Bis‐NHC Chelate Complexes of Nickel(0) and Platinum(0)

Abstract

For a long time d(10)-ML2 fragments have been known for their potential to activate unreactive bonds by oxidative addition. In the development of more active species, two approaches have proven successful: the use of strong σ-donating ligands leading to electron-rich metal centers and the employment of chelating ligands resulting in a bent coordination geometry. Combining these two strategies, we synthesized bis-NHC chelate complexes of nickel(0) and platinum(0). Bis(1,5-cyclooctadiene)nickel(0) and -platinum(0) react with bisimidazolium salts, deprotonated in situ at room temperature, to yield tetrahedral or trigonal-planar bis-NHC chelate olefin complexes. The synthesis and characterization of these complexes as well as a first example of C-C bond activation with these systems are reported. Due to the enforced cis arrangement of two NHCs, these compounds should open interesting perspectives for bond-activation chemistry and catalysis.

Crystal structure of (η4-cyclooctadiene)(3,3′-dimesityl-1,1′-methylenediimidazoline-2,2′-diylidene)nickel(0) tetrahydrofuran monosolvate

“…The remaining NHC bond lengths to the carbene are 1.377 (4) Å for N1-C1, 1.374 (3) Å for N2-C1, 1.379 (3) Å for N3-C4, and 1.374 (3) Å for N4-C4. These are comparable to the analagous NHC carbene distances reported for ( Dipp NHC 2 Me)Ni(COD) of 1.374 (4), 1.387 (4), 1.379 (4), and 1.386 (4) Å , respectively (Brendel et al, 2014). The portions of the COD ligand that are coordinated to nickel have C C bond distances of 1.411 (4) Å for C29 C30 and 1.374 (4) Å for C26 C33, consistent with unsaturated double bonds.…”

“…The portions of the COD ligand that are coordinated to nickel have C C bond distances of 1.411 (4) Å for C29 C30 and 1.374 (4) Å for C26 C33, consistent with unsaturated double bonds. These are slightly longer than the analagous C C COD distances reported for ( Dipp NHC 2 Me)-Ni(COD) of 1.383 (5), and 1.355 (5) Å , respectively (Brendel et al, 2014). The remaining C-C bond distances of the COD fragment are in the range of 1.512 (4)-1.539 (4) Å , consistent with saturated C-C single bonds, and comparable to the range of bond lengths reported for ( Dipp NHC 2 Me)Ni(COD) of 1.502-1.529 Å (Brendel et al, 2014).…”

“…The distances between the nickel center and the ( Mes NHC 2 Me) ligand are 1.909 (3) Å for Ni1-C1 and 1.916 (3) Å for Ni1-C4. These are slightly shorter than the analagous distances of 1.938 (3) and 1.953 (3) Å , respectively, reported for ( Dipp NHC 2 Me)Ni(COD) (Brendel et al, 2014). The distances from the nickel center to the COD ligand are 1.921 (3) and 2.018 (3) Å as measured from Ni1 to the mid-points of C29-C30 and C26-C33, respectively.…”

“…N-heterocyclic carbene (NHC) ligands, which have found extensive use in catalysis and organometallic chemistry, coordinate to metal centers via the lone pair of electrons of the carbene (Arduengo, 1999;Hopkinson et al, 2014;Lummiss et al, 2015). Bidentate NHC ligands (NHC 2 ) may be formed by linking two NHC ligands together; however, coordination to first row transition metals has been limited (Brendel et al, 2014;Herrmann et al, 1999;Douthwaite et al, 1999;Huffer et al, 2013;Harrold & Hillhouse, 2013). Nickel(0)cyclooctadiene complexes with {1,1 0 -di(isopropyl)phenyl-3,3 0 -methylenediimidazolin-2,2 0 -diylidene} and {1,1 0 -tert(butyl)-3,3 0 -methylenediimidazolin-2,2 0 -diylidene} ligands have been reported, but the mesityl variant is not known (Brendel et al, 2014).…”

“…Bidentate NHC ligands (NHC 2 ) may be formed by linking two NHC ligands together; however, coordination to first row transition metals has been limited (Brendel et al, 2014;Herrmann et al, 1999;Douthwaite et al, 1999;Huffer et al, 2013;Harrold & Hillhouse, 2013). Nickel(0)cyclooctadiene complexes with {1,1 0 -di(isopropyl)phenyl-3,3 0 -methylenediimidazolin-2,2 0 -diylidene} and {1,1 0 -tert(butyl)-3,3 0 -methylenediimidazolin-2,2 0 -diylidene} ligands have been reported, but the mesityl variant is not known (Brendel et al, 2014). Herein, a synthetic procedure for the synthesis of {1,1 0 -di-(mesityl)-3,3 0 -methylenediimidazolin-2,2 0 -diylidene}nickel(0)cyclooctadiene, ( Mes NHC 2 Me)Ni(COD), and its crystallographic characterization are reported.…”