Octahedral geometry adducts

Diketonate cobalt(III) complexes with alkyl peroxo adducts have been prepared recently and characterized structurally, and their value in hydrocarbon oxidation and olefin epoxidation examined.980 Compounds Co(acac) 2(L) (O O / - B u) with L = py, 4-Mepy and 1-Meim, as well as the analog of the first with dibenzoylmethane as the diketone, were prepared. A distorted octahedral geometry with the monodentates cis is consistently observed, and the Co—O bond distance for the peroxo ligand lies between 1.860(3) A and 1.879(2) A. 

The presence of /3-hydrogen in the nitroxide radical may lead to disproportionation reactions. In spin-trapping experiments, N-t-butyl-a-phenyl nitrone yields rather unstable spin adducts. This type of radical can be stabilized by coordination to Nin. The Ni11 complex with N-oxy-A-r-butyl-(2-pyridyl)phenylmethanamine (923) reveals a distorted octahedral geometry with antiferromagnetic interactions between the unpaired electrons of the metal ion and the radical spins.00... 

Porphyrin (8) and phthalocyanine complexes stabilize a square planar structure, probably as a result of extensive electron delocalization. Square planar complexes often give paramagnetic bis adducts with a Irans octahedral geometry. 

Tetrakis adducts of ammonia, [NiX2(NH3)4] (X = NCS,MS NO2646), have been reported with tetragonal octahedral geometry and Ni—N(NH2) bond lengths in the range 215-210 pm. 

Use of less basic triphenylsiloxide ligands also allowed the isolation of mononuclear complexes (Table 1) [46,47]. In addition to the silylamide route, anhydrous nitrates and isopropoxides were employed as synthetic precursors (Eqs. 1,2). The siloxide bridges in the solvent-free dimeric systems Ln2(OSiPh3)6 are readily disrupted by donor solvents like THF, OP Bu3 or DME. The m s-THF adducts of lanthanum, cerium (Fig. 5) and yttrium adopt an approximately /ac-octahedral geometry. 

Diels-Alder reaction of 2-bromoacrolein and cyclopentadiene using 10 mol% of titanium catalyst 74 gave the synthetically versatile (R)-bromoaldehyde adduct 75 in 94% yield, 67 1 exo. endo diastereoselectivity, and 93% ee. The absolute stereochemical outcome of the reaction is consistent with the proposed transition state assembly 76 in which the dienophile coordinates at the axial site of the metal, proximal to the indane moiety through Ji-attractive interactions. In this complex, the 7t-basic indole and the Ji-acidic dienophile can assume a parallel orientation facilitated by the octahedral geometry of the transition metal. The aldehyde would then react through a preferential s-cis conformation (Scheme 17.27).54... 

Diorganoantimony(V) halides form monomeric covalent adducts, R2SbX3 L, with various oxygen donor ligands (e.g. DMSO, HMPA, TPPO, PyO)91,97). An octahedral geometry has been proposed on the basis of infrared and H NMR spectral data. Out of the three possible geometrical isomers, the existence of the following isomer has been proposed ... 

Carbene adducts of the heavier pnictogen pentaflu-orides have been reported. Reaction of AsFs or SbFs with carbene (1) (R = Mes, R = Cl) in 1,3-bis(trifluoromethyl)benzene resulted in the isolation of(l) AsF5 (112) and (1) SbFs (113). The crystallographic analysis for (112) and (113) reveals the expected octahedral geometry at the pnictogen center with a long As C (2.009(5)A) and Sb-C (2.175(5)A) bond distance respectively. Recently, a novel hypervalent antimonide complex was reported. The nucleophihc addition of carbene (1) (R = Mes, R = H) to Sb(CF3)3 (equation 12) resulted in the... 

Other methods for its preparation invariably result in the isolation of Lewis base adducts. The complexes U(BH4)3(THF) t and U(BH4)3(18-crown-6) were prepared by the metathesis reaction of LiBH4 with UCl3(THF) , or UCl3(18-crown-6) in TFIF. Although the stoichiometry of the THF adduct was not characterized in the initial report, the compound was later prepared from the reaction of UH3 and BFls in THF, and characterized to be U(BH4)3(THF)3. The molecular structure of the compound reveals that it adopts an octahedral geometry about the metal center with the borohydride and THF ligands mutually facial all borohydride ligands are tridentate. 

The pyridine adduct (py)3ln(N3)3 (3) is monomeric in the solid state. The indium atom adopts mer-octahedral geometry. In pyridine, the IR absorption bands corresponding to azide stretch appear at 2,084, 2,068, and 2,055 cm Cl2lnN3(THF)2 (4) forms dimers in the solid state, with a planar In2N2 core. Azido groups occupy the bridging sites. The X-ray crystal structures of [(py)2Na][(py)2ln(N3)4] and (2,2, 2"-terpyridine)In(N3)2(02C(CH2)2CH20H) have also been reported. 

The nucleophilic carbene (112) has been shown to react with pnicogen pentafluorides (113a-c) to form adducts (114ac) with octahedral geometry at P (P N = 1.898 A), As (As-N = 1.999 A) and Sb (Sb-N = 2.175 A). The structures are therefore those of internal zwitterions with an imidazolium cation and a pnictogen anion. The strong nature of the bonds to the carbene... 

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