Gastone Paiaro

The Organometallic Chemistry of Carbon Suboxide

Abstract Carbon suboxide, C3, O2, reacts with a great variety of organometallic compounds. With organo-silicon and aluminium compounds it reacts with the C˭O moiety, giving sililation and carboalumination reactions. Insertion reactions of C˭C are performed with compounds having M-H, M-OR, M-NR2, M-PR2 bonds (M ≠ Si, Al), giving mono-metal derivatives (ketenyl) or di-metal derivatives of acil groups (amides, esthers, phospides). The coordination of C˭O or C˭C to transition metal complexes, the formation of allenic compounds and the decarbonylation reactions allow the synthesis of a series of particular metal derivatives (ketenyl, ketenylidene and carbonyl complexes) which, in some cases, present a peculiar reactivity.

Chemical and structural characterization of some π-allylic derivatives of rhodium(III)

Abstract The reaction of rhodium trichloride trihydrate and trans, trans, trans-1,5,9-cyclo- dodecatriene in boiling ethanol yields the red, diamagnetic dichloro(cyclododeca-1,5-dienyl)rhodium(III), insoluble in all common organic solvents. This compound is polymeric through chlorine bridges and reacts with many Lewis bases (e.g., carbon monoxide, amines, olefins) to give octahedral derivatives such as C12H19RhCl12B2 (B is a monodentate basic ligand). The chemical and structural characterization of this compound is reported through a study of its derivatives by X-rays, IR and NMR spectra and a possible mechanism is proposed.

Carbon suboxide polymers

Abstract On the basis of pyrolysis and hydrolysis measurements, we propose for the polymers of carbon suboxide (prepared with cationic, anionic and radical initiators) a structure consisting of condensed rings of α and γ-pyrone units. On thermolysis the polymer gives CO and CO2 as the sole gaseous species, with a characteristic thermal spectral pattern. By titration with bases, at least two types of acid sites have been found: they are to be ascribed to α and γ-pyrones with different hydrolysis rates. Measurements of molecular weight by VPO, in water, on the polypyranonic derivative show 6–8 monomeric units per chain.

Reactivity of a platinum η1-formylketenyl complex synthesis of a platinum α-pyrone derivative via generation and trapping of a C3H2O2 species. 20

Abstract The formylketenyl platinum complex, trans -bis(tricyclohexylphosphine)(η 1 -formylketenyl)(hydride)platinum(II), trans -(PCy 3 ) 2 (H)Pt[η 1 -C(CHO)CO] ( 1 ), reacts with acids causing the cleavage of the PtC bond and generating the species C 3 H 2 O 2 which is trapped by an excess of 1 . The reaction gives rise to the formation of the addition product trans -(PCy 3 ) 2 (H)Pt(C 6 H 3 O 4 ), where C 6 H 3 O 4 is an α-pyrone ligand σ-bonded to Pt. The crystal structure of the Pt α-pyrone derivative has been determined. The crystal are monoclinic, space group P 2 1 / a , with a = 19.404(9), b = 11.889(6), c = 18.534(9), β = 91.3(1)°, Z = 4. The plane of the α-pyrone ligand is almost orthogonal to the coordination plane of Pt. IR, 1 H and 31 P NMR and mass spectra also support the structure.

Synthesis of a pyrone derivative from carbon suboxide and acetylacetone catalyzed by acetylacetonate-metal complexes

Abstract Bis(pentane-2,4-dionate)-metal, M(acac) 2 , (where M = Zn, Co, Ni and Cu) reacts quickly and in high yield with carbon suboxide, C 3 O 2 , at the methine position. The reaction produces 1:2 adducts which are insoluble in all organic solvents. The reaction of these adducts with aqueous HCl forms 5-acetyl-2-hydroxy-6-methyl-4-pyrone (AHMP). The above-mentioned metal-acetylacetonates also catalyze the addition of C 3 O 2 to free Hacac, but Cr(acac) 3 , Fe(acac) 3 and Mn(acac) 3 do not. The relative catalytic efficiency of these pentane-2,4-dionates was determined. A mechanism for these reactions is proposed.

Catalytic dimerisation of olefins by a cationic platinum(II) complex

The new complex [Pt(MeCN)4][(BF4)2] catalyses the dimerisation of branched olefinic monomers in nitromethane solution.

Reactions of some methoxydienylplatinum(II) complexes with carbon monoxide

Abstract Carbon monoxide reacts readily with methoxydienylplatinum(II) complexes, but carbonyl insertion into the α-PtC bonds does not occur; instead (chloro)(carbonyl) or (chloro)(methoxycarbonyl) complexes are formed, depending on the nature of the dienyl system.

[C2O2]+· ions of unusual structure

The structure of the C 2 O 2 +. ion, obtained by electron impact ionization of C 3 O 2 , is reported. A double-focusing instrument was used to carry out metastable ion and collisional spectroscopic studies. Comparison of the data showed that a C 2 O 2 +. species structurally different from those originating from other precursors is obtained by ionization of C 3 O 2 . A four-membered ring is proposed as the possible structure of the C 2 O 2 +. ion

Rhodium(III) complexes of (EEE)-1,5,9-cyclododecatriene. Syntheses, structures and absolute configurations of derivatives of catena-poly-[μ-dichloro-(1,2,12-η)-1,5,8 cyclododecatrienylrhodium]☆

Abstract The reaction of RhCl 3 ·3H 2 O with ( EEE )-1,5,9-cyclododecatriene in alcohols gives a red polymeric solid compound with chlorine bridges, 1 , in which the hydrocarbon moiety has been reported to be bonded to the metal via an η 3 -allylic bond. Re-examination of this reaction has led to the isolation of soluble derivatives obtained by breaking the chlorine bridges with chelating diphosphines and diamines. An X-ray analysis on single crystals of a diphosphino and a diamino derivative, indicates that the cyclo-olefin residue with composition C 12 H 17 has undergone isomerization. The two double bonds not involved in the bonding to the metal are 5,8 rather than 5,9.

Stereochemical pattern of phosphine oxidation by a peroxometallacyclic platinum complex. Evidence of an intramolecular process

Abstract The prochiral peroxometallacyclic ketenyl platinum complex [(PPh3)2 PtOOC(O)C CO] (1) reacts with (S)-(−)-α-methylbenzylamine to give the diastereomeric amidic derivatives, 2. One of the two possible diastereomers, 2a, has been obtained pure and the absolute configuration at the carbon atom σ-bonded to the metal is inferred from its CD spectrum. Compound 2a has been used to oxidize the chiral racemic phosphine (RS)-PPhCyPr using a molar ratio, PPhCyPr 2a = 2: 1. The reaction products contains an enantiomeric excess of (S)-(−)-OPPhCyPr whereas unreacted PPhCyPr shows the prevalent (S) configuration, indicating that the reaction occurred with asymmetric induction. These findings are rationalized by a mechanism based on the coordination to the metal of PPhCyPr mainly in the (R) configuration, followed by an intramolecular oxidation by the peroxide moiety.