Fluxionality in Solution

Combined1H and 13 C NMR studies indicate that several of the above-mentioned processes may occur simultaneously within a single molecule (442-444). In some instances the solvent appears to have an influence on which dynamic processes predominate under a particular set of conditions (58). 

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The volatile, air-sensitive Hquid species (CH3)2AlB3Hg and (CH3)2GaB3Hg are prepared by the direct reaction of the corresponding main group metal hahde and salts of the [B3Hg] ion, in the absence of solvent (178). The reaction of (CH3)2AlB3Hg and A1(BH 3 results in the species (BH 2AlB3Hg. These small metallaboranes are fluxional in solution and have limited thermal stability at room temperature. 

The structure of MeIn(C5H5B-Me)2 has been explored, and it has been determined to be fluxional in solution on the NMR time scale, with average C2V symmetry.29 An X-ray crystallographic investigation has revealed soft structural parameters of the indium-ring coordination, consistent with the solution studies. 

Although the boron atoms in B9CI9 are not equivalent (three B atoms are of connectivity four, and six atoms of connectivity five), the 11B NMR spectrum shows only one signal. This indicates that the compound is fluxional in solutions making all boron atoms on the NMR time scale equivalent [138]. 

Reduction of the pentaalkyl-1,5-dicarba-closo-pentaboranes(5) 44 with elemental K opens the cluster and subsequent reaction with I2 enforces oxidative fusion of two C2B3 units to give a C4B6 cage (Scheme 3.2-36). The peralkylated hexaboraadamantane derivatives 70 (R = Me, Et X-ray structure analysis for R = Me [89]) rearrange irreversibly into the carboranes 71 with a wido-C4B6 framework [89] (X-ray structural analysis for R = Et [90]). The structure of the nido-C Bf, cluster is fluxional in solution [91]. 

Several types of 1,2,4-triphospholide transition metal complexes are known, that is complexes with f/ -coordination of P-1 (in rare cases of P-4) to one or two metal centers and sometimes additional f/ -coordination of the remaining four ring members, as well as with f/ -coordination and sometimes additional f/ -coordination of P-1 and P-2 <94CCR1,95CCR20i>. f/ -Complexes are fluxional in solution as the metal atom undergoes an intramolecular shift between P-1 and P-2. The structural consequences of two bonding modes (1, 2) for f/ -complexes are mentioned in Section 4.22.2.2, molecular structures of four examples are found in Table 6. 

These two clusters are both diamagnetic derivatives of formally M" " metals, but they have very different structures and spectroscopic properties. The Cu Sn9 ion has a centered Cu atom in a D3h - type Sn9 cluster however, the solid-state structure has only approximate C2v symmetry [44]. Regardless, the complex is fluxional in solution giving a single Sn resonance at — 1,440 ppm with J( Sn-" Sn) = 85 Hz. The remarkable feature of the spectrum is the well-resolved coupling to the quadrupolar Cu atom ( Cu, 69.1% abund., I = 3/2 ... 

The yttrium compound with LiR gave the crystalline [Y(44) CH(SiMe3)2 ] or the oily CH2SiMe3 analogue From the latter and benzene, or the chloride and LiPh, the product was 67 Reduction of the Y or Lu chloride with KCg in toluene/diethyl ether in the presence of naphthalene, 2-MeC]oH7 or anthracene gave crystalline [ Ln(44) 2-(p-ri" r " -CioH7R)] (R = H orMe) or Ln(44) 2(p-r il -Ci4Hio)], which were fluxional in solution. 

The reaction of [W(CN)814 with H2 at 400 °C was reported to give a green-black product of composition l W CN ]. Recently the same reaction has been shown to give [W(CN)7H]4, and in the presence of base the following equilibrium is established,261 as depicted in equation (14). [W(CN)7]5 can also be prepared directly from [W2Cl9]3- with an excess of cyanide. The sharpness of the 13C NMR lines suggests that on the NMR time scale there is no exchange of coordinated cyanide and that both structures are fluxional in solution. 

Protonation of the series [Mo(CNR)2(dppe)2] (Section 36.2.2.1.2) gives the seven-coordinate hydrides [MoH(CNR)2(dppe)2]+ which, like their carbonyl analogues (Section 36.2.4.1.1), are fluxional in solution with the hydride moving between face-capping sites in an octahedral structure.71... 

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