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)](2) 1 (LH) reacts with [Pd(OAc)(2)] (1:1 molar ration 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)-kappa-C,N,N)] 2 (abbreviated as [Pd(OAc)(L-kappa-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-kappa-C,N,N)] 3. The reaction of 3 with AgClO4 and neutral or anionic ligands L' (1:1:1 molar ratio) affords [Pd(L-kappa-C.N,N)(L')](ClO4) (L' = PPh, 4a, NCMe 5, pyridine 6. p-nitroaniline 7) or [Pd(I)(L-kappa-C,N,N)] 8. Complex 4a reacts with wet CDC1, giving [Pd(C6H2-4,5-(OMe) (2)-2-CH=N'-(1R.2R)-C6H10)-NH2-kappa-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 C-aryl 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-kappa-C,N)] 9 and [Pd(L-kappa-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-kappa-C,N,N)(kappa'-N-phen)](ClO4) 10 and [Pd(L-kappa-C,N,N)(kappa'-N-bipy)](ClO4) 11. Treatment of I with PtCl2(DMSO)(2) (1:1 molar ratio) in refluxing 2-methoxyethanol gives Cl2Pt[(NH2)(2)C6H10-N,N'] 13a and [Pt(Cl)(C6H2-4.5-(OMe)(2)-2-CH=N-(1R,2R)-C6H10-NH2-kappa-C,N,N)] 13b. while [Pt(Cl)(L-kappa-C,N,N)] 14 can be obtained by reaction of [Pt(mu-Cl)(eta(3)-2-Me-C3H4)], 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 847000. Complex 3 also catalyzes the hydroarylation of 2-norbornene. but with lower yields and without enantioselectivity. (C) 2002 Elsevier Science B.V. All rights reserved.