SYNTHESIS AND SUBSTITUTION-REACTIONS OF DINUCLEAR MOLYBDENUM COMPLEXES CONTAINING MO-MO QUADRUPLE BONDS AND LABILE SOLVENT LIGANDS

The kinetically labile acetonitrile ligands of [Mo2(O2C-t-Bu)3(MeCN)2]+(BF4-) (1) have been selectively replaced by the anions derived from deprotonation of 6-hydroxy-2-methylpyridine (mhp) and 2,6-dimethylpyridine (dmp) to yield the triscarboxylate complexes Mo2(O2C-t-Bu)3 (Mhp) (3) and Mo2(O2C-t-BU)3 (dmp) (4), respectively. In contrast to complexes containing mixed tetracarboxylate ligand sets, the ligand sets of 3 and 4 were found to be inert with respect to scrambling reactions in solution. 4 crystallized in the centrosymmetric space group C2/c, a = 19.732 (3) angstrom, b = 11.733 (1) angstrom, c = 24.648 (3) angstrom, beta = 94.57 (1)-degrees, and Z = 8. Treatment of 1 with 1 equiv of 2-(diphenylphosphino)pyridine (dppy) promoted a ligand scrambling reaction to yield equimolar amounts of [Mo2(O2C-t-Bu)2(dPPY)2]2+(BF4-)2 (5) and MO2(O2C-t-BU)4. 5 was also prepared quantitatively by the reaction between [MO2(O2C-t-Bu)2(MeCN)6)2+(BF4-)2 (2) and 2 equiv of dppy. The MeCN ligands of 2 were also substituted with alpha,alpha'-bipyrimidine (bpym) to afford [MO2(O2C-t-BU)2(bpym)]2+(BF4-)2 (6). The crystal structure of 6 was solved in the monoclinic space group P2(1)/n at -177-degrees-C, a = 11.144 (1) angstrom, b = 10.054 (1) angstrom, c = 35.751 (6) angstrom, beta = 91.32 (1)-degrees, and Z = 4. The two bpym ligands of 6 each formed five-membered chelate rings employing cis-equatorial positions on the Mo-Mo quadruple bond. Treatment of 6 with an equimolar amount of 2 did not result in a polymer supported by bpym bridges, rather ligand scrambling was again observed. The novel solvated complex [Mo2(mhp)3(MeCN)2]+(BF4-) (7) was prepared by alkylation of Mo2(mhp)4 in acetonitrile. The cation in 7 crystallized as a dimer of Mo2 units connected by two Mo-O axial interactions involving one mhp ligand on each dinuclear cation; at -172-degrees-C, space group = P2(1)/n, a = 17.899 (6) angstrom, b = 14.515 (4) angstrom, c = 21.897 (7) angstrom, beta = 97.04 (2)-degrees, and Z = 4.