Abstract
A series of octahedral tungsten coordination compounds have been prepared containing chloride,
phosphine, and pyridyl ligands. The electron-rich, 16-electron complex WCUtPMesMbpy)
undergoes chloride substitution with acetonitrile, benzonitrile, and pivalonitrile to form complexes
of the type [WCl(PMe3)2(bpy)(L)]+, in which the nitrile (L) is i?2-bound to the metal. These
unusual side-bound nitrile complexes exhibit electrochemical, spectroscopic, magnetic, and
structural features similar to those of the ubiquitous “four-electron-donor” alkyne complexes
of Mo(II) and W(II) previously reported and theoretically evaluated. Thus, the model used to
describe the bonding interactions of alkyne complexes is extended to include T?2-nitrile complexes.
The nitrile is proposed to stabilize the W(II) center through donation of electron density from
both its tt|| and ± orbitals while its * orbital simultaneously renders it a acid. The W(II)
alkyne complexes WCl2(PMe3)3(»?2-2-pentyne) and [W(bpy) (PMe3)2(7?2-2-pentyne)]2+ have also
been prepared in order to make a direct comparison with their nitrile analogs. Crystal structures
of the complexes [W(bpy)(PMe3)2ClO?2-CH3CN)]+ and WCl2(PMe3)3(t?2-CH3CN) show that the
nitrogen and carbon of the nitrile group are nearly equidistant from the metal (ca. 2.00 A) and
that the N-C bond is lengthened by as much as 0.12 A compared to that of the free ligand. In
addition, crystal structures are reported for WCl2(PMe3)2(bpy) and WCl3(PMe3)2(py).
WCl3(PMe3)2(py): a (A)= 10.025(3), b (A)= 22.228(6), c (A)= 8.232(1), orthorhombic, 2 2 2
(No. 19), Z= 4. WCl2(PMe3)2(bpy): a (A)= 13.975(5), b (A)= 9.408(3), c (A)= 18.456(6), ß
= 103.38(3), (monoclinic, P2i/c (No. 14), Z=
. WCl2(PMe3)3(i?2-CH3CN): a (A)= 16.792(5),
b (A)= 12.611(3), c (A)= 18.971(5), ß (deg)
97.78(3), monoclinic, P2Jc (No. 14), Z= 8.
