Platinum complexes vinylidenes

Quite recently, a platinum(II) vinylidene complex was reported. Its synthesis was accomplished by reaction of Pt(PPh3)2(CH3)(CCR) with triflic acid and tetrafluoroboric acid, respectively, to give the resulting cationic Pt(II) complex. (CH3)(PPh3)2Pt(=C= CHR)]+ X- (X = BF4-. Cp3S03-). ° No data on the catalytic activity of this complex, which has not been isolated but whose structure has been proven by NMR experiments, have been reported so far. 

The phthalocyanine containing polymer films were electrochemically investigated for their electrochromic reductions and reoxidations [406,411]. Under irradiation the reduction of O2 to water was studied in photoelectrochemical cells [407,409,412]. Especially Zn(II)-phthalocyanine in poly(vinylidene fluoride) shows high cathodic photocurrents. Also the electrochemical carbox dioxide and proton reduction by Co(II)-phthalocyanines in a low concentration monomolecular in a polyvinylpyridine matrix were investigated as part of a photoenergy systems [413,414]. As an active catalyst for proton reduction also a bipyridyl platinum complex in a polymer Nafion membrane was found [415]. In order to construct such a photochemical energy conversion system, the research in this field was extended for the electrocatalytic water oxidation to O2 [416-419]. The Ru-complexes cj5-[Ru(bpy)2Cl2] and especially Ru-red ([(NHsjs Ru >-Ru(NH3)4-0-Ru(NH3)5] ) are active as electrocatalysts. 

The conventional vinylidene complex could be isolated when the hydroxyl group was protected as the tetrahydropyranyl ether derivative reaction of this with acid immediately gave the cyclic carbene complex, even under mild conditions. The reaction is related to the formation of similar nickel(II)- and platinum(IV)-carbene complexes from the [Pg.71]

The reaction with 4-pentyn-l-ol gave only [Fe t/2-CH2=C(CH2)30) (CO)2(t/-C5H5)]+, and 3-hexyn-l-ol afforded (64, R = Et) (84) no evidence for the participation of the vinylidene tautomers was found. With ruthenium (45) and platinum (47) complexes, on the other hand, rearrangement to the vinylidene is faster than internal attack on the >/2-alkyne, and only the cyclic carbene complex is formed. 

The isolation of stable vinylidene complexes and elucidation of many of their reactions have given substance to speculations concerning their intermediacy in many reactions. Indeed, the reactions of many alkynes with a series of platinum(II) complexes were explained several years ago by considering the formation of metal-stabilized carbonium ions as nonisolable intermediates (10). Summarized below are several reactions that may reasonably be assumed to proceed via vinylidene complexes. 

They may be readily transformed to r] -aUcynyl and vinylidene complexes. The coupling of two ) -alkynyl ligands results in platinacyclopentadiene species." A platinum(II) disilyl( -alkyne) undergoes insertion (see Insertion) and reductive elimination (see Reductive Elimination) to disilacyclohexene (Scheme 31)." Metal-diaUcynyls can also play jr-donors to form the coordination complexes of various configurations, as shown in (10-13) and so on." Such a,tt-bridging modes may have interconversion. Multi- aUcynyl complexes can even constitute clusters or higher-order stractures. ... 

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