Amines orthometallated

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.

One particularly interesting reaction of coordinated (phosphino)amines is their ability to undergo orthometallation, as observed for ligands (198) and (199) at platinum(ll) and rhodium(III) metal centers.444 These constitute the first examples of CH activation of a (phosphino)amine, in... 

Orthometallation is observed in aryl ethers " and also in an aryl tertiary amine when vigorous conditions are used ... 

Cyclopalladated complexes, which are most conunonly prepared from tetrachloropaUa-date(II) and appropriate amines or imines, have drawn the attention of inorganic, coordination, and organometallic chemists since the first report in 1965 (for imines) and in 1968 (for amines) by Cope and co-workers. ° These palladacycle species can easily be transformed into chiral form by employing corresponding chiral amines or imines. Two representative examples of the chiral cyclopalladated species are illustrated in Figure 1. This section will describe three examples that represent applications of these chiral orthometallated palladium complexes in organic synthesis. 

In 1971, an interesting application of the chlorobridged Pd(II) complexes with orthometallated chiral amines was demonstrated by Otsuka and co-workers resolution of racemic chiral phosphincs. The binuclear species reacts with tertiary phosphines or arsines to form two equivalents of mononuclear complexes (Scheme 3). If both the phosphines and the orthometallated palladium complexes were chiral, the mononuclear products could be a mixture of diastereomers. With appropriate combinations of the chiral racemic phosphines and the enantiomerically pure orthometallated palladium species, one of the two enantiomers of the phosphines reacts with the palladium complex selectively to give a specific diastereomer of the mononuclear palladium complexes, leaving the other enantiomer of the phosphine unreacted. 

In 1997, Resolutions of Tertiary Phosphines and Arsines with Orthometallated Palladium(ll)-Amine Complexes, by Wild [3]... 

Figure 4.6 Coordination of orthometallated dimethyl(l-(a-naphtyl)-ethyl)amine.

Pd(II) complexes with enantiomerically pure orthometallated benzylamines have been studied in detail because they are used for the resolution of chiral ligands. For dimethyl(l-(a-naphtyl)-ethyl)amine it is clear that the chelate prefers the conformation with the benzylic Me in axial position, thus avoiding interactions with the naphtyl ring. This leads to a 8 conformation for the R amine (Figure 4.6), and to a X conformation for the Samine [23-26]. 

A cross-experiment mixing equal amounts of the enantiomers RRR and SSS (the first letter corresponds to the configuration of the orthometallated amine) prepared independently showed, in the equilibrium, a mixture of diastereomers (Figure 4.7) containing RRR + SSS) (RSS + SRR) = 1 19. 

Figure 4.7 Possible isomers of a square planar complex with orthometallated dimethy 1( 1 -(a-naphtyl)-ethyl)amine and N, N, N, iV -tetramethyl-2,3-butanediamine. Reproduced with permission from S. Y. M. Chooi et al. Inorg. Chem. 33, 3097 (1994) [27]. Copyright (1993) American Chemical Society.

Wild SB. Resolutions of tertiary phosphines and arsines with orthometallated palladium(II)-amine complexes. Coord. Chem.Rev. 1997 166 291-311. 

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