Jean-Claude Leblanc

Insertion of activated acetylenes into the metal-hydride bond of [(η5-C5H5)2M(CO)H] (M = Nb, Ta)

Abstract Reactions of [Cp 2 M(CO)H] (M = Nb, Ta; Cp = η 5 -C 5 H 5 ) with various acetylenes RCCR having electron-withdrawing groups were investigated. They give the σ-al- kenyl complexes [Cp 2 M(CO)(CRCHR)] via insertion of the alkyne into the MH bond. On the basis of 1 H and 19 F NMR data the reactions were shown to be: (i) regioselective, monosubstituted alkynes giving only the α-R metallated complex; (ii) stereoselective, exclusive formation of the Z -isomer being observed with hexafluorobut-2-yne. The Z isomer has been shown to exist as two conformers, the steric requirements of the ligands creating a barrier to rotation of the alkenyl group around the MC σ bond.

First NMR observation of 47Ti and 49Ti in cyclopentadienyl complexes

Abstract 47Ti and 49Ti NMR spectra of some mono and biscyclopentadienyl complexes are reported for the first time. The resonances span a relatively large range : electron donating substituents on the cyclopentadienyl ring causes an unexpected downfield shift.

Complexes derives du dichlorure de titanocene a pseudoasymetrie centrometallee

Abstract The tetrasubstituted derivatives: (η 5 -C 5 H 4 C ★ HMeC 6 H 5 ) 2 TiXY are prepared from the corresponding dichlorides. The three possible stereochemical arrangements of these complexes (two pseudoasymetric and a chiral form) are separated and identified. These stereostable compounds are convenient substrates for studying dynamic stereochemistry around a titanium atom.

Addition of Cr(CO)5 to the M(η2- S2) moiety of Cp2 M(S2H (Cp′ = tBuC5H4 : M = Ta; CpX = C5Me4Et: M = Nb) and crystal structures of Cp′2TaS2H · [Cr(CO)5]n (n = 1, 2)

Reaction of Cp′2TaS2H (Cp′ = tBuC5H4) or Cp2xNbS2H (Cpx = C5Me4Et) with an excess of Cr(CO)5THF gives the adducts Cp′2TaS2H · Cr(CO)5 1, Cp′2TaS2H · 2Cr(CO)5 2, and Cp2xNbS2H · Cr(CO)5 3 respectively. 1 and 2 are separated by fractional crystallisation. The crystal structures show the Cr(CO)5 fragment in 1 to be coordinated to the ‘outer’ sulfur, and in 2 both Cr(CO)5 fragments are coordinated to each sulfur of the S2 ligand in a trans fashion. In all cases approximate sp3 hybridisation of the S atoms is observed. The new compounds are thermally labile and give CO-free, trinuclear compounds of the type Cp4M2S4Cr upon heating their solutions.

Insertion d'heterocumulenes dans la liaison MH des complexes Cp2M(L)H (M = Nb et Ta; L = CO et PMe2Ph)

Abstract Various heterocumulenes RNCX (X = O, S, NR) insert readily into the MH bound of d 2 complexes [Cp 2 M(L)H](M = Nb, Ta and L = CO, PMe 2 Ph) to give the O -, S - or N -metallated derivatives [Cp 2 M(L)(η 1 -XCHNR)]. These products are photosensitive and by irradiation give quantitatively the heterometallacyclic compounds Cp 2 M(η 3 -XCHNR) by internal substitution of the L ligand.

The reaction of Cp2M(CO)H (M = Nb or Ta) complexes with acyl chlorides, a new way to transform acyl chlorides into aldehydes

Abstract Cp 2 M(CO)H complexes react immediately with acyl chlorides to give the chloro complexes Cp 2 M(CO)CL and aldehydes. This reaction can also be applied to dichlorides.

Comparative studies in the Cp2M(η2-S2) H series (Cp = t-BuC5H4,C5Me Et; M = Nb, Ta) on the reactivity of hydrie and disulfide ligands

Reactions of Cp′2Ta(S2)H(1;′ =t-BuC5H4)and CP2xNb(S2)H(2;Cpx =C5Me4Et) with S8, I2, CH3 and CH3I are investigated Sulfur insertion into the MH bond of1 results in the formation of Cp′3Ta3S12 and Cp′4Ta4S13, where structures are known by analogy, and Cp′6Ta8S17, which is characterised spectroscopically. Complex2 gives in the analogous reaction Cp3xNb3 S12 as the only product. This compound desulfurises in boiling decane to give Cp3xNb3S7 (8). An X-ray diffraction analysis of8 revealed an unusual M3S7 core containing four monosulfide and one trisulfide ligand. The polysulfide ligand is arranged in such a way that its inner sulfur atom is at the top of the molecule in a noncoordinating fashion. Whereas reaction of1 or2 with I2 gives spectroscopically characterised Cp′2Ta(S2)I and Cp2xNb(S2)I by an H/I exchange, only the reaction of1 with CH3I leads to well defined products. At 0°C [Cp′2Ta(S2CH3)H]I is formed as an intermediate product which converts into Cp′2Ta(=S)I at higher temperatures. The attack of CH3I at the disulfide ligand gives rise to the formation of a chiral sulfur site as inferred from 1H NMR data.

Reactivity studies on tantalocene(sulfido)hydride Cp′2Ta(S)H (Cp′= ButC5H4): cycloaddition on and protonation of the Ta=S ligand

Reactions of the tantalocene(sulfido)hydride Cp′2Ta(S)H with PhNCS and HCl exhibit a surprisingly low metal-hydride reactivity; the TaS bond being involved either in a [2 + 2] cycloaddition or a protonation.

Derives heterobimetalliques du tantale: Synthese des complexes (η5-C5H4R)2Ta(CO)(μ-H)MLn (M = Cr, Mo, W, Mn)

Abstract The monohydrides (η 5 -C 5 H 4 R) 2 Ta(CO)H (R = H, CMe 3 ) react as two electron donors towards the unsaturated (MLn) fragments Cr(CO) 5 , W(CO) 5 , Mo(CO) 5 and (η 5 -C 5 H 5 )Mn(CO) 2 and lead to the heteronuclear hydrogen-bridged complexes (η 5 -C 5 H 4 R) 2 Ta(CO)(μ-H)MLn.

Oxothiophosphoramides of niobocene or tantalocene as organometallic ligands: synthesis of heterobimetallic complexes [Cp2M(CO)(μ,η1: η1-PR2X)M′Ln] (M Nb or Ta; X O or S; M′ Cr Mo, W, Mn, Fe or Sn)

Abstract The phosphido complexes Cp 2 M(CO)(PR 2 ) (with M  Nb or Ta and R  Me or Ph) react with H 2 O 2 or S 8 , leading to the corresponding oxides and sulfides. The oxygen and the sulfur derivatives have similar reactivities towards organic electrophilic reagents such as MeI and MeCOCl. Unlike organometailic electrophilic species, the sulfur derivatives afford a new class of bimetallic complex [Cp 2 M(CO)(μ,η 1 :η 1 -PR 2 S)M′L n ] (M′L n  Cr(CO) 5 Mo(CO) 5 , W(CO) 5 , CpMn(CO) 2 or Fe(CO) 4 )). In contrast, the oxygen compounds react only with organometallic tin complexes such as Bu 3 SnCl. The crystallographic analyses of [Cp 2 Nb(CO)(PPh 2 SMe)]I and [Cp 2 Ta(CO)(μ,η 1 :η 1 - PMe 2 S)W(CO) 5 ] are reported and discussed.