Propargyl complexes with platinum

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... 

The reactions with tertiary amines or phosphines that have no active hydrogen atoms result in platinacyclobutene cations, a rare species for late transition metal (Scheme 39). Substituted carbanions are added to the jj -aUenyl/propargyl platinum complex to yield the neutral substituted- ) -TMM derivatives that undergo huther [3 + 2] cycloaddition with good tt-acids as TCNE or maleic anhydride to produce highly substituted cyclopentanoids (Schemes 40, 41). 

Reverse processes, that is reactions of propargyl or allenylidene ligands coordinated to mononuclear centers with water, methanol, amines, and other ligands are known. Tungsten l and platinum complexes give a series of reactions (some of which are mediated by surfaces) comparable with those discussed for clusters. 

Equation (46)). The reaction involves coordination of the G=G triple bond to the PRO) center as the ratedetermining step. The //<3 / .s -chloro(propargyl)platinum complex 184 is equilibrated with the allenyl complex 185... 

Oh and coworkers successively developed a series of highly efficient methods for the construction of various types of fused polycyclic heterocycles from enynals with a pendant unsaturated bond [72]. Enynals with a benzyloxy substituent at the propargylic position 155 were successfully cyclized via platinum-catalyzed Huisgen-type cycloaddition to form polycyclic Pt-carbene complex intermediate 156, which undergo insertion into a C-H bond to afford various types of fused polycyclic heterocycles 157 (Scheme 12.68) [73]. 

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