Edmond Samuel

Homogeneous Catalytic Hydrosilylation of Pyridines

The color change from yellow to violet allows the formation of the intermediate [Cp2 Ti(SiHMePh)(pyridine)] to be monitored in the reaction of PhMeSiH2 with a pyridine in the presence of the precatalyst [Cp2 TiMe2 ] [Eq. (a)]; the hydride [Cp2 TiH] is postulated to be the key intermediate in the catalytic cycle. The regioselective hydrosilylation of pyridine and also substituted pyridines can be catalyzed by the titanocene [Cp2 TiMe2 ]. R=Me, CO2 Et.

Characterisation by infrared of π- and σ-bonding in metal—indenyl complexes: A study of mercury, tin and palladium derivatives

Abstract Synthesis of the new indenyl compound, Ind 2 Hg as well as IndHgX (X = CI, Br), is described. Although their structure could not yet be elucidated from NMR measurements, a comparison of their IR spectra with those of π-indenyl complexes shows that in the CH stretching and deformation regions, the presence of some characteristic bands indicates a σ-metal-to-carbon bonding. Another new indenyl compound (IndPdCl) 2 is also described. Preliminary IR and NMR measurements do not allow the nature of palladium-indenyl bonding to be determined with certainty.

Homogen katalysierte Hydrosilylierung von Pyridinen

Anhand des Farbwechsels von Gelb zu Violett last sich die Bildung der Zwischenstufe [Cp2Ti(SiHMePh)(Pyridin)] bei der Reaktion von PhMeSiH2 mit einem Pyridin in Gegenwart der Katalysatorvorstufe [Cp2TiMe2] verfolgen [Gl. (a)]; als Schlusselintermediat im Katalysecyclus wird das Hydrid [Cp2TiH] diskutiert. Mit dem Titanocen [Cp2TiMe2] kann die regioselektive Hydrosilylierung von Pyridinen katalysiert werden, die auch substituiert sein konnen. R=Me, COOEt.

Substituent effects in cyclopentadienyl derivatives of titanium and zirconium

Abstract Study of ring-substituted π-cyclopentadienyl dichlorides of Ti and Zr shows that the metal-to-ring and metal-to-chloride bonds are sensitive to the donor and acceptor character of the substituent. The preparation of new compounds is reported, namely Cp(Ind)TiCl 2 (I), (IndH 4 )TiCl 3 (II) and the oxides [(IndH 4 )TiCl 2 ] 2 O (III) and [(IndH 4 )TiClO] 4 (IV) derived from (II), and their NMR spectra are given. The previously reported ABC spectrum of the C 5 ring protons in [(IndH 4 ) 2 ZrCl] 2 O (V) is further confirmed by spin decoupling experiments. The nonequivalent environments of these protons is suggested as a possible explanation of their peculiar NMR behaviour.

Phosphine complexes of Ti(III) and Zr(III): detection in solution by EPR/electrochemical methods☆

Abstract A comparative study by EPR is made on the electrolytic reduction of Cp 2 MX 2 , Cp 2 M(CH 3 ) 2 , (Cp = η 5 -C 5 H 5 , cyclopentadienyl ligand; M = Ti, Zr; X = Cl, Br) and Ind 2 Ti(CH 3 ) 2 (Ind = η 5 -C 9 H 7 , indenyl ligand) in the presence of phosphines. In the case dihalides, the monohalo(phosphines) were characterized. In the case of the dimethyl compounds, Cp 2 M(CH 3 )(PMe 3 ) and Ind 2 Ti(CH 3 )(PMe 3 ) were identified at 230 K from their EPR spectra. At room temperature and for M = Ti, intramolecular rearrangement takes place to yield the presumably chelated dimethylphosphinomethyl compound Cp 2 Ti(III)CH 2 PMe 2 while Ind 2 Ti(CH 3 )(PMe 3 ) remains stable.

Photo-degradation studies on Di-η5-Cyclopentadienyldimethylvanadium, Di-η5-Cyclopentadienylmethylvanadium, Di-η5-Cyclopentadienyldimethylniobium, and some deuterated analogs

Abstract The photolysis of alkyl metallocene derivatives of vanadium and niobium in hydrocarbon solvents results in cleavage of the carbon—metal σ-bond. In the cases of (η 5 -C 5 H 5 ) 2 VCH 3 and (η 5 -C 5 H 5 ) 2 Nb(CH 3 ) 2 , only methane (>99%) is produced photochemically. (η 5 -C 5 H 5 ) 2 V(CH 3 ) 2 , prepared on a convenient new synthesis from (η 5 -C 5 H 5 ) 2 VCl 2 and methyllithium in toluene, degrades under photochemical conditions to yield both methane and ethane in a 2 : 1 ratio. The ethane arises from intra- and intermolecular methyl dimerization. Deuterium labeling studies have shown that the methyl group, the cyclopentadienyl ring, and the solvent are all sources of hydrogen in the formation of methane in these photolyses. The extent to which each source participates in the hydrogen abstraction process cannot be quantitatively determined because of the influence of an isotope effect. Chemical reactions with carbon monoxide during the photolyses give low yields of (η 5 -C 5 H 5 )V(CO) 4 from (η 5 -C 5 H 5 ) 2 VCH 3 or (η 5 -C 5 H 5 ) 2 V(CH 3 ) 2 , and of (η 5 -C 5 H 5 ) 2 Nb(CO)CH 3 from (η 5 -C 5 H 5 ) 2 Nb(CH 3 ) 2 .

Photocatalytic homogeneous hydrogenation of olefins with alkyltitanocene compounds

Abstract Dialkyltitanocene compounds, (η 5 -C 5 H 5 ) 2 TiR 2 (R = CH 3 ; CH 2 C 6 H 5 ; C 6 H 5 ), when photolyzed under hydrogen are efficient catalyst precursors for the hydrogenation of linear and cyclic olefins under mild conditions (25°C; 1 atm). With R = CH 3 and CH 2 C 6 H 5 hydrogenation is photocatalytic whereas with R = C 6 H 5 it is photoassisted. The latter precursor selectively hydrogenates linear dienes to monoenes. These catalytic reactions are suspected to proceed by light-induced homolytic cleavage of titaniumcarbon bonds. Formation of Ti 3+ species in significant proportions was revealed by ESR.

The formation and molecular structure of bis(η5-cyclopentadienyl)bis(pentafluorophenyl)-vinylenevanadium: an acetylene derivative of vanadocene

A reaction between vanadocene and bis(pentafluorophenyl)acetylene in benzene solution has produced the title compound, (η 5 -C 5 H 5 ) 2 V[η 2 -C 2 (C 6 F 5 ) 2 ], in 66% yield. The product has been characterized by infrared, mass spectral, and electron spin resonance data, as well as by a single crystal X-ray diffraction study. The compound crystallizes in the monoclinic space group C 2/ c with a = 11.961(6), b = 10.010(5), c = 16.670(8) A, β = 98.42(5)°, and ρ calc = 1.81 g cm -3 for Z = 4. Least-squares refinement based on 984 observed reflections led to an R value of 0.039. The molecule resides on a crystallographic two-fold axis. The VC(η 2 ) bond length is 2.077(5) A, while the VC(η 5 ) distances range from 2.268(6) to 2.291(5) A and average 2.282(8) A. Within the acetylenic ligand the CC length is 1.269(9) A, and the CCC(C 6 F 5 ) angle is 142.3(4)°.

Cyclization of phenylpropiolic acid on titanocene. Synthesis and molecular structure of di-η5-cyclopentadienyl(cinnamylato-C3,O)titanium/phenylpropiolic acid (1/1), a novel titanacycle. Synthesis of dicyclopentadienylbis(phenylpropiolato)titanium

Dimethyltitanocene reacts with phenylpropiolic acid under hydrogen and with the assistance of light to yield the dark red titanium(IV) compound [{Ti(η5-C5H5)2C6H5CCH-COO}·C6H5CCCOOH]. X-ray structure analysis showed the unit cell to be composed of a titanocene metallacycle in which titanium is η5-bonded to two cyclopentadienyl rings and to one carbon and one oxygen atom in a 5-membered metallacycle, the whole molecule being in a 1/1 hydrogen bonded association with phenylpropiolic acid. The complex crystallizes in the monoclinic space group P21/c with unit cell parameters a 12.435(4), b 13.046(4), c 14.326(5) A, β 92.50(4)°, and Dc 1.34 g cm−3 for Z = 4. Least-squares refinement based on 1812 independent observed reflections led to a final R value of 0.079. Reaction of dimethyltitanocene with phenylpropiolic acid in toluene gives the compound [(η5-C5H5)2Ti(OOC-CC-C6H5)2] as an air stable orange crystalline solid.

Metal-ligand vibration frequencies in π- and σ-indenyl- and cyclopentadienyl-metal complexes

Abstract The Raman and infrared spectra of π-indenyl complexes of Fe and Ru and of σ-indenyl complexes of Hg have been examined in the low-frequency region, and a tentative assignment of the metal-to-ring and metal-to-carbon symmetrical stretching frequencies made. These are compared with the frequencies in the homologous cyclopentadienyl compounds, and the observed shifts in frequencies are discussed.