Stereoselectivity in the Formation of Metallomacrocycles from [Mo(NO){HB(3,5-Me2C3HN2)3}I2] and Ditopic Proligands:  The X-ray Crystal Structures of anti-[[Mo(NO){HB(3,5-Me2C3HN2)3}{1,4-(OCH2)2C6H4}]2·4CHCl3, syn-[Mo(NO){HB(3,5-Me2C3HN2)3}{1,4-(OCH2)2C6H4}]2·2CH2Cl2, and anti-[Mo(NO){HB(3,5-Me2C3HN2)3}{(4-OC6H4)2CH2}]2·2CHCl3·CH2Cl2

The reaction between the chelating ligand 1,2-(HOCH2)2C6H4 and [Mo(NO)(tp*)I2] {tp* = HB(3,5-Me2C3HN2)3} in the presence of NEt3 affords the monometallic complex [Mo(NO)(tp*){(OCH2)2C6H4}], 1. However, reactions involving the nonchelating ditopic proligands HE-EH {HE-EH = 1,4-(HOCH2)2C6H4, 1,3-(HOCH2)2C6H4, and 4,4‘-(HOC6H4)2CH2} afford the binuclear metallocyclophanes [Mo(NO)(tp*)(E−E)]2 as mixtures of syn- and anti-isomers. These binuclear complexes are formed under kinetic control so that syn-[Mo(NO)(tp*){1,4-(OCH2)2C6H4}]2, 2s, forms more rapidly than anti-[Mo(NO)(tp*){1,4-(OCH2)2C6H4}]2, 2a, but in lower yield. Some kinetic control is also apparent in the formation of the syn- and anti-isomers of [Mo(NO)(tp*){4,4‘-(OC6H4)2CH2}]2, 4, and [Mo(NO)(tp*){1,3-(OCH2)2C6H4}]2, 3, but in these cases the reaction is less stereoselective. The X-ray crystal structures of three complexes were determined to establish their isomeric structures: anti-[[Mo(NO){HB(3,5-Me2C3HN2)3}{1,4-(OCH2)2C6H4}]2·4CHCl3, C46H60B2Mo2N14O6·4CHCl3, triclinic, space group P1̄, a = 11.967(3) Å, b = 18.004(2) Å, c = 8.740(2) Å, α = 102.31(1)°, β = 109.32(1)°, γ = 82.08(1)°, Z = 1; syn-[Mo(NO){HB(3,5-Me2C3HN2)3}{1,4-(OCH2)2C6H4}]2, C46H60B2Mo2N14O6·2CH2Cl2, monolinic, space group P21/a, a = 16.576(3) Å, b = 20.844(2) Å, c = 17.024(2) Å, β = 109.32(1)°, Z = 4; anti-[Mo(NO){HB(3,5-Me2C3HN2)3}{(4,4‘-OC6H4)2CH2}]2, C56H64B2Mo2N14O6·2CHCl3·CH2Cl2, triclinic, space group P1̄, a = 12.665(2) Å, b = 13.013(2) Å, c = 11.894(2) Å, α = 111.80(1)°, β = 95.48(1)°, γ = 94.78(2)°, Z = 1. All three structures are characterized by short Mo−O bond distances indicative of some Opπ→Modπ bonding. In the case of 2a evidence for weak hydrogen bonds between solvating CHCl3 molecules and the alkoxide oxygens was found.