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The reaction of [ Cp 2 ∗ Nb ( Te 2 H ) ] (Cp∗ = η5-C5Me5) with [Pd(DBA)2] (DBA = dibenzylidenacetone) and dppm (bis(diphenylphosphanyl)methane) gave the new tetratelluropalladate cluster [ ( Cp 2 ∗ Nb ) 2 PdTe 4 ] (1), which has been characterised by means of elemental analysis, FD-MS and X-ray crystallography. The structure of compound 1 contains a planar PdTe4 rectangle to which two niobocene groups are coordinated. DFT calculations on the hypothetical [PdTe4]2− anion and comparison of the results with those of the W and Ni homologues show that the planar arrangement of Te ligands in 1 is due to the intrinsic property of the central Pd atom.

The reaction of [1,4-{SiMe3(H)N}2C6Me4] (1) with 2 equivalents of LiBun followed by the addition of SiMe3Cl gave the diamine compound [1,4-{(SiMe3)2N}2C6Me4] (2). [Ta(η5-C5H4SiMe3)Cl4] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η5-C5H4SiMe3)Cl2}2(μ-1,4-NC6Me4N)] (3), and mononuclear, [Ta(η5-C5H4SiMe3)Cl2{ NC6Me4-4-(N(SiMe3)2)}] (4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacuation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated from the reaction of [Ta(η5-C5H4SiMe3)Cl4] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-ray diffraction studies. [TaCl3(CH3CN)2{ NC6Me4-4-(N(SiMe3)2)}] (5) has been prepared by the reaction of one molar equivalent of TaCl5 with 2 in a CH3CN/CH2Cl2 solvent mixture. The synthesis of the niobium complexes, [{Nb(η5-C5H4SiMe3)Cl2}2(μ-1,4-NC6Me4N)] (6) and [Nb(η5-C5H4SiMe3)Cl2{ NC6Me4-4-(N(SiMe3)2)}] (7), was achieved in a similar manner to their tantalum analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or lithium dimethylamide, has been studied and the following compounds prepared:[Nb(η5-C5H4SiMe3)RCl{ NC6Me4-4-(N(SiMe3)2)}] (R = η5-C5H4SiMe3 (8), PhC(NSiMe3)2 (9), NMe2 (10)). In an attempt to form the hetero bimetallic complex, [{Nb(η5-C5H4SiMe3)Cl2}(μ-1,4-NC6Me4N){Ta(η5-C5H4SiMe3)Cl2}] (11), the reaction of 7 with [Ta(η5-C5H4SiMe3)Cl4] has been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3 and 6.

Reaction of various neutral LXH bidentate ligands (2-aminobenzoic acid, acetylacetone, dibenzoylmethan and 2-aminobenzenethiol) with [Cp′2TaH2]+, obtained in situ from Cp′2TaH3 treated with triphenylmethan cation, affords after dihydrogen elimination the corresponding cationic species [Cp′2Ta(H)(LX)]+ in BF4 or PF6 salts. Complexes [Cp′2TaH(η2-O2CC6H4-o-NH2O,O′)]PF6 (3), {Cp′2Ta[η2-OC(Me)CHC(Me)OO,O′]}BF4 (4a), {Cp′2TaH[η2-OC(Ph)CHC(Ph)OO,O′]}BF4 (4b) and [Cp′2TaH(η2-SC6H4-o-NH2S,N)]PF6 (5) are characterised by analytical and spectroscopic methods. With thiopyridine, the kinetic (6) and the thermodynamic (6′) isomers [Cp′2TaH(η2-2-SC5H4NS,N)]PF6 are identified. Crystal structures are reported for complexes 3, 5 and 6′.

The reaction of [Cp*2NbCl2] (Cp*=η5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*2Nb(O)H] (1), the new compound [Cp*2Nb(O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*2Nb(O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*2Nb(O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η1-S-thiocarbamato (3) or η1-O-carbamato ligand (4) along with a terminal NbO group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*2NbH{OC(O)NPh}] (5) along with some 4. The molecular structure of 5 contains a niobocene unit comprising η2-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the NbO group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess PhNCO gave a mixture of heterocycles (PhNCO)2 (6) and (PhNCO)3 (7) in the approximate ratio 3:2. By contrast, the reaction of [Cp*2Nb(O)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7.

The syntheses of ferrocenyl phosphines with bulky substituents are reported using the reaction between FeCl2 and the suitably substituted cyclopentadienyl salts, LiC5H3-1,3-(PPh2)2, LiC5H3-1-PPh2-3- t Bu, LiC5H2-1,2-(PPh2)2-4- t Bu. This strategy leads to bi-, tri- and tetraphosphines, which cannot be obtained by the other access paths used to prepare substituted ferrocenes. [C5H3-1,3(PPh2)2](C5H5)Fe, [C5H3-1-PPh2-3- t Bu]2Fe racemic and meso and [C5H2-1,2-(PPh2)2-4- t Bu](C5H5)Fe have been characterized by single-crystal X-ray diffraction studies. © 2000 Elsevier Science S.A. All rights reserved.

The reaction of [Pd(η3-C4H7)]CF3SO3 (η3-C4H7=η3-2-MeC3H4) (1), prepared in situ by reaction of [Pd(η3-C4H7)Cl]2 with AgCF3SO3, with various thionate ligands, gives new polymeric complexes formulated as [Pd(η3-C4H7)(RS)]n (2) [RS=pyS (pyridine-2-thionate)], im(Me)S(imidazole-3-methyl-2-thionate) (3), pm(Me)2S (pyrimidine-4,6-dimethyl-2-thionate) (4). A solution of 4 contaminated with KCF3SO3 evolves to give crystals that correspond to a new polymeric species whose X-ray crystal molecular structure indicates the presence of cationic infinite chains built of trinuclear units, [Pd3(η3-C4H7)3{pm(Me)2S}2]+ (5). Finally, the formation of a mononuclear thionate-containing palladium complex [Pd{pm(Me)2S}2] (6) occurs from a solution of 5 after prolonged periods. An X-ray crystal structure determination indicates a square-planar disposition of two thionate ligands around the Pd atom. The different complexes were characterized by spectroscopic techniques.

The trihydrides Cp2MH3 (M  Nb, Ta) react with chlorophosphines PR2Cl (R  Me, Ph) affording phosphonium salts [Cp2MH2(PR2H)]+, Cl− (2 (a, b) 2′ (a, b)). Depending on the metal (Nb or Ta) and on the nature of the phosphine substituent (Me or Ph), deprotonation of these salts leads to hydride phosphino Cp2MH(PR2H) (3 (a, b) 3′a) or hydrided phosphido Cp2 TaH2(PPh2) (4′b) metalloligands. These two kinds of complexes are able to bind [M′(CO)5] or [M′(CO)4] (M′  Cr, Mo, W) organometallic fragments to give mono- or di-bridged heterobimetallic systems. The crystallographic analysis of Cp2Ta(H)(μ-H)(μ-PMe2)Cr(CO)4 (7′aCr) is reported and discussed.

Irradiation of Cp 2 ∗ Nb(η 2 S 2 )H (Cp ∗ = C 5 Me 5 ) 1a in the presence of Fe(CO) 5 gives the CO-free complex [Cp 2 ∗ NbS 2 ] 2 Fe 2a . The core of 2a contains an FeS 4 tetrahedron which is ligated by two niobocene ligands as shown by X-ray diffraction analysis. In the reaction of 1a or Cp 2 x Nb(η 2 S 2 )H (CP x = C 5 Me 4 Et) 1b with Co 2 (CO) 8 , compounds 3a and 3b of the same type are formed. Electrochemical studies of 2a and 3a,b show that they undergo three reversible 1e − steps. The oxidation of 3b exerts a considerable influence on its absorption spectrum. A qualitative EHMO analysis is in agreement with a strong delocalisation of electron density over the whole NbS 2 MS 2 Nb system.

Reactions of complexation of tetraazamacrocycles L with Group 6 metal carbonyls [M(CO)6](M = Cr, Mo, or W) lead to [LM(CO)4], [LM(CO)3] or [LM(CO)2] entities, depending both on the size of the macrocycle and on the metal M. The structure of one representative complex [(permethylcyclam)Mo(CO)4] has been determined by X-ray diffraction (permethylcyclam: 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane).

(η6-Benzamide)tricarbonylchromium and tricarbonyl(η6-phenylacetamide)chromium (1 and 2) have been synthesized from the corresponding amides and chromium hexacarbonyl. Decalin, a mixture of decalin and butyl acetate, and neat butyl acetate have been used as the reaction media. The first system gave best yields. Both amide complexes form adducts with non-complexed molecules of the type [(CO3)CrL] · L through hydrogen bonds, suggested on the basis of 1H and 13C NMR spectroscopy. Similar associations by hydrogen bonds exist in the solid state structure of 3 and 4. The π-donor-acceptor abilities of the substituents on the rings are discussed on the basis of geometrical parameters and 13C NMR data.