Mono complexes anionic adducts

Titanium imido complexes supported by amidinate ligands form an interesting and well-investigated class of early transition metal amidinato complexes. Metathetical reactions between the readily accessible titanium imide precursors Ti( = NR)Cl2(py)3 with lithium amidinates according to Scheme 84 afforded either terminal or bridging imido complexes depending on the steiic bulk of the amidinate anion. In solution, the mononuclear bis(pyridine) adducts exist in temperature-dependent, dynamic equilibrium with their mono(pyiidine) homologs and free pyridine. 

By the stepwise thermal decomposition of the tris chelate, mono adducts of the type [NiX2(N—N)] (X = halides, NCS) were obtained.852-854 These complexes are polynuclear six-coordinate with bridging anions. In the thiocyanato derivative the nickel atoms are ferromagnetically coupled. 

Monoanionic boratabenzene ligands are isoelectronic to cyclopentadienide anion and can be nsed to synthesize Zr equivalent metallocenes (eqnation 29). A more congested complex of 9-phenyl-9-borata-anthracene (C 1-synunetry) was obtained by a similar way. Mono and bis boratabenzene complexes can also be prepared by reaction of a nentral boratabenzene-PMes adduct with tetrabenzyl zirconium or hafnium. Boratabenzene ansa metallocenes with CH2-CH2 or Si(CH3)2 bridges as well as Cp-boratabenzene mixed complexes or CG complexes were synthesized. 

Tantalum enolate chemistry shows the dichotomy for the carbonylation reaction " of Cp Ta(CH2R)Cl3 with CO which results in the mono-THF adduct of rj -acyl complex Cp Ta(0=CCH2R)Cl3(THF) for R = t-Bu (the acyl group is anionic) but the isomeric enolate Cp Ta((Z)-7j -OCH=CHR)Cl3 for R = p-Tol. This invites the question of the relative thermodynamic stabilities of metal complexes of RCH2CO and RCHCHO and additionally the question of Z vs. E enolate stabilities. Only for organometalhc compounds (X = [M]) do we find examples where RCH2COX is less stable than RCH=CHOX. 

Ozonolysis of the corresponding meso-precursor 18 [97] gave the dialdehyde also as a complex mixture of isomeric forms, from which tandem aldolization with FruA expectedly delivered a non symmetrical, bisfuranoid undecodiulose 19 as the sole product which was isolated in 25% yield [56]. No intermediary mono adduct could be detected by t.l.c. from which follows that, no matter which of the enantiotopic aldehyde groups was attacked first, the second addition step must be kinetically faster, most likely due to steric reasons and the presence of anionic charge in the intermediates. 

Double deprotonation of the bifunctional mono-CpH/alcohol racemic ligand linked by the 2,6-pyridyl unit followed by salt metathesis with ZrGL yielded the ansa-Cp/oxo zirconium dichloride complex 555, but with the concomitant formation of the undesired complex 556 incorporating the mono-anionic form of the ligand and the simple adduct of the neutral ligand and Z1CI4 0 (Scheme 126). The latter two undesired species have been structurally characterized however, complex 555 obtained forms an insoluble oligomeric species after the loss of THF upon purification. 

Titanium-Carbon a-Bonded Complexes. A full report of the mono- and di-nuclear anionic derivatives of MeTiXj (X = Cl or Br) has now been published, together with a discussion of the structure of MeTiClj in the solid state, and a brief report of both O2 and SO2 insertions into Ti—C bonds. Pb(CH=CH2)4 reacts with TiQ (1 1) to form (CH2=CH)TiQ3. This purple compound is less stable than MeTiCl3 and decomposes rapidly at temperatures above — 30°C however, 1 2 THF and 1 1 dimethoxyethane adducts may be prepared, and these moisture-sensitive green solids are more thermally stable than the parent compound. The observed thermal decomposition products of (CH2=CH)TiCl3, ethylene, butadiene, and a little acetylene, are more consistent with a mechanism involving homolytic fission of the Ti-vinyl bond than with p-elimination. Wolfsberg-Helmholtz calculations have... 

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