZE and MEKC separations. 

Bismuth tribromide may be prepared by dissolving Bi O in excess concentrated hydrobromic acid. The slurry formed is allowed to dry in air, then gendy heated in a stream of nitrogen to remove water, and finally distilled in a stream of dry nitrogen. Bismuth tribromide is soluble in aqueous solutions of KCl, HCl, KBr, and KI but is decomposed by water to form bismuth oxybromide [7787-57-7] BiOBr. It is soluble in acetone and ether, and practically insoluble in alcohol. It forms complexes with NH and dissolves in hydrobromic acid from which dihydrogen bismuth pentabromide tetrahydrate [66214-38-8] H2BiBr 4H2O, maybe crystallized at —lO C. 

Stable U ansition-metal complexes of dihapto-dihydrogen (ij -H2) discovered by G. Kubas. 

The method may be standardised, if desired, with pure potassium dihydrogen-orthophosphate (see below) sufficient 1 1 hydrochloric acid must be present to prevent precipitation of quinoline molybdate the molybdophosphate complex is readily formed at a concentration of 20 mL of concentrated hydrochloric acid per 100 mL of solution especially when warm, and precipitation of the quinoline salt should take place slowly from boiling solution. A blank determination should always be made it is mostly due to silica. 

Cationic hydrides have been important in studying dihydrogen complexes [94]... 

The dinitrogen complex [Os(NH3)5N2]2+ is a useful synthetic intermediate, while the presence of the weakly nucleophilic triflate group enables it to be easily removed in the synthesis of the dihydrogen complex. 

One family of porphyrin complexes that will be treated in the review, even though they do not contain metal-carbon bonds, are metalloporphyrin hydride and dihydrogen complexes. As in classical organometallic chemistry, hydride complexes play key roles in some reactions involving porphyrins, and the discovery of dihydrogen complexes and their relationship to metal hydrides has been an important advance in the last decade. 

The first step consists in the attack of a proton on the W-H bond to yield a labile dihydrogen intermediate (Eq. (3)) that rapidly releases H2 to form a coordi-natively unsaturated complex (Eq. (4)). This complex adds water in the next step to form an aqua complex (Eq. (5)) that completes the reaction by substituting the coordinated water by the X anion (Eq. (6)). Steps (3)-(6) are repeated for each W-H bond and the factor of 3 in the rate constants appears as a consequence of the statistical kinetics at the three metal centers. The rate constants for both the initial attack by the acid (ki) and water attack to the coordinatively unsaturated intermediate (k2) are faster in the sulfur complex, whereas the substitution of coordinated water (k3) is faster for the selenium compound. 

Reduction of unsaturated organic substrates such as alkenes, alkynes, ketones, and aldehydes by molecular dihydrogen or other H-sources is an important process in chemistry. In hydrogenation processes some iron complexes have been demonstrated to possess catalytic activity. Although catalytic intermediates have rarely been defined, the Fe-H bond has been thought to be involved in key intermediates. 

Complex 5 was more active than the well-known precious-metal catalysts (palladium on activated carbon Pd/C, the Wilkinson catalyst RhCl(PPh3)3, and Crabtree s catalyst [lr(cod)(PCy3)py]PFg) and the analogous Ai-coordinated Fe complexes 6-8 [29] for the hydrogenation of 1-hexene (Table 2). In mechanistic studies, the NMR data revealed that 5 was converted into the dihydrogen complex 9 via the monodinitrogen complex under hydrogen atmosphere (Scheme 4). 

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