Hydrido complexes, /-metal

A trimeric thorium hydride Th3H6(0 — 2, 6-/-Bu2C6H3)6, which represents a rare example of an early-metal hydrido complex supported exclusively by aryloxide ligation, was synthesized according to reaction (5.69), and its structure is shown in 985 [352] ... 

The formation of this gold-rhodium cluster compound has been attributed to a mechanism involving partial reduction of the Au(PPh3)N03 species by the metal hydrido complex. 

Although the experimental evidence suggests that the observed photogeneration of hydrogen may not involve homogeneous metal dithiolene photocatalysts, a theoretical study by Alvarez and Hoffmann addressed possible mechanisms for hydrogen elimination from ds square-planar bis(dithiolene) complexes (77). Concerted elimination of H2 from protonated sulfur atoms in the complex was proposed to be a thermally forbidden but photochemically allowed pathway, and protonation of a metal hydrido complex was also considered, as shown in Scheme 3. 

Figure 5.38. In recent times these have included the rearrangement of terminal alkynes in combination with late transition metal hydrido complexes, presumably via vinylidene intermediates (see below).

Alkene complexes of late transition metals have been known for over a century. Transition metal hydrido complexes... 

Compound [Cr(C0)g(02CCF3)] may be prepared by oxidative substitution of Ag(02CCF3) or Hg(02CCF3)2 on [Cr2(CO)io] (218). Transition metal hydrido complexes have been obtained by oxidative addition reactions of trifluoroacetic acid which often lead to the formation of trifluoroacetato complexes. Equation (3) is an example of such a... 

It has been shown that in a number of transition-metal hydrido complexes H atoms are directly bonded to M and occupy definite coordination positions (as in K2ReH9, HPtBr[P(C2Hs)3] 2, etc., for which see Chapter 27). This would also appear to be true in certain carbonyl hydrides, though the H atoms have been directly located by n.d. in only one form of Mn(CO)5H. In Mn(CO)5H five CO are situated at five of the vertices of an octahedron (Mn-C, 1 -84 A) and the H atom is situated at the sixth vertex, with Mn-H, 1-60 (C-0, M34 A). 

Reaction with metal-hydrido complexes 8, 4.8.2.15.4 C2H5Na Na[CH,CH2)... 

The nature of the ligand into which the CO is to be inserted strongly influences the ease of CO insertion. The metal to hydride bond is known to be resistant to CO insertion, whereas deinsertion from the formyl to the hydride proceeds readily [26]. However, in certain cases the unfavored insertion into metal hydrido complexes takes place when a -formyl bond is formed, giving an extra stability to the product [27]. 

These reactions occur via attack of various atoms or groups on the terminal carbon atom. The following entities may be utilized for the attack H, RCO, RO, Cl, and AcO. The most commonly utilized complexes for this purpose are the transition metal hydrido complexes. 

Fig. 8 Dependence of Vmh frequency of transition metal hydrido complexes bearing various ligands on the metal position in the Periodic table. Data from...

Geometry and Properties of Transition Metal Hydrido Complexes... 

Bond distances M-H as derived from structure analysis within the transition metal hydrido complex are close to the sum of the covalent radius for the transition metal M and a radius of 28 pm for the hydrogen atom, supporting the picture of a covalent M-H bond within the hydrido complexes [MmH/j] . H-H distances are longer... 

Strong acidic metal hydrido complexes such as HCofCO) or complexes with Lewis acid properties, such as Rh2Cl2(CO)4, [Ru(MeCN)3(triphos)](CF3S03)2, [Pt(H20)2(dppe)](CF3S03)2, [Pd(H20)2(dppe)](CF3S03)2, or [Ir(MeCN)3(tri-phos)] (CF3S03)3, are able to act in alcohols as acetahzation catalysts, which means they can mediate the transformation of the newly formed aldehydes into acetals (see Section 5.3). 

Dimetallic elimination reactions leading to metal-metal bond formation are the amine or alkane eliminations that result from the condensation of a late transition metal hydrido complex with an early transition metal amido or alkyl complex, respectively. Examples of this method are Selegue s synthesis of the first Ti-Fe and Ti-Ru complexes 8a,b [8, 9] and the reaction of [Zr(CH2Ph)4) with [CoH(CO)4], although only spectroscopic evidence was provided for compound 18 (Scheme 4.3) [20]. 

---