Stabilization of a Two‐Coordinate Mononuclear Cobalt(0) Compound

Abstract

Compound (Me2 -cAAC:)2 Co(0) (2; Me2 -cAAC:=cyclic (alkyl) amino carbene; :C(CH2 )(CMe2 )2 N-2,6-iPr2 C6 H3 ) was synthesized by the reduction of the precursor (Me2 -cAAC:)2 Co(I) Cl (1) with KC8 in THF. The cyclic voltammogram of 1 exhibited one-electron reduction, which suggests that synthesis of a bent 2-metallaallene (2) from 1 should be possible. Compound 2 contains one cobalt atom in the formal oxidation state zero, which is stabilized by two Me2 -cAAC: ligands. Bond lengths from X-ray diffraction are 1.871(2) and 1.877(2) Å with a C-Co-C bond angle of 170.12(8)°. The EPR spectrum of 2 exhibited a broad resonance attributed to the unique quasi-linear structure, which favors near degeneracy and gives rise to very rapid relaxation conditions. The cAACCo bond in 2 can be considered as a typical Dewar-Chatt-Duncanson type of bonding, which in turn retains 2.5 electron pairs on the Co atom as nonbonding electrons.

Correlations and Contrasts in Homo‐ and Heteroleptic Cyclic (Alkyl)(amino)carbene‐Containing Pt0 Complexes

“…The NMR spectroscopicd ata of our materialw as found to be essentially the same as the published data. Single crystals of 1·C 6 H 6 suitable for ad iffraction study were grown from ben-zene, and showeds tatistically insignificantP t ÀCb ond-length variation from the published moleculars tructure of 1·0.5 THF (1·C 6 H 6 :1 .965(2), 1.969(2) ; 1·0.5 THF:C ÀPt 1.964(5), 1.967 (5) ). The CAACl igandsi nboth structures were found to coordinate in an approximately linear fashion across the Pt center( C-Pt-C angle: 1·C 6 H 6 :1 71.13(7)8; 1·0.5 THF:1 70.9(2)8).…”

“…[12] Electrochemical measurements [6c] This event was attributed by the authors to ao ne-electrono xidation on the basis of DFT calculations,a nd also seems consistentw ith the unique stability of the [M(CAAC) 2 ] n + system in oxidation states between those usually expected fort he metals. [3][4][5][6][7][8] In contrast, the remaining complexes all showedi rreversible oxidation waves (2: E pa = À0.09 V; 3: E pa = À0.11V;[ Pt(PCy 3 ) 2 ]: E pa = 0.00 V; [Pt(PiPr 3 ) 2 ]: E pa =+0.12 V). If we set aside the unique behavior of 1,w e can infer slightly strongerr eductivea bility of compounds 2 and 3 compared to the two homoleptic bis(phosphine) complexes.…”

“…This adaptability has been exploitedv ery recently in the synthesiso fc omplexes of the form [M(CAAC) 2 ] n + (M = Group 7-12 metals; III; Figure 1) by an umber of groups working both separately and collaboratively,t hose of Bertrand, Roesky,F renking, Dittrich, Kaim, Parameswaran, Neidig, Deng, Meyer,U ngur,S talke, Dalal, Peters,and Ackermann. [3][4][5][6][7][8] The sheer quantity of work on complexes of the form [M(CAAC) 2 ] n + published since the beginning of 2013( to say nothingo ft he equally unusualc hemistry of main-group CAAC adducts [2f] )i sa stounding and reflective of the unique abilities of these ligands.…”

“…These complexes have already shown, for example, electrochemicala nd catalytic activity,a nd the ability to activate small molecules, such as dihydrogen and carbon dioxide. [3][4][5][6][7][8] Our entry into this field was motivatedb yadesire to prepare alternatives to the very useful and strongly Lewis basic complexes [Pt(PR 3 ) 2 ]( R= Et, iPr,C y) for variousp urposes,s uch as catalytic dehydrocoupling, [9] oxidative addition of EÀXb onds, [10] and the formation of metal-only Lewis pairs (MOLPs). [10e, 11] Herein, we describet he synthesis of both homoleptic [Pt(CAAC) 2 ]a nd heteroleptic zero-valent complexes of platinum and their reactivity towardsLewis acidic main-group compounds.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Highly reduced cobalt complexes containing Bertrand carbene ligands (e.g. 947, 948) were prepared through reduction of the corresponding cobalt(II) NHC complex 946[1045,1046]. Either of the complexes 947 948 could be prepared, depending upon the amount of reducing agent employed.…”