Synthesis, characterization and catalytic activity in Heck-type reactions of orthometallated PdII and PtII complexes derived from (1R,2R)-1,2-diaminocyclohexane

The chiral bis-imine (1R,2R)-C6H10-[ENCHC6H33,4-(OMe)2]21 (LH) reacts with [Pd(OAc)2] (1:1 molar ratio; OAc=acetate) giving the orthometallated [Pd(OAc)(C6H24,5-(OMe)22-CHN-(1R,2R)-C6H10NCHC6H3-3′,4′-(OMe)2-κ-C,N,N)] 2 (abbreviated as [Pd(OAc)(L-κ-C,N,N)]), through CH bond activation on only one of the aryl rings and N,N-coordination of the two iminic N atoms. 2 reacts with an excess of LiCl to give [Pd(Cl)(L-κ-C,N,N)] 3. The reaction of 3 with AgClO4 and neutral or anionic ligands L′ (1:1:1 molar ratio) affords [Pd(L-κ-C,N,N)(L′)](ClO4) (L′=PPh34a, NCMe 5, pyridine 6, p-nitroaniline 7) or [Pd(I)(L-κ-C,N,N)] 8. Complex 4a reacts with wet CDCl3 giving [Pd(C6H24,5-(OMe)22-CHN-(1R,2R)C6H10NH2-κ-C,N,N)(PPh3)](ClO4) 4b as a result of the hydrolysis of the CN bond not involved in the orthometallated ring. The molecular structure of 4b·CH2Cl2 has been determined by X-ray diffraction methods. Cleavage of the PdN bond trans to the Caryl atom can be accomplished by coordination of strongly chelating ligands, such as acetylacetonate (acac) or bis(diphenylphosphino)ethane (dppe), forming [Pd(acac-O,O′)(L-κ-C,N)] 9 and [Pd(L-κ-C,N)(dppe-P,P′)](ClO4) 12, while classical N,N′-chelating ligands such as 1,10-phenantroline (phen) or 2,2′-bipyridyl (bipy) behave as monodentate N-donor ligands yielding [Pd(L-κ-C,N,N)(κ1-N-phen)](ClO4) 10 and [Pd(L-κ-C,N,N)(κ1-N-bipy)](ClO4) 11. Treatment of 1 with PtCl2(DMSO)2 (1:1 molar ratio) in refluxing 2-methoxyethanol gives Cl2Pt[(NH2)2C6H10N,N′] 13a and [Pt(Cl)(C6H24,5-(OMe)22-CHN-(1R,2R)C6H10NH2-κ-C,N,N)] 13b, while [Pt(Cl)(L-κ-C,N,N)] 14 can be obtained by reaction of [Pt(μ-Cl)(η3-2-MeC3H4)]2 with 1 in refluxing CHCl3. Complexes 2 and 3 catalyzed the arylation of methyl acrylate giving good yields of the corresponding methyl cinnamates and TON up to 847 000. Complex 3 also catalyzes the hydroarylation of 2-norbornene, but with lower yields and without enantioselectivity.