Aryl complexes stability

A distorted butterfly CU4 unit with Cu-Cu distances less than 240 pm is found for (4-methyl-2-cupriobenzyl)dimethylamine tetramers . Copper aryl complexes stabilized by the amine nitrogen lone pair are prepared from CuBr and the appropriate aryllithium reagent in ether in 40-60% yields... 

Iron(II) alkyl anions fFe(Por)R (R = Me, t-Bu) do not insert CO directly, but do upon one-electron oxidation to Fe(Por)R to give the acyl species Fe(Por)C(0)R, which can in turn be reduced to the iron(II) acyl Fe(Por)C(0)R]. This process competes with homolysis of Fe(Por)R, and the resulting iron(II) porphyrin is stabilized by formation of the carbonyl complex Fe(Por)(CO). Benzyl and phenyl iron(III) complexes do not insert CO, with the former undergoing decomposition and the latter forming a six-coordinate adduct, [Fe(Por)(Ph)(CO) upon reduction to iron(ll). The failure of Fe(Por)Ph to insert CO was attributed to the stronger Fe—C bond in the aryl complexes. The electrochemistry of the iron(lll) acyl complexes Fe(Por)C(0)R was investigated as part of this study, and showed two reversible reductions (to Fe(ll) and Fe(l) acyl complexes, formally) and one irreversible oxidation process."" ... 

Examples of silver(l) alkyl and alkenyl (including aryl) complexes have been known from as early as 1941 6-9 however, the number of examples is fairly limited with respect to that of the heavier congeners, copper(l) and gold(l). Such a phenomenon can readily be attributed to the relatively low stability of this class of complexes, both photochemically and thermally. Simple homoleptic alkyl and alkenyl complexes of silver(i) are known to be very unstable under ambient temperature and light, and successful isolation of this class is fairly limited and mainly confined to those involving perfluoroorganics.10 The structures and the metal-carbon bond-dissociation energies for... 

In an effort to impart selectivity and enhance complex stability for this class of anion receptor novel ditopic biscobaltocenium receptor molecules (Fig. 42) have been synthesized and their coordination and electrochemical properties have been studied (Beer et al., 1993f, 1995h). The two positively charged metallocene centres linked by various alkyl, aryl and calix[4]arene spacers... 

The most common route to alkyl or aryl complexes of the type [AuRL] is by the treatment of a halide complex with an alkyl- or aryllithium reagent. The first reactions of this type were performed (15) in 1959 [Eq. (5)], and the methyl and phenyl compounds were found to have chemical and thermal stabilities intermediate between those of the previously known organopalladium and -platinum complexes. 

The products of oxidative addition of acyl chlorides and alkyl halides to various tertiary phosphine complexes of rhodium(I) and iridium(I) are discussed. Features of interest include (1) an equilibrium between a five-coordinate acetylrhodium(III) cation and its six-coordinate methyl(carbonyl) isomer which is established at an intermediate rate on the NMR time scale at room temperature, and (2) a solvent-dependent secondary- to normal-alkyl-group isomerization in octahedral al-kyliridium(III) complexes. The chemistry of monomeric, tertiary phosphine-stabilized hydroxoplatinum(II) complexes is reviewed, with emphasis on their conversion into hydrido -alkyl or -aryl complexes. Evidence for an electronic cis-PtP bond-weakening influence is presented. 

A study has been made of the reactivity of high-oxidation state tantalum-alkylidene complexes stabilized by the aryldiamine ligand [C6H3(CH2NMe2)2-2, 6] , and an unusual rearrangement involving the unique activation of an aryl C—H bond by the alkylidenetantalum moiety has been observed.531... 

Sulfur dioxide insertion with the aryl complexes also proceeds initially to the corresponding 0-sulfinates. A moderate p value of —4.3 is to be compared with p = —1.87 for SO2 insertion into the Sn—R bonds of MeaSnR (51,52). It reflects some stabilization by the substituent X of the positive charge developing on the ring during the reaction. A transition state approximating (X) (or a corresponding closed structure), similar to the classical a complex of electrophilic aromatic substitution reactions (103), seems reasonable on this basis. 

Treatment of Ir(CO)Cl(PPh3)2 (29) with alkyl or aryl grignard reagents produces the corresponding alkyl or aryl iridium complexes R-Ir(CO)(PPh3)2 (63). These compounds are substantially more stable than the frilly phosphinated alkyl iridium compounds. The stability of these compounds also increases in the order aryl > alkyl with the fluoro substituted aryl complexes being the most stable. 

Oxo ligands help to stabilize high oxidation state alkyl complexes. Some 0x0 alkyl and aryl complexes of osmium(VI) can be prepared from OSO4. A mesityl complex,... 

Bis-amido tin porphyrins trans (TTP)Sn(N(R)Ph)2 (R = H, Ph) and cis (TTP)Sn(l,2-(NH)2C6H4) have been prepared and shown to be more stable than the analogous Sn—C bonded alkyl or aryl complexes. The increased stability of these nitrogen bound ligands is probably a function of their increased basicity. ... 

Amidolithium complexes of type RR NLi (e.g. R and R = alkyl, aryl, silyl) exhibit a fascinating structural diversity as above, bulky amido ligands are essential for complex stabilization. Planar Li2N2-rings are common structural units, and these appear in a variety of laddered structures which may be polymeric or discrete molecular as in [ BuHNLijgj (Figure 10.10). 

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