Syntheses and structures of di(carboxylato)hexakis(acetonitrile)-dimolybdenum(II) bis(tetrafluoroborate) and trans-[di(μ-acetato)-di(acetonitrile)di(μ-bis(diphenylphosphino)amine) dimolybdenum (II)] bis(tetrafluoroborate)

Article abstract of DOI:10.1016/s0020-1693(96)05320-0

Di(carboxylato)hexakis(acetonitrile)dimolybdenum(II) bis(tetrafluoroborate) s, [Mo₂(μ-O₂CR)₂(CH₃CN) ₆](BF₄)₂(R = CH₃,CH₂Cl, C(CH₃)₃, CF₃) (3a-d), are easily accessible by reacting [Mo₂(CH₃CN)₈](BF₄)₄ (2) with a stoichiometric amount or a slight excess of the appropriate carboxylic acid and anhydride in acetonitrile. A large excess of carboxylic acid leads to the formation of tetracarboxylates. As an example cis-[Mo₂(μ-O₂CCH₂Cl)₂(CH ₃CN)₆](BF₄)₂ (3b) has been structurally characterized. Crystallographic data are as follows: space group: I42d (No. 122), a = b = 10.733(2), c = 59.448(5) A?, V = 6848(2) A?³, Z = 8, d(Mo-Mo) = 2.140(1) A?. Trans-[Mo₂(μ-O₂CCH₃)₂(dppa) ₂(CH₃CN)₂](BF₄)₂ (4) can be synthesized from cis-[Mo₂(μ-O₂CCH₃)₂(CH ₃CN)₆](BF₄)₂ (3a) and bis(diphenylphosphino)amine (dppa) at room temperature. This result contradicts earlier reports where bulky diphosphines such as dppm (sterically very similar to dppa) did not lead to bis-diphosphine products. Furthermore our results indicate that in all the syntheses reported to date for [Mo₂(μ-O₂CCH₃)₂(LL) ₂](BF₄)₂ type-compounds [Mo₂(μ-O₂CCH₃)₂(CH ₃CN)₆](BF₄)₂ acts as the precursor compound. Crystallographic data for 4 are as follows: P2₁/c (No. 14), a = 19.683(3), b = 15.129(2), c = 21.084(1) A?, β = 101.30(1)°, V = 6848(2) A?³, Z = 4. There are two independent molecules of the cation in the unit cell, d(Mo-Mo) = 2.133(1) and 2.136(1) A?.