The ligands (L) (E)-2,2'-bis(diphenylphosphino)stilbene, (E)-o-Ph2PC6H4CH=CHC6H4PPh2-o
(bdps), (E)-1,3-bis[2-(diphenylphosphino)phenyl]propene, (E)-o-Ph2PC6H4CH=CHCH2C6H4PPh2-o
(bdpp), and (E)-1,3-bis[2-(diphenylphosphino)phenyl]but-1-ene,( E)-o-Ph2PC6H4CH=CHCHMeC6-
H4PPh2-o (bdpb), form complexes of general formula M(CO)3L (M = Cr, Mo, W). N.m.r. (1H,
13C and 31P) and i.r. data indicate that the metal atoms are octahedrally coordinated by mutually
trans phosphorus atoms and the double bond of the olefinic tertiary diphosphines and by meridionally
disposed carbonyl groups. Conformational isomers of the complexes of bdpb can be detected
by n.m.r, spectroscopy, but there is no evidence for similar conformers in the corresponding complexes
of bdps and bdpp. The crystal and molecular structure of W(CO)3(bdpp),0.5CH2C12 has been determined
by single-crystal X-ray diffraction analysis. The crystals are triclinic, space group PI, with
a 10.1 13(Z), b 13.820(2), c 14.512(3) A, α 76.24(1), β 88.08(1), γ 76.31(1)°. The structure, solved
by the heavy-atom method and refined to a conventional R of 0.049 for 8418 diffractometer data,
confirms the conclusions drawn from spectroscopic studies. The olefinic double bond of bdpp is
attached symmetrically to the metal atom [W-C(olefin) 2.403(8), 2.387(9) Ǻ] and is roughly parallel
to the P-W-P axis. The C=C bond length of 1.359(11) Ǻ is only slightly longer than that expected
for the free ligand and is indicative of relatively weak metal-olefin back-bonding. Other important
bond lengths are: W-P 2.450(2), 2.462(2) Ǻ and W-C(C0) 2.020(7), 2.024(7) Ǻ (CO trans to CO)
and 1.971(7) Ǻ (CO trans to olefin).
