Aryloxide compounds

In THF, monomeric RMgX (I) and R2Mg (II) co-exist over a wide concentration range for the chlorides, bromides and iodides. The fluorides are present as the F-bridged dimers across the whole concentration range. Similarly, the alkoxide and aryloxide compounds, RMgOR, are present as the R2Mg(/r-OR )2Mg species in THF. 

TABLE 8. Selected H and NMR data for magnesium alkoxide and aryloxide compounds... 

Aryloxide compounds of T1(I) without Tl-C bonds, also dimerize. Thus, 2,4,6-tris(trifluoromethyl)phenoxide, TIOC6H2(CF3)3, is a dimer, 109, with identical but longer Tl-0 bonds in a four-membered TI2O2 ring [336]. 

Mixed halo, aryloxide compounds are sometimes obtained either by control of the stoichiometry and reaction conditions or by the use of sterically demanding aryloxide ligands (Eqs 6.21 °° and 6.22 ). 

The homoleptic metal dialkylamides are an important class of compounds in inorganic chemistry. They are typically synthesized by treatment of the corresponding halide with lithium or sodium dialkylamide. Although involving an extra synthetic step, there are numerous examples where metal dialkylamide intermediates are useful in the synthesis of metal aryloxide compounds. The reaction normally involves the simple addition of the parent phenol to the metal dialkylamide in a nonprotic, typically hydrocarbon, solvent (Eqs 6.36, 6.37, and 6.38 ). 

The elimination of H2 by addition of phenolic reagents to metal hydrides is an excellent method for the synthesis of alkali metal aryloxide compounds (Eqs 6.54, ° 6.55, and 6.56 ). 

When one begins to consider structural parameters (and indeed chemistry) of later d-block metal aryloxides one is confronted with a different situation. This is highlighted by the values of Ao,c calculated for later transition metal alkyl, aryloxide compounds (Table 6.4). It can be seen that values range from close to zero to positive numbers, Le. in some compounds the M-OAr bond lengths exceed M-C(alkyl) bond lengths This is a dramatically different picture from that seen for early transition metal compounds. 

The relative rates of the insertion reaction were found to be CS2 > SCO > CO2 with Cr > W. The substitution compounds [M(CO)4(L)(OAr)] were found to undergo insertion of CO2 much more slowly than the parent carbonyl with L = P(OMe)3 > PMc3 > PPh3 and in this case W > Cr. It was argued there was a steric inhibition of the insertion reaction. It was also found that the more bulky aryloxide compound [W(CO)5(OC6H3Ph2-2,6)] did not react with CO2 but would cleanly form the thiocarbonate (S-bound) with SCO. " The mechanism of these reactions is believed to... 

Ruthenium chemistry typically finds aryloxide ligands attached to the metal in low oxidation states. The extensive number of carbonyl aryloxide compounds reported for this metal exemplifies this (Table 6.34). The cluster compound [(H)2Ru6(CO)i6(M2-0-f -C6H4)] and derivatives contain the metallated phenoxide bridging two metal centres as well as -bound to another. 

Despite steric hindrance, all monomeric aryloxide compounds reported to date have readily formed Lewis acid-base complexes, in which the aluminum is four-coordinate [106, 109, 110]. For their intrinsic attractive features, sterically hindered three-coordinate aluminum aryloxides have been developed and subsequently used as Lewis acid catalysts for stereo-, regio-, and chemo-selective carbon-carbon bond-forming reactions [111]. Compared with classical Lewis acids, these aluminum reagents coordinate strongly with various oxygen-containing substrates, and this coordination is affected by the steric environment of then-ligands. 

The general formula for boric acid esters is B(OR)2. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7] ethyl borate [130-46-9J, and phenyl borate [1095-03-0] respectively. Some of the most common boric acid esters used in industrial appHcations are Hsted in Table 1. The nomenclature in the boric acid ester series can be confusing. The lUPAC committee on boron chemistry has suggested using trialkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older Hterature as boron alkoxides and aryloxides. CycHc boric acid esters, which are trimeric derivatives of metaboric acid (HBO2), are known as boroxines (1). 

The stereochemistry of Mg and the heavier alkaline earth metals is more flexible than that of Be and, in addition to occasional compounds which feature low coordination numbers (2, 3 and 4), there are many examples of 6, 8 and 12 coordination, some with 7, 9 or 10 coordination, and even some with coordination numbers as high as 22 or 24, as in SrCdn, BaCdn and (Ca, Sr or Ba)Zni3. " Strontium is 5-coordinate on the hemisolvate [Sr(OC6H2Bu3)2(thf)3]. jthf which features a distorted trigonal bipyramidal structure with the two aryloxides in equatorial positions. ... 

A hither facet of research has involved the structural characterisation of aluminium complexes which incorporate polydentate salen-type ligands. These have been noted in both neutral and monocationic (ion-separated) contexts (the latter requiring that the metal centre be stabilised by an external Lewis base) [35]. While such charged systems are invariably mononuclear the same is only usually true of their neutral analogues by virtue of the sterically demanding bis(aryloxide), chelating ligand. In the context of these latter complexes, dimerisation has been noted [251] while, more recently, the employment of flexible alkyl chains between two salen-coordinated aluminium ions has enabled the observation of dinuclear compounds [160, 161]. 

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