Modeling the Formation of Molybdenum Oxides from Alkoxides:  Crystal Structures of [Mo4O4Cl4(μ2-OEt)4(HOEt)2(μ3-O)2] and [PPN]+[Et3NH]+[Cl2(O)Mo(μ2-O)2Mo(O)Cl2]2

The reactions of the binuclear oxomolybdenum(V) complex [Cl2(O)Mo(μ-OEt)2(μ-HOEt)Mo(O)Cl2] (1) with Me3Si(allyl) and SbF3 produce the compounds [Mo6O6Cl6(μ3-O)2(μ2-OEt)6(μ2-Cl)2] (2) and [Mo8O8Cl6(μ3-O)4(OH)2(μ2-OH)4(μ2-OEt)4(HOEt)4] (3), respectively. Treatment of 1 with the Lewis base PMe3 affords the tetrameric complex [Mo4O4Cl4(μ2-OEt)4(HOEt)2(μ3-O)2] (4), which represents another link in the chain of clusters produced by the reactions of 1 and simulating the build-up of polymeric molybdenum oxides by sol−gel methods. The crystal structure of 4 has been determined [C12H32Cl4Mo4O12, triclinic, P1̄, a = 7.376(2) Å, b = 8.807(3) Å, c = 11.467(4) Å, α = 109.61(1)°, β = 92.12(3)°, γ = 103.75(2)°, Z = 1]. By contrast, reaction of 1 with the nitrogen base NEt3, followed by treatment with [PPN]Cl·2H2O ([PPN]+ = [Ph3PNPPh3]+), gives the complex [PPN]+[Et3NH]+[Cl2(O)Mo(μ2-O)2Mo(O)Cl2]2- (6) in 90% yield. Its crystal structure [C36H30Cl4MoNOP2, triclinic, Pna21, a = 21.470(6) Å, b = 16.765(2) Å, c = 9.6155(14) Å, α = 90°, β = 90°, γ = 90°, Z = 16] includes the anion [Cl2(O)Mo(μ2-O)2Mo(O)Cl2]2-, which is a charged derivative of the species forming the gels in sol−gel processes starting from chloromolybdenum ethoxides. Furthermore, compound 1 is found to be catalytically active in esterification and dehydration reactions of alcohols.