Dinuclear (d(3)-d(3)) Diolate Complexes of Molybdenum and Tungsten. 1. Preparation and Characterization of Complexes Derived from 2,5-Dimethylhexane-2,5-diol.

Reaction of M(2)(O(t)Bu)(6) (M = Mo, W) with 3 equiv of 2,5-dimethylhexane-2,5-diol (LH(2)) in hexane/THF produces orange crystals of M(2)(&mgr;-L(3))(2), Ia (M = Mo), Ib (M = W), in high yield (80%). Treatment of M(2)(NMe(2))(6) with excess (>8 fold) LH(2) in THF/hexane solution at -20 degrees C produces exclusively green crystals of M(2)(&mgr;-L)(eta(2)-L)(2)(HNMe(2))(2), IIa (M = Mo), IIb (M = W), in high yield (75%). Dissolving IIa and IIb in toluene at room temperature slowly produces Ia and Ib, respectively, the process being accelerated by heat (t(1/2) = 10 min at 60 degrees C). Compounds Ia, Ib, IIa, and IIb were characterized by (1)H NMR, IR, melting point, and microanalysis, and Ib and IIb were also characterized by X-ray crystallography. Addition of excess HNMe(2) to a solution of Ia or Ib at -50 degrees C does not produce any IIa or IIb after 2 months, but at +25 degrees C, 40% IIa and IIb are produced with HNMe(2) after 2 days. Crystal data for Ib: W(2)(&mgr;-L)(3) at -171 degrees C, a = 12.568(2) Å, b = 12.568(3) Å, c = 37.075(8) Å, Z = 8, d(calcd) = 1.822 g/cm(3), space group I4(1)/a. The molecule Ib adopts an "ethane-like" staggered conformation with three eight-membered diolate rings spanning the W-W triple bond: W&tbd1;W = 2.3628(11) Å; W-O = 1.87 Å (average). Crystal data for compound IIb: W(2)(&mgr;-L)(eta(2)-L)(2)(HNMe(2))(2) at -170 degrees C, a = b = 20.198(3) Å, c = 17.819(3) Å, Z = 8, d(calcd) = 1.629 g/cm(3), space group P4/ncc. IIb has two essentially square planar WO(3)N units connected by a W-W triple bond, W&tbd1;W = 2.3196(12) Å, W-O = 1.95 Å (average), and W-N = 2.294(11) Å, and one bridging eight-membered diolate ring. The other two diolate ligands chelate at opposite ends of the molecule forming two seven-membered rings.