Coordinated hydride

The simple Co(I) complexes may reversibly pick up a proton to give what is essentially a Co(III) complex with a coordinated hydride, i.e.,... 

Kinetic studies of the hydride cluster [W3S4H3(dmpe)3] with acids in a non-coordinating solvent, i.e., dichloromethane, under the pseudo-first-order condition of acid excess, show a completely different mechanism with three kineti-cally distinguishable steps associated to the successive formal substitution of the coordinated hydrides by the anion of the acid, i.e., Ch in HCl [37]. The first two kinetic steps show a second-order dependence with the acid concentration. 

In a manner similar to OsH(OH)(CO)(P Pr3)2, the hydride-metallothiol complex OsH(SH)(CO)(P Pr3)2 adds Lewis bases that are not bulky such as CO and P(OMe)3 to give the corresponding six-coordinate hydride-metallothiol derivatives OsH(SH)(CO)L(P Pr3)2 (L = CO, P(OMe)3). OsH(OH)(CO)(PiPr3)2 and OsH(SH)(CO)(P Pr3 also show a similar behavior toward dimethyl acetylenedi-carboxylate. Treatment of OsH(SH)(CO)(P Pr3)2 with this alkyne affords 6sH SC(C02Me)CHC(OMe)6 (CO)P Pr3)2, which is the result of the tram addition of the S—H bond to the carbon-carbon triple bond of the alkyne. Phenyl-acetylene, in contrast to dimethyl acetylenedicarboxylate, reacts with OsH(SH) (CO)(P Pr3)2 by insertion of the carbon-carbon triple bond into the Os—H bond to give the unsaturated alkenyl-metallothiol derivative Os ( )-CH=CHPh (SH) (CO)(P Pr3 )2, the inorganic counterpart of the organic a, (3-unsaturated mercaptans (Scheme 46).92... 

The fact that isomers 8a, 8b and 8c are the lowest energy styrene coordinated complexes have potentially important ramifications that concern the modified-Chalk-Harrod mechanism and the regioselectivity observed in the hydrosilylation. With the modified-Chalk-Harrod mechanism olefin insertion into the M-Si bond follows styrene coordination. However, in all three isomers depicted in Figure 8, the coordinated hydride lies between the... 

Nyholm (59) has suggested that this isomerization takes place because, on coordination, the allyl side chain suffers hydride abstraction by the metal to form an unstable seven coordinate hydride species. Fig. 43 a. 

The cocondensation of chromium vapour and the phosphorus ligand is used to prepare [Cr(dmpe)3] and the trimethyl phosphite complex [Cr P(OMe)3 6] (Table 8). The former has a distorted octahedral structure, and the latter forms a seven-coordinate hydride CrH2 P(OMe)3 5 which, with other chromium(II) complexes of P donor ligands, is considered in Section 35.3.4. 

Protonation of the series [Mo(CNR)2(dppe)2] (Section 36.2.2.1.2) gives the seven-coordinate hydrides [MoH(CNR)2(dppe)2]+ which, like their carbonyl analogues (Section 36.2.4.1.1), are fluxional in solution with the hydride moving between face-capping sites in an octahedral structure.71... 

Dissociation of DIBAH from (16) then creates a vacant site for CO coordination. Hydride migration from Zr or external attack by hydride from DIBAH leads to the formation of a formyl that is then reduced by the aluminum hydride species (81). The steps for chain propagation and termination are outlined below. Since the exact nature of the Zr and A1 species is unknown in these steps, they are represented by (Zr) and (Al), respectively. 

High coordination number hydrides are not uncommon seven-, eight- and nine-coordinate hydrides so far seem to have been found only in pentagonal biprismatic, dodecahedral and tricapped trigonal prismatic geometries, respectively. 

Nevertheless, the hydrides or alkyls preferentially crystallize as pentaco-ordinate species, due to the strong frans-effect of the coordinated hydride or alkyl. RhMe(OEP), e.g., has been crystallized from n-hexane/dichloromethane solutions in the presence of I-Meim [172] (path o blocked ). 

The carbonyl is readily converted into the five-coordinate hydride ... 

A simple example of this reaction is provided by the addition of H-Bcat to the zero oxidation state complex, Os(CO)2(PPh3)3, to form (l)4 (see Scheme 1). (1) has mutually trans phosphine ligands and is coordinatively saturated. In contrast, H-Bcat addition to RuHCl(CO)(PPh3)3, which presumably reacts via the five-coordinate hydride, RuHCl(CO)(PPh3)2, and is accompanied by dihydrogen loss, yields the coordinatively unsaturated Beat complex, Ru(Bcat)Cl(CO)(PPh3>2 (2).5 A variety of related boranes react in the same manner and an example is provided by compound (3). To access the... 

The two established pathways for transition metal-catalyzed alkene isomerization are the jr-allyl metal hydride and the metal hydride addition-elimination mechanisms. The metal hydride addition-elimination mechanism is the more common pathway for transition metal-catalyzed isomerization. In this mechanism, free alkene coordinates to a metal hydride species. Subsequent insertion into the metal-hydride bond yields a metal alkyl. Formation of a secondary metal alkyl followed by y3-elimination yields isomerized alkene and regenerates the metal hydride. The jr-allylhydride mechanism is the less commonly found pathway for alkene isomerization. Oxidative addition of an activated allylic C-H bond to the metal yields a jr-allyl metal hydride. Transfer of the coordinated hydride to the opposite end of the allyl group yields isomerized alkene. 

Furthermore, the unusually high stability of these Ir(in) hydrido-thiophene complexes allowed some interesting studies to be carried out, involving the transformation of the coordinated thiophene through intramolecular migration of a coordinated hydride to the C=C bond (Eq. 2.6). This led to a particularly rare example of the mild homogeneous hydrogenation of thiophene to tetrahydrothiophene described in detail in Chapter 3. 

Upon interaction of the Jt-basic metal fragment (W(Tp)(NO)(L/) with L (L = Melm or PMe3 L = benzene, acetaldehyde, acetone, ethyl acetate, methyl formate, and N,N-dimethylformamide) stable [W(Tp)(NO)(PMe3)(r]2-L)] complexes formed. When the tungsten fragment is combined with a carboxylic acid, oxidative addition yields the seven-coordinate hydride complex [W(Tp)(NO)(H)(PMe3)C(=0)R] (Fig. 2.43).108... 

Fig. 2.43. Synthesis of the seven-coordinate hydride complex [W(Tp)(NO)(H)-(PMe3)C(=0)R],...

The carbonyl can be readily converted into the 5-coordinate hydride fro i-IrCl(CO)(PPh3)2 g IrCl(CO)2(PPh3)2 - f- .IrH(CO)2(PPli3)2... 

The five-coordinate hydride-dihydrogen complex [OsH(T)2-H2) (CO)(P Pr3)2]BF4 acting as a template for the carbon-carbon coupling between methyl propiolate and 1,1-diphenyl-2-propyn-l-ol... 

Treatment at room temperature of tetrahydrofuran solutions of 1 with NaHS affords the five coordinate hydride-metallothiol derivative RuH(SH)(CO)(P Pr3)2 (17), which reacts with acetylenedicarboxylic methyl ester by insertion of the carbon-carbon triple bond of the alk5me into the S-H bond of 17 (Scheme 5) [14]. In the resulting monothio-P-diketonato complex 18, the hydride ligand lies trans to the sulfur atom. In toluene at room temperature, complex 18 is unstable and evolves into the isomer 19 after 15 min. This compound contains the hydride ligand trans to the oxygen atom of the chelate group. 

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