η²-Benzyne and η¹-benzylidene complexes of niobium with ancillary imido ligands

Abstract

Rare q2-benzyne and benzylidene complexes of niobium have been synthesised from [Nb(C5R5)(NR')C12] (R = H, Me; R' = 2,6-Pri2C6H3) via intermediate diphenyl and dibenzyl species and their molecular structures have been determined: these complexes are analogues of well-established zirconocene derivatives.Recently? we described a series of half-sandwich imido useful relationship since zirconocene reagents are widely complexes of niobium of the general type [Nb(C5R5)-exploited in organic synthesis2 and polymerisation ~atalysis.~ (NR')]C12] (R = H, Me; R' = 2,6-Pri2C6H3, But, Me),l and Herein, we report the synthesis and characterisation of rare noted the similarities between the shapes and energies of the examples of benzyne and benzylidene complexes of niobium frontier orbitals of the [Nb(CSRs)(NR')] fragment with those which are direct analogues of synthetically useful zirconocene of the bent metallocene unit [Zr(C5R5)2]. This is a potentially derivatives.

Non‐Innocent Behaviour of Imido Ligands in the Reactions of Silanes with Half‐Sandwich Imido Complexes of Nb and V: A Silane/Imido Coupling Route to Compounds with Nonclassical SiH Interactions

“…[14, 15,16] We then turned to the Cp/imido ligand set, which had proved to be isolobal with the Cp 2 ancillary, [1,17] …”

Synthesis and characterization of η5-cyclopentadienyl–silylallyl niobium and tantalum complexes

“…The typical spectral pattern of the allyldimethylsilyl group consists of two high field signals observed as one singlet for both equivalent silicon methyl groups and one doublet for the methylene silicon-bound group, together with three low field signals appearing as two doublets for the olefinic methylene group and one multiplet due to the internal olefinic proton. The ring proton resonances are shifted upfield for imido complexes (5)(6)(7)(8) compared with the tetrachloro niobium derivative 1, whereas the resonances due to SiMe 2 , Si-CH 2 and olefinic CH@CH 2 protons of the dimethylsilylallyl group are shifted low field, the Si-CH 2 being the most sensitive signals. These displacements are related to the stronger r-p-donating character of the imido ligand, causing the metal to require less electron density from the aromatic ring.…”

“…In this way, reaction of 1 with Li(C 5 unique component in 90% yield by a redistribution reaction when an equimolar mixture of 5 and 7 was heated in toluene at 120°C. The alkyl complexes 6-8 were isolated as waxy brown air sensitive solids, very soluble in all organic solvents including hexanes.…”

“…These results encouraged us to prepare similar group 5 metal derivatives, which would allow comparison of the nature of the metal-olefin interaction of the related d 0 and d 2 metal complexes. The weakly coordinating properties reported [3] for the dicyclopentadienyl [MCp 2 R 2 ] + cations, which are stabilized by strong a-agostic interactions [4], recommended the isolobal analogs [5][6][7][8], cyclopentadienyl imido compounds (a), as better models for d 0 , whereas the neutral dicyclopentadienyl metal(III) (b) derivatives were the most suitable models for d 2 species, as shown in Scheme 1. The results of these studies have been reported [9] separately.…”

Ligand Architecture on Stereocontrol of Half‐Metallocene Benzylidene Complexes of Tantalum

“…[5,7,9 -11,33 -35] We have demonstrated that half-metallocene-diene fragments of group 5 metals are isoelectronic and isolobal to metallocene fragments of group 4 metals. [36 -40] Figure 2 shows some typical alkylidene complexes of group 4 metals [41,42] and group 5 metals [43,44] with isoelectronic fragments. This review briefly describes our studies on the synthesis and characterization of benzylidene complexes of tantalum and their stereochemistry of the benzylidene moiety, which was tunable and was highly depending on the kinds of ancillary ligands such 1,3-butadiene (1), [45,46] 2,3-dimethyl-1,3-butadiene (6), [47] o-xylylene (7), [46] 1,4-diaryl-1,4-diaza-1,3-butadiene (8), [48] and 1,4-diaryl-1-aza-1,3-butadiene (9).…”