Ligand synthesis metal ligands, palladium complexes

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

The two oxygen-activating complexes [Co(L)j [L = salophen, tetra-tert-butylsalo-phen (55)] have been prepared and were also synthesized within dehydrated zeolite NaY using the intrazeolite ligand synthesis method [164]. These encapsulated metal complexes were shown to be capable of oxidizing hydroquinone and so were then used in a triple catalytic system to mediate the palladium-catalyzed aerobic 1,4-diacetoxylation of 1,3-dienes (Figure 5.28) [165]. The catalytic system involved [Pd(OAc)2], hydroquinone and the [Co(salophen)] complex in acetic acid (Co Pd diene hydroquinone LiOAc = 1 2.23 50 8.3 690, acetic acid, 25 °C,... 

Bidentate ferrocene ligands containing a chiral oxazoline substituent possess both planar chiral and center chiral elements and have attracted much interest as asymmetric catalysts.However, until recently, preparation of such compounds had been limited to resolution. In 1995, four groups simultaneously communicated their results on the asymmetric synthesis of these structures using an oxazoline-directed diastereoselective lithiation (Scheme 8.141). " When a chiral oxazolinylferrocene 439 was metalated with butyllithium and the resulting aryllithium species trapped with an electrophile, diastereomer 442 was favored over 443. The structure of the major diastereomer 442 was confirmed, either by conversion to a compound of known stereochemistry or by X-ray crystallography of the product itself or of the corresponding palladium complex. ... 

Catalytic enantioselective synthesis of 4,4-dimethyl-l-phenyl-l,2-pentadiene from 4,4-dimethyl-1,2-pentadiene and iodobenzene using 0.4 to 1 mol % of palladium complexes containing chiral phosphane ligands as the catalyst for the enantioselective cross coupling134 is the only example of substoichiometric transition metal catalyzed enantioselective allene synthesis. 

Complex compounds with halide bridges are prepared by immediate interaction of unsaturated hydrocarbons with metal salts (Sec. 2.2.4.1). Their examples are classic 7i-complexes of the type 123 which are characteristic for fi 8-metals [75]. Such complexes are also formed by the method of ligand exchange. The bridges of this type are widespread in products of cyclometallation reactions with the use of metal halides (Sec. 2.2.5.1) 371-374, 381, 382 [41,46,48]. An example of such a synthesis is the reaction of arylhydrazones of 2-oxopropionic aldehyde and benzoylformalde-hyde, as well as butadiene-2,3-dione 635, with palladium dichloride, leading (3.71) to dipalladium complexes 636 [88] ... 

Nielsen et al. have introduced a monoether linked bis-carbene [209] modelled on an amino linked bis-carbene ligand that acts as a C,N,C pincer ligand in a corresponding palladium(II) complex [156]. Synthesis of the ether linked bis-carbene is facile and involves the reaction of the l-co-dichloro-diethylether with 2 equiv. of methylimidazole. Subsequent reaction with silver oxide and carbene transfer to suitable transition metal precursor complexes affords the corresponding complexes (see Figure 3.73). 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

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