The zwitterionic N,N‘-dialkyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium derivatives [C6H2(NHCH2CH2X)2(O)2] (X = NMe2, 9; X = NHEt, 10; X = OMe, 11), previously prepared from 4,6-diaminoresorcinol by a transamination reaction, and 12 (X = N(CH2CH2)2O) behave as tridentate ligands when reacted with [Ni(acac)2] to form the corresponding octahedral Ni(II) 2:1 complexes (13−16), respectively. In contrast, ligand 9 reacted | with NiCl2·6H2O in a tandemlike manner to afford the stabilized Ni(II) zwitterionic organometalate 1:1 complex (17). The bonding parameters | of complexes 13·H2O·CH2Cl2 and 17, determined by X-ray diffraction, and the conformation of the ligands around the nickel center as well as the supramolecular arrangements are discussed and compared with those of their previously reported Zn(II) analogues. Complexes 13−17 were tested in catalytic ethylene oligomerization with MAO and AlEtCl2 as cocatalysts. Complex 17 yielded the highest turnover frequencies, with values up to 20 300 and 48 200 mol of C2H4/((mol of Ni) h), in the presence of 400 equiv of MAO and 10 equiv of AlEtCl2, respectively. Selectivities for ethylene dimers were slightly higher when using MAO:  94% (14 in the presence of 100 equiv of MAO) and 90% (14 in the presence of 6 equiv of AlEtCl2). The selectivities for 1-butene within the C4 fraction were much higher when using MAO as cocatalyst, with values up to 68% (15 in the presence of 100 equiv of MAO). The fact that 17, which contains only one tridentate ligand per nickel center, leads to higher activities than 13−16 underlines the importance of the metal center accessibility in the catalytic process.

A novel catalyst system based on a chiral strontium complex which promotes the catalytic asymmetric Michael addition reactions of malonates to enones has been developed. The conjugate addition reactions proceeded smoothly in the presence of 5 mol % of the chiral strontium catalyst, at room temperature, to afford the desired adducts in high yields and excellent enantioselectivities. This method provides an efficient approach to the preparation of building blocks possessing various functional groups and possible sites for further functionalization.

The phosphinito-oxazoline ligand 4,4-dimethyl-2-[methoxy(diphenylphosphine)]-4,5-dihydrooxazole (2a) and the phosphonite-oxazoline ligand 4,4-dimethyl-2-[methoxy(6H-dibenz[c,e][1,2]oxaphosphorin)]-4,5-dihydrooxazole (8a) were prepared by deprotonation of (4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol (1a) and reaction with the corresponding P-Cl function, similar to the ligands 2b (4,4-dimethyl-2-[1-oxy(diphenylphosphine)-1-methylethyl]-4,5-dihydrooxazole) and 8b (4,4-dimethyl-2-[1-oxy(6H-dibenz[c,e][1,2]oxaphosphorin)-1-methylethyl]-4,5-dihydrooxazole) reported previously. These ligands react with [PdClX(COD)] to give complexes of the type [PdClX(P,N)] (3a P,N = 2a, X = Cl; 4a P,N = 2a, X = Me; 4b P,N = 2b , X = Me; 9a P,N = 8a, X = Cl; 9b P,N = 8b, X = Cl; 10a P,N = 8a, X = Me; 10b P,N = 8b, X = Me). Complexes 4a,b and 10a,b reacted with AgCF(3)SO(3) to yield [PdMe(P,N)OSO(2)CF(3)] 5a,b and 11a,b, respectively. From the stepwise insertion reaction of CO and ethylene into the Pd-C bond of 5a and 11a,b, the alkyl ketone chelate complexes [Pd{CH(2)CH(2)C(O)Me}(P,N)]CF(3)SO(3) 7a and 14a,b respectively, have been isolated and spectroscopically characterized. Complexes 3a.CH(2)Cl(2), 5a, 9b, 10a,b, [PdMe(H(2)O)(P,N)]CF(3)SO(3) 12b, (P,N = 8b) and 14a,b have also been characterized by X-ray crystallography and the structures of 14a,b represent still rare examples of structurally characterized CO/ethylene coupling products.