A unique Pd4 platform with CH3 and mu-CH2 groups and its C-C coupling reaction with simple olefins

Formation of Transient Anionic Metal Clusters in Palladium/Diene-Catalyzed Cross-Coupling Reactions

Despite their considerable practical value, palladium/1,3-diene-catalyzed cross-coupling reactions between Grignard reagents RMgCl and alkyl halides AlkylX remain mechanistically poorly understood. Herein, we probe the intermediates formed in these reactions by a combination of electrospray-ionization mass spectrometry, UV/Vis spectroscopy, and NMR spectroscopy. According to our results and in line with previous hypotheses, the first step of the catalytic cycle brings about transmetalation to afford organopalladate anions. These organopalladate anions apparently undergo SN 2-type reactions with the AlkylX coupling partner. The resulting neutral complexes then release the cross-coupling products by reductive elimination. In gas-phase fragmentation experiments, the occurrence of reductive eliminations was observed for anionic analogues of the neutral complexes. Although the actual catalytic cycle is supposed to involve chiefly mononuclear palladium species, anionic palladium nanoclusters [Pdn R(DE)n ]- , (n=2, 4, 6; DE=diene) were also observed. At short reaction times, the dinuclear complexes usually predominated, whereas at longer times the tetra- and hexanuclear clusters became relatively more abundant. In parallel, the formation of palladium black pointed to continued aggregation processes. Thus, the present study directly shows dynamic behavior of the palladium/diene catalyst system and degradation of the active catalyst with increasing reaction time.

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.

Di-μ-chlorido-bis-{[μ-1,8-bis-(diisopropyl-phosphan-yl)-9,10-dihydro-9,10-ethano-anthracene-κP:P']-μ-chlorido-μ-methyl-idene-dipalladium(II)} tetra-hydro-furan penta-solvate

The title compound, [Pd₄(CH₂)₂Cl₄(C₂₈H₄₀P₂)₂]·5C₄H₈O, possesses a tetra­nuclear palladium core with four bridging chlorido ligands and two bridging methyl­ene units, as well as two bridging anthracene-based bis-phosphine ligands. This tetra­nuclear complex can be considered as being composed of two μ-chlorido-bridged LPd₂ units. The structural motif of these LPd₂ units shows two doubly bridged palladium centers between the P atoms of the bis-phosphine ligand. One of these bridges is a μ-Cl atom, the other a μ-methyl­ene group. The coordination environment around each palladium center is essentially square planar. We ascribe the oxidation state +II to the palladium centers and do not assume Pd—Pd bonds [shortest distances 2.8110 (5) and 2.8109 (6) Å]. Co-crystallized with the palladium complex we found five non-coordinating tetra­hydro­furan solvent mol­ecules, one of which is disordered over two positions in a 0.429 (9):0.571 (8) ratio.