Complex hydride defined

Copper has a long history in chemistry. Nevertheless, Al-heterocycUc carbene (NHC)-copper systems have been known and used only these last 20 years since Arduengo et al. reported the first NHC-copper system in 1993 [1]. Since then, the NHC-copper chemistry has undergone continuous expansion with the synthesis of new complexes (well-defined systems, hydrides, hydroxides, and cationic species) and the development of various applications (catalysis, transme-talation reagents, antitumor reagents, etc.). NHC-copper systems have become an example of a best-seller in organometallic chemistry. 

The use of isotopic substitution to detennine stmctures relies on the assumption that different isotopomers have the same stmcture. This is not nearly as reliable for Van der Waals complexes as for chemically bound molecules. In particular, substituting D for H in a hydride complex can often change the amplitudes of bending vibrations substantially under such circumstances, the idea that the complex has a single stmcture is no longer appropriate and it is necessary to think instead of motion on the complete potential energy surface a well defined equilibrium stmcture may still exist, but knowledge of it does not constitute an adequate description of the complex. 

Other Ion Affinities Binding affinities for many different types of ions to neutrals are defined analogously to hydride affinity, as the 298 K enthalpy required to dissociate the complexed species. The ion can be a cation or an anion. Conversely, ion affinities can be described in terms of the dissociation. 

The xanthene-backbone derived diphosphines (129) also led to well-defined rhodium dicarbonyl hydride complexes. They were used in one-phase catalysis and two-phase separation after careful acidification of the system.415... 

One of the most defining characteristics of the late metal a-diimine polymerization systems is the uniquely branched polyolefins that they afford. This arises from facile p-hydride elimination that late transition metal alkyl complexes undergo. The characteristics of the isomerization process have been the subject of much investigation, particularly with the more easily studied Pd(II) a-diimine system. The process is initiated by P-hydride elimination from the unsaturated alkyl agostic complex 1.17, followed by hydride reinsertion into olefin hydride intermediate 1.18 in a non-regioselective manner (Scheme 5). In doing so, the metal center may migrate... 

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

The organometaUic starting reagents are the MCM-41 supported ](=SiO)2TaH] and ](=SiO)2TaH3] described in the previous section. The MCM-41 supported hydrides cleave N-H bonds of ammonia at room temperature to yield the weU-defined imido amido surface complex ](=SiO)2Ta(NH)(NH2)] [9]. Dihydrogen is released in the gas phase during the reaction (Scheme 2.20). 

In summary, the tantalum hydride system adds to the few previously reported well-defined organometallic complexes capable of cleaving N-H bonds of ammonia to yield either an amido or an imido complex, and achieves unprecedented dinitrogen N=N triple bond cleavage with dihydrogen on isolated tantalum atoms to yield reduction of both N atoms. 

The bidentate oxazoline ligands 85 and 86 (and derivatives thereof) are excellent reporter ligands, and several studies have used NOEs to determine the nature of their chiral pockets [61, 113, 114, 126]. NOESY studies on the cations [Ir(l,5-COD)(86)]+ and several cationic tri-nudear Ir(iii)(hydrido) compounds [110], e. g. [Ir3(p3-H)(H)5(86)3] +, 87, in connection with their hydrogenation activity, allowed their 3-D solution structures to be determined. In addition to the ortho P-phenyl protons, the protons of the oxazoline alkyl group are helpful in assigning the 3-D structure of both the catalyst precursors and the inactive tri-nudear dusters. Specifically, for one of these tri-nudear Ir(iii) complexes, 87 [110], with terminal hydride ligands at d -17.84 and d -21.32 (and a triply bridging hydride at 5 -7.07), the P-phenyl and oxazoline reporters define their relative positions, as shown in Scheme 1.5. 

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