| Abstract: | A new family of the quintuply bonded dichromium complexes Cr2{μ‐κ2‐HC(N‐2,6‐R2C6H3)2}2(μ‐κ2‐HCNAr]2)] (R = iPr, Ar = 4‐MeC6H4 ( 5 ), Ar = 3,5‐Me2C6H3 ( 6 ), and Ar = 2,6‐Me2C6H3 ( 7 ); R = Et, Ar = 4‐MeC6H4 ( 8 ), Ar = 3,5‐Me2C6H3 9 ], and Ar = 2,6‐Et2C6H3 ( 10 )) with a heteroleptic lantern configuration was obtained upon the addition of one equivalent of amidinate to the quintuply bonded dichromium amidinates Cr{μ‐κ2‐HC(N‐2,6‐R2C6H3)2}]2 (R = iPr, Et). Additionally, the same approach was applied to the preparation of the acetate derivative Cr2{μ‐κ2‐HC(N‐2,6‐ iPr2C6H3)2}2(μ‐κ2‐CH3CO2)] ( 11 ), which represents the first example that the quintuply bonded dinuclear complex contains an oxygen‐containing ligand. Of particular interest is that the Cr‐Cr bond lengths in these new trigonal paddlewheel quintuple Cr‐Cr bond species are comparable with those in their precursor compounds. They show ultrashort Cr‐Cr bond lengths in a narrow range of 1.740–1.755 å on the basis of single‐crystal X‐ray crystallography. The small Mayer bond orders of the long Cr‐N bonds as well as divergent, C2v and D3h, structural conformations in 5 – 11 suggest that the metal–ligand interactions possess minor covalent character and the electrostatic interactions play a dominant role. As a result, these extremely short Cr‐Cr quintuple bonds are caused by the overlap between five pairs of d orbitals that do not involve much in metal–ligand bonding. Additionally, anionic lantern dichromium trisamidinates 5 – 10 can be chemically oxidized by one electron, supported by electrochemistry, and their ease to undergo oxidation is presumably associated with their neutral lantern dichromium trisamindinate products, whose structures inherently display a Jahn‐Teller distortion, exemplified by the structure of the homoleptic dichromium complex Cr2{μ‐κ2‐HC(N‐2,6‐Et2C6H3)2}3] 12 ] determined by X‐ray crystallography. These results unambiguously support the Cr‐Cr quintuple bonding in these novel anionic lantern dichromium complexes. |
