Orthometalated complexes

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). 

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). 

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. 

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). 

Most of the chemistry performed on orthometallated ylides has been carried out with Pd and Pt as metal centers. Few examples dealing with other metals (Co, Ru, and Os mainly, see 62 and 63) have been reported. Complex (74) has been prepared by reaction of a Ru-vinylidene with PPh3 [153] while Os derivative (75) has been obtained after treatment of the methylimido complex with PPh3 [154]. Orthoruthe-nated indenyl complexes [155] have been synthesized by reaction of the halomethyl precursors with PPh3, and the oxidative addition of the yUde Ph3P=CHC(0)H to clusters of Ru and/or Os also allows the synthesis of orthometallated complexes... 

There are many phosphine and phosphite complexes of iron(O), sometimes acting as P,C-donors in orthometallated complexes. In general this area is deemed to be organometallic chemistry, so we shall cite just one recent reference to act as a possible point of entry to this area, relating to [Fe(CO)2 P(OPlfi3 P(OPh)2(OC6Fl4) which contains both a P- and a P,C-donor triphenylphosphite ligand. ... 

Instead of metal carbonyls, a variety of other complexes can also be used as complex precursors. [MC14]2 anions (M = Pd, Pt) were found to react readily with p,p -disubstituted thiobenzophenones to form a mixture of the bis(thiobenzophenone) complexes [MCbJV-S= C(C6H4R-p)2 2] (R = H, Me, OMe, NMe2) and the orthometallated chloride-bridged dimers. Cleavage of the dimers by triphenylphosphine afforded the monomeric orthometallated complexes ll.130... 

Aromatic trans-diazenes easily form orthometallated complexes, sometimes accompanied by cleavage of the N=N bond to give the o-semidine containing products. These reactions have been recently reviewed by Bruce and Goodall2a ... 

There is a pronounced tendency for ruthenium cyclopentadienyl complexes with attached phosphorus ligands to undergo a wide variety of intramolecular metallation reactions. Heating (T75-C5H5)(PPh3)2RuMe in decalin for 24 hours leads to the orthometallated complex 135 in reasonable yield [Eq. (Ill)] (6,103). The mechanism presumably involves initial loss of... 

Complexes 98 [L = PPh3, P(Ph-p-F)3, P(Ph-p-Me)3] react with methyl-lithium to give, after methanolysis, the orthometallated complexes 99 (Scheme 5). Complex 98 (L = PPh3) also leads to 99 by reaction with phenyllithium or Red-Al 54). The formation of 99 suggests that the initial reduction of 98 leads to a 16-electron ruthenium (0) intermediate followed by C—H bond activation as for the transformations of 90 and 91. Treatment of complex 98 (L = P-i-Pr3) with methyllithium produces the cyclo-metallated diastereoisomers 100. Complexes 101 and 102 are obtained by treatment of 98 (L = PPh2-f-Bu) with methyllithium at -78°C and at +70°C, respectively. Complex 101 isomerizes to 102 by a first-order process (k 0.2 hour-1 in C6D6 at 50°C) when L is PPh2-i-Pr 98 leads to 103 which isomerizes to the orthometallated complex 104 54). 

Cluster [Ru5C(CO)i5] reacts with 2,2 -bipyridine and 1,10-phenanthroline in the presence of McaNO to yield the major monosubstitution products 38 and the orthometalated complexes 39 in minor amount (both structures illustrate the 2,2 -bipyridine complexes) (97JCS(D)2705). 

Stable orthometallated complexes with nitrogen donors in four-membered rings are made by exchange reactions from ortholithium derivatives, but not by direct orthometallation. 

Orthometallated complexes are intermediates in numerous cyclic carbonylation reactions involving aromatics with nitrogen donor groups in their side chains. For example, aromatic ketoximes and azobenzene are carbonylated at elevated temperatures and pressures with a cobalt carbonyl catalyst to form five-membered ring heterocycles in which a carbonyl group has replaced the metal in the presumed orthometallated intermediate ... 

THF, EtOPh, Et20). In the latter case an additional, ligand-centred, C-H activation is observed, viz. orthometallation of one 3-phenyl substituent, as was previously observed during the attempted synthesis of Tp Ir( 2114)2, which instead afforded mono- (196) and di- (197) orthometallated complexes (Scheme 11). ... 

Structural proof for the orthometallated species has not always been convincing. Parshall reported the ortho-deuterium incorporation in phosphite ligands [56]. In agreement with this, Coolen showed that the hydrogenation catalyst HRh[P(OPh)3]4 provided ortho-deuterated product when stirred under deuterium atmosphere [55], Both researchers suggested that the deuterium exchange proceeded via orthometallation. The intermediate orthometallated complex was characterized hy P NMR [55],... 

We bave previously prepared and described binuclear orthometallated complexes of palladium(II) which could be used as precursors to prepare potoitially mixed-valence compounds. Hie presence of unusual Pd-N amido bonds in these complexes adds further interest based cm the reactivity shown by amides of the platinum group metals. ... 

Recently, Bedford and Cazin reported the use of orthometallated complex 45 as a catalyst precursor as it is readily accessible from N,N-dimethylbenzylamine, which is commercially available and inexpensive. Complex 45 reacts readily with tricydo-hexylphosphine in dichloromethane to generate adduct 46, which shows good air-and moisture-stability, and is a highly active catalyst for Suzuki coupling of aryl chlorides (Equation 81) [113]. 

An example of a doubly orthopalladated aryl bis(phosphinite) ligand 95 has been reported. " Aryloxopalladium(ii) complexes were synthesized using the Herrmann-Beller palladacycle. Coordination of the 2-acylphenolates to palladium results in a significant perturbation of the delocalization within the aromatic ring. Another example involves a doubly orthometallated complex from o-G6H4(PBu )2 and Pd(OAc)2. ... 

An orthometallated complex was obtained from dibenzylamine and Pd(OAc)2, subsequent reaction with NaBr gives a bridged dimer [Pd(/x-OAc) G6H4(GH2NHGH2Ph)-2 ]2 Insertion reactions with alkynes were carried out. It is noted that double insertion can occur. Furthermore, reactions with Tl(acac), PPh3NH(GH2Ph)2, and AgX were studied. Internal acetylenes can be inserted into orthopalladated a-methylbenzylamine. Double and tri-insertion may occur depending on the alkyne. 

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