The synthesis and structural characterization of the hitherto unknown parent Co(bz) (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO salt, or directly from Co (CO) and a Ag salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR ) ] and [F{Al(OR ) } ] {R =C(CF ) } and the solvent ortho-difluorobenzene (o-DFB). The magnetic properties of Co(bz) were measured and compared in the condensed and gas phases. The weakly bound Co(o-dfb) salts are of particular interest for the preparation of further Co salts, for example, the structurally characterized low-coordinate 12 valence electron Co(P Bu ) and Co(NHC) salts.

The synthesis and structural characterization of the hitherto unknown parent Co(bz) 2 + (bz = benzene) complex and several of its derivatives are described. Their synthesis starts either from aC oCO 5 + salt, or directly from Co 2 (CO) 8 and aAg + salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR F ) 4 ] À and [F{Al(OR F ) 3 } 2 ] À {R F = C(CF 3 ) 3 }a nd the solvent ortho-difluorobenzene (o-DFB). The magnetic properties of Co(bz) 2 + were measured and compared in the condensed and gas phases.T he weakly bound Co(o-dfb) 2 + salts are of particular interest for the preparation of further Co I salts, for example,t he structurally characterized low-coordinate 12 valence electron Co(P t Bu 3 ) 2 + and Co(NHC) 2 + salts.After the discovery of bis(benzene)chromium as the first sandwich compound bearing two neutral arene ligands in 1955, [1] it did not take long until the first cobalt analogue Co(hmb) 2 + [PF 6 ] À (hmb = hexamethylbenzene) was reported as ap aramagnetic 20 valence electron (VE) complex with at riplet spin state configuration, [2] of which the crystal structure remains the only reported example. [3] Subsequent attempts to isolate Co(arene) 2 + complexes with arenes other than the very electron rich hmb (e.g.,w ith mesitylene, [2] toluene, [4] bz [4,5] )f ailed. Va rious Co(hmb) 2 + salts were the subject of further studies [6,7] and served for the synthesis of novel Co I compounds,for example,with dienes. [8,9] However, only one hmb ligand could be displaced and the fragment (hmb)Co + was always incorporated.By contrast, advanced mass spectrometric (MS) methods [10] have permitted the gas phase preparation and study of the parent cations M(bz) 2 + (M = transition metal). [11,12] The large majority of those cations remain unknown as stable salts in condensed phases,e .g., of M = Co,R ha nd Ir.A mongst those characterized is the gaseous Co(bz) 2 + cation, [12][13][14] reported also with IR data, [12] but currently without magnetic measurements.F rom ag eneral perspective,i tw ould be very interesting to compare the spectroscopic and magnetic data of gaseous Co(bz) 2 + and as table Co(bz) 2 + [X] À salt. Thus,i t represented an interesting fundamental challenge to work on both issues.From as ynthetic perspective,h omoleptic metal arene cations [M(arene) n ] + (n = 1-3) have received significant interest due to their possible applications in olefin oligomerization (M = Ga), [15] arene functionalizations and as building blocks for organometallic pharmaceuticals (M = Re,Tc) [16] as well as the unprecedented arene-to-cyclopentadienyl ring contraction (M = Tc). [17] Furthermore,u nivalent M(arene) n + complexes with more electron-deficient fluoroarenes,l ike fluorobenzene (fb) or o-dfb,c an be considered as sources of "naked" metal ions M + .T hus,for M = Ga I ,In I as eries of P-,