Hydrides mixed valence

The A-frame hydride [Pt2H2(/i-H)(/i-dppm)2] undergoes reductive elimination of H2 in the presence of tertiary phosphine ligands, L, to give the platinum(I) dimer, [Pt2HL(//-dppm)2]. Hill and Puddephatt have shown that this occurs via the intermediate [Pt2II2(/i-H)L(//-dppm)2] (14).99 Carbon monoxide reacts rapidly and reversibly with [PtH(/r-PP)2Pt(CO)]+, PP = R2P-CH2-PR2, R = Et or Ph, to give [PtH(/i-PP)2Pt(CO)2]+ and [PtH(CO)(/u-PP)2Pt(CO)2]+, the first reported mixed valence, platinum(0)-platinum(ll) complexes.100... 

Re(jj -C6H6)Cp] is a sandwich complex and (147) is a bent metallocene like ReCp2H. Protonation of several of the reported complexes gives new Re hydrides, and complex [Re(jj -C6H6)Cp] has a remarkable chemistry in this respect. Compound (149) can be considered as a Re-Re bonded mixed valency d" -d species. Double-bond hydrogenation also occurs, for example, with (148). 

We propose the unusual mixed-valence, semi-hydride-bridged Rh(I)/Rh(III) structure for 13rr due to the considerable difference in chemical shifts between the two halves of the complex. The resonances centered at 60 and 75 ppm have... 

Other unique properties are encountered at high H/Yb ratios. Bischof et al. (1983) prepared pure YbH2 55 at 300°C and 120atm, and point out that the unusually large lattice constant (see fig. 8) does not fit the rare-earth pattern and implies the coexistence of both Yb and Yb+ in the lattice. This constitutes the first occurrence of mixed valence in a rare-earth hydride. Accompanying optical emission measurements showed the material to be metallic, implying an unusual homogeneously mixed valence. 

Additional areas of lanthanide halide chemistry that have been reviewed include the synthesis, phase studies, and structures of complex lanthanide halides - compounds formed between one or more group 1 cation and lanthanide element halides (Meyer 1982). Halides in combination with lanthanide elements in the II, III, and IV oxidation states were considered with the chemistry of the heavier halides being emphasized. More recently the reduced ternary lanthanide halides (Meyer 1983) and the reduced halides of the lanthanide elements were reviewed (Meyer 1988). The latter review considered lanthanides in which the formal oxidation state of the cation was 2 and included hydride halides, oxide halides, mixed-valence ternary halides, and reduced halide clusters. Corbett et al. (1987) discussed the structures and some bonding aspects of highly reduced lanthanide halides and compounds stabilized by a second-period element bound within each cluster, e.g., SC7CIJ2B, SC5CI5B, YjCljC. 

An interesting deoxygenation of ketones takes place on treatment with low valence state titanium. Reagents prepared by treatment of titanium trichloride in tetrahydrofuran with lithium aluminum hydride [205], with potassium [206], with magnesium [207], or in dimethoxyethane with lithium [206] or zinc-copper couple [206,209] convert ketones to alkenes formed by coupling of the ketone carbon skeleton at the carbonyl carbon. Diisopropyl ketone thus gave tetraisopropylethylene (yield 37%) [206], and cyclic and aromatic ketones afforded much better yields of symmetrical or mixed coupled products [206,207,209]. The formation of the alkene may be preceded by pinacol coupling. In some cases a pinacol was actually isolated and reduced by low valence state titanium to the alkene [206] (p. 118). 

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