Synthesis, Properties, and Reactivity of Linear Open‐Shell 3d‐Metal(I) Complexes

Abstract

Linear complexes with two‐coordinate, open‐shell 3d‐metal(I) ions are a young and rare class of compounds in coordination chemistry and are known so far for chromium to nickel. These complexes combine an uncommon coordination motif with an, for these metals, unusual oxidation state. The isolation of such compounds relies mostly on the use of sterically encumbering and/or electronically stabilizing ligands, such as bulky amides or N ‐heterocyclic carbenes, to support the highly unsaturated metal center. Given the labile nature of these linear complexes as well as their only recent history, the physical properties, as well as their reactivity concerning small molecules and various bonding types are only partially explored. Reports concerning their respective behavior indicate a high potential, for example remarkable single‐molecule magnetic properties or first use in catalysis. Herein, we wish to give a comprehensive overview about the current knowledge, and by this shed the scientific spotlight on this, in our eyes, underused yet highly intriguing class in coordination chemistry.

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis

“…Knowledge in this field was summarized by Amatore and Jutand in the year 2000. 290 More recently, Koszinowski investigated the phosphine-palladate complexes [(PR 3 ) 2 PdX] − [X = Br (337), nBu (338), Ph (339); PR 3 = tris[3,5-bis(trifluoromethyl)phenyl]phosphine] by means of negative-ion mode electrospray-ionization mass spectrometry, electrical conductivity measurements, and NMR spectroscopy. 291,292 The species 337−339 were generated by treating the zerovalent compound [(PR 3 ) 2 Pd] (340) with LiBr or a Grignard reagent, RMgCl (R = nBu or Ph).…”

“…11,14 The chemistry of linear 3d-metal(I) compounds has been summarized by Werncke and Goḿez in a recent book chapter. 22 Metallocene anions are the subject of another recent review. 23 The chemistry of cobalt complexes and their application in C−H functionalization reactions, presumably involving low-valent intermediates, was reviewed in 2014.…”

Synthesis, Properties, and Reactivity of a Linear NHC-Based Chromium(I) Silylamide

“…Yield: 52 mg, 0.067 mmol, 48%. 1 )] (48.23 mg, 0.07 mmol, 1 equiv.) was dissolved in Et 2 O (0.8 mL).…”

“…Yield: 8 mg, 0.0107 mmol, 15%). 1 [(IMes)Cr(Br)(N{Dipp}Si i Pr 3 )] (3). [(IMes)Cr(N{Dipp}Si i Pr 3 )] (60 mg, 0.153 mmol, 1 equiv.)…”

“…Complexes with two-coordinate, open-shell 3d-metal­(I) ions, known for chromium to nickel, are a particular class of compounds in coordination chemistry. − They show interesting single molecule magnetic properties, − and can be used for bond activation, which has focused so far on the metals iron, − cobalt, ,,− and especially nickel. − In contrast, the chemistry of two-coordinate chromium­(I) is considerably less developed. This is remarkable as the linear chromium­(I) complex [TerCr­(PMe 3 )] (Ter = 2,6-Tripp 2 -3,5- i Pr 2 -C 6 H, Tripp = 2,4,6- i Pr 2 -C 6 H 2 ) was the very first example within this class of molecules (Figure A) .…”