P,N-chelate

The P-N chelate (91) (dapdmp) exhibits a variety of coordination geometries in complexes with divalent Co. Pseudotetrahedral Co(dapdmp)X2 (X = C1, Br, I, NCS), low-spin five-coordinate [Co(dapdmp)2X]+ (X = C1, Br, I), planar [Co(dapdmp)2]2+ and pseudo-octahedral Co(dapdmp) (N03)2 were all identified.390 The tetradentate P2N2 Schiff base complex (92) is formed by reacting the free ligand with CoI2. The iodo complex is low spin and square pyramidal.391... 

Various mixed tridentate ligands with P,N,0/S/N donor sets have been explored in Ni11 chemistry. For example, condensation of 2-(diphenylphosphino)aniline with substituted (5-chloro-, 5-nitro, 5-bromo-, 5-methoxy-, and 3-methoxy-) salicylaldehydes yields (253).697 The deprotonated ligand coordinates through its P,N,0 donor set in a square planar geometry with some distortion, which is probably due to the bulk of the phosphine group and to the bite angle of the P,N chelate. 

Other important examples of immobilized palladium catalysts (48)-(50) which were employed in Heck, Suzuki-Miyaura and allylic alkylation reactions are summarized in Fig. 4.4 [123]. Catalyst (49) is particularly noteworthy as it is a recyc-able amphiphilic resin-supported P,N-chelating Pd-complex which performs asymmetric allylic alkylations in water. 

Later, the same group [18] reported more detailed studies on the hydrogenation of prochiral ketones in the presence of P,N-chelated Ir complexes and a strong base under hydrogen pressure. A general scheme summarizing the cationic 3-aminophosphine complexes used is shown in Scheme 4.5. 

Figures 8E.3-8E.6 show a selection of some ligands that have been successfully used in the palladium-catalyzed AAA reaction. They are classified into four categories 1) chiral phosphines, 2) dinitrogen ligands, 3) P,N-chelate ligands, and 4) mixed chelate ligands. Although this...

Diphenylphosphino-l -naphthyl)isoquinoline forms P,N-chelate 245 (93T(A)743). 8-Diphenylphosphinoquinoline with trans-chloro(l-naphthyl)bis(triphenylphosphine)nickel gives chelate 246 (02NJC1474). 8-Dimethylphosphinoquinoline and -2-methylquinoline with [(r 4-cod) Pd(Me)Cl] give [Pd(T)2(N,P)-L)(Me)Cl], which with 2,6-Me2C6H3NC... 

Methyl-2-diphenylphosphino-3-(l -isoquinolyl)indole with pallada-cycle derived from dimethyl-1-naphthyl ethylamine and potassium hexa-fluorophosphate yields chelate 310 (97T4035). With [(r)3-PhCH = CH = CHPh)Pd( j.-Cl)]2, allyl 311 follows in the presence of silver tetrafluor-oborate. Addition of ligands 312 (R = R1 = H, Me) to [(r 3-PhCHCHCHPh)Pd (Cl) ]2 under conditions of allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate leads to the formation of P,N-chelates 313 (R = R1 = H, Me), the active species of the catalytic reaction (00T(A)4753). 

Figure 3.10 Examples of a CO insertion and b CH3 migration, in a square-planar Pd complex with a P—N chelating ligand. Note that the migration mechanism retains the cis configuration between the CO group and the chelate nitrogen atom.

The chelate effect is important in the oxidative additions of P—C bonds which, in the case of nickel, give P—O and P—N chelate complexes of the type used as ethylene oligomerization catalysts in the Shell higher olefin process (SHOP),91 for example,... 

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