(μ-Oxo)diiron Complexes of Gated Glyoximes. Structural Changes Accompanying Ligation Trans to the Oxo Bridge

Structures of new low-spin oxo-bridged complexes of bis[(diphenylboryl)dimethylglyoximato]iron, Fe((DMG)BPh 2 ) 2, are reported. The pentacoordinate complex, 1 = [Fe((DMG)BPh 2 ) 2 ] 2 O, contains a bent Fe−O−Fe bridge (166.0°) with the irons each displaced 0.3 Å out of the N 4 planes toward the oxo ligand. The Fe−μ-O bond length (1.7097(10) Å) is the shortest yet reported. Both axial phenyl groups are directed to the trans face, creating a superstructure which is collapsed around the vacant binding site. In the butylamine derivative, 2 = [(BuNH 2 )Fe((DMG)BPh 2 ) 2 )] 2 O, the Fe−O−Fe bridge is linear (178.6°) with iron in the N 4 plane and Fe−O bond lengths of 1.766(6) Å. The BuNH 2 ligand is sandwiched between the axial phenyl groups in intimate contact with them. Structural changes accompanying ligation and their consequences are compared with those in heme systems. Crystal data for 1: orthorhombic, Pnna, a = 17.440(3) Å, b = 21.381(4) Å, c = 16.896(3) Å, V = 6300(2) Å 3, Z = 4, R = 0.068. Crystal data for 2 (CHCl 3 disolvate): triclinic, P 1̄, a = 13.445(3) Å, b = 14.525(4) Å, c = 23.877(6) Å, α = 96.01°, β = 92.61°, γ = 117.40(1)°, V = 4094(2) Å 3, Z = 2, R = 0.086.