Preagostic Rh−H Interactions and C−H Bond Functionalization:  A Combined Experimental and Theoretical Investigation of Rhodium(I) Phosphinite Complexes

Abstract

Three Rh−phosphinite complexes with the general structural formula [RhCl(i-Pr2POXy)(L)]2 (Xy = 2,3-xylyl; L = PPh3, PMe3, t-BuNC) were synthesized. Characterization of these complexes using crystallographic and spectroscopic techniques revealed rare examples of preagostic C−H···M interactions. 1H NMR chemical shielding calculations on a geometry-optimized model complex were used to provide a connection between the solution and solid-state data, which additionally supported assignment of the preagostic interaction. One of these Rh−phosphinite complexes (L = PPh3) was used to catalyze the ortho alkylation of phosphinites and phenols with an unactivated alkene. Finally, DFT calculations were used to provide evidence for the involvement of the observed preagostic interaction in the cyclometalation step of the catalytic cycle.

Formation and structures of Pd(II) N,S-heterocyclic carbene-pyridyl mixed-ligand complexes

“…The terminal Pd-I is understandably the shortest (2.5856(6) Å) whereas the bridged bonds that are trans to the carbenes are the longest (2.6594(7) Å), due to the strong trans influence of the NSHC carbene. In agreement with the 1 H NMR data, the isopropyl CH groups are orientated toward the metal center with C-HÁ Á ÁPd at 2.66 Å and C-HÁ Á ÁPd angles 122.6°, which lie within the broad range of 2.3-2.9 Å and 110-170°respectively reported for weak anagostic interactions [53][54][55][56][57][58][59][60][61][62][63]. Such electrostatic contact in sq planar d 8 system could involve interaction of the Pd(II) filled d pseudo-octahedral structure for Pd(II).…”

“…xz/yz orbital and the C-H r * orbital[53][54][55][56][57][58][59][60][61][62][63]. Albinati, Pregosin and co-workers have reported such C-HÁ Á ÁM (M = Pt II or Pd II ) interactions in non-carbene systems[64][65][66].…”

Transition‐Metal‐Catalyzed Direct Arylation of (Hetero)Arenes by CH Bond Cleavage

“…Transesterification with the corresponding phenol leads to the desired 2-arylated phenol. [202,203] As a result, the specific phosphinite co-catalyst needs to be prepared for each individual substrate prior to catalysis to avoid formation of undesired and difficult to separate by-products. This limitation was independently addressed by Oi, Inoue et al [204] as well as by Bedford and Limmert, [205] with the use of inexpensive P(NMe 2 ) 3 as the cocatalyst.…”

Nickel(ii) dithiocarbamate complexes containing the pyrrole moiety for sensing anions and synthesis of nickel sulfide and nickel oxide nanoparticles

“…4) and intramolecular C-HÁ Á ÁS interactions (Fig. 38,39 Hydrogen bonds are 3-centre-4-electron interactions with an almost linear geometry. C-HÁ Á ÁM interaction are of three types: (i) hydrogen bond (ii) agostic and (iii) anagostic or preagostic.…”