Insertion of CO and Alkenes into the (methyl)Pd Complexes of the Bidentate Porphyrin Ligand

Kinetics, Mechanism and Theoretical Studies of Norbornene-Ethylene Alternating Copolymerization Catalyzed by Organopalladium(II) Complexes Bearing Hemilabile α-Amino-pyridine

Cationic methylpalladium complexes bearing hemilabile bidentate α-amino-pyridines can serve as effective precursors for catalytic alternating copolymerization of norbornene (N) and ethylene (E), under mild conditions. The norbornyl palladium complexes in the formula of {[RHNCH₂(o-C₆H₄N)]Pd(C₇H10Me)(NCMe)}(BF₄) (R = iPr (2a), tBu (2b), Ph (2c), 2,6-Me₂C₆H₃ (2d), 2,6-iPr₂C₆H₃ (2e)) were synthesized via single insertion of norbornene into the corresponding methylpalladium complexes 1a-1e, respectively. Both square planar methyl and norbornyl palladium complexes exhibit facile equilibria of geometrical isomerization, via sterically-controlled amino decoordination-recoordination of amino-pyridine. Kinetic studies of E-insertion, N-insertion of complexes 1 and 2, and the geometric isomerization reactions have been examined by means of VT-NMR, and found in excellent agreement with the results estimated by DFT calculations. The more facile N-insertion in the cis-isomers, and ready geometric isomerization, cooperatively lead to a new mechanism that accounts for the novel catalytic formation of alternating COC.

Methyl Complexes of the Transition Metals

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH3 compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

Kinetic and mechanistic studies of geometrical isomerism in neutral square-planar methylpalladium complexes bearing unsymmetrical bidentate ligands of alpha-aminoaldimines

A series of hemilabile ligands of alpha-aminoaldimines and their methylpalladium complexes have been prepared and characterized. Neutral square-planar methylpalladium complexes in the form of [R(1)R(2)NCMe(2)CH horizontal lineNR]Pd(Me)Cl (R = Me, R(1) = R(2) = Me (3a); R = Me, R(1) = R(2) = Et (3b); R = Et, R(1) = R(2) = Me (4a); R = (n)Pr, R(1) = R(2) = Me (5a); R = (i)Pr, R(1) = R(2) = Me (6a); R = (i)Pr, R(1) = R(2) = Et (6b); R = (i)Pr, (R(1), R(2)) = c-C(4)H(8) (6c); R = (i)Pr, R(1) = (i)Pr, R(2) = H (6d); R = (i)Pr, R(1) = (t)Bu, R(2) = H (6e); R = (t)Bu, R(1) = R(2) = Me (7a); R = (t)Bu, R(1) = R(2) = Et (7b); R = (t)Bu, (R(1), R(2)) = c-C(4)H(8) (7c); R = (t)Bu, R(1) = (i)Pr, R(2) = H (7d); R = (t)Bu, R(1) = (t)Bu, R(2) = H (7e); R = Ph, R(1) = R(2) = Me (8a); R = Ph, R(1) = R(2) = Et (8b)) show geometrical isomerism. The relative ratios of trans/cis isomers appear to be predominated by the steric hindrance between the Pd-bound methyl group and imino or amino substituents (R and R(1) and R(2)). The NMR studies for the substitution reaction of (COD)Pd(Me)Cl with Et(2)NCMe(2)CH horizontal lineN(i)Pr at -20 degrees C indicate that cis-6b is the major kinetic product, which isomerizes to the thermodynamic product in trans form quantitatively above -5 degrees C. Kinetic results show that the ligand substitution reaction likely undergoes an associative pathway, and the isomerization reaction proceeds via an intramolecular process that comprises imine dissociation and recoordination.