The synthesis, using hexamethyldialuminium, and reactivity of new (1–5-η-cyclopentadienyl)methyl(nitrosyl)molybdenum complexes. Crystal structure of bromo(η5-cyclopentadienyl)methyl(nitrosyl)(triphenylphosphine)-molybdenum

Abstract

Under appropriate conditions the reaction of [{Mo(η⁵-C₅H₅)(NO)X}₂(µ-X)₂][X = Cl (1), Br (2), or I (3)] with Al₂Me₆, gives the new (probably dimeric) methyl complexes [{MoMe(η⁵-C₅H₅)(NO)}₂(µ-X)₂](4)–(6) which react with an equimolar amount of different ligands to give the monomeric neutral complexes [MoMe(η⁵-C₅H₅)(NO)XL][L = tetrahydrothiophene (tht), X = Br (7); L = PPh₃, X = Cl (8), Br (9), or I (10); L = OPPh₃, X = Cl (11) or Br (12)] and the anionic complex [PPh₄][MoMe (η⁵-C₅H₅)(NO)Br₂](13). One of the routes to prepare complexes (7)–(12) gives instead of (12) a solid, (14), which contains a cation of variable composition and the same anion as in (13). The complexes (5) and (9) react with Tl(C₅H₅) to give the known [MoMe(ηⁿ-C₅H₅)₂(NO)](the value of n is unknown). The molybdenum–carbon bond in (9) suffers cleavage only by addition of highly concentrated solutions of strong protonic acids to give the neutral complex [Mo(η⁵-C₅H₅)(NO) Br₂(PPh₃)] with HBr, or the dicationic complex [Mo(η⁵-C₅H₅)(NO)(PPh₃)₂L]²⁺[L = Me₂CO (15)] with HBF₄. The same compound (9) reacts with LiR to give dialkyl complexes [MoMe(R)(η⁵-C₅H₅)(NO)(PPh₃)][R = Me (16), C₂Ph (17), or C₆F₅(18)]. The structure of complex (9) has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P2₁/a with a= 18.778(5), b= 14.713(5), c= 8.354(3)Å, β= 102.77(2)°, and Z= 4. The structure has been solved from diffractomer data by Patterson and Fourier methods and refined by full-matrix least-squares methods to R= 0.036 for 2 532 observed reflections. The structure is of the ‘four-legged piano stool’ type with the PPh₃ and Me ligands in trans positions. The Mo–N and N–O bond distances [1.814(6) and 1.115(8)Å respectively] indicate considerable Mo–NO back-bonding. The Mo–N–O group is nearly linear [171.3(6)°].