Exploring Coordination Modes: Late Transition Metal Complexes with a Methylene‐bridged Macrocyclic Tetra‐NHC Ligand

Abstract

A tetranuclear silver(I) N-heterocyclic carbene (NHC) complex bearing a macrocyclic, exclusively methylene-bridged, tetracarbene ligand was synthesized and employed as transmetalation agent for the synthesis of nickel(II), palladium(II), platinum(II), and gold(I) derivatives. The transition metal complexes exhibit different coordination geometries, the coinage metals being bound in a linear fashion forming molecular box-type complexes, whereas the group 10 metals adapt an almost ideal square planar coordination geometry within the ligand's cavity, resulting in saddle-shaped complexes. Both the Ag(I) and the Au(I) complexes show ligand-induced metal-metal contacts, causing photoluminescence in the blue region for the gold complex. Distinct metal-dependent differences of the coordination behavior between the group 10 transition metals were elucidated by low-temperature NMR spectroscopy and DFT calculations.

A hybrid imidazolylidene/imidazolium nickel NHC complex: an isolated intermediate

“…The first coordination sphere of (Zhou et al, 2008;Altmann et al, 2015Altmann et al, , 2016Altmann & Pö thig, 2016a). The distance between the Ni1 and Ni2 atoms is 3.4521 (5) Å , which is slightly greater than the sum of the van der Waals radii of 3.26 Å (Bondi, 1964).…”

Synthesis, Structures, and Catalytic Properties of Dinuclear Iridium(I) Complexes with a Hexadentate Macrocyclic Diamine‐Tetracarbene Ligand

“…Since the isolation of the first stable N‐heterocyclic carbene (NHC) by Arduengo and co‐workers, NHCs have been extensively employed as ancillary ligands in organometallic chemistry due to the facile tuning of their electronic and steric effects through introduction of substituents on the heterocyclic rings In the past decades, metal complexes with various types of macrocyclic NHC‐containing ligands[2l] including bidentate, tridentate, and tetradentate ligands as well as high‐denticity ligands with more than four donors, have been reported, some of which have found potential applications as luminescent materials,[3a] medicines,[4a] and catalysts. [8c], [10c]…”

“…Among the various NHC‐containing macrocyclic ligands, the macrocyclic tetracarbene ligands with different linkers have been considerably studied. The resulting complexes exhibit diverse conformations due to the flexibility of macrocyclic ligands 2l] They can be roughly classified into two types.…”

“…[2l] They can be roughly classified into two types. The first type are those containing exclusively four NHC groups, which have been substantially employed to prepare many metal complexes . The second type are those with more than four donor atoms including donor atoms other than the four NHC groups .…”

“…The first macrocyclic tetra‐NHC platinum(II) complex ( A , Scheme ) was synthesized in a template‐controlled reaction by Hahn et al[6a] Subsequently, a variety of macrocyclic tetra‐NHC metal complexes have been obtained by in situ deprotonation or transmetalation . Most tetracarbene metal complexes are mononuclear with coordination number 4–6, especially for the first‐type tetra‐NHC ligands . Dinuclear or multinuclear structures are found for Au I , Ag I , or Cu I complexes, in which each metal ion is coordinated with two NHC donors in a linear fashion (e.g., B , Scheme ).…”