Preparation and Characterization of Bis[dihalo(μ-bis(diphenylphosphino)amine)molybdenum(II)] Complexes

Complexes having the formula
Mo2X4(μ-dppa)2 (X = Cl
(2) Br (3); dppa =
bis(diphenylphosphino)amine) can
be synthesized by the reaction of Mo2(OAc)4
(OAc = μ-CH3COO) with dppa and an excess of
(CH3)3SiX under
reflux conditions. Both compounds were characterized by IR and
UV/vis spectroscopy and by 31P{1H} and
1H
NMR spectroscopy. Single-crystal diffraction studies afford the
following pertinent crystal data for 2 and
3,
respectively:  monoclinic P21/c,
a = 15.522(4) Å, b = 17.881(5) Å,
c = 16.898(3) Å, β = 91.15(2)°,
Z = 4;
orthorhombic P212121,
a = 19.654(2), b = 19.865(2)
c = 14.792(1), Z = 4. Both
compounds exhibit significant
torsion angles but, nevertheless, have comparatively short Mo−Mo bond
distances (2, d(Mo−Mo) = 2.134(1)
Å;
3, d(Mo−Mo) = 2.137(2) Å).