Orthometallation

Orthoferrites Ortho isomer Orthometallation Orthomumetal Orthonol... 

Other notable examples are the orthometallation (orthophenylatioti) reactions of many complexes of aryl phosphines (PAr3) and aryl phosphites P(OAr)3 with platinum metals in pailiculai, e,g, ... 

It is interesting to notice that the complex 58 is also able to react with soft donor hgands such as triphenylphosphine resulting in the formation in very mild conditions of the unexpected orthometallated complex 59 (Scheme 23) [89,91, 92]. The ligand here is linked to the metal through both an aromatic and an ylidic carbon. Other transformations are realized from 58 leading, including the compounds of the previous scheme, to four different structures for the bis-ylide (i) C,C-chelate (ii) C,C-orthometallated (iii) C,C-orthometallated and free ylide (iv) C,C,C-terdentate (Scheme 23). 

The most frequently reported mixed C/N-donor ligands are the 2-phenylpyridine anion, ppy (170), orthometalated 2,2 -bipyridine, C3N bpy (171), and derivatives, for example (172). 

Palladium(II) complexes containing orthometalated chiral amines such as those shown in Figure 7 are useful reagents ... 

Figure 7 Palladium(II) complexes containing orthometalated chiral amines.

Scheme 3. (i) Orthometallation (ii) CF3C=CCF3 insertion (iii) CO insertion (iv) ring closure and N-protonation. 

Diarylthioketones are converted in good yields into orthometallated complexes by diiron enneacarbonyl.141 These in turn can be transformed oxidatively (Ce4+) or photochemically into isobenzothiophenes (see Section IV,C,2), or by reaction with mercuric trifluoroacetate into isobenzofurans (Scheme 78)142 the formation of methoxy esters is a competing process in... 

Diaryl thioketones are converted by diiron enneacarbonyl into products of orthometallation.141 Oxidative or photochemically induced deligation of these complexes provides an unusual and valuable synthetic entry into compounds in the uncommon isobenzothiophene category142,151 (Scheme 84). Moreover, the photochemical procedure provides the novel complex, (tetracyanoethylene)tetracarbonyl iron. The orthometallated complexes (68) can also be used to prepare isobenzofurans (see Section IV,B,5). 

It is interesting to note that orthometallation occurs preferentially at the aryl ring in the thiolactone 69 despite the availability of oxygen as a potential donor ligand oxidation of the dinuclear complex 70 by ceric ion gives the condensed isobenzothiophene derivative 71 in unspecified yield152 (Scheme 85). 

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

An orthometallation procedure for the preparation of condensed iso-thiazolium salts from appropriately substituted arenes has been described earlier in this Section (Scheme 117)180 an example illustrating the way in which this approach can be elaborated to the synthesis of condensed 1,2-dithiolylium perchlorates is given in Scheme 123. 

Good yields of l-arylaminoquinolin-2-ones are obtained when the azo-arene complexes 116 are treated with hexafluorobut-2-yne (Scheme 141).214 This procedure is particularly novel in the chemistry of orthometallated complexes in that the primary organometallic products (117) arise from the formal insertion of a three carbon unit [CO + C2(CF3)2] into the aryl-cobalt bond of 116. A wider study of the scope of this type of process using a variety of orthometallated complexes would be desirable. 

An initial step of orthometallation probably also occurs when aniline is allowed to react with ethylene in the presence of a rhodium(I) catalyst. 2-Methylquinoline (10 turnovers relative to the metal) and JV-ethylaniline (30 turnovers) are formed after 72 h in what are probably two independent reaction pathways (Scheme 144).216 It is interesting to note that the intramolecular cyclization step in the proposed216 mechanism (Scheme 144) has precedent in the palladium-promoted quinoline synthesis reported by Hegedus et al.16 (see Scheme 142), but the transformation 118->119 is unusual in the chemistry of organometallic insertion reactions.106... 

The orthometallation-carbonylation sequence illustrated in Scheme 155 affords a useful regiospecific methoxycarbonylation of the aryl ring of 4-chromanones.232 Unfortunately an extra step is incurred in the synthesis because of the unreactivity of the dimeric complexes (126) toward carbonyl insertion. 

The orthometallation-carbonylation sequence described earlier (Scheme 155) has been used to effect regiospecific methoxycarbonylation of 4-thiachromanones (Scheme 161 ).232... 

A reaction of this type is sometimes referred to as orthometallation because it is from the ortho position that the hydrogen is transferred to the metal. 

RuCl(PPh3 )3(alkyl) (90). Because of the fact that the orthometallated complex reacts with H2 to re-form HRuCl(PPh3)2, catalytic hydrogenation of olefins can result via such pathways, although product formation via reaction (11) is kinetically preferred (88). 

The reaction involves a key transesterification of the phenol with the phosphinite ligand. Orthometallation of the resulting phosphinite leads to a metallacycle. After reductive elimination, the biaryl product is formed and undergoes a transesterification to afford the phenol product (Scheme 27).123... 

The addition to a double bond is observed in aromatic substrates where the reaction is assisted by chelation. The initial success of such reactions was achieved with the double alkylation of phenol with ethene (Equation (2)).1 This reaction occurs at the or/ -positions selectively by using an orthometallated ruthenium phosphate complex 1. 

The efficiency of the orthometallated Pd(II) complexes [Pd(NC)X]2 [39, 40] (3 in Scheme 4.3) in coordinating solvents such as DMF or DMSO was considered to be in favor of the initial dissociation of the dimers 3 into the mononuclear species 6 (Scheme 4.6). The heterolytic splitting of H2 leads to the formation of the hydride 7 plus HC1 or AcOH. The solvato-hydride intermediate 7 was characterized spectroscopically and its elemental analysis furnished [39] regrettably, no data regarding its catalytic activity were reported. 

The ferrocene-oxazoline catalyst 19 (Fig. 29.7) has recently been used to hydrogenate substituted quinolines [18]. The ligand synthesis is again similar to that of the original PHOX ligand, with introduction of phosphorus via orthometallation. 

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