Reductive Trapping of [(OC)₅W–W(CO)₅]²⁻ in a Mixed‐Valent Sm^II/III Calix[4]pyrrolide Sandwich

The ditungsten decacarbonyl dianion

“…The solid--state structure of 1 (Figure 1a) confirms (i) the unsupported metal--metal bond formulation with one axial and four equatorial carbonyls per tungsten, (ii) the separated ion pair nature, and (iii) that the [(OC)5W--W(CO)5] 2-dianion unit surprisingly adopts an exact D4h rather than D4d geometry, since the centre of the W--W bond resides on a crystallographic inversion centre. Point (iii) contrasts to the situation found in I, 8 and for binary homobimetallic carbonyls generally. The W--W distance in 1 is 3.2421(8) Å, which is significantly longer than the values of 2.74 and 2.79(2) Å for the sum of the single bond covalent radii of two tungsten atoms 12 and II, 9 respectively, but it is closer to the W--W bond lengths of 3.1107(6) Å in I 8 and 3.2881(1) Å in [{(h 5 --C5Me5)W(CO)3}2].…”

“…Prominent by its absence from the exemplars above is structural authentication of the free [(OC)5W--W(CO)5] 2-dianion, even though [Na2W2(CO)10] was first reported in 1963, 7 and the Cr and Mo congeners were structurally characterised in 1970. 3d Much more commonly, [W2(CO)10(µ--X)] (X = formally anionic ligand) moieties are known, and structural authentication of (OC)5W--W(CO)5 as an unbridged unit is limited to [{(THF)2Sm(N4Et8)Sm(THF)}2{(µ--CO)2W2(CO)8}] (I, N4Et8 = meso--octaethylcalix [4]pyrrolide) where the W2(CO)10 unit has D4d symmetry and is stabilised, 8 and thus influenced, by carbonyl--bound cations as is most likely the case in [Na2W2(CO)10] itself. 7 Thus, after almost six decades a structure of free [(OC)5W--W(CO)5] 2-unperturbed by bridging ligands or stabilising counter cations has remained elusive, with the closest relative being homotrimetallic [Na(DME)3][(OC)5W--W(CO)4--W(CO)5] (II).…”

3d–4f heterometallic complexes by the reduction of transition metal carbonyls with bulky LnII amidinates

“…[15][16][17][18] Edelmann and co-workers have isolated the formally Sm III 19 Some of us isolated the elusive [W 2 (CO) 10 ] 2− anion in a mixed-valent Sm II/III calix [4]pyrrolide sandwich by the reduction of [W(CO) 6 ] with a divalent samarium meso-octaethylcalix [4]pyrrolide. 20 Also, Ln II -TM carbonyl complexes have been accessed either by redox-transmetallation between Hg salts of TM carbonyl complexes and elemental Ln 0 or by reduction of TM carbonyl complexes with Ln/Hg amalgam. 10,[21][22][23][24][25][26] Depending on the bonding situation between the two metal centres, Ln-TM carbonyl complexes can be divided into three major categories: (i) solvent-separated ion pairs, 22,27 (ii) Ln-TM bonded compounds, 11,12,14,23,28,29 and (iii) compounds with isocarbonyl-linkages 10,16,30 between both metals.…”

Rhenium is different: CO tetramerization induced by a divalent lanthanide complex in rhenium carbonyls

“…In 2017, Deacon and co-workers trapped the elusive [W 2 (CO) 10 ] 2À anion featuring an unsupported W-W bond by the reduction of W(CO) 6 with a divalent samarium mesooctaethylcalix[4]pyrrolide. 13 Recently, single-electron reduced rhenium carbonyl complexes have shown electrocatalytic reduction of CO 2 to CO. 14 Herein, we report the reduction of Re 2 (CO) 10 with divalent lanthanide complexes, which leads to a tetramerization of CO to give a Fischer-type rhenacycle. We also studied the effect of the ligands on the reduction ability of the lanthanide complexes and compared the reactivity of Re 2 (CO) 10 to that of Mn 2 (CO) 10 .…”

“…The reactivity observed is in sharp contrast to all the reports on Ln-TM carbonyl complexes discussed earlier. 13,19 Recently, we have shown that using sterically demanding ligands in the coordination sphere of divalent lanthanides, different activations of main-group elements and complexes can be achieved. 20 We therefore investigated the reduction of TM carbonyls with [(DippForm) 2 Sm II (thf) 2 ] 21 (DippForm = N,N 0bis(2,6-diisopropylphenyl)formamidinate), another sterically demanding divalent samarium reagent.…”