Complex anions rotation

Treatment of 348 with Na[EIBEt3] has also been reported, affording initially the Pt(II) formyl complex anion [Tp PtMe C(0)H ] (355 ), as determined by 1EI and 13C NMR spectroscopic data that again reveal a chiral metal center. At 193 K two formyl environments (2 1 ratio) are apparent, which coalesce at 201 K. These are attributed to restricted rotation about the Pt—C linkage, and AG for conversion of the minor to major isomer was calculated at 8.8 kcal mol-1.120 Protonation of 355 affords exclusively the Pt(IV) formyl complex Tp PtMe C(0)H H (356), with no evidence for protonation of either pyrazole or the formyl, or... 

The arrangement of the groups around the central metal atom is governed by the size of the complex anion (X) and the relatively rigid geometry of the bulky 1 -substituted azaphospholene molecule, which limits rotation of the N-bonded... 

Rotation in inorganic compounds is necessarily confined to those structures in which discrete atomic groups are to be found among the structures so far discussed the ions NH4+, CN" and OH- are examples. There are, however, many other inorganic structures of greater complexity, notably the salts of the common oxy-acids, which contain complex anions and in which rotation of these anions about one or more axes is often observed. These structures are discussed in chapter 10. 

In their opinion the salts are largely dissociated even in comparatively concentrated solution, and the complex anion is unusually stable and subject but little to hydrolysis as the molecular rotation changes but little on dilution. They found the molecular rotation of these salts extraordinarily high. They were calculated on the basis of the water free simplest formulas. KBe,C H,OT = -f 225.3 NaB CgHjOj = -f 225.1 NH,Be,C,H,0, = + 241.7. 

The nucleophilicity of the sulphur in (toluene)Ct(CO)2(CS) has allowed adduction by Cr(CO)s. The oxidation of (hmb)M(CO)3 (M= Mo or W) by I2 has allowed the isolation of the complex ((hmb)H(CO)3l] and a series of polyhalometallate anions.The interaction of (arene)Cr(CO)3 with solvents has been examined using nmr spectroscopy. Particularly large upfield shifts are found for the aromatic hydrogens in aromatic solvents.Other nmr spectroscopic studies include the investigation of relaxation times for Mo, and O in (arene)Mo(CO)3 complexes and a nmr study of cyclophaneMo(CO)3 complexes.Intramolecular rotational processes have been examined by nmr in the (C5Et5 )M(CO) 2l< (I = CS or PR3) complexes. 

The X-ray structure of lithium l-(dimethylamido)boratabenzene, reported in 1993, provided the first crystallographic characterization of a transition metal-free boratabenzene (Scheme 13).18a The observed bond lengths are consistent with a delocalized anion and with significant B—N double-bond character. In a separate study, the B—N rotational barrier of [C5H5B—NMeBnjLi has been determined to be 10.1 kcal/mol, and it has been shown that TT-complexation to a transition metal can increase this barrier (e.g., 17.5 kcal/mol for (C5H5B-N(i-Pr)2)Mn(CO)3).24... 

The intermediate Jt-allyl complex is formally the palladium(II) complex of an allylic anion that can be represented by the two mesomeric forms shown in Scheme 17.2. It is important to note that this is not a fast equilibrium between two cr-allyl complexes but a stable species where palladium is simultaneously bound to both carbon-1 and carbon-3. All eight atoms of the Jt-allyl moiety are almost in the same plane. All three carbon atoms have sp2 character and the rotation between the Cl-C2 and C2-C3 bonds is blocked. As a consequence of the hindered rotation, four dia-stereomeric Jt-allyl complexes are possible. For example, in Scheme 17.2 both R and R are syn to the hydrogen on carbon-2, therefore this complex is called the syn,syn diastereomer. 

As seen from Scheme 7.2, the epoxy-ring cleavage and nickel oxidation proceed simultaneously. The nickel-oxygen bond is formed. This results in the formation of the carbon-nickel biradical in which Ph-CH fragment can rotate freely. The cleavage of the (NiO)-C bond leads to the formation of a mixture of styrenes. At early reaction stages (30 min), cis and trans olefins are formed in 50 50 ratio. After a prolonged contact (30 h), when all possible transformations should be completed, the trans isomer becomes the main product and cis trans ratio becomes 5 95. Such enrichment of the mixture with the trans isomer follows from the formation of the di-P-(trimethylsilyl)styrene anion-radical and its isomerization. The styrene formed interacts with an excess of the nickel complex. 

The carborane is bonded to the rhodium center via a thiolate anion and a bridging B-H-Rh bond. Complex 95 undergoes B-H/B-H-Rh interchange coupled with an apparent rotation of the Rh(COD)+ fragment. Variable temperature NMR spectra were recorded between 293 and 179 K. The apparent rotation of 1, 5-COD is found in a rather large number of Rh-complexes [152]. 

In earlier theoretical studies Shen and coworkers used Hartree-Fock self-consistent-field (HF) calculations with different basis sets to study water complexes of anionic ONO—O-30. Two stable ONO—O isomers, cis and trans, formed hydrogen bonds with H2O molecules at different positions. Second-order Mpller-Plesset perturbation theory (MP2) with a 6-311+G(d,p) basis set has also been applied to the study of ONO—O-, (H2O), (n = 1 or 2) complexes31. Koppenol and Klasinc studied the cis and trans conformers as well as the transition state for torsional motion of ONO—O- at the HF/6-31(d) level32. In their calculations, the trans conformer is slightly more stable than the cis form, and the rotational barrier was thought to be quite high. However, correlated methods (MP2) were also used to study this molecule, and they predict that the cis conformer is more stable than the trans conformer33,34. 

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