Hydride ligand bonding

It is noteworthy that while the electron rich Cp 2SmH is only moderately stable in solution, the analogous more strained dinuclear bridging complex is less stable and must be kept under hydrogen in order to record the NMR spectrum [2]. The synthesis of a samarium hydride supported by a calix-tetrapyrrolyl system was recently published [9] (Scheme 2), with the hydride ligand bonded to one samarium and to two lithium atoms. This cage affords an efficient protection against bimolecular collisions and the complex is described as thermally robust. 

Figure 6 shows the linearity of the Cg aldehyde produced versus the molar quantities of y6-CD. This selectivity decreases dramatically for increasing amounts of transfer agent. Such a behavior is consistent with the effect of the steric hindrance of the host on to the C=C double bond, which should be increasingly included in the cavity, so that the hydride ligand bond to rhodium is preferentially transferred to the terminal carbon atom in a step where the rhodium-alkyl species is formed. 

Migration of a hydride ligand from Pd to a coordinated alkene (insertion of alkene) to form an alkyl ligand (alkylpalladium complex) (12) is a typical example of the a, /(-insertion of alkenes. In addition, many other un.saturated bonds such as in conjugated dienes, alkynes, CO2, and carbonyl groups, undergo the q, /(-insertion to Pd-X cr-bonds. The insertion of an internal alkyne to the Pd—C bond to form 13 can be understood as the c -carbopa-lladation of the alkyne. The insertion of butadiene into a Ph—Pd bond leads to the rr-allylpalladium complex 14. The insertion is usually highly stereospecific. 

The suggested mechanism involves breaking of a platinum-ligand bond, again forming a platinum(IV) hydride that can then eliminate the alkane. 

Hi ly dispersed supported bimetallic catalysts with bimetallic contributions have been prepared from molecular cluster precursors containing preformed bimetallic bond [1-2]. For examples, extremely high dispersion Pt-Ru/y-AUOa could be prepared successfully by adsorption of Pt2Ru4(CO)ison alumina [2]. By similar method, Pt-Ru cluster with carbonyl and hydride ligands, Pt3Ru6(CO)2i(p3-H)(p-H)3 (A) was used in this work to adsorb on MgO support. The ligands were expectedly removable from the metal framework at mild conditions without breaking the cluster metal core. 

Abstract Organic syntheses catalyzed by iron complexes have attracted considerable attention because iron is an abundant, inexpensive, and environmentally benign metal. It has been documented that various iron hydride complexes play important roles in catalytic cycles such as hydrogenation, hydrosilylation, hydro-boration, hydrogen generation, and element-element bond formation. This chapter summarizes the recent developments, mainly from 2000 to 2009, of iron catalysts involving hydride ligand(s) and the role of Fe-H species in catalytic cycles. 

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