Reactions of cyclopalladated complexes with boronic acids

Various ArB(OH)2 react with C(sp2),N and C(sp3),N cyclopalladated complexes having PPh3 as an auxiliary ligand to form C(sp2)–C(sp2) and C(sp3)–C(sp2) bonds. The couplings require the use of a base and temperatures ≥60 oC. The reaction of p-NO2C6H4B(OH)2 with a C*(sp3),N palladacycle is stereoselective. [Display omitted] •C(sp2),N and C(sp3),N palladacycles react with ArB(OH)2 to form a CC bond.•C(sp3)–C(sp3) bonds can be formed using pinacol esters of BnB(OH)2.•Reactions of palladacycles with RB(OH)2 require a base and temperatures ≥ 60 °C.•The reaction of p-NO2C6H4B(OH)2 with a C*(sp3),N palladacycle is stereoselective. Six known C(sp2),N and C(sp3),N cyclopalladated complexes derived from N,N-dimethylbenzylamine, 4,4-dimethyl-2-phenyl-2-oxazoline, 2-tert-butyl-2,2-dimethyl-2-oxazoline, O-methyloxime of d-camphor, 8-methylquinoline, and N,N-dimethylhydrazone of d-camphor were synthesized and used in CC bond formation reactions with aryl, benzyl and allylboronic acids or esters. Two protocols for a successful CC coupling were developed; both involve the use of a base and the conversion of dimeric cyclopalladated complexes to the mononuclear derivatives with PPh3 as an auxiliary ligand. The C(sp2)–C(sp2) bond formation was achieved by reacting mononuclear complexes of N,N-dimethylbenzylamine and 4,4-dimethyl-2-phenyl-2-oxazoline with ArB(OH)2 in acetone at 60 °C in the presence of Cs2CO3. Reactions of (i) C(sp3),N complexes PPh3-6, PPh3-8 and PPh3-10 with ArB(OH)2 (Ar = Ph, p-NO2C6H4, p-MeOC6H4, 8-quinolyl and 3-pyridyl) and (ii) C(sp2),N oxazoline-derived complex PPh3-4 with pinacol esters of allyl- and benzylboronic acids occurred in a refluxing 4:1 mixture of dioxane-water in the presence of K3PO4 and afforded C(sp2)–C(sp3) coupling products in 46–89% yield. Desirable compounds with an C(sp3)–C(sp3) bond were isolated in 17–67% yield in the reactions of pinacol ester of benzylboronic acid with C(sp3),N complexes PPh3-6 and PPh3-8. The stereoselectivity of the transformation was investigated using reactions of p-NO2C6H4B(OH)2 with two diastereomeric complexes, (1S,2S,4R,Z)-12 and (1S,2R,4R,Z)-12, which were obtained from N,N-dimethylhydrazone of d-camphor, and had different absolute configurations of the chiral center attached to the metal. Both reactions yielded the same isomer, (1R,3R,4R,Z)-1,1-dimethyl-2-[1,7,7-trimethyl-(4-nitrophenyl)bicyclo[2.2.1]heptan-2-ylidene]hydrazine, as the major product. The X-ray crystallographic study of this product prov