Alkyne complexes ruthenium porphyrins

The reactive (TPP)Rh in Scheme II is electrogenerated from l(TPP)Rh(L)d ci in the presence of an alkene or an alkyne. The formation of an intermediate is observed. This intermediate is not detected by chemical reaction methods and was tentatively assigned as a it complex(15). Similar it complexes have been reported for ruthenium porphyrin species(17 18). 

Aryl acetylenes undergo dimerization to give 1-aryl naphthalenes at 180 °C in the presence of ruthenium and rhodium porphyrin complexes. The reaction proceeds via a metal vinylidene intermediate, which undergoes [4 + 2]-cycloaddition vdth the same terminal alkyne or another internal alkyne, and then H migration and aromatization furnish naphthalene products [28] (Scheme 6.29). 

Enantioselective cyclopropanation is currently being explored. The ruthenium complex shown previously in Figure 7 also reacts with EDA and styrene to afford a transxis ratio of 4 1, with 46% ee of the trans isomer. The cis isomer is nearly racemic (<10% ee). The use of four-substituted stjrrene derivatives dramatically increases the diastereoisomeric excess of the trans isomer, with 4-fluorostyrene giving an 11 1 ratio, with 50% ee (74). Conversely, as shown in Figure 21, the porphyrin-like [RuCl(PNNP)]+ precatalyst reacts with EDA/ styrene to afford the cis isomer at a ratio of 10 1, with an enantiomeric excess of 87% (76). These types of ruthenium complexes have also been described as epoxi-dation catalysts above clearly there are mechanistic similarities between the oxo-and carbene- intermediates, which could help elucidate the reasons behind such variable enantioselectivity. Other ruthenium complexes that catalyze cyclopropanation include CpRu(II) catalysts, arene ruthenium complexes, and ruthenium-salen complexes. Cp Ru(cod)Cl is also known to catalyze the related reaction of diazo compounds with alkynes, affording the corresponding 1,3-diene (Figure 22) (77). 

Some general reviews relating to the chemistry of Ru/Os-r hydrocarbon complexes appear in the literature the reactivity of Ru-H bonds with alkenes and alkynes/ aspects of ruthenium/osmium vinylidene/allenylidene/cumul-enylidene complexes,equilibria of M-R/M=CR2/M=CR complexes, the organometallic chemistry of metal porphyrin complexes, and the reactions of [Os(P Pr3)2(CO)HGl], ruthenium pyrazoly I borate complexes,and metallabenzynes. Other reviews relate more to applications of some of the complexes outlined in this chapter. See, for example, metal vinylidenes in catalysis,the development of Grubbs-type alkene metathesis catalysts, applications of ruthenium/osmium carbene complexes in metathesis polymerization, and the role of Ru /V-hetero-cyclic carbene complexes in metathesis polymerization. ... 

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