Inter- versus Intramolecular C−H Activation: Synthesis and Characterization of a Novel Platinum-Carbene Complex

Abstract

C NMR spectroscopy as well as the short bond between the platinum and the C4 atom of the pyridine ring in 1 (1.95 Å) indicate the formation of a novel carbene species. Compound 1 is remarkably stable (m.p. 246°C), probably due to the presence of intramolecular hydrogen bonds, and is formed instead of the expected cyclometalated product. R=n-hexyl.

Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

“…This created the dimeric complex 163, featuring two remote NHC ligands (see Scheme 54). 114 Crystallographic analysis shows a Pt-C bond distance of 1.951(9) Å, which is short for a nonchelating ligand. The dihedral angle between the ligand heterocycle and the metal square plane in 163 deviates remarkably (∼39°) from the in-plane or perpendicular orientation that would be expected for effective d-π back-donation.…”

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

“…Singlets in the 31 The relative energies of the model systems M3 and M4 follow the trend 2-pyridylidene << 3-pyridylidene < 4-pyridylidene which is the same order that has been reported for the corresponding free carbene isomers of pyridine, in which one proton is located on the nitrogen atom. 24,27,28 However, the energy differences are much smaller in the complexes which can be rationalized by the calculated stronger interactions in 3-and 4-pyridylidene complexes which partly compensate the energy difference in the free pyridylidenes.…”

“…Depending on the ring substitution pattern, both 2-and 4-pyridylidene complexes have been prepared by such a rearrangement. [30][31][32][33][34] In contrast, C-H activation of N-alkylated pyridinium precursors that could allow for C2-or C4-coordination, exclusively leads to metallation at the 4-position. [35][36][37][38][39] This observation has been attributed to the steric bulk of the N-alkyl group.…”

Cyclopalladated acetate dimers: Crystal structures and VT-NMR

“…We have recently published a couple of papers dealing with the mono-and di-cycloplatination of diphenylpyridines [7,8], and another one that dealt with the unusual situation that can lead to the formation of a carbene species [9]. Here, we discuss some aspects of the cyclopalladation of diphenylpyridines, and the structure of the resulting complexes.…”