Hydrido complexes preparation

First hydrido complex of a transition metal prepared by W. Hieber and F. Leutert. 

While the reductive elimination is a major pathway for the deactivation of catalytically active NHC complexes [127, 128], it can also be utilized for selective transformations. Cavell et al. [135] described an interesting combination of oxidative addition and reductive elimination for the preparation of C2-alkylated imida-zohum salts. The in situ generated nickel catalyst [Ni(PPh3)2] oxidatively added the C2-H bond of an imidazolium salt to form a Ni hydrido complex. This complex reacts under alkene insertion into the Ni-H bond followed by reductive elimination of the 2-alkylimidazolium salt 39 (Fig. 14). Treatment of N-alkenyl functionalized azolium salts with [NiL2] (L = carbene or phosphine) resulted in the formation of five- and six-membered ring-fused azolium (type 40) and thiazolium salts [136, 137]. 

The apparatus and procedures are similar to those in the preparation above and a 1L flask is used. A solution of lithium tri-ferf-butoxyhydridoaluminate 9 (28.6 g, 113 mmole) in purified THF (100 mL) is added slowly to a solution of ZrCl2(i7s-C5Hs)2 (32.9 g, 113 mmole) in THF (500 mL) with stirring. After complete addition, stirring is continued for 1 hour, after which the mono-hydrido complex is collected by anearobic filtration (Fig. 1) and washed with THF (yield 26.3 g, 90%). Anal. Calcd. for C10H ClZr ash (Zr02), 47.77% hydrolyzable H, 1.00 g-atom/mole Cl, 13.75. Found ash, 47.0% hydrolyzable H, 1.02 g-atom/mole Cl, 13.4. One-quarter mole of Li[AlH4] may be used instead of the tri-terr-butoxy hydrido complex, but the essential control of stoichiometry is more difficult (see Properties). 

Other hydridozirconium derivatives that have been prepared from aluminum hydrides are ZrH(CH3)(i75-C5Hs)2, ZrH(AlH4Xf 5-CsHs)2, the complex ZrH2(i75-C5Hs)2-[ZrH(i75-CsHs)2]20, and deuterido derivatives corresponding to all of these hydrido complexes.8... 

In addition to the protonalion route, hydrido complexes may be prepared by reaction of carbonyl complexes with hydride donors ... 

Hydrido complexes with various tertiary phosphines have been prepared using different synthetic routes under anaerobic conditions (equations 135-138).1204-1215 In the... 

Hydrido complexes can be prepared by the oxidative addition of hydrogen to coordinatively unsaturated metals (e.g. Vaska s compound) or by reduction of higher valent compounds with borohydride or similar reagents. 

Similarly, the thioaldehyde complexes 66a,b were formed via addition of thiols to the vinylidene complex 64 and elimination of ethene. The vinylidene complex 64 reacted with benzyl mercaptan to yield the isolable intermediate 65. On heating 65 lost ethene in a first-order reaction to give 66b.188 The complexes 66a-d could also be prepared from the benzyne-(hydrido) complex 67 and thiols RCH2SH (Scheme 18).188... 

The formation of the unsaturated intermediate Run(OEP) from the hydrido-complex RumH(OEP) is supposed to occur from a LMCT excited state. As a consequence, the dimeric [RuH(OEP)]2 with a metal-metal interaction is formed [245]. Irradiation of some systems containing Fein(Por)N3 leads to p-nitrido bridged binuclear mixed-valence complexes [(Por)Fem-N-Fe,v(Por)] [134, 162], In both cases photochemistry was used as a conventional preparative route for synthesis of the binuclear complexes. 

It might be thought that reductive methods would be suitable for the preparation of hydrido-complexes. In fact, most such compounds are prepared by substitution reactions, using a source of H such as NaBH4 the formation of, e.g., NaBCl4 as a product assists the thermodynamics (cf. the use of LiAlH4 in the preparation of SiH4 in Section 10.3 above). 

Preparative methods for hydrido complexes vary widely. Some of the more frequently used of them are ... 

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