Arylimido niobium(V) complexes: mononuclear and dendritic derivatives (original) (raw)
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Carbosilane dendrimers containing peripheral cyclopentadienyl niobium- and tantalum-imido complexes
Journal of Organometallic Chemistry, 2006
Anilines Gn-{(C 6 H 4 )N(SiMe 3 ) 2 } m , based on simple or dendritic carbosilanes, have been used to synthesized (imido)tantalum compounds Gn-{(C 6 H 4 )NTaCl 2 Cp * } m (1, n = 0, m = 1; 2, n = 1, m = 4; Cp * = g 5 -C 5 Me 5 ), by the reaction with [TaCl 4 Cp * ] and elimination of SiMe 3 Cl. (Imido)niobocene compounds of general formula Gn-fðC 6 H 4 ÞNNbClCp 0 2 g m (3-5; n = 0, 1, 2; m = 1, 4, 8, respectively) have been readily prepared from their corresponding half-sandwich complexes Gn-{(C 6 H 4 )NNbCl 2 Cp 0 } m by the reaction with m equiv. of LiCp 0 (Cp 0 = g 5 -C 5 H 4 SiMe 3 ). Compounds 1-5 are all found to be exceedingly moisture sensitive, and in the case of the (imido)niobocene materials the hydrolytic reaction selectively leads to the formation of ½NbClðOÞCp 0 2 (6). The molecular structure of 6 has been determined by X-ray diffraction studies.
Polyhedron, 2005
Reactions of the magnesium imides [Mg(NAr)(THF)] 6 (Ar = 2,6-Me 2 C 6 H 3 , 1a; Ph, 1b) with [NbCp Cl Cl 4 ] (Cp Cl = g 5 -C 5 H 4 (SiMe 2 Cl)) afforded the imido complexes [NbCp Cl Cl 2 (NAr)] (Ar = 2,6-Me 2 C 6 H 3 , 2a; Ph, 2b) in good yield. Compound 2a reacted with excess LiNH(2,6-Me 2 C 6 H 3 ) to give the silyl-g-amido complex [Nb(g 5 -C 5 H 4 SiMe 2 -g 1 -NAr)Cl(NAr)] (Ar = 2,6-Me 2 C 6 H 3 , 3a). Hydrolysis of the Si-Cl bond of compounds 2a and 2b yielded the dinuclear complexes [{NbCl 2 (NAr)} 2 {(g 5 -C 5 H 4 SiMe 2 ) 2 (l-O)}] (Ar = 2,6-Me 2 C 6 H 3 , 4a; Ph, 4b), respectively. All of the new compounds reported were characterized by NMR spectroscopy and the molecular structure of 3a was determined by X-ray diffraction methods.
ACS Omega
Reactions of Nb(NAr)(NC t Bu 2) 3 (3a, Ar = 2,6-Me 2 C 6 H 3) with 1.0, 2.0, or 3.0 equiv of Ar′OH (Ar′ = 2,6-i Pr 2 C 6 H 3) afforded Nb(NAr)(NC t Bu 2) 2 (OAr′), Nb-(NAr)(NC t Bu 2)(OAr′) 2 , or Nb(NAr)(OAr′) 3 , respectively (at 25°C), whereas the reaction with 2.0 equiv of 2,6-t Bu 2 C 6 H 3 OH afforded Nb(NAr)(NC t Bu 2) 2 (O-2,6-t Bu 2 C 6 H 3) upon heating (70°C) without the formation of bis(phenoxide) and the reaction of 3a with 2.0 equiv of 2,4,6-Me 3 C 6 H 2 OH afforded Nb(NAr)(NC t Bu 2)(O-2,4,6-Me 3 C 6 H 2) 2 (HNC t Bu 2). Similar reactions of 3a with 1.0 equiv of (CF 3) 3 COH or 2.0 equiv of (CF 3) 2 CHOH afforded Nb(NAr)(NC t Bu 2) 2 [OC(CF 3) 3 ](HNC t Bu 2) or Nb-(NAr)(NC t Bu 2)[OCH(CF 3) 2 ] 2 (HNC t Bu 2), respectively. On the basis of their structural analyses and the reaction chemistry, it was suggested that these reactions proceeded via coordination of phenol (alcohol) to Nb and the subsequent proton (hydrogen) transfer to the ketimide (NC t Bu 2) ligand. The reaction of Nb(NAr)(NC t Bu 2) 2 (OAr′) with 1.0 equiv of 2,4,6-Me 3 C 6 H 2 OH gave the disproportionation products Nb(NAr)(NC t Bu 2)(OAr′) 2 and Nb(NAr)(NC t Bu 2)(O-2,4,6-Me 3 C 6 H 2) 2 (HNC t Bu 2) with 1:1 ratio, clearly indicating the presence of the above mechanism and the fast equilibrium (between the ketimide and the phenoxide). The reaction of 3a with 1.0 or 2.0 equiv of C 6 F 5 OH afforded Nb(N C t Bu 2) 2 (OC 6 F 5) 3 (HNC t Bu 2) as the sole isolated product, which was formed from once generated Nb(NAr)(N C t Bu 2) 2 (OC 6 F 5)(HNC t Bu 2) by treating with C 6 F 5 OH.
Journal of Organometallic Chemistry, 1999
The imido niobium complexes [Nb(NAr)Cl 3 (dme)] (Ar= C 6 H 4 Me-4 (1), C 6 H 4 OMe-4 (2)) have been prepared and characterised. The half-sandwich complex [Nb(NBu t)CpCl 2 ] (3) (Cp = h 5-C 5 H 5) has been synthesised by a new method via the reaction of NaCp and [Nb(NBu t)Cl 3 (py) 2 ] and in a similar manner the novel complex [Nb(NC 6 H 4 Me-4)CpCl 2 ] (4) was prepared by the reaction of NaCp with 1. The preparation of [Nb(NBu t)Cp%Cl 2 ] (5) (Cp%=h 5-C 5 H 4 SiMe 3) yielded an essentially inseparable mixture of 5 and [Nb(NBu t)Cp% 2 Cl] (6). The imido niobocene(V) complex 6 was prepared and isolated as the unique product by a new synthetic pathway via the reaction of two equivalents of LiCp% and [Nb(NBu t)Cl 3 (py) 2 ] and in a similar manner the novel complexes [Nb(NAr)Cp% 2 Cl] (Ar =C 6 H 4 Me-4 (7), C 6 H 4 OMe-4 (8)) were prepared. The molecular structure of 8 has been determined by X-ray diffraction studies. The mixed metallocene complex [Nb(NBu t)CpCp%Cl] (9) was prepared by the reaction of Li(C 5 H 4 SiMe 3) and 3. The alkylation of 6-8 by ClMgCH 2 CH CH 2 yielded the h 1-allyl complexes [Nb(NR)Cp% 2 (CH 2 CH CH 2)] (R =Bu t (10), C 6 H 4 Me-4 (11), C 6 H 4 OMe-4 (12)).
1,4-Diaza-1,3-diene niobium chlorides: syntheses and X-ray crystal structures of (t-Bu-DAD)NbCl3(THF), (t-Bu-DAD)2NbCl, and (t-Bu-DAD)NbCl4
Polyhedron, 2002
The new 1,4-diaza-1,3-diene niobium complexes (t-Bu-DAD)NbCl 3 (THF) (2) and (t-Bu-DAD) 2 NbCl (3) [t-Bu-DAD (t-Bu)N CHCH N(t-Bu)] have been prepared in 75-82% isolated yields by replacing of two or four chlorine atoms of NbCl 5 by the sterically demanding t-Bu-DAD ligand. In addition, we also describe the ionic Nb(V) complex [(t-Bu-DAD)NbCl 4 ](H 3 Nt-Bu) (6) which was formed as a byproduct during the preparation of 2. The new compounds have been characterized in solution by NMR measurements as well as by X-ray analyses in solid state. The structural parameters within the t-Bu-DAD ligand of 6 are in agreement with a chelating enediamido dianion. On the other hand the N C and C C bond distances of the t-Bu-DAD ligand of 2 are rather comparable to those found in complexes having a radical-anionic t-Bu-DAD ligand. The higher steric crowding at the niobium center caused by two 1,4-diaza-1,3-diene ligands in 3 leads to a significant asymmetric distortion of the 1,3-diaza-2-niobacyclopent-4-ene rings. However, none of the 1,4-diaza-1,3-diene ligands of 2, 3 or 6 is coordinated in the sterically less demanding p2-C,N bonding mode as found in the binuclear complex (t-Bu-DAD) 5 Nb 2 (4).
Journal of Organometallic Chemistry, 2006
The hydridoirida-β-diketone [IrH{[PPh 2 (o-C 6 H 4 CO)] 2 H}Cl] (1) reacts with silver salts of potentially coordinating anions such as tosylate ( -OTs) or triflate ( -OTf) to afford the mononuclear neutral derivatives [IrH{[PPh 2 (o-C 6 H 4 CO)] 2 H}(X)] [X = OTs (2), OTf (3)]. In acetone solution the triflate anion in 3 is displaced by the solvent to afford the cationic complex [IrH{[PPh 2 (o-C 6 H 4 CO)] 2 H}(acetone)]OTf (4), which is stable only in acetone solution. The reaction of 1 with halide scavengers containing less coordinating anions such as PF 6 or BF 4 results in the formation of cationic compounds [{IrH[{PPh 2 (o-C 6 H 4 CO)} 2 H]} 2 (µ-Cl)]A [A = BF 4 (5), PF 6 (6)] containing a dinuclear species with a single chlorine atom bridging two hydridoirida-β-diketone fragments. Both fragments are magnetically non-equivalent and the acylphosphane groups in each hydridoirida-β-diketone fragment are chemically equivalent. This species undergoes a fluxional [a]
Dalton Transactions, 2005
Treatment of the allyl-containing compounds Me 2 Si(CH 2 CH=CH 2 ) 2 and MeSi(CH 2 CH=CH 2 ) 3 with thioacetic acid in the presence of AIBN gave Me 2 Si[(CH 2 ) 3 SC(O)CH 3 ] 2 and MeSi[(CH 2 ) 3 SC(O)CH 3 ] 3 , respectively, which were reduced with LiAlH 4 to the dithiols Me 2 Si[(CH 2 ) 3 SH] 2 (3) and MeSi[(CH 2 ) 3 SH] 3 (4). This protocol was applied to the first and second generations of the doubly and triply-branched carbosilane allyl dendrimers, Si[(CH 2 ) 3 SiMe(CH 2 -CH=CH 2 ) 2 ] 4 (G(1) allyl-8 ), Si[(CH 2 ) 3 SiMe{(CH 2 ) 3 SiMe(CH 2 CH=CH 2 ) 2 } 2 ] 4 (G(2) allyl-16 ), Si[(CH 2 ) 3 Si(CH 2 CH=CH 2 ) 3 ] 4 (G(1) allyl-12 ), and Si[(CH 2 ) 3 Si{(CH 2 ) 3 Si(CH 2 CH=CH 2 ) 3 } 3 ] 4 (G(2) allyl-36 ) to give the corresponding SH functionalised surface dendrimers Si[(CH 2 ) 3 SiMe(CH 2 CH 2 CH 2 SH) 2 ] 4 (G(1) SH-8 ), G(2) SH-16 , G(1) , and G(2) . Reactions of 3 with [M(acac)(diolefin)] (M = Rh, Ir; diolefin = 1,5-cyclooctadiene, 2,5-norbornadiene) gave the compounds of the type [M 2 (l-Me 2 Si[(CH 2 ) 3 S] 2 )(diolefin) 2 ] n . These diolefin complexes are octanuclear (n = 4) in solution while the complex [Rh 2 (l-Me 2 Si[(CH 2 ) 3 S] 2 )(cod) 2 ] n (5) is tetranuclear in the solid state. The structure of 5, solved by X-ray diffraction methods, consists of a 20-membered metallomacrocycle formed by two dimethylbis(propylthiolate)silane moieties bridging four fragments Rh(cod) in a l 2 fashion through the sulfur atoms. Treatment of [Rh(acac)(CO) 2 ] with 3 gave [Rh 2 (l-Me 2 Si[(CH 2 ) 3 S] 2 )(CO) 4 ] n , which is a mixture of tetra (n = 2) and octanuclear (n = 4) complexes in a 2 : 1 ratio in solution, while the related complex [Rh 2 (l-Me 2 Si[(CH 2 ) 3 S] 2 )(CO) 2 (PPh 3 ) 2 ] 2 is tetranuclear. Reactions of [Rh(acac)(L-L)] (L-L = cod, (CO) 2 , (CO)(PPh 3 )) with 4 and the dendrimers G(1) SH-8 , G(2) SH-16 , and G(1) SH-12 , gave microcrystalline solids of formulae [Rh 3 (MeSi[(CH 2 ) 3 S] 3 )(L-L) 3 ] n , [Si[(CH 2 ) 3 SiMe{(CH 2 ) 3 SRh(cod)} 2 ] 4 ] n ([G(1) Rh(cod)-8 ] n ), [Si[(CH 2 ) 3 Si{(CH 2 ) 3 SRh(cod)} 3 ] 4 ] n ([G(1) Rh(cod)-12 ] n ), etc., which presumably are tridimensional coordination polymers. 3 0 9 2 D a l t o n T r a n s . , 2 0 0 5 , 3 0 9 2 -3 1 0 0 T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
Sandwich and Half‐Sandwich (Imido)niobium Complexes
European Journal of Inorganic Chemistry, 2003
This review discusses the study we have carried out towards the synthesis, structure and reactivity of (imido)niobium complexes, which contain at least one cyclopentadienyl ligand. The following families of niobium complexes are described: (i) half‐sandwich imido complexes; (ii) metallocene imido compounds; (iii) imido complexes containing ansa‐cyclopentadienyl ligands; (iv) dinuclear imido complexes such as [{Nb(η5‐C5H4SiMe3)2Cl}2(μ‐1,3‐N2C6H4)]. In addition we describe spectroscopic and structural features of the (imido)niobium complexes. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)
Synthesis and reactivity of alkynyl niobocene complexes
Journal of Organometallic Chemistry, 2003
The synthesis of alkynyl containing niobocene complexes with differing auxiliary ligands is described. The niobium(III) derivatives of the general formula [Nb(h 5 -C 5 H 4 SiMe 3 ) 2 (C Å/CR)(L)] where L is either carbonyl, phosphine, phosphite, or isocyanide, were prepared by the reaction of the bis(alkynyl)magnesium reagent with the corresponding cloro-niobocene precursor. In a similar manner the niobium(V) imido compounds, of the general formula, [Nb( Ä/NR?)(h 5 -C 5 H 4 Rƒ) 2 (CÅ/CR)], were prepared. The characterization of these complexes is discussed. The reactivity of the alkynyl compounds towards oxidation and protonation has been studied. #