Four-versus five-co-ordination in palladium(II) and platinum(II) complexes containing 2,9-dimethyl-1,10-phenanthroline (dmphen). Crystal structures of [PtCl₂(dmphen)] and [Pt(η²-C₂H₄)Cl₂(dmphen)]

Insertions of Allenes into Palladium−Carbon Bonds of Complexes Containing Bidentate Nitrogen Ligands. Structural and Mechanistic Studies

“…Dissociation of the nitrogen donor trans to the R group would be favored because of the higher trans influence of the R group compared to halides. 72 The threecoordinate species (intermediate V) formed then isomerizes to the more stable T-shaped intermediate VI having the R group and the halide in a trans position, which has also been proposed by Natile et al 67 Subsequent to allene coordination (intermediate VII) migration of the R group now occurs resulting in product IV.…”

“…A vacant site may be created by dissociation of one of the nitrogen donor atoms of the bidentate nitrogen ligand thereby forming intermediate V (Scheme 2). We previously have suggested that the CO insertion into the Pd-C bond of complexes containing bidentate nitrogen ligands may follow such a route, as derived from the work of Natile et al [66][67][68] and other groups, 51,69,70 who found that even with very rigid bidentate nitrogen ligands (partial) dissociation of one nitrogen donor may occur. Moreover, work done in our and other laboratories has shown that dissociation of one nitrogen donor in the complexes (2,2′-bipyrimidine)Pd(C(dNR)Me)Cl 71 and (2,2′-bipyrimidine)-Pd(η 3 -allyl)BF 4 60 occurs in solution.…”

Synthesis, stability and reactivity of palladium(0) olefin complexes bearing labile or hemi-labile ancillary ligands and electron-poor olefins

“…This is the earliest and most frequently proposed mechanism [30,42,43,[46][47][48]; (2) olefin-metal dissociation followed by recombination [30]; (3) intermolecular associative process with free alkene, via (4) metal-L or metal-L 0 bond dissociation followed by rotation of the ancillary ligand and recombination (olefin pseudorotation) [42,43]; (5) intermolecular exchange with the free ancillary ligand L-L 0 . In this case, a mechanism has been proposed which involves an olefin-metal dissociation step [30].…”

Hindrance, Donor Ability of Men∩NN Chelates and Overall Stability of Pentacoordinate [PtCl2(η2‐CH2=CH2)(Men∩NN)] Complexes as Observed by η2‐Olefin 1JPt,C Modulation: An NMR Study

“…In particular, the [PtXY(η 2 -alkene)(_ NN)] trigonal bipyramidal species show peculiar common features such as (i) the Pt-X and Pt-Y distances are very similar to those generally found in the analogous four-coordinate species; [17] (ii) the length of the equatorial platinum-alkene bond (in the trigonal plane) is generally shorter than that found in square-planar species, [26][27][28] with a greater activation energy for rotation about the platinum-alkene bond; [20] (iii) the equatorial Pt-N bonds are generally weaker and about 0.2 Å longer than observed in square-planar species obtained by olefin loss; [17][18][19]29,30] (iv) the optimal N-Pt-N angle between metal-bis-nitrogen ligand is lower than 80°( with a preference for the low-membered chelate rings); (v) the unsaturated ligand is able to reduce the electron density on the metal (back electron-donation from filled d orbitals of the metal to the empty π* orbital of the olefin), which favors coordination of the second N-donor of the chelate. [5,[17][18][19] Previous data and the theoretical description of pentacoordinate complexes, made by Kepert [17,31] and Lin, [32] following the fundamental studies by Hoffmann and coworkers, [33] did not rule out the possibility of thinking of this kind of pentacoordinate complex as particular squareplanar "trans" complexes (pseudo-trans in the following text), where the same coordination position is occupied by the two N-donors.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16] Although some very stable pentacoordinate complexes are well known, [17][18][19][20] [PtXY(η 2 -alkyne)(_ NN)] and [PtXY(η 2 -alkene)(_ NN)] complexes generally undergo characteristic decomposition patterns, including loss of alkyne or alkene, loss of an axial ligand, chelate ring opening, reductive elimination, and insertion of the unsaturated ligand into a σ-bond. [18] In this context, the main decomposition pattern generally involves the formation of reactive cationic intermediates of the type [PtX(η 2 …”